U.S. Department of Health and Human Services 
 
U.S. Department of Health and Human Services 
   
Office of Inspector General 
 
 
 
 
Adverse Events in Hospitals: 
A Quarter of Medicare 
Patients Experienced Harm in 
October 2018 
 
 
Christi A. Grimm 
Inspector General 
May 2022, OEI-06-18-00400  U.S. Department of Health and Human Services 
 
O  ffice of Inspector General 
 
Report in Brief 
 
M  ay 2022, OEI-06-18-00400 
 
Adverse Events in Hospitals: A Quarter of Medicare 
Why OIG Did This Review 
In 2010, OIG reported the first  Patients Experienced Harm in October 2018 
national incidence rate of patient 
harm events in hospitals What OIG Found 
27 percent of hospitalized Medicare  Key Takeaway  Twenty-five percent of Medicare 
patients experienced harm in  patients experienced patient harm 
One in four hospitalized Medicare 
October 2008.  During that month,  during their hospital stays in October 
patients experienced harm during 
hospital care associated with these  2018.  Patient harm includes adverse 
October 2018.  For nearly a quarter 
events cost Medicare and patients  events and temporary harm events. 
of these patients, harm events 
an estimated $324 million in 
resulted in additional costs to 
reimbursement, coinsurance, and  Twelve percent of patients experienced 
Medicare.  Physician-reviewers 
deductible payments.  Nearly half of  adverse events, which are events that led 
determined that 43 percent of the 
these events were preventable.    to longer hospital stays, permanent 
harm events could have been 
harm, life-saving intervention, or death.  
OIG conducted a new study to  prevented if patients had been 
In addition to the patients who 
update the national incidence rate  provided better care.   
experienced adverse events, 13 percent 
of patient harm events among 
of patients experienced temporary harm 
hospitalized Medicare patients in 
events, which required intervention but did not cause lasting harm, prolong 
October 2018.  This work included 
hospital stays, or require life-sustaining measures.  Temporary harm events were 
calculating a new rate of 
sometimes serious and could have caused further harm if providers had not 
preventable events and updating 
promptly treated patients. 
the cost of patient harm to the 
Medicare program.   Categories of Harm Events.  The most common type of harm event was related 
to medication (43 percent), such as patients experiencing delirium or other 
HHS leads national efforts to 
changes in mental status.  The remaining events related to patient care 
promote quality health care and 
(23 percent), such as pressure injuries; to procedures and surgeries (22 percent), 
prevent patient harm.  Several 
such as intraoperative hypotension; and to infections (11 percent), such as 
agencies share this responsibility, 
hospital-acquired respiratory infections. 
including the Agency for Healthcare 
Research and Quality (AHRQ), which   Preventability of Harm Events.  Physician-reviewers determined that 43 percent 
leads HHSs efforts to improve  of harm events were preventable, with preventable events commonly linked to 
health care quality, and the Centers  substandard or inadequate care provided to the patient.  (The overall harm rate 
for Medicare & Medicaid Services  would be 13 percent if we were to include only events that our physician-
(CMS), which is the Nations largest  reviewers determined were preventable.)  Reviewers determined that 56 percent 
health care payer and oversight  of harm events were not preventable and occurred even though providers 
entity.   followed proper procedures.  Events were determined not preventable for several 
reasons, including that the patients were found to be highly susceptible to the 
Although HHS agencies have 
events because of their poor health status. 
reported progress during the past 
decade toward improving patient   CMSs Lists of Hospital-Acquired Conditions.  CMSs two policies on hospital-
safety, protecting the health and 
acquired conditions (HACs) create payment incentives for harm prevention by 
safety of HHS beneficiaries remains 
reducing payment for certain HACs.  However, because the policies use narrowly 
one of HHSs top management and 
scoped lists of HACs and employ specific criteria for counting harm events, they 
performance challenges.  An 
have limited effectiveness in broadly promoting patient safety.  The lists did not 
increased understanding of the 
cover most of the harm events that patients in our study experienced.  Of the 
prevalence and nature of patient 
harm events we identified, only 5 percent were on CMSs HAC Reduction 
harm will further assist efforts to 
Program list and only 2 percent were on CMSs Deficit Reduction Act HAC list. 
reduce patient harm events and the 
factors contributing to these events.   
   
 
Report in Brief (continued) 
Report No. OEI-06-18-00400 
How OIG Did This Review   Harm Events Resulting in Costs to Medicare.  Nearly a quarter of Medicare 
patients who experienced harm events (23 percent), either preventable or 
We reviewed medical records for a 
nonpreventable, required treatment that led to additional Medicare costs.  These 
random sample of 770 Medicare 
events also potentially increased patient costs in the form of coinsurance and 
patients who were discharged from 
deductible payments.  Costs were incurred during the sample hospital stay or for 
acute-care hospitals during October 
an additional hospital stay necessary to ameliorate the harm.  Combined, we 
2018.  We conducted a two-stage 
estimated the costs for all events to be in the hundreds of millions of dollars for 
medical record review to estimate a 
October 2018.  
national incidence rate of adverse 
events and temporary harm events.   What OIG Recommends and How the Agencies Responded  
Our review included all causes of 
Given the scale and persistence of patient harm in hospitals in the decade since 
patient harm regardless of whether 
our last report, HHS leadership and agencies must work with urgency to reduce 
the harm was preventable. 
patient harm in hospitals.  Although HHS agencies took steps to improve patient 
safety in hospitals, including implementing many of our prior recommendations, 
Stage 1: Nurses screened the 
substantial efforts are still needed.  We made seven recommendations and 
records for possible patient harm 
received concurrences from CMS and AHRQ on all: 
events using a trigger tool 
method.  A trigger is a clinical clue   We made the following three recommendations to CMS: (1) update and broaden 
(e.g., documentation of a fall) that 
its lists of HACs to capture common, preventable, and high-cost harm events; 
may indicate harm.  From the 
(2) explore expanding the use of patient safety metrics in pilots and 
Medicare claims data, nurses also 
demonstrations for health care payment and service delivery, as appropriate; and 
reviewed present-on-admission 
(3) develop and release interpretive guidance to surveyors for assessing hospital 
indicators to identify harm that 
compliance with requirements to track and monitor patient harm.  In its response 
developed after the patient was 
to our draft report, CMS provided details about ongoing and planned efforts to 
admitted.  We automatically 
improve patient safety.  
referred records to Stage 2 when 
patients were readmitted within   We made the following four recommendations to AHRQ: (1) with support from 
30 days of discharge, regardless of  HHS leadership, coordinate agency efforts to update agency-specific Quality 
whether the nurse identified harm  Strategic Plans; (2) optimize use of the Quality and Safety Review System, 
(these include readmissions in  including assessing the feasibility of automating data capture for national 
October and November).  measurement and to facilitate local use; (3) develop an effective model to 
disseminate information on national clinical practice guidelines or best practices 
Stage 2: Physicians reviewed the  to improve patient safety; and (4) continue efforts to identify and develop new 
records flagged during Stage 1 as  strategies to prevent common patient harm events in hospitals.  After receiving 
containing possible harm events.   AHRQs comments, we revised our first recommendation to make the 
Physician-reviewers identified harm  recommended actions clearer and we revised the second recommendation to 
events and assessed the severity of  acknowledge recent progress by AHRQ regarding its event surveillance system. 
events, whether events were 
   
preventable, and factors that 
contributed to events. 
We calculated the potential cost 
incurred by Medicare and patients 
as a result of these events.  We also 
determined whether events were on 
CMSs lists of hospital-acquired 
conditions.  Finally, we compared 
the results of this report to our 
2010 report and explained the 
limitations of this comparison. 
   
TABLE OF CONTENTS 
 
 
BACKGROUND  1 
Methodology  11 
FINDINGS  16 
A quarter of hospitalized Medicare patients experienced harm during their hospital stays  16 
Medication-related harm events were the most common type of harm events  19 
Physician-reviewers determined that 43 percent of adverse events and temporary harm  24 
events were preventable 
CMSs two policies on hospital-acquired conditions create payment incentives for harm  28 
prevention but do not apply to the vast majority of harm events that patients experienced 
Nearly a quarter of patients who experienced harm events required treatment that led to  29 
additional Medicare costs  
CONCLUSION AND RECOMMENDATIONS  31 
CMS should update and broaden its lists of hospital-acquired conditions to capture  31 
common, preventable, and high-cost harm events 
CMS should explore expanding the use of patient safety metrics in pilots and  32 
demonstrations for health care payment and service delivery, as appropriate 
CMS should, as OIG previously recommended, develop and release interpretive guidance  33 
to surveyors for assessing hospital compliance with requirements to track and monitor 
patient harm events 
AHRQ should, with support from HHS leadership, coordinate agency efforts to update  33 
agency-specific Quality Strategic Plans 
AHRQ should optimize use of the Quality and Safety Review System (QSRS), including  33 
assessing the feasibility of automating data capture for national measurement and to 
facilitate local use 
AHRQ should develop an effective model to disseminate information on national clinical  34 
practice guidelines or best practices to improve patient safety 
AHRQ should continue efforts to identify and develop new strategies to prevent common  34 
patient harm events in hospitals 
AGENCY COMMENTS AND OIG RESPONSE  36 
COMPARISON TO THE 2010 REPORT  38 
MEDICAL RECORD REVIEW METHODOLOGY  41 
   
   
TABLE OF CONTENTS (contd)
 
 
 
APPENDICES  46 
A.  N  ational Quality Forum List of Serious Reportable Events   46 
B. HHS Agency Efforts To Improve Quality and Safety in Hospitals  49 
C. CMS Lists of Hospital-Acquired Conditions  52 
D.  Glossary of Selected Terms  55 
E.  Trigger Tool Used To Screen for Patient Harm Events  59 
F.  Estimates, Confidence Intervals, and Key Statistics  61 
G.  Rates of Patient Harm Events by Patient Days and Hospital Admissions  67 
H. Patient Harm Events Identified in the Sample  68 
 I.  Agency Comments  90 
ACKNOWLEDGMENTS AND CONTACT  101 
ABOUT THE OFFICE OF INSPECTOR GENERAL  102 
ENDNOTES  103 
 
 
   
BACKGROUND 
 
Objectives 
1.  To estimate the incidence of adverse events and temporary harm events for 
hospitalized Medicare patients. 
2.  To assess the extent to which adverse events and temporary harm events 
were preventable, to identify contributing factors, and to estimate the 
associated costs to Medicare. 
 
Patient Harm in Health Care 
Patient harm refers collectively to adverse events and temporary harm events.  An 
adverse event is defined as harm to a patient as a result of medical care or in a 
health care setting, including the failure to provide needed care.  An adverse event 
indicates that care resulted in an undesirable clinical outcomean outcome not 
caused by underlying diseasethat prolonged the patient stay, caused permanent 
patient harm, required life-saving intervention, or contributed to death.  We also 
identify temporary harm events, which are events that resulted in patient harm and 
required medical intervention but did not prolong hospital stays, cause lasting harm, 
or require life-sustaining intervention.  Adverse events are often more serious than 
temporary harm events, but temporary harm events can also be serious and lead to 
more severe consequences if left untreated.  For example, if treated promptly, 
hypoglycemia (low blood glucose) is usually a temporary harm event, but it can 
become a life-threatening adverse event if left untreated. 
Patient harm events may involve medical errors and general substandard care that 
result in harm, such as infections caused by using contaminated equipment.  
However, harm events do not always involve errors, negligence, or poor quality of 
care, and as a result they are not always preventable.  For example, an allergic 
reaction might not have been preventable if it was unexpected.  The Institute for 
Healthcare Improvement, a nonprofit advisory group dedicated to improving health 
and health care worldwide, states that unpreventable events are only an innovation 
away from being preventable and that including all causes of harm in research 
allows for better comparisons over time.1  All-cause harm includes any event during 
the care process that results in harm to a patient, regardless of the cause.2   
Reducing the incidence of patient harm events in hospitals is fundamental to 
improving patient safety and quality of care.  In the past few decades, there has been 
increased national attention devoted to identifying and preventing patient harm.  In 
2000, the Institute of Medicine helped launch the current patient safety movement 
with its report To Err Is Human: Building a Safer Health System.3  The Institute (now 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 1   
the National Academy of Medicine) cited two medical record reviews to identify 
adverse events.  The studies found that between 2.9 and 3.7 percent of hospitalized 
patients experienced patient harm events and that these events caused at least 
44,000 and perhaps as many as 98,000 deaths in hospitals each year.4, 5, 6 
OIG Studies on Adverse Events 
Beginning in 2008, the Office of Inspector General (OIG) has released 17 reports 
regarding adverse events in hospitals and other health care settings.7  The Tax Relief 
and Health Care Act of 2006 required that OIG report to Congress regarding the 
incidence of never events (i.e., a subset of adverse events that should never occur, 
such as surgery on the wrong patient) among Medicare patients.  The Act also 
required OIG to examine the extent to which the Medicare program paid, denied 
payment, or recouped payment for services furnished in connection with such events; 
and to examine the processes that the Centers for Medicare & Medicaid Services 
(CMS) uses to identify such events and deny or recoup payment.8  To meet the 
requirements of the Act, OIG published a study of adverse events in two counties and 
then published a study on the national incidence rate of adverse events in acute-care 
hospitals.9, 10  Each OIG study on adverse events captured all causes of harm, as well 
as the preventability of patient harm events.  
First National Study of Adverse Events.  In 2010, OIG provided the first nationwide 
estimate of patient harm.  In Adverse Events in Hospitals: National Incidence Among 
Medicare Beneficiaries (the 2010 report), OIG found that 27 percent of hospitalized 
Medicare patients experienced adverse events and temporary harm events in 
October 2008.  Forty-four percent of harm events were preventable, and care 
associated with events cost Medicare and patients an estimated $324 million in that 
single month.11  For that same period, OIG estimated that adverse events contributed 
to approximately 15,000 deaths among hospitalized Medicare patients.12 
Subsequent OIG Reports on Adverse Events.  Subsequent OIG reports on adverse 
events have focused on incident reporting and incidence rates in different health care 
settings.  In a 2012 followup report, OIG found that only 14 percent of patient harm 
events were reported to hospitals incident reporting systems or other internal 
surveillance systems.13  In a series of reports regarding the incidence of harm events 
in post-acute settings, OIG found that 32 percent of Medicare residents in skilled 
nursing facilities, 29 percent of Medicare patients in rehabilitation hospitals, and 
46 percent of Medicare patients in long-term care hospitals experienced harm.14, 15, 16 
Identifying Patient Harm Events From Medical Record Review 
Each OIG study on the incidence of adverse events used a two-stage medical record 
review in which nurses screened inpatient medical records for potential patient harm 
events using a Global Trigger Tool (GTT), and physicians then reviewed the full 
records when nurses suspected harm events.  The Institute for Healthcare 
Improvement (IHI) developed the original GTT to systematically screen records for 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 2   
triggers (clinical clues) that may indicate patient harm.  In OIGs reviews of adverse 
events, we used a modified version of this GTT. 
A prior OIG study found that compared to other detection methods, the GTT 
identified a wider range of patient harm events.17  In addition, some researchers 
consider medical record review by a physician to be the gold standard of adverse 
event detection because of the rich clinical information contained in medical records 
that can provide details about both the harm event and the circumstances, such as 
the patients condition before and after the event.18, 19   
Other researchers and organizations have also studied the incidence of adverse 
events.  Studies from the academic literature have used variations of the GTT 
methodology, reviews of administrative data, and other methods to identify and 
estimate rates of adverse events in hospitals and other health care settings.  Using 
these variations of the GTT method, researchers have found harm rates ranging from 
9 to 33 percent in hospitals (see Exhibit 1).  
Exhibit 1: Patient Safety in HospitalsSelected Research Using the Global Trigger Tool 
Study  Description  Harm Rate 
Office of Inspector  OIG randomly selected a sample of 780 Medicare patients who had inpatient stays at  27% of patients 
General20 (2010)  Medicare-certified hospitals in October 2008.  OIG identified 302 harm events  (13.5% had an 
(174 temporary harm events) using an OIG-modified version of the GTT.    adverse event) 
Landrigan et al.21  Researchers randomly selected 2,341 adult patient admissions from 10 hospitals for  18% of patient 
(2010)  admissions occurring between 2002 and 2007.  They identified 588 events, including  admissions 
those present on admission (POA), across 423 patient admissions using the IHI GTT.    (including POA) 
Classen et al.22  Researchers randomly selected 795 adult patient admissions from 3 hospitals during  33% of patient 
(2011)  October 2004.  They identified 393 harm events (354 events identified using the IHI GTT).  admissions 
Kirkendall et al.23  Researchers randomly selected 240 pediatric admissions from a hospital medical center in  26% of patients 
(2012)  2009.  They identified 88 harm events (74 events were not POA) across 62 patients using  (including POA) 
the IHI GTT. 
Kennerly et al.24  Researchers randomly selected 9,017 adult patient encounters from 8 hospitals from a  21% of admissions 
(2014)  health care system between 2007 and 2011.  They identified 3,430 harm events  (33% of admissions 
(2,129 events not POA) using the IHI GTT.    including POA) 
Adler et al.25  Researchers randomly selected 21,007 adult patient records from 24 hospitals in a large  26% of patients 
(2018)  multistate health system from 2009 to 2012.  They identified 5,397 patients who  (12.3% had an 
experienced harm (2,579 patients with adverse events and 2,818 patients with temporary  adverse event) 
harm events) using the IHI GTT. 
Griffey et al.26  Researchers randomly selected 2,594 adult patient records from four emergency  9% of emergency 
(2018)  departments from 2016 to 2017.  They identified 240 harm events (72 events involving  department visits 
patient harm and not POA) using an Emergency Department Trigger Tool.  (including POA) 
Stockwell et al.27  Researchers randomly selected 3,790 pediatric patient records from 16 hospitals from  11% of patients* 
(2018)  2007 to 2012.  They identified 414 adverse events (210 preventable adverse events) using  (including POA) 
the Global Assessment of Pediatric Patient Safety (GAPPS) Trigger Tool.   
*The incidence rate of 11 percent was not specifically included in the article.  We calculated 11 percent by using numbers presented in the article. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 3   
Classification of Patient Harm Events 
Researchers, policymakers, and health care entities sometimes focus on different 
types of patient harm events.  For example, government agencies and researchers 
study specific types of harm events, such as health care-associated infections (HAIs) 
and adverse drug events (ADEs).  Researchers also distinguish events by their level of 
harm and preventability.  Thus, entities tracking events may find different rates of 
patient harm depending on which list they use to identify and classify events.   
The National Quality Forum List of Serious Reportable Events 
One list that researchers and government agencies have used to track and classify 
patient harm events is the list of serious reportable events (SREs) developed by the 
National Quality Forum (NQF) to facilitate uniform and comparable public reporting.  
NQF is a public-private membership organization for health care quality measurement 
and reporting.28  This list focuses on events that are serious, largely preventable, and 
often associated with injury or death.  Several State reporting systems and quality 
improvement organizations use this list to track harm events in hospitals.29  In the 
2010 OIG report, OIG found that these types of events constitute a small percentage 
of adverse events, with less than 1 percent of Medicare patients experiencing events 
that were included on the NQF list.  NQF last updated the list of SREs in 2011.  (See 
Appendix A for the NQFs list of SREs.) 
NCC MERP Levels of Patient Harm 
Researchers and health care entities also adopt different standards for distinguishing 
degrees of harm and defining what constitutes a patient harm event.  The National 
Coordinating Council for Medication Error Reporting and Prevention (NCC MERP) 
devised an index to categorize medication errors by the degree of harm and 
additional resources expended to treat the patient.30  The NCC MERP Index ranks 
errors from A to I, with levels A through D constituting near misses in which the 
error did not result in patient harm, and levels E through I progressing from 
temporary harm (E) to contributing to death (I).   
Although the NCC MERP Index was initially developed to categorize the effect of 
medication errors, researchers have modified the Index to measure and distinguish 
other types of harm events.  For example, the IHI uses a modified version of the NCC 
MERP Index to measure the severity of harm events.31  Building off IHIs version, OIG 
also uses a modified version of the NCC MERP Index in our adverse events work.32  
(See Exhibit 2 on page 13 for the OIG-modified version of the NCC MERP Index.) 
HHS Efforts To Improve Quality and Safety in Hospitals 
The Department of Health and Human Services (HHS) is tasked with leading the 
Nation in promoting quality health care and preventing patient harm.  In 2011, 
pursuant to the Patient Protection and Affordable Care Act (ACA), HHS created a 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 4   
National Strategy for Quality Improvement in Health Care (National Quality Strategy) 
with auxiliary, coordinated plans developed by each HHS agency.33, 34  The first priority 
within the overarching National Quality Strategy is making care safer by reducing 
harm caused in the delivery of care.35  To achieve this end, HHS agencies use a series 
of levers to effect change, such as publicly reporting quality data for health care 
facilities, providing technical assistance to organizations, and implementing payment 
incentives, among others.  As mandated by the ACA, HHS conducts annual progress 
reviews of the National Quality Strategy and sends these reports to Congress.36 
HHS also developed targeted national action plans, in collaboration with other 
Federal departments and agencies, to reduce certain types of patient harm events.  
These plans include the HAI Action Plan and the ADE Action Plan.37, 38  Led by HHSs 
Office of Disease Prevention and Health Promotion, these two action plans are related 
to HHSs Healthy People initiative.39  These action plans include goals to reduce 
patient harm events.  The ADE Action Plan called for a 10-percent reduction in ADEs 
related to three classes of drugs (anticoagulants, diabetes agents, and opioids) by 
2020.40  The HAI Action Plan called for reductions of 25 to 50 percent in various 
hospital-onset HAIs by 2020, as compared to 2015.41  (The plan uses 5-year 
increments and at the time of this report, HHS had not yet released the 2020 data.)   
Each agency within HHS contributes to the National Quality Strategy and the HAI and 
ADE action plans while pursuing agency-specific goals to improve quality and safety.  
Agencies contributing to these efforts include: the Agency for Healthcare Research 
and Quality (AHRQ), which leads efforts to improve health care quality; CMS, which is 
the Nations largest health care payer and is the primary oversight entity of health 
care nationally; and the Centers for Disease Control and Prevention (CDC), which leads 
efforts to study and prevent HAIs and ADEs and manages the National Healthcare 
Safety Network (NHSN), the Nations most widely used HAI surveillance system.42  
These agencies created agency-specific Quality Strategic Planslast updated in 
2016aligned with the National Quality Strategy.43  (See Appendix B for more 
information about other HHS agency-specific efforts to improve quality and safety in 
hospitals.) 
CMS Oversight of Hospitals and Payment Policies To Reduce 
Patient Harm Events  
CMS is the primary Federal regulatory body responsible for overseeing care and 
enforcing Federal requirements for care provided in hospitals under the Medicare and 
Medicaid programs.44  CMS promotes patient safety by regulating and overseeing the 
care provided in hospitals and by using payment policies designed to reduce patient 
harm and improve quality of care.  
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 5   
CMS Oversight of Hospitals for Patient Health and Safety 
As part of its role to protect patients from harm in hospitals, CMS oversees hospital 
compliance with a set of patient health and safety requirements known as the 
Medicare hospital Conditions of Participation (CoPs).45  The CoPs set baseline 
standards for a range of hospital services and areas, including medical staff, infection 
control, nursing services, medical records, and pharmaceutical services.  These 
standards are, in part, designed to minimize harm events.  To verify compliance with 
the CoPs, three types of entitiesCMS regional offices; State survey agencies; and 
Medicare-approved accreditation organizations, such as the Joint Commission
conduct onsite surveys of hospitals.46   
One CoP requires hospitals to develop, implement, and maintain an effective, 
ongoing, hospitalwide, data-driven Quality Assessment and Performance 
Improvement (QAPI) program that focuses on indicators related to improving health 
outcomes and preventing and reducing medical errors.47  To satisfy the QAPI CoP, 
hospitals must track medical errors and adverse patient events, analyze their causes, 
and implement preventive actions and mechanisms.48  A QAPI program must include 
an ongoing effort that shows measurable improvement in indicators for which there 
is evidence that it will improve health outcomes and identify and reduce medical 
errors.49  CMS provides interpretive guidance and survey procedures regarding the 
hospital CoPs in its State Operations Manual.50 
CMS Payment Policies for Improving Patient Safety and Reducing 
Costs Associated With Hospital-Acquired Conditions  
As mandated by Congress, CMS implemented, in fiscal years (FYs) 2009 and 2015, two 
payment policies focused on hospital-acquired conditions (HACs) under Medicare.  
These payment policies are designed to reduce payment to hospitals for certain 
HACs.51  (See Appendix C for CMSs two lists of HACs and see Appendix B for 
additional CMS pay-for-performance programs focused on patient safety.) 
Inpatient Prospective Payment System Payments.  For most patient stays, 
Medicare pays eligible hospitals through the inpatient prospective payment system 
(IPPS), under which payment amounts are based on the average cost of care for 
patients with similar conditions.52  In FY 2019, Medicare classified patient stays into 
1 of 759 Medicare SeverityDiagnosis Related Groups (MS-DRGs) based on the 
diagnosis and procedure codes included on the Medicare claim, as well as on the 
patients age, sex, and discharge status.  Providers may submit up to 25 diagnosis 
codes and 25 procedure codes on a claim.53  These MS-DRGs correlate to the 
payment that Medicare allows for the stay.  In calendar year 2018, Medicare certified 
3,334 short-stay acute-care hospitals.54  In the same year, these hospitals served over 
6 million Medicare patients, with Medicare program payments totaling $750 billion or 
a monthly average of about $63 billion.55, 56  In addition to payments made by 
Medicare, patients are responsible for deductible and, in certain situations, 
coinsurance payments. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 6   
1.  Deficit Reduction Act (DRA) List.  The first CMS policy prevents hospitals from 
receiving increased payments resulting from HACs that develop during the 
hospital stay.57  The DRA of 2005 required the Secretary of HHS to select 
diagnosis codes associated with at least two conditions for which hospitals would 
not receive higher Medicare payments.58  The original DRA HAC list of FY 2009 
was composed of 10 conditions, most of which included several diagnosis codes.  
Last updated in FY 2013, the list now consists of 14 conditions that CMS selected 
in collaboration with CDC using the following criteria: 
 
conditions that are high-cost, high-volume, or both; 
 
conditions that, when present as a secondary diagnosis, result in assignment 
of a case to a category that has a higher payment; and 
 
conditions that could be reasonably prevented using readily available 
evidence-based guidelines.59   
As required by this payment policy, Medicare-certified hospitals assign one of 
five present on admission (POA) indicators to each diagnosis on a patients 
claim to identify whether each diagnosis was present at the time of admission.  
For example, these indicators could include Y (POA), N (not POA), 
U (documentation insufficient to determine), W (clinically undetermined), or 
1 (unreported or not used).60  CMS then uses these indicators on claims to 
identify specific HACs (as defined above) and thereby deny higher payment in 
cases where such HAC diagnoses would have resulted in higher payment.61   
In examining the incidence of these harm events in the 2010 report, OIG found 
that the FY 2009 list of HACs represented a small percentage of harm events, with 
only about 1 percent of Medicare patients having experienced these events.   
2.  Hospital-Acquired Condition Reduction Program (HACRP) List.  Another 
payment policy that hospitals are subject to is a Medicare pay-for-performance 
program that adjusts payments to hospitals with high rates of HACs relative to 
other hospitals.62  The ACA established the HACRP, which CMS implemented 
beginning in FY 2015.63  HACRPs metrics include five equally weighted HAI 
measures and one patient safety composite indicator to measure hospital 
performance.64  These measures are based on administrative claims data and 
reporting of HAIs.  The HACRP list was last updated in FY 2017.  If a hospital 
performs in the lowest quartile of eligible hospitals, CMS reduces the hospitals 
payments by 1 percent of its annual Medicare inpatient fee-for-service payments.  
CMS uses the following criteria for selecting conditions for inclusion in the 
program: 
 
conditions identified as HACs under the DRA or by the Secretary, 
 
conditions that are high-cost or high-volume, 
 
conditions that are easily preventable using evidence-based guidelines, and  
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 7   
 
conditions that do not require additional system infrastructure for data 
submission and collection.65, 66 
Non-IPPS Payments.  CMS does not explicitly prohibit payment for HACs under 
Medicare managed care programs that are not paid through IPPS.  Medicare 
coverage not paid under IPPS includes inpatient care services covered under Medicare 
managed care organizations (i.e., Medicare Advantage plans) and inpatient care 
services provided at hospitals excluded from IPPS, including hospitals in Maryland and 
some specialty hospitals nationwide, such as cancer treatment centers.67  Payment 
under managed care is arranged through capitation (a fixed payment for each 
enrolled patient per time period) rather than fee-for-service (payments for each 
service).68  CMS calculates capitated payments to managed care organizations using a 
risk-adjustment methodology.69  In 2018, about one in three Medicare patients were 
covered under managed care and other non-IPPS programs.70  Similar to IPPS 
patients, non-IPPS patients are responsible for deductible and, in certain situations, 
coinsurance payments. 
CMS Models for Health Care Payment and Service Delivery.  In addition to its 
broader oversight and payment functions, CMS also designs, tests, and manages new 
health care payment and service delivery payment models focused on improving 
quality of care and addressing the rising costs of health care.  The Center for Medicare 
and Medicaid Innovation (CMS Innovation Center), authorized under the ACA, tests 
the effectiveness of these models at improving quality of care and reducing health 
care costs through pilots and demonstrations.71, 72   
AHRQ Programs for Reducing Patient Harm in Hospitals 
AHRQ contributes to reducing patient harm events in hospitals through a variety of 
programs and initiatives, particularly through research that generates evidence on 
how to deliver high-quality care; educational efforts to improve clinical practice; and 
data and analytics to track nationwide rates of patient harm.  
Patient Safety Organization Program.  As part of wider agency efforts to improve 
patient safety, AHRQ manages the patient safety organization (PSO) program 
authorized by the Patient Safety and Quality Improvement Act of 2005 (Patient Safety 
Act).73  This program allows hospitals to voluntarily report patient safety work product 
information to PSOs for learning and quality improvement.74, 75  This information may 
include data about patient harm events and falls under Federal confidentiality and 
privilege protections.  PSOs aggregate and analyze this information and offer expert 
feedback and advice to hospitals, physicians, and other health care providers to 
prevent patient harm events.  In 2019, OIG found that over half of hospitals worked 
with a PSO, and most of these hospitals (97 percent) reported that they found the 
relationship with a PSO valuable.76 
AHRQ Patient Safety Initiatives.  AHRQ maintains a range of toolkits, educational 
materials, and trainings for providers to improve patient safety and quality of care.  
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 8   
One initiative is AHRQs Comprehensive Unit-based Safety Program (CUSP), which 
provides a method to help clinical teams make care safer by combining improved 
teamwork, clinical best practices, and the science of safety.77  A number of projects 
have been designed using the CUSP method, including tools and resources 
developed under AHRQs HAI program to prevent and reduce HAIs.  This program 
funds work through grants and contracts to help clinicians prevent HAIs by improving 
how care is delivered to patients.78 
In November 2021, AHRQ released Strategies To Improve Patient Safety: Final Report 
to Congress, as required by the Patient Safety Act.79, 80  The report outlined strategies 
for reducing medical errors and increasing patient safety as well as measures to 
accelerate and encourage the health care community to adopt these strategies.  The 
report built on AHRQs series of reports, Making Healthcare Safer, which detail existing 
and emerging evidence-based patient safety practices for reducing certain patient 
harm events.81  AHRQ reported in 2018 that it was working to identify additional 
models for disseminating and accessing evidence-based clinical practice guidelines.82 
Public Reports on Nationwide Patient Harm.  AHRQ publishes nationwide rates of 
HACs tracked through patient safety surveillance programs in its series of reports: 
National Scorecard on Hospital-Acquired Conditions.83  AHRQ also publishes health 
care quality and health disparities data collected from multiple programs in its 
National Healthcare Quality and Disparities Report and via a public interface with 
selected patient safety data.84  Since 2014, AHRQ has included progress reviews of the 
National Quality Strategy in these annual reports to Congress.85 
CDC Programs and Initiatives Focused on Patient Safety 
CDC operates surveillance systems that track certain types of harm events.  CDCs 
surveillance focuses on HAIs tracked through NHSN and ADEs tracked through the 
National Electronic Injury Surveillance System-Cooperative Adverse Drug Events 
Surveillance System.86, 87  In collaboration with the relevant HHS programs, CDCs 
National Center for Health Statistics monitors HHSs progress toward meeting the 
goals of HHSs Healthy People initiative and action plans to reduce the national 
incidence of HAIs and ADEs.88  CDC publishes national HAI rates collected from NHSN 
in its HAI Progress Reports and on its Antibiotic Resistance & Patient Safety Portal 
(formerly the Patient Safety Atlas).89 
CDC also provides guidance and conducts research in patient safety to inform clinical 
and infection control practices.90  CDC works with States, local health departments, 
and academic medical center partners to develop strategies and resources to prevent 
HAIs.91  AHRQ and CMS use CDCs data, guidelines, and other resources to carry out 
their patient safety programs and initiatives. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 9   
Progress in Reducing Patient Harm Events in Hospitals 
In the decade since the release of OIGs 2010 report, HHS agencies have reported 
progress toward improving patient safety nationwide.  This progress has involved 
reported reductions of specific kinds of patient harm events with cost savings, 
advances in patient safety practices within the health care community, and HHS 
agencies implementation of OIGs prior recommendations. 
Reported Reductions in Specific Types of Harm.  Since 2010, several HHS agencies 
have reported progress in reducing particular types of patient harm eventsHACs, 
HAIs, and ADEs.  AHRQ reported significant declines in the rate of HACs, with a 
17-percent reduction between 2010 and 2014 and a 13-percent reduction between 
2014 and 2017.92, 93  On the basis of these data, CMS reported that its HAC payment 
policies and initiatives have been successful in reducing HACs.94  CDC also reported 
that the rates of most HAIs tracked by NHSN fell from 2006 to 2019.95, 96  For example, 
the rate of Clostridioides difficile (C. diff) infections in acute-care hospitals fell by an 
estimated 7 percent from 2010 to 2015 and by 42 percent from 2015 to 2019, and 
central line-associated bloodstream infections (CLABSIs) fell by 40 percent from 2006 
to 2015 and by 31 percent from 2015 to 2019.97, 98   
Advances in Patient Safety Practices.  HHSs focus on patient safety, in addition to 
substantial efforts by health care organizations and hospitals, has led to advances in 
hospital and clinical practices.  Research has shown that these improved safety 
practicessuch as medication barcoding, surgical checklists, and bundles of patient 
safety best practiceshave helped reduce medical errors and substandard care.99  
Some harm events, such as CLABSIs, are now considered widely preventable if 
providers follow proper protocols.100  This focus on safety in providing patient care is 
ongoing.  In September 2020, the IHI's National Steering Committee for Patient Safety 
(formed in 2018) called for a comprehensive action plan to improve patient safety.101  
The committee included 27 organizations, including CMS, AHRQ, and the Joint 
Commission.  The action plan made recommendations to leaders of health care 
organizations, including hospitals, to improve patient safety.  
Prior OIG Recommendations.  In the 2010 report, OIG recommended that CMS and 
AHRQ broaden patient safety efforts to include all types of adverse events; that both 
agencies enhance efforts to identify adverse events; and that CMS provide incentives 
to reduce the incidence of adverse events through its payment and oversight 
functions.102  Both agencies implemented these recommendations through a series of 
actions, including a nationwide initiative focused on hospital safety and a new 
national surveillance system for monitoring patient harm. 
 
In 2011, CMS began its Partnership for Patients initiative, which was designed 
to decrease preventable HACs by 40 percent compared to 2010.103  The 
initiative also expanded CMSs collection of health care quality data among 
participating hospitals.  Prior reports indicate that this program, along with the 
new Medicare payment incentives, prompted a period of concerted attention 
by hospitals throughout the country to reduce adverse events.104  In 2016, 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 10   
this initiative was integrated into the Quality Improvement Organization (QIO) 
program to sustain nationwide progress toward reducing patient harm. 
 
In December 2020, AHRQ deployed an expanded patient harm surveillance 
system to measure national rates of patient harm using information from 
patient medical records, the Quality and Safety Review System (QSRS).  QSRS 
replaced a prior harm event surveillance system with the goal of automating 
the capture of data from medical records to reduce manual data entry, 
increasing the types of events detected to identify all causes of harm, 
improving harm estimates by standardizing event definitions, and facilitating 
use by individual hospitals and health systems as a method for facilities to 
identify and measure events.105   
CMS also implemented an OIG recommendation to ensure that hospitals code claims 
accurately and completely to allow for identification of HACs that should reduce 
payment pursuant to the DRA HAC payment policy.106  CMS reported to OIG that to 
promote proper hospital coding practices, it had established a process to provide 
coding advice to hospitals and had directed its contractors to examine issues related 
to coding accuracy of POA indicators and HACs.  Although CMS has taken steps to 
implement OIGs recommendations, CMS has still not implemented prior 
recommendations for it to develop and release guidance to surveyors and accreditors 
in assessing hospital compliance to track and monitor patient harm in their 
facilities.107 
Methodology 
Scope 
In this study, we revisited the national incidence rate of harm among hospitalized 
Medicare patients and largely replicated the methodology used in the 2010 study.  
We estimated the incidence of adverse events and temporary harm events 
experienced by Medicare patients during inpatient stays in Medicare-certified 
short-term acute-care hospitals during October 2018.108  This assessment included all 
causes of patient harm, regardless of whether the harm was preventable.  We did not 
include events that occurred in hospital outpatient settings, such as emergency 
departments, unless they resulted in a direct hospital admission, nor did we include 
events that occurred before or after the patients hospital stay unless it resulted in a 
readmission.109  We estimated the cost of these events to Medicare, and we treated 
claims paid through managed care and Marylands payment system the same as 
those paid through IPPS, reporting those costs separately.  We generalized our 
findings to Medicare patients discharged during October 2018 nationwide.  The care 
provided to patients in this review occurred before the COVID-19 pandemic. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 11   
Sample Selection 
We selected a simple random sample of Medicare patients from the National Claims 
History file.  Of the 1,076,344 Medicare patients who were discharged from short-term 
acute-care hospitals during October 2018, we selected a sample of 800 patients.  We 
excluded 30 patients from our analysis because their inpatient stay occurred in a 
hospital currently under OIG investigation for an unrelated matter or because the 
hospital was unable to provide complete medical records.110  Our final sample 
consisted of 770 patients from 629 hospitals nationwide.  Some patients had more 
than one hospital stay.  The patients in our sample had a combined 834 eligible 
hospital admissions with discharges in October 2018 and an average length of stay of 
4.9 days.111 
Data Collection 
We requested complete medical records, as well as abbreviated records 
(i.e., discharge summaries, emergency department summaries, and operative reports) 
for stays that occurred within 30 days after the last discharge for sampled patients 
hospital stays.  We reviewed the medical records for completeness and made 
additional requests for any missing components.   
Medical Record Reviews   
We conducted a two-stage medical record review using OIG-contracted reviewers to 
identify adverse events and temporary harm events experienced by hospitalized 
Medicare patients.  (See the Medical Record Review Methodology for more 
information on identifying events and determining preventability and Appendix D for 
a glossary of selected clinical terms used to describe events.) 
Stage 1: Nurse Screening.  Registered nurses screened all 834 admissions using the 
OIG-modified GTT methodology to look for triggersclinical cluesthat indicated 
possible patient harm in the medical record.  (See Appendix E for the trigger tool.)  
From the Medicare claims data, nurses also reviewed POA indicators of N (not POA) 
or U (documentation insufficient to determine) as additional clinical clues indicating 
possible patient harm.  When nurses identified possible patient harm, they flagged 
the records for the second stage of review.  When nurses did not identify possible 
harm, a quality assurance reviewer re-screened the records to verify the nurses 
results.  We automatically referred records for patients who were readmitted within 
30 days of discharge (these include readmissions in October and November) to 
identify possible events that may have been missed by the screener. 
Stage 2: Physician Review.  Physicians reviewed the complete medical record for 
each of the 393 admissions flagged during Stage 1.  Physicians either confirmed or 
refuted the presence of patient harm events using evidence in the record and 
independently identified any additional events.  For each harm event, physician-
reviewers determined whether events were preventable (i.e., events that could have 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 12   
been avoided if the patients had been given better care).  They assigned each event 
to one of five preventability determinations: clearly preventable, likely preventable, 
likely not preventable, clearly not preventable, or unable to determine.  Physician-
reviewers also assigned each event to one of five harm severity levels using an 
OIG-modified version of the NCC MERP Index.  (See Exhibit 2 for a description of the 
severity levels used in this report.) 
Exhibit 2: OIG-Modified Version of the NCC MERP Index for Categorizing 
Events 
Event Type  Level  Description 
Harm occurred that may have contributed to or 
  I 
resulted in the patients death. 
Harm occurred that required intervention to sustain 
  H 
the patients life. 
Harm occurred that contributed to or resulted in 
Adverse Event  G 
permanent patient harm. 
Harm occurred that contributed to or resulted in 
  F  prolonged facility stay, elevation in level of care, 
transfer to another facility, or subsequent admission. 
Harm occurred that caused temporary harm that 
Temporary Harm Event  E 
required intervention. 
Source: Adapted from the NCC MERP Index for Categorizing Errors.  Revised on February 20, 2001. 
Medical Coder Reviews 
Certified medical coders reviewed all patient harm events identified by the physicians 
to identify potential costs associated with these events.  To do this, coders reviewed 
the medical records, physician findings, and the associated Medicare claims to identify 
diagnosis and procedure codes that would not have been included in the claim if the 
event(s) had not occurred.  The coders then used the TruCode Encoder software to 
determine the revised MS-DRG for the hospital claims and the resulting payment 
amounts.112  Coders also identified costs associated with patients 30-day hospital 
readmissions related to harm events. 
Data Analysis 
We analyzed the results of medical record reviews and generated national estimates 
about adverse events and temporary harm events among Medicare patients with 
hospital stays in October 2018.  (See Appendix F for point estimates, 95-percent 
confidence intervals, and statistical tests.) 
Incidence Analysis.  We estimated the national incidence rate of adverse events and 
temporary harm events as the percentage of patients who experienced at least one 
harm event during their hospital stays.  We also generated separate estimates for 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 13   
harm events that met the criteria for CMSs two lists of HACs.  We projected these 
incidence rates to the population of Medicare patients discharged from hospitals 
during October 2018.  
As an additional measure, we estimated two ratios of incidence density commonly 
used by hospitals and medical researchers: events per 1,000 patient days and events 
per 100 hospital admissions.  (See Appendix G for incidence density estimates.) 
Preventability Analysis.  We estimated proportions for each preventability 
classification and analyzed contributing factors for each classification.  We also 
conducted t-tests to identify statistically significant differences between preventable 
and not preventable harm events within clinical categories.  We report the p-values 
associated with the mean differences to describe the statistical significance. 
Medicare Cost Analysis.  We estimated the cost to Medicare and patients for care 
provided in response to adverse events and temporary harm events in October 2018.  
For each claim, we calculated the MS-DRG and associated payment amount using 
information from the hospitals Medicare claim.  We then recalculated the payment 
amount excluding diagnosis and procedure codes that coders determined were the 
direct result of any patient harm event experienced by the patient.  Finally, we 
calculated the costs of patient harm events as the difference between these two 
amounts.  These amounts do not include costs for care provided after discharge from 
the hospital, such as followup doctor visits.  (See Appendix F for projected cost 
estimates and 95-percent confidence intervals.)   
We presented Medicare claims that were paid under IPPS separately from those paid 
by managed care organizations, those paid by Marylands all-payer system, and those 
exempt from IPPS.  (We refer to these as non-IPPS claims.)  We presented the 
estimated costs for these two groups separately because claims paid through IPPS 
use an MS-DRG-associated payment amount, but the non-IPPS claims use alternative 
payment methods.  We used the MS-DRG-associated payment amount for both 
groups; therefore, the IPPS amount is an accurate representation of costs and the 
non-IPPS amount is an approximation of the costs. 
Limitations 
Our estimates, as with all medical record reviews, are subject to physician 
interpretation and clinical judgment.  It is unlikely that the reviewers identified all 
patient harm events within our sample of Medicare patients.  Medical record reviews 
also depend on available documentation and omitted information could lead 
reviewers to miss some events or assess the severity or preventability differently.  
Preventability determinations may also be affected by hindsight bias given the 
retrospective nature of medical reviews. 
The sample size was insufficient to effectively compare the results of this report to the 
harm rates identified in the 2010 report.  The sample size did not allow us to detect 
small differences between the rates or to conduct comparisons of individual 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 14   
subgroups of events.  Therefore, we do not include a comparison of the reports in our 
findings.  We offer a discussion of this comparison that includes its limitations 
beginning on page 38.   
The sample size was also insufficient to calculate the total dollar amounts of cost 
estimates with a high level of precision.  Further, the cost estimates for patients who 
received care in Maryland or through a managed care organization may be less 
precise because we used IPPS payment rates as a proxy for other payment systems.   
Finally, the Medicare population consists of patients who are either aged or disabled 
and may have more comorbidities than younger, healthier patients.  The presence of 
comorbidities has been tied to a higher risk of patients experiencing harm events.113  
These  patients may also require more complex treatments and, due to their 
underlying conditions, may be more susceptible to harm.  Therefore, the findings of 
this review do not fully apply to the broader patient population.   
Standards 
We conducted this study in accordance with the Quality Standards for Inspection and 
Evaluation issued by the Council of the Inspectors General on Integrity and Efficiency.  
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Background | 15   
FINDINGS 
 
A quarter of hospitalized Medicare patients experienced harm 
during their hospital stays 
Of the roughly 1 million Medicare patients discharged from hospitals in October 2018, 
about 1 in 4 (25 percent) experienced at least 1 adverse event or temporary harm 
Color Key  event during their stays.  This projects to almost 260,000 Medicare patients having 
We use the following 
experienced harm as a result of medical care received during hospital stays that 
color scheme in the 
ended in October 2018.  (See Appendix F for confidence intervals associated with the 
Findings for Exhibits 
point estimates.)   
and Patient Stories: 
Medicare patients who experienced harm events were in two groups: 12 percent 
All Events 
experienced adverse events, and an additional 13 percent experienced temporary 
Adverse Events 
harm events.  Some patients (8 percent) experienced multiple unrelated adverse 
Temporary Harm 
events or temporary harm events during their stays.  Adverse events are often more 
Events 
serious than temporary harm events.  However, some temporary harm events are also 
 
serious and could have developed into adverse events if hospital staff had not 
intervened.  (See page 18 for more details about temporary harm events.)  Exhibit 3 
shows an overview of the rates of harm.  (See Appendix H for a list of the harm events 
identified in our sample.) 
Exhibit 3: Patient Harm Events at a Glance 
All Events  Adverse Events*  Temporary Harm Events** 
           
25% of patients  12% of patients  13% of patients 
258,323 patients  121,089 patients  137,234 patients 
           
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
* The rate and number of patients who experienced adverse events consists of patients who experienced at least one 
adverse event.  Four percent of patients (41,708) counted in this group also experienced temporary harm events.114 
** The rate and number of patients who experienced temporary harm events consists of patients who experienced at 
least one temporary harm event and no adverse events.   
Twelve percent of hospitalized Medicare patients experienced 
adverse events during their stays 
Twelve percent of Medicare patients experienced adverse events during their hospital 
stays.  Adverse events fall under the four highest levels of harm (F through I) on the 
OIG-modified NCC MERP index.  These are events that prolonged the hospital stay, 
led to permanent harm, required life-saving intervention, or resulted in or contributed 
to death.  (See Exhibit 4 on the next page for the percentages of adverse events in 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 16   
each harm level.)  This projects to 121,089 Medicare patients having experienced at 
least 1 adverse event during the 1-month study period.   
Exhibit 4: Adverse Events Classified as F Through I on OIGs Modified NCC 
MERP Index (n=115)  
Percentage of   
Level of Harm  Adverse Events*  
F Level 
Resulted in a prolonged hospital stay, an elevation in the level of  74% 
care, a transfer to another facility, or a subsequent admission 
G Level 
10% 
Contributed to or resulted in permanent patient harm  
H Level 
7% 
Required intervention to sustain the patients life  
I Level 
10% 
Contributed to or resulted in patient death 
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
* Column does not equal 100 percent due to rounding. 
 
Most adverse events resulted in prolonged hospital stays, elevations in level of 
care, or subsequent admissions.  Seventy-four percent of adverse events resulted in 
F-level harm.  (This equates to 28 percent of all events when temporary harm events 
are included.)  Over half of these events resulted in a longer hospital stay.115  The 
remainder were classified at this level of harm because they resulted in a subsequent 
admission, elevated the patients level of care, or resulted in the current admission.  
For example, seven patients in our sample experienced excessive bleeding that 
prolonged their hospital stays and three patients experienced hyperkalemia (elevated 
potassium) that resulted in a subsequent admission.  Another two patients 
experienced respiratory failure that elevated their level of care to the intensive care 
unit (ICU) for monitoring and treatment. 
Fewer adverse events contributed to permanent harm or required life-saving 
intervention.  In addition to F-level harm, 10 percent of adverse events contributed 
to or resulted in permanent harm (G-level harm) and 7 percent required intervention 
to sustain the patients life (H-level harm).  Several of the events that resulted in 
permanent harm involved complications from major surgeries, such as strokes related 
to surgery that resulted in permanent cognitive and physical impairment.  For 
example, one patient was unable to read and had partial loss of vision due to a stroke 
following surgery.  Of the few adverse events that were H-level harms, hospital staff 
intervened after patients experienced life-threatening harm events.  This included one 
patient whose heart stopped during surgery, thus requiring life-saving intervention. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 17   
Some Medicare patients experienced adverse events that contributed to their 
deaths.  Ten percent of adverse events contributed to the patients deaths (I-level 
harm).  This translates to 1.4 percent of the roughly 1 million hospitalized Medicare 
patients14,800 patientsduring the 1-month study period.116  (See page 27 for the 
preventability determinations for these adverse events.) 
Although no single type of event was prominent within the sample as contributing to 
death, patients who died as a result of adverse events shared some commonalities.  In 
our sample, most had multiple, complex comorbidities, including cancer, morbid 
obesity, dementia, kidney failure, or diabetes.  Although the comorbidities were not 
directly related to the adverse events, they may have caused patients health to be 
more fragile and increased the complexity of their care.  For some patients, harm 
events may have hastened their deaths because they were already terminally ill or had 
a poor prognosis for survival.  For example, one patient with metastatic lung cancer 
experienced excessive gastrointestinal bleeding from anticoagulants (blood thinners) 
that were being used to treat atrial fibrillation (irregular heartbeat).  The bleeding led 
to other harms, including hypotension (low blood pressure), acute kidney injury, and 
ultimately death. 
Within our sample, 11 patients experienced adverse events that contributed to their 
deaths.  Of those patients, 7 experienced a series of related harm eventstermed 
cascade eventsthat contributed to their deaths.  Initial events progressed and 
triggered other related harm events that resulted in the patients death.  For example, 
one patient acquired a methicillin-susceptible Staphylococcus aureus (MSSA) infection 
during the hospital stay.  The infection led to septic shock, which contributed to the 
patients death.  Another cascade event involved substandard treatment of sepsis with 
insufficient fluid administration and inadequate antibiotic treatment, which led to 
septic shock, respiratory failure, and the patients death. 
An additional 13 percent of hospitalized Medicare patients 
experienced temporary harm during their hospital stays 
An additional 13 percent of Medicare patients experienced a temporary harm event 
during their hospital stays.  (This 13 percent of patients added to the 12 percent of 
patients who experienced an adverse event forms the 25-percent patient harm rate.  
Four percent of patients experienced both an adverse event and a temporary harm 
event; they are represented among the 12 percent who experienced an adverse 
event.)117  These temporary harm events required medical intervention but did not 
prolong stays, necessitate transfers to a higher level of care, require life-saving 
interventions, cause permanent harm, or contribute to death (i.e., E-level harm on the 
OIG-modified NCC MERP Index).  This projects to 137,234 Medicare patients 
experiencing only temporary harm events during their hospital stays in the 1-month 
study period. 
Although many cases of temporary harm represented minor occurrences, some 
temporary harm events could have developed into adverse events if hospital staff had 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 18   
not intervened.  For example, episodes of hypoglycemia (low blood glucose) can lead 
to coma and even death without prompt intervention.118  All of the hypoglycemic 
events in our sample that were classified as temporary harm (12 events) occurred in 
patients receiving insulin, with blood glucose levels ranging from 34 to 67 milligrams 
per deciliter (mg/dL).  The normal range for blood glucose is 80 to 130 mg/dL before 
a meal.119  One of these events involved a diabetic patient whose blood glucose level 
fell to 50 mg/dL after staff gave the patient a high dose of fast-acting insulin (70 units 
per milliliter) prior to a meal.  The patient experienced dizziness and staff took 
immediate steps to address the hypoglycemia by giving the patient orange juice and 
glucose tablets to raise the patients blood glucose.  They also adjusted subsequent 
insulin doses to prevent recurrence.  If left untreated, this event could have resulted in 
life-threatening complications. 
Medication-related harm events were the most common type of 
harm events 
Medication was the most common clinical category for both adverse events and 
temporary harm events.  Combined, 43 percent of patient harm events were related 
to medication.  The remaining harm events related to patient care (23 percent), 
procedures or surgeries (22 percent), and infections (11 percent).  (See Exhibit 5 for 
the percentage of events in each of the four clinical categories.) 
Exhibit 5: Adverse Events and Temporary Harm Events by Clinical Category 
All Events  Adverse Events  Temporary Harm 
Harm Event Categories 
(n=299)*  (n=115)   Events (n=184)*  
Medication  43%  41%   45% 
Patient Care  23%  13%  29% 
Procedure or Surgery  22%  28%  19% 
Infection  11%  18%  7% 
Total  100%  100%  100% 
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
* Column does not equal 100 percent due to rounding. 
 
Medication.  Forty-three percent of patient harm events were related to medication.  
These events commonly involved patients who experienced delirium (confusion, 
disordered speech, and/or hallucinations) or other changes in mental status or 
patients who experienced hypotension.  Many of the patients in our sample who 
experienced delirium or other changes in mental status were taking a combination of 
opioids.  For example, one patientwho was admitted to the hospital with chest and 
back pain related to spinal compressionexperienced delirium with difficulty 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 19   
speaking after staff gave the patient several different opioids (fentanyl, hydrocodone, 
and oxycodone).  Hospital staff intervened by adjusting the patients medication. 
Several patients experienced hypotension related to the use of opioids or 
antihypertensive medications.  For example, one patient was admitted to the hospital 
for right knee arthroplasty (total knee replacement) and experienced hypotension and 
dizziness after receiving two doses of an opioid (oxycodone) within 1 hour.  To resolve 
the hypotension, hospital staff stopped giving the patient the opioid and gave a 
substitute nonopioid drug for pain.   
Other common types of medication-related harm events included acute kidney 
injuries or excessive bleeding.  Acute kidney injuries were often related to the use of 
intravenous contrast agents, which enhance the visibility of the internal structure for 
imaging but can also pose a risk to the kidneys.  Excessive bleeding was often related 
to anticoagulants, which are used to prevent blood clots but can also cause bleeding.  
(See Exhibit 6 for the top five types of harm events related to medication within the 
sample.) 
Exhibit 6: Top Five Types of Harm Events Related to Medication Within the 
Sample  
Medication-Related  All Events  Adverse Events  Temporary Harm  
Harm Event Types  (n=299)  (n=115)  Events (n=184) 
Delirium or other change 
28  8  20 
in mental status 
Hypotension  19  5  14 
Acute kidney injury or 
18  8  10 
insufficiency 
Excessive bleeding  18  12  6 
Hypoglycemia  13  1  12 
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
 
PATIENT STORY 1: Excessive use of opioids led to severe hypotension 
  One medication-related adverse event involved a 67-year-old patient who was 
admitted for a right knee arthroplasty.  Two days after the procedure, the patient 
received a total of four doses of an opioid (oxycodone, 5 milligrams each) for 
postoperative pain in the morning.  The patient was also given one dose of another 
opioid (tramadol) following a short time interval the same morning.  Staff gave the 
patient these opioids within less than 4 hours.  Later that morning, the patient 
developed dizziness and hypotension (systolic blood pressure was less than 
90 millimeters of mercury (mmHg)).  To address the patients hypotension and 
dizziness, the provider lowered the dosage and frequency of the opioid and 
observed the patient in the hospital for an additional day.  Our physician-reviewers 
determined that the level of opioids given to the patient was excessive. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 20   
Patient Care.  Twenty-three percent of harm events related to patient care.  Patient 
care pertains to the daily care of patients, which is often performed by nurses.  These 
events commonly involved patients who experienced pressure injuries.  Pressure 
injuries ranged from unstageable to Stage 2 (on a scale increasing in severity from 
unstageable to Stage 4) and were identified on various parts of the body.120  For 
example, one patient developed two Stage 2 sacral (lower spine) pressure injuries 
several days after being admitted for abdominal pain and frequent diarrhea.  Another 
patient had a preexisting pressure injury on a hip that progressed from Stage 1 to 
Stage 2 during the hospital stay.   
Other common patient care-related harm events included skin tears or falls or other 
traumas with injury.  Skin tears, abrasions, and breakdowns occurred on different 
parts of the body, including the face, arm, and buttock.  For example, after having 
blood drawn, one frail patient experienced a skin tear on the left hand with a blister 
and wound drainage.  Another patient experienced two skin tears on the arm as the 
result of leaning directly against the bed rail.  For that event, the hospital treated the 
skin tears and placed a pillow between the patients arm and bed rail to prevent 
further injury.  Falls or other traumas also occurred during hospital stays and resulted 
in injuries ranging from minor abrasions to more serious injuries to the head and hip.  
For example, one patient experienced a traumatic hematoma (an abnormal 
accumulation of blood inside the body) of the right knee after accidently hitting a bed 
rail.  (See Exhibit 7 for the top five types of harm events related to patient care within 
the sample.) 
Exhibit 7: Top Five Types of Harm Events Related to Patient Care Within the 
Sample  
Patient Care-Related  All Events  Adverse Events  Temporary Harm 
Harm Event Types  (n=299)  (n=115)  Events (n=184) 
Pressure injury  22  2  20 
Skin tear, abrasion, or 
11  0  11 
breakdown 
Fall or other trauma with 
9  2  7 
injury 
Fluid or electrolyte disorders   9  5  4 
Intravenous catheter 
9  0  9 
infiltration, burn, or phlebitis  
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
 
Procedures and Surgeries.  Physician-reviewers categorized 22 percent of harm 
events as being related to procedures or surgeries.  These events often involved 
patients who experienced new episodes of hypotension as the result of a procedure 
or surgery.  For hypotension events that were associated with anesthesia, we 
categorized these events as related to a surgery or procedure rather than related to 
medication.  These instances of hypotension arose directly from the administration of 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 21   
anesthesia that was required to perform the procedure or surgery.  For example, one 
patient experienced hypotension during surgery to repair an inguinal (groin) hernia 
and another patient experienced hypotension during hip replacement surgery.  Both 
instances were related to anesthesia and required sustained treatment with 
vasopressors (medicine to raise blood pressure).   
Patients also experienced excessive bleeding as the result of a procedure or surgery.  
For example, one patient experienced serious bleeding after being given an 
anticoagulant (warfarin) following a colonoscopy to remove two polyps (small 
growths in the colon).  As a result, providers were able to remove only one polyp and 
the patient had to be readmitted days later for a second procedure to safely remove 
the remaining polyp after the initial bleeding had ceased.  (See Exhibit 8 for the top 
five types of harm events related to procedures and surgeries within the sample.) 
Exhibit 8: Top Five Types of Harm Events Related to Procedures and 
Surgeries Within the Sample  
Procedure and Surgery- All Events  Adverse Events  Temporary Harm 
Related Harm Event Types  (n=299)  (n=115)  Events (n=184) 
Hypotension  15  2  13 
Excessive bleeding  13  6  7 
Embolisms (i.e., vascular and fat 
5  4  1 
embolisms) 
Cerebrovascular accident  5  5  0 
Prolonged ileus  4  4  0 
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
 
 
PATIENT STORY 2: Postoperative bleeding led to other complications  
  One surgery-related adverse event involved a 46-year-old patient who was 
morbidly obese and had end-stage kidney disease, hypertension (elevated blood 
pressure), and diabetes.  The patient was admitted for a gastric sleeve resection 
(a procedure to remove part of the stomach) for weight loss.  A day after the 
operation, the patient developed hypotension and delirium.  The hospital staff 
subsequently identified bleeding from the patients surgical wound, which resulted 
in hemorrhagic shock.  The hospital then transferred the patient to the ICU where a 
central line was placed for rapid infusion of vasopressors to manage the patients 
blood pressure.  A scan of the patients abdomen revealed a large hematoma at the 
surgical site.  The shock led to severe acidosis and hyperkalemia and the patient 
required dialysis.  To compensate for the bleeding, providers gave the patient a 
total of 4 units of blood, transfused over 2 days until the bleeding resolved.  Our 
physician-reviewers determined that a proper surgical technique would have likely 
prevented this event. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 22   
Infections.  Physician-reviewers categorized 11 percent of harm events as being 
related to infections.  These harm events commonly involved patients who 
experienced respiratory infections.  In our sample, most of the respiratory infections 
were related to two types of pneumonia: ventilator-associated pneumonia and 
aspiration pneumonia.  For example, one patient was admitted to the hospital for a 
stroke resulting in dysphagia (difficulty swallowing).  The patient received tube 
feedings that led to aspiration pneumonia after the patient inhaled the feedings.  
Other common infections included surgical site infections, thrush, sepsis, and C. diff 
infections.  (See Exhibit 9 for the top five types of harm events related to infections 
within the sample.) 
Exhibit 9: Top Five Types of Harm Events Related to Infections Within the 
Sample  
Infection-Related Harm  All Events  Adverse Events  Temporary Harm 
Event Types  (n=299)  (n=115)  Events (n=184) 
Respiratory infection  8  6  2 
Surgical site infection  6  6  0 
Thrush  5  0  5 
Sepsis  4  4  0 
C. diff infection  3  3  0 
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
 
 
PATIENT STORY 3: An infected hip implant required readmission for surgery   
  One infection-related adverse event involved a 69-year-old patient who was 
hospitalized for a fall and required hip replacement surgery with placement of a 
prosthesis (implant).  While the patient was being seen during a followup 
appointment at an outpatient clinic 10 days after discharge from the hospital, the 
provider found purulent drainage (pus) at the patients surgical site indicating an 
infection.  The wound culture tested positive for methicillin-resistant Staphylococcus 
aureus (MRSA).  After the provider identified the infection, the patient was given 
antibiotics.  The patient was then readmitted to the hospital 5 days later for 
additional surgery to clean the wound and replace the infected implant.  The 
patient was discharged after 7 days of recovery.  Our physician-reviewers 
determined that this event was likely preventable. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 23   
Physician-reviewers determined that 43 percent of adverse 
events and temporary harm events were preventable 
The incidence rates for adverse events and temporary harm events include all events 
regardless of preventability, but physician-reviewers also assessed whether each event 
could have been prevented.  They determined that 43 percent of adverse events and 
temporary harm events were preventable, and that 56 percent were not preventable.  
Physician-reviewers were unable to determine preventability for the remaining three 
events within the sample because of incomplete documentation or complexities in the 
patients conditions.121  Exhibit 10 shows the percentages of events within each 
preventability assessment.   
Exhibit 10: Adverse Events and Temporary Harm Events by Preventability 
Determination 
All Events  Adverse Events  Temporary Harm 
Preventability Assessment* 
(n=299)  (n=115)  Events (n=184) 
Preventable 
Harm could have been avoided 
43%  45%  41% 
through improved assessment or 
alternative actions 
Not Preventable  
Harm could not have been avoided 
56%  53%  58% 
given the complexity of the patients 
condition or care required 
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
* We cannot reliably project the proportion of harm events where preventability was unable to be determined. 
If we included only preventable events in the estimated incidence rate of harm among 
Medicare patients, the overall harm rate would be 13 percent (rather than 25 percent), 
the rate of adverse events would be 6 percent (rather than 12 percent), and the rate of 
additional patients experiencing temporary harm events would be 7 percent (rather 
than 13 percent). 
Events related to procedures or surgeries were more likely to be determined by our 
physician-reviewers to be not preventable.122  However, we did not find statistically 
significant differences in the preventability determinations for medication or patient 
care-related events.123  Because of the small number of events, we were not able to 
determine the difference in preventability for infection-related events.  In our sample, 
physician-reviewers indicated that most of the procedure-related and surgery-related 
events that were not preventable occurred even though providers followed proper 
preparation and procedures.  Many of these patients were also in poor health, which 
made them more susceptible to the events.  For example, one particularly frail patient, 
who had multiple medical problems and was in declining health prior to admission, 
experienced gastrointestinal bleeding after undergoing surgery to remove the 
gallbladder.  Given the patients poor health and complex diagnosis (the patient had 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 24   
ampullary stenosis, a bile duct obstruction), our physician-reviewers determined that 
the bleeding was likely not preventable.  Exhibit 11 shows the percentages of 
preventable and not preventable harm events within each clinical category. 
Exhibit 11: Preventable and Not Preventable Adverse and Temporary Harm 
Events Within Each Clinical Category 
Clinical Category  Preventable Events  Not Preventable Events 
Medication (n=130)*  42%  57% 
Patient Care (n=69)  52%  48% 
Procedure or Surgery (n=67)*   25%  72% 
Infection (n=33)**  --  -- 
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
Note: The 95-percent confidence intervals for patient care and procedure or surgery preventability estimates exceed 
10-percent absolute precision. 
* Row does not sum to 100 percent because reviewers were unable to determine the preventability for 1 or more 
events. 
** We are unable to reliably project the proportion of infection-related events due to the small sample size. 
 
Similarities in Preventability Assessments.  Within the clinical categories, 
physician-reviewers often gave the same preventability assessment for events with 
similar characteristics.  For example, they assessed 15 of 18 excessive bleeding events 
related to medication as not preventable because the patients received appropriate 
care, but poor health or comorbidities made them susceptible to a bleeding event or 
made them difficult to treat.  For the remaining three events, physician-reviewers 
determined that two were preventable and one was unable to be determined.  One of 
the preventable excessive bleeding events involved a patient who was admitted with 
jaundice and diagnosed with autoimmune hepatitis (a condition where the body 
attacks the liver), which can lead to internal bleeding.  The patient was prescribed an 
anticoagulant to prevent blood from clotting and resulting in melena (black, tarry 
stools associated with upper gastrointestinal bleeding).   
Differences in Preventability Assessments.  In other cases, preventability 
determinations for similar events differed based on the patients health and whether 
providers took preventative measures.  For example, physician-reviewers often 
described pressure injuries as preventable when patients at risk for pressure injuries 
did not receive proper preventative care.  One high-risk patient, who was immobile 
and had chronic diarrhea, was admitted to the hospital with fever and sepsis.  While in 
the hospital, the patient was not turned regularly in bed and developed two pressure 
injuries in different locations (the sacrum and elbow).  Physician-reviewers described 
pressure injuries as not preventable when they found evidence that the patient 
received proper preventative care but still developed pressure injuries because of 
comorbidities that increased the patients risk.  Another patient with dementia and 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 25   
numerous preexisting pressure injuries was admitted for pneumonia and sepsis.  
During the hospital stay, the patient was on a strict turning schedule but did not 
always cooperate because of their dementia.  This led to a new pressure injury over 
the patients coccyx (tailbone) that our physician-reviewers determined was likely not 
preventable. 
Preventable events were commonly linked to substandard or 
inadequate care provided to the patient 
Based on their clinical judgment, physician-reviewers selected one or more rationales 
to support each preventability determination.  These contributing factors are not 
necessarily mutually exclusive, and our physician-reviewers often identified multiple 
factors as having contributed to preventable events.  Among preventable events, 
physician-reviewers determined that 33 percent involved patients receiving 
substandard treatment or therapeutic care and 31 percent involved patients receiving 
substandard or inadequate preventative care.  In one such case, a patient became 
unresponsive after receiving multiple medications post-surgery for an ankle fracture, 
including three opioids (hydrocodone, fentanyl, and morphine).  After reviving the 
patient, hospital staff discontinued the opioids.  Our physician-reviewers determined 
that this event likely could have been prevented by using a less aggressive pain 
management regimen after surgery.  (See Appendix F, Exhibit F-3 for a complete list 
of the rationales cited by physician-reviewers for preventable events.) 
 
PATIENT STORY 4: A delay in surgery led to a cascade of preventable harm 
events, additional treatment, and contributed to the patients death. 
  One preventable adverse event involved an 89-year-old patient who had a recent 
stroke and a history of chronic obstructive pulmonary disease.  The patient was 
hospitalized for sepsis after complaining of abdominal pain and nausea.  Providers 
determined that the patient required surgery to remove dead tissue that they found 
in the patients small intestine.  However, providers unnecessarily delayed surgery 
for 5 days while the patient continued to deteriorate.  This delay led to a cascade of 
harms that included worsening of the small intestine, contamination of the 
abdomen with pus, septic shock with an associated kidney injury, and delirium.  
These conditions required additional surgeries and intubation, ultimately resulting 
in the patients death.  Our physician-reviewers determined that this event was 
likely preventable because of the delay in care that our reviewer determined was an 
error related to medical judgment and patient management. 
Events that were not preventable commonly occurred despite 
providers following proper preparation and procedures 
Among events that were not preventable, physician-reviewers determined that over 
half (51 percent) occurred despite providers following proper preparation and 
procedures and 36 percent occurred because patients were highly susceptible to the 
events due to poor health status.  As with preventable events, these rationales are not 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 26   
mutually exclusive, and physician-reviewers often cited multiple reasons for events 
being not preventable.  Examples of events occurring despite providers following 
proper preparation and procedures included acute kidney injuries and new episodes 
of hypotension resulting from necessary medications.  For example, one patient 
experienced an unexpected new episode of hypotension while on a medication 
required during surgery to repair a fractured humerus (arm bone).  Physicians 
determined that this event was not preventable because the patient needed the 
medication during the surgery, so providers had followed proper preparation and 
procedures.  (See Appendix F, Exhibit F-3 for a complete list of the rationales cited by 
physician-reviewers for events that were not preventable.) 
  PATIENT STORY 5: Complications associated with chemotherapy for a stem cell 
transplant that were considered not preventable 
  A 76-year-old patient with non-Hodgkins lymphoma (cancer of the immune system) 
was admitted for chemotherapy and a stem cell transplant and experienced multiple 
harm events that were not preventable.  While receiving chemotherapy medication 
(cytarabine and etoposide) prior to the transplant, the patient developed a 
medication-induced toxic skin rash with peeling over the torso and upper extremities 
that lasted several days.  The patient also experienced episodes of diarrhea due to the 
chemotherapy medication.  The last harm event was a respiratory infection, 
neutropenic (low white blood cell count) pneumonia, that developed about a week 
into the stay.  Our physician-reviewers determined that these events were likely not 
preventable because these are known complications associated with chemotherapy 
that are difficult to prevent and providers followed proper preparation and procedures. 
In our sample, 7 of the 11 adverse events that contributed to or 
resulted in death were preventable 
Our physician-reviewers determined that 7 of the 11 events that contributed to or 
resulted in death were preventable.  Reviewers indicated that preventable events 
involved substandard treatment or therapeutic care, inadequate patient monitoring, 
inadequate care plans, inadequate admission assessments, and provider errors.  For 
example, one patient was administered total parenteral nutrition against the 
recommendation of a nutritionist leading to pulmonary edema (fluid in the lungs) and 
refeeding syndrome (a dangerous shift in fluids and electrolytes), which ultimately 
hastened the patients death.  Another patient experienced severe bradycardia (slow 
heart rate) as the result of poorly managed hyperkalemia while being transported to a 
different floor within the hospital for an x-ray and required emergency assistance.  
The emergency response team was unable to locate the patient, who suffered cardiac 
arrest and died. 
Physician-reviewers determined that the remaining four events that contributed to or 
resulted in death were not preventable.  Poor health status and complex diagnoses 
contributed to events not being preventable.  Two of these events also occurred even 
though providers followed proper preparation and procedures.  For example, one 
patient was admitted for surgery to remove a large necrotized (dead) part of the 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 27   
colon.  The patient received appropriate care, but excessive bleeding and anemia 
following the surgery contributed to the patients death. 
CMSs two policies on hospital-acquired conditions create 
payment incentives for harm prevention but do not apply to the 
vast majority of harm events that patients experienced 
CMSs two HAC policies (HACRP and DRA HAC) do not apply to the vast majority of 
harm events that patients experienced.  These programs create incentives for harm 
prevention by reducing payments to hospitals for HACs from two separate lists.  
Despite CMSs reported success in reducing HACs, both lists are narrow in scope and 
employ specific criteria for inclusion of events, limiting the effectiveness of these 
programs in addressing patient safety broadly.  (See Appendix H for the harm events 
that were included on these lists and Appendix A for the NQF list.) 
Hospital-Acquired Condition Reduction Program (HACRP).  CMS established the 
HACRP list in FY 2015 as a pay-for-performance program that adjusts payments to 
hospitals with high rates of HACs relative to other hospitals.  Under this program, 
CMS reduces hospital payments based on metrics identified through administrative 
claims data and reporting of hospital-acquired infections.  The HACRP list 
incorporates only 15 types of harm events as having implications for a hospital, and 
few of the harm events we found were affected by this program.   
We found that 5 percent of harm events experienced by Medicare patients were on 
the HACRP list.  These events included hospital-acquired infections, sepsis, a fall with 
a hip fracture, a pulmonary embolism (lung artery blockage caused by a blood clot), 
and hemorrhage (bleeding).  In our sample, infections were the most common type of 
event that qualified for the HACRP list.  These included surgical site infections, a 
CLABSI, a MRSA infection, a C. diff infection, and catheter-associated urinary tract 
infections (CAUTIs). 
In addition to designating a small number of event types under the HACRP list, CMS 
uses narrow criteria that further limit its ability to capture harm events.  For example, 
with surgical site infections, HACRP counts only infections associated with procedures 
involving the colon or an abdominal hysterectomy (a surgery to remove all or part of 
the uterus).  Although we did identify surgical site infections that met these criteria, 
some infections did not, including one that occurred after a laminectomy (back 
surgery). 
Deficit Reduction Act Hospital-Acquired Conditions (DRA HAC).  CMS established 
the DRA HAC list to comply with the DRA of 2005 to prevent hospitals from receiving 
increased payment resulting from certain HACs that develop during the hospital stay.  
CMS uses POA indicators assigned by hospitals to each claim to identify certain HACs 
that developed during the stay.  The DRA HAC list, which overlaps with the HACRP list, 
includes only 14 types of events and few of the harm events we observed were 
affected by the policy.  We found that 2 percent of harm events experienced by 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 28   
Medicare patients were on CMSs DRA HAC list.  These events involved a fall resulting 
in hip fracture; a trauma resulting in rib fracture; two CAUTIs; and a CLABSI, which is a 
type of vascular catheter-associated infection.   
For the few events on the DRA HAC list, hospitals did not always include the diagnosis 
codes on claims that CMS uses to identify these events.  Only one of the five HACs 
identified in our sample was included in the associated Medicare claim.  As a result, 
the remaining four HACs were not identifiable through analysis of the claims data that 
CMS uses to implement the DRA HAC payment policy.  For example, we found that 
hospitals coded the two CAUTIs with a less specific diagnosis that would not be 
detected by the policy.  Hospitals omitting the specific codes CMS monitors for this 
policy may limit its awareness of the HACs occurring in Medicare-certified hospitals.  
Since our review, CMS has taken additional steps to flag claims with unspecified code 
types (e.g., unspecified site or etiology) and to educate providers about more specific 
codes that may be available.124  Additionally, new ICD-10-CM Official Guidelines for 
Coding and Reporting FY 2022 were released with language requiring providers to 
code to the highest level of specificity for diagnoses and procedures.125   
CMSs narrow criteria for specific harm event types on the DRA HAC list also limited 
the agencys ability to capture harm events.  For example, like the HACRP, the DRA 
HAC list also narrowly defines surgical site infections.  As a result, none of the surgical 
site infections we identified met the DRA HAC criteria because it applies only to 
infections following a limited set of procedures.  For example, one event that did not 
qualify was an infection following an orthopedic procedure involving the hip because 
the procedure did not involve the spine, neck, shoulder, or elbow. 
Nearly a quarter of patients who experienced harm events 
required treatment that led to additional Medicare costs 
Combining both Medicare IPPS patients (i.e., patients whose hospital care was paid 
directly by Medicare according to a diagnosis related group) and non-IPPS patients 
(i.e., patients whose care was paid through another arrangement, such as a managed 
care organization), 23 percent of patients who experienced a patient harm event, 
either a preventable or nonpreventable, required treatment that led to additional 
Medicare costs.  The events also potentially increased patient costs in the form of 
coinsurance and deductible payments.126  These costs were incurred either during the 
patients hospital stay or for an additional stay necessary to ameliorate the harm.  
Because of the variability of these costs and the small number of sampled patients 
with events that resulted in additional costs, we could not estimate the total dollar 
amount with a high level of precision.  Below, we provide the estimated costs for both 
IPPS and non-IPPS patients, as well as the associated 95-percent confidence intervals.  
The cost of events was substantial for some patients with individual amounts over 
$40,000.  Combined, we estimated the costs for all events to be in the hundreds of 
millions of dollars for October 2018.   
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 29   
  PATIENT STORY 6: An increase in potential Medicare payment due to 
complications from a heart valve replacement procedure 
  One harm event that increased the allowable Medicare payment of a hospital stay 
involved an 81-year-old patient admitted for a transcatheter aortic valve 
replacement (heart valve replacement).  During the procedure, the patient 
experienced a likely preventable adverse event involving a prolonged period 
(around 1 hour) of hypotension while under sedation.  This led to pulseless 
electrical activity (a state where the pulse cannot be felt).  Staff intervened with 
cardiopulmonary resuscitation, vasopressors, and insertion of a heart pump.  
Although staff successfully revived the patient, the patient experienced acute 
encephalopathy (altered brain function) as a result of the initial harm.  We found 
that the hypotension-related event potentially increased the Medicare payment by 
$48,000 (from about $63,000 to just over $111,000).   
IPPS Costs.  Two-thirds of patients received care that was paid under the Medicare 
IPPS.  We found that 20 percent of patients covered by IPPS who experienced harm 
events incurred additional costs to the Medicare program and potentially to the 
patients themselves as a result.127  In one case, a patient experienced a stroke 
following an outpatient angioplasty that resulted in an unplanned hospital admission.  
The additional hospital stay needed to treat the stroke cost Medicare $44,000.   
We estimated that Medicare spent $520 million on IPPS costs associated with patient 
harm events during October 2018.128  The 95-percent confidence interval for this 
estimate spans $223 million to $818 million.  This correlates to between 2 and 
8 percent of Medicare IPPS expenditures for October 2018. 
Non-IPPS Costs.  The remaining one-third of patients received care that was paid 
under managed care plans or other non-IPPS payment systems.129  We found that 
28 percent of non-IPPS patients who experienced harm events incurred additional 
costs to the Medicare program and potentially to the patients themselves as a result.  
In one case, a non-IPPS patient incurred an additional $28,000 during the sampled 
hospital stay because the patient experienced respiratory failure due to anesthesia, 
which required the hospital to transfer the patient to the ICU with ventilator support.   
Using the IPPS payment rates as a proxy for the payments associated with non-IPPS 
patients, we estimated that Medicare spent $281 million on hospital costs associated 
with harm events for non-IPPS patients during October 2018.130  The 95-percent 
confidence interval for this estimate spans $124 million to $439 million.   
Additional Costs.  In addition to the Medicare costs associated with hospital care in 
October 2018 and readmissions within 30 days, some patients likely required followup 
care on an outpatient basis or even hospital readmissions after our study period.  
These additional costs are not reflected in our estimates.  This additional care may 
include physician office visits, medication, and rehabilitation services during and after 
our study period.  Further, some patients may not regain the full functional status they 
had prior to the harm events, leaving them at greater risk for poor health outcomes in 
the future, with their associated costs, and lost wages for them and their caregivers. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Findings | 30   
CONCLUSION AND RECOMMENDATIONS 
 
In the decade since OIG reported the first national incidence rate of patient harm 
among hospitalized Medicare patients and more than 20 years since the publication 
of the Institute of Medicine report To Err Is Human: Building a Safer Healthcare 
System, increased national attention has been devoted to patient safety.  HHS and 
health care organizations across the Nation have since taken steps to improve patient 
safety with advances in hospital practices, both in patient safety and clinical practice.  
The nationwide patient safety movement has also experienced increased Federal 
involvement in tracking and reducing preventable patient harm.  
As the Federal Governments principal Department for protecting the health of 
Americans, HHS is uniquely positioned to lead national efforts to reduce patient harm 
events in hospitals.  A number of agencies within HHS share responsibility for 
addressing patient harm, including AHRQ, which leads HHS efforts to improve health 
care quality and CMS, which is the Nations largest health care payer and oversight 
entity.  In addressing the recommendations in OIGs 2010 report, and as part of wider 
patient safety efforts, both agencies launched new programs and initiatives designed 
to better track, reduce, and contain the costs associated with treating harm events.   
Addressing patient harm and promoting patient safety takes on added urgency in 
light of the ongoing pandemic and its effects on hospital operations.131  Despite 
substantial action by HHS agencies and success in reducing certain types of events, 
patient harm remains pervasive, is often preventable, and continues to cost the 
Medicare program and patients.  We found that an estimated 25 percent (about 1 in 
4) of Medicare patients experienced patient harm events during their hospital stays in 
October 2018, and that 43 percent of events could have been prevented if patients 
had received better care.  Nearly a quarter of patients who experienced harm events 
incurred additional Medicare costs and patient costs as a result.  Given our findings, 
HHS leadership and agencies must work with urgency to address these persistent 
harm rates and promote patient safety in hospitals. 
We recommend that CMS: 
Update and broaden its lists of hospital-acquired conditions to 
capture common, preventable, and high-cost harm events 
CMS should look for opportunities to broaden or expand its lists of hospital-acquired 
conditions, particularly the DRA HAC or HACRP list.  As the largest health care payer 
in the Nation, CMS is uniquely positioned to align payment with quality by ensuring 
that coverage and payment are available to support only appropriate clinical 
practices.  Although CMS reported success in reducing HACs through the DRA HAC 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Conclusion and Recommendations | 31   
and HACRP programs, we found that these lists addressed few of the harm events 
that Medicare patients experienced. 
CMS should update one or both of its lists of HACs to include additional harm events.  
Although CMS annually considers new measures for its quality improvement 
programs, CMS last added measures to the DRA HAC list in FY 2013 and the HACRP 
list in FY 2017.  If adopted, the current measures under consideration may further 
incentivize hospitals to improve patient safety.  We encourage CMS to continue 
studying other types of harm events that may be good candidates for one of the HAC 
lists and working with HHS agencies, such as AHRQ and CDC, to identify other 
conditions that would be appropriate to include  in its lists of HACs.   
Explore expanding the use of patient safety metrics in pilots and 
demonstrations for health care payment and service delivery, as 
appropriate 
As part of broader efforts to connect payment to quality of care, CMS should explore 
ways to expand the use of patient safety metrics with existing or new pilots and 
demonstrations for health care payment and service delivery.  An important 
component in this effort is the CMS Innovation Centerauthorized under the ACA
which focuses on designing, testing, and implementing new health care payment and 
service delivery models to improve quality of care and address rising health care 
costs.  The CMS Innovation Center independently evaluates these models through 
pilots and demonstrations for impact on both expenditures and quality of care to 
determine whether to maintain and expand them.   
In refining and developing these new methods for health care payment and service 
delivery, CMS should consider new options for using patient safety metrics to 
evaluate the effectiveness of its models.  This could include assessing reductions in 
the incidence of preventable patient harm events to measure model effectiveness.  
The CMS Innovation Center could leverage harm event surveillance programs to 
monitor rates of different types of harm in participating hospitals and factor in the 
cost savings from reductions in these harm events.  This approach could bolster 
CMSs efforts to identify effective demonstrations and pilots that promote quality of 
care while reducing costs to Medicare. 
 
 
 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Conclusion and Recommendations | 32   
As OIG previously recommended, develop and release 
interpretive guidance to surveyors for assessing hospital 
compliance with requirements to track and monitor patient 
harm events 
Our findings lend new urgency to OIGs prior recommendation that CMS provide 
interpretive guidance to surveyors for assessing hospital compliance with QAPI 
requirements to track and monitor patient harm.132  The QAPI Condition of 
Participation for Medicare requires that hospitals have a program to track adverse 
events and to demonstrate quality improvement.  In 2019, CMS reported to OIG that 
it had developed this interpretive guidance and was engaged in the rulemaking 
process to finalize its release but has not yet released the guidance.  This 
recommendation supersedes OIGs prior recommendation on this issue. 
We recommend that AHRQ: 
With support from HHS leadership, coordinate agency efforts to 
update agency-specific Quality Strategic Plans  
In the years since HHS created its National Quality Strategy to improve health care, 
and subsequent national action plans to reduce patient harm events, protecting the 
health and safety of Medicare patients remains a top management challenge.  
Although HHS agencies have reported reductions in certain types of harm events, the 
overall rate of harm demonstrates a strong need for further action.   
With support from HHS leadership, AHRQ should coordinate agency efforts to update 
agency-specific Quality Strategic Plans and ensure alignment with the priorities of the 
National Quality Strategy.  These Quality Strategic Plans have not been updated on 
AHRQs website since 2016.  AHRQ could assist the agencies in a number of ways, for 
example by providing a common framework for agencies to assess their plans and 
patient safety initiatives, facilitating communication among the agencies about the 
plans, and providing guidance and technical assistance to agencies as needed.  
AHRQs role in supporting quality and safety planning throughout HHS would 
promote information-sharing and a coordinated approach to patient safety among 
HHS operating divisions. 
Optimize use of the Quality and Safety Review System (QSRS), 
including assessing the feasibility of automating data capture 
for national measurement and to facilitate local use  
In its response to the draft report, AHRQ reported that it is currently using QSRS to 
measure rates of patient harm at the national level but has not yet fully deployed the 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Conclusion and Recommendations | 33   
systems planned functionality.  AHRQ has not yet reported data from the new 
system.  QSRS still requires manual data entry, which individual hospitals and health 
systems reported to AHRQ is a significant barrier to use.  AHRQ reported to OIG that 
it is assessing the feasibility of automating the capture of data from medical records 
which would help facilitate use by individual hospitals and health systems.  
Automating data capture would likely also enable AHRQ to be more efficient in its 
measurement of national data. 
AHRQ should continue to optimize use of QSRS, including completing its feasibility 
assessment of automating data capture.  AHRQ should also review the events we 
identified in this study and consider whether it should add additional types of harm 
events to the system.  We encourage AHRQ to share data from QSRS with CMS to 
help expand its lists of HACs and with other agencies, such as CDC, to inform and 
coordinate patient safety activities. 
Develop an effective model to disseminate information on 
national clinical practice guidelines or best practices to improve 
patient safety 
Our findings suggest that educating providers on national clinical practice guidelines 
or best practices could help reduce preventable patient harm events such as pressure 
injuries.  Given these benefits, AHRQ should develop an effective model to 
disseminate information on these guidelines and best practices to improve patient 
safety.  Despite an agency effort to identify new models for disseminating and 
accessing evidence-based clinical practice guidelines, AHRQ has not released 
information on the status of this initiative.  AHRQ could consider tailoring the scope 
of a new model to focus on patient safety best practices, including topics related to 
reducing some of the types of patient harm events we identified.  AHRQ could also 
solicit input from stakeholders, such as medical specialty societies, to compile 
evidence-based practices for harm reduction and leverage its Making Healthcare Safer 
series of reports to promote these practices.  Using these resources, AHRQ should 
establish a new method to share evidence on effective clinical practices to make such 
information readily discoverable, accessible, and useable to frontline health care 
practitioners to improve patient safety. 
Continue efforts to identify and develop new strategies to 
prevent common patient harm events in hospitals 
AHRQ should continue to invest in new research, tools, and projects to provide a 
mechanism to improve quality of care by developing evidence-based approaches to 
reduce all causes of patient harm.  These efforts could culminate in effective strategies 
to prevent some of the types of patient harm events that we identified such as new 
episodes of hypotension related to medications like opioids and anesthesia.   
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Conclusion and Recommendations | 34   
AHRQ should use the insights from our evaluation to inform and bolster patient 
safety research.  This could include new toolkits and resources for providers to 
address the most common harm events identified in this report.  AHRQ should then 
assess the impact of these new tools with implementation projects and impact case 
studies.  As advances in medicine and technology continue, AHRQ should focus on 
ensuring that patient safety efforts remain abreast of these advances and work with 
urgency to help guide national efforts to improve our understanding of the extent 
and causes of patient harm in hospitals.  To help accomplish this, AHRQ should 
actively and continually coordinate with stakeholders, including providers, accreditors, 
researchers, and States, to combat patient harm in hospitals. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Conclusion and Recommendations | 35   
AGENCY COMMENTS AND OIG RESPONSE 
 
CMS and AHRQ concurred with our recommendations.  CMS concurred with three 
recommendations and AHRQ concurred with four recommendations.  OIG appreciates 
the efforts of CMS, AHRQ, and other HHS agencies to improve patient safety and 
promote quality of care.  Their comments are summarized below and for the full text 
of their comments, see Appendix I on page 90.   
CMS Comments and OIG Response 
CMS stated that preventable adverse and temporary harm events are unacceptable 
and reported ongoing efforts to improve patient safety.  CMS also described evidence 
of specific improvements in patient safety during the past decade resulting from 
these efforts, including reducing the incidence of several HACs, such as adverse drug 
events and injuries from falls.   
CMS described several programs and policies it uses to achieve its quality of care 
goals: (1) establishing and enforcing minimum standards for care through the CoPs, 
including the QAPI CoP which requires hospitals to monitor adverse events and 
develop improvement plans; (2) implementing a range of quality reporting and value-
based purchasing programs; and (3) managing the QIO program, which is dedicated 
to improving health care quality for Medicare beneficiaries and has a focus on 
engaging hospitals to implement best practices and improve patient safety. 
In its response to the draft report, CMS also commented on OIGs sample size and on 
comparing the results from this study to those of the 2010 OIG report.  Regarding the 
sample size, OIG selected the number of sampled patients to allow for national 
projections at the 95-percent confidence interval (see Appendix F).  Regarding the 
comparison between reports, there are important limitations to comparing the results 
of this study with the prior study and therefore we did not include a comparison in 
our report findings.  We offer a discussion of the comparison that includes its 
limitations beginning on page 38.   
Recommendation 1: CMS concurred with the recommendation to update and 
broaden its lists of HACs to capture common, preventable, and high-cost harm 
events.  CMS reported that it is considering new measures for inclusion in several 
CMS payment programs, including HACRP, through the annual pre-rulemaking 
measure selection process and subsequent rulemaking.  CMS added two new 
measures for reporting to the Hospital Inpatient Quality Reporting Program 
beginning in 2023 (i.e., measures for reporting glycemic management).  
Recommendation 2: CMS concurred with the recommendation to explore expanding 
the use of patient safety metrics in pilots and demonstrations for health care payment 
and service delivery, as appropriate.  CMS provided two examples of models that 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Agency Comments and OIG Response | 36   
incorporate patient safety measures and reported that it will continue to consider new 
opportunities to include patient safety metrics in pilots, demonstrations, and models. 
Recommendation 3: CMS concurred with the recommendation to develop and 
release interpretive guidance to surveyors for assessing hospital compliance with 
QAPI requirements to track and monitor patient harm events.  In 2010, CMS 
concurred with a version of this recommendation.  CMS reported that it is still 
considering the best option for updating the interpretive guidance and cited evidence 
that surveyors are conducting such assessments without formal guidance. 
AHRQ Comments and OIG Response 
AHRQ stated that it appreciates the focus the report gives to its role in promoting 
patient safety and reducing patient harm. 
Recommendation 4: AHRQ concurred with the recommendation to coordinate 
agency efforts to update agency-specific Quality Strategic Plans, ensuring alignment 
with the priorities of HHSs National Quality Strategy.  After receiving AHRQs 
comments, we clarified how AHRQ might implement the recommendation, including 
assisting agencies in performing their own assessments as they update their Quality 
Strategic Plans.  We anticipate that AHRQ may provide a framework for agencies to 
conduct their individual assessments and that it will act as the coordinating agency 
for these efforts across the Department. 
Recommendation 5: AHRQ generally concurred with the recommendation as 
originally written but explained that QSRS has been fully deployed at the national 
level and that it is currently assessing the feasibility of automating the capture of data 
from medical records.  In response, we revised the recommendation to reflect the 
current status of the system.  We now recommend that AHRQ should optimize use of 
QSRS, including assessing the feasibility of automating data capture for national 
measurement and to facilitate local use.  AHRQ has since concurred with this revised 
recommendation. 
Recommendation 6: AHRQ concurred with the recommendation to develop an 
effective model to disseminate information on national clinical practice guidelines or 
best practices to improve patient safety.  AHRQ reported that it will explore working 
with the National Steering Committee for Patient Safety, and other similar groups, to 
achieve this shared objective. 
Recommendation 7: AHRQ concurred with the recommendation to continue efforts 
to identify and develop new strategies to prevent common patient harm events in 
hospitals.  AHRQ reported that it will continue to invest in new research, tools, and 
projects consistent with its mission to produce evidence to make health care safer, 
higher quality, more accessible, equitable, and affordable; and will work within HHS 
and with other partners to make sure that the evidence is understood and used.   
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Agency Comments and OIG Response | 37   
COMPARISON TO THE 2010 REPORT 
 
Patient harm events are common and often preventable, similar 
to OIGs findings in the 2010 report 
Our findings suggest that patient harm events continue to be widespread among 
Medicare patients in hospitals since the publication of our 2010 report, with an 
estimated 27 percent of Medicare patients experiencing harm in 2008 and an 
estimated 25 percent of Medicare patients experiencing harm in 2018.  We conducted 
both studies using a similar sample size and the same general methodology.  When 
comparing the results, we did not detect a statistically significant difference in the 
rates of patient harm, severity of harm events, or preventability of harm events over 
time, but due to sample size constraints, our ability to identify small statistical 
differences between those rates, or within specific types of harm, is limited.133  
Changes in the Medicare population and slight changes in the study methodology 
(described below) also limit the appropriateness of a comparison.  Notably, reports by 
AHRQ and CDC indicate success in reducing specific types of harm.134  Exhibit 12 
shows the patient harm event estimates and preventability for both reports, and 
below we explain the differences between the two studies. 
Exhibit 12: Patient Harm Event Estimates in 2008 and 2018 
Incidence of Patient Harm  2008   2018 
Patients Who Experienced Harm Events  (n=780)  (n=770) 
Adverse event or temporary harm event  27%  25% 
Adverse event  13%  12% 
Temporary harm event*  13%  13% 
Severity Level of Harm Events  (n=302)  (n=299) 
Adverse events  42%  38% 
Temporary harm events  58%  62% 
Preventability of Harm Events   (n=302)  (n=299) 
Preventable events  44%  43% 
Not preventable events  51%  56% 
Sources: OIG analysis of hospital stays for 770 Medicare patients in October 2018 and 780 Medicare patients in 
October 2008 (OEI-06-09-00090). 
Note: Our definition of adverse events in the 2010 report included all harm events identified on the HAC and NQF lists.   
* The rate of patients who experienced temporary harm events is composed of patients who experienced at least one 
temporary harm event and no adverse events.  
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Comparison to the 2010 Report | 38   
Medicare data indicates that patients have higher rates of some 
chronic diseases since the 2010 report 
To provide more context to the comparison between the two reports, we examined 
the proportion of Medicare patients with chronic diseases using CMS statistics from 
2008 compared to 2018 (the years of data collection for both reports).  (We did not 
assess the incidence of chronic diseases for our specific sample of patients.)  Research 
indicates that the prevalence of comorbidities is rising in the Medicare population, 
and that Medicare patients are being treated for more clinically complex conditions 
and diagnoses than in the past.135  Comorbidities have been tied to a higher risk of 
patient harm events.136  For example, patients with chronic kidney disease may be at 
greater risk for harm such as acute kidney injury or insufficiency.137  As a result, harm 
rates may be affected, in part, by the complexity of care required to treat a patient 
population with more comorbidities.  
The data showed that Medicare patients tended to have more chronic diseases in 
2018 than in 2008 with higher rates of comorbidities for 15 of the 21 conditions 
tracked by CMS.138  According to CMS program statistics, Medicare patients had 
higher rates of chronic kidney disease, hyperlipidemia (elevated cholesterol), and 
hypertension, among others.139  Conversely, some rates were lower for certain 
diseases and conditions such as ischemic heart disease and heart failure.  Exhibit 13 
shows selected rates of chronic diseases with some of the greatest changes among 
Medicare patients between 2008 and 2018. 
Exhibit 13: Differences in Rates of Selected Chronic Diseases and Conditions 
Between 2008 and 2018 in the Medicare Patient Population 
Percentage of  Percentage of 
Chronic Disease or  Difference in Rates 
Medicare Patients  Medicare Patients 
Condition  2008 vs 2018 
in 2008  in 2018 
Chronic kidney disease  12.3%  24.5%  +12.2% 
Hyperlipidemia  41.9%  47.7%  +5.8% 
Hypertension  54.9%  57.2%  +2.3% 
Heart failure  16.3%  14.0%  -2.3% 
Ischemic heart disease  31.0%  26.8%  -4.2% 
Source: OIG analysis of CMS, Chronic Conditions.  Accessed at https://www.cms.gov/Research-Statistics-Data-and-
Systems/Statistics-Trends-and-Reports/Chronic-Conditions/CC_Main on January 28, 2021.  
Note: These data include only Medicare fee-for-service patients and exclude patients enrolled in Medicare Advantage. 
Changes in review process from the 2010 report   
We largely replicated the methodology we used for the 2010 report, adjusting the 
screening process slightlywe updated the trigger tool and allowed nurses to review 
present-on-admission indicators as part of their review.  We also expanded and 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Comparison to the 2010 Report | 39   
revised the clinical guidance document for reviewers to incorporate updated clinical 
guidance and practices.  The guidance document was built on more than a decade of 
OIG research and experience studying adverse events.   
Over time, our definitions of certain types of harm events have evolved.  We now 
include a broader range of events resulting from omissions of care, and we updated 
our definition of sepsis, acute kidney injuries, and other events to be consistent with 
newer guidelines.140, 141, 142, 143  We also improved our use of clinical thresholds 
(e.g., laboratory results or blood pressure readings) for determining harm.  The same 
information was used to identify harm events in the prior study, but the decisions 
were based on group consensus about harm instead of a threshold.  For example, we 
adopted specific guidelines, based on the patients mean arterial blood pressure, for 
determining the point at which intraoperative hypotension associated with anesthesia 
is counted as a harm event or requires a consensus discussion.144   
In addition to these changes to our review, some event types are now associated with 
different clinical categories.  For example, we now consider aspiration events that lead 
to pneumonia as related to infection rather than patient care and now include 
intravenous volume overload under fluid and electrolyte disorders. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Comparison to the 2010 Report | 40   
MEDICAL RECORD REVIEW METHODOLOGY 
 
We conducted a two-stage medical record review using OIG-contracted reviewers to 
identify adverse events and temporary harm events experienced by hospitalized 
Medicare patients during October 2018.  We also conducted quality assurance 
activities to ensure consistency and accuracy of results. 
Stage 1: Nurse Screening   
In the first stage, registered nurses screened all 834 admissions using the OIG-
modified GTT methodology to look for triggers that indicated possible patient harm 
in the medical record.  A trigger is a clinical clue (e.g., a laboratory test showing low 
blood glucose, or a patient care event such as a fall) that required the nurse-screener 
to explore the medical record to determine whether adverse or temporary harm 
events likely occurred.  A trigger could be the harm itself, such as a pressure injury, or 
a reference that indicates possible harm, such as a transfer to a higher level of care.  
The GTT included triggers in four categories: patient care, intensive care, medication, 
and procedures/surgery.  (See Appendix E for a list of the triggers used to identify 
events.)   
From the Medicare claims data, nurses also reviewed POA indicators of N (not POA) 
or U (documentation insufficient to determine) as additional clinical clues for 
possible patient harm.  As part of Medicare payment policies required under the DRA, 
CMS requires hospitals to include POA indicator codes on claims to discern whether 
each diagnosis was present at the time of admission.   
When nurses identified possible patient harm events during the hospital stays, they 
flagged them for the second stage of review.  For each possible event, the nurse-
screeners recorded a description of the event, the level of harm, and the relevant 
evidence in the medical record.  The flagged records could include more than one 
possible harm event.  When nurses did not identify possible patient harm, a quality 
assurance reviewer re-screened the records to verify the nurses results.  In total, 
nurses and quality assurance reviewers flagged 244 admissions (220 from nurse 
review and 24 from quality assurance review).  We automatically referred 
149 admissions (among those not already flagged by a nurse) for patients who were 
readmitted within 30 days of discharge (these include readmissions in October and 
November 2018). 
Stage 2: Physician Review 
In the second stage, physicians reviewed the complete medical record for each of the 
393 admissions flagged during Stage 1.  Physicians either confirmed or refuted the 
presence of patient harm events using evidence in the record and independently 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Medical Record Review Methodology | 41   
identified any additional events.  For each harm event, physician-reviewers used their 
clinical expertise and followed a structured protocol requiring them to assess the 
following: 
Clinical Category.  Physician-reviewers classified each event under one of four clinical 
categories: medication, infection, patient care, and surgery or procedure.  Medication-
related events were those that involved adverse reactions to medication.  Infection-
related events included health care-associated infections acquired during the hospital 
stay.  Patient care-related events included harm occurring during the daily care of 
patients and were not related to the other clinical categories.  Surgery or procedure-
related events included harm or complications attributed to the surgery or procedure 
and adverse reactions to medications (e.g., anesthesia) required during the operation. 
Harm Event Lists.  Physician-reviewers determined whether each event qualified as 
an event on CMSs lists of HACs or NQFs list of SREs (events could qualify for more 
than one list).  For the NQF list, we re-reviewed each event to confirm whether it 
qualified for the list.  For the CMS DRA HAC list, we confirmed whether each event 
met the criteria for this list based on the claims data and checked if hospitals did not 
code for diagnoses and procedures related to the harm event.  For the CMS HACRP 
list, we requested that AHRQ review each admissions claims data to detect HACs 
using its patient safety indicators software and we had an NHSN specialist confirm the 
HAIs on this list.  We then independently confirmed whether events fell on this list 
from these reviews.   
Preventability.  Physicians assigned each event to one of five preventability 
determinations and identified one or more factors that contributed to each event.  
(See the preventability scale in Exhibit 14.)  Physicians also explained their rationale 
for each harm event determination based on a list of 24 contributing factors gleaned 
from prior research and experience in OIG studies of adverse events.145 
Exhibit 14: Preventability Scale and Descriptions  
Preventability 
Description 
Determination 
Patient harm could definitely have been avoided through 
Clearly preventable 
improved assessment or alternative actions. 
Patient harm could have been avoided through improved 
Likely preventable 
assessment or alternative actions. 
Patient harm could not have been avoided given the 
Likely not preventable 
complexity of the patients condition or the care required. 
Patient harm could definitely not have been avoided given 
Clearly not preventable 
the complexity of the patients condition or the care required. 
Physicians were unable to determine preventability because 
Unable to determine 
of incomplete documentation or case complexity. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Medical Record Review Methodology | 42   
Contributing factors varied depending on the circumstances of each event.  For 
example, preventable events may be related to substandard treatment, medical error, 
and inadequate monitoring depending on the factors involved.  Events that are not 
preventable may be related to a patients diagnosis or treatment being unusual or 
complex and thereby making care difficult, or a patient being highly susceptible to 
harm because of poor health.  These factors are not necessarily exclusive of each 
other and their definitions are often subjective.  For example, substandard care 
generally refers to the failure to adhere to professional standards of practice in the 
delivery of care, but practitioners may not always agree on what this includes, and 
their determination depends on the strength of the evidence available to substantiate 
whether a patient received substandard care.   
As a result, preventability determinations are necessarily subjective and required the 
physicians to use clinical experience and judgment.  Physicians based decisions on the 
circumstances of the specific case and also considered accepted standards of care; the 
expected frequency of certain events; guidance developed during the review process; 
and group discussion of the patients and events.  Physicians were allowed to choose 
multiple contributing factors for the rationale behind their determinations.  
Assessing an event as clearly preventable or clearly not preventable required a greater 
degree of certainty on the part of the reviewer.  The expanded scale enabled 
physicians to make more precise determinations, while our primary statistics collapse 
clearly and likely into the larger categories of preventable or not preventable. 
The physician-reviewers represented a variety of specializations and experience, 
including a hospitalist and cardiology, infectious disease, internal medicine, 
orthopedics, neurology, rehabilitation, intensive care, emergency medicine, and 
pulmonology.  Three of the six had served as physician-reviewers in prior OIG studies 
of adverse events.  In addition to our physician-reviewers, a seventh physician, also 
contracted by OIG, was our lead physician, having extensive experience with OIGs 
prior adverse event studies and the GTT methodology.  The lead physician was 
involved in training physicians in reviewing records and engaging in quality assurance 
reviews of physicians reviews. 
Severity of Event.  As in prior OIG studies, physician-reviewers assigned each event 
to one of five levels of harm using an OIG-modified version of the NCC MERP Index.  
We separately identify temporary harm events (level E on the index) because the 
effect of these events was typically not comparable to the more severe adverse 
events (levels F through I on the index).  In addition, we use the term patient harm 
events as a combination of both adverse events and temporary harm events because 
both types represent harm resulting from medical care.  (See Exhibit 2 on page 13.) 
Medical Coder Reviews 
Certified medical coders reviewed all patient harm events identified by the physicians 
to identify potential costs incurred to Medicare because of these events.  To do this, 
coders reviewed the medical records, physician findings, and the associated Medicare 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Medical Record Review Methodology | 43   
claims to identify diagnosis and procedure codes that would not have been included 
in the claim if the event(s) had not occurred.  The coders then used the TruCode 
Encoder software to determine the revised MS-DRG for the hospital claims and the 
resulting payment amounts.146  To simplify the review process, coders treated claims 
paid through managed care or Marylands payment system the same as IPPS claims. 
Efforts To Improve Consistency and Quality of Reviews 
To promote consistency and accuracy across reviews, we issued a study-specific 
guidance document for improved decision making, we provided training to all 
clinician reviewers and certified medical coders, we facilitated consensus calls with the 
physician-reviewers, and we conducted quality assurance reviews of nurse reviews, 
physician reviews, and coder reviews.  
Guidance Document.  We provided reviewers with a guidance document that 
included event definitions, considerations for specific types of events, and a list of 
frequently asked questions.  We created the guidance document to align with clinical 
research literature, professional and government guidelines (such as evidence-based 
practices), and decisions made in prior OIG studies; and consultations with subject-
matter experts.  The document also provides instructions that are applicable to a wide 
range of events, including how to assess event timing, underlying disease, related 
events, and recurring events: 
 
Present on admission (POA)We excluded events that occurred before the 
patient entered the hospital or that were attributable to care provided prior to 
admission.   
 
Underlying diseaseWe excluded events that were part of the underlying 
disease process unless there was an omission of care resulting in an 
exacerbation of the underlying disease. 
 
Related eventsWhen an initial event caused a series of related and 
dependent events, we combined the events into a cascade event and 
counted it as a single event.   
 
Multiple similar eventsWhen a patient experienced multiple similar events 
during a hospital stay (e.g., multiple episodes of hypoglycemia), we counted 
these as separate events with some exceptions.  We collapsed multiple 
hypoglycemic events within 24 hours into a single event and counted 
recurrences after 24 hours as separate events.  We collapsed multiple pressure 
injuries into a single event when the pressure injury was: (1) at the same 
anatomical site and (2) occurred within 24 hours of the initial pressure injury.  
We counted pressure injuries at different anatomical sites as separate events 
even if they occurred within 24 hours of one another. 
Trainings.  We conducted several training sessions for each reviewer type (nurses, 
physicians, and coders) to train them on our study protocols and practices, harm 
identification techniques, use of the database, and our guidance document.  Prior to 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Medical Record Review Methodology | 44   
beginning reviews, each reviewer performed pre-test reviews and received feedback 
on the results of those reviews.  
Consensus Calls.  We facilitated 10 conference calls to further promote consistency 
across physician-reviewers.  During these calls, physician-reviewers discussed events 
that were complex, difficult to assess, involved issues outside their area of expertise, 
or had possible implications for other cases.  Patient harm events were directly taken 
to consensus calls when events were determined to have contributed to or resulted in 
death; events in which the reviewer was unable to provide a preventability assessment 
(i.e., unable to determine); and for cases with a series of related harm events (termed 
cascade).  Physicians were also encouraged to bring cases to group discussion at 
their discretion.  Some cases were also discussed between physician-reviewers and 
the lead physician.  We documented the discussions and conclusions made during 
these weekly calls to further promote consistency.   
Quality Assurance Reviews.  Our clinicians and coders conducted quality assurance 
reviews for each type of review to gauge accuracy and adherence to the protocols 
throughout the study.  We selected admissions for these quality assurance reviews 
based on prior experience and data anomalies identified during preliminary analysis.  
The quality assurance reviews for the GTT screening included all admissions not 
referred to a physician-reviewer; 29 admissions that received physician review; and 
113 admissions that received coding review.  In addition to these quality assurance 
reviews, we also referred certain health care-associated infections to an infection 
prevention nurse specialist (with expertise in NHSN guidelines) to assess physician-
reviewer determinations of these type of events.  We also conducted extensive checks 
of the events for consistency in preventability determinations and event 
categorization; reassessed whether events qualified under CMSs HAC lists and NQFs 
SRE list; and identified and reassessed outlier cases. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Medical Record Review Methodology | 45   
APPENDIX A 
 
National Quality Forum List of Serious Reportable Events 
The NQF list of SREs is separated into seven categories.  The term serious describes 
loss of a body part, disability, or loss of bodily function lasting more than 7 days or 
that is still present at time of discharge from an inpatient health care facility or, when 
referring to other than an adverse event, an event whose occurrence is not trivial.147  
The list was last updated in 2011 and reflected several changes from the prior version, 
including the retirement of three care-management events and the addition of four 
new events.148  Exhibit A-1, on the next page, shows the NQF SRE list that we used for 
this reports analysis. 
Patient Harm Events on the NQF List 
One harm event within our sample was on NQFs list of SREs.  This event involved a 
patient who was hospitalized for hip replacement surgery.  The patient was left 
unattended following surgery and fell in the bathroom, which resulted in a new 
fracture requiring additional surgery.  Our physician-reviewers determined that this 
event was clearly preventable because the patient was at high risk for a fall and 
should not have been left unattended in the bathroom. 
The rest of the events that we identified were not on NQFs list of SREs because this 
list focuses primarily on a small number of events that result in serious injury or death.  
Although we identified events that were similar in type, these events did not result in 
disability or death, and thus did not qualify for this list.  For example, we identified 
several patients who were injured as a result of a fall in a hospital.  However, none of 
these falls resulted in serious injury or death, except for the hip fracture we identified.  
NQF also adds other restrictions to certain event types, such as with pressure injuries.  
Although we identified 22 pressure injuries, none of these pressure injuries qualified 
because NQF includes only severe pressure injuries (Stage 3, Stage 4, and 
unstageable) for reporting on the NQF list.  
   
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix A | 46   
Exhibit A-1: The NQF List of Serious Reportable Events 
Surgical or Invasive Procedure Events 
A.  Surgery or other invasive procedure performed on the wrong site 
B.  Surgery or other invasive procedure performed on the wrong patient 
C.  Wrong surgical or other invasive procedure performed on a patient 
D.  Unintended retention of a foreign object in a patient after surgery or other invasive 
procedures performed  
E.  Intraoperative or immediately postoperative/postprocedure death in an ASA Class 1 
patient149 
Product or Device Events 
A.  Patient death or serious injury associated with the use of contaminated drugs, devices, 
or biologics provided by the health care setting 
B.  Patient death or serious injury associated with use or function of a device in patient 
care, in which the device is used or functions other than as intended 
C.  Patient death or serious injury associated with intravascular air embolism that occurs 
while being cared for in a health care setting 
Patient Protection Events 
A.  Discharge or release of a patient/resident of any age, who is unable to make decisions, 
to other than an authorized person 
B.  Patient death or serious injury associated with patient elopement (disappearance) 
C.  Patient suicide, attempted suicide, or self-harm that results in serious injury, while being 
cared for in a health care setting 
Care Management Events 
A.  Patient death or serious injury associated with a medication error 
B.  Patient death or serious injury associated with unsafe administration of blood products 
C.  Maternal death or serious injury associated with labor or delivery in a low-risk 
pregnancy while being cared for in a health care setting 
D.  Death or serious injury associated with neonate associated with labor or delivery in a 
low-risk pregnancy 
E.  Patient death or serious injury associated with a fall while being cared for in a health 
care setting 
F.  Any Stage 3, Stage 4, and unstageable pressure ulcers acquired after 
admission/presentation to a health care setting 
G.  Artificial insemination with the wrong donor sperm or wrong egg 
H.  Patient death or serious injury resulting from the irretrievable loss of an irreplaceable 
biological specimen 
I.  Patient death or serious injury resulting from failure to follow up or communicate 
laboratory, pathology, or radiology test results 
Environmental Events 
A.  Patient or staff death or serious injury associated with an electric shock in the course of 
a patient care process in a health care setting 
B.  Any incident in which systems designated for oxygen or other gas to be delivered to a 
patient contains no gas, the wrong gas, or are contaminated by toxic substances 
C.  Patient or staff death or serious injury associated with a burn incurred from any source 
in the course of a patient care process in a health care setting 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix A | 47   
Continued From Previous Page 
D.  Patient death or serious injury associated with the use of physical restraints or bedrails 
while being cared for in a health care setting 
Radiologic Events 
A.  Death or serious injury of a patient or staff associated with the introduction of a 
metallic object into the magnetic resonance imaging (MRI) area 
Potential Criminal Events 
A.  Any instance of care ordered by or provided by someone impersonating a physician, 
nurse, pharmacist, or other licensed health care provider 
B.  Abduction of a patient/resident of any age 
C.  Sexual abuse/assault on a patient or staff member within or on the grounds of a health 
care setting 
D.  Death or serious injury of a patient or staff member resulting from a physical assault 
(i.e., battery) that occurs within or on the grounds of a health care setting 
Source: NQF, List of Serious Reportable Events.  Accessed at 
https://www.qualityforum.org/Topics/SREs/List_of_SREs.aspx on April 22, 2021. 
 
 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix A | 48   
APPENDIX B 
 
HHS Agency Efforts To Improve Quality and Safety in Hospitals 
HHS is tasked with leading the Nation in promoting quality health care and 
preventing patient harm.  As such, each agency within HHS contributes to the 
National Quality Strategy and the HAI and ADE action plans while pursuing their own 
goals to improve quality and safety.  The roles of CMS, AHRQ, and CDC are described 
on pages 5 to 11.  Additional information about these agencies efforts to reduce 
patient harm and improve quality and safety is below. 
CMS Programs To Track and Prevent Adverse Events   
CMS Pay-for-Performance Programs.  CMS has multiple programs and initiatives 
beyond the DRA HAC payment provision and HACRPs payment adjustments.  These 
other efforts include the Hospital Readmissions Reduction Program (HRRP) and the 
Hospital Value-Based Purchasing (HVBP) program, both authorized under the ACA.150  
HRRP reduces payments to hospitals with a high number of readmissions for six 
conditions and procedures.151  HVBP rewards high-quality care with financial 
incentives.  This program measures hospital performance on six outcomes, including 
patient safety, and those with the highest scores and most improvement receive a 
payment adjustment on each claim as an incentive to deliver safer care.152  These 
programs build on CMSs agency-specific national quality strategy, released in 2016, 
which focused on leveraging CMSs unique authorities to improve quality of care and 
patient safety nationwide.153   
CMS Data Collection of Quality Measures.  To track harm events, CMS collects data 
on quality measures from care provided in hospitals and other health care facilities.  
CMS highlighted patient safety as a quality measurement priority in its triennial 
National Impact Assessment of CMS Quality Measures report to address gaps and 
inform future measurement development.154  CMS promotes transparency of quality 
measurement data collected from the Hospital Inpatient Quality Reporting Program 
through its consumer-oriented Care Compare website (formerly on Hospital 
Compare).155, 156  Care Compare aggregates information on patient outcomes, 
including HAIs and other complications, and the provision of care in U.S. hospitals and 
other health care facilities, such as the use of recommended practices and patient 
survey results.157  It is intended as a tool for consumers to make informed health care 
decisions and to support efforts to improve quality of care.   
CMS also manages electronic clinical quality measures (eCQMs), such as certain 
patient safety metrics, under the Hospital Inpatient Quality Reporting Program and 
the Promoting Interoperability Programs (formerly the Medicare and Medicaid 
Electronic Health Record Incentive Programs).158  Under these programs, providers are 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix B | 49   
required to demonstrate meaningful use of certified electronic health record 
technology, including the reporting of eCQMs.159  
CMS Quality Improvement Initiatives.  CMS maintains numerous initiatives aimed 
at improving quality of care.  The CMS Innovation Center, authorized under the ACA, 
focuses on designing, implementing, and testing new health care payment and 
service delivery models to improve quality of care and address rising health care 
costs.160  CMS also funds contracts to create support networks that spread best 
practices and prevent adverse events.  CMS-funded Quality Improvement 
Organizations (QIOs) bring together patients, providers, and communities into Quality 
Improvement Networks to spread best practices for better care, including preventing 
adverse events.   
AHRQ Programs To Track and Prevent Adverse Events   
AHRQ Tools To Track Harm Events.  AHRQ maintains tools to help hospitals track 
harm events and learn from these events.  AHRQ makes available free Patient Safety 
Indicators software that hospitals can use with their existing administrative data to 
track potential adverse events and other complications.161  AHRQ also developed 
common definitions (known as the Common Formats) for PSOs working with hospitals 
and other providers.162  The AHRQ Common Formats make it possible to collect, 
aggregate, and analyze uniformly structured information about patient safety events 
for local, regional, and national learning.  The AHRQ Common Formats are available in 
the public domain to encourage their widespread adoption, but the privilege and 
confidentiality protections available under the Patient Safety Act only apply to 
information created as patient safety work product by providers working with 
federally listed PSOs.163, 164  AHRQ also maintains a Network of Patient Safety 
Databases under the PSO program to enable learning on a national scale about the 
causes of harm events.165   
AHRQ Patient Safety Resources.  AHRQ works to improve the quality and safety of 
the health care system through research and implementation of evidence-based 
practices.  AHRQ provides resources such as strategies and tools to reduce specific 
types of adverse events.  These resources include a range of toolkits, education, and 
trainings for providers to improve patient safety such as the CUSP method and HAI 
resources and toolkits.166  Until 2018, AHRQ managed the National Guideline 
Clearinghouse, which was a public resource website for summaries on evidence-based 
clinical practice guidelines.167  Another program, the National Quality Measures 
Clearinghouse, is no longer managed by AHRQ.  Instead, these measures are provided 
by CMSs Measure Inventory Tool, which provides information on measures that CMS 
uses to promote health care quality.168  AHRQ also publishes a series of reports, 
Making Healthcare Safer, that detail existing and emerging evidence-based patient 
safety practices for reducing certain patient harm events.169 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix B | 50   
CDC Programs To Track and Prevent Adverse Events  
CDC HAI Surveillance Initiatives.  CDC has several surveillance initiatives to track 
and prevent HAIs.  NHSN is a HAI surveillance system with more than 25,000 
participating medical facilities, including hospitals.  NHSN provides real-time data to 
these facilities, enabling them to track medical events such as HAIs and blood safety 
errors, and assists with State and Federal reporting mandates.170  CDC also monitors 
HAIs through its Emerging Infections Programs Healthcare-Associated Infections
Community Interfacea collaboration with a network of State health departments 
and their academic medical center partners.171  This program provides population-
based data and detailed patient-level information to evaluate the epidemiology and 
public health impact of HAIs and antimicrobial resistance.   
CDC Quality Improvement Initiatives.  CDC has several initiatives focused on 
preventing HAIs and improving quality of care nationwide, including providing 
support to HAI programs in all State and several large local health departments to 
detect, prevent, respond to, and contain HAIs and antimicrobial pathogens.172  CDC 
has developed resources and strategies to prevent HAIs such as the Targeted 
Assessment for Prevention (TAP) Strategy as a framework for quality improvement.173  
CDC also manages the Prevention Epicenters Program, a network of academic centers 
with which CDC performs collaborative research on the epidemiology and prevention 
of HAIs.174  In addition, in 2011 CDC formed the Safety and Healthcare Epidemiology 
Prevention Research Development program, which provides a mechanism for 
developing and implementing HAI prevention research on a contractual basis.175  
Finally, CDCs Modeling Infectious Diseases in Healthcare Network supports research 
that models the spread of HAIs and antibiotic resistant infections and it includes six 
centers that collaborate to study the transmission of health care-associated 
pathogens and evaluate the effect of prevention measures.176 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix B | 51   
APPENDIX C 
 
CMS Lists of Hospital-Acquired Conditions 
The Centers for Medicare & Medicaid Services (CMS) maintains two lists of 
hospital-acquired conditions (HACs), one related to the Deficit Reduction Act of 2005 
(DRA) and another related to the Hospital-Acquired Conditions Reduction Program 
(HACRP).   
The DRA list of HACs includes 14 conditions.  The original list, issued in fiscal year (FY) 
2009, had 10 conditions.  The list was last updated in FY 2013, at which time CMS 
added two new conditions.  In a prior update, CMS separated surgical site infections 
into three conditions.  Exhibit C-1 shows the current DRA list of HACs used for this 
reports analysis.   
The HACRP list of HACs consists of 2 types of measures: a composite measure 
consisting of 10 patient safety indicators (PSIs) collected by the Agency for Healthcare 
Research and Quality (AHRQ), and 5 health care-associated infections (HAIs) collected 
by the National Healthcare Safety Network (NHSN).  CMSs PSI composite is based on 
a pooled measure of 10 weighted PSIs.  CMS has recalibrated the PSI and HAI 
measures for Medicare fee-for-service claims and the acute-care hospital setting.  The 
list was last updated in FY 2017.  Exhibit C-2 shows the current HACRP list of HACs 
used for this reports analysis.   
Exhibit C-1: The DRA HAC List 
Hospital-Acquired Condition 
1. Foreign object retained after surgery 
2. Air embolism 
3. Blood incompatibility 
4. Pressure ulcers Stages 3 and 4 
5. Falls and trauma 
A.  Fractures 
B.  Dislocations 
C.  Intracranial injuries 
D.  Crushing injuries 
E.  Burn 
F.  Other injuries 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix C | 52   
6. Manifestations of poor glycemic control 
A.  Diabetic ketoacidosis 
B.  Nonketotic hyperosmolar coma 
C.  Hypoglycemic coma 
D.  Secondary diabetes with ketoacidosis 
E.  Secondary diabetes with hyperosmolarity 
7. Catheter-associated urinary tract infection 
8. Vascular catheter-associated infection 
9. Surgical site infection, mediastinitis, following coronary artery bypass graft  
10. Surgical site infection following certain bariatric surgical procedures for obesity 
A.  Laparoscopic gastric bypass 
B.  Gastroenterostomy 
C.  Laparoscopic gastric restrictive surgery 
11. Surgical site infection following certain orthopedic procedures involving the: 
A.  Spine 
B.  Neck 
C.  Shoulder 
D.  Elbow 
12. Surgical site infection following cardiac implantable electronic device 
13. Deep vein thrombosis/pulmonary embolism following certain orthopedic procedures:   
A.  Total knee replacement 
B.  Hip replacement 
14. Iatrogenic pneumothorax with venous catheterization 
Source: CMS, Hospital Acquired Conditions.  Accessed at https://www.cms.gov/Medicare/Medicare-Fee-for-Service-
Payment/HospitalAcqCond/Hospital-Acquired_Conditions on April 30, 2021. 
 
Exhibit C-2: The HACRP List of HACs 
CMS Patient Safety Indicator Composite 
PSI 03  Pressure ulcer rate 
PSI 06  Iatrogenic pneumothorax rate 
PSI 08  In-hospital fall with hip fracture rate 
PSI 09  Perioperative hemorrhage or hematoma rate 
PSI 10  Postoperative acute kidney injury requiring dialysis 
PSI 11  Postoperative respiratory failure rate 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix C | 53   
PSI 12  Perioperative pulmonary embolism or deep vein thrombosis rate 
PSI 13  Postoperative sepsis rate 
PSI 14  Postoperative wound dehiscence rate 
PSI 15  Unrecognized abdominopelvic accidental puncture/laceration rate 
NHSN Healthcare-Associated Infections 
CLABSI  Central line-associated bloodstream infection 
CAUTI  Catheter-associated urinary tract infection 
SSI  Surgical site infection (colon and hysterectomy) 
MRSA  Methicillin-resistant Staphylococcus aureus bacteremia 
C. diff  Clostridioides difficile infection 
Source: CMS, Hospital-Acquired Condition (HAC) Reduction Program, last modified in July 2018.  Accessed at 
https://www.cms.gov/Medicare/Quality-Initiatives-Patient-Assessment-Instruments/Value-Based-
Programs/HAC/Hospital-Acquired-Conditions.html on April 22, 2021. 
 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix C | 54   
APPENDIX D 
 
Glossary of Selected Terms 
AcidosisAn abnormal condition of reduced alkalinity of the blood and tissues that 
is marked by sickly sweet breath; headache; nausea and vomiting; and visual 
disturbances and is usually a result of excessive acid production. 
Acute encephalopathyAn acute or subacute global, functional alteration of the 
mental status due to systemic factors. 
Acute kidney injurySudden loss of the kidneys ability to remove waste, also 
referred to as acute kidney failure.   
Acute renal insufficiencyPoor functioning of the kidneys because of reduced 
blood flow to them.  May progress to acute kidney failure. 
Adverse eventHarm to a patient as a result of medical care or in a health care 
setting, including the failure to provide needed care.  (Adverse events are Levels F 
through I on the OIG-modified NCC MERP Index.) 
Ampullary stenosisThe narrowing of the ampulla of Vater (the small opening that 
enters into the first portion of the small intestine, known as the duodenum), which 
can lead to a bile duct blockage. 
AnemiaA condition in which the blood is deficient in red blood cells, in 
hemoglobin, or in total volume. 
AnesthesiaMedicines used to prevent pain during surgery and other procedures.  
Local anesthesia numbs a small part of the body.  Regional or epidural anesthesia 
numbs larger areas of the body such as an arm or leg, or below the waist.  General 
anesthesia affects the whole body. 
AngioplastyA procedure used to open clogged heart arteries. 
AnticoagulantMedication that hinders blood coagulation, typically used to avoid 
blood clots.  Referred to as blood-thinning medication. 
ArthroplastyA surgical procedure to restore the function of a joint. 
Aspiration pneumoniaAn infectious process caused by the inhalation of 
oropharyngeal secretions (food, liquid, or gastric contents) that are colonized by 
pathogenic bacteria. 
AspirationAccidental inhalation of foreign material into the lungs. 
Atrial fibrillationA quivering or irregular heartbeat that can lead to blood clots, 
stroke, heart failure, or other heart-related complications. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix D | 55   
Autoimmune hepatitisA disease in which the immune system attacks the liver. 
BradycardiaA slower than normal heart rate. 
CascadeA chain of events initiated by an unexpected result or other incident that 
may result in patient harm. 
Catheter-associated urinary tract infection (CAUTI)An infection involving any 
part of the urinary system, including urethra, bladder, ureters, and kidney, that is 
associated with a urinary catheter, which is a tube inserted into the bladder through 
the urethra to drain urine. 
Central line-associated bloodstream infection (CLABSI)A serious infection that 
occurs when germs (usually bacteria or viruses) enter the bloodstream through the 
central line.  This is a type of vascular catheter-associated infection. 
Clostridioides difficile (C. diff)A bacterium that can cause symptoms ranging 
from diarrhea to life-threatening inflammation of the colon. 
ColonoscopyAn exam used to detect changes or abnormalities in the large 
intestine (colon) and rectum. 
ComorbidityWhen more than one disease or condition is present in the same 
person at the same time.  Conditions described as comorbidities are often chronic or 
long-term conditions. 
DeliriumA mental disturbance characterized by acute confusion, disordered 
speech, and/or hallucinations. 
DementiaA group of symptoms affecting memory, thinking, and social abilities 
severely enough to interfere with daily life. 
DysphagiaThe condition of having difficulty swallowing. 
Fluid and electrolyte balanceElectrolytes are minerals in the body, such as sodium 
and potassium, that have an electric charge and are in body fluids.  Maintaining the 
right balance of electrolytes helps maintain normal biochemical and physiologic 
functions. 
Gastric sleeve resectionA type of bariatric surgery used to permanently reduce the 
size of the stomach. 
Gastrointestinal bleedingBleeding from one or more areas of the digestive tract. 
HematomaA pool of clotted or partially clotted blood in an organ, tissue, or body 
space, usually caused by a broken blood vessel. 
HerniaWhen an internal organ pushes through a weak spot in the muscle or tissue. 
HyperkalemiaThe condition of having elevated potassium levels in the blood. 
HypertensionThe condition of having abnormally high blood pressure. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix D | 56   
HypoglycemiaThe condition of having abnormally low level of blood sugar 
(glucose). 
HypotensionThe condition of having abnormally low blood pressure. 
HysterectomyA surgery to remove all or part of the uterus. 
IleusA lack of normal muscle contractions of the intestines, marked by bloating, 
cramps, nausea, vomiting, and severe constipation. 
Intensive care unit (ICU)A specialized hospital or hospital department that 
provides critical care and life support for acutely ill and injured patients. 
Intravenous contrast agentsIodine and gadolinium-based substances that are 
injected into a vein and are used to improve pictures of the inside of the body 
produced by x-rays, computed tomography, and magnetic resonance imaging. 
Intravenous infiltrationA situation in which fluids administered by entering a vein 
accidentally enter the surrounding tissue. 
LaminectomyA type of surgery in which a surgeon removes part or all of the 
vertebral bone. 
Methicillin-resistant Staphylococcus aureus (MRSA)A type of staph bacteria that 
is resistant to several antibiotics used to treat ordinary staph infections. 
Methicillin-susceptible Staphylococcus aureus (MSSA)A type of staph bacteria 
that responds well to antibiotics used to treat staph infections. 
NaloxoneA life-saving drug that can reverse the effects of an opioid overdose 
when administered in time. 
OpioidA class of drugs most often prescribed to treat moderate to severe pain, 
notable for their addictive potential. 
Patient harm eventAny harm to a patient as a result of medical care.  This term 
encompasses both adverse events (Levels F through I on the OIG-modified NCC MERP 
Index) and temporary harm events (Level E on this index). 
PneumoniaAn infection that inflames the air sacs in one or both lungs. 
PneumothoraxA collapsed lung that occurs when air leaks into the space between 
the lung and chest wall. 
Pressure injuryUlceration of tissue deprived of adequate blood supply by 
prolonged pressure, also called decubitus ulcer or bedsore.  Pressure injuries are 
classified into four stages: Stage 1 is intact skin with nonblanchable redness; Stage 2 is 
a shallow ulcer or blister indicating damage to the epidermis; Stage 3 is damage 
extending through all layers of the skin; and Stage 4 is damage through all the layers 
of the skin and underlying muscle, tendons, or bone.  Unstageable pressure injuries 
are when the extent of the tissue damage cannot be confirmed because it is obscured 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix D | 57   
by slough or eschar.  Deep tissue pressure injuries are persistent nonblanchable deep 
red, maroon, or purple discoloration of the skin revealing a dark wound or blood-
filled blister.177 
Pulmonary edemaAbnormal accumulation of fluid in the lungs. 
Pulmonary embolismObstruction of a pulmonary (lung) artery caused by a blood 
clot, often marked by shortness of breath; chest pain with inhalation; and, in severe 
cases, low blood pressure and death. 
Pulseless electrical activityA condition characterized by unresponsiveness and 
impalpable (unable to be felt) pulse in the presence of sufficient electrical discharge. 
Refeeding syndromeThe potentially fatal shifts in fluids and electrolytes that may 
occur in malnourished patients receiving artificial refeeding. 
SepsisA life-threatening organ dysfunction caused by a dysregulated host response 
to infection. 
Septic shockA subset of sepsis with circulatory and cellular/metabolic dysfunction 
associated with a higher risk of mortality. 
Temporary harmHarm to a patient that required intervention but did not cause 
lasting harm or prolong the hospital stay.  Classified as Level E on the OIG-modified 
NCC MERP Index. 
ThrushAn infection of the mouth and throat, caused by fungus. 
Total parenteral nutritionA method of feeding that bypasses the gastrointestinal 
tract. 
Transcatheter aortic valve replacementA minimally invasive procedure to replace 
a narrowed aortic valve that fails to open properly. 
Urinary tract infection (UTI)An infection of the tract through which urine passes 
and can include the kidney, ureters, bladder, and/or urethra. 
Vascular catheter-associated infectionAn infection associated with a catheter 
used for vascular access and placement. 
VasopressorsA group of medications that tighten blood vessels and raise blood 
pressure. 
Ventilator-associated pneumoniaA lung infection that develops in a person who 
is on a ventilator.  A ventilator is a machine that is used to help a patient breathe by 
giving oxygen through a tube placed in a patients mouth or nose, or through a hole 
in the front of the neck.  An infection may occur if germs enter through the tube and 
get into the patients lungs. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix D | 58   
APPENDIX E 
 
Trigger Tool Used To Screen for Patient Harm Events 
OIG and its contracted clinical consultants developed an OIG-modified trigger tool to 
screen for patient harm events specific to acute-care hospital stays based on the 
Institute for Healthcare Improvements (IHIs) global trigger tool (GTT).  The 2010 OIG 
report on adverse events used this as a method to screen records for harm events.  
For this study, we modified the trigger tool by reviewing and selecting triggers from 
the IHI GTT and from triggers that were included in prior OIG studies of adverse 
events.  See Exhibit E-1 for the list of triggers used by clinicians to screen medical 
records for potential patient harm events. 
Exhibit E-1: OIG-Modified Trigger Tool Worksheet 
Care Triggers 
C1  Acute mental status change 
C2  Transfusion or use of blood products   
C3  Code/arrest/rapid response team  
C4  Acute dialysis 
C5  Positive culture (e.g., blood, urine, stool) 
Studies for emboli, pulmonary embolism (PE) or deep vein thrombosis (DVT) such as 
C6  D-Dimer, computerized tomography (CT) pulmonary angiogram (CTPA), or lung 
ventilation-perfusion scan 
C7  Abrupt or significant decrease in hemoglobin or hematocrit 
C8  Patient fall or other trauma 
C9  Pressure injury/skin breakdown from medical device 
C10  Readmission within 30 days 
C11  Restraint use  
C12  Hospital-acquired infections 
C13  In-hospital stroke/transient ischemic attack (TIA) 
C14  Transfer to higher level of care 
C15  Any procedure complication 
C16  Urinary retention 
C17  Aspiration 
C18  Care  other 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix E | 59   
Medication Triggers 
M1  Clostridioides difficile positive stool test 
M2  Partial thromboplastin time greater than (>) 100 seconds 
M3  International normalized ratio (INR) greater than (>) 6   
M4  Glucose less than (<) 50 mg/dL 
M5  Rising blood urea nitrogen (BUN) or serum creatinine greater than (>) 2 times baseline 
M6  Vitamin K, Factor Xa reversal agents (andexanet alfa, idarucizumab administration) 
M7  Diphenhydramine use   
M8  Flumazenil use   
M9  Naloxone use  
M10  Anti-emetic use 
M11  Abrupt decrease in blood pressure 
M12  Abrupt medication stop 
Sodium polystyrene (kayexalate administration) or potassium greater than or equal to 
M13 
() 6 mEq/L 
M14  Abnormal drug levels 
M15  Medication  other 
Surgical Triggers 
S1   Unplanned return to surgery 
S2   Unplanned change in procedure 
S3   Unplanned admission to intensive care post-operation 
Intubation/reintubation/bilevel positive airway pressure (BiPAP) in post anesthesia care 
S4  
unit (PACU)  
Unplanned x-ray/CT scan/magnetic resonance imaging (MRI) or other imaging 
S5  
intraoperatively or in PACU 
S6   Intraoperative or postoperative death 
S7   Mechanical ventilation greater than (>) 24 hours postoperatively 
S8   Intra-operative epinephrine, norepinephrine, naloxone, or flumazenil 
Abnormal postoperative troponin level, including sensitive or highly sensitive troponin I or 
S9  
troponin T 
S10   Injury, unplanned repair or removal of organ 
S11   Operative complication  other 
Intensive Care Unit Triggers 
I1  Hospital-acquired pneumonia onset 
I2  Readmission or unplanned admission to intensive care  
I3  In-unit procedure 
I4  Intubation/reintubation  
I5  Intensive care unitother 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix E | 60   
APPENDIX F 
 
Estimates, Confidence Intervals, and Key Statistics 
The estimates included in this report are based on a sample of 770 Medicare patients 
discharged from short-term acute-care hospitals in October 2018.  The resulting 
incidence rates were projected to the population of 1,076,344.  Below, we present the 
corresponding 95-percent confidence intervals.  Exhibit F-1 provides patient-level 
estimates, Exhibit F-2 provides event-level estimates, Exhibit F-3 provides the 
estimates of preventability rationales assigned to events by physician-reviewers, 
Exhibit F-4 provides the estimates and statistical test results for the preventability 
analysis, Exhibit F-5 provides estimates of Medicare costs associated with harm 
events, and Exhibit F-6 provides estimates of patients who experienced harm events 
with associated Medicare costs by IPPS status. 
Exhibit F-1: Patient-Level Estimates, Confidence Intervals, and Key Statistics (n=770) 
95-Percent  95-Percent 
Number  Estimated  Confidence Interval  Estimated  Confidence Interval 
of Patients  Percentage of  Lower  Upper  Number of  Lower  Upper 
Estimate Description  in Sample   Patients  Bound  Bound  Patients  Bound  Bound 
Patients Who Experienced Adverse Events and/or Temporary Harm Events  
At least one adverse event 
192  24.94%  22.00%  28.12%  258,323  226,412  290,233 
or temporary harm event 
More than one adverse 
event or temporary harm  64  8.31%  6.56%  10.49%  86,108  65,837  106,378 
event 
An adverse event and 
31  4.03%  2.84%  5.67%  41,708  27,288  56,129 
temporary harm event* 
A preventable adverse 
event or temporary harm  102  13.25%  11.03%  15.83%  137,234  112,313  162,155 
event 
Patients Who Experienced Adverse Events  
At least one adverse event  90  11.69%  9.60%  14.16%  121,089  97,479  144,698 
More than one adverse 
18  2.34%  1.48%  3.68%  24,218  13,137  35,299 
event* 
Adverse event only  59  7.66%  5.98%  9.77%  79,380  59,852  98,909 
A preventable adverse 
49  6.36%  4.84%  8.33%  65,926  48,010  83,842 
event 
A preventable adverse 
39  5.06%  3.72%  6.86%  52,472  36,382  68,562 
event only* 
An adverse event that 
contributed to or resulted  11  1.43%  0.79%  2.56%  14,800  6,099  23,501 
in death (I-level harm)* 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix F | 61   
95-Percent  95-Percent 
Number  Estimated  Confidence Interval  Estimated  Confidence Interval 
of Patients  Percentage of  Lower  Upper  Number of  Lower  Upper 
Estimate Description  in Sample   Patients  Bound  Bound  Patients  Bound  Bound 
Patients Who Experienced Temporary Harm Events  
At least one temporary 
133  17.27%  14.76%  20.11%  178,942  151,124  206,760 
harm event 
More than one temporary 
37  4.81%  3.50%  6.57%  49,781  34,088  65,474 
harm event* 
Temporary harm only  102  13.25%  11.03%  15.83%  137,234  112,313  162,155 
A preventable temporary 
63  8.18%  6.44%  10.34%  84,762  64,637  104,887 
harm event 
A preventable temporary 
53  6.88%  5.29%  8.91%  71,308  52,724  89,891 
harm only 
Source: Office of Inspector General analysis of hospital stays for 770 Medicare patients in October 2018. 
* The 95-percent confidence intervals for projected number of patients exceed 30-percent relative precision. 
Exhibit F-2: Event-Level Estimates, Confidence Intervals, and Key Statistics 
95-Percent Confidence Interval 
Number in  Percentage 
Estimate Description  Sample   Estimate   Lower Bound  Upper Bound 
Adverse Events and/or Temporary Harm Events (n=299)   
Adverse events  115  38.46%  32.63%  44.29% 
Temporary harm events  184  61.54%  55.71%  67.37% 
Preventability of Events 
Preventable events  128  42.81%  36.99%  48.63% 
Clearly preventable events  14  4.68%  2.26%  7.11% 
Likely preventable events  114  38.13%  32.49%  43.77% 
Not preventable events  168  56.19%  50.33%  62.04% 
Clearly not preventable events  9  3.01%  1.08%  4.94% 
Likely not preventable events  159  53.18%  47.52%  58.84% 
Unable to determine preventability of events**  3  --  --  -- 
Clinical Category of Events 
Medication-related events  130  43.48%  37.80%  49.15% 
Patient care-related events  69  23.08%  18.09%  28.07% 
Surgery/Procedure-related events  67  22.41%  17.16%  27.65% 
Infection-related events  33  11.04%  7.38%  14.69% 
F-level harmProlonged hospital stay  85  28.43%  22.88%  33.98% 
Event on NQF SRE list**  1  --  --  -- 
Event on DRA HAC list  5  1.67%  0.27%  3.08% 
Event on HACRP-HAC list  14  4.68%  2.08%  7.29% 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix F | 62   
95-Percent Confidence Interval 
Number in  Percentage 
Estimate Description  Sample   Estimate   Lower Bound  Upper Bound 
Adverse Events and/or Temporary Harm Events within Each Clinical Category  
Medication (n=130)         
Preventable medication-related events  55  42.31%  33.55%  51.07% 
Not preventable medication-related events  74  56.92%  48.14%  65.70% 
Patient Care (n=69)         
Preventable patient care-related events*  36  52.17%  41.49%  62.86% 
Not preventable patient care-related events*  33  47.83%  37.14%  58.51% 
Surgery/Procedure (n=67)         
Preventable surgery/procedure-related events*  17  25.37%  14.83%  35.91% 
Not preventable surgery/procedure-related 
48  71.64%  60.20%  83.09% 
events* 
Infection (n=33)         
Preventable infection-related events***  20  --  --  -- 
Not preventable infection-related events***  13  --  --  -- 
Adverse Events (n=115)   
Preventability of Adverse Events 
Preventable adverse events  52  45.22%  36.33%  54.11% 
Not preventable adverse events  61  53.04%  43.91%  62.17% 
Unable to determine preventability of adverse 
2  --  --  -- 
events** 
Clinical Category of Adverse Events 
Medication-related adverse events  47  40.87%  31.38%  50.36% 
Patient care-related adverse events  15  13.04%  6.78%  19.31% 
Surgery/Procedure-related adverse events  32  27.83%  19.53%  36.12% 
Infection-related adverse events  21  18.26%  11.50%  25.02% 
Harm Level of Events         
F-level harmProlonged hospital stay  85  73.91%  65.97%  81.85% 
G-level harmPermanent patient harm  11  9.57%  3.94%  15.19% 
H-level harmLife-saving intervention required  8  6.96%  2.32%  11.59% 
I-level harmContributing to or resulting in 
11  9.57%  4.11%  15.02% 
death 
F-Level Harm Results (n=85)   
Prolonged the patients stay*  51  60.00%  49.11%  70.89% 
Elevated the patients level of care  13  15.29%  7.91%  22.67% 
Resulted in a subsequent admission*  18  21.18%  10.86%  31.49% 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix F | 63   
95-Percent Confidence Interval 
Number in  Percentage 
Estimate Description  Sample   Estimate   Lower Bound  Upper Bound 
Other**  3  --  --  -- 
Temporary Harm Events (n=184)  
Preventability of Temporary Harm Events 
Preventable temporary harm events  76  41.30%  34.03%  48.58% 
Not preventable temporary harm events  107  58.15%  50.87%  65.44% 
Unable to determine preventability of 
1  --  --  -- 
temporary harm events** 
Clinical Category of Temporary Harm Events 
Medication-related temporary harm events  83  45.11%  37.61%  52.61% 
Patient care-related temporary harm events  54  29.35%  22.25%  36.45% 
Surgery/Procedure-related temporary harm 
35  19.02%  12.84%  25.20% 
events 
Infection-related temporary harm events  12  6.52%  2.71%  10.34% 
Source: Office of Inspector General analysis of hospital stays for 770 Medicare patients in October 2018. 
* The 95-percent confidence intervals for projected proportion of harm events exceed 10-percent absolute precision. 
** We are unable to reliably project the proportion for this item because of the small number of sample occurrences. 
*** We are unable to reliably project the proportion for this item because of the small sample size. 
Exhibit F-3: Physician Rationale Event-level Estimates, Confidence Intervals, and Key Statistics 
95-Percent Confidence Interval 
Number in  Percentage 
Estimate Description  Sample   Estimate   Lower Bound  Upper Bound 
Adverse Events and/or Temporary Harm Events  
Physician Rationale for Preventable Events (n=128) 
Inadequate admission assessment of the 
8  6.25%  2.02%  10.48% 
patient 
Inadequate care plan used to treat the patient  24  18.75%  11.38%  26.12% 
Inadequate monitoring of the patient  10  7.81%  2.46%  13.17% 
Patient received substandard or inadequate 
40  31.25%  22.12%   40.38%  
preventative care 
Patient received substandard treatment or 
42  32.81%  24.17%   41.46% 
therapeutic care 
Necessary treatment was not provided to 
5  3.91%  0.59%   7.22% 
patient 
Provider made an error related to medical 
26  20.31%  12.61%  28.02% 
judgment, skill, or patient management 
Poor communication between caregivers*  1  --  --  -- 
Event rarely happens when proper precautions 
1  --  --  -- 
and procedures are followed* 
Other factor contributing to preventable event*  3  --  --  -- 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix F | 64   
95-Percent Confidence Interval 
Number in  Percentage 
Estimate Description  Sample   Estimate   Lower Bound  Upper Bound 
Physician Rationale for Not Preventable Events (n=168) 
Event occurred even though providers followed 
86  51.19%  43.38%  59.00% 
proper preparation and procedures 
Provider could not have anticipated this event 
15  8.93%  4.59%  13.26% 
with the information available at the time 
Patients diagnosis was unusual or complex, 
19  11.31%  6.51%  16.11% 
making care difficult 
Patients treatment was unusual or complex, 
13  7.74%  2.69%  12.79% 
making care difficult 
Patient was highly susceptible to this type of 
60  35.71%  27.89%  43.53% 
event due to poor health status 
Harm was foreseeable but was considered 
19  11.31%  6.64%  15.98% 
acceptable given alternatives 
Other factor contributing to not preventable 
1  --  --  -- 
event* 
Source: Office of Inspector General analysis of hospital stays for 770 Medicare patients in October 2018. 
Note: Physician-reviewers often choose more than one contributing factor for an event. 
* We are unable to reliably project the proportion for this item because of the small number of sample occurrences. 
Exhibit F-4: Estimates and Statistical Test Results for Preventability Subanalysis 
95-Percent Confidence 
P-Value for 
Interval 
Number  Percentage  Difference in 
Estimate Description  in Sample   Estimate   Lower Bound  Upper Bound  Proportions 
Statistical Test for Relationship Among Preventability Determinations by Clinical Category  
Medication (n=130) 
Preventable medication-related 
55  42.31%  33.55%  51.07% 
events 
0.1011 
Not preventable medication-
74  56.92%  48.14%  65.70% 
related events 
Patient Care (n=69) 
Preventable patient care-
36  52.17%  41.49%  62.86% 
related events** 
0.6897 
Not preventable patient care-
33  47.83%  37.14%  58.51% 
related events** 
Surgery/Procedure (n=67) 
Preventable surgery/ 
17  25.37%  14.83%  35.91% 
procedure-related events** 
<0.0001* 
Not preventable surgery/ 
48  71.64%  60.20%  83.09% 
procedure-related events** 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix F | 65   
95-Percent Confidence 
P-Value for 
Interval 
Number  Percentage  Difference in 
Estimate Description  in Sample   Estimate   Lower Bound  Upper Bound  Proportions 
Infection (n=33) 
Preventable infection-related 
20  --  --  -- 
events*** 
-- 
Not preventable infection-
13  --  --  -- 
related events*** 
Source: Office of Inspector General analysis of hospital stays for 770 Medicare patients in October 2018. 
Note: We conducted t-tests to identify statistically significant differences between preventable and not preventable harm events within clinical categories.   
* P-values are statistically significant at the 95-percent confidence level. 
** The 95-percent confidence intervals for projected proportions exceed 10-percent absolute precision. 
*** We are unable to reliably project the proportion for this item because of the small sample size. 
Exhibit F-5: Estimates and Confidence Intervals for Analysis of Medicare Costs and Patient 
Costs Associated with Adverse Events and Temporary Harm Events 
Number of  Projected  95-Percent Confidence 
Patients in  Number of  Interval 
Sample with Cost  Patients with  Projected  Lower  Upper 
Estimate Description  Implications  Cost Implications  Cost Estimate   Bound  Bound 
Estimated Medicare and Patient Costs for Associated Harm Events 
Costs associated with harm 
25  33,636*  $520,352,452  $223,083,937  $817,620,968 
events for IPPS patients 
Costs associated with harm 
19  25,563**  $281,381,118  $123,834,314    $438,927,922 
events for non-IPPS patients 
Source: Office of Inspector General analysis of hospital stays for 770 Medicare patients in October 2018. 
Note: Confidence intervals for projected numbers exceed 30-percent relative precision. 
* The 95-percent confidence interval for this estimate spans 20,635 to 46,636. 
** The 95-percent confidence interval for this estimate spans 14,186 to 36,940. 
Exhibit F-6: Estimates and Confidence Intervals of Patients Who Experienced Adverse and 
Temporary Harm Events with Associated Medicare Costs and Patient Costs, by IPPS Status 
Number of  95-Percent Confidence Interval 
Patients in  Percentage 
Lower Bound  Upper Bound 
Estimate Description  Sample  Estimate 
IPPS and Non-IPPS Payment Systems (n=770)  
IPPS patients  508  65.97%  62.55%  69.24% 
Non-IPPS patient  262  34.03%  30.76%  37.45% 
Adverse Events and/or Temporary Harm Events with Cost Implications  
Patients with harm events (n=192) and cost 
44  22.92%  17.51%  29.40% 
implications 
IPPS patients with harm events (n=123) 
25  20.33%  14.11%  28.37% 
and cost implications 
Non-IPPS patients with harm events 
19  27.54%  18.29%  39.21% 
(n=69) and cost implications 
Source: Office of Inspector General analysis of hospital stays for 770 Medicare patients in October 2018. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix F | 66   
APPENDIX G 
 
Rates of Patient Harm Events by Patient Days and Hospital 
Admissions 
Hospitals and researchers commonly measure patient harm events by incidence 
density, which accounts for the period during which patients are observed.  For 
example, incidence density is often used in measuring hospital-acquired infections 
because risk can increase as the length of stay increases.178  IHI, a nonprofit advisory 
group to hospitals that promotes quality of care, cites advantages to using incidence 
density metrics over standard incidence rates that measure the number of events per 
patient.179  IHI reports that measuring total events by patient days or hospital 
admissions enables hospitals to count multiple events experienced by the same 
patient.  As a result of these benefits, since the 2010 report, OIG has estimated the 
incidence density of patient harm across health care settings. 
We found that in October 2018, hospitalized Medicare patients experienced 
72.5 harm events per every 1,000 days and 35.9 events per every 100 admissions.  We 
calculated patient days by subtracting the admission date for each hospital stay from 
its discharge date.  The sample of 770 Medicare patients included 834 total eligible 
hospital stays (admissions) and a total of 4,119 days in the hospital (patient days).  
Exhibit G-1 provides the estimated ratios for adverse and temporary harm events per 
1,000 patient days and per 100 admissions.   
Exhibit G-1: Rates of Adverse Events and Temporary Harm Events in the Sample by Patient 
Days and Hospital Admissions 
95-Percent   95-Percent  
Confidence Interval  Confidence Interval 
Per 1,000  Per 100 
Patient Days  Lower  Upper  Admissions  Lower  Upper 
Category  (n=770)  Bound  Bound  (n=834)  Bound  Bound 
Adverse events and/or 
72.5  63.2  81.8  35.9  30.3  41.4 
temporary harm events 
Adverse events  27.9  22.5  33.2  13.8  10.8  16.8 
Temporary harm events  44.6  37.3  52.0  22.1  18.1  26.0 
Source: OIG analysis of hospital stays for 770 Medicare patients in October 2018. 
   
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix G | 67   
APPENDIX H 
 
Patient Harm Events Identified in the Sample  
Exhibit H-1 contains information about adverse events in our sample and Exhibit H-2 
contains information about temporary harm events (E-level harm events) in our 
sample.  Within the exhibit tables we include each harm events description, harm 
level, preventability, and whether the event was on one or more of the NQF, DRA 
HAC, or HACRP lists of events.  Events are grouped based on the broad clinical 
categories of medication, patient care, infection, and procedure or surgery.  Within 
each group similar types of harm events are grouped together, and these are ordered 
by descending frequency in our sample.  Harm levels are labeled as E through I, in 
accordance with the OIG-modified NCC MERP Index.  Preventability determinations 
are labeled as CP (clearly preventable), LP (likely preventable), LNP (likely not 
preventable), CNP (clearly not preventable), and UTD (unable to determine).  
Exhibit H-1: Adverse Events by Clinical Category, Harm Level, Preventability, and Harm Event 
List (n=115)
 
Harm  Preventability  Event 
  Level  Determination  List 
Adverse Events Related to Medication (47) 
Excessive bleeding (12) 
1.  Cascade with excessive bleeding while on anticoagulant 
medication (enoxaparin) prophylaxis for atrial fibrillation leading 
I  LNP   
to hypotension leading to acute kidney injury and ultimately 
request for comfort care and contributing to death  
2.  Cascade with lower gastrointestinal bleeding (melena) due to 
anticoagulant medication (heparin) leading to hypotension 
F  LNP   
requiring endoscopy, discontinuation of anticoagulant 
medication, transfusion, and intravenous fluids 
3.  Cascade with overdiuresis leading to failure to recognize anemia 
due to bleeding gastric ulcer upon admission while on high dose 
anticoagulant (enoxaparin) and antiplatelet (clopidogrel, aspirin) 
F  LP   
medications requiring esophagogastroduodenoscopy with gastric 
clipping associated with hypotension, respiratory failure, 
intubation, and acute kidney injury 
4.  Cascade with subarachnoid hemorrhage with residual aphasia 
and likely exacerbation of postoperative seizures, while on 
anticoagulant (enoxaparin, warfarin) and antiplatelet (aspirin) 
medications given status post cerebral/carotid artery aneurysm  G  LNP   
repair during prior admission, leading to uncal (brain) herniation 
requiring readmission to the intensive care unit and urgent 
craniotomy 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 68   
Harm  Preventability  Event 
  Level  Determination  List 
5.  Excessive bleeding while on anticoagulant medications (heparin, 
enoxaparin, aspirin) for treatment of atrial fibrillation requiring  F  LNP   
10 blood transfusions  
6.  Gastrointestinal bleeding while on anticoagulant (apixaban) and 
antiplatelet (aspirin) medications leading to anemia requiring 
F  LNP   
readmission, transfusion, discontinuation of anticoagulant and 
antiplatelet medications 
7.  Gastrointestinal bleeding while on anticoagulant (heparin) and 
antiplatelet (clopidogrel, aspirin) medications during cardiac 
F  LNP   
catheterization requiring discontinuation of anticoagulant and 
antiplatelet medications 
8.  Gastrointestinal bleeding while on anticoagulant medication 
(heparin) requiring discontinuation of anticoagulant medication, 
F  LNP   
transfusion, and esophagogastroduodenoscopy prolonging 
length of stay 
9.  Gross hematuria while on anticoagulant (apixaban) and 
antiplatelet (aspirin) medications requiring bladder fulguration 
F  LNP   
and clot evacuation, holding medications, and giving 
desmopressin (DDAVP) 
10. Hematuria while on anticoagulant medications (warfarin, 
enoxaparin) with elevated blood clotting test (international 
F  LNP   
normalized ratio 7.9) requiring holding one anticoagulant 
medication and giving Vitamin K 
11. Hemorrhagic conversion of stroke following administration of 
G  UTD   
tissue of thrombolytic agent (tissue plasminogen activator) 
12. Postoperative (hemicolectomy) bleeding from incision site while 
on anticoagulant medications (enoxaparin, warfarin) for 
F  LNP   
suspected venous-thromboembolism requiring surgical 
intervention to stop bleeding 
Acute kidney injury or insufficiency (8) 
1.  Acute kidney injury due to a nonsteroidal anti-inflammatory 
F  LP   
medication (ketorolac) resulting in readmission 
2.  Acute kidney injury on chronic kidney disease due to decreased 
F  LNP   
fluid intake and diuretics (torsemide, spironolactone) 
3.  Acute kidney injury on chronic kidney disease due to overdiuresis 
F  LP   
(metolazone, spironolactone, torsemide) resulting in readmission 
4.  Acute tubular necrosis due to nonsteroidal anti-inflammatory 
medications (ibuprofen, ketorolac) with delayed recognition of  F  LP   
renal insufficiency on admission 
5.  Cascade with acute kidney injury and hyperkalemia (requiring 
treatment) due to postoperative hypotension and diuretic  F  LNP   
(furosemide) given for fluid overload 
6.  Cascade with hypotension due to the antiarrhythmic medication 
F  LNP   
(diltiazem) leading to acute kidney injury 
7.  Contrast-induced (required for cardiac catheterization) acute 
F  CNP   
kidney injury due to intravenous contrast agent 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 69   
Harm  Preventability  Event 
  Level  Determination  List 
8.  Contrast-induced acute kidney injury (following computed 
F  LNP   
tomography scan) requiring readmission 
Delirium or other change in mental status (8) 
1.  Cascade after placement of watchman device with acute 
encephalopathy and possible serotonin syndrome due to opioid 
F  LNP   
pain medications (fentanyl, other opioids) leading to elbow skin 
tear 
2.  Delirium due to patient-controlled analgesia (hydromorphone) 
requiring discontinuation of medication and starting atypical  F  LP   
antipsychotic medication (quetiapine) 
3.  Delirium while on antiseizure medication (levetiracetam) requiring 
discontinuation of antiseizure medication and administration of 
F  LNP   
antipsychotic (haloperidol) and benzodiazepine antianxiety 
(lorazepam) medications 
4.  Hypoactive delirium requiring discontinuation of atypical 
F  LNP   
antipsychotic medication (quetiapine) 
5.  Lethargy due to opioid pain medications (morphine, meperidine, 
oxycodone) and antihistamine (phenothiazine) prolonging  F  LP   
hospital stay 
6.  Post-cardiac catheterization psychosis while on multiple 
medications including benzodiazepine antianxiety (midazolam) 
F  LNP   
and opioid pain (fentanyl) medications requiring an inpatient 
admission 
7.  Prolonged acute respiratory failure and lethargy due a failure to 
provide adequate intravenous naloxone in a patient admitted to 
F  CP   
the emergency department with a long-acting opioid pain 
medication (methadone) overdose 
8.  Unresponsiveness post ankle fracture surgery due to 
polypharmaceuticals (including multiple opioid pain 
[hydrocodone, fentanyl, morphine], anticholinergic [oxybutynin] 
H  LP   
and benzodiazepine antianxiety [lorazepam] medications) 
requiring naloxone, discontinuation of opioid pain medications, 
and intravenous antiseizure medication (levetiracetam) 
Hypotension (5) 
1.  Cascade with symptomatic hypotension (blood pressure of 
51/29 mmHg) due to local anesthetic (lidocaine) progressing to 
unresponsiveness requiring rapid response team, intravenous  H  LNP   
fluids, and discontinuation of lidocaine and hallucinations after 
event 
2.  Dizziness due to hypotension (blood pressure of 76/51 mmHg) 
secondary to multiple doses of opioid pain medication 
F  CP   
(oxycodone) to manage postoperative pain requiring adjustment 
of medication 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 70   
Harm  Preventability  Event 
  Level  Determination  List 
3.  Hypotension (blood pressure of 80/60s mmHg) due to 
antihypertensive medication (metoprolol) excessive dose at time 
F  CP   
of discharge resulting in readmission and adjustment of 
medication 
4.  Hypotension (blood pressure of 82/38 mmHg) with syncope 
following administration of antihypertensive medication 
(labetalol) prior to discharge resulting in syncope in car and a  F  LP   
return to hospital bed requiring adjustment of medication and 
intravenous fluids 
5.  Hypotension (mean arterial pressure of 45 mmHg) due to 
antihypertensive medication (beta blocker) and possibly anemia 
F  LNP   
requiring rapid response team, move to intensive care unit, and 
intravenous fluids 
Respiratory failure (4) 
1.  Cascade with amiodarone-induced pulmonary toxicity leading to 
F  LNP   
respiratory failure and hypotension requiring reintubation 
2.  Cascade with delirium due to opioid pain medication (fentanyl) 
withdrawal leading to continuation of opioid pain medication  F  LNP   
prolonging respiratory failure and intubation 
3.  Cascade with type two respiratory failure (oxygen desaturation 
80s) due to opioid pain medication (fentanyl) leading to 
H  LP   
significant hypotension and patient becoming unresponsive 
requiring reintubation  
4.  Postprocedure (cranial clipping) respiratory failure requiring 
prolonged two-day intubation related to sedation in patient with  F  LNP   
renal failure 
Fluid, electrolyte, and metabolic disorders (3) 
1.  Fluid overload while on total parenteral nutrition (TPN) requiring 
discontinuation of TPN, diuretic (furosemide), and contributing to  I  CP   
death 
2.  Hyperkalemia (potassium of 6.1) due to diuretic (spironolactone) 
resulting in a readmission treated with a potassium-removing  F  LNP   
agent (sodium polystyrene sulfonate) and holding medication 
3.  Hyperkalemia (potassium of 7.5) due to diuretics (metolazone, 
spironolactone, torsemide) and potassium supplements requiring  F  LP   
readmission, discontinuation of medications and treatment  
Cardiac dysrhythmia (2) 
1.  Rapid onset pulmonary edema related to inadequate atrial 
fibrillation management requiring conversion to normal sinus  F  LP   
rhythm 
2.  Severe asymptomatic bradycardia (heart rate in 30s) secondary to 
antihypertensive medications (clonidine, beta blockers) requiring 
F  LP   
discontinuation of antihypertensive medications and monitoring 
at higher level of care 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 71   
Harm  Preventability  Event 
  Level  Determination  List 
Venous thromboembolism (2) 
1.  Left lower extremity deep vein thrombosis while on anticoagulant 
medication (heparin) requiring transition to different  F  LNP   
anticoagulant medication (apixaban) 
2.  Pulmonary embolism with delay in recognition without a 
computed tomography scan on admission in a patient with 
pneumonia, hemoptysis, and an inferior vena filter initially placed 
F  LP   
on low dose intravenous drip of anticoagulant medication 
(heparin) with transition to different anticoagulant medication 
(apixaban) 
Hypoglycemia (1) 
1.  Hypoglycemia (blood glucose of 33 mg/dL, 30 mg/dL) with 
unresponsiveness requiring treatment with glucose by emergency 
H  LP   
medical services, received and treated in emergency department 
with subsequent admission 
Urinary retention (1) 
1.  Postoperative (cerebral/carotid artery aneurysm repair) urinary 
retention due to anesthesia and preexisting benign prostatic  F  CNP   
hypertrophy requiring urinary catheterization 
Vascular skin injury (1) 
1.  Bilateral heels and toes red/purple/maroon discoloration while on 
G  LNP   
vasopressor (norepinephrine) 
Adverse Events Related to Procedure or Surgery (32) 
Excessive bleeding (6) 
1.  Cascade with surgical site bleed (hemorrhage) following bariatric 
sleeve gastrectomy leading to shock, requiring vasopressors, 
F  LP   
further leading to severe acidosis and hyperkalemia requiring 
emergent hemodialysis 
2.  Postoperative bleeding at colostomy site with significant anemia 
I  LNP  HACRP 
requiring transfusion and contributing to death 
3.  Postoperative hernia repair with lysis of adhesions complicated 
by enterotomies (small intestinal serosal tears and lacerations)  G  LNP   
requiring small bowel resection 
4.  Postprocedure (biliary stent placement) complication requiring 
hepatic embolization and transfusion with a readmission for  F  LNP   
presumed abscess 
5.  Postprocedure (endoscopic biliary stent with percutaneous drain) 
gastrointestinal bleeding requiring hepatic artery embolization  F  LNP   
with microcoils and requiring readmission 
6.  Postprocedure bleeding following removal of one of two colon 
polyps while on anticoagulant medication (warfarin) requiring  F  LP   
readmission and removal of second polyp 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 72   
Harm  Preventability  Event 
  Level  Determination  List 
Cerebrovascular accident (5) 
1.  Cerebral hemorrhage due to anticoagulant (heparin) and 
anti-platelet (clopidogrel) medications associated with 
I  LNP   
percutaneous coronary intervention of right coronary artery and 
balloon of left anterior descending stent contributing to death 
2.  Postoperative (atrial valve replacement) acute cerebrovascular 
G  LP   
accident leading to readmission 
3.  Postoperative (cerebral/carotid artery aneurysm repair) 
G  LNP   
complicated by cerebrovascular accident 
4.  Postoperative (hip replacement) complicated by a left occipital 
G  LNP   
lobe infarction 
5.  Postprocedure (angioplasty with stenting of bilateral iliac and 
femoral arteries) complicated by cerebrovascular accident 
H  LP   
requiring thrombolytic tissue plasminogen activator and stenting 
of left internal carotid artery 
Embolisms (i.e., vascular and fat embolisms) (4) 
1.  Cascade with failure to recognize atrial thrombus prior to valve 
replacement and coronary artery bypass graft resulting in 
prolonged surgery following discovery with interruption of blood 
I  LP   
supply leading to shock liver injury (aspartate aminotransferase 
= 12,948, alanine transaminase = 3927), renal injury (serum 
creatinine = 4.08), and contributing to death 
2.  Cascade with postoperative (lung transplant) atrial fibrillation 
leading to embolism with colon ischemia and ileus requiring 
G  LNP  HACRP 
hemicolectomy with resultant septic shock (hypotension) leading 
to acute kidney injury 
3.  Postoperative (open reduction internal fixation humerus [arm] 
fracture) complicated by incomplete occlusive thrombus of the 
F  LNP   
right common femoral (leg) vein requiring anticoagulant 
medication (heparin) and inferior vena cava filter 
4.  Postoperative hip prosthesis revision complicated by hypoxemia, 
F  LNP   
hypotension, and delirium likely due to fat emboli 
Prolonged ileus (4) 
1.  Postoperative (lumbar fusion) ileus requiring holding opioid pain 
medication (hydromorphone), administered an enema and opioid 
F  LP   
receptor antagonist (methylnaltrexone bromide) for 
opioid-induced constipation 
2.  Postoperative (resection rectum) ileus with abdominal distention 
F  LNP   
leading to prolongation of hospital stay 
3.  Postoperative colectomy (resection colon) ileus day 4 requiring 
F  LNP   
nasogastric tube with prolongation of hospital stay 
4.  Prolonged postoperative (cholecystectomy [gall bladder 
removal]) ileus with nausea and vomiting and abdominal 
F  LNP   
distension requiring treatment with intravenous ondansetron and 
extending the hospital stay 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 73   
Harm  Preventability  Event 
  Level  Determination  List 
Cardiac dysrhythmia (2) 
1.  Intraoperative (left craniotomy [aneurysm repair]) complicated by 
pulseless ventricular tachycardia requiring vasopressor  H  LNP   
(epinephrine) 
2.  Postoperative (coronary artery bypass graft) atrial fibrillation with 
F  LNP   
rapid ventricular response 
Hypotension (2) 
1.  Postoperative hypotension (blood pressure of 82/35 mmHg, 
mean arterial pressure of 51 mmHg) with possible bleeding after 
ambulatory surgery for open reduction internal fixation of left  F  LNP   
humerus treated with fluids and admitted for observation due to 
underlying thrombocytopenia and liver disease 
2.  Sustained postprocedure (internal carotid artery stent and 
angioplasty) hypotension (blood pressure of 89/29 mmHg, mean 
F  LNP   
arterial pressure of 45 mmHg) requiring vasopressor therapy 
(dopamine) 
Postoperative seroma/infection (other than infections above) (2) 
1.  Postoperative (lumbar fusion) wound seroma requiring 
F  UTD   
readmission for incision and drainage 
2.  Postoperative (small bowel resection) surgical site abscess 
F  LNP   
requiring readmission for drainage and antibiotics 
Respiratory issues (other than infections) (2)       
1.  Postoperative (laminectomy with tumor resection) respiratory 
failure due to anesthesia and pain medications resulting in 
F  LNP   
remaining intubated with bilevel positive airway pressure and 
transfer to intensive care unit 
2.  Postoperative (mitral and aortic valve replacement) oxygen 
desaturation due to perioperative fluid overload requiring 
F  LNP   
intravenous diuretic (furosemide) and discontinuation of 
intravenous fluids 
Acute kidney injury or insufficiency (1) 
1.  Cascade with postoperative vomiting (five times in less than 
24-hour period) and dehydration (no intravenous fluids given)  F  LP   
leading to acute kidney injury and requiring readmission 
Nausea and vomiting (1) 
1.  Postoperative (bariatric surgery) vomiting (two episodes) and 
nausea for three days requiring prolonged intravenous antiemetic  F  LNP   
medication (ondansetron) and hospital stay 
Pneumothorax (1) 
1.  Postprocedure (outpatient lung biopsy) pneumothorax (lung 
F  CNP   
collapse) requiring chest tube and hospital admission 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 74   
Harm  Preventability  Event 
  Level  Determination  List 
Surgery or procedure-related cardiac event (1) 
1.  Cascade with prolonged hypotension during transcatheter aortic 
valve replacement leading to pulseless electrical activity requiring 
cardiopulmonary resuscitation, vasopressor medication, heart  G  LP   
pump insertion, and fluid resuscitation resulting in diagnosis of 
global cerebral hypoperfusion with possible hippocampus stroke 
Urinary incontinence (1) 
1.  Postoperative (prostatectomy) bladder leakage requiring 
F  LP   
readmission 
Adverse Events Related to Infection (21) 
Respiratory infection (6) 
1.  Cascade with aspiration of high-volume tube feedings leading to 
aspiration pneumonia, respiratory failure, sepsis, and cardiac 
I  LP   
arrest requiring intubation with mechanical ventilation and 
contributing to death 
2.  Cascade with chemotherapy-induced severe neutropenia leading 
F  LNP   
to acute rhinovirus respiratory infection 
3.  Cascade with CDC-defined ventilator-associated (Klebsiella 
oxytoca) pneumonia with secondary bacteremia leading to septic  F  LP   
shock 
4.  Failure to recognize pneumonia during first admission resulting in 
F  LP   
readmission 
5.  Postoperative (hemicolectomy) right lower lobe pneumonia  F  LNP   
6.  CDC-defined ventilator-associated pneumonia  F  LP   
Surgical site infection (6) 
1.  Cascade with infected (MRSA) hip prosthesis leading to 
F  LP  HACRP 
hypotension requiring readmission for revision 
2.  Cascade with surgical wound dehiscence following total 
hysterectomy leading to readmission, ventral hernia and partial  F  LP  HACRP 
small bowel obstruction requiring surgical repair 
3.  Postoperative (laminectomy) surgical site infection with 
dehiscence requiring computed tomography-drainage, washout 
and drainage procedure, debridement of skin, subcutaneous  F  LP   
tissue, and fascia, placement of wound vacuum pump, 
peripherally inserted central catheter, and two readmissions 
4.  Postoperative colon cancer resection abdominal wall cellulitis 
F  LNP  HACRP 
requiring readmission 
5.  Postoperative persistent serious wound drainage (likely infection) 
treated with wound vacuum pump and antibiotic  F  LNP   
(trimethoprim-sulfamethoxazole) 
6.  Postoperative wound dehiscence with intraabdominal infection 
G  LNP  HACRP 
due to anastomotic leak requiring intestinal revision 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 75   
Harm  Preventability  Event 
  Level  Determination  List 
Sepsis (4) 
1.  Cascade with central line-associated bloodstream 
infection/catheter-associated urinary tract infection 
I  LNP   
(CLABSI/CAUTI) MSSA bacteremia leading to septic shock and 
contributing to death 
2.  Cascade with omission of empiric antibiotics on admission for 
underlying small bowel obstruction and micro-aspiration, septic 
F  LP   
shock, and respiratory failure requiring mechanical ventilation 
and vasopressor medication 
3.  Cascade with substandard treatment of sepsis with insufficient 
fluid administration and inappropriate antibiotic coverage leading  I  LP   
to septic shock, respiratory failure, and contributing to death 
4.  Failure to treat urinary tract infection during first admission 
resulting in readmission due to sepsis with infectious  F  CP   
encephalopathy  
Clostridioides difficile (C. diff) infection (3) 
1.  Cascade with C. diff infection leading to septic shock requiring 
intensive care unit admission and treatment with vasopressor  F  LP  HACRP 
medication (vasopressin) 
2.  C. diff infection  F  LP  HACRP 
3.  C. diff infection  F  LP  HACRP 
Central line-associated bloodstream infection (CLABSI) (1) 
1.  Staphylococcus epidermidis primary bacteremia and Klebsiella  DRA, 
F  LP 
oxytoca secondary bacteremia (CLABSI) requiring line change  HACRP 
Intraabdominal infection with delayed treatment (1) 
1.  Cascade with five-day delay of surgery for patient admitted with 
sepsis and abdominal symptoms leading to worsening of necrotic 
small intestine, purulent gross contamination of abdomen, septic 
I  LP   
shock with associated acute kidney injury, and hypoactive 
delirium treated with multiple surgeries and intubation and 
contributing to death 
Adverse Events Related to Patient Care (15) 
Fluid and electrolyte disorders (5) 
1.  Cascade with substandard intervention for hyperkalemia (6.4) 
leading to severe bradycardia (30s) per telemetry with inadequate 
I  CP   
emergency response due to difficulty locating patient leading to 
cardiac arrest and contributing to death 
2.  Cascade with volume overload due to fluid resuscitation for 
pneumonia with sepsis leading to acute respiratory distress  F  LP   
requiring diuretics (furosemide) and thoracentesis 
3.  Fluid overload due to volume resuscitation for suspected sepsis 
F  LNP   
requiring diuretics (furosemide, spironolactone) and thoracentesis 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 76   
Harm  Preventability  Event 
  Level  Determination  List 
4.  Inadequate management of potassium during first admission 
leading to readmission due to hyperkalemia (potassium = 6.2)  F  LP   
requiring sodium polystyrene (kayexalate) 
5.  Pulmonary edema shortly after the placement of the dialysis 
H  LNP   
catheter 
Acute myocardial infarction  delayed diagnosis (3) 
1.  Cascade with delayed diagnosis of Type 2 myocardial infarction 
leading to hypotension, congestive heart failure, and episode of  G  LP   
delirium 
2.  Delayed recognition of acute inferior myocardial infarction led to 
a two-day delay with cardiac arrest during catheterization, a failed  I  CP   
attempt to resuscitate the patient, and contributing to death 
3.  Delayed recognition of Type 2 myocardial infarction with 
pulmonary edema resulting in cardiac arrest requiring  H  CP   
resuscitation, intubation, and right jugular catheter 
Respiratory issues (other than infections) (3) 
1.  Acute on chronic respiratory failure with hypoxia/hypercapnia in 
obesity hypoventilation syndrome patient not on continuous 
F  LP   
positive airway pressure on admission requiring transfer to 
intensive care unit 
2.  Large aspiration of liquid requiring suctioning after intubation  F  LNP   
3.  Multiple episodes of food and tube feeding aspirations related to 
intravenous opioid pain medication (morphine) and history of 
F  LNP   
cerebrovascular accident treated with percutaneous 
esophagogastrostomy tube 
Fall or other trauma with injury (2) 
1.  Cascade with fall following elective hip replacement resulting in  NQF, 
new fracture with excessive bleeding and need for revision  F  CP  DRA, 
surgery  HACRP 
2.  Traumatic hematoma to right knee following a bed rail injury  F  LNP   
Pressure injury (2) 
1.  Deep tissue pressure injury left heel  F  LP   
2.  Deep tissue pressure injury of bilateral buttocks  F  LP   
Source: Office of Inspector General analysis of hospital stays for 770 Medicare patients in October 2018. 
 
 
 
 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 77   
Exhibit H-2: Temporary Harm Events (E-level harm) by Clinical Category, Preventability, and 
Harm Event List (n=184) 
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
Temporary Harm Events Related to Medication (83) 
Delirium or other change in mental status (20) 
1.  Acute toxic encephalopathy while on opioid pain medication 
(fentanyl) leading to discontinuation of medication with naloxone  E  LP   
administration 
2.  Change in mental status resulting in discontinuing 
benzodiazepine antianxiety medication (temazepam) and  E  LP   
prescribing atypical antipsychotic medication (risperidone) 
3.  Confusion due to anticholinergic (scopolamine) and opioid 
agonist pain (tramadol) medications requiring discontinuation of  E  CNP   
medications and femoral nerve block  
4.  Confusion due to toxic metabolic encephalopathy associated with 
E  LNP   
age, anesthesia, and health status 
5.  Delirium due to opioid pain medications (fentanyl, 
E  LNP   
hydromorphone) requiring medication adjustment 
6.  Delirium while on benzodiazepine antianxiety medication 
(lorazepam) requiring antipsychotic medications (haloperidol,  E  LNP   
quetiapine) 
7.  Delirium while on opioid pain medication (hydrocodone) 
E  LNP   
requiring discontinuation of medication 
8.  Delirium while on opioid pain medications (fentanyl, 
E  LP   
hydrocodone, oxycodone) requiring medication adjustment 
9.  Hallucinations while on opioid pain medication (oxycodone) 
E  LP   
requiring discontinuation and changing of medication 
10. Increased depression and irritability due to serotonin-
norepinephrine reuptake inhibitor antidepressant (desvenlafaxine  E  LNP   
succinate) requiring discontinuation of medication 
11. Lethargy due to benzodiazepine antianxiety (lorazepam) and 
opioid pain (hydrocodone) medications requiring dose  E  LNP   
adjustment 
12. Lethargy due to increase of atypical antipsychotic medication 
E  LP   
(quetiapine) requiring adjustment of medication  
13. Mild metabolic encephalopathy (change in mental status) due to 
E  LNP   
anesthesia  
14. Multiple episodes of oversedation while on opioid pain 
medications (fentanyl, morphine) requiring medication  E  LP   
adjustment 
15. New onset delirium while on hypnotic medication (zolpidem) 
E  LP   
requiring discontinuation of medication 
16. Oversedation and confusion while on multiple opioid pain 
E  LP   
medications (oxycodone, morphine, hydromorphone, fentanyl) 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 78   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
17. Oversedation due to antipsychotic (haloperidol, olanzapine) and 
benzodiazepine antianxiety (lorazepam) medications requiring  E  LNP   
discontinuation of medications 
18. Somnolence and inability to follow commands while on 
benzodiazepine antianxiety medication (lorazepam) in  E  LP   
combination with anticonvulsants (valproic acid, levetiracetam) 
19. Somnolence while on benzodiazepine antianxiety (lorazepam) 
and opioid pain (morphine and hydrocodone) medications  E  LP   
resulting in discontinuing benzodiazepine antianxiety medication 
20. Visual hallucinations due to multiple medications (anti-nausea 
[scopolamine], antiseizure [gabapentin], and opioid pain 
E  LP   
[tramadol, fentanyl, hydrocodone, oxycodone] medications) 
resulting in discontinuation of medications 
Hypotension (14) 
1.  Hypotension (blood pressure of 90/47 mmHg mean arterial 
pressure of 61 mmHg) related to opioid pain medications 
E  LNP   
(fentanyl, oxycodone-acetaminophen, hydromorphone) requiring 
fluids 
2.  Hypotension (blood pressure of 151/89 mmHg to 90/54 mmHg) 
due to topical vasodilator medication (nitroglycerin) requiring  E  LP   
discontinuation of medication 
3.  Hypotension (blood pressure of 77/64 mmHg) due to intravenous 
antihypertensive medication (esmolol) continuing at the same 
dosage while adding an oral antihypertensive medication 
E  LP   
(metoprolol) leading to confusion and unresponsiveness to verbal 
and painful stimuli while consciousnesses remained intact 
requiring medication discontinuation 
4.  Hypotension (blood pressure of 78/50 mmHg) due to 
continuation of home antihypertensive medications (metoprolol, 
triamterene) in a patient with an admission systolic blood 
E  LP   
pressure in low 100s mmHg requiring adjustment of 
antihypertensive medications and administration of intravenous 
fluids 
5.  Hypotension (blood pressure of 80/45 mmHg) due to 
antihypertensive medications (metoprolol, triamterene) requiring  E  LP   
medication adjustment and intravenous fluids 
6.  Hypotension (blood pressure of 83/48 mmHg) with mean arterial 
E  LNP   
pressure in 50s mmHg requiring vasopressor (norepinephrine) 
7.  Hypotension (blood pressure of 84/64 mmHg) due to oral 
calcium-channel blocker antihypertensive medication (diltiazem)  E  LP   
requiring adjustment of medication 
8.  Hypotension (blood pressure of 86/45 mmHg) due to 
inappropriate continuation of home antihypertensive medication 
E  CP   
(prazosin) in the hospital requiring discontinuation of medication 
and intravenous fluids 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 79   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
9.  Hypotension (blood pressure of 89/41 mmHg) due to opioid pain 
medications (hydromorphone, hydrocodone) requiring  E  LP   
intravenous fluid bolus and holding antihypertensive medications 
10. Hypotension (blood pressure of 89/41 mmHg) with dizziness due 
to two doses of opioid pain medication (oxycodone) within 1  E  LP   
hour requiring discontinuation of medication 
11. Hypotension (systolic blood pressure dropped from above 
200 mmHg to 70s mmHg) due to benzodiazepine antianxiety  E  LNP   
medication (lorazepam) requiring intravenous fluids 
12. Orthostatic hypotension (systolic blood pressure 130s mmHg to 
60s mmHg) with symptoms persisting due to volume depletion 
E  LP   
and polypharmacy, including anticonvulsant (gabapentin) and 
antihypertensive medication (metoprolol) 
13. Prolonged hypotension (blood pressure of 83/48 mmHg, mean 
arterial pressure of 50s mmHg) related to anesthetic (propofol), 
opioid pain medication (fentanyl), and benzodiazepine sedative  E  LP   
medication (midazolam) while on mechanical ventilation requiring 
medication adjustment and intravenous fluids 
14. Symptomatic hypotension (precipitous drop of blood pressure of 
189/69 mmHg to 126/54 mmHg and mean arterial pressure from 
E  LNP   
112 mmHg to 80 mmHg) due to antihypertensive vasodilator 
medication (hydralazine) requiring discontinuation of medication 
Hypoglycemia (12) 
1.  Hypoglycemia (blood glucose of 34 mg/dL) due to insulin with 
drowsiness treated with apple juice, crackers, and adjustment of  E  LP   
insulin 
2.  Hypoglycemia (blood glucose of 37 mg/dL, twice within 
2-1/2 hours) due to receiving insulin drip while on mechanical 
E  CP   
ventilation requiring treatment with intravenous dextrose and 
discontinuation of insulin drip 
3.  Hypoglycemia (blood glucose of 40 mg/dL) due to insulin 
E  LP   
requiring glucose and insulin adjustment 
4.  Hypoglycemia (blood glucose of 41 mg/dL) due to insulin 
E  LNP   
requiring glucose and insulin adjustment 
5.  Hypoglycemia (blood glucose of 44 mg/dL) due to insulin 
E  CP   
requiring dextrose infusion and adjustment of insulin dose 
6.  Hypoglycemia (blood glucose of 48 mg/dL) due to insulin  E  LNP   
7.  Hypoglycemia (blood glucose of 48 mg/dL) requiring dextrose 
E  LNP   
(D50W) 
8.  Hypoglycemia (blood glucose of 49 mg/dL, 46 mg/dL) treated 
E  LNP   
with intravenous dextrose (D50W) 
9.  Hypoglycemia (blood glucose of 49 mg/dL) managed with 
E  LNP   
orange juice 
10. Hypoglycemia (blood glucose of 49 mg/dL) due to insulin treated 
E  LP   
with intravenous dextrose (D50W) 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 80   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
11. Hypoglycemia (blood glucose of 50 mg/dL) with dizziness due to 
insulin treated with orange juice, glucose tablet, and insulin  E  CP   
adjustment 
12. Hypoglycemia (blood glucose of 67 mg/dL) due to insulin with 
dizziness following blood glucose of 231 mg/dL and 173 mg/dL  E  LP   
requiring orange juice, snack, and discontinuation of insulin 
Acute kidney injury or insufficiency (10) 
1.  Acute kidney injury due to acute tubular necrosis, pre-renal 
E  LNP   
events, and multiple medications 
2.  Acute kidney injury due to antibiotic (vancomycin) requiring 
E  CNP   
adjustment of dose 
3.  Acute kidney injury due to diuretics (furosemide, spironolactone)   E  LP   
4.  Acute kidney injury due to intravenous diuretic (furosemide)  E  LNP   
5.  Acute kidney injury on chronic kidney disease due to diuretic 
E  LNP   
(furosemide)  
6.  Contrast-induced acute kidney injury and in combination with the 
E  LNP   
intravenous diuretic (furosemide) 
7.  Contrast-induced acute kidney injury  E  LNP   
8.  Contrast-induced acute kidney injury following multiple 
E  LNP   
computed tomography scans  
9.  Contrast-induced acute kidney injury on chronic disease  E  LNP   
10. Contrast-induced acute kidney injury on chronic kidney disease 
E  LNP   
requiring intravenous fluid and discontinuation of diuretics 
Excessive bleeding (6) 
1.  Gastrointestinal bleeding while on anticoagulant medication 
E  LNP   
(apixaban) 
2.  Gross hematuria and clotting of urinary catheter while on 
anticoagulant medication (apixaban) requiring discontinuation of  E  LNP   
anticoagulant medication and new catheter  
3.  Lower gastrointestinal bleed (melena) while on anticoagulant 
E  LP   
medication (heparin) requiring discontinuation 
4.  Postoperative coronary artery bypass graft day 3 bleeding while 
on anticoagulant medication (enoxaparin) requiring pressure and  E  LNP   
transfusion 
5.  Retroperitoneal and upper arm hematoma while on thrombolytic 
E  LNP   
agent (tissue plasminogen activator) requiring cryoprecipitate 
6.  Significant anemia while on anticoagulant medication 
E  LNP   
(enoxaparin) requiring transfusion 
Allergic reaction/hypersensitivity reaction (5) 
1.  Chemotherapy-induced toxic skin rash   E  LNP   
2.  Generalized pruritus due to opioid pain medication (intravenous 
morphine) treated with antihistamine (hydroxyzine) and  E  CNP   
discontinuation of opioid pain medication  
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 81   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
3.  Rash on chest following administration of rocuronium requiring 
treatment with antihistamine medication (diphenhydramine) and  E  LNP   
histamine (H-2) receptor agonist (famotidine) 
4.  Rash with pruritis at peripheral intravenous site requiring removal 
E  LNP   
of the line and treatment with ice 
5.  Skin rash due to opioid pain medication (fentanyl) treated with 
antihistamine (diphenhydramine), steroids, histamine (H-2) 
E  CNP   
receptor agonist, epinephrine, and discontinuation of opioid pain 
medication 
Noninfectious diarrhea (5) 
1.  Chemotherapy-induced proctocolitis of rectum, sigmoid, and 
E  LNP   
descending colon due to translocation of gut microflora 
2.  Diarrhea after receiving multiple laxatives (bisacodyl, polyethylene 
glycol, sennosides-docusate) resulting in the patient refusing  E  LNP   
laxatives and resolution of diarrhea 
3.  Diarrhea due to antibiotic (cefpodoxime) resulting in 
E  LNP   
discontinuation 
4.  Diarrhea due to laxatives (magnesium sulfate, sorbitol, senna) 
E  LNP   
given for postoperative constipation requiring laxatives to be held 
5.  Diarrhea while on multiple antibiotics (azithromycin, ceftriaxone, 
metronidazole, levofloxacin, meropenem, vancomycin, cefdinir)  E  LNP   
requiring antidiarrhea medication (loperamide) and probiotic 
Cardiac dysrhythmia (4) 
1.  Complete heart block exacerbated by antihypertensive 
E  LP   
medication (clonidine) requiring discontinuation of medication 
2.  Presyncope manifested by weakness with bradycardia related to 
antihypertensive medication (beta blocker) requiring  E  LNP   
discontinuation of medication 
3.  Prolonged cardiac pauses requiring discontinuation of 
antiarrhythmic medication (digoxin) and administration of  E  LP   
intravenous fluids 
4.  Severe bradycardia due to calcium channel blocker (diltiazem) 
E  LNP   
requiring discontinuation 
Prolonged constipation obstipation and ileus (3) 
1.  Functional ileus with symptoms of nausea, vomiting, and anorexia 
likely due to anesthesia and opioid pain medications 
E  LP   
(hydromorphone, hydrocodone) treated with an antiemetic 
medication (ondansetron) and bowel rest 
2.  Prolonged symptomatic postoperative constipation due to a 
combination of surgery, sedation, and immobility requiring 
E  LNP   
laxatives, enema, and a dopamine antagonist medication 
(metoclopramide) 
3.  Prolonged, symptomatic constipation related to inadequate 
E  LP   
preventative regimen and requiring laxative (polyethylene glycol) 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 82   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
Urinary retention (2) 
1.  Acute urinary retention in a patient with benign prostatic 
hypertrophy after receiving nebulized bronchodilator 
E  LP   
(ipratropium) requiring discontinuation and urinary 
catheterization 
2.  Urinary retention likely due to opioid pain medication (fentanyl) 
E  LP   
treated with straight urinary catheterization 
Fluid, electrolyte, and metabolic disorders (1) 
1.  Acute gout due to diuretics requiring colchicine  E  LNP   
Seizure (1) 
1.  Generalized seizure due to holding antiseizure medication 
(levetiracetam) because of aspiration requiring restarting 
E  LP   
medication with intravenous benzodiazepine antianxiety 
medication (lorazepam) 
Temporary Harm Events Related to Patient Care (54) 
Pressure injury (20) 
1.  Deep tissue pressure injury buttocks requiring specialty mattress  E  LP   
2.  Multiple sacral deep tissue pressure injuries which progressed 
E  LNP   
from admission Stage 1 pressure injury  
3.  Penile Texas urinary catheter pressure injury  E  LP   
4.  Progression from Stage 1 to Stage 2 pressure injury right hip  E  LP   
5.  Progression of Stage 1 to Stage 2 sacral pressure injury while 
E  LNP   
using specialty mattress 
6.  Progression Stage 1 to Stage 2 coccyx pressure injury  E  LNP   
7.  Progression Stage 1 to Stage 2 coccyx pressure injury  E  LNP   
8.  Stage 1 bilateral elbows pressure injuries  E  LP   
9.  Stage 1 coccyx pressure injury   E  LP   
10. Stage 1 elbow pressure injury  E  LP   
11. Stage 1 sacral pressure injury   E  LNP   
12. Stage 1 sacral pressure injury   E  LP   
13. Stage 1 sacral pressure injury in a patient with pre-admission 
E  LP   
C. diff diarrhea 
14. Stage 2 bilateral ankle pressure injuries  E  LP   
15. Stage 2 bilateral buttocks pressure ulcers  E  LP   
16. Stage 2 coccyx pressure injury  E  LNP   
17. Stage 2 coccyx/sacrum pressure injury  E  LP   
18. Stage 2 right buttock pressure injury  E  LP   
19. Stage 2 sacral pressure injury  E  LNP   
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 83   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
20. Stage 2 sacral pressure injury  E  LP   
Skin tear abrasion, breakdown, or inflammation (11) 
1.  Incontinence-associated dermatitis treated with a moisture 
E  LNP   
barrier  
2.  Inframammary (beneath breast) skin rash with ecchymosis  E  LP   
3.  Mechanical trauma to bilateral buttocks related to repositioning 
E  LNP   
in a debilitated patient resulting in skin tear with blistering 
4.  Moisture dermatitis perineal and buttock area treated with 
E  LNP   
moisture barrier and nystatin cream 
5.  Penile excoriation due to urinary catheter requiring 
E  LP   
discontinuation of catheter and symptomatic treatment  
6.  Perineal dermatitis due to urinary and fecal incontinence  E  LNP   
7.  Skin tear at intravenous site right forearm requiring dressing and 
E  LP   
continued skin care  
8.  Skin tear in gluteal fold in a patient with diarrhea treated with 
E  LNP   
skin barrier cream 
9.  Skin tear with blister and serosanguinous drainage of left hand at 
E  LNP   
blood draw site requiring dressing 
10. Skin tears bilateral upper extremities requiring hydration, 
E  LP   
nonadhesive dressings, and positioning 
11. Skin wound of left cheek due to endotracheal tube anchoring 
E  LP   
tape treated with nonadhesive tape dressing 
Intravenous (IV) catheter infiltration/burn/phlebitis (9) 
1.  Acute right upper extremity (proximal and mid right cephalic 
vein) occlusive thrombus at the IV site treated with anticoagulant  E  LNP   
medications (apixaban, heparin) 
2.  Extravasation of computed tomography scan contrast into left 
E  LP   
arm requiring an ice pack 
3.  Infiltration of peripheral line IV site leading to arm swelling 
requiring elevation of the arm, replacement of the line, and local  E  LNP   
measures for comfort 
4.  IV infiltrate right arm with swelling and blistering requiring 
E  LP   
discontinuation of IV and dressings   
5.  IV infiltrate with pain and swelling of right forearm requiring 
discontinuing and changing IV to other forearm, elevation, and  E  LNP   
compresses 
6.  IV site infiltration with significant right arm swelling and 
discoloration requiring removal of IV, elevation, and cold  E  LNP   
compress 
7.  IV infiltrate of cardiac medication (dopamine) with pain, swelling, 
redness, and soreness to the left upper extremity requiring 
E  LNP   
discontinuation of medication and treatment with IV 
phentolamine mesylate to avoid necrosis 
8.  Several small areas of skin breakdown at IV site requiring dressing 
E  LNP   
and site change 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 84   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
9.  Superficial vein thrombophlebitis at left upper extremity IV site 
E  LP   
with removal and replacement of IV 
Fall or other trauma with injury (7) 
1.  Cascade with overdosage of antiseizure medication 
(carbamazepine) causing dizziness leading to a fall with facial  E  CP   
injury 
2.  Cascade with rib fractures due to cardiopulmonary resuscitation 
leading to traumatic pneumothorax and subcutaneous  E  LNP  DRA 
emphysema while on mechanical ventilation requiring chest tube 
3.  Fall while on opioid pain medication (oxycodone) resulting in 
E  LNP   
abrasion and hematoma to right knee  
4.  Fall while on opioid pain medication (oxycodone) resulting in 
E  LP   
pelvic pain 
5.  Fall with abrasion right shoulder  E  LNP   
6.  Fall with ankle pain requiring opioid pain medication (oxycodone)  E  LNP   
7.  Fall with injury to forehead with altered mental status and left 
E  LP   
peri-orbital ecchymosis  
Fluid and electrolyte disorders (4) 
1.  Acute pulmonary edema due to intravenous fluid overload 
E  LP   
requiring intravenous furosemide 
2.  Cascade with fluid overload leading to demand cardiac ischemia 
E  LNP   
evidenced by increased troponin 
3.  Fluid overload due to blood transfusion for anemia requiring 
E  LNP   
intravenous furosemide   
4.  Nonsustained ventricular tachycardia with electrolyte imbalance 
E  LNP   
requiring increase in antihypertensive medication (carvedilol) 
Excessive bleeding (1) 
1.  Hematuria due to urethral trauma during a urinary catheter 
E  LNP   
removal 
Noninfectious conjunctivitis (1) 
1.  Conjunctivitis with blistering (chemosis) result of inadequate 
preventative care in a patient with the inability to close eyelids  E  LP   
while on ventilator 
Respiratory issues (other than infections) (1) 
1.  Decreased oxygen saturation level (59 percent on room air) due 
to patient with known chronic obstructive pulmonary disease  E  LNP   
removing their oxygen supplementation 
Temporary Harm Events Related to Procedure or Surgery (35) 
Hypotension (13) 
1.  Cascade with hypotension following liver abscess 
biopsy/aspiration leading to change in mental status treated with  E  LNP   
intravenous fluids bolus 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 85   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
2.  Hypotension (blood pressure of 63/30 mmHg, mean arterial 
pressure of 41 mmHg) and likely bradycardia (low heart rate of 
49) related to sedating medication (dexmedetomidine) during  E  LNP   
trans-catheter aortic valve replacement requiring vasopressor 
(epinephrine) 
3.  Hypotension (blood pressure of 82/44 mmHg, mean arterial 
pressure of 57 mmHg) related to epidural requiring dose  E  LNP   
adjustments and increased monitoring 
4.  Intraoperative (colectomy) hypotension (blood pressure of 
80s/50s mmHg, mean arterial pressure of 45 mmHg) requiring  E  LNP   
vasopressors (phenylephrine, ephedrine), and intravenous fluids 
5.  Intraoperative (inguinal hernia repair) hypotension (blood 
pressure of 75/52 mmHg, mean arterial pressure of 52 mmHg) 
E  LNP   
while on anesthesia medications (propofol, sevoflurane, 
midazolam, rocuronium) requiring vasopressor (phenylephrine) 
6.  Intraoperative (knee arthroplasty) hypotension (blood pressure of 
60/48 mmHg) due to excessive dose of induction agent 
E  LP   
(propofol) requiring treatment with vasopressors (ephedrine, 
phenylephrine) 
7.  Intraoperative (shoulder arthroplasty) prolonged hypotension 
(blood pressure of 71/46 mmHg, mean arterial pressure of  E  LNP   
49 mmHg) requiring vasopressor (phenylephrine) 
8.  Intraoperative hypotension (blood pressure of 86/44 mmHg) after 
receiving benzodiazepine sedative (midazolam) and opioid pain 
E  LNP   
(fentanyl) medications requiring vasopressor (phenylephrine) and 
intravenous fluids 
9.  Multiple hypotensive readings intraoperatively (blood pressure of 
66/4885/62 mmHg) and 6 hours postoperatively (blood pressure 
of 78/50 mmHg) while on benzodiazepine sedative medication  E  LNP   
(midazolam) in occupational therapy with significant 
lightheadedness 
10. Postoperative (coronary artery bypass graft) hypotension (blood 
pressure of 73/37 mmHg, mean arterial pressure of 49 mmHg)  E  CNP   
requiring vasopressor and intravenous fluids 
11. Postoperative (lumbar decompression) hypotension (blood 
pressure of 86/46 mmHg) with lightheadedness requiring  E  LNP   
intravenous fluids 
12. Postoperative hypotension (mean arterial pressure of 76 mmHg 
to 47 mmHg) lasting 30 minutes following Hickman Catheter  E  LP   
placement requiring intravenous fluids 
13. Prolonged intraoperative (total hip replacement) hypotension 
(blood pressure of 90s/70s mmHg) requiring vasopressor agent  E  UTD   
(epinephrine) and intravenous fluids 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 86   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
Excessive bleeding (7) 
1.  Bleeding at Jackson-Pratt surgical drain site with patient cold, 
clammy, and lightheaded and blood pressure of 97/71 mmHg,  E  LP   
requiring intravenous fluid bolus and drain removal 
2.  Bleeding due to laceration of lip into oropharynx from bite block 
inserted during endoscopic retrograde 
E  LP   
cholangiopancreatography while on subcutaneous anticoagulant 
medication (heparin) 
3.  Excess bleeding at transcatheter aortic valve replacement catheter 
E  LNP   
site requiring manual pressure 
4.  Excessive bleeding from femoral line leading to acute anemia 
requiring pressure dressing, transfusion, and removal of femoral  E  LP   
line 
5.  Postoperative (mitral valve repair) anemia while on anticoagulant 
(heparin) and antiplatelet (aspirin) medications and requiring a  E  LNP   
transfusion 
6.  Postoperative (proctectomy, colostomy) anemia while on 
preoperative anticoagulant medication (heparin) requiring  E  LP   
transfusion 
7.  Postprocedure (percutaneous endoscopic gastrostomy [PEG] 
tube) bleeding requiring surgical consultation and extra gauze  E  LNP   
packing 
Blood transfusion reaction (2) 
1.  Blood transfusion reaction treated with diphenhydramine   E  LNP   
2.  Blood transfusion reaction without diphenhydramine pre-
E  LP   
medication with history of prior reaction 
Cardiac dysrhythmia (2) 
1.  Postoperative (mitral valve repair) arrhythmia (atrial fibrillation) 
E  LNP   
requiring treatment with antiarrhythmic medication (amiodarone) 
2.  Postoperative (mitral valve repair, aortic valve replacement) atrial 
fibrillation requiring antiarrhythmic medication (amiodarone) and  E  LNP   
temporary cardiac pacing 
Extremity weakness due to regional anesthesia (2) 
1.  Quadriceps (leg) muscle weakness and numbness due to partial 
block of femoral nerve from fascia iliaca block requiring leg  E  LNP   
immobilizer 
2.  Supratherapeutic effect of continuous epidural infusion resulting 
E  LNP   
in inability to lift left leg and requiring decrease of epidural rate 
Pneumothorax (2) 
1.  Postoperative (upper lung lobectomy) complicated by 
pneumothorax (collapsed lung) with air leak requiring Heimlich  E  LNP   
valve insertion 
2.  Postprocedure (thoracentesis) small left apical pneumothorax 
E  LNP   
(9mm) requiring monitoring 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 87   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
Surgery or procedure-related trauma (other than above) (2) 
1.  Intraoperative (knee arthrodesis [fusion]) fracture of distal tibia 
requiring modification of implanted device (rod) and boot  E  LNP   
orthosis 
2.  Postcardioversion burn on chest with swelling and redness 
E  LNP   
requiring monitoring 
Embolisms (i.e., vascular and fat embolisms) (1) 
1.  Postoperative (bladder fulguration) in patient with advanced 
bladder cancer and gross hematuria complicated by pulmonary  E  CNP  HACRP 
emboli requiring inferior vena cava filter 
Nausea and vomiting (1) 
1.  Postoperative (abdominal hysterectomy) nausea and vomiting 
lasting 2 days while on multiple pain medications requiring  E  LP   
antiemetic medications (ondansetron, prochlorperazine) 
Respiratory issues (other than infections) (1) 
1.  Postoperative abdominal aneurysm repair atelectasis resulting in 
E  LNP   
oxygen desaturation (81 percent) requiring diuretic (furosemide) 
Seizure (1) 
1.  Postoperative (complex aneurysm repair via craniotomy) seizure 
while on postoperative seizure prophylaxis requiring additional  E  LNP   
seizure medication and electroencephalogram monitoring 
Urinary incontinence (1) 
1.  Dislodgment of ureteral stent resulting in leakage of urine with 
E  LNP   
subsequent removal of stent 
Temporary Harm Events Related to Infection (12) 
Thrush (5) 
1.  Hoarseness/dysphagia related to delay in recognition and 
E  LP   
treatment of thrush 
2.  Oral thrush while on antibiotics   E  LP   
3.  Oral thrush while on antibiotics and steroids  E  LNP   
4.  Oral thrush while on multiple antibiotics  E  LNP   
5.  Oral thrush while on prednisone  E  LNP   
Soft tissue or other nonsurgical infection (3) 
1.  Acute cellulitis on chronic sacral osteomyelitis due to fecal 
E  LNP   
contamination 
2.  Balanitis with penile pain associated with a three-way catheter for 
E  LP   
bladder irrigation 
3.  Fungal infection groin and buttocks   E  LNP   
Catheter-associated urinary tract infection (CAUTI) (2) 
1.  Cascade with CDC-defined CAUTI leading to hypotension and  DRA, 
E  LP 
catheter replacement  HACRP 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 88   
Harm  Preventability  Event 
Clinical Category  Level  Determination  List 
DRA, 
2.  CDC-defined CAUTI  E  LP 
HACRP 
Respiratory infection (2) 
1.  Aspiration pneumonia  E  LNP   
2.  Aspiration pneumonia due to tube feedings in a patient with a 
E  LNP   
history of dysphagia due to a cerebrovascular accident 
Source: Office of Inspector General analysis of hospital stays for 770 Medicare patients in October 2018.   
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix H | 89   
APPENDIX I 
 
Agency Comments: Centers for Medicare & Medicaid Services 
 
 
DATE:   February 25, 2022   
  
TO:     Christi A. Grimm 
Principal Deputy Inspector General 
Office of Inspector General 
 
FROM:   Chiquita Brooks-LaSure  
Administrator 
 
Centers for Medicare & Medicaid Services 
 
SUBJECT:   Office of Inspector General (OIG) Draft Report: Adverse Events in Hospitals: A 
Quarter of Medicare Patients Experienced Harm in October 2018, OEI-06-18-
00400 
 
The Centers for Medicare & Medicaid Services (CMS) appreciates the opportunity to review and 
comment on the OIG draft report on Medicare patients who experienced adverse and temporary 
harm events as a result of medical care, including failure to provide needed care, in hospitals. 
CMS serves the public as a trusted partner and steward and is dedicated to improving health 
outcomes. Preventable adverse and temporary harm events are unacceptable and CMS strives to 
hold providers and health care systems accountable for preventable health care harm through 
multiple levers, including survey requirements, quality reporting and value-based purchasing, 
and innovative quality improvement programs. 
 
As described below, sustained efforts are underway to improve patient safety in hospitals 
through the reduction of preventable harm events, and progress has been made in several areas. 
However, more work needs to be done to protect patients from these events. While OIGs review 
did not look at care provided to patients during the current COVID-19 public health emergency 
(COVID-19 PHE), CMS agrees with OIG that addressing patient harm and promoting patient 
safety takes on added urgency in light of the ongoing pandemic and its effects on hospital 
operations. In addition to its sustained efforts to improve overall quality of care in hospitals, 
CMS has remained vigilant in assessing the health care needs of the American population and 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 90   
health care providers during the COVID-19 PHE and continues to evaluate flexibilities and their 
effect on patient safety in health care settings. 
 
Health care professionals, such as physicians, nurses, pharmacists, and other allied health 
professionals qualified in the clinical practice of medicine, work together with hospitals to care 
for patients to ensure the quality and value of clinical care. Medicare patients are often frail and 
living with multiple complex clinical conditions. Unfortunately, not every adverse or temporary 
harm event is preventable. As OIG noted in the report, their reviewers determined that 56 percent 
of harm events studied were not preventable and occurred even though providers followed 
proper preparation and procedures. OIG noted that events were determined not preventable for 
several reasons, including that the Medicare patients were found to be highly susceptible to the 
event due to poor health status. However, CMS appreciates OIGs distinction in their reporting to 
provide more insight into whether an event is preventable. 
 
It is important to note the limitations of the report. As OIG explains, the preventability of certain 
adverse events may be overstated based on the retrospective nature of medical review. In 
addition, the prevalence of comorbidities is rising in the Medicare population, and Medicare 
patients are being treated for more clinically complex conditions and diagnoses than in the past. 
Comorbidities put patients at a higher risk for the occurrence of adverse events and often factor 
into the preventability of an event. OIG noted that CMS data showed that Medicare patients 
tended to have more chronic diseases in 2018 than in 2008 with higher rates of comorbidities for 
15 of the 21 conditions tracked by CMS. This is an important distinction when comparing OIGs 
prior adverse event review and this current review. As these reports selected patients using a 
simple random sampling without adjustment, changes in the Medicare population do not appear 
to have been accounted for, which can impair efforts to make a meaningful comparison to their 
previous work or identify the effects of improvements in patient safety. 
 
While CMS and Agency for Healthcare Research and Quality (AHRQ) data have shown 
improvements in patient safety in hospitals, we also know that improvements in detection and 
surveillance of adverse events have occurred during this time period. Due to increased detection, 
it is expected that the number of these events will increase before subsequently decreasing due to 
better care management. 
 
Overall, due to sustained efforts by health care professionals and hospitals, the data demonstrates 
significant improvements in patient safety have occurred over the past decade. Data released by 
AHRQ showed national efforts to reduce hospital-acquired conditions (HACs), such as adverse 
drug events and injuries from falls, helped prevent an estimated 20,700 deaths and generated 
$7.7 billion in Medicare cost savings in 2015-2017 compared to what would have been expected 
based on HACs in 2014. Based on the HAC reductions seen in 2015, 2016, and 2017, compared 
with 2014, AHRQ estimates a total of 910,000 fewer HACs occurred between 2015 and 2017. 
This is an overall rate reduction of HACs of 13 percent from 2014 to 2017. These gains in safety 
among hospital patients echoed earlier successes, including 2.1 million HACs avoided between 
2010 and 2014. HACs overall dropped 17 percent from 2010 to 2014, saving an estimated $19.9 
billion in health care costs and preventing an estimated 87,000 deaths.1 
 
 
1 AHRQ, AHRQ National Scorecard on Hospital-Acquired Conditions Final Results for 2014 Through 2017, 
https://www.ahrq.gov/sites/default/files/wysiwyg/professionals/quality-patient-safety/pfp/Updated-hacreportFInal2017data.pdf  
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 91   
For the AHRQ data described above, depending on the year, the sample size varied from 
approximately 18,000 to 28,000 patient charts reflecting care delivered in approximately 800 to 
1,600 hospitals. The OIGs sample size for this report was 770 Medicare patients from 629 
hospitals, which represents 0.07 percent of Medicare patients who were discharged from short-
term acute-care hospitals during October 2018. Given this small sample size and high variability 
in adverse events across patients and hospitals, the extrapolation of the OIGs findings to a 
national population may have limited reliability. Further, as the OIG notes, this sample size was 
insufficient to effectively compare the results within their current report to the harm rates 
identified in their 2010 report, which looked at 2008 data. 
 
In its continuing efforts to improve the measurement and reporting of adverse events and to 
address prevention of the underlying causes, CMS uses a number of policy levers to achieve 
quality of care goals, including the reduction of preventable adverse and temporary harm events, 
as outlined in the CMS Quality Strategy.2 First, CMS sets standards for providers that support 
patient safety and quality improvement, known as the Conditions of Participation (CoPs), and 
surveys providers against these standards. CMS provides guidance to state survey agencies and 
accreditation organizations for conducting hospital surveys to verify compliance with the CoPs. 
While many of the CoPs have an impact on patient safety and quality, the Quality Assessment 
and Performance Improvement (QAPI) CoP focuses specifically on standards for facilities to 
improve quality and safety. As part of this CoP, hospitals must track adverse patient events, 
analyze their causes, and implement preventive actions and mechanisms that include feedback 
and learning through the hospital. 
 
Second, as required by law, CMS also administers a number of quality reporting and value-based 
purchasing programs, which measure a hospitals quality of care, including hospital-associated 
infections (HAIs) and other adverse events. CMS provides payment incentives based on those 
measures, publicly reports performance measures, and includes many of the measures in Hospital 
Star Ratings. CMS collects quality data from hospitals paid under the Inpatient Prospective 
Payment System, with the goal of driving quality improvement through measurement, payment 
incentives, and transparency by publicly displaying data on the Care Compare website to help 
consumers make more informed decisions about their health care. 
 
The Hospital Inpatient Quality Reporting (IQR) program requires hospitals to report specified 
quality measures, and hospitals that do not satisfactorily report the measures are subject to a 
payment reduction equal to one-quarter of the hospital update.3 In addition, selected patient 
safety measures are used for hospital programs that make payments based on the quality and 
efficiency of care, including the Hospital Value-Based Purchasing (VBP) Program, the Hospital-
Acquired Condition Reduction Program (HACRP), and Hospital Readmissions Reduction 
Program. These programs include measures that address avoidable adverse events, such as HAI 
measures (central line-associated bloodstream infections, catheter associated urinary tract 
infections, surgical site infection from colon surgery or abdominal hysterectomy, methicillin-
resistant Staphylococcus Aureus blood laboratory-identified events, Clostridium difficile 
laboratory-identified events) and a measure on the death rate among surgical inpatients with 
serious treatable complications. These measures are also publicly reported on the Care Compare 
 
 CMS, CMS Quality Strategy, 2016, 
2   
 Section 1886(b)(3)(B)(viii) of the Achtt tps://www.ahrq.gov/sites/default/files/wysiwyg/workingforquality/2016-cms-agency-
specific-plan.pdf
3
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 92   
website and contribute to Hospital Star Ratings.4 Data from the HAI measures listed above are 
used in both the Hospital VBP Program and HACRP. 
 
CMS is statutorily limited in the payment adjustments that can be made under the quality 
reporting and value-based purchasing programs. As noted above, the reduction for failing to 
report to the Hospital IQR program is one-quarter of the hospital update. The Hospital VBP 
program reduces hospital payments by two percent in order to create a funding pool that is 
redistributed to hospitals based on a Total Performance Score.5 The HACRP reduces hospital 
payments by one percent for those hospitals that fall in the bottom quartile based on their 
performance on HAC measures.6 
 
CMS is constantly working to ensure that CMS programs have sufficient measures to identify 
and report on adverse and temporary harm events and through the Meaningful Measures 
initiative, CMS has ensured that patient safety is a prominent theme in the measure areas. CMS 
regularly evaluates whether new measures should be added to its quality reporting and value-
based purchasing programs. This process occurs yearly and starts with CMS soliciting new 
measures and noting priority areas for the agency. CMS highlighted patient safety as a CMS 
quality measurement priority in the triennial 2021 National Impact Assessment of CMS Quality 
Measures Report,7 in which CMS identified and analyzed patient safety measure performance 
trends. During the pre-rulemaking process, CMS releases the Measures Under Consideration list 
no later than December 1st, and multi-stakeholder groups provide recommendations on the list 
no later than February 1st. The pre-rulemaking process provides CMS with a vehicle to hear 
from stakeholders for early consideration of measures. CMS then considers any feedback on the 
new measures and selects measures to propose in the Federal Register, allowing comment before 
a final rule is issued. For example, CMS finalized two new medication-related adverse event 
electronic clinical quality measures (eCQMs) for reporting glycemic management, which were 
recommended in the pre-rulemaking process, into the Hospital IQR Program beginning with the 
calendar year 2023 reporting period.8 For the 2021 measure development cycle, CMS noted 
areas of need and priorities for measures addressing causes of hospital harm and adverse drug 
events, among other areas.9 The current list of Measures Under Consideration includes new and 
updated measures on healthcare-associated clostridioides difficile infection outcomes, hospital-
onset bacteremia and fungemia outcomes, opioid-related adverse events, and severe obstetric 
complications.10 
 
 
 CMS, Hospital Compare Overall Ratings Data Collection Periods, April 2021, 
4   
 Section 1886(o)(7)(C)(v) of the Act  https://qualitynet.cms.gov/inpatient/public-
r5 eSpeocrtitoinng 1/8o8v6e(rpa)l(l1-r) aotfi nthges /Adcatt a-collection
6 CMS, 2021 National Impact Assessment of the Centers for Medicare & Medicaid Services (CMS) Quality Measures Report, June 2021, 
7 .  
 CMS, Medicare Program; Hospital Inpatient Prospective Payment Systems for Acute Care Hospitals and the Long-Term Care Hospital 
hP8trotpsps:e/c/tiwvew Pwa.ycmmesn.gto Svy/sftielems /adnodc Puomliecny tC/2h0an2g1e-sn aantido nFaislc-iaml Ypaecatr- 2a0ss2e2s Rsmateens;t -Qreupaloitryt .pPdrofgrams and Medicare Promoting Interoperability 
Program Requirements for Eligible Hospitals and Critical Access Hospitals; Changes to Medicaid Provider Enrollment; and Changes to the 
Medicare Shared Savings Program, (86 FR 44774), August 13, 2021. 
 CMS, Program-Specific Measure Needs and Priorities 2021 Measures Under Consideration List, March, 24, 2021, 
9 .  
 CMS, List of Measures Under Consideration for December 1, 2021, 
h10ttps://www.cms.gov/files/docum. e nt/2021-muc-list-program-specific-measure-needs-and-priorities.pdf
https://www.cms.gov/files/document/measures-under-
consideration-list-2021-report.pdf
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 93   
Finally, CMS had success focusing the attention of health care professionals and hospitals 
through the Partnership for Patients (PfP) initiative which was a public-private partnership 
working to improve the quality, safety and affordability of health care for Medicare, Medicaid 
and CHIP beneficiaries, and by extension, all Americans. Subsequently, in 2016, CMS awarded 
16 national, regional, or state hospital associations and health system organizations to serve as 
Hospital Improvement Innovation Networks. These awards integrated the PfP networks into the 
Quality Improvement Organization (QIO) program, one of the largest federal programs dedicated 
to improving health quality for Medicare beneficiaries and an integral part of CMSs Quality 
Strategy. This integration maximized the strengths of the QIO program and the PfP to sustain 
and expand national reductions in patient harm and 30-day readmissions for the Medicare 
program.11 With the current QIO contract cycle, launched in 2019, the QIO program again 
refocused hospital patient safety efforts as the Hospital Quality Improvement Contractor 
program to further increase these efforts. An essential element of this work is a commitment to 
improving health equity, and organizations will give specific attention to identifying and 
reducing health care disparities. This program continues to engage the hospital, provider and 
broader caregiver communities to quickly implement well-tested and measured best practices to 
improve patient safety and the quality of care in the Medicare program. 
 
In summary, while sustained efforts are underway to improve patient safety in hospitals and 
progress has been made in several areas over the last decade, more work needs to be done to 
protect patients from these events. In addition to CMSs efforts, CMS looks forward to continued 
focus on this area from health professionals, hospitals, and the OIG. 
 
The OIGs recommendations and CMSs responses are below. 
 
OIG Recommendation 
Update and broaden its hospital-acquired conditions lists to capture common, preventable, and 
high-cost harm events. 
 
CMS Response 
CMS concurs with this recommendation. As noted above, several hospital programs to promote 
quality and safety have been created in the past decade. 
 
Under the Deficit Reduction Act Hospital Acquired Conditions (DRA HAC) program, the 
hospital-acquired conditions (HAC) list is reviewed to determine if any of the newly created 
diagnosis or procedure codes should be added to the existing HAC categories. Under the DRA 
HAC provision, Medicare no longer assigns an inpatient hospital discharge to a higher paying 
Medicare Severity-Diagnosis Related Group (MS-DRG) if a selected HAC was not present on 
admission. That is, the case will be paid as though the secondary diagnosis was not present. Any 
additional updates, such as consideration for a new candidate condition to the current list of HAC 
categories, would require notice and comment rulemaking. Separately, CMS considers updates to 
the HAC list through the annual pre-rulemaking measure selection process and through 
subsequent rulemaking related to the HAC Reporting Program (HACRP) set out at section 
1886(p) of the Act. 
 
 CMS, Partnership for Patients and the Hospital Improvement Innovation Networks: 
11
CMSC,o ntinuing Forward Momentum on Reducing Patient Harm , September 29, 2016, https://www.cms.gov/newsroom/fact-
sheets/partnership-patients-and-hospital-improvement-innovation-networks-continuing-forward-momentum.  
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 94   
 
The HACRP was implemented in fiscal year (FY) 2015 and includes several patient safety 
measures. CMS finalized two new medication-related adverse event electronic clinical quality 
measures for reporting glycemic management into the Hospital Inpatient Quality Reporting 
Program (IQR) beginning with the calendar year 2023 reporting period.12 For the 2021 measure 
development cycle, CMS noted areas of need and priorities for measures addressing causes of 
hospital harm and adverse drug events, among other areas.13 The current list of Measures Under 
Consideration includes new and updated measures on healthcare-associated clostridioides 
difficile infection outcomes, hospital-onset bacteremia and fungemia outcomes, opioid-related 
adverse events, and severe obstetric complications for several of CMSs payment programs, 
including the HACRP and the Hospital IQR Program.14 CMS is in the process of evaluating 
additional digital safety measures while identifying ways to more closely align to Centers for 
Disease Control and Prevention and Agency for Healthcare Research and Quality safety metrics 
for consideration of future adoption into one or more quality reporting programs.  
 
CMS must follow statutory requirements for programs when considering updates to its measure 
lists. Even as the list of HAC measures continues to expand, CMS is statutorily limited in the 
payment adjustments that can be made under its pay-for-reporting and value-based purchasing 
programs. For example, the HACRP is limited to a one percent payment reduction for those 
hospitals in the worst-performing quartile, and the Hospital Value-Based Purchasing program 
can reduce hospital payments by a maximum of two percent in response to poor performance or 
increase payments for good performance. Some measures, such as those regarding hospital-
associated infections, are included in both programs and can therefore have a greater payment 
impact. However, the structure of the HACRP is such that only the worst 25 percent of 
performers receive the one percent reduction each year. Hospitals that routinely are in the top 
three quarters of performance do not have a financial incentive through the HACRP to improve 
more. 
 
OIG Recommendation 
Explore expanding the use of patient safety metrics in pilots and demonstrations for health care 
payment and service delivery as appropriate. 
 
CMS Response 
CMS concurs with this recommendation. The CMS Center for Medicare and Medicaid 
Innovation (CMS Innovation Center) tests innovative service and delivery models to reduce 
program expenditures and improve quality for Medicare and Medicaid beneficiaries. While all 
models are intended to maintain or enhance patient safety, two models currently being tested 
specifically address hospital patient safety, the Bundled Payments for Care Improvement 
Advanced (BPCI Advanced) model and the Maryland Total Cost of Care model. The BPCI 
 
 CMS, Medicare Program; Hospital Inpatient Prospective Payment Systems for Acute Care Hospitals and the Long-Term Care Hospital 
1P2rospective Payment System and Policy Changes and Fiscal Year 2022 Rates; Quality Programs and Medicare Promoting Interoperability 
Program Requirements for Eligible Hospitals and Critical Access Hospitals; Changes to Medicaid Provider Enrollment; and Changes to the 
Medicare Shared Savings Program, (86 FR 45382), August 2, 2021 
 CMS, Program-Specific Measure Needs and Priorities 2021 Measures Under Consideration List, March, 24, 2021, 
13   
 CMS, List of Measures Under Consideration for December 1, 2021, 
1h4ttps://www.cms.gov/files/docum  ent/2021-muc-list-program-specific-measure-needs-and-priorities.pdf
https://www.cms.gov/files/document/measures-under-
consideration-list-2021-report.pdf
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 95   
Advanced model15 tests payment for clinical episodes for Medicare beneficiaries while using 
some of the same patient safety measures that are in CMSs statutorily mandated inpatient 
programs. Similarly, the Maryland Total Cost of Care model16 includes similar patient safety 
measures as those in CMSs inpatient programs to further incentivize quality improvement and 
reduce patient safety events in support of its aim to reduce total cost of care. CMS will continue 
to consider new opportunities to include patient safety metrics in pilots, demonstrations, and 
models for health care payment and service delivery. 
 
OIG Recommendation 
As OIG previously recommended, develop and release interpretive guidance to surveyors for 
assessing hospital compliance with requirements to track and monitor patient harm events. 
 
CMS Response 
CMS continues to concur with this recommendation. CMS requires that providers have internal 
quality assessment and performance improvement (QAPI) programs in place and that such 
programs include the practiced capability to track adverse patient events, analyze their causes, 
and implement preventive actions and mechanisms. While CMS is considering how best to 
update the State Operations Manual with interpretive guidance for surveyors to ensure 
consistency when assessing QAPI systems, surveyors already assess hospital compliance with 
these requirements as laid out in the hospital Conditions of Participation (CoPs). For example, 
surveyors cited hospitals for non-compliance with QAPI, generally, 465 times in fiscal year (FY) 
2019 (the last year prior to the COVID-19 PHE where comparable data exists). Specific to the 
requirement to track and monitor patient harm events, hospitals were cited 103 times in FY 2019 
for failure to comply. In FY 2019, QAPI and the patient safety tracking and monitoring 
requirement were the 15th and 16th top cited deficiencies for hospitals out of 405 total 
deficiency tags. Of note, roughly 80 percent of hospitals are deemed and surveyed by accrediting 
organizations that are required to effectively evaluate a facility using accreditation standards 
which meet or exceed the CoPs. CMS intends to continue to hold hospitals accountable for their 
compliance with the CoPs while updating guidance to surveyors. 
   
 
 CMS, BPCI Advanced,    
15 CMS, Maryland Total Cost of Care Model,    
https://innovation.cms.gov/innovation-models/bpci-advanced
16
https://innovation.cms.gov/innovation-models/md-tccm
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 96   
Agency Comments: Agency for Healthcare Research and Quality 
 
To:   Christi A. Grimm    
   Principal Deputy Performing Duties of the Inspector General 
Department of Health and Human Services   
   
From:   David Meyers, M.D.    DSM 
Deputy Director, Agency for Healthcare Research and Quality  
 
Date:  March 18, 2022 
 
Subject:   OIG Draft Report: Adverse Events in Hospitals: A Quarter of Medicare Patients 
Experienced Harm in October 2018, OEI-06-18-00400 
 
Thank you for the opportunity to review the draft report entitled Adverse Events in Hospitals: A 
Quarter of Medicare Patients Experienced Harm in October 2018, OEI-06-18-00400, and for 
you and the OIG teams ongoing dedication and support for improving patient safety and 
healthcare quality.   
 
AHRQ provides the following specific responses to each of the OIGs recommendations: 
 
1.  Recommendation #1: With support from HHS leadership, reassess patient safety efforts 
across the Department by ensuring that agencies update quality strategic plans, identify 
weaknesses, and address gaps in these efforts. 
 
  AHRQ concurs with this recommendation.  
 
AHRQ appreciates the focus the report gives to the Agencys role in promoting patient 
safety and reducing patient harms. AHRQs mission is to produce evidence to make 
health care safer, higher quality, more accessible, equitable, and affordable, and to work 
within the U.S. Department of Health and Human Services and with other partners to 
make sure that the evidence is understood and used.  The Agency, within its current 
capacity, supports HHS efforts to coordinate patient safety activities across the 
Department and works collaboratively with other agencies to achieve the Departments 
goals and objectives.  With specific direction and engagement by the HHS Secretary, 
AHRQ stands ready to begin implementation of this recommendation in a manner 
determined to be feasible by HHS.  One clear prerequisite would be an assessment of the 
additional resources and infrastructure development required for AHRQ to become 
sufficiently resourced to assess patient safety efforts across the Department and ensure 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 97   
that all HHS agencies, including the Centers for Medicare and Medicaid Services and the 
Centers for Disease Control, update and implement their quality strategic plans.  
 
2.  Recommendation #2: Optimize use of QSRS, including assessing the feasibility of 
automated data capture for national measurement and to facilitate local use.  
 
AHRQ concurs with this recommendation.   
 
Regarding QSRS use for national measurement, AHRQ will continue to implement 
QSRS to measure a national rate of hospital-acquired adverse events among hospital 
patients covered by Medicare and to create a baseline to assess the impact of national 
patient safety initiatives.  AHRQ will assess the feasibility of incorporating automatic 
data capture into the system and will review the event types identified in OIGs report for 
potential inclusion into the system.  AHRQ will also continue to share data from QSRS, 
as it is available, with CMS in accordance with AHRQs Memorandum of Understanding 
with CMS and will consider ways to share data with other agencies, such as CDC, as 
appropriate.  Additionally, AHRQ will continue to explore the best application of the 
QSRS measures (i.e., the event descriptions and algorithms) and underlying Common 
Formats for Surveillance at the local level.   
 
3.   Recommendation #3: Develop an effective model to disseminate information on national 
clinical practice guidelines or best practices to improve patient safety 
AHRQ concurs with this recommendation.  
 
AHRQ appreciates that OIG is highlighting the critical importance of using evidence-
based strategies to improve patient safety.  AHRQ currently employs a number of 
approaches to disseminating evidence-based patient safety improvement resources that 
are readily discoverable, accessible, and usable.  These approaches are continually 
evolving as new patient safety issues, new evidence, and new strategies emerge.  AHRQ 
concurs with the recommendation to develop new approaches to disseminating 
information about evidence-based patient safety practices.  For example, AHRQ will 
explore working with the National Steering Committee for Patient Safety, and other 
similar groups, to achieve this shared objective.  The approach will be developed in 
concert with recognized patient safety principles, such as those set forth in Safer 
Together: A National Action Plan to Advance Patient Safety. [National Steering 
Committee for Patient Safety. Safer Together: A National Action Plan to Advance Patient 
Safety.  Boston, Massachusetts: Institute for Healthcare Improvement. 
(http://www.ihi.org/SafetyActionPlan).] 
 
4.   Recommendation #4: Continue efforts to identify and develop new strategies to prevent 
common patient harm events in hospitals 
 
AHRQ concurs with this recommendation.  
 
AHRQ will continue to invest in new research, tools, and projects consistent with its 
mission to produce evidence to make health care safer, higher quality, more accessible, 
equitable, and affordable, and to work within HHS and with other partners to make sure 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 98   
that the evidence is understood and used. In determining its research and program 
priorities, AHRQ will consider this OIG evaluation along with the continually evolving 
evidence base, statutory requirements, national priorities, Departmental goals, and input 
from a variety of other sources, including the National Advisory Council for Healthcare 
Research and Quality. 
 
Although the Agencys mission to improve patient safety and quality spans all health care 
settings and patient populations, the following are examples of AHRQ portfolios and 
projects that can inform and/or be deployed in improvement work to address adverse 
events that occur in acute care hospitals: 
 
  Diagnostic Safety: Diagnostic safety improvement is a critical patient safety issue 
that is relevant to preventing patient harm in all settings.  AHRQ is supporting 
diagnostic safety research, has developed several tools and resources to support 
diagnostic safety improvement efforts, and has others under development. For 
example, in March 2022, AHRQ plans to release a new TeamSTEPPS module for 
Diagnosis Improvement, which aims to raise diagnostic safety awareness and 
provide assessment and training tools to support local efforts to improve 
communication among all members of the care team, including non-clinicians and 
patients and their families.  AHRQ also plans to release a new Common Formats for 
Event Reporting-Diagnostic Safety in 2022.  
 
  Patient Safety Learning Laboratories: AHRQ-funded Patient Safety Learning 
Laboratories conduct research that facilitates collaboration between the health care 
disciplines and those such as architecture, design, and engineering to develop new 
and innovative patient safety approaches.  The Patient Safety Learning Laboratories 
demonstrate AHRQs focus on remaining abreast of advances in safety science and 
encouraging evidence development that can inform more effective patient safety 
improvement efforts.  Such transdisciplinary approaches show promise in 
generating innovative strategies that have the potential to alter the status quo and 
shape a safer future rather than simply layering new toolkits on top of existing 
systems that may require foundational change.  
 
  AHRQ Safety Program for Improving Surgical Care and Recovery (ISCR): 
AHRQ contracted with the Johns Hopkins University Armstrong Institute for 
Patient Safety and Quality and its partners, including the American College of 
Surgeons, the University of California San Francisco, Westat, and the Johns 
Hopkins Applied Physics Lab to conduct and evaluate the ISCR.  The project 
focuses on helping hospitals implement evidence-based enhanced recovery 
pathways that include preoperative, intraoperative, and postoperative practices that 
can decrease complications and accelerate recovery.  In order to facilitate broader 
adoption of these evidence-based practices among U.S. hospitals, this AHRQ 
project uses the Comprehensive Unit-based Safety Program approach known as 
CUSP, a combination of clinical and cultural (i.e., technical and adaptive) 
intervention components.  Adaptive elements include promoting leadership and 
frontline staff engagement; improvement in safety culture; close teamwork among 
surgeons, anesthesia providers, and nurses; and enhancing patient communication 
and engagement.  Tools and resources used, and lessons learned by the hospitals 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 99   
participating in this project, will be compiled into a toolkit that AHRQ will make 
publicly available.  The final report and toolkit are expected to be available some 
time in 2023. 
 
 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Appendix I | 100   
ACKNOWLEDGMENTS AND CONTACT 
 
Acknowledgments 
Jennifer Gist and Jesse Valente served as the team leaders for this study, and 
Demetrius Martinez served as the lead analyst.  Office of Evaluation and Inspections 
staff who provided support include Joe Chiarenzelli, Althea Hosein, and 
Christine Moritz.   
This report was prepared under the direction of Ruth Ann Dorrill, Regional Inspector 
General for Evaluation and Inspections in the Dallas regional office, and Amy Ashcraft, 
Deputy Regional Inspector General. 
Contact 
To obtain additional information concerning this report, contact the Office of Public 
Affairs at Public.Affairs@oig.hhs.gov.  OIG reports and other information can be found 
on the OIG website at oig.hhs.gov. 
Office of Inspector General 
U.S. Department of Health and Human Services 
330 Independence Avenue, SW 
Washington, DC 20201 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Acknowledgments and Contact | 101   
 
ABOUT THE OFFICE OF INSPECTOR GENERAL 
 
 
The mission of the Office of Inspector General (OIG), as mandated by Public Law 
95-452, as amended, is to protect the integrity of the Department of Health and 
Human Services (HHS) programs, as well as the health and welfare of beneficiaries 
served by those programs.  This statutory mission is carried out through a nationwide 
network of audits, investigations, and inspections conducted by the following 
operating components: 
The Office of Audit Services (OAS) provides auditing services for HHS, 
either by conducting audits with its own audit resources or by overseeing audit work 
done by others.  Audits examine the performance of HHS programs and/or its 
grantees and contractors in carrying out their respective responsibilities and are 
intended to provide independent assessments of HHS programs and operations.  
These audits help reduce waste, abuse, and mismanagement and promote economy 
and efficiency throughout HHS. 
The Office of Evaluation and Inspections (OEI) conducts national 
evaluations to provide HHS, Congress, and the public with timely, useful, and reliable 
information on significant issues.  These evaluations focus on preventing fraud, waste, 
or abuse and promoting economy, efficiency, and effectiveness of departmental 
programs.  To promote impact, OEI reports also present practical recommendations 
for improving program operations. 
The Office of Investigations (OI) conducts criminal, civil, and administrative 
investigations of fraud and misconduct related to HHS programs, operations, and 
beneficiaries.  With investigators working in all 50 States and the District of Columbia, 
OI utilizes its resources by actively coordinating with the Department of Justice and 
other Federal, State, and local law enforcement authorities.  The investigative efforts 
of OI often lead to criminal convictions, administrative sanctions, and/or civil 
monetary penalties. 
The Office of Counsel to the Inspector General (OCIG) provides 
general legal services to OIG, rendering advice and opinions on HHS programs and 
operations and providing all legal support for OIGs internal operations.  OCIG 
represents OIG in all civil and administrative fraud and abuse cases involving HHS 
programs, including False Claims Act, program exclusion, and civil monetary penalty 
cases.  In connection with these cases, OCIG also negotiates and monitors corporate 
integrity agreements.  OCIG renders advisory opinions, issues compliance program 
guidance, publishes fraud alerts, and provides other guidance to the health care 
industry concerning the anti-kickback statute and other OIG enforcement authorities.
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  About OIG | 102   
ENDNOTES   
 
 
1 Griffin, F.A., and Resar, R.K., IHI Global Trigger Tool for Measuring Adverse Events (Second Edition), Institute for Healthcare 
Improvement (IHI) Innovation Series, 2009, p. 5.  
2 CMS, AHRQ Common FormatsInformation for Hospitals and State Survey Agencies (SAs)Comprehensive Patient Safety 
Reporting Using AHRQ Common Formats, S&C: 13-19-Hospitals, March 2013. 
3 Kohn et al., To Err Is Human: Building a Safer Health System, A Report of the Committee on Quality of Health Care in America, 
Institute of Medicine, National Academy Press, 2000. 
4 Kohn et al., To Err Is Human: Building a Safer Health System, A Report of the Committee on Quality of Health Care in America, 
Institute of Medicine, National Academy Press, 2000. 
5 Brennan et al., Incidence of Adverse Events and Negligence in Hospitalized Patients Results of the Harvard Medical Practice 
Study I, The New England Journal of Medicine, Vol. 324, No. 6, February 1991. 
6 Thomas et al., Incidence and Types of Adverse Events and Negligent Care in Utah and Colorado, Medical Care, Vol. 38, 
Issue 3, 2000. 
7 OIG released 17 reports on adverse events from 20082020, including reports about the incidence of adverse events, 
methods for identifying adverse events, State reporting systems, and public disclosure of event information.  All reports are 
available at https://oig.hhs.gov. 
8 Tax Relief and Health Care Act of 2006, P.L. No. 109-432  203.   
9 OIG, Adverse Events in Hospitals: Case Study of Incidence Among Medicare Beneficiaries in Two Counties, OEI-06-08-00220, 
December 2008. 
10 OIG, Adverse Events in Hospitals: National Incidence Among Medicare Beneficiaries, OEI-06-09-00090, November 2010. 
11 OIG, Adverse Events in Hospitals: National Incidence Among Medicare Beneficiaries, OEI-06-09-00090, November 2010 p. 27. 
12 OIG, Adverse Events in Hospitals: National Incidence Among Medicare Beneficiaries, OEI-06-09-00090, November 2010, pp. 19 
and 46. 
13 OIG, Hospital Incident Reporting Systems Do Not Capture Most Patient Harm, OEI-06-09-00091, January 2012. 
14 OIG, Adverse Events in Skilled Nursing Facilities: National Incidence Among Medicare Beneficiaries, OEI-06-11-00370, 
February 2014. 
15 OIG, Adverse Events in Rehabilitation Hospitals: National Incidence Among Medicare Beneficiaries, OEI-06-14-00110, July 2016. 
16 OIG, Adverse Events in Long-Term-Care Hospitals: National Incidence Among Medicare Beneficiaries, OEI-06-14-00530, 
November 2018. 
17 OIG, Adverse Events in Hospitals: Methods for Identifying Events, OEI-06-08-00221, March 2010. 
18 AHRQ, Measurement of Patient Safety, September 2019.  Accessed at https://psnet.ahrq.gov/primer/measurement-patient-
safety on March 2, 2022. 
19 Some researchers also consider medical record review to be an imperfect gold standard, see Shojania et al., Identifying 
Adverse Events: Reflections on an Imperfect Gold Standard After 20 Years of Patient Safety Research, BMJ Quality & Safety, 
2020, 29:265-270. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 103   
 
20 OIG, Adverse Events in Hospitals: National Incidence Among Medicare Beneficiaries, OEI-06-09-00090, November 2010. 
21 Landrigan et al., Temporal Trends in Rates of Patient Harm Resulting from Medical Care, The New England Journal of 
Medicine, Vol. 363, No. 22, November 2010. 
22 Classen et al., Global Trigger Tool Shows That Adverse Events In Hospitals May Be Ten Times Greater Than Previously 
Measured, Health Affairs, Vol. 30, No. 4, April 2011. 
23 Kirkendall et al., Measuring Adverse Events and Levels of Harm in Pediatric Inpatients With the Global Trigger Tool, 
Pediatrics, Vol. 130, Issue 5, November 2012. 
24 Kennerly et al., Characterization of Adverse Events Detected in a Large Health Care Delivery System Using an Enhanced 
Global Trigger Tool over a Five-Year Interval, Health Services Research, Vol. 49, No. 5, October 2014. 
25 Adler et al., Impact of Inpatient Harms on Hospital Finances and Patient Clinical Outcomes, Journal of Patient Safety, Vol. 
14, No. 2, June 2018. 
26 Griffey et al., Multicenter Test of an Emergency Department Trigger Tool for Detecting Adverse Events, Journal of Patient 
Safety, published before print on July 2018. 
27 Stockwell et al., Adverse Events in Hospitalized Pediatric Patients, Pediatrics, Vol. 142, Issue 2, August 2018. 
28 NQF, Serious Reportable Events, 2019.  Accessed at 
http://www.qualityforum.org/Topics/SREs/Serious_Reportable_Events.aspx on March 12, 2019. 
29 OIG, Adverse Events in Hospitals: State Reporting Systems, OEI-06-07-00471, December 2008.  For quality improvement 
organizations use of the list of serious reportable events, see FY 2012 Final IPPS Rule, 76 Fed. Reg. 51476, pp. 51648-51649 
(Aug. 18, 2011). 
30 NCC MERP (the National Coordinating Council for Medication Error Reporting and Prevention), Index for Categorizing 
Medication Errors, 2001.  Accessed at http://www.nccmerp.org/sites/default/files/indexColor2001-06-12.pdf on April 27, 2021. 
31 Griffin, F.A., and Resar, R.K., IHI Global Trigger Tool for Measuring Adverse Events (Second Edition), IHI Innovation Series, 2009, 
p. 5.   
32 OIG has used this index each of its adverse event incidence rate studies, beginning in 2008.  See OIG, Adverse Events in 
Hospitals: Case Study of Incidence Among Medicare Beneficiaries in Two Counties, loc. cit. 
33 ACA, P.L. No. 111148  3011, which added section 399HH to the Public Health Service Act (PHSA). 
34 AHRQ, About the National Quality Strategy, last modified in March 2017.  Accessed at 
https://www.ahrq.gov/workingforquality/about/index.html on February 12, 2019. 
35 AHRQ, About the National Quality Strategy, last modified in March 2017.  Accessed at 
https://www.ahrq.gov/workingforquality/about/index.html on February 12, 2019. 
36 PHSA  399HH(c). 
37 The Office of Disease Prevention and Health Promotion (ODPHP), National Action Plan to Prevent Health Care-Associated 
Infections: Road Map to Elimination, 2013.  Accessed at https://health.gov/our-work/health-care-quality/health-care-
associated-infections/national-hai-action-plan on August 19, 2020. 
38 ODPHP, National Action Plan for Adverse Drug Event Prevention, 2014.  Accessed at 
https://health.gov/sites/default/files/2019-09/ADE-Action-Plan-508c.pdf on August 19, 2020. 
39 ODPHP, Healthy People 2030 Building a healthier future for all.  Accessed at https://health.gov/healthypeople on 
August 19, 2020. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 104   
 
40 ODPHP, National Action Plan for Adverse Drug Event Prevention, 2014, pp. 1-2.  Accessed at 
https://health.gov/sites/default/files/2019-09/ADE-Action-Plan-508c.pdf on August 19, 2020. 
41 ODPHP, National Action Plan to Prevent Health Care-Associated Infections: Road Map to Elimination, National HAI Targets & 
Metrics, Table 1: 2020 National Acute Care Hospital HAI Metrics. 
42 CDC, National Healthcare Safety Network (NHSN).  Accessed at https://www.cdc.gov/nhsn/about-nhsn/index.html on 
February 8, 2019.   
43 AHRQ, Agency-Specific Quality Strategic Plans, last updated in November 2016.  Accessed at 
https://www.ahrq.gov/workingforquality/about/agency-specific-quality-strategic-plans/index.html#ahrq on May 5, 2021. 
44 Social Security Act (SSA)  1861(e) and 1905(a); 42 Fed. Reg. 13262 (Mar. 9, 1977); 66 Fed. Reg. 39450 (July 31, 2001); CMS, 
Medicare & Medicaid Milestones 1937-2015 (July 2015).  Accessed at https://www.cms.gov/About-CMS/Agency-
Information/History/Downloads/Medicare-and-Medicaid-Milestones-1937-2015.pdf on August 20, 2021. 
45 The Secretarys authority to establish the Conditions of Participation is at Social Security Act  1861(e)(9) and 1871.  The 
current Conditions are found at 42 CFR part 482.  Conditions of Participation for Critical Access Hospitals are found at 42 CFR 
 485.601 to 485.647. 
46 SSA  1864 and 1865. 
47 42 CFR  482.21. 
48 42 CFR  482.21(c)(2). 
49 42 CFR  482.21(a)(1). 
50 CMS, State Operations Manual, Appendix ASurvey Protocol, Regulations and Interpretive Guidelines for Hospitals, Rev. 
200, February 2021. 
51 CMS, Hospital-Acquired Conditions Present on Admission Indicator.  Accessed at 
https://www.cms.gov/Medicare/Medicare-Fee-for-Service-Payment/HospitalAcqCond on August 20, 2021.  CMS, 
Hospital-Acquired Condition Reduction Program.  Accessed at https://www.cms.gov/Medicare/Medicare-Fee-for-Service-
Payment/AcuteInpatientPPS/HAC-Reduction-Program on August 20, 2021. 
52 CMS, Acute Inpatient PPS.  Accessed at https://www.cms.gov/Medicare/Medicare-Fee-for-Service-
Payment/AcuteInpatientPPS on April 21, 2021. 
53 CMS, MS-DRG Classifications and Software.  Accessed at https://www.cms.gov/Medicare/Medicare-Fee-for-Service-
Payment/AcuteInpatientPPS/MS-DRG-Classifications-and-Software on August 20, 2021. 
54 CMS, CMS Program Statistics, Medicare Providers Section, 2018.  Accessed at https://www.cms.gov/research-statistics-
data-systems/cms-program-statistics/2018-medicare-providers on April 27, 2021. 
55 CMS, CMS Program Statistics, Medicare Utilization and Payment Section, 2018.  Accessed at 
https://www.cms.gov/research-statistics-data-systems/cms-program-statistics/2018-medicare-providers on April 27, 2021. 
56 CMS, CMS Office of the Actuary Releases 2018 National Health Expenditures, December 2019.  Accessed at 
https://www.cms.gov/newsroom/press-releases/cms-office-actuary-releases-2018-national-health-expenditures on January 20, 
2021. 
57 SSA,  1886(d)(4)(D); FY 2009 Final IPPS Rule, 73 Fed. Reg. 48434, 48471-48491 (Aug. 19, 2008). 
58 Deficit Reduction Act of 2005 (DRA), P.L. No. 109-171  5001(c)(1), SSA,  1886(d)(4)(D). 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 105   
 
59 SSA,  1886(d)(4)(D)(iv); CMS, Hospital-Acquired Conditions.  Accessed at https://www.cms.gov/Medicare/Medicare-Fee-
for-Service-Payment/HospitalAcqCond/Hospital-Acquired_Conditions on August 20, 2021; CMS, ICD-10 HAC List.  Accessed 
at https://www.cms.gov/Medicare/Medicare-Fee-for-Service-Payment/HospitalAcqCond/icd10_hacs on August 20, 2021. 
60 CMS, Coding, last modified in July 2020.  Accessed at https://www.cms.gov/Medicare/Medicare-Fee-for-Service-
Payment/HospitalAcqCond/Coding on September 22, 2020. 
61 Some HACs that were not POA will not result in a payment reduction.  If the claim includes another (non-HAC) secondary 
diagnosis that qualifies for the same MS-DRG, the HAC payment policy will not result in reassignment to a different MS-DRG 
and will not affect payment.  Additional information about this program can be found at CMS, Publicly Reported DRA HAC 
Measure: Frequently Asked Questions 2021.  Accessed at https://www.cms.gov/files/document/frequently-asked-questions-
publicly-reported-deficit-reduction-act-dra-hospital-acquired-condition.pdf on March 2, 2021. 
62 CMS, Hospital-Acquired Condition Reduction Program.  Accessed at https://www.cms.gov/Medicare/Medicare-Fee-for-
Service-Payment/AcuteInpatientPPS/HAC-Reduction-Program on August 20, 2021; SSA  1886(p)(1) and ACA, P.L. No. 111148, 
 3008(p). 
63 ACA  3008(a), SSA  1886(p). 
64 CMS, Hospital-Acquired Condition Reduction Program, last modified in July 2018.  Accessed at 
https://www.cms.gov/medicare/medicare-fee-for-service-payment/acuteinpatientpps/hac-reduction-program.html on 
March 21, 2019. 
65 SSA  1886(p). 
66 CMS, Program-Specific Measure Needs and Priorities, April 2019, p. 34.  Accessed at 
https://www.cms.gov/Medicare/Quality-Initiatives-Patient-Assessment-Instruments/QualityMeasures/Downloads/2019-CMS-
Measurement-Priorities-and-Needs.pdf on December 11, 2020. 
67 42 CFR  412.20 through 412.23. 
68 Medicare Payment Advisory Commission, Medicare Advantage Program Payment System, Payment Basics, October 2016. 
69 CMS, Report To Congress: Risk Adjustment In Medicare Advantage, December 2021.  Accessed at 
https://www.cms.gov/files/document/report-congress-risk-adjustment-medicare-advantage-december-2021.pdf on March 2, 
2022. 
70 Kaiser Family Foundation, A Dozen Facts About Medicare Advantage in 2020, January 2021.  Accessed at 
https://www.kff.org/947fe62/ on February 12, 2021. 
71 ACA  3021, SSA  1115A. 
72 CMS, CMMI Model Certifications, last modified in January 2021.  Accessed at https://www.cms.gov/Research-Statistics-
Data-and-Systems/Research/ActuarialStudies/CMMI-Model-
Certifications#:~:text=CMMI%20Model%20Certifications%20Section%201115A%20of%20the%20Social,test%20innovative%20
payment%20techniques%20and%20service%20delivery%20models on April 16, 2021. 
73 PHSA  901 (42 U.S. Code  299(a)); Patient Safety and Quality Improvement Act of 2005  2(a), adding sections 921 to 926 of 
the PHSA (42 U.S. Code  299b-21 to 299b-26). 
74 AHRQ, Patient Safety Organization (PSO) Program.  Accessed at https://pso.ahrq.gov/ on April 14, 2021. 
75 Patient safety work products include information collected and created during the reporting and analysis of patient safety 
events.  The Patient Safety and Quality Improvement Act of 2005 provides Federal privilege and confidentiality protections for 
such information.  See HHS, Understanding Patient Safety.  Accessed at Understanding Patient Safety Confidentiality | 
HHS.gov on October 21, 2021. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 106   
 
76 OIG, Patient Safety Organizations: Hospital Participation, Value and Challenges, OEI-01-17-00420, September 2019. 
77 AHRQ, The CUSP Method.  Accessed at https://www.ahrq.gov/hai/cusp/index.html on September 8, 2021. 
78 AHRQ, AHRQ's Healthcare-Associated Infections Program.  Accessed at https://www.ahrq.gov/hai/index.html on 
September 8, 2021. 
79 AHRQ, Strategies to Improve Patient Safety: Final Report to Congress, November 2021.  Accessed at 
https://pso.ahrq.gov/sites/default/files/wysiwyg/strategies-improve-patient-safety-final.pdf on December 14, 2021. 
80 For requirement, see the Patient Safety and Quality Improvement of 2005, P.L. No. 10941  2(a), adding section 922(j) of the 
PHSA. 
81 AHRQ, AHRQ's Making Healthcare Safer Reports: Shaping Patient Safety Efforts in the 21st Century, last modified in 
March 2020.  Accessed at https://www.ahrq.gov/research/findings/making-healthcare-safer/index.html on May 17, 2021.  
82 AHRQ, Information about the National Guideline Clearinghouse (NGC), lasted updated in September 2018.  Accessed at 
https://www.ahrq.gov/gam/updates/index.html on May 14, 2021. 
83 AHRQ, AHRQ National Scorecard on Hospital-Acquired Conditions.  Accessed at https://www.ahrq.gov/hai/pfp/index.html 
on March 7, 2022. 
84 AHRQ, 2019 National Healthcare Quality and Disparities Report, Pub. No. 20(21)-0045-EF, December 2020; AHRQ, 2019 
National Chartbook on Patient Safety, Pub. No. 21-0012, February 2021; AHRQ, Data Query.  Accessed at 
https://nhqrnet.ahrq.gov/inhqrdr/data/query on August 31, 2020. 
85 AHRQ, 2015 National Healthcare Quality and Disparities Report and 5th Anniversary Update on the National Quality Strategy, 
Pub. No. 16-0015-4-EF, April 2016.  Accessed at https://archive.ahrq.gov/research/findings/nhqrdr/nhqdr15/index.html on 
February 8, 2021. 
86 CDC, National Healthcare Safety Network (NHSN).  Accessed at https://www.cdc.gov/nhsn/about-nhsn/index.html on 
February 8, 2019.   
87 CDC, Medication Safety Program, last modified June 2018.  Accessed at 
https://www.cdc.gov/medicationsafety/campaign_initiatives.html on March 21, 2018. 
88 CDC, Healthy People 2020, page last reviewed: December 2020.  Accessed at 
https://www.cdc.gov/nchs/healthy_people/hp2020.htm on February 8, 2021. 
89 CDC, Current HAI Progress Report, last reviewed in December 2020.  Accessed at 
https://www.cdc.gov/hai/data/portal/progress-report.html on April 29, 2021; CDC, Antibiotic Resistance and Patient Safety 
Portal (AR&PSP).  Accessed at https://arpsp.cdc.gov/ on August 31, 2020. 
90 CDC, Healthcare-Associated Infections.  Accessed at https://www.cdc.gov/hai/index.html on March 7, 2022. 
91 CDC, Healthcare-Associated Infections.  Accessed at https://www.cdc.gov/hai/index.html on March 7, 2022. 
92 AHRQ, Saving Lives and Saving Money: Hospital-Acquired Conditions Update, Content last reviewed January 2018.  Accessed 
at https://www.ahrq.gov/professionals/quality-patient-safety/pfp/2014-final.html on March 25, 2019. 
93 AHRQ, AHRQ National Scorecard on Hospital-Acquired Conditions Final Results for 2014 Through 2017, p. 1.  Accessed at 
https://www.ahrq.gov/sites/default/files/wysiwyg/professionals/quality-patient-safety/pfp/Updated-
hacreportFInal2017data.pdf on August 20, 2020. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 107   
 
94 CMS, Declines in Hospital-Acquired Conditions Save 8,000 Lives and $2.9 Billion in Costs, Press release, June 2018.  
Accessed at https://www.cms.gov/newsroom/press-releases/declines-hospital-acquired-conditions-save-8000-lives-and-29-
billion-costs on December 14, 2021. 
95 CDC, 2019 National and State Healthcare-Associated Infections Progress Report, December 2019.  Accessed at 
https://www.cdc.gov/hai/data/portal/progress-report.html?ACSTrackingID=USCDC_425-
DM43858&ACSTrackingLabel=New%202019%20National%20and%20State%20Healthcare-
Associated%20Infections%20Progress%20Report%20&deliveryName=USCDC_425-DM43858 on January 5, 2021. 
96 CDC, Data Summary of HAIs in the US: Assessing Progress 20062016.  Accessed at 
https://www.cdc.gov/hai/data/archive/data-summary-assessing-progress.html on September 9, 2021. 
97 CDC, 2019 National and State Healthcare-Associated Infections Progress Report, December 2019.  Accessed at 
https://www.cdc.gov/hai/data/portal/progress-report.html?ACSTrackingID=USCDC_425-
DM43858&ACSTrackingLabel=New%202019%20National%20and%20State%20Healthcare-
Associated%20Infections%20Progress%20Report%20&deliveryName=USCDC_425-DM43858 on January 5, 2021. 
98 CDC, 2015 SIRs Using Historical Baselines.  Accessed at https://www.cdc.gov/hai/data/archive/2015-SIR-report.html on 
September 9, 2021. 
99 Bates, D.W., and Singh, H., Two Decades Since To Err Is Human: An Assessment of Progress and Emerging Priorities in 
Patient Safety, Health Affairs, Vol. 37, No. 11, November 2018. 
100 Bates, D.W., and Singh, H., Two Decades Since To Err Is Human: An Assessment of Progress and Emerging Priorities in 
Patient Safety, Health Affairs, Vol. 37, No. 11, November 2018. 
101 IHI, Safer Together: A National Action Plan to Advance Patient Safety, National Steering Committee for Patient Safety, 
September 2020.  Accessed at http://www.ihi.org/Engage/Initiatives/National-Steering-Committee-Patient-
Safety/Pages/National-Action-Plan-to-Advance-Patient-Safety.aspx on January 5, 2021. 
102 OIG, Adverse Events in Hospitals: National Incidence Among Medicare Beneficiaries, OEI-06-09-00090, November 2010, 
pp. 30-32. 
103 CMS, About the Partnership for Patients.  Accessed at https://partnershipforpatients.cms.gov/about-the-
partnership/aboutthepartnershipforpatients.html on January 29, 2019. 
104 AHRQ, National Scorecard on Rates of Hospital-Acquired Conditions 2010 to 2015: Interim Data from National Efforts to Make 
Health Care Safer, December 2016.  Accessed at https://www.ahrq.gov/professionals/quality-patient-safety/pfp/2015-
interim.html on April 22, 2019. 
105 AHRQ, AHRQ Quality and Safety Review System (QSRS).  Accessed at 
https://www.ahrq.gov/cpi/about/otherwebsites/qsrs.ahrq.gov/index.html and https://www.ahrq.gov/patient-
safety/resources/qsrs/index.html on April 20, 2021. 
106 OIG, Adverse Events in Hospitals: Methods for Identifying Events, OEI-06-08-00221, March 2010, pp. 1718. 
107 OIG, Hospital Incident Reporting Systems Do Not Capture Most Patient Harm, OEI-06-09-00091, January 2012, p. 21.  Also 
see, OIG, Adverse Events in Hospitals: Methods for Identifying Events, OEI-06-08-00221, March 2010, p. 18. 
108 In our incidence rate calculations, we include patients enrolled in Medicare managed care programs (i.e., Medicare 
Advantage plans) and in the State of Maryland who are not covered under the traditional fee-for-service payment model. 
109 Patient harm events that occurred during the initial hospital stay (index stay) and that resulted in or contributed to a 
patients 30-day readmission were attributed to the index stay.  Harm events that subsequently occurred during readmissions 
were not included in the analysis unless those events were related to the first event (i.e., part of a cascade event), thus counting 
as one event across admissions and attributable to the index stay. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 108   
 
110 In our sample, we had one patient with both an eligible and ineligible hospital admission.  We included the patient in our 
sample and attributed any harm events to the patients eligible admission. 
111 The average length of stay of 4.9 days includes the day of discharge. 
112 The TruCode Encoder classifies hospital claims into MS-DRG categories expected to have similar hospital resource 
requirements.  This software was developed by TruCode LLC.  Accessed at https://www.trucode.com/products/trucode-
encoder/ on August 13, 2019. 
113 Naessens et al., Effect of Illness Severity and Comorbidity on Patient Safety and Adverse Events, American Journal of 
Medical Quality, Vol. 27, Issue 1, October 2011. 
114 The 95-percent confidence interval for the number of patients who experienced an adverse event and temporary harm 
event spans 27,288 to 56,129, which exceeds 30-percent relative precision. 
115 The 95-percent confidence interval for the percentage of F-level events that resulted in a longer hospital stay spans 49 to 71 
percent, which exceeds 10-percent absolute precision. 
116 The 95-percent confidence interval for the number of patients who experienced an event that contributed to or resulted in 
death (I-level harm) spans 6,099 to 23,501, which exceeds 30-percent relative precision. 
117 The 95-percent confidence interval for the number of patients who experienced an adverse event and temporary harm 
event spans 27,288 to 56,129, which exceeds 30-percent relative precision. 
118 NIH, Hypoglycemia, National Diabetes Information Clearinghouse, Pub. No. 09-3926, October 2008.  Accessed at 
https://www.niddk.nih.gov/-/media/Files/Diabetes/hypoglycemia_508.pdf on April 29, 2021. 
119 CDC, Living with Diabetes, page last reviewed in April 2021.  Accessed at 
https://www.cdc.gov/diabetes/managing/manage-blood-sugar.html on July 2, 2021. 
120 See pressure injury definition in glossary for further explanation on the stages of pressure injuries. 
121 We cannot reliably project the proportion of harm events that were unable to determine. 
122 The difference between the procedure or surgery preventability rates was statistically significant at the 95-percent 
confidence level (p=<0.0001). 
123 The differences between the preventability rates for medication (p=0.1011) and patient care (p=0.6897) events were not 
statistically significant at the 95-percent confidence level.   
124 86 Fed. Reg. 44774 (August 13, 2021), see Table 6P.3a. 
125 CMS, ICD-10-CM Official Guidelines for Coding and Reporting FY 2022 (October 1, 2021September 30, 2022), effective with 
Oct. 1, 2021 discharges/visits.  Accessed at https://www.cms.gov/files/document/fy-2022-icd-10-cm-coding-guidelines.pdf on 
October 12, 2021. 
126 The patients who were harmed and incurred additional costs (23 percent) includes non-IPPS patients for which additional 
Medicare costs were calculated as a proxy measure. 
127 One reason that more events did not affect payment is that Medicare bases IPPS payment on a standardized code typically 
driven by the patients primary diagnosis and not the individual components of care.  As a result, only events that have a 
profound effect on the care provided will incur additional costs.   
128 The relative precision for the point estimate of $520 million in IPPS payments is 57 percent, indicating a high degree of 
uncertainty in the point estimate. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 109   
 
129 Other non-IPPS payment systems includes all hospitals serving Medicare patients in the State of Maryland and IPPS-
Exempt Cancer Hospitals. 
130 The relative precision for the point estimate of $281 million in non-IPPS payments is 56 percent, indicating a high degree of 
uncertainty in the point estimate.   
131 OIG, Hospitals Reported That the COVID-19 Pandemic Has Significantly Strained Health Care, OEI-09-21-00140, March 2021. 
132 See OIG, Adverse Events in Hospitals: Methods for Identifying Events, OEI-06-08-00221, March 2010. 
133 The differences between patient harm rates from 2008 and 2018 were not statistically significant at the 95-percent 
confidence level.  We conducted statistical tests for differences between the rates of adverse and temporary harm events 
combined (p=0.3722); adverse events (p=0.2926); and temporary harm events (p=0.9012).  We also tested for differences in 
severity level between the 2 years for the proportion of events that were adverse events (p=0.3466) and temporary harm 
events (p=0.3466).  Lastly, we tested for differences in rates of preventable harm events between the 2 years (p=0.7747) and 
for not preventable harm events (p=0.2606). 
134 See page 10 for a description of reported progress by HHS agencies in reducing specific types of harm events. 
135 Institute of Medicine, Best Care at Lower Cost: The Path to Continuously Learning Health Care in America, The National 
Academies Press, 2013. 
136 Naessens et al., Effect of Illness Severity and Comorbidity on Patient Safety and Adverse Events, American Journal of 
Medical Quality, Vol. 27, Issue 1, October 2011. 
137 NIH, Acute kidney injury, chronic kidney disease each a risk of the other, July 2014.  Accessed at 
https://www.nih.gov/news-events/news-releases/acute-kidney-injury-chronic-kidney-disease-each-risk-other on October 25, 
2021.   
138 NIH, Acute kidney injury, chronic kidney disease each a risk of the other, July 2014.  Accessed at 
https://www.nih.gov/news-events/news-releases/acute-kidney-injury-chronic-kidney-disease-each-risk-other on October 25, 
2021. 
139 CMS, Chronic Conditions.  Accessed at https://www.cms.gov/Research-Statistics-Data-and-Systems/Statistics-Trends-and-
Reports/Chronic-Conditions/CC_Main on January 28, 2021.   
140 Levy et al., The Surviving Sepsis Campaign Bundle: 2018 Update, Critical Care, Vol. 44, Issue 6, June 2018. 
141 Bellomo et al., Acute renal failure definition, outcome measures, animal models, fluid therapy and information technology 
needs: the Second International Consensus of the Acute Dialysis Quality Initiative (ADQI) Group, Critical Care, Volume 8, 
Issue 4, August 2004. 
142 Mehta et al., Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury, Critical Care, 
Vol. 11, March 2007. 
143 Acute Kidney Injury Work Group, KDIGO Clinical Practice Guideline for Acute Kidney Injury, Kidney International 
Supplement, Vol. 2, Issue 1, March 2012. 
144 In addition to their clinical judgment, physician-reviewers considered hypotension as possible harm: (1) if the mean arterial 
blood pressure was less than 60 mmHg, or (2) if less than 65 mmHg and requiring sustained treatment and monitoring for 
15 minutes, or (3) if the drop in blood pressure was more than within 20 percent of the baseline. 
145 We have an other option for each preventability determination category.  (There are 21 total without the other category, 
24 total with the other category for each preventability determination, and 22 total with the other category only once.) 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 110   
 
146 The TruCode Encoder classifies hospital claims into MS-DRG categories expected to have similar hospital resource 
requirements and calculates the estimated payment.  This software was developed by TruCode LLC.  Accessed at 
https://www.trucode.com/products/trucode-encoder/ on August 13, 2019. 
147 Kizer, K.W., and Stegun, M.B., Serious Reportable Adverse Events in Health Care, Advances in Patient Safety, From Research to 
Implementation (Vol. 4: Programs, Tools, and Products), 2005, p. 346.  Accessed at 
https://www.ncbi.nlm.nih.gov/books/NBK20598/ on April 30, 2021. 
148 NQF, Serious Reportable Events In Healthcare2011 Update: A Consensus Report, Washington, DC: NQF, 2011. 
149 According to the American Society of Anesthesiologists (ASA), an ASA Class 1 is defined as a normally healthy patient 
(e.g., healthy, nonsmoking, no or minimal alcohol use).  For full list, see https://www.asahq.org/standards-and-guidelines/asa-
physical-status-classification-system.  Accessed on April 30, 2021. 
150 ACA,  3001 and  3025. 
151 CMS, Hospital Readmissions Reduction Program (HRRP), last modified on January 2019.  Accessed at 
https://www.cms.gov/medicare/medicare-fee-for-service-payment/acuteinpatientpps/readmissions-reduction-program.html 
on March 21, 2019. 
152 CMS, The Hospital Value-Based Purchasing (VBP) Program, last modified August 2018.  Accessed at 
https://www.cms.gov/Medicare/Quality-Initiatives-Patient-Assessment-Instruments/Value-Based-Programs/HVBP/Hospital-
Value-Based-Purchasing.html on March 21, 2019. 
153 CMS, CMS Quality Strategy 2016, 2016.  Accessed at https://www.cms.gov/Medicare/Quality-Initiatives-Patient-Assessment-
Instruments/QualityInitiativesGenInfo/Legacy-Quality-Strategy on February 8, 2021. 
154 CMS, 2021 National Impact Assessment of the Centers for Medicare & Medicaid Services (CMS) Quality Measures Report, June 
2021. 
155 CMS, Hospital Inpatient Quality Reporting Program, last modified September 2017.  Accessed at 
https://www.cms.gov/Medicare/Quality-Initiatives-Patient-Assessment-
Instruments/HospitalQualityInits/HospitalRHQDAPU.html on February 12, 2019. 
156 CMS, CMS Care Compare Empowers Patients when Making Important Health Care Decisions, Press release, 
September 2020.  Accessed at https://www.cms.gov/newsroom/press-releases/cms-care-compare-empowers-patients-when-
making-important-health-care-decisions on January 5, 2021. 
157 CMS, Hospital Compare.  Accessed at https://www.cms.gov/Medicare/Quality-Initiatives-Patient-Assessment-
Instruments/HospitalQualityInits/HospitalCompare#:~:text=Hospital%20Compare%20is%20a%20consumer,to%20go%20for%2
0health%20care.&text=General%20information,Survey%20of%20patients'%20experiences on January 5, 2021. 
158 CMS, Promoting Interoperability Programs, page last modified on February 2021.  Accessed at 
https://www.cms.gov/Regulations-and-Guidance/Legislation/EHRIncentivePrograms on April 5, 2021. 
159 CMS, Electronic Clinical Quality Measures Basics, page last modified on February 2021.  Accessed at 
https://www.cms.gov/Regulations-and-Guidance/Legislation/EHRIncentivePrograms/ClinicalQualityMeasures on April, 5, 2021. 
160 Under Section 1115A (c) of the Social Security Act, the Secretary may, through rulemaking, expand the duration and scope 
of a model test if the Secretary determines that such expansion is expected to reduce spending without reducing the quality of 
care or improve the quality of patient care without increasing spending. 
161 AHRQ, AHRQ QI Software.  Accessed at https://qualityindicators.ahrq.gov/Software/Default.aspx on March 21, 2019. 
162 AHRQ, Common Formats.  Accessed at https://www.pso.ahrq.gov/common on October 30, 2019. 
 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 111   
 
163 PHSA  901 (42 U.S. Code  299(a)); Patient Safety and Quality Improvement of 2005  2(a), adding sections 921 to 926 of 
the PHSA (42 U.S. Code  299b-21 to 299b-26). 
164 42 CFR  3.204-3.212. 
165 AHRQ, What Is the Network of Patient Safety Databases (NPSD)?  Accessed at https://www.ahrq.gov/npsd/what-is-
npsd/index.html on April 22, 2021. 
166 AHRQ, Patient Safety and Quality Improvement.  Accessed at Patient Safety and Quality Improvement | Agency for 
Healthcare Research and Quality (ahrq.gov) on March 2, 2022. 
167 AHRQ, Guideline and Measure Summaries, last reviewed July 2018.  Accessed at 
https://www.ahrq.gov/gam/summaries/index.html on February 5, 2021. 
168 CMS, CMS Measures Inventory Tool About Page, June 2020.  Accessed at https://cmit.cms.gov/CMIT_public/View_About 
on February 5, 2021. 
169 AHRQ, AHRQ's Making Healthcare Safer Reports: Shaping Patient Safety Efforts in the 21st Century, last modified in 
March 2020.  Accessed at https://www.ahrq.gov/research/findings/making-healthcare-safer/index.html on May 17, 2021.  
170 CDC, National Healthcare Safety Network (NHSN).  Accessed at https://www.cdc.gov/nhsn/about-nhsn/index.html on 
February 8, 2019.   
171 CDC, Healthcare-Associated Infections Community Interface.  Accessed at https://www.cdc.gov/hai/eip/index.html on 
March 21, 2019. 
172 CDC, State-Based HAI Prevention Activities.  Accessed at https://www.cdc.gov/hai/state-based/index.html on February 18, 
2022. 
173 CDC, The Targeted Assessment for Prevention (TAP) Strategy.  Accessed at https://www.cdc.gov/hai/prevent/tap.html on 
September 8, 2021. 
174 CDC, Prevention Epicenters Program.  Accessed at https://www.cdc.gov/hai/epicenters/index.html on August 19, 2020. 
175 CDC, Developing Healthcare Safety Research (SHEPheRD).  Accessed at 
https://www.cdc.gov/hai/research/safehealthcare.html on August 19, 2020. 
176 CDC, Modeling Infectious Diseases in Healthcare Network (MInDHealthcare).  Accessed at 
https://www.cdc.gov/hai/research/MIND-Healthcare.html on February 18, 2022. 
177 National Pressure Injury Advisory Panel, National Pressure Ulcer Advisory Panel (NPUAP) announces a change in 
terminology from pressure ulcer to pressure injury and updates the stages of pressure injury, Press release, April 2016. 
178 Hauck, K., and Zhao, X., How dangerous is a day in hospital?: A model of adverse events and length of stay for medical 
inpatients, Medical Care, Vol. 49, Issue 12, pp. 10681075, December 2011. 
179 Griffin, F.A., and Resar, R.K., IHI Global Trigger Tool for Measuring Adverse Events (Second Edition), IHI Innovation Series, 
2009, pp. 13 and 14. 
Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018 
OEI-06-18-00400  Endnotes | 112