Department of Veterans Affairs

Health Services Research & Development Service Evidence-based Synthesis Program

Colonoscopy Outcomes 

by Duration of NPO Status 

Prior to Colonoscopy with 

Moderate or Deep 

Sedation

January 2015

Prepared for:

Department of Veterans Affairs

Veterans Health Administration

Quality Enhancement Research Initiative

Health Services Research & Development Service

Washington, DC 20420

Prepared by:

Evidence-based Synthesis Program (ESP) Center

Minneapolis VA Medical Center

Minneapolis, MN

Timothy J. Wilt, MD, MPH, Director

Investigators:

Principal Investigator: 

Aasma Shaukat, MD, MPH

Co-Investigators: 

Joseph Wels, MD

Ashish Malhotra, MD

Nancy Greer, PhD

Timothy J. Wilt, MD, MPH

Research Assistants: 

Roderick MacDonald, MS

Maureen Carlyle, MPH

Indulis Rutks, BS
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

PREFACE 

Quality Enhancement Research Initiative’s (QUERI) Evidence-based Synthesis Program (ESP) 

was established to provide timely and accurate syntheses of targeted healthcare topics of 

particular importance to Veterans Affairs (VA) clinicians, managers and policymakers as they 

work to improve the health and healthcare of Veterans. The ESP disseminates these reports 

throughout the VA, and some evidence syntheses inform the clinical guidelines of large 

professional organizations. 

QUERI provides funding for four ESP Centers and each Center has an active university 

affiliation. The ESP Centers generate evidence syntheses on important clinical practice topics, 

and these reports help: 

• develop clinical policies informed by evidence;

• guide the implementation of effective services to improve patient 

outcomes and to support VA clinical practice guidelines and performance 

measures; and

• set the direction for future research to address gaps in clinical knowledge. 

In 2009, the ESP Coordinating Center was created to expand the capacity of HSR&D Central 

Office and the four ESP sites by developing and maintaining program processes. In addition, the 

Center established a Steering Committee comprised of QUERI field-based investigators, VA 

Patient Care Services, Office of Quality and Performance, and Veterans Integrated Service 

Networks (VISN) Clinical Management Officers. The Steering Committee provides program 

oversight, guides strategic planning, coordinates dissemination activities, and develops 

collaborations with VA leadership to identify new ESP topics of importance to Veterans and the 

VA healthcare system.

Comments on this evidence report are welcome and can be sent to Nicole Floyd, ESP 

Coordinating Center Program Manager, at Nicole.Floyd@va.gov. 

Recommended citation: Example: Shaukat A, Wels J, Malhotra A, Greer N, MacDonald R, 

Carlyle M, Rutks I, and Wilt T J. Colonoscopy Outcomes by Duration of NPO Status Prior to 

Colonoscopy with Moderate or Deep Sedation. VA ESP Project #09-009; 2015. 

This report is based on research conducted by the Evidence-based Synthesis Program (ESP) Center 

located at the Minneapolis VA Medical Center, Minneapolis, MN, funded by the Department of Veterans 

Affairs, Veterans Health Administration, Office of Research and Development, Quality Enhancement 

Research Initiative. The findings and conclusions in this document are those of the author(s) who are 

responsible for its contents; the findings and conclusions do not necessarily represent the views of the 

Department of Veterans Affairs or the United States government. Therefore, no statement in this article 

should be construed as an official position of the Department of Veterans Affairs. No investigators have 

any affiliations or financial involvement (eg, employment, consultancies, honoraria, stock ownership or 

options, expert testimony, grants or patents received or pending, or royalties) that conflict with material 

presented in the report.

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

TABLE OF CONTENTS

EXECUTIVE SUMMARY

 Introduction ..............................................................................................................................1 

 Methods ....................................................................................................................................2 

 Data Sources and Searches ..............................................................................................2 

 Study Selection ................................................................................................................2 

 Data Abstraction and Risk of Bias Assessment ...............................................................2 

 Data Synthesis and Analysis ............................................................................................2 

Results ......................................................................................................................................3 

 Results of Literature Search .............................................................................................3 

 Overview ..........................................................................................................................3 

 Executive Summary Table 1. Summary of Outcomes Reported in Included Studies .....3 

 Summary of Results for Key Questions ...........................................................................4 

Discussion ................................................................................................................................6 

 Key Findings and Strength of Evidence ..........................................................................6 

 Applicability .....................................................................................................................7 

 Research Gaps/Future Research .......................................................................................7 

 Conclusions ......................................................................................................................7 

 Abbreviations Table .................................................................................................................8 

INTRODUCTION..........................................................................................................................9 

METHODS

 Topic Development ................................................................................................................11 

Search Strategy ......................................................................................................................11 

Study Selection ......................................................................................................................11 

Data Abstraction ....................................................................................................................11 

 Risk of Bias Assessment ........................................................................................................12 

Data Synthesis ........................................................................................................................12 

Rating the Body of Evidence .................................................................................................12 

Peer Review ...........................................................................................................................12 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

RESULTS

Literature Flow .......................................................................................................................13 

Overview ................................................................................................................................14 

 Key Question 1. Does the incidence of aspiration and other anesthesia-related harms for 

colonoscopy vary by NPO status or bowel prep timing (eg, > 6 hours, 2-6 hours, < 4 hours, 

and < 2 hours)? Does the incidence of anesthesia-related harms by NPO status vary by: a) 

patient characteristics (age, race, sex, obesity, comorbidities) or b) sedation (moderate, 

deep)? .....................................................................................................................................21 

 Key Question 2. What is the effect of variable timing of bowel prep and NPO status on the 

quality of the bowel preparation, diagnostic yield, and colonoscopy procedural quality 

indicators (eg, completion rates, adenoma detection rate, total procedure time, cecal 

intubation time and withdrawal time)? ..................................................................................23 

 Key Question 3. What is the effect of NPO status prior to colonoscopy on resource use (eg, 

costs, unused procedure slots, delays in rescheduling, delays in diagnosis, increased volume 

of procedures, scheduler and nursing time associated with cancelled or delayed 

procedures)? ...........................................................................................................................27 

 Key Question 4. What is the effect of bowel preparation and NPO status prior to 

colonoscopy on patient adherence to bowel preparation, colonoscopy, and/or rescheduled 

colonoscopy and satisfaction with bowel preparation and/or colonoscopy? .........................27 

SUMMARY AND DISCUSSION

 Key Findings and Strength of Evidence ................................................................................29 

Discussion ..............................................................................................................................30 

Limitations and Applicability ................................................................................................34 

Research Gaps/Future Research.............................................................................................35 

 Conclusions ............................................................................................................................36 

REFERENCES .............................................................................................................................37 

TABLES

 Table 1. Summary of Baseline Characteristics ......................................................................14 

Table 2. Overview of Outcomes Reported ............................................................................16 

FIGURES

 Figure 1. Literature Flow Chart .............................................................................................13 

 Figure 2. Minimum Time from End of Bowel Preparation to Procedure (Blue Lines) or 

Time Before Procedure when Liquids were Stopped (Red Lines) ........................................15 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

 Figure 3. Completion Rate, Adenoma Detection Rate, and Diagnostic Yield: Outcomes 

from Randomized Controlled Trials ......................................................................................26 

Figure 4. Completion Rate and Adenoma Detection Rate: Outcomes from Observational 

Studies ....................................................................................................................................26 

APPENDIX A. Search Strategy ....................................................................................................42 

APPENDIX B. Peer Review Comments/Author Responses ........................................................43 

APPENDIX C. Evidence Tables ..................................................................................................50 

Table 1. Study Characteristics ...............................................................................................50 

Table 2. Primary Outcomes ...................................................................................................78 

 Table 3. Procedural Outcomes ...............................................................................................79 

Table 4. Time and Patient Outcomes .....................................................................................90 

 Table 5. Hospitalizations, Costs, and Adverse Events ...........................................................94 

 Table 6. Gastric Contents Outcomes .....................................................................................95 

APPENDIX D. Strength of Evidence ...........................................................................................96 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

EXECUTIVE SUMMARY

INTRODUCTION 

Fourteen million colonoscopies are performed annually in the United States for screening, 

diagnosis, surveillance, and treatment of numerous colonic conditions. Colonoscopies require 

bowel preparation for cleansing to sufficiently visualize the colon lining, identify and treat 

suspected lesions, and maximize quality and safety. To optimize colon lining visualization, 

patients are advised to divide the bowel preparation regimen over two sessions (known as “splitdose preparation”): 1) the evening prior to the colonoscopy (PM dose) and 2) the morning of the 

colonoscopy (AM dose), the latter taken ideally within 2-6 hours of the planned procedure. In 

addition, some level of sedation (typically moderate or deep) is used in almost all colonoscopies 

to facilitate patient comfort and procedure quality. 

There is significant variation among anesthesia providers as to the acceptable timing of NPO 

(“nothing by mouth”), including how many hours prior to the planned procedure the last bowel 

preparation dose can be taken, in order to minimize anesthesia risk (primarily pulmonary 

aspiration requiring hospitalization). Practice guidelines from the American Society of 

Anesthesiologists suggest a minimum fasting period of 2 hours for clear liquids and 6 hours for a 

light meal (ie, toast and clear liquids). The guideline authors note that published clinical evidence 

is insufficient to clearly define a relationship between NPO status and risk of emesis/reflux or 

aspiration. 

There is a need to balance optimal colonic preparation, patient convenience, and scheduling 

efficiency (typically a shorter NPO window status) with anesthesia safety concerns for an 

elective procedure (typically a longer NPO status). In addition, performing procedures with

moderate or deep sedation requires development of and adherence to local and/or national policy 

measures that cross multiple procedures and physician specialties. These policies include 

recommendations regarding NPO status. 

The purpose of this report was to review the evidence on the relationship between timing of NPO 

and 1) the incidence of aspiration and other anesthesia-related harms during elective colonoscopy 

and 2) colonoscopy rescheduling. We also reviewed the evidence on the benefits and harms of 

variable timing of NPO status on colonoscopy outcomes including colonoscopy quality 

measures, resource use, and patient satisfaction. The review may be used to guide policy within 

the VA. We addressed the following key questions: 

Key Question 1. Does the incidence of aspiration and other anesthesia-related harms for 

colonoscopy vary by NPO status or bowel prep timing (eg, > 6 hours, 2-6 hours, < 4 hours, and < 

2 hours)? Does the incidence of anesthesia-related harms by NPO status vary by: a) patient 

characteristics (age, race, sex, obesity, comorbidities) or b) sedation (moderate, deep)?

Key Question 2. What is the effect of variable timing of bowel prep and NPO status on the 

quality of the bowel preparation, diagnostic yield, and colonoscopy procedural quality indicators 

(eg, completion rates, adenoma detection rate, total procedure time, cecal intubation time and 

withdrawal time)?

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Key Question 3. What is the effect of NPO status prior to colonoscopy on resource use (eg, 

costs, unused procedure slots, delays in rescheduling, delays in diagnosis, increased volume of 

procedures, scheduler and nursing time associated with cancelled or delayed procedures)? 

Key Question 4. What is the effect of bowel preparation and NPO status prior to colonoscopy on 

patient adherence to bowel preparation, colonoscopy, and/or rescheduled colonoscopy, and 

satisfaction with bowel preparation and/or colonoscopy? 

METHODS

Data Sources and Searches

We searched MEDLINE (OVID) for articles published from 1990 through October 2014. Our

search was designed to identify studies of any design. We limited the search to studies involving 

human subjects published in the English language. Search terms included the following Medical 

Subject Headings (MeSH): Colonoscopy, Cathartics, Polyethylene Glycols, Phosphates, and 

Respiratory Aspiration of Gastric Contents. We also searched reference lists of guidelines, 

existing reviews, and included studies and we received reference suggestions from stakeholders, 

Technical Expert Panel (TEP) members, and peer reviewers. 

Study Selection

Abstracts of citations identified from the literature search were assessed for relevance by an 

investigator. Full text reports of studies identified as potentially eligible (or indeterminate, eg,

title only) were obtained for further review by 2 independent investigators. We included studies 

of any design that reported outcomes following bowel preparation if at least one preparation was 

completed within 8 hours of the colonoscopy procedure. Only studies of adults, undergoing 

colonoscopy with moderate or deep sedation, and reporting outcome during colonoscopy or 

recovery from colonoscopy were included. We also included population-based studies of adverse 

events during colonoscopy. 

Data Abstraction and Risk of Bias Assessment

From studies of different preparation-to-procedure or NPO intervals, study characteristics 

(inclusion/exclusion criteria and details about the preparation interventions or NPO status), 

patient characteristics, and outcomes data were abstracted onto tables by one investigator and 

verified by a second. Risk of bias (low, moderate, or high) was determined for each included 

study.

Data Synthesis and Analysis

We described and qualitatively compared the patient characteristics, study characteristics, 

intervention timing, and findings of included studies. Due to variation in the preparation-toprocedure interval and/or NPO status across studies and different systems used to report 

outcomes, we summarized most outcomes narratively. Strength of evidence was assessed for 

primary and secondary outcomes. 

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RESULTS

Results of Literature Search

Our literature search yielded 1177 abstracts or titles. We excluded 1069 and performed a full text 

review of 108 articles, excluding 74 articles and including 34. A hand-search of reference lists of 

guidelines, existing reviews, and included studies yielded another 6 articles for a total of 40 

included studies of different bowel preparation or NPO status intervals (28 randomized 

controlled trials [RCTs], 2 controlled clinical trials [CCTs], and 10 observational studies). Of the 

28 RCTs, 10 were low risk of bias, 16 were moderate risk of bias, and 2 were high risk of bias. 

Of the 10 observational studies, 3 were low risk of bias, 6 were moderate risk of bias, and one 

was high risk of bias. Both CCTs were high risk of bias. 

Overview

An overview of outcomes reported is presented in Executive Summary Table 1. Our predefined 

primary and secondary outcomes were rarely reported. All but one study reported quality of the 

bowel preparation. Few or no studies reported other secondary or intermediate outcomes. 

Executive Summary Table 1. Summary of Outcomes Reported in Included Studies

Category Outcome (Number of Studies Reporting)a

Primary Outcomes Aspiration (k=6)

Rescheduled Colonoscopies (k=1)

Secondary Outcomes

Bowel Perforation (k=1)

Other Adverse Events (k=7)

Diagnostic Yield (k=3)

Completion Rate (k=11)

Adenoma Detection Rate (k=7)

False Negative Colonoscopy

Intermediate Outcomes

Hospitalizations

Costs

Quality of Bowel Preparation (k=39)

Total Procedure Time (k=3)

Cecal Intubation Time (k=4)

Withdrawal Time (k=5)

Patient Adherence (k=11)b

Patient Satisfaction (k=11) b

Unused Procedure Slots

Delays, Rescheduling

Delays, Diagnosis

Increased Volume, Procedures

Scheduler/Nurse Time

Volume of Gastric Contents (k=2)

pH of Gastric Contents a Total of 40 studies included in review

b Data on patient adherence and patient satisfaction extracted only from studies using same bowel preparation 

substance in the study groups (k=21)

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Summary of Results for Key Questions

Key Question 1. Does the incidence of aspiration and other anesthesia-related harms 

for colonoscopy vary by NPO status or bowel prep timing (eg, > 6 hours, 2-6 hours, < 4 

hours, and < 2 hours)? Does the incidence of anesthesia-related harms by NPO status 

vary by: a) patient characteristics (age, race, sex, obesity, comorbidities) or b) sedation 

(moderate, deep)?

Five studies (3 RCTs and 2 observational studies, total n=2,318) of split-dose bowel preparation 

regimens (completed at least 2 hours before colonoscopy) compared to evening-before regimens 

reported either no aspiration events during colonoscopy or in the 30 days following colonoscopy, 

or no complications related to sedation. Two of the 5 studies also specified that liquids were 

allowed up to 3 hours prior to the procedure. One of the observational studies reported no 

difference in gastric volume.

An additional RCT compared morning-only preparation to a split-dose regimen with both groups 

completing bowel preparation 4 hours before colonoscopy but allowed clear liquids up to 2.5 

hours before. This study reported one aspiration event requiring 24 hour hospital observation in 

the morning-only group. 

Although hospital- or population-based studies have reported on aspiration requiring 

hospitalization during colonoscopy, none documented NPO status of the patients at the time of 

the colonoscopy. One study reported a slightly higher incidence of aspiration requiring 

hospitalization (0.14% vs 0.10%) for Medicare patients having diagnostic colonoscopy with deep 

sedation versus moderate sedation. An Australian study of 23,508 outpatient colonoscopies 

reported one patient (0.004%) who had colonoscopy following general anesthesia had an

aspiration event requiring hospitalization. 

In an Italian study of 3,155 colonoscopies, there were 5 aspiration events requiring “some 

intervention by an anesthesiologist” (0.16%) but it was unclear what type of sedation the 5 

patients received. Patients followed fasting guidelines of the study time period which allowed 

clear liquids at least 2 hours before the procedure and a light meal at least 6 hours before. 

Key Question 2. What is the effect of variable timing of bowel prep and NPO status on 

the quality of the bowel preparation, diagnostic yield, and colonoscopy procedural 

quality indicators (eg, completion rates, adenoma detection rate, total procedure time, 

cecal intubation time and withdrawal time)?

Thirty-nine studies (28 RCTs, 2 CCTs, and 9 observational studies) reported on the effect of 

variable timing of bowel preparation on quality of the bowel preparation. Eleven of these studies 

(6 RCTs, 1 CCT, 4 observational) also reported the time prior to colonoscopy when water or 

other clear liquids were allowed, ranging from 4 hours until the time of the procedure. Although 

different rating scales were used to rate the quality of the bowel preparation, quality was 

consistently rated higher for NPO intervals of 6 hours or less compared to intervals of more than 

8 hours. The difference was observed whether the minimum time was based on the completion of 

bowel preparation to procedure time (1 to 6 hours) or the time that liquids were allowed prior to 

the procedure (0 to 4 hours). 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Pooled results from 5 RCTs (total n=1,795) found no difference in completion rate between 

shorter and longer NPO status (based on bowel preparation) groups. A retrospective 

observational study (n=5,175) reported a significantly higher completion rate (96% vs 94%, P = 

.008) in the shorter NPO group. One RCT reported no difference in adenoma detection rate 

based on NPO status while pooled results from 3 observational studies showed an improved 

detection rate with shorter NPO time. Diagnostic yield was reported in 3 RCTs with mixed 

findings for all polyps or lesions. One RCT reported no documented complications of bowel 

perforation on discharge from the endoscopy unit. No studies reported on false negative 

colonoscopies or hospitalizations. 

Key Question 3. What is the effect of NPO status prior to colonoscopy on resource use 

(eg, costs, unused procedure slots, delays in rescheduling, delays in diagnosis, 

increased volume of procedures, scheduler and nursing time associated with cancelled 

or delayed procedures)?

One moderate risk of bias RCT (n=113) reported a significantly lower percentage of rescheduled 

colonoscopies (3%) in the split-dose group compared to 2 groups that completed preparation the 

evening before the colonoscopy (8% and 24%). However, preparation agents differed in the 3 

study groups. No other resource use outcomes were reported. 

Key Question 4. What is the effect of bowel preparation and NPO status prior to 

colonoscopy on patient adherence to bowel preparation, colonoscopy, and/or 

rescheduled colonoscopy, and satisfaction with bowel preparation and/or colonoscopy?

We extracted data on adherence and satisfaction from studies where the same bowel preparation 

substance (eg, polyethylene glycol) was used for all patients. Adherence to the bowel preparation 

regimen was typically higher with a split-dose regimen but several studies reported no difference 

between split-dose and same day (day before colonoscopy) regimens. 

We extracted elements of satisfaction that would be impacted by different schedules for bowel 

preparation. Results were inconsistent for time lost from work or school and sleep disruption. 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

DISCUSSION 

Key Findings and Strength of Evidence

• Hospital- or population-based studies have reported that the risk of aspiration serious 

enough to require hospitalization during colonoscopy is very low (1 in 1000 or less). 

However, these studies have not documented NPO status and it is possible that the low 

rates are driven by more individuals having longer rather than shorter NPO status. 

• In 3 RCTs and 2 observational studies (total n=2,318) comparing shorter NPO status to 

NPO status of at least 8 hours, no aspiration events were reported. Bowel preparation was 

completed at least 2 hours prior to colonoscopy in 2 studies and at least 3 hours prior to 

colonoscopy in one study. Another study allowed clear liquids up to 3 hours prior to 

colonoscopy and the remaining study only reported that bowel preparation was 

completed in the morning for an afternoon colonoscopy. 

• One small RCT (n=113) reported a significantly lower percentage of rescheduled 

colonoscopies in the split-dose group compared to 2 groups that completed preparation 

the evening before the colonoscopy, although different preparation agents were used in 

the 3 groups. No studies reported on other resource use outcomes including unused 

procedure slots or increased volume of procedures by NPO status. 

• Few studies assessing NPO status specified adverse events associated with colonoscopy 

as an outcome of interest and therefore adverse events may be underreported. 

• Time from completion of colonic preparation to colonoscopy of 1 to 6 hours is associated 

with greater bowel preparation quality than time intervals of greater than 8 hours. Of 24 

studies comparing split-dose versus non-split-dose preparation, 20 reported higher quality 

of bowel preparation with split-dose. 

• Completion rate was not significantly different between NPO status groups in 5 RCTs; 

one large observational study reported a greater completion rate with shorter NPO status. 

Results were mixed for diagnostic yield and adenoma detection rate with no consistent 

findings based on NPO status. One study reported no documented complications of 

bowel perforation; no study reported on false negative colonoscopy. 

• Among studies reporting adherence to the bowel preparation regimen, time lost from 

work, or sleep disruption, results were mixed with no clear benefit of split-dose regimens 

over same day regimens.

• Studies of NPO status typically excluded patients with serious comorbidities.

• For our co-primary outcomes, strength of evidence was low for aspiration and 

insufficient for rescheduled colonoscopies. For secondary outcomes, strength of evidence 

was moderate for completion rate based on pooled results from 5 RCTs, low for adenoma 

detection rate based on pooled results from 3 observational studies, and insufficient for 

diagnostic yield, bowel perforation, and false-negative colonoscopy. 

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Applicability

Populations enrolled in eligible studies were broadly applicable to many individuals undergoing 

elective colonoscopy in the United States. Eligible studies typically included patients 45 to 65 

years with approximately 50% of patients enrolled in studies done in the US. Nearly one-half

patients were male and two-thirds of colonoscopies were performed for cancer screening. The 

largest study reporting on aspirations requiring hospitalization was completed in a US Medicare 

population. However, aspiration by NPO status was not provided in this study and few other 

studies were adequately designed to directly assess the role of NPO status on aspirations 

requiring hospitalizations or colonoscopy rescheduling. 

Research Gaps/Future Research

Future studies are needed that systematically assess duration of NPO status in relation to timing 

of colonoscopy and record serious adverse events, including aspiration requiring hospitalization. 

Such studies could include prospective registries or pooling currently collected adverse event 

outcomes across the Veterans Health Administration (VHA). Future studies are also needed to 

determine and understand variability in NPO duration policies and practices across VA 

(especially practices that appear not to adhere to national society guidance statement) and to 

implement interventions to reduce variation. There is also a need for larger studies comparing 

shorter durations of NPO prior to colonoscopy (such as 2 to 4 hours) to longer intervals of NPO 

prior to colonoscopy (such as ≥ 6 hours) that directly assess for colonoscopy effectiveness (such 

as detection rate of adenoma and neoplasia, completion rate) and safety outcomes. We also need 

studies evaluating the effect of variable duration of NPO status prior to colonoscopy on patient 

satisfaction, adherence to colonoscopy, and impact on endoscopy scheduling processes, 

including delays in timely receipt of colonoscopy. Finally, evidence-based multi-society 

consensus conference guidelines are needed that bring together patient representatives and 

members from anesthesia, gastroenterology, and general medicine. Important items include 

determining the “clinically important” balance between important outcomes to anesthesiologists, 

gastroenterologists and patients including aspiration rates due to NPO status, colonoscopy 

quality measures, resource use, and patient satisfaction and adherence. 

Conclusions

Aspiration incidence requiring hospitalization during colonoscopy with moderate or deep 

sedation is very low and on the order of magnitude commonly accepted for adverse effects of 

similar clinical importance due to other elective procedures. Participants in hospital- and 

population-based studies likely had wide ranges of timing from NPO to colonoscopy and many 

were likely longer than 2 to 4 hours. No study documenting NPO status found that shorter NPO 

status prior to colonoscopy increased aspiration risk. We did not find direct evidence of the effect 

of NPO status on colonoscopy rescheduling. Shorter time from completion of colonic 

preparation to colonoscopy is associated with greater bowel preparation quality than longer time 

intervals. 

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ABBREVIATIONS TABLE

ASA American Society of Anesthesiologists

CCT Controlled clinical trial

NPO Nil per os (nothing by mouth)

RCT Randomized, controlled trial

VA Department of Veterans Affairs

VHA Veterans Health Administration

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

EVIDENCE REPORT

INTRODUCTION

Fourteen million colonoscopies are performed annually in the United States for screening, 

diagnosis, surveillance, and treatment of numerous colonic conditions. Colonoscopies require 

bowel preparation for cleansing to sufficiently visualize the colon lining and maximize quality 

and safety. However, inadequate preparation occurs in approximately 25% of colonoscopies,

leading to cancellations, rescheduling, difficulty in detecting colonic polyps or other 

pathology,1,2 poor patient adherence, as well as longer procedure time. Increased financial and 

opportunity costs and patient dissatisfaction result.3

To optimize colon lining visualization, patients are advised to divide the bowel preparation 

regimen over two sessions (known as “split-dose preparation”): 1) the evening prior to the 

colonoscopy (PM dose) and 2) the morning of the colonoscopy (AM dose); the latter taken 

ideally within 2-6 hours of the planned procedure.4-7 In addition, some level of sedation

(typically moderate or deep) is used in almost all colonoscopies to facilitate patient comfort and 

procedure quality.

8,9

For both moderate and deep sedation there is significant variation among anesthesia providers as 

to the acceptable timing of NPO (“nothing by mouth”) including how many hours prior to the 

planned procedure the last bowel preparation dose can be taken in order to minimize anesthesia 

risk (primarily aspiration). Practice guidelines from the American Society of Anesthesiologists 

Committee on Standards and Practice Parameters for preoperative fasting for healthy patients 

undergoing elective procedures suggest the following minimum fasting periods with the goal of 

minimizing anesthesia-related risks (primarily aspiration): 2 hours for clear liquids (eg, water, 

fruit juice without pulp, carbonated beverages, clear tea, and black coffee), 6 hours for nonhuman milk, and 6 hours for a light meal (ie, toast and clear liquids).10 The guideline authors 

note that published clinical evidence is insufficient to clearly define a relationship between NPO 

status and risk of emesis/reflux or pulmonary aspiration. Furthermore, it is unclear how different 

bowel preparation agents would be classified (clear liquids or not), how the potential toxicity of 

bowel preparation agents might impact anesthesia-related risks, and how the volume of bowel 

preparation agent consumed might differ from the volume of liquids considered acceptable in the 

guidelines.

An optimal bowel preparation and NPO status seeks to balance the need for optimal colonic 

preparation, patient convenience, and scheduling efficiency (typically a shorter NPO window 

status) with anesthesia safety concerns for an elective procedure (typically a longer NPO status). 

Furthermore, performing procedures with moderate or deep sedation requires development of 

and adherence to local and/or national policy measures that cross multiple procedures and 

physician specialties. These policies include recommendations regarding NPO status. Failure to 

adhere to NPO status can result in cancellation or rescheduling of procedures or poor procedure 

preparation. This can lead to reduced procedure quality, resource efficiency, patient satisfaction, 

and adherence.

The purpose of this report was to review the evidence on the relationship between timing of NPO 

and the incidence of aspiration and other anesthesia-related harms during elective colonoscopy as 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

well as colonoscopy rescheduling. In addition, we also reviewed the evidence on the benefits and 

harms of variable timing of NPO status on colonoscopy outcomes including colonoscopy quality 

measures, rescheduling, resource use, and patient satisfaction. The review may be used to guide 

policy within the VA. With input from stakeholders and TEP members, we developed the 

following Key Questions:

Key Question 1. Does the incidence of aspiration and other anesthesia-related harms for 

colonoscopy vary by NPO status or bowel prep timing (eg, > 6 hours, 2-6 hours, < 4 hours, and < 

2 hours)? Does the incidence of anesthesia-related harms by NPO status vary by: a) patient 

characteristics (age, race, sex, obesity, comorbidities) or b) sedation (moderate, deep)?

Key Question 2. What is the effect of variable timing of bowel prep and NPO status on the 

quality of the bowel preparation, diagnostic yield, and colonoscopy procedural quality indicators 

(eg, completion rates, adenoma detection rate, total procedure time, cecal intubation time and 

withdrawal time)?

Key Question 3. What is the effect of NPO status prior to colonoscopy on resource use (eg, 

costs, unused procedure slots, delays in rescheduling, delays in diagnosis, increased volume of 

procedures, scheduler and nursing time associated with cancelled or delayed procedures)?

Key Question 4. What is the effect of bowel preparation and NPO status prior to colonoscopy on 

patient adherence to bowel preparation, colonoscopy, and/or rescheduled colonoscopy, and 

satisfaction with bowel preparation and/or colonoscopy?

We defined the following Population, Intervention, Comparator, Outcomes, Timing, and Setting 

(PICOTS) for the review:

Population: Adults undergoing bowel preparation and elective colonoscopy with moderate or 

deep sedation

Intervention(s): NPO status 2-4 hours (liquids and bowel preparation allowed up to 2 hours 

prior to procedure)

Comparator(s): Alternative timing of NPO 

Outcome(s): (NOTE: limited to findings according to NPO status prior to colonoscopy)

Co-primary outcomes: aspiration, rescheduled colonoscopies

Secondary outcomes: adverse events (including bowel perforation and other anesthesiarelated harms), diagnostic yield, completion rate, adenoma detection rate, false negative 

colonoscopies

Intermediate outcomes: quality of bowel preparation, hospitalizations, costs, total 

procedure time, cecal intubation time, withdrawal time, unused procedure slots, delays in 

rescheduling, delays in diagnosis, increased volume of procedures, scheduler and nursing 

time, patient adherence, patient satisfaction, volume of gastric contents, pH of gastric 

contents

Timing: Start of sedation for colonoscopy to completion of sedation for colonoscopy

Setting: Inpatient or outpatient clinics

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

METHODS

TOPIC DEVELOPMENT

This topic was nominated by Jason Dominitz, MD, MHS, National Program Director for 

Gastroenterology, Office of Patient Care Services. Additional stakeholders were identified to 

include both gastroenterology and anesthesiology: John Sum-Ping, MD, Chair, National 

Director, Anesthesia Service; Art Wallace, MD, PhD, Chief, Anesthesia Service, San Francisco 

VA Medical Center; and Deborah Fisher, MD, MHS, Chair, National VA Gastroenterology Field 

Advisory Committee. The key questions were formulated with input from a Technical Expert 

Panel (TEP) consisting of gastroenterologists and anesthesiologists.

SEARCH STRATEGY

We searched MEDLINE (OVID) for articles published from 1990 through October 2014. Our

search was designed to identify studies of any design. We limited the search to studies involving 

human subjects published in the English language. Search terms included the following Medical 

Subject Headings (MeSH): Colonoscopy, Cathartics, Polyethylene Glycols, Phosphates, and 

Respiratory Aspiration of Gastric Contents. The full search strategy is presented in Appendix A. 

We also searched reference lists of guidelines, existing reviews, and included studies and we 

received reference suggestions from stakeholders and TEP members.

STUDY SELECTION

Abstracts of citations identified from the literature search were assessed for relevance by an

investigator. We included studies of any design that reported outcomes following bowel 

preparation if at least one preparation was completed within 8 hours of the colonoscopy 

procedure. We also include population-based studies of adverse events during colonoscopy.

Additional inclusion criteria were as follows:

• Study of adults

• Study of colonoscopy with moderate or deep sedation (studies related to colorectal 

surgery or involving general anesthesia were excluded)

• Reports outcomes of interest during colonoscopy or recovery from colonoscopy (ie,

studies of aspiration during bowel preparation were excluded)

Full text reports of studies identified as potentially eligible (or indeterminate, eg, title only) were 

obtained for further review using the inclusion and exclusion criteria described above. Each 

article was independently reviewed by 2 investigators. Reasons for excluding a study at full text 

review were noted.

DATA ABSTRACTION

Eligible studies were reviewed for outcomes of interest by investigators. From studies of 

different preparation-to-procedure or NPO intervals, study characteristics (inclusion/exclusion 

criteria and details about the preparation interventions or NPO status), patient characteristics, and 

outcomes data were abstracted onto tables by one investigator and verified by a second. Our 

11
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

focus was on outcomes from different preparation-to-procedure intervals and not different 

preparation substances.

RISK OF BIAS ASSESSMENT

We assessed the risk of bias of randomized controlled trials (RCTs) and controlled clinical trials 

(CCTs) based the following criteria: allocation sequence generation, allocation concealment, 

blinding, completeness of outcome reporting, and selectiveness of outcome reporting – a 

modification of the Cochrane approach to determining risk of bias.

11 For observational studies 

we identified the following criteria and evaluated risk of bias for each study:

1) Study design (prospective vs retrospective)

2) Population (consecutive or not)

3) Analysis of findings 

a. Was the method for handling missing data reported and appropriate?

b. Were the characteristics the different NPO groups similar?

Individual studies were rated as low, moderate, or high risk of bias. Low risk of bias RCTs had 

adequate allocation sequence generation and allocation concealment, blinding, and few patients 

with incomplete data. Low risk of bias observational studies were prospective, enrolled 

consecutive patients, had appropriate methods for handling missing data (or no missing data), 

and characteristics of the NPO groups were similar.

DATA SYNTHESIS

We described and qualitatively compared the patient characteristics, study characteristics, 

intervention timing, and findings of included studies. Due to variation in the preparation-toprocedure interval and/or NPO status across studies and different systems used to report 

outcomes, we summarized most outcomes narratively. 

RATING THE BODY OF EVIDENCE

We rated the overall strength of the body of evidence for our primary and secondary outcomes 

using the method reported by Owens et al.12 Separate ratings were generated for RCTs/CCTs and 

observational studies. 

PEER REVIEW

A draft version of this report was reviewed by clinical content experts and clinical leadership. 

Their comments and our responses are presented in Appendix B and the report has been

modified as needed.

12
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

13

RESULTS

LITERATURE FLOW 

Our literature search yielded 1177 abstracts or titles (Figure 1). After reviewing the abstracts we 

excluded 1069 and performed full text review of 108 articles. We excluded 74 articles and 

included 34. A hand-search of reference lists of guidelines, existing reviews, and included 

studies yielded another 6 articles for a total of 40 included studies of different bowel preparation 

or NPO status intervals (28 RCTs, 2 controlled CCTs, and 10 observational studies).

Figure 1: Literature Flow Chart

Hand Search: 4 References Added

• 4 RCTs 

• 1 CCT

• 1 Observational Study

Search Results:

1177 References

Full Text Review:

108 References

Included Studies:

28 RCTs

2 CCTs

10 Observational Studies

Abstracts Excluded: 1069

Excluded: 74 References

• Pediatric 0

• Not colonoscopy 9

• Not moderate or deep sedation 1

• Not a report of different NPO status 61

• No outcomes of interest 3
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

OVERVIEW 

Baseline characteristics for the 40 RCTs, CCTs, and observational studies13-53 reporting 

outcomes of interest are presented in Table 1. A total of 22,936 patients were evaluated; 

approximately one-half of the patients were from the United States or Canada. Mean age was 57 

years in the 34 studies reporting. Sixty-one percent of colonoscopies were screening 

colonoscopies. Detailed study characteristics and risk of bias criteria are presented in Appendix 

C, Table 1. 

From each included study, we identified a minimum time from the end of preparation until the 

procedure. Three studies36,38,43 did not provide enough information to determine a minimum 

time. We also extracted information about timing of liquids allowed prior to the procedure from 

the 11 studies that reported that information. Figure 2 displays the minimum times based on 

bowel preparation time and the time before the procedure that clear liquids were allowed. 

An overview of outcomes reported in each study is presented in Table 2. An NPO status of > 8 

hours indicates that the bowel preparation was completed the night before colonoscopy but the 

exact time of completion and time of colonoscopy were not reported. Our predefined primary 

and secondary outcomes were rarely reported. Six studies reported our co-primary outcome of 

aspiration29,31,41,43,44,52; one reported rescheduled colonoscopies.38 Of our secondary and 

intermediate outcomes, all but one study reported quality of the bowel preparation. Few studies 

reported other adverse events, diagnostic yield, completion rates, adenoma detection rate, total 

procedure time, cecal intubation time, withdrawal time, patient adherence, patient satisfaction, or 

volume of gastric contents. No studies reported false negative colonoscopies, hospitalizations, 

costs, unused procedure slots, delays in rescheduling, delays in diagnosis, increased volume of 

procedures, scheduler and nursing time, or acidity of the gastric contents. Detailed outcome data 

are presented in Appendix C, Tables 2 through 6. 

Table 1. Summary of Baseline Characteristics 

Characteristic Mean (range)

Unless Otherwise Noted

Number of Studies

Reporting

Total number of patients evaluated 22,936 (80 to 5175) 40

Randomized controlled trials, number of patients 9304 (80 to 895) 28

Controlled clinical trials, number of patients 740 (328 to 412) 2 

Observational studies, number patients 12,892 (100 to 5175) 10

Age of subjects, years (range of means) 57 (44 to 63) 34

Age of subjects, range of median years 55 to 65 3

Gender, male, % of patients 46 (28 to 81) 38

Indication for colonoscopy-screening, % of patients 61 (0a to 100) 20

Location - USA/Canada, number of patients 12,208 (100 to 5175) 17

Location - Asia/Australia, number of patients 8045 (80 to 3079) 14

Location - Europe, number of patients 2683 (160 to 895) 9 a Two studies reported that screening was not an indication for colonoscopy. Chiu 200620 included participants who 

had colorectal neoplasms detected at a screening colonoscopy and were scheduled for a second colonoscopic 

examination for either elective polypectomy or endoscopic mucosectomy. Manno 201240 included participants with 

a positive fecal occult test or those in surveillance post-polypectomy. 

14
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Figure 2. Minimum Time from End of Bowel Preparation to Procedure (Blue Lines) or Time Before Procedure when Liquids 

were Stopped (Red Lines)a,b,c

a 3 studies did not provide sufficient information to determine a minimum time from end of preparation to procedure (Khan 2010,36 Kolts 1993,38 Mathus-Vliegen 

201343) b Studies where patients were allowed liquids until time of procedure are indicated by a time of 0.25 hours c Citations are author, year (reference number)

0

1

2

3

4

5

6

7

Eun 2010 (25)

Voiosu 2013 (53)

Paoluzi 1993 (45)

Koh 2011 (37)

Abdul-Baki 2008 (13)

Aoun 2005 (14)

Parra-Blanco 2006 (48)

Huffman 2010 (31)

Kastenberg 2001 (34)

Manno 2012 (41)

Arya 2013 (15)

El Sayad 2003 (24)

Park 2007 (46)

Marmo 2010 (42)

Park 2010 (47)

Johanson 2007 (32)

Seo 2012 (50)

Barclay 2004 (17)

Longcroft-Wheaton 2012 (40)

Varughese 2010 (52)

Di Palma 2011 (23)

Frommer 1997 (27)

Gurudu 2010 (29)Gurudu 2012 (30)

Flemming 2012 (26)

Matro 2010 (44)

Kao 2011 (33)

Bryant 2013 (18)

De Salvo 2006 (22)

Chiu 2011 (19)

Rex 2013 (49)

Church 1998 (21)

Athreya 2011 (16)

Vanner 2011 (51)

Gupta 2007 (28)

Chiu 2006 (20)

Kössi 2007 (39)

Time (hours)

Prep

Liquids

15
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Table 2. Overview of Outcomes Reported

Author, Year

NPO Status 

Groupsa 

Primary 

Outcomes Secondary Outcomes Intermediate Outcomes Aspiration (k=6) Rescheduled Colonoscopies (k=1) Bowel Perforation (k=1) Other Adverse Events (k=7) Diagnostic Yield (k=3) Completion Rate (k=11) Adenoma Detection Rate (k=7) False Negative Colonoscopy Hospitalizations Costs Quality of Bowel Preparation (k=39) Total Procedure Time (k=3) Cecal Intubation Time (k=4) Withdrawal Time (k=5) Patient Adherence (k=11)b Patient Satisfaction (k=11) b Unused Procedure Slots Delays, Rescheduling

Delays, DiagnosisIncreased Volume, ProceduresScheduler/Nurse TimeVolume of Gastric Contents (k=2)pH of Gastric Contents

Abdul-Baki 200813

Group 1: ≥ 1.5 

hours

Group 2: > 8 hours 

    

Aoun 200514

Group 1: ≥ 1.5 

hours 

Group 2: > 8 hours 

    

Arya 201315

Group 1: ≥ 2 hours 

Group 2: > 8 hours 

  

Athreya 201116

Group 1: 5-9 hours

Group 2: > 8 hours

     

Barclay 200417

Group 1: < 3 hours 

Group 2: ≥ 5 hours 

     

Bryant 201318

Group 1: 5-7.5 

hours

Group 2: > 8 hours

  

Chiu 201119

Group 1: 5-9 hours 

Group 2: >8 hours 

   

Chiu 200620

Group 1: 6-8 hours

Group 2: > 8 hours

    

Church 199821

Group 1: 5-8 hours

Group 2: > 8 hours

      

16
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Author, Year

NPO Status 

Groupsa 

Primary 

Outcomes Secondary Outcomes Intermediate Outcomes Aspiration (k=6) Rescheduled Colonoscopies (k=1) Bowel Perforation (k=1) Other Adverse Events (k=7) Diagnostic Yield (k=3) Completion Rate (k=11) Adenoma Detection Rate (k=7) False Negative Colonoscopy Hospitalizations Costs Quality of Bowel Preparation (k=39) Total Procedure Time (k=3) Cecal Intubation Time (k=4) Withdrawal Time (k=5) Patient Adherence (k=11)b Patient Satisfaction (k=11) b Unused Procedure Slots Delays, Rescheduling

Delays, DiagnosisIncreased Volume, ProceduresScheduler/Nurse TimeVolume of Gastric Contents (k=2)pH of Gastric Contents

De Salvo 200622

Group 1: 5-8 hours 

Group 2: >8 hours 

   

Di Palma 201123

Group 1: 3-9 hours

Group 2: > 8 hours

  

El Sayed 200324

Group 1: ≥ 2 hours

Group 2: > 8 hours

  

Eun 201125

Group 1: ≥ 1 hour

Group 2: > 7 hours

   

Flemming 201226

Group 1: ≥ 4 hours

Group 2: > 8 hours

     

Frommer 199727

Group 1: 3-9 hours

Group 2: > 8 hours

  

Gupta 200728

Group 1: ≥5 hours

Group 2: > 8 hours

   

Gurudu 201029

Group 1: ≥ 4 hours

Group 2: > 8 hours

   

Gurudu 201230

Group 1: ≥ 4 hours

Group 2: > 8 hours

     

Huffman 201031

Group 1: ≥ 2 hours

Group 2: > 8 hours

 

17
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Author, Year

NPO Status 

Groupsa 

Primary 

Outcomes Secondary Outcomes Intermediate Outcomes Aspiration (k=6) Rescheduled Colonoscopies (k=1) Bowel Perforation (k=1) Other Adverse Events (k=7) Diagnostic Yield (k=3) Completion Rate (k=11) Adenoma Detection Rate (k=7) False Negative Colonoscopy Hospitalizations Costs Quality of Bowel Preparation (k=39) Total Procedure Time (k=3) Cecal Intubation Time (k=4) Withdrawal Time (k=5) Patient Adherence (k=11)b Patient Satisfaction (k=11) b Unused Procedure Slots Delays, Rescheduling

Delays, DiagnosisIncreased Volume, ProceduresScheduler/Nurse TimeVolume of Gastric Contents (k=2)pH of Gastric Contents

Johanson 200732

Group 1: 2.5-4.5 

hours

Group 2: > 8 hours

   

Kao 201133

Group 1: 4-8 hours

Group 2: > 8 hours

  

Kastenberg 2001, 

200734,35

Group 1: 2-4 hours 

Group 2: > 8 hours

   

Khan 201036

Group 1: Split-dosec 

Group 2: > 8 hours

  

Koh 201137

Group 1: 1.5-3.5 

hours

Group 2: 6-8 hours

  

Kolts 199338

Group 1: Split-dosec

Group 2: > 8 hours

Group 3: > 8 hours 

  

Kössi, 200739

Group 1: ≤ 6 hours

Group 2: 6-12 hours

Group 3: ≥ 12 hours

    

LongcroftWheaton 201240

Group 1: > 3 hours

Group 2: > 5 hours

     

Manno 201241

Group 1: 2 hours 

Group 2: >8 hours

    

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Author, Year

NPO Status 

Groupsa 

Primary 

Outcomes Secondary Outcomes Intermediate Outcomes Aspiration (k=6) Rescheduled Colonoscopies (k=1) Bowel Perforation (k=1) Other Adverse Events (k=7) Diagnostic Yield (k=3) Completion Rate (k=11) Adenoma Detection Rate (k=7) False Negative Colonoscopy Hospitalizations Costs Quality of Bowel Preparation (k=39) Total Procedure Time (k=3) Cecal Intubation Time (k=4) Withdrawal Time (k=5) Patient Adherence (k=11)b Patient Satisfaction (k=11) b Unused Procedure Slots Delays, Rescheduling

Delays, DiagnosisIncreased Volume, ProceduresScheduler/Nurse TimeVolume of Gastric Contents (k=2)pH of Gastric Contents

Marmo 201042

Group 1: ≤ 2 hours

Group 2: >8 hours

   

Mathus-Vliegen 

201343

Group 1: Split-dosec

Group 2: > 8 hours

   

Matro 201044

Group 1: 4 hours

Group 2: 4 hours 

(split-dose)

         

Paoluzi 199345

Group 1: 1-2.5 

hours

Group 2: > 8 hours

  

Park 200746

Group 1: ≥ 2 hours

Group 2: > 8 hours 

     

Park 201047

Group 1: 2-5 hours

Group 2: > 8 hours

    

Parra-Blanco 

200648

Group 1: 1.7-7 

hours

Group 2: > 8 hours

    

Rex 201349

Group 1: 5-9 hours 

Group 2: > 8 hours

     

Seo 201250

Group 1: ≤ 3 hours 

Group 2: > 8 hours 

  

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Author, Year

NPO Status 

Groupsa 

Primary 

Outcomes Secondary Outcomes Intermediate Outcomes Aspiration (k=6) Rescheduled Colonoscopies (k=1) Bowel Perforation (k=1) Other Adverse Events (k=7) Diagnostic Yield (k=3) Completion Rate (k=11) Adenoma Detection Rate (k=7) False Negative Colonoscopy Hospitalizations Costs Quality of Bowel Preparation (k=39) Total Procedure Time (k=3) Cecal Intubation Time (k=4) Withdrawal Time (k=5) Patient Adherence (k=11)b Patient Satisfaction (k=11) b Unused Procedure Slots Delays, Rescheduling

Delays, DiagnosisIncreased Volume, ProceduresScheduler/Nurse TimeVolume of Gastric Contents (k=2)pH of Gastric Contents

Vanner 201151

Group 1: > 5 hours

Group 2: > 8 hours

   

Varughese 201052

Group 1: ≥ 3 hours

Group 2: > 8 hours

        

Voiosu 201353

Group 1: 1-7 hours

Group 2: > 8 hours

   

a NPO status > 8 hours indicates bowel preparation completed the night before colonoscopy but exact time of completion and time of colonoscopy not reported

b Data on patient adherence and patient satisfaction extracted only from studies using same bowel preparation substance in the study groups (k=21) c Time of morning dose or time of colonoscopy not reported

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

KEY QUESTION 1. Does the incidence of aspiration and other 

anesthesia-related harms for colonoscopy vary by NPO status or 

bowel prep timing (eg, > 6 hours, 2-6 hours, < 4 hours, and < 2 

hours)? 

Does the incidence of anesthesia-related harms by NPO status vary 

by:

A) Patient characteristics (age, race, sex, obesity, comorbidities)

B) Sedation (moderate, deep)?

Findings from Trials of Different Bowel Preparation Protocols

Aspiration Risk (Appendix C, Table 2)

Six studies reported on aspiration (sample sizes ranged from 136 to 1,345).29,31,41,43,44,52 In 5 of 

these studies no aspirations occurred during colonoscopy29,31 or during colonoscopy or within the 

30 days post-colonoscopy,43 or there were no complications related to sedation.41,52

One observational study (moderate risk of bias) reported no aspiration events in 1,345 patients.29

Bowel preparation regimens were completed either the morning of the procedure (at least 4 hours 

prior to colonoscopy) or the evening before the colonoscopy. All patients were allowed to drink 

clear liquids up to 3 hours before the procedure. 

The second study, also observational and moderate risk of bias, enrolled 301 patients.31 One 

group completed bowel preparation at least 2 hours before the procedure (mean NPO time of 5.1 

hours). The second group completed bowel preparation the evening before (mean NPO time of 

13.5 hours). No patient had “clinical evidence” of aspiration. The volume of the gastric contents 

did not differ significantly. 

One RCT used medical charts and a complications database to identify aspiration events during 

colonoscopy or in the 30 days following colonoscopy for 200 patients.43 No events were 

reported. 

The 2 studies reporting no complications related to sedation were both RCTs with enrollments of 

13652 and 33641 respectively. In the first study, with moderate risk of bias, patients in one group 

completed preparation by 10 am for an afternoon colonoscopy (1 pm or later); the other group 

completed preparation the night before the procedure.52 Both groups were allowed clear liquids 

until 10 am. In the second study, with low risk of bias, one group completed preparation 2 hours 

before the procedure and the other group completed preparation the day before.41 

One small (n=125 randomized), low risk of bias RCT reported one aspiration event requiring 

hospitalization during colonoscopy under moderate sedation.44 The patient was described as 

severely obese (BMI = 40 kg/m2) but with no other obvious risk factors for aspiration. The 

patient was assigned to consume 1 L of a bowel preparation agent 7 hours before colonoscopy 

and an additional 1 L 4 hours before. Patients in this trial were allowed clear liquids until 2.5 

hours before the procedure. The patient was hospitalized for 24 hours and treated with oral 

antibiotics for one week.

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Other Harms (Appendix C, Table 5)

Seven studies (6 moderate risk of bias, 1 low risk of bias) reported on other harms. In 4 studies, 

there were no adverse events, specifically no complications of bowel perforation or bleeding up 

to the time of leaving the endoscopy office26 or no serious adverse events.17,21,53 One of these 

studies interviewed patients 2 days post-colonoscopy,17 one recorded adverse events through 

approximately 2 hours post-colonoscopy,53 and one did not provide a timeframe.17 

Three studies reported adverse events with harms occurring in less than or equal to 1% of 

procedures. In 2 studies, there was one event in the longer NPO status group and no events in the 

shorter NPO status group.32,43 One RCT with 402 patients reported lower gastrointestinal 

bleeding post-colonoscopy in one patient (0.5%) who completed bowel preparation more than 8 

hours before colonoscopy.32 Another RCT, with 200 patients, reported severe retrosternal pain in 

one patient (1%) 3 hours after the colonoscopy. Anteroseptal infarction was diagnosed. The 

patient was in the group that had morning colonoscopies following bowel preparation completed 

the evening before.43 A third RCT, with 603 patients, reported acute pancreatitis in one patient 

(0.3%) who completed bowel preparation between 5-9 hours before colonoscopy and noncardiac chest pain in one patient (0.3%) who completed bowel preparation more than 8 hours 

before colonoscopy.49 It was unclear if these events occurred during bowel preparation, during 

colonoscopy, or post-colonoscopy. The study included follow-up visits at 24 to 48 hours, one 

week, and 4 weeks. 

Gastric Volume and Acidity (Appendix C, Table 6)

Two studies reported no difference in volume of gastric contents. In one low risk of bias RCT,

14

141 patients were assigned to complete bowel preparation the morning of and at least 1.5 hours 

prior to the procedure or the evening before the procedure. Both groups were allowed water until 

the time of the procedure. Approximately 25% of patients in each group underwent tandem 

esophagogastroduodenoscopy (EGD) and gastric volume was assessed. The second study was a 

moderate risk of bias observational study.31 The split-dose preparation group completed 

preparation by 2 hours prior to the procedure. Findings were compared to a group that completed 

bowel preparation the day before the colonoscopy; additional clear fluids were allowed “as 

desired.” EGD was performed immediately before colonoscopy for both groups. No study 

reported the acidity of the gastric contents.

Additional Studies of Aspiration during Colonoscopy

Several hospital- or population-based studies have also reported on aspiration during 

colonoscopy. However, none documented duration of NPO status prior to the colonoscopy. In a 

large database study, the incidence of aspiration requiring hospitalization during 165,527 

outpatient diagnostic colonoscopies in 100,359 Medicare patients age 66 years and older (mean 

age = 76 years) was 0.14% for patients having colonoscopy under deep sedation requiring 

anesthesia assistance (as identified by a CPT-4 code) and 0.10% for patients under moderate 

sedation without anesthesia assistance.54 A study of 23,508 outpatient colonoscopies at 3 

hospitals in Australia reported one case (0.004%) of aspiration requiring hospitalization in a 

patient undergoing colonoscopy with general anesthesia.55 A study of 3,155 colonoscopies 

performed with sedation managed by an anesthesiologist in adults at a single hospital in Italy 

reported that 0.16% of patients undergoing colonoscopy had an aspiration requiring “some 

intervention by an anesthesiologist.”56 Aspirations requiring hospitalizations were not reported. 

22
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Patients were instructed to fast according to guidelines in place at the time – clear liquids up to 2 

hours before the procedure and a light meal (toast and clear liquid) up to 6 hours before the 

procedure.

KEY QUESTION 2. What is the effect of variable timing of bowel prep 

and NPO status on the quality of the bowel preparation, diagnostic 

yield, and colonoscopy procedural quality indicators (eg, completion 

rates, adenoma detection rate, total procedure time, cecal intubation 

time and withdrawal time)?

Quality of the Bowel Preparation

Thirty-nine studies (28 RCTs, 2 CCTs, and 9 observational studies) reported on the effect of 

variable timing of bowel preparation on quality of the bowel preparation (Appendix C, Table 

3).13-30,32-53 Eleven of these studies (6 RCTs, 1 CCT, 4 observational) also reported the time prior 

to colonoscopy when water or other clear liquids were allowed, ranging from 4 hours until the 

time of the procedure.13,14,16,18,21,29,30,33,44,50,52 Although different rating scales were used to rate 

the quality of the bowel preparation, quality of the bowel preparation was consistently rated 

higher for NPO intervals of 6 hours or less compared to intervals of more than 8 hours. 

Of the 28 studies (n=11,698) that only reported timing of bowel preparation and compared 

shorter (1-6 hours) versus longer intervals (8-12 hours) between bowel preparation 

administration and colonoscopy, 21 reported significantly higher quality of bowel preparation 

with a shorter interval between preparation and colonoscopy and 7 reported no significant 

difference.

Limited data suggest that consumption of water or clear liquids, including preparation solutions, 

from 0 to 4 hours prior to colonoscopy does not affect quality of the bowel preparation. Of the 11 

studies (n=10,931) reporting timing of liquid consumption, 3 allowed water or other clear liquids 

up to the time of the procedure and 2, 1, 3, and 2 studies allowed water intake up to 2 hours, 2.5 

hours, 3 hours, and 4 hours prior to colonoscopy, respectively. Nine studies reported 

significantly higher quality rating of the preparation in the group completing bowel preparation 

less than 8 hours prior to colonoscopy (minimum NPO status based on bowel preparation of 1.5 

to 6 hours) compared to the group completing bowel preparation more than 8 hours prior to 

colonoscopy. One study reported no significant difference in quality of preparation between 

groups completing bowel preparation the morning of the colonoscopy or in a split-dose (evening 

before/morning of colonoscopy). Both groups completed bowel preparation 4 hours prior to 

colonoscopy. The remaining study reported higher quality in the shorter NPO duration group but 

no statistical analysis was possible.

Other Secondary or Intermediate Outcomes

Few studies reported other secondary or intermediate outcomes. 

Diagnostic yield (k=3) (Appendix C, Table 3; Figure 3) 

One moderate risk of bias RCT (n=121) reported a significantly higher total number of lesions 

detected in patients with who completed bowel preparation 6 to 8 hours before colonoscopy 

compared to more than 8 hours (2.8 vs 1.9, P = .03).20 No differences were noted for either 

23
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

proximal lesions or advanced lesions. All patients in this study had colon neoplasms detected 

during a previous colonoscopy. 

A second moderate risk of bias RCT (n=197) reported a significantly greater yield of flat lesions 

in patients who completed bowel preparation 1 to 7 hours before colonoscopy compared to those 

who completed preparation more than 8 hours before (22% vs 9%, P < .05); no difference were 

reported for “any polyp” (52% vs 45%) or “protruding polyps” (40% vs 42%).48

A low risk of bias RCT (n=125) reported significantly more “findings” (adenoma or cancer) per 

patient (0.70 vs 0.46, P = .047) in the group that completed bowel preparation in the morning 

compared to a group that used a split-dose protocol.44 Both groups completed the preparation 4 

hours prior to colonoscopy and were allowed clear liquids up to 2.5 hours before the procedure. 

Completion rates (k=11) (Appendix C, Table 3; Figure 3; Figure 4) 

Results from 5 RCTs providing sufficient information to permit pooling found no difference in 

completion rates between shorter and longer NPO status (RR 1.00 [95%CI 0.98, 1.01).20-22,26,34

One additional low risk of bias RCT (n=895) reported an overall completion rate of 95% but 

significantly fewer aborted procedures due to inadequate bowel preparation when the preparation 

was completed 2 hours or less before colonoscopy (93%) compared to more than 8 hours before 

colonoscopy (79%).42

A high risk of bias observational study (n=5,175) reported a significantly higher colonoscopy 

completion rate in patients completing bowel preparation 4 hours or more before colonoscopy 

(96%) compared to 8 hours or more (94%). Patients in both groups were allowed liquids until 3 

hours before the procedure.30

Another study, a low risk of bias RCT not included in the figure because both groups completed 

bowel preparation 4 hours before colonoscopy, reported no significant difference in completion 

rate between the single dose (98%) or split-dose (100%) groups.44

Three studies provided completion rates but did not report separate results for the NPO status 

groups: a moderate sized RCT,49 a moderate sized observational study,39 and a small 

observational study.51 The completion rates were 96%,39 99%,49 and 95%.51

Adenoma detection rate (k=7) (Appendix C, Table 3; Figure 3; Figure 4) 

One high risk of bias observational study (n=5,175) reported a significantly higher adenoma 

detection rate of in patients who completed bowel preparation 4 hours or more before 

colonoscopy compared to those completing preparation more than 8 hours before (32% vs 27%, 

P < .001).30 All patients in this study were allowed liquids until 3 hours prior to the procedure. 

Another observational study (n=3,079, moderate risk of bias) found significantly higher 

detection of proximal adenomas in patients who completed bowel preparation 5 to 9 hours before 

colonoscopy compared to more than 8 hours (11% vs 9%, P = .04) although overall detection did 

not differ (17% vs 15%, P = .11).19 Four studies (3 moderate risk of bias, 1 low risk of bias) 

reported no difference in detection rate between groups with shorter versus longer times between 

completion of bowel preparation and the procedure.29,40,48,52 One of the studies allowed liquids 

until 3 hours prior to the procedure.29 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

In the study comparing single dose to split-dose preparation, both completing preparation 4 hours 

before colonoscopy with liquids allowed until 2.5 hours before, the overall detection rate was 

higher in the morning-only preparation group (37% vs 25%, P = .04).44 For high-risk adenoma or 

cancer, the difference was not significantly different (13% vs 11%, P = .28). 

Total procedural time (k=3) (Appendix C, Table 4)

Total procedure time, reported in 3 studies, did not differ between groups. In one high risk of 

bias CCT (n=325) completion of bowel preparation 5 to 9 hours before the procedure was

compared to preparation the night before.16 In the second study, a moderate risk of bias RCT 

(n=136), bowel preparation was completed 3 hours or more before the procedure compared to 

more than 8 hours.52 The third study, a low risk of bias RCT (n=125), compared morning-only 

preparation to split-dose preparation.44 One of these studies allowed patients to consume clear 

fluids up to 4 hours before the procedure16 and another up to 2.5 hours before the procedure.44

The other study required all patients to be NPO after 10 am for an afternoon colonoscopy.52

Cecal intubation time (k=4) (Appendix C, Table 4)

One low risk of bias RCT (n=303) reported shorter cecal intubation time (a measure of higher 

bowel preparation and colonoscopy quality) in patients who completed bowel preparation at least 

2 hours before colonoscopy compared to more than 8 hours.46 Times did not differ in the 2 other, 

moderate risk of bias, RCTs (n=453)21,52 or the CCT (n=325)16 reporting this outcome. In one of 

the RCTs finding no difference, patients were allowed water until the time of the procedure.21

The other 2 studies (1 moderate risk of bias RCT, 1 high risk of bias CCT) allowed clear fluids 

until 4 hours before the procedure16 or required patients to be NPO after 10 am prior to an 

afternoon colonoscopy.52

Withdrawal time (k=5) (Appendix C, Table 4)

One high risk of bias observational study (n=5,175) reported a shorter withdrawal time (a 

measure of higher bowel preparation and colonoscopy quality) in patients with a time from 

completion of bowel preparation of 4 hours or greater compared to more than 8 hours (12 

minutes vs 15 minutes, P < .001).30 Patients were allowed clear liquids until 3 hours before 

colonoscopy. Three other studies (1 low risk of bias RCT, 2 moderate risk of bias RCTs, and one 

high risk of bias CCT) reporting withdrawal time found no difference between shorter and longer 

NPO intervals16,21,52 or between morning-only and split-dose preparation.44 One RCT allowed 

water until the time of the procedure, one RCT allowed clear liquids up to 2.5 hours before the 

procedure, one RCT required patients to be NPO after 10 am for an afternoon procedure, and the 

CCT allowed clear fluids until 4 hours before colonoscopy. 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Figure 3. Completion Rate, Adenoma Detection Rate, and Diagnostic Yield: Outcomes 

from Randomized Controlled Trials

Figure 4. Completion Rate and Adenoma Detection Rate: Outcomes from Observational 

Studies

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

KEY QUESTION 3. What is the effect of NPO status prior to 

colonoscopy on resource use (eg, costs, unused procedure slots, 

delays in rescheduling, delays in diagnosis, increased volume of 

procedures, scheduler and nursing time associated with cancelled or 

delayed procedures)?

One moderate risk of bias RCT reported rescheduled colonoscopies.38 The percentage of 

rescheduled colonoscopies was significantly lower (P = .011) in the group that completed bowel 

preparation on the morning of the procedure (3%) taking a split-dose of a sodium phosphate 

regimen than in groups consuming a polyethylene glycol solution (8%) or a castor oil solution 

(24%) the evening before the procedure. Differences in the bowel preparation solutions between 

groups limit our ability to draw firm conclusions about the role of NPO status on rescheduling. 

No other study reported resource use. Although some studies reported inadequate bowel 

preparation quality, they did not report whether the colonoscopy was repeated. 

KEY QUESTION 4. What is the effect of bowel preparation and NPO 

status prior to colonoscopy on patient adherence to bowel 

preparation, colonoscopy, and/or rescheduled colonoscopy and 

satisfaction with bowel preparation and/or colonoscopy?

Data are limited on the effect of bowel preparation and NPO status on patient adherence, 

colonoscopy rescheduling, and satisfaction. We extracted data on adherence and satisfaction

from studies where the same bowel preparation substance (eg, polyethylene glycol) was used for 

all patients (Appendix C, Table 4). Compared to a same-day regimen (completed the day before 

colonoscopy), a split-dose regimen was associated with greater adherence to bowel preparation 

in 4 studies13,14,41,46 with a significantly greater adherence in 2 of those studies, both low risk of 

bias RCTs.

13,14 Two studies, one low risk of bias observational study and one moderate risk of 

bias RCT, that included a dose on the day of the procedure for all patients reported better 

completion of the preparation in patients who finished the preparation closer to the time of the 

procedure (approximately 3 hours vs 5 hours or more in both studies).17,40 A third study, a low 

risk of bias observational study, reported no difference between groups completing bowel 

preparation less than 4 versus more than 4 hours prior to colonoscopy.25 Three studies, high, 

moderate, and low risk of bias RCTs, reported no difference in compliance with a split-dose 

regimen compared to a same day regimen.44,47,52 One low risk of bias RCT reported treatmentemergent adverse events leading to discontinuation of the preparation in 2 of 603 patients (0.3%) 

with no difference between the split-dose or same-day groups.49

We extracted elements of satisfaction that would be impacted by different schedules for bowel 

preparation (Appendix C, Table 4). Five studies reported on work or school time lost. Two low 

risk of bias RCTs found no difference in the percentage of patients reporting work or school time 

missed between split-dose and same-day groups.13,14 Another low risk of bias RCT reported that 

85% of the morning-only preparation group compared to 55% of the split-dose group (P = .019) 

reported no interference with work on the day before the procedure. One moderate risk of bias 

RCT reported significantly fewer hours lost form work with a split-dose regimen.28 The fourth 

study, a low risk of bias observational study, reported that completion of the bowel preparation 

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regimen closer to the time of the procedure (3 hours or more compared to 5 hours or more) 

caused less interruption of sleep.40 

Eight studies reported on sleep disturbance. Two moderate risk of bias RCTs found less sleep 

disruption in patients on a split-dose protocol28,52 and a third low risk of bias observational study 

found less sleep disruption with a protocol that required completion of the preparation regimen 

closer to the procedure time (3 hours or more compared to 5 hours or more).40 Five RCTs, 3 low 

and 1 high risk of bias, found no difference in sleep disruption between split-dose and same-day 

regimens.13,14,44,45,47 One low risk of bias observational study reported no differences in difficulty 

traveling to the colonoscopy among patients who completed the preparation fewer than 6 hours 

(3.8%), 6 to 12 hours (5.6%), or more than 12 hours (4.9%) before the procedure.39

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SUMMARY AND DISCUSSION

KEY FINDINGS AND STRENGTH OF EVIDENCE

Key Findings and Strength of Evidence 

• Hospital- or population-based studies have reported that the risk of aspiration serious 

enough to require hospitalization during colonoscopy is very low (1 in 1000 or less). 

However, these studies have not documented NPO status and it is possible that the low 

rates are driven by more individuals having longer rather than shorter NPO status. 

• In 3 RCTs and 2 observational studies (total n=2,318) comparing shorter NPO status to 

NPO status of at least 8 hours, no aspiration events were reported. Bowel preparation was 

completed at least 2 hours prior to colonoscopy in 2 studies and at least 3 hours prior to 

colonoscopy in one study. Another study allowed clear liquids up to 3 hours prior to 

colonoscopy and the remaining study only reported that bowel preparation was 

completed in the morning for an afternoon colonoscopy. 

• One small RCT (n=113) reported a significantly lower percentage of rescheduled 

colonoscopies in the split-dose group compared to 2 groups that completed preparation 

the evening before the colonoscopy, although different preparation agents were used in 

the 3 groups. No studies reported on other resource use outcomes including unused 

procedure slots or increased volume of procedures by NPO status. 

• Few studies assessing NPO status specified adverse events associated with colonoscopy 

as an outcome of interest and therefore adverse events may be underreported. 

• Time from completion of colonic preparation to colonoscopy of 1 to 6 hours is associated 

with greater bowel preparation quality than time intervals of greater than 8 hours. Of 24 

studies comparing split-dose versus non-split-dose preparation, 20 reported higher quality 

of bowel preparation with split-dose. 

• Completion rate was not significantly different between NPO status groups in 5 RCTs; 

one large observational study reported a greater completion rate with shorter NPO status. 

Results were mixed for diagnostic yield and adenoma detection rate with no consistent 

findings based on NPO status. One study reported no documented complications of 

bowel perforation; no study reported on false negative colonoscopy. 

• Among studies reporting adherence to the bowel preparation regimen, time lost from 

work, or sleep disruption, results were mixed with no clear benefit of split-dose regimens 

over same day regimens.

• Studies of NPO status typically excluded patients with serious comorbidities. 

• For our co-primary outcomes, strength of evidence was low for aspiration and 

insufficient for rescheduled colonoscopies. For secondary outcomes, strength of evidence 

was moderate for completion rate based on pooled results from 5 RCTs, low for adenoma 

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detection rate based on pooled results from 3 observational studies, and insufficient for 

diagnostic yield, bowel perforation, and false-negative colonoscopy (Appendix D). 

DISCUSSION 

Colonoscopy is now the most frequently performed procedure in the US.

57 The indications for 

colonoscopy include diagnostic evaluation of symptoms, screening, and surveillance. The goals 

of a successful colonoscopy program are safe and high-quality colonoscopic exams. Challenges 

to these goals include limited colonoscopy capacity, complexity of patient scheduling, and 

adequate bowel cleansing to ensure a high-quality exam. Quality of bowel preparation may be 

improved by administering the purgative agent closer to the time of colonoscopy, a practice 

widely adopted by the gastroenterology community in the form of split-dose preparation. 

However, optimizing bowel preparation quality needs to be balanced against potential increased 

risk of adverse events related to shorter duration of NPO status prior to colonoscopy. 

This systematic review was conducted to review the evidence on the relationship between timing 

of NPO and the incidence of aspiration and colonoscopy rescheduling. Other outcomes included 

other anesthesia-related harms, bowel preparation quality, colonoscopy quality measures, 

resource use, and patient satisfaction.

NPO Status and Aspiration Requiring Hospitalization

The most important potential risk of a shorter NPO duration is aspiration requiring 

hospitalization. The overall reported risk of aspiration events serious enough to require 

hospitalization during colonoscopy is extremely low. A population-based study in the US 

reported that between 0.1% and 0.14% of adults age 66 and older (mean = 75 years) had an 

aspiration requiring hospitalization during colonoscopy. Aspiration requiring hospitalization 

reported in adults of younger age was much lower. Although aspiration risk appears to be related 

to deep sedation, it is unknown if other factors, such as patient comorbidities, may be 

confounding that relationship. We found 5 studies (n=2,318) reporting no episodes of aspiration 

or sedation-related complications with NPO durations as low as 2 to 4 hours. One additional 

RCT (n=125) reported a single aspiration event but NPO status was 4 hours or less in both study 

groups. The “tolerable” rate of aspiration threshold for individuals undergoing an elective 

procedure that could potentially be modified by NPO status is not known. However, as with all 

procedures, adverse events will not be zero and the reported percents of aspirations requiring 

hospitalization events are of similar magnitude to other commonly accepted adverse effects of 

similar severity encountered in other procedures. Although the studies enrolled a total of 2,443 

patients, the numbers may be still too small to assess for a rare outcome such as aspiration. We 

found 7 studies assessing other harms related to colonoscopy but none of the harms were related 

to timing of NPO prior to colonoscopy. 

Gastric volume and acidity are regarded as markers of potential aspiration risk and severity. We 

found 2 studies that showed no difference in gastric volume with shorter (less than 2 hours 

before colonoscopy) versus overnight duration of NPO status prior to colonoscopy.14,31 Other 

studies of NPO status and gastric volume/pH before endoscopy or surgery also reported no 

differences. A 1996 study measured volume and pH of gastric aspirate in 88 patients undergoing 

endoscopy.58 Patients were randomly assigned to an overnight fast (both food and fluids) or 

consumption of 330 ml water at 7:30 am on the day of the procedure (with no food after 

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midnight). The mean time from the fluid intake until endoscopy was 117 minutes. There was no 

significant difference between the 2 study groups in gastric volume (12.5 ml in the fluid intake 

group, 10.0 ml in the fasting group) or pH (2.0 in both groups). A subsequent study found no 

difference in gastric volume or pH between groups of patients assigned to drink 200 ml of water 

or full fat milk 90 minutes before endoscopy.59 Similarly, a study of 126 patients scheduled for 

elective surgery with general anesthesia found no difference in gastric fluid volume or pH 

between groups of patients who drank 300 mL of clear liquid of their choice 2 hours before the 

procedure and those who continued to fast after midnight.60 These results suggest that gastric 

volume and acidity do not differ whether water or other liquids are consumed 2 hours prior to a 

procedure compared to longer NPO durations. 

It is important to note that not all aspirations are clinically significant pulmonary aspirations and 

many authors may include passive regurgitation. Warner et al61 outlined the diagnostic criteria 

for pulmonary aspirations as follows: 1) the presence of bilious secretions or particulate matter 

within the tracheo-bronchial tree by direct suctioning or by fiberoptic bronchoscopy, or 2) after 

the episode of passive regurgitation, postoperative chest radiograph demonstrated a new infiltrate 

that did not exist in the preoperative chest radiograph or on physical examination and that 

developed postoperatively within 24 hours. Using these criteria, a large population-based study 

reported a 4 year retrospective analysis (2001-2004) of perioperative pulmonary aspiration 

events.62 Of 99,441 surgical cases in adults performed with anesthesia, 14 had aspiration events 

for a rate of 1 in 7,103 or 0.014%. Ten of the 14 cases (70%) were the result of improper 

anesthesia technique. This suggests that the true risk of pulmonary aspiration may be lower than 

1 in 1000. Studies of a US Medicare population,54 outpatients from 3 hospitals in Australia,55and 

a single hospital in Italy56 provide supporting evidence. For aspiration events serious enough to 

require hospitalization, the risk may be as low as 0.01%. These risks need to be weighed against 

the benefit of shorter NPO. 

The concern shared by anesthesia providers is the risk of aspiration due to short duration 

between administration of purgative and the procedure. This concern is addressed by the 

American Society of Anesthesiology (ASA) guideline that recommends 2 hours of NPO prior to 

moderate sedation.10 Adherence to this guideline would permit use of split-dose regimens and 

reduce procedure cancellations due to patient oral ingestion at intervals greater than 2 hours prior 

to a procedure. However, based on responses from 55 VA chiefs of anesthesiology in March 

2014, anesthesiologists across VHA appear to have differing policies and practices regarding 

NPO for elective procedures. For example 38% stated they require NPO after midnight, 15% 

require NPO for 6 hours, 11% require NPO for 6 hours for food and 4 hours for clear liquids 

(including 1 liter of bowel preparation solution), 32% require NPO for 6 hours for food and 2 

hours for clear liquids (including 1 liter of bowel preparation solution), 2% require NPO for 6 

hours for food and one hour for clear liquids (including 1 liter of bowel preparation solution), 

and 4% don’t have a rule for NPO status for gastrointestinal procedures.(Personal 

Communication, Art Wallace, March 2014) 

Possible reasons for not adhering to the ASA guidelines are concerns that laxatives may not be 

treated similar to ingestion of clear liquids and that the volume of laxative may be larger than 

that of other clear liquids. Studies that evaluated ingestion of clear liquids up to 2 hours prior to 

anesthesia administration suggest that this ingestion does not affect stomach volume or pH 

compared to earlier ingestion.14,31,58-60 Other reasons for non-adherence of anesthesia providers to 

the ASA guidelines need to be explored. 

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NPO Status and Adequacy of Bowel Cleansing

For an effective and safe colonoscopy program, the adequacy of bowel cleansing is paramount. 

We found 39 studies (n=22,629) that reported the association of duration of NPO and quality of 

preparation comparing shorter (1 to 6 hours) versus longer duration (8 to 12 hours) between 

bowel preparation and colonoscopy. Thirty-one reported higher quality of bowel preparation 

with a shorter interval between preparation and colonoscopy and 8 reported no significant 

difference. 

We were most interested in studies that reported NPO of < 4 hours compared to longer durations 

of NPO, as this is likely the most commonly used duration of NPO with the newer split-dose 

bowel preparations. We found 23 studies (RCTs or observational) that compared or included 

duration of NPO of < 4 hours to longer durations (usually > 8 hours). Nineteen reported a higher 

quality preparation with shorter duration (< 4) of NPO, 3 showed no difference, and 1 did not 

report on prep quality. 

Multiple gastroenterology societies in the US and Europe have established guidelines in response 

to the recognized importance of adequate bowel preparation quality. The US Multi-Society Task 

Force on Colorectal Cancer, the European Society of Gastrointestinal Endoscopy and others5,7,63

now recommend using split-dose regimens for bowel preparation, such that the second dose of 

laxative is administered 4 to 6 hours before the colonoscopy with completion at least 2 hours 

before the exam.

Inadequate bowel preparation has multiple adverse consequences, both direct and downstream, 

that can broadly be categorized as the following: 

1) Efficacy: Inadequate bowel preparation is associated with lower adenoma detection rates 

and lower cecal intubation rates which are risk factors for missed lesions, thus reducing the 

effectiveness of colonoscopy.64,65

2) Safety: Inadequate bowel preparation is associated with increased risk of electrocautery, 

longer procedure time, and reduced patient comfort, which can reduce the safety of 

colonoscopy.66 

3) Capacity: Demand for colonoscopy is high given both screening and diagnostic 

indications, and the current capacity is inadequate to meet this demand. The VHA devotes a 

large amount of resources to improve the colonoscopic capacity and many VA facilities rely 

heavily on fee-basis and non-VA care to meet the colonoscopic capacity. Hence, maximizing 

capacity is of key importance in the VHA. Inadequate bowel preparation may reduce the 

colonoscopic capacity through cancelled procedures and resources required for rescheduling. 

Additionally, this may lead to poor patient satisfaction and delays in care. One study reported 

that for every 1% increase in inadequate bowel preparation, the cost of colonoscopy delivery 

increased by 1%.

3

 

4) Effectiveness: Inadequate bowel preparation impairs a thorough inspection of the colonic 

mucosa and results in incomplete exams. Patients with incomplete exams may never 

reschedule, or at the very least, have delayed diagnostic evaluation due to rescheduling. 

Delays in diagnostic or screening exams may reduce the effectiveness of a colonoscopy 

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program. The current VHA directive requires a colonoscopy within 60 days of a positive 

FOBT. Inadequate bowel preparation resulting in rescheduling colonoscopy may contribute 

to delays in colonoscopy. Unsatisfactory quality of cleansing also results in physicians 

recommending a repeat colonoscopy exam at a shorter interval compared to intervals 

recommended by multi-society guidelines. In one study, bowel preparations of fair quality 

were associated with more aggressive follow-up intervals in 60% of average risk 

asymptomatic individuals undergoing screening colonoscopy.67 

Furthermore, quality of bowel preparation, adenoma detection rate, and cecal intubation rate are 

proposed quality measures for colonoscopy programs, at the facility and individual level. These 

have been adopted by the Centers for Medicare & Medicaid Services (CMS) as metrics in the 

physician quality reporting system (PQRS), associated with financial incentives, and starting in 

2015, financial penalties to eligible practices.

68 

There are multiple bowel preparation agents available in the US, all with a single goal of 

achieving high quality of colon cleansing. Recent studies have focused on the different regimens 

of administration of the purgative and clearly demonstrate that, for better cleansing, splitting the 

dose, in which the laxative is split into two doses taken the day before and the day of 

colonoscopy, is superior to administering the entire laxative the night before the colonoscopy.4 A 

recent meta-analysis of 29 studies comparing split-dose regimens to night-before regimens 

reported a rate difference of 22% (95%CI 16%, 27%) in achieving better cleansing with splitdose prep.

69 The study also found that the time interval between last administration of laxative 

and colonoscopy was the main factor driving the effect. The risk difference between split and 

non-split preparation was maintained when colonoscopy was performed within 3 hours from the 

end of laxative intake, but decreased after 4 to 5 hours (risk difference 18%), and was not 

statistically significant when the time interval was >5 hours. The authors also found higher 

compliance with the split-dose regimen (risk difference 9.4%; 95%CI 0.06, 0.13) regardless of 

type of laxative.

NPO Status and Other Outcomes

We also examined the effect of variable timing of NPO on resource use, such as no-shows, 

cancellation, rescheduling, and other missed opportunities. Hypothetically, a shorter duration of 

NPO could improve capacity, if it reduced cancellations or aborted procedures due to poor 

preparation. On the contrary, a shorter duration of prep could be more difficult to adhere to, or to 

tolerate, resulting in missed appointments that would need to be rescheduled. We found one 

study (insufficient evidence) that reported fewer rescheduled colonoscopies in the shorter NPO 

status group and no studies reporting on other resource use outcomes. 

Eleven studies reported on adherence to preparation or colonoscopy. Of these, 2 reported 

significantly higher adherence to preparation regimens with NPO of ≥ 1.5 hours versus > 8 hours 

and NPO of < 3 hours versus > 8 hours respectively.13,21 The other 9 studies reported no 

difference in adherence to colonoscopy or to the preparation with variable duration of NPO. 

Patient satisfaction and willingness to repeat the preparation was higher with shorter duration of 

NPO, while less sleep loss was reported in 2 studies with NPO durations of ≥ 5 hours versus > 8 

hours and ≥ 3 hours versus > 8 hours respectively. Of note, most studies had broad time ranges 

for duration of NPO status, and we were unable to derive a mean or median estimate. 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Summary of Evidence

In summary, we found low-strength evidence that procedure-related harms, such as risk of 

aspiration or other anesthesia-related harms from colonoscopy are not related to duration of NPO 

status prior to colonoscopy (Appendix D). Aspiration requiring hospitalizations among 

individuals undergoing colonoscopy is very low (1 in 1000 or less) and consistent in magnitude 

with complications of similar severity occurring during elective procedures. It is important to 

acknowledge that in the US there are no systematic tracking methods to track complications from 

colonoscopy, especially related to NPO status, and there is the possibility of under- or misreporting. We found evidence that shorter duration of NPO status prior to colonoscopy (< 4 

hours) is associated with higher-quality bowel cleansing compared to longer duration of NPO 

prior to colonoscopy (> 8 hours). We found moderate strength evidence that shorter duration of 

NPO is not associated with higher rates of completion, and insufficient or low-strength evidence 

that shorter duration of NPO affects adenoma detection rates, diagnostic yield, or false negative 

colonoscopy (Appendix D). While there are many studies evaluating the association of bowel 

preparation quality and colonoscopy yield and quality indicators, there is limited evidence 

showing the direct relationship between duration of NPO and these outcomes. Only one study 

reported the effect of NPO status prior to colonoscopy on resource use. Results were mixed for 

patient adherence and patient satisfaction.

LIMITATIONS AND APPLICABILITY

Our findings are limited by the relative paucity of information directly addressing the key 

questions. None of the studies were directly designed to address the key questions. Instead we 

used studies that primarily evaluated the effect of different regimens on bowel preparation to 

assess the effect of varying NPO status on the outcomes of interest for this report. Except for 

bowel preparation quality, few studies reported our outcomes of interest. In fact, only 5 studies 

reported on aspiration according to NPO status and one reported on rescheduling (our co-primary 

outcomes). Most studies examining different bowel preparation and NPO status were not 

adequately powered to detect aspirations requiring hospitalizations or designed to assess 

rescheduling due to NPO status. 

Hospital- or population-based studies that reported on aspiration for individuals undergoing 

colonoscopy with sedation did not report NPO status. The largest study, and the only one 

conducted in the US, reported on patients age 66 and older (mean age 75 years). The 

applicability of results to younger individuals is uncertain, though the reported percentage may 

overestimate aspiration risk. Participants likely had wide ranges of NPO status timing, especially 

time from NPO to colonoscopy longer than 2 to 4 hours. Thus it is difficult to determine from 

these studies if and by how much aspiration risk may be effected by varying NPO status. 

Definitions of aspiration methods for diagnosing aspiration varied. We were limited to reporting 

what was provided in published articles. 

Many studies excluded patients with serious comorbidities. Few studies recorded mean or range 

of NPO status timing (including time of last ingestion of water, clear liquids, or bowel 

preparation substance). Furthermore, only 26 of 40 included studies reported on use of sedation 

during colonoscopy. 

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Populations enrolled in eligible studies were broadly applicable to many individuals undergoing 

elective colonoscopy in the United States. Eligible studies typically included patients 45 to 65 

years with approximately 50% of patients enrolled in studies done in the US. Nearly one-half of 

patients were male and two-thirds of colonoscopies were performed for cancer screening. The 

largest study reporting on aspirations requiring hospitalization was completed in a US Medicare 

population. However, aspiration by NPO status was not provided in this study and few other 

studies were adequately designed to directly assess the role of NPO status on aspirations 

requiring hospitalizations or colonoscopy rescheduling. 

RESEARCH GAPS/FUTURE RESEARCH

Our findings indicate important gaps including: 1) accurate assessment of aspiration requiring 

hospitalization and other serious anesthesia-related adverse events according to NPO status, 2) 

extent of and reasons for variation in anesthesia NPO status practice and policy, 3) effect of NPO 

status on procedure rescheduling and patient adherence and satisfaction, and 4) reasons for 

reduced patient adherence to recommendations for NPO status and bowel preparation. 

Future studies to close these knowledge gaps could improve care quality. Studies are needed that 

systematically assess duration of NPO status in relation to timing of colonoscopy and record 

serious adverse events, such as aspiration requiring hospitalization, with standardized diagnostic 

criteria. This can be done through setting up prospective registries of Veterans undergoing 

colonoscopy to record timing of preparation, duration of NPO, and sedation procedures, and then 

tracking adverse events over the next 48 to 72 hours. Reporting of anesthesia-related 

complications is required per VHA and Joint Commission policy, and most VA medical centers 

have electronic reporting systems in place. Future efforts could be directed towards developing 

standard methods to collate this information and initiate analyses to assess the association of 

duration of NPO and colonoscopy outcome. In this regard, special populations at higher risk of 

aspiration and other anesthesia-related outcomes would be of particular interest, such as elderly 

patients, patients with high comorbidities, and those with disabilities that limit ability to follow 

and complete the bowel preparation instructions. 

Future studies are also needed to determine and understand variability in NPO duration policies 

and practices across VA (especially practices that may not adhere to national society guidance 

statements) and to implement interventions to reduce variation. There is also a need to evaluate 

the effect of variable durations of NPO status prior to colonoscopy on patient satisfaction, 

adherence to colonoscopy, and impact on endoscopy scheduling processes, including delays in 

timely receipt of colonoscopy. A better understanding of why some patients do not adhere to 

NPO status recommendations and methods to improve communication and adherence are 

needed. Alternative scheduling methods, including later but same day colonoscopy, could also be 

evaluated to reduce “cancellations” due to NPO non-adherence. Colonoscopy without moderate 

or deep sedation, commonly used in other developed countries, could be offered to some 

patients, though concerns exist regarding patient comfort and colonoscopy quality. 

National and international multi-society (gastroenterology, gastrointestinal endoscopy, colon and 

rectal surgery, and gastrointestinal and endoscopic surgery) guidelines5,7,63 now recommend 

using split-dose regimens for bowel preparation, such that the second dose of laxative is 

administered 4 to 6 hours before the colonoscopy, with completion at least 2 hours before the 

exam. Additionally, the ASA guidelines support NPO of 2 hours after clear liquids.10 However, 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

there is a need for larger studies comparing shorter durations of NPO prior to colonoscopy (such 

as 2 to 4 hours) to longer intervals of NPO prior to colonoscopy (such as ≥ 6 hours) that directly 

assess for colonoscopy effectiveness (such as detection rate of adenoma and neoplasia, 

completion rate) and safety outcomes (including aspiration). We also need studies evaluating the 

effect of variable duration of NPO status prior to colonoscopy on patient satisfaction, adherence 

to colonoscopy, and impact on endoscopy scheduling processes, including delays in timely 

receipt of colonoscopy. 

Finally, evidence-based multi-society consensus guidelines are needed that bring together patient 

representatives and members from anesthesia, gastroenterology, and general medicine. 

Recommendations for NPO status also affect other gastroenterology procedures as well as 

procedures performed by other specialties (eg, pulmonary and cardiology). Therefore, including 

representatives across a wide range of disciplines and procedures would be helpful in developing 

evidence-based recommendations targeted to specific procedures and likely benefits and harms. 

Important items in guideline development include determining the “clinically important” balance 

between critical outcomes to anesthesiologists, gastroenterologists (and other specialty groups 

performing procedures), and patients, including aspiration rates due to NPO status, colonoscopy 

quality measures, resource use, and patient satisfaction and adherence. 

CONCLUSIONS

Aspiration incidence requiring hospitalization during colonoscopy with moderate or deep 

sedation is very low and on the order of magnitude commonly accepted for adverse effects of 

similar clinical importance due to other elective procedures. Participants in hospital- and 

population-based studies likely had wide ranges of timing from NPO to colonoscopy and many 

were likely longer than 2 to 4 hours. No study documenting NPO status found that shorter NPO 

status prior to colonoscopy increased aspiration risk. We did not find direct evidence of the effect 

of NPO status on colonoscopy rescheduling. Shorter time from completion of colonic 

preparation to colonoscopy is associated with greater bowel preparation quality than longer time 

intervals. 

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35. Kastenberg D, Barish C, Burack H, Dalke DD, Duckor S, Putnam W, et al. Tolerability and 

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39. Kössi J, Krekelä I, Patrikainen H, Vuorinen T, Luostarinen M, Laato M. The cleansing result 

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40. Longcroft-Wheaton G, Bhandari P. Same-day bowel cleansing regimen is superior to a splitdose regimen over 2 days for afternoon colonoscopy: results from a large prospective series. 

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41. Manno M, Pigo F, Manta R, Barbera C, Bertani H, Mirante VG, et al. Bowel preparation 

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42. Marmo R, Rotondano G, Riccio G, Marone A, Bianco MA, Stroppa I, et al. Effective bowel 

cleansing before colonoscopy: a randomized study of split-dosage versus non-split dosage 

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regimens of high-volume versus low-volume polyethylene glycol solutions. Gastrointest 

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46. Park JS, Sohn CI, Hwang SJ, Choi HS, Park JH, Kim HJ, et al. Quality and effect of single 

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47. Park SS, Sinn DH, Kim YH, Lim YJ, Sun Y, Lee JH, et al. Efficacy and tolerability of splitdose magnesium citrate: low-volume (2 liters) polyethylene glycol vs. single- or split-dose 

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2010;105(6):1319-26. 

48. Parra-Blanco A, Nicolas-Perez D, Gimeno-Garcia A, Grosso B, Jimenez A, Ortega J, et al. 

The timing of bowel preparation before colonoscopy determines the quality of cleansing, and 

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J Gastroenterol. 2006;12(38):6161-6. 

49. Rex DK, Katz PO, Bertiger G, Vanner S, Hookey LC, Alderfer V, et al. Split-dose 

administration of a dual-action, low-volume bowel cleanser for colonoscopy: the SEE 

CLEAR I study. Gastrointest Endosc. 2013;78(1):132-41. 

50. Seo EH, Kim TO, Park MJ, Joo HR, Heo NY, Park J, et al. Optimal preparation-tocolonoscopy interval in split-dose PEG bowel preparation determines satisfactory bowel 

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2012;75(3):583-90. 

51. Vanner S, Hookey LC. Timing and frequency of bowel activity in patients ingesting sodium 

picosulphate/magnesium citrate and adjuvant bisacodyl for colon cleansing before 

colonoscopy. Can J Gastroenterol. 2011;25(12):663-6. 

52. Varughese S, Kumar AR, George A, Castro FJ. Morning-only one-gallon polyethylene 

glycol improves bowel cleansing for afternoon colonoscopies: a randomized endoscopistblinded prospective study. Am J Gastroenterol. 2010;105(11):2368-74. 

53. Voiosu T, Ratiu I, Voiosu A, Iordache T, Schipor A, Baicus C, et al. Time for individualized 

colonoscopy bowel-prep regimens? A randomized controlled trial comparing sodium 

picosulphate and magnesium citrate versus 4-liter split-dose polyethylene glycol. J 

Gastrointestin Liver Dis. 2013;22(2):129-34. 

54. Cooper GS, Kou TD, Rex DK. Complications following colonoscopy with anesthesia 

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55. Viiala CH, Zimmerman M, Cullen DJE, Hoffman NE. Complication rates of colonoscopy in 

an Australian teaching hospital environment. Intern Med J. 2003;33:355-9.

56. Agostoni M, Fanti L, Gemma M, Pasculli N, Beretta L, Testoni PA. Adverse events during 

monitored anesthesia care for GI endoscopy: an 8 –year experience. Gastrointest Endosc. 

2011;74:266-75. 

57. Lieberman DA, Williams JL, Holub JL, et al. Colonoscopy utilization and outcomes 2000 to 

2011. Gastrointest Endosc. 2014;80(1):133-43. 

58. Greenfield SM, Webster GJM, Brar AS, Ah Mun K, Beck ER, Vicary FR. Assessment of 

residual gastric volume and thirst in patients who drink before gastroscopy. Gut. 

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59. Webster GJ, Bowling TE, Greenfield SM, et al. Drinking before endoscopy: milk or water? 

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60. Maltby JR, Pytka S, Watson NC, McTaggart Cowan RA, Fick GH. Drinking 300 mL of clear 

fluid two hours before surgery has no effect on gastric fluid volume and pH in fasting and 

non-fasting obese patients. Can J Anesth. 2004;51(2):111-5. 

61. Warner MA, Warner ME, Weber JG. Clinical significance of pulmonary aspiration during 

the perioperative period. Anesthesiology. 1993;78:56-82. 

62. Sakai T, Planinsic RM, Quinlan JJ, Handley LJ, Kim T-Y, Hilmi IA. The incidence and 

outcome of perioperative pulmonary aspiration in a University Hospital: a 4-year 

retrospective analysis. Anesth Analg. 2006;103:941-7. 

63. Wexner SD, Beck DE, Baron TH, et al. A consensus document on bowel preparation before 

colonoscopy: prepared by a task force from the American Society of Colon and Rectal 

Surgeons (ASCRS), the American Society for Gastrointestinal Endoscopy (ASGE), and the 

Society of American Gastrointestinal and Endoscopic Surgeons (SAGES). Gastrointest 

Endosc. 2006;63(7):894-909.

64. Corley DA, Jensen CD, Marks AR, et al. Adenoma detection rate and risk of colorectal 

cancer and death. N Engl J Med. 2014;370(14):1298-306. 

65. Kaminski MF, Regula J, Kraszewska E, et al. Quality indicators for colonoscopy and the risk 

of interval cancer. N Engl J Med. 2010;362(19):1795-803. 

66. Ladas SD, Karamanolis G, Ben-Soussan E. Colonic gas explosion during therapeutic 

colonoscopy with electrocautery. World J Gastroenterol. 2007;13(40):5295-8. 

67. Menees SB, Kim HM, Elliott EE, Mickevicious JL, Graustein BB, Schoenfeld PS. The 

impact of fair colonoscopy preparation on colonoscopy use and adenoma miss rates in 

patients undergoing outpatient colonoscopy. Gastrointest Endosc. 2013;78:510-6. 

68. Centers for Medicare & Medicaid Services. Physician Quality Reporting System/Analysis 

and Payment. Available at: http://www.cms.gov/Medicare/Quality-Initiatives-PatientAssessment-Instruments/PQRS/AnalysisAndPayment.html. Accessed 30 December 2014.

69. Bucci C, Rotondano G, Hassan C, et al. Optimal bowel cleansing for colonoscopy: split the 

dose! A series of meta-analyses of controlled studies. Gastrointest Endosc. 2014:80:566-76. 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

APPENDIX A. SEARCH STRATEGY 

Database: Ovid MEDLINE(R)

--------------------------------------------------------------------------------

1 colonoscopy/ 

2 colonic.ti,ab. 

3 (endoscop$ and (colon$ or rect$)).ti,ab. 

4 or/1-3 

5 cathartics/ or polyethylene glycols/ or phosphates/ or laxatives/ or senna extract/ or 

bisacodyl/ or cascara/ or enema/ or administration, oral/ 

6 (prepara$ or enema$ or cathart$ or (polyethylene adj glycol$) or phosphat$ or laxativ$ or 

(senna adj extract$) or bisacodyl or cascara or PEG or miralax or golytely or nulytely or 

halflytely or fleet or dulcolax or pico selax or bowel prep$ or bowel purgative or oral or 

liquid).mp. 

7 5 or 6 

8 respiratory aspiration of gastric contents/ or respiratory aspiration/ or pneumonia, aspiration/ 

or dyspnea/ or vomiting/ 

9 (emesis or vomit$ or reflux or bronchoaspirat$ or aspirat$ or quality or detection).ti,ab. 

10 8 or 9 

11 4 and 7 and 10 

12 limit 11 to yr="1990 -Current" 

13 limit 12 to English language 

14 limit 13 to humans 

15 limit 14 to ("all infant (birth to 23 months)" or "all child (0 to 18 years)" or "newborn infant 

(birth to 1 month)" or "infant (1 to 23 months)" or "preschool child (2 to 5 years)" or "child (6 to 

12 years)" or "adolescent (13 to 18 years)") 

16 limit 14 to ("all adult (19 plus years)" or "young adult (19 to 24 years)" or "adult (19 to 44 

years)" or "young adult and adult (19-24 and 19-44)" or "middle age (45 to 64 years)" or "middle 

aged (45 plus years)" or "all aged (65 and over)" or "aged (80 and over)") 

17 14 not 15 

18 16 or 17 

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

APPENDIX B. PEER REVIEW COMMENTS/AUTHOR RESPONSES

Are the objectives, scope, and methods for this review clearly described?

Yes Thank you

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Is there any indication of bias in our synthesis of the evidence?

No Thank you

No

No

No

No

No

No

No

Are there any published or unpublished studies that we may have overlooked?

Yes - Diagnostic and Therapeutic Endoscopy published online July 14, 2008 (see comments below, 

and also attachment) Complications Following Colonoscopy With Anesthesia Assistance: A PopulationBased Analysis FREE

Gregory S. Cooper, MD; Tzuyung D. Kou, PhD; Douglas K. Rex, MD 

Thank you for the suggestions. The first article is 

Schanz 2008. We have reviewed this article and 

would not include it because all three groups 

completed the prep regimen by 7 am for an 

afternoon colonoscopy. The article does not report 

aspiration or other adverse events associated with 

the colonoscopy procedure. The article is a 

comparison of prep agents, not timing.

The second article suggested is Cooper 2013 

which we have already included.

No

No

No

No

No

No

Yes - Though it seems reasonable on the face of it to restrict the review only to papers that compare 

different durations of NPO status, one could make an argument for inclusion of papers that examine the 

impact of an inadequate bowel preparation on colonoscopic findings. Though this could be considered 

indirect evidence, there is direct evidence that longer NPO status is associated with lower quality bowel 

preparation. Therefore, I believe that many key references may have been missed, especially 

concerning the impact of a poor bowel preparation on neoplasia miss rates. For example: 1) Froehlich 

As noted, the suggested references do not directly 

assess the effect of NPO status, the focus of the 

review. Froehlich 2005 and Harewood 2003 

provide no information about NPO status. Siddiqui 

2009 compared prep completed < 14 hours before 

colonoscopy to > 14 hours.

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

F, Wietlisbach V, Gonvers JJ, et al. Impact of colonic cleansing on quality and diagnostic yield of 

colonoscopy: the European Panel of Appropriateness of Gastrointestinal Endoscopy European 

multicenter study. Gastrointest Endosc 2005;61:378–384. 2) Harewood GC1, Sharma VK, de Garmo P. 

Impact of colonoscopy preparation quality on detection of suspected colonic neoplasia. Gastrointest 

Endosc. 2003 Jul;58(1):76-9. Also, 3) Siddiqui AA1, Yang K, Spechler SJ, Cryer B, Davila R, Cipher D,

Harford WV. Duration of the interval between the completion of bowel preparation and the start of 

colonoscopy predicts bowel-preparation quality. Gastrointest Endosc. 2009 Mar;69(3 Pt 2):700-6. doi: 

10.1016/j.gie.2008.09.047.

We have modified the discussion to address the 

reviewer’s point about indirect evidence.

Additional suggestions or comments can be provided below. If applicable, please indicate the 

page and line numbers from the draft report.

1. There was not any discussion regarding the risk of aspiration of the actual prep solution which was 

used for the bowel preps. In private practice, there is some amount of variability with the choice of 

preps used (sodium phosphate vs PEG) and the fact that PEG is hygroscopic, and may incite an 

ongoing inflammatory resp reaction once aspirated, whereas sodium phosphate may be more benign, 

although there does not seem to be much evidence in animal literature to support that.

2. Diagnostic and Therapeutic Endoscopy July 14, 2008 (published online) compared sodium 

phosphate to PEG and found greater patient tolerability and at least equivocal conditions for 

colonoscopy with 2PEG prep volume deliveries. For difficult, non-compliant patients, this may be a 

good option for the VA population, since this is a much lower volume fluid, and provided at least as 

good scoping conditions for most endoscopists (it was a double-blinded study).

3. In reading the actual JAMA article on complications from colonoscopy (JAMA Intern Med. 

2013;173(7):551-556. doi:10.1001/jamainternmed.2013.2908.), the authors did identify some possible 

origins of the 173 occurrences of aspiration, including a deeper plane of anesthesia with anesthesia 

providers, and higher patient morbidity, which may also affect prep potential, going along with patient 

compliance with prep instructions and ability to complete the volume load prior to the scope.

1. Discussion of individual prep agents and 

aspiration during bowel preparation were outside 

the scope of our review. 

2. Schanz 2008. As noted above, this is a 

comparison of prep agents and not timing. The 

focus of our review is a comparison of NPO status 

prior to colonoscopy.

3. We would refrain from suggesting certain 

populations may be better candidates for shorter 

NPO based on anesthesia risk, since we find such 

little evidence to support risk overall with shorter 

NPO.

My answer to the last boiler-plate Q should be "I don't know".

Additionally:

1. Only moderate and deep sedation are mentioned as far as anesthesia methods are concerned. In 

fact - most of anesthestics delivered by anesthesia teams for colonoscopies are TIVA (total intravenous 

anesthesia), i.e. general anesthesia (GA) (be it - without airway instrumentation). Per ASA document 

from 2011, the definition of GA is:

"General Anesthesia is a drug-induced loss of consciousness during which patients are not arousable, 

even by painful stimulation. The ability to independently maintain ventilatory function is often impaired. 

Patients often require assistance in maintaining a patent airway, and positive pressure ventilation may 

be required because of depressed spontaneous ventilation or drug-induced depression of 

neuromuscular function. Cardiovascular function may be impaired."

Since the goal of our intervention is to have an insensate/ amnestic and IMMOBILE patient (i.e. not 

responding with movement to painful stimulation) - what we do easily satisfies the definition of GA (and 

we code it locally as such).

2. Page 4, lines 26-29: what is the meaning of the statement "... two (studies) reported aspiration with 

no episodes"?

1. The key questions, developed with input from 

stakeholders and technical expert panel 

members, focused on moderate or deep sedation. 

We could only comment on the level of sedation 

as reported (or often not reported) in the individual 

studies.

2. Two studies reported that they were specifically 

monitoring patients for aspiration events but did 

not observe any events. We have attempted to 

clarify this statement.

3. That is correct – the stakeholders nominated 

the topic and may use the findings of the review to 

guide VA policy. As with a journal, peer reviewers 

do not have an ongoing connection to the topic.

4. Thank you.

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

3. Page 8, lines 13-19: I did not see my name among the stakeholders. As such I understand that my 

input into this project is completed.

4. I read very carefully the "executive summary" and speed-read the detailed report. It is exhaustive and 

well executed.

1. Please note that the four studies that addressed aspiration and sedation related complications did 

not include those with significant comorbidities. This is a key theme that needs to be emphasized. 

Subjects that may be at a theoretical risk for aspiration are not necessarily included in the studies 

addressing the efficacy of split dose preps.

2. Another important issue is the definition of aspiration and how it would be diagnosed. Clearly one 

could theorize that a transient episode of hypoxemia during the colonoscopy may in and of itself the 

related to an aspiration episode. However without radiographic evidence or clinical suspicion this would 

be undetected.

3. In the studies addressing gastric volume and acidity, please ensure that potential confounders such 

as the concomitant use of anti-secretary agents, antispasmodics or narcotic analgesics have been 

included in the methodology.

4. We still do not know whether deeper levels of sedation do indeed impart an increased risk for 

aspiration. According to the ASA Continuum of Sedation, we would expect this to be the case. 

5. Additionally, all cases that are performed under anesthesia assistance, please comment as to 

whether elective endotracheal intubation was performed. This would perhaps, lead to confounding by 

protecting the airway as opposed to MAC without ET intubation.

All of this needs to be discussed in the Research Gaps/Future Research section

1. This was noted in the Limitations section of the 

full report. We have also added a statement to the 

key findings in the Executive Summary.

2. Thank you – we have added a statement 

addressing this limitation in the Limitations 

section. We also updated the discussion on 

aspiration definitions and implications. Most 

clinicians would agree that aspiration needs to be 

a clinically significant event. Having said that, we 

were limited by the definition used by individual 

studies.

3. One of the studies reporting gastric volume did 

not report on the potential confounders listed. The 

other reported only that patients taking 

metoclopramide without proven gastroparesis 

were not excluded.

4. Risk of aspiration appears greater with deeper 

sedation, but we did not find enough studies to 

distinguish the harms of moderate versus deeper 

sedation prior to colonoscopy in relation to NPO. 

We have added this concern to the Research 

Gaps/Future Research section.

5. We provided information about sedation as 

reported in the published studies. Unfortunately, 

few details were provided. Furthermore, if the 

overall risk of aspiration is low, it would not be 

helpful to split it between anesthesia with or 

without endotracheal intubation. 

We have modified the Research Gaps/Future 

Research to address these concerns.

It would been better if moderate sedation, deep sedation and general anesthesia are reviewed 

separately. There is mention that aspiration rate is higher with deep sedation compare to moderate 

sedation. Would the rate be even higher with general anesthesia and how would the rate change if the 

patient was intubated versus no intubation.

The other comment is that there is not enough research to answer the questions asked.

As noted in the review, only 26 of 40 included 

studies reported on use of sedation during 

colonoscopy and few details were provided.

We agree that more research is needed.

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

The review is well written and comes to well formulated and reasonable conclusions based on the 

evidence. I would make a few minor changes. The most fundamental is the concept of low risk. To an 

anesthesiologist 0.1% risk of aspiration is not low risk. That is a significant risk.

Page 4 Line 24: I would not say “the risk of aspiration during colonoscopy is very low (1 in 1000 or 

less). If the risk is 0.1%, that is a high risk to an anesthesiologist. The risk of aspiration during general 

anesthesia for C-Section without intubation is listed as 1:200. That risk is considered, extremely high. 

The risk for general anesthesia is quoted as 1:20,000. So, 1:1000 is high.

Page 5 Line26 I would not say “Aspiration incidence during colonoscopy with moderate or deep 

sedation is very low. 0.1% is a high risk to an anesthesiologist.

Page 6 Line 39. You need to include a statement about the contents and volume of colon prep 

solutions. Colon prep solutions contain ethylene glycol which is toxic to the lung. Colon prep solutions 

may be transparent but would not be considered “clear liquids”. Moreover, the volume, 1 liter, is more 

than what is standard in NPO guidelines. 

Page 6 Line 16 If colon preps are inadequate 25% of the time, the efforts of GI docs to understand and 

correct that causes of failure: compliance, volume, diet may be more fruitful than merely having the 

prep closer to the time of anesthesia.

Page 19 Paragraph 30-38. This paragraph isn’t clear enough. There are two very separate issues. 

What is the time for NPO for clear liquids (water, clear juice) and what is the time for completing bowel 

preparations? The liquids in bowel prep solutions are very different from water. They have ethylene 

glycol. This paragraph needs to be in two parts. Time for NPO for clear liquids (water, clear juice). Then 

there needs to be a separate paragraph for Time for NPO for bowel preparation solutions. The issues 

are fundamentally separate to an anesthesiologist. Aspirating water is different from aspirating a liter of 

ethylene glycol containing salt water.

Page 20 line 9: 8 hours versus 1-7 isn’t very helpful. The range of 1-7 is too wide.

Page25 Line 13 1:1000 is not “very low”. To an anesthesiologist, 1:1000 is a serious problem.

Page 25 Line 24 The granularity of your time scale is too coarse. 1-6 hours versus 8 is not very helpful. 

How about 0-2, 2-4, 4-6? Is there a difference in 0-2, 2-4, 4-6?

Page 25 Line 19 An absence of reported complications does not imply an absence of complications. I 

am suspicious when there are no events reported. No hospitalizations after a procedure is suspicious.

Page 28 Line 34 “Many studies excluded patients with serous comorbidities. “ This sentence is critical 

to applicability. The VA patients have a high risk population with higher ages and many, many 

comorbidities.

Page 29 Paragraph 11-31 Yes. Very well stated.

Page 29 Line 35 An aspiration risk of 0.1% is NOT very low. 1:1000 is a big deal to an anesthesiologist.

Thank you. In general a 0.1% risk of an event, 

where the clinical consequences are not clear, 

would be regarded as low.

Page 4. See above

Page 5. See above

Page 6. We have added information about 

contents and volume.

Page 6. We have included the need to better 

understand patient compliance in our Research 

Gaps/Future Research section. 

Page 19. This section has been rearranged for 

clarity. No study reported on differences in quality 

of preparation between water up to the time of 

procedure vs no water. The studies that allowed 

liquids up to the time of procedure did so for all 

patients.

Page 20. Few studies provided exact times 

between completion of preparation and 

procedure. We are only able to be as precise as 

the reported information.

Page 25. See above

Page 25. There were few comparisons between 

0-2, 2-4, etc. so we are comfortable with this 

statement as written. 

Page 25. We have modified this statement to 

clarify that few studies specified adverse events 

as an outcome of interest.

Page 28. As noted above, we have added this 

statement to the key findings.

Page 29. Thank you.

Page 29. See above

46
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

This was a very high quality review. I have few comments on the methodology. Unfortunately, the 

evidence base itself was insufficient to enable a meaningful conclusion regarding the key questions 

posed. 

My comments are mostly minor:

Page 4 “Of 16 studies with NPO duration prior to colonoscopy (either bowel preparation or liquids) as 

low as 0 to 2 hours, 2 reported aspiration with no episodes.” – No episodes of what? Reported no 

episodes or did aspiration events not occur? 

Page 4 “Strength of evidence was insufficient for our primary outcomes of aspiration” – Does this mean 

the strength of evidence was insufficient for the entire meta-analysis or only for this one key question?

“ and rescheduled colonoscopy.” – Was the primary outcome rescheduling? Were there multiple 

primary outcomes? There is some confusion here between key questions (of which there can be many) 

and primary outcomes (of which there should only be one)

Page 5 – Conclusion- This is very well written and very clear

Page 6 Lines 35-37 – these are important since they define what current standards of practice are for 

NPO. Later this will factor in when reviewing the literature since few of the studies examined NPO 

status outside of these standard windows. Thus, few studies contributed to any new knowledge on this 

topic. 

Page 9 Line 26 – What scale or system was used to assess risk of bias? Please also specify at this 

point in the report what constitutes low, moderate or high risk of bias. Also, I applaud the investigators 

for not using the GRADE system. There is an increasing trend for evidence-synthesizing bodies to use 

GRADE –However, GRADE is very subjective and not an optimal system

Thank you.

Page 4. We have clarified this statement.

Page 4. Strength of evidence is evaluated for key 

outcomes. For aspiration and for rescheduled 

colonoscopies, our primary outcomes of interest, 

we found insufficient evidence. We have 

separated this into 2 bullet points to clarify. 

Although “primary” implies only one, we chose to 

designate a harm (aspiration) and a resource use 

(rescheduled colonoscopy) outcome as the key 

outcomes for the review based on input from 

stakeholders and Technical Expert Panel 

members.

Page 5. Thank you

Page 6. As noted, the guideline authors 

acknowledge that there is insufficient clinical 

evidence.

Page 9. For RCTs we used a modification of the 

Cochrane approach. For observational studies, 

we used a 3 criteria system that we developed. 

We have added information about what we 

considered low, moderate, or high risk of bias.

1) Page 11, Table 1: There appear to be errors in the row labels. Specifically, the age values appear to 

be the "range of means" not the actual range of ages. Also, the Location percentages seem to be 

incorrectly labeled. 

2) There seems to be an important gap in the analysis of the evidence with respect to the impact of an 

inadequate bowel preparation on patient outcomes. The authors do a very nice job reviewing the direct 

evidence linking NPO status with bowel preparation quality. However, while there may be limited direct 

evidence on the impact of NPO status on downstream patient outcomes, such as adenoma detection 

rate (ADR) or interval cancers, there is considerable evidence on the impact of an inadequate bowel 

preparation on these important outcomes. Recent evidence has linked the ADR to interval colorectal 

cancer incidence and mortality (Corley NEJM 2014). Since longer NPO status results in lower quality 

bowel preparation, and other studies have documented that lower quality bowel preparation is 

associated with lower rates of adenoma or polyp detection, then it would seem that this would be 

indirect evidence of lower adenoma detection with longer NPO status. This would then raise concern 

that longer NPO status will result in increased risk of interval cancer incidence and mortality. The risk of 

cancer in a VA screening colonoscopy population is between 0.5% and 1%. Among FOBT/FIT positive 

patients, it is as high as 5%. The lifetime risk of colorectal cancer is around 7% and it is estimated that 

around 5% of all cancers are now interval cancers. Most of these interval cancers are believe to be due 

1. The row labels have been corrected

2. The Discussion section has been modified to 

address the indirect evidence.

3. We have modified this statement.

4. We have modified this paragraph.

5. See above – we have modified this paragraph. 

6. We have modified the reporting of the survey 

results. 

7. The Research Gaps/Future Research section 

has been modified.

8. We have modified this paragraph.

47
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

to missed lesions during colonoscopy. Therefore, the impact of poor bowel preparation on true patient 

outcomes is more than a hypothetical concern. 

3) Page 26, line 14: The study showing higher aspiration incidence associated with deep sedation may 

be due to confounding by indication (i.e. patients at higher risk for aspiration may have anesthesia 

assistance brought in to reduce the risk). Endoscopists chose to have anesthesia assistance for any of 

a number of reasons, including significant comorbidity.

4) Page 27, line 39: The Discussion on resource implications seems incomplete. Clearly if a longer 

NPO status leads to lower quality bowel preparation, there will be important resource implications. 

Current guidelines call for repeating the exam within 1 year (Johnson et al. USMSTF Guidelines. Gastro 

2014). In many cases, the patient is asked to ingest additional bowel preparation and return the 

following day. The paper by Rex et al. discusses the cost of inadequate bowel preparation. Within the 

VA, there are many facilities that lack adequate capacity for providing colonoscopy to the Veterans who 

need it and, therefore, they send the Veterans to the community at considerable expense. Besides the 

direct financial implications, there are also direct and indirect patient costs. Moreover, some Veterans 

decline to return for a follow-up examination, increasing the risk of missed pathology (and subsequent 

increased risk of morbidity and mortality). Another key related issue is that the variable policies of 

individual anesthesiologists with respect to NPO status leads to canceled procedures. It is common 

practice at my facility for anesthesiologists to cancel a colonoscopy on the day of the procedure 

because the patient ingested bowel preparation <6 hours before the procedure even when some of 

their colleagues have a 2 hour NPO rule. This variability has resulted in our nurses advising all patients 

to ingest their preparation the night before and to be NPO for 6 hours. Therefore, our anesthesia cases 

frequently have a poor quality preparation and need to return for a repeat procedure. This exposes the 

Veteran to increased risk from repeat procedures and repeat sedation, in addition to the inconvenience 

and cost. Despite the lack of studies on this issue, these issues are commonplace in the VA and merit 

discussion. 

5) Page 27, line 42: It seems strange to hypothesize that a shorter NPO status might be more difficult to 

tolerate or adhere to when there are published meta-analyses that demonstrate that patients generally 

prefer a split-dose prep which generally requires a shorter NPO status. Which is even stated by the 

authors at line 52. 

6) Page 28: Applicability Section: It is interesting that this informal survey was included in the report. 

There is no doubt that some patients will have an aspiration event during sedation. But there are two 

major issues with presenting this information. First, related to risk: what evidence is there that a 2 hour 

NPO status would increase the risk of aspiration compared to 4 or 6 hours? The data presented from 

the EGD studies shows that there is no difference in gastric contents between shorter and longer NPO 

status. Since liquids empty very rapidly, it is unlikely that there is a clinically significant difference. 

Second, there is no consideration of the benefits of a shorter NPO status. Clearly, anesthesiologists 

focus on trying to reduce the risk of sedation-related complications. However, it is the responsibility of 

the care team (including the endoscopy AND the anesthesiologist) to consider both the risks and 

benefits of the procedure. If the colonoscopy has an inadequate bowel preparation, then there is risk of 

missed neoplasia AND risk of sedation for an inadequate examination. The authors should take a step 

back and discuss the overall risks and benefits. I suspect a survey of gastroenterologists will yield 

anecdotal reports of poor bowel preparation, interval cancers and patients who have cases canceled by 

48
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

anesthesiologists and then never show for their repeat exam. What value is added by including this 

section other than to document that anesthesiologists don't follow their own professional society 

guidelines? This variability leads to endoscopy units being held hostage by the anesthesia providers. 

7) Page 29: Research Gaps: While it would be nice to have high quality evidence to answer all 

questions in clinical practice, the reality is that this is unlikely to happen. Given that the current standard 

of care is to use split-dose bowel preparation for all colonoscopy, one might question the ethics of a 

randomized study of 2 hour vs. 6 hour NPO status. The current European guidelines state that the 

bowel preparation should be finished no more than 4 hours before the procedure begins. The USMSTF 

guidelines state that the last dose of preparation (typically 1-2 liters) should begin no more than 4-6 

hours prior to the procedure (essentially finished 2-4 hours before the procedure start time). Therefore, 

any study that requires completing the preparation more than 6 hours before the procedure is 

intentionally asking patients to expose themselves to a greater risk of a poor bowel preparation. As 

noted by the authors, there is no evidence of harm from a shorter NPO status. Therefore, it is 

questionable whether an IRB would actually approve such a study. Even if it was ethical to do such a 

study, the low risk of aspiration would suggest that a study would need tens of thousands of subjects in 

each treatment arm. Perhaps the authors should include an estimated sample size for a randomized 

study (e.g. to show a 30% increase in aspiration risk, a study would require X subjects in each arm). 

There are some patients who decline a split-dose bowel preparation and have a >6 hour NPO status. 

However, they are not randomly selected. This raises concern about bias in observational studies in an 

era of split-dose preparation. 

8) As noted by the anesthesiologist survey results, there is variable practice within the VA. As noted by 

the authors, there is no evidence that longer NPO status increases safety for colonoscopy. Can the 

authors shed any light on why the anesthesiologists believe that more than 2 hours is required despite

the ASA recommendation for 2 hours for clear liquids?

49
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

APPENDIX C. EVIDENCE TABLES 

Table 1. Study Characteristics

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Abdul-Baki 

200813

Location: 

Lebanon

Study design: 

RCT (4-way)

Funding source: 

Industry

Inclusion Criteria: ambulatory 

outpatient adults undergoing

elective colonoscopies

Exclusion Criteria: patients 

<18 years of age, presence of 

severe renal impairment, 

moderate or severe hepatic 

impairment, a history of bowel 

obstruction, known allergies 

to PEG or tegaserod

N=382

Age (yr): 55

Gender (Male %): ~61

Race (%): NR

BMI: NR

Co-existing conditions (%)

Inflammatory bowel disease: 4

Indications for colonoscopy 

(%) 

Screening: 25

Abdominal pain: 24

Changes in bowel habits: 15

Rectal bleeding: 21

Anemia: 4

Surveillance of colon 

cancer/polyps: 7

NPO status group 1a: Split-dose PEG-E with 2L 

consumed evening before and 2L day of 

colonoscopy (to be completed 2 hours before 

the procedure) + tegaserod 6 mg pills (1 tablet 

night before and one 2.5 hours before 

procedure); (n=92) 

NPO status group 1b: matched placebo (n=107)

Patients allowed regular diet until 6 pm day 

before colonoscopy and water until procedure 

time

NPO status group 2a: PEG-E consumed 

evening before colonoscopy + tegaserod 6 mg 

pills (1 tablet night before and one 1.5 hours 

before procedure) (n=94)

NPO status group 2b: matched placebo (n=89) 

Patients allowed liquid diet until 6 pm day 

before colonoscopy and water until procedure 

time

Sedation: conscious

Study withdrawals: none

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: yes, 

endoscopist, participant 

(tegaserod) 

Incomplete outcome data: 

no 

Selective outcome 

reporting: no

Risk of bias: Low

50
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Aoun 200514

Location: 

Lebanon

Study design: 

RCT

Funding source: 

None reported

Inclusion Criteria: ambulatory 

outpatient adults undergoing

elective colonoscopies

Exclusion Criteria: patients 

<18 years of age, presence of 

a severe illness (cardiac, 

renal, or

metabolic), active alcoholism, 

drug addiction, major

psychiatric illness, known 

allergies to PEG

N=141

Age (yr): 57 (range 20-84)

Gender (Male %): 57

Race (%): NR

BMI: NR

Co-existing conditions (%)

Inflammatory bowel disease: 4

Indications for colonoscopy 

(%) 

Abdominal pain: 28

Screening: 25

Changes in bowel habits: 15

Rectal bleeding: 14

Anemia: 4

Family history of colorectal

cancer: <1

NPO status group 1: PEG-E split-dose - 2L 

night prior and 2L morning; finish morning dose 

at least 1.5 hours before procedure, regular diet 

until 6:30 pm day before colonoscopy; water 

allowed up to colonoscopy (n=68) 

NPO status group 2: 4L PEG-E - 6:00 to 10:00 

pm day before procedure; liquid diet only day 

before colonoscopy; only water after midnight 

(n=73) 

Sedation: conscious

Study withdrawals: none

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: yes, 

endoscopists

Incomplete outcome data:

no 

Selective outcome 

reporting: no

Risk of bias: :Low

Arya 201315

Location: USA

Study design: 

RCT

Funding source: 

None reported

Inclusion Criteria: patients 

21–70 years of age referred 

for colonoscopy with good 

general physical status

(American Society of 

Anesthesiologists [ASA] class 

1 or 2)

Exclusion Criteria: history of 

chronic heart, liver, or kidney 

disease; hypertension,

diabetes mellitus, arthritis 

(spine, shoulder, hip and

knee joints) severe 

constipation, or concurrent 

severe diarrhea, ileus, 

suspected intestinal 

obstruction, bowel 

perforation, previous 

gastrointestinal tract surgery,

gastro-paresis, toxic colitis, 

ulcerative colitis, pregnancy, 

and lactation

N=147, 14 excluded. 133 

completed study 

(demographics based on 133)

Age (yr): 44

Gender (Male %): 38

Race (%): white 88; black 8

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%) 

Screening: 42

Rectal bleeding: 20

Mild constipation: 19

Abdominal pain: 11

Anemia: 3

Mild diarrhea: 3

NPO status group 1: Rapid-prep ShudhTM colon 

cleanse (SCC) - patients start SCC around 6 

am on morning of colonoscopy drinking 240-

480 ml every 5 minutes (total 1-2 L); last glass 

≥2 hours prior to procedure (n=74)

Day prior to colonoscopy, patients instructed to 

eat light breakfast up to 12 pm and then stay on 

clear liquids

NPO status group 2: Half-Lytely®

 colon prep 

(HCP) - 2 bisacodyl delayed-release tablets 

taken at 1 pm; patients start drinking 2L solution 

after a bowel movement or around 7 pm if no 

bowel activity occurred (n=73)

Patients stay on clear liquids entire day prior to

colonoscopy 

Sedation: NR 

Study withdrawals: 10% (n=14) excluded prior 

to procedure (no-shows)

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

unclear

Blinding: yes, 

endoscopists

Incomplete outcome data:

yes 

Selective outcome 

reporting: no

Risk of bias: Moderate

51
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Athreya 201116

Location: 

Australia

Study design: 

CCT

Funding source: 

None reported

Inclusion Criteria: elective 

colonoscopy patients

Exclusion Criteria: prior 

surgical resection, patients 

who had taken GlycoPrepTM 

(polyethylene glycol 

electrolyte) as the bowel 

preparation or those 

administered a FleetTM 

enema on arrival, and failure 

to achieve caecal intubation 

N=325

Age (yr): 57 (24-92)

Gender (Male %): 50

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%) 

Symptoms (not specified): 36

Screening: 35

Family history: 21

Family history & symptoms: 8

NPO status group 1: PM group- 2 sachets 

PicoPrep-3TM day prior and 3rd sachet 6 to 7 am 

on day of procedure; solids ceased after 8 am 

day prior; clear fluids continued until 4 hrs prior 

to procedure (n=150) 

NPO status group 2: AM group- 3 sachets 

PicoPrep-3TM day prior to procedure; solids 

ceased after 8 am day prior; clear fluids 

continued until midnight prior to procedure

(n=175) 

Sedation: conscious

Study withdrawals: none

For RCTs

Sequence generation: not 

applicable

Allocation concealment: 

inadequate (alteration)

Blinding: Investigator

Incomplete outcome data: 

no 

Selective outcome 

reporting: no 

Risk of bias: High

Barclay 200417

Location: USA

Study design: 

RCT

Funding source: 

Industry

Inclusion Criteria: ambulatory 

outpatient adults undergoing 

elective colonoscopies

Exclusion Criteria: patients 

<18 years of age, congestive 

heart failure, renal 

insufficiency (creatinine > 120 

lmol/L), ascites

N=303 randomized, 47 

excluded. 256 completed study 

(demographics based on 256)

Age (yr): medians 57-59

Gender (Male %): 45

Race (%): NR

BMI: NR

Co-existing conditions (%)

Diabetes: 9

On diuretics: 11 

Indications for colonoscopy 

(%) 

Rectal bleeding/+ FOBT: 29

Abdominal pain: 25

Screening: 23

Changes in bowel habits: 20

NPO status group 1: 3-dose regimen; aqueous

NaP day before procedure; 2nd dose 5 hours 

later; 3rd dose 3 hours before scheduled time of 

procedure (n=131) 

NPO status group 2: 2-dose regimen (n=125)

a) morning colonoscopy; aqueous NaP day 

before procedure; 2nd dose 5 hours later (same 

day)

b) afternoon colonoscopy; aqueous NaP day 

before procedure; 2nd dose 5 hours before 

scheduled time of procedure 

All patients: clear fluid diet for 24 hours before 

colonoscopy; instructed to drink 3.8L of 

commercially available carbohydrate-electrolyte 

solution during preparation period

Sedation: NR

Study withdrawals: 18% (n=47) excluded prior 

to procedure

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

not reported

Blinding: yes, 

endoscopists

Incomplete outcome data: 

yes 

Selective outcome 

reporting: no 

Risk of bias: Moderate

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Bryant 201318

Location: 

Australia

Study design: 

Retrospective 

observational 

Funding source: 

None reported

Inclusion Criteria: mostly 

outpatients (89%) undergoing 

colonoscopy

Exclusion Criteria: patients 

with a prior history of large 

bowel resection, 

colonoscopies where cecal 

intubation could not be

achieved due to an 

obstructing lesion, and 

colonoscopy reports which 

did not report on bowel 

preparation

N=1,785

Age (yr): <55 34%; ≥55 66%

Gender (Male %): 53

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%) 

Anemia/Rectal bleeding: 37

Screening: 34

Altered bowel habit: 12

Colitis: 6

Other: 11

NPO status group 1: Afternoon colonoscopies; 

prep to procedure interval 5-7.5 hrs (n=768)

a) 2L PEG at 5-7 pm day before + 2L PEG 

before 8 am day of colonoscopy

b) 2 sachets sodium picosulphate at 1 pm and 5 

pm day before + 1L PEG before 8 am day of 

colonoscopy

NPO status group 2: Morning colonoscopies; 

prep to procedure interval 8.5-17 h; (n=1,017) 

a) 4L PEG between 2 pm and 7 pm day before 

colonoscopy

b) 2 sachets sodium picosulphate at 9 am and 1 

pm day before + 1L PEG at 4 pm

All patients: low-residue diet 2 days before and 

only clear fluids 1 day before colonoscopy; fast 

for 4-6 hours before procedure

Sedation: by proceduralist using fentanyl and 

midazolam, or with propofol sedation by 

anesthetist

Study withdrawals (%): NA

1) Study design: 

retrospective

2) Population: consecutive 

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

appears to be no missing 

data

b. Were the 

characteristics of the

different NPO groups 

similar? unclear

Risk of bias: Moderate

Chiu 200620

Location: Taiwan

Study design: 

RCT

Funding source: 

None

Note: Secondary 

colonoscopy

Inclusion Criteria: patients 

who had colon neoplasms 

detected during the first 

screening colonoscopy 

Exclusion Criteria: inability to

discontinue the use of 

antiplatelet agents or 

anticoagulants, presence of 

minute polyps that had been 

removed during the screening 

colonoscopy using biopsy 

forceps, invasive cancer that 

required surgical intervention, 

failure to complete total 

colonoscopy for any reason 

at the health checkup

N=121

Age (yr): 57

Gender (Male %): 68

Race (%): NR, presumed all 

Asian 

BMI: 25

Co-existing conditions (%): NR

Indications for colonoscopy 

(%) 

Colorectal neoplasms 100

NPO status group 1: PEG-ELS; 2L between 5 

and 6 am day of colonoscopy (6-8 hr NPO 

interval) (n=61) 

NPO status group 2: PEG-ELS 2L at 8 pm 

evening before colonoscopy (13-16 hr NPO 

interval) (n=60) 

Low-fiber diet advised for two days before the 

procedure

Sedation: conscious

Study withdrawals: 3 (2%) did not ingest prep 

and were excluded

For RCTs

Sequence generation: not 

described

Allocation concealment: 

unclear (“sealed 

envelopes”)

Blinding: colonoscopist

Incomplete outcome data: 

yes 

Selective outcome 

reporting: no

Risk of bias: Moderate

53
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Chiu 201119

Location: Taiwan

Study design: 

Retrospective 

observational 

Funding source: 

In part by 

research grant 

from Department 

of Health of 

Taiwan

Inclusion Criteria: Chinese

patients age 40 to 80 years; 

received total colonoscopy; 

considered average-risk (a) 

no history CRC, adenoma, or 

IBD; b) no criteria for 

hereditary non-polyposis 

CRC, familial adenomatous 

polyposis, or other polyposis 

syndrome; c) no 1st degree 

relative with CRC; d) no 

symptoms of colorectal

malignancy [bloody stool, 

abdominal pain, change in 

body weight, or documented 

iron deficiency anemia]; e) no 

history of CRC screening 

tests within 5 yrs; and f) no 

long-term use of aspirin, nonsteroidal anti-inflammatory

drug, or a cyclooxygenase 2 

inhibitor)

Exclusion Criteria: NR

N=3,079

Age (yr): 51

Gender (Male %): 53

Race (%): Asian 100

BMI: NR (abdominal girth 

reported)

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: PEG-ELS 2L between 3 

and 4 am morning of colonoscopy (5-9 hr NPO 

interval) (n=1,552) 

NPO status group 2: PEG-ELS 2L between 8 

and 9 pm evening before colonoscopy (>8 hr 

NPO interval) (n=1,527) 

2 days before procedure, patients advised to 

start low-fiber diet; 1 day before procedure, 

patients advised to drink only clear liquids and 

avoid solid foods

Sedation: NR

Study withdrawals: None 

1) Study design: 

retrospective

2) Population: consecutive

3) Analysis of findings

a. Was the method for 

handling missing data 

reported and appropriate?

appears to be no missing 

data

b. Were the 

characteristics of the

different NPO groups 

similar? no, differences in 

abdominal girth between 

groups

Risk of bias: Moderate

Church 199821

Location: USA

Study design: 

RCT 

Funding source: 

None reported

Inclusion Criteria: ambulatory 

outpatient adults undergoing 

elective colonoscopies in the 

afternoon

Exclusion Criteria: NR

N=317

Age (yr): 60

Gender (Male %): 57

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%) 

Neoplasm follow-up: 48

Family history of CRC: 14

Symptoms (not specified): 14

Polyp on prior exam: 11

Other: 13

NPO status group 1: 4L PEG starting at 8 am 

day of procedure (n=157)

NPO status group 2: 4L PEG starting at 6 pm

evening before procedure (n=160)

All patients; liquid diet day before; after prep 

allowed water by mouth only until examination

Sedation: NR

Study withdrawals: none

For RCTs

Sequence generation: not 

described 

Allocation concealment:

not described 

Blinding: yes, 

endoscopists

Incomplete outcome data: 

no 

Selective outcome 

reporting: no

Risk of bias: Moderate

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

De Salvo 200622

Location: Italy 

Study design: 

RCT

Funding source: 

None reported

Inclusion Criteria: patients 

scheduled for colonoscopy 

who were able to follow 

cleansing regimen

Exclusion Criteria: pregnancy, 

age >75 years, previous 

operation on small/large 

bowel, renal failure, known 

electrolyte disorders, heart 

failure, liver disease with 

ascities

N=273 (demographic 

information for 265 who 

followed the cleansing 

regimen)

Age (yr): 61

Gender (Male %): 53

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: Sodium phosphate 40 mL 

at 6 pm day prior to colonoscopy and 6 am day 

of colonoscopy (≥5 hours) (n=83) 

NPO status group 2: Magnesium sulfate 15mg 

and senna 12mg in 200 mL water 5 pm day 

prior to colonoscopy (>8 hours) (n=92) 

NPO status group 3: PEG 2 L at 6 pm day prior 

to colonoscopy plus Biscodyl 4 tablets at 10 pm 

day prior to colonoscopy (>8 hours) (n=98) 

On day before colonoscopy, patients to avoid 

solid food after 12 pm; colonoscopy performed 

after 11 am

Study withdrawals: 8/273 (3%)

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

NR

Blinding: colonoscopists 

that scored bowel 

preparation

Incomplete outcome data: 

yes 

Selective outcome 

reporting: 

Risk of bias: Moderate

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NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Di Palma 201123

Location: USA

Study design: 

RCT

Funding source: 

Industry

Inclusion Criteria: adult 

outpatients undergoing 

colonoscopy for routine 

clinical indications

Exclusion Criteria: ileus or

suspected bowel obstruction, 

bowel perforation, previous

alimentary tract surgery,

significant gastroparesis or 

gastric outlet obstruction, 

toxic colitis or megacolon, 

severe ulcerative colitis or 

those pregnant or lactating

Study 1 (ITT population)

N=364

Age (yr): 56

Gender (Male %): 46

Race (%): white 86, black 9

BMI: NR

Indications for colonoscopy 

(%): NR

Study 2 (ITT population)

N=387

Age (yr): 57

Gender (Male %): 45

Race (%): white 87, black 11

BMI: NR

Indications for colonoscopy 

(%): NR

Co-existing conditions (%): 

Overall 356/787 subjects

(45%) had a history of heart 

disease, renal failure,

hypertension, and diabetes

Study 1 (split dose)

NPO status group 1a: oral sulfate solution (16 

oz + additional water) evening before 

colonoscopy; 2nd dose at approximately 6 am 

day of colonoscopy (hours unclear) (n=190) 

NPO status group 1b: 1L PEG-EA evening 

before colonoscopy and 1L approximately 6 am

day of colonoscopy (hours unclear) (n=189) 

Study withdrawals: 16/379 (4%)

Study 2 (same day)

NPO status group 2a: oral sulfate solution (total 

of 32oz + additional water) evening before 

colonoscopy (hours unclear) (n=204) 

NPO status group 2b: 2L PEG-EA evening 

before colonoscopy (hours unclear) (n=204) 

Study withdrawals: 26/408 (6%)

Sulfate preparation subjects had light breakfast 

and clear liquids for lunch and dinner; PEG-EA 

subjects had normal breakfast, light lunch, and 

clear soup or yogurt for dinner

Sedation: NR

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: colonoscopists

Incomplete outcome data: 

yes 

Selective outcome 

reporting: no 

Risk of bias: Moderate

56
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

El Sayed 200324

Location: 

Lebanon

Study design: 

RCT 

Funding source: 

None Reported

Inclusion Criteria: ambulatory 

outpatients scheduled for 

elective morning colonoscopy

Exclusion Criteria: age < 18, 

presence of serious 

conditions such as severe 

cardiac, renal or metabolic 

diseases, active alcoholism, 

drug addiction, major 

psychiatric illness; known 

allergy to PEG or bisacodyl, 

and refusal to consent to the 

study

N=187

Age (yr): 56

Gender (Male %): 56

Race (%): NR

BMI: NR

Co-existing conditions (%) 

History of surgery:

None: 95

Abdominoperineal resection: 1

Left colectomy: 2

Right colectomy: 1

Segmental colectomy: 1

Indications for colonoscopy 

(%) 

Anemia: 6

Abdominal pain: 23

Rectal bleeding: 24

Follow-up after colonic 

resection: 5

Family history of CRC: 7

Change in bowel habits: 24

Follow-up after polypectomy: 4

Positive FOBT: 3

Screening: 18

Follow-up of IBD: 5

NPO status group 1: 2L PEG at 6 pm day 

before colonoscopy; no dietary restrictions 

except for light liquid dinner before 7 pm; 5mg 

of bisacodyl at 8 pm; 1L PEG at least 2 hrs 

before colonoscopy (n=91) 

NPO status group 2: 3 Sachets of PEG in 3L of 

water beginning 6 pm (finish within 4 hrs); start 

clear liquid diet on morning of day before 

colonoscopy; fast after midnight (n=96) 

Sedation: Moderate sedation (Midazolam and 

Mepiridine)

Study withdrawals: NR

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: single-blinded 

(endoscopist)

Incomplete outcome data: 

no 

Selective outcome 

reporting: no 

Risk of bias: Low

57
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Eun 201125

Location: Korea

Study design: 

Prospective 

observational 

Funding source: 

Research Fund 

of Hanyang 

University

Inclusion Criteria: Outpatients 

aged between 18 and 80 

years scheduled for elective 

colonoscopy

Exclusion Criteria: Age<18, 

presence of serious illness 

such as severe cardiac, renal 

or metabolic disease, drug 

addiction or major psychiatric 

illness; known allergy to PEG, 

prior history of bowel 

resection and refusal of 

consent to study

N=300

Age (yr): 52

Gender (Male %): 51

Race (%): NR

BMI: 23

Co-existing conditions (%)

Chronic diseases: 32

Constipation: 11

Prior Hysterectomy: 11

Indications for colonoscopy 

(%) 

Screening: 25

Family history of CRC: 2

Surveillance: 6

Hematochezia: 12

Anemia: 3

Abdominal pain: 30

Bowel habit changes: 17

Suspicion of polyp on imaging: 

6

NPO status group 1: 4L PEG consumed over 3 

hours starting at 5 am for morning colonoscopy 

(mean time from end of prep to procedure = 3.7 

hrs) (n=149) 

NPO status group 2: Same but starting at 8 am 

for afternoon colonoscopy (mean time from end 

of prep to procedure = 4.9 hrs; P < .001 vs

group 1) (n=151)

Sedation: NR

Study withdrawals: 7 failed to reach cecum

1) Study design: 

prospective

2) Population consecutive 

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

none reported

b. Were the 

characteristics of the

different NPO groups 

similar? yes

Risk of bias: Low 

58
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Flemming 201226

Location: Canada

Study design: 

RCT

Funding source: 

University 

research unit

Inclusion Criteria: age 18 and 

older, elective colonoscopy at 

1 hospital

Exclusion Criteria: ileus or 

bowel obstruction, significant 

constipation (<3 bowel 

movements/week with or 

without regular laxatives), 

previous colorectal surgery, 

ascites, previously 

recognized renal impairment, 

active IBD, pregnancy, recent 

(<6 mos) MI or unstable 

angina

N=250 enrolled; demographic 

data for 236 (14 randomized 

but never participated because 

target numbers reached)

Age (yr): 56

Gender (Male %): 46

Race (%): NR

BMI: NR

Co-existing conditions (%)

Hypertension: 28%

Diabetes: 7%

Indications (%)

Family history CRC: 44%

Screening: 12%

History of adenoma: 18%

Positive FOBT: 6.8%

Bleeding: 6.9%

Altered bowel habits: 6.0%

Diarrhea: 3.4%

Other: 3.0%

NPO status group 1: Picosulfate, magnesium 

oxide, & citric acid (Pico-Salax); 1st dose at 7 

pm, 2nd dose 4 hrs before colonoscopy (n=119) 

NPO status group 2: Pico-Salax; 2 doses 

evening before colonoscopy (5 pm, 11 pm) 

(n=117) 

Both groups: 2 5-mg tablets bisacodyl for 2 

consecutive nights before colonoscopy; only 

clear fluids on day before colonoscopy; 

encouraged to drink 3-4 L Gatorade or similar 

evening before colonoscopy

Sedation: NR

Study withdrawals: 14 (6%); 6 split dose, 8 

evening before dose

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: endoscopists 

blinded to dosing regimen

Incomplete outcome data: 

6% withdrawals 

Selective outcome 

reporting: 

Risk of bias: Moderate

59
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Frommer 199727

Location: 

Australia

Study design: 

RCT 

Funding source: 

In part by CB 

Fleet Company 

Inc.

Inclusion Criteria: NR

Exclusion Criteria: inability to 

understand instructions, heart 

failure, pregnancy, age above 

90, raised creatinine, right 

hemicolectomy, use of 

additional agents (enemas or 

defoaming agents), a 

significant error in having 

performed cleansing 

instructions, and failure to 

reach cecum or IC valve

N=487

Age (yr): 63 

Gender (Male %): 55

Race (%): NR

BMI: NR

Co-existing conditions (%): 

Diverticulosis:3.3

Indications for colonoscopy 

(%): NR

NPO status group 1: 45 ml NaP solution at 6 

pm day before colonoscopy and 6 am on 

morning of colonoscopy (n=166)

NPO status group 2: 3L PEG at 2 pm day 

before colonoscopy (N=160)

NPO status group 3: 45ml NaP at 7 am and 7 

pm on day before colonoscopy; instructed to 

drink minimum of 800 ml water or clear fluid 

within 1 hr (n=161)

All patients: avoid foods with small seeds and 

nuts for 5 days; take 3 tablets of bisacodyl in 

afternoon two days before colonoscopy; day 

before colonoscopy no solid food/clear liquids 

throughout the day

Sedation: NR

Study withdrawals: NR

For RCTs

Sequence generation: 

unclear

Allocation concealment: 

unclear

Blinding: single blinded

Incomplete outcome data:

no 

Selective outcome 

reporting: no 

Risk of bias: Moderate

Gupta 200728

Location: India

Study design: 

RCT

Funding source: 

Not reported

Inclusion Criteria: age 

between 18 and 80

Exclusion Criteria: prior bowel 

surgery, suspected bowel 

obstruction, contraindication 

to phosphate preparation 

(cardiovascular or renal 

insufficiency); inconvenienced 

by the timing of bowel 

preparation

N=201

Age (yr): NR

Gender (Male %): NR

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NOTE: reported groups were 

comparable in terms of 

demographic data and 

indications for colonoscopy

NPO status group 1: NaP-based fluid (90 mL 

with 300 mL lemonade) at 6 am on day of 

colonoscopy (“colonoscopy preferably 

scheduled” after11 am) (n=102) 

NPO status group 2: NaP-based fluid (same) at 

5 pm day before (“timing of colonoscopy for the 

evening group was adjusted as indicated by the 

scheduled appointment list”) (n=99) 

Both groups: allowed to consume clear liquids 

(as desired) in the preceding 12 hours 

(UNCLEAR WHAT THIS MEANS)

Sedation: combination of pethidine 

hydrochloride (50mg) and midazolam (2mg) as 

an intravenous bolus unless contraindicated 

(1/2 dose for pts over 65 yrs)

Study withdrawals: None

For RCTs

Sequence generation: 

unclear

Allocation concealment: 

adequate

Blinding: investigators 

blinded to timing of prep

Incomplete outcome data: 

no 

Selective outcome 

reporting: no

Risk of bias: Moderate

60
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Gurudu 201029

Location: USA

Study design: 

Retrospective 

observational 

Funding source: 

None

Inclusion Criteria: consecutive 

afternoon colonoscopies 

(after 1 pm) from July 2008 to 

April 2009

Exclusion Criteria: None

N=1,345

Age (yr): 61 

Gender (Male %): 52

Race (%): NR

BMI: Overall NR, reported for 

poor, good prep etc.

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): 

Screening/surveillance: 61%

Anemia/bleeding: 11%

Diarrhea: 8%

Abdominal pain; 4%

Colitis: 3%

Constipation: 2%

Other: 11%

NPO status group 1: Split-dose prep

1) 4L PEG am (n=226): start 4L PEG at 5 am 

day of procedure

2) 2L PEG am (n=39): start 2L PEG + 4 tablets 

bisacodyl at 5 am day of procedure 

3) Split Dose: 2L PEG evening before 

procedure and starting at 5 am day of (n=48)

NPO status group 2: 1 day prep

1) 2L PEG pm (n=656): 2L PEG + 4 tablets 

bisacodyl day prior to procedure

2) 4L PEG pm (n=376): 4L PEG day prior 

All patients allowed drink clear liquids up to 3 

hrs before procedure

Sedation: Conscious sedation

Study withdrawals: None

1) Study design: 

retrospective 

2) Population: consecutive

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

appears to be no missing 

data

b. Were the 

characteristics of the

different NPO groups 

similar? bowel 

preparations were not 

distributed equally

(difference adjusted

statistically)

Risk of bias: Moderate

Gurudu 201230

Location: USA

Study design: 

Retrospective 

observational

Funding source: 

None

Inclusion Criteria: patients 

undergoing screening/ 

surveillance colonoscopy 

Exclusion Criteria: incomplete 

data, prior colon resection, 

and colonoscopy for 

indications of bleeding, 

anemia, IBD, repeated 

colonoscopy in same patient 

during the study after an 

initial colonoscopy detected 

adenomas was also excluded

N=5,175

Age (yr): 61 

Gender (Male %): 50

Race (%): NR

BMI: 28 

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): 

Screening and surveillance 

included only

NPO status group 1: POST-SDP - Split prep

(PEG or MoviPrep), 3L night before starting at 6 

pm and 1 L at least 4 hours before scheduled 

procedure; NPO for at least 3 hours prior to 

procedure (n=1,615)

NPO status group 2: Pre-SDP - All prep (PEG 

or MoviPrep) the night before (n=3,560) 

All patients instructed to be NPO for at least 3 

hrs before procedure

Sedation: mainly moderate, few got MAC also

Study withdrawals: NR

1) Study design: 

retrospective 

2) Population: consecutive

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

yes, all included

b. Were the 

characteristics of the

different NPO groups 

similar? yes 

Risk of bias: High

61
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Huffman 201031

Location: USA

Study design: 

Prospective 

observational 

Funding source: 

None

Inclusion Criteria: scheduled 

for EGD and colonoscopy on 

same day after split-dose 

bowel prep

Exclusion Criteria: gastric 

resection, known 

gastroparesis, or slow GE

N=301

Age (yr): 55

Gender (Male %): 41

Race (%): NR

BMI: NR

Co-existing conditions (%):

DM: 18

Opioid use:15

Metocloporamide Use: 3

Indications for colonoscopy 

(%): NR

NPO status group 1: Various split-dose bowel 

preps (PEG, NaP); complete prep by at least 2 

hrs before procedure (mean NPO = 5.1 hrs) 

(n=254) 

NPO status group 2: Various bowel preps 

(PEG, NaP) evening before (mean NPO = 13.5 

hrs) (n=47)

Sedation: NR

Study withdrawals: NR

1) Study design: 

prospective 

2) Population: not 

consecutive 

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

NR

b. Were the 

characteristics of the

different NPO groups 

similar? yes, group sizes 

and outpatient to inpatient 

ratios differed between 

groups

Risk of bias: Moderate

62
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Johanson 200732

Location: 10 

sites, USA

Study design: 

RCT 

Funding source: 

Pharmaceutical 

industry

Inclusion Criteria: males and 

non-pregnant, non-lactating 

females ≥18 years; scheduled 

for colonoscopy 

Exclusion Criteria: renal

insufficiency; serum 

electrolyte abnormalities at 

screening; uncontrolled CHF, 

unstable angina, untreated 

dysrhythmia, current use of 

digitalis preparations or 

medications known to prolong 

QT interval; MI, PTCA or 

CABG within previous 3 

months; ascites; current 

acute exacerbation of IBD; 

toxic colitis or toxic megacolon; severe chronic 

constipation; ileus; 

perforation; ileostomy; 

colostomy, hypomotility 

syndrome; gastric bypass or 

stapling; history of gastric 

retention; impaired gag reflex; 

history of aspiration; 

dysphagia; treatment with 

investigational drug or 

product; participation in drug 

study within past 30 days; 

treatment within 21 days with 

another NaP preparation; 

known allergy to NaP; or any 

other clinically significant 

disease that would expose 

the patient to increased risk 

of an adverse event

N=402

Age (yr): 56

Gender (Male %): 44

Race (%): white 86; black 10; 

other 3

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: 20 NaP tablets at 6 pm 

evening before colonoscopy and 12 tablets next 

day 3-5 hrs before colonoscopy (n=200); this 

group was allowed light breakfast day before 

colonoscopy (up to 12 noon) with no solid food 

after noon (clear liquids only)

NPO status group 2: 4 bisacodyl tablets with 

water at 12 noon day prior colonoscopy 

followed by 2L PEG taken after a bowel 

movement or a maximum of 6 hrs after 

ingestion of bisacodyl tablets (n=202); this 

group allowed only clear liquids entire day 

before colonoscpy

Sedation: Patients were sedated but type of 

sedation not reported

Study withdrawals: 1 patient withdrew; 16% 

excluded from final analysis

For RCTs

Sequence generation: not 

described

Allocation concealment: 

adequate

Blinding: single blinded

Incomplete outcome data:

16% excluded from final 

analysis

Selective outcome 

reporting: no 

Risk of bias: Moderate

63
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Kao 201133

Location: Canada

Study design: 

RCT

Funding source: 

None

Inclusion Criteria: ambulatory 

GI clinic patients between 18-

75 years who underwent 

elective outpatient 

colonoscopy

Exclusion Criteria: renal 

insufficiency, CHF, acute 

coronary syndrome recent or 

unstable angina, liver 

cirrhosis or ascites, chronic 

furosemide therapy, previous 

colon resection, and known or 

suspected bowel obstruction, 

megacolon or ileus

N= 834

Age (yr): 50

Gender (Male %): 39

Race (%): NR

BMI: NR

Co-existing conditions (%): 

NR

Indications for colonoscopy 

(%): NR

NPO status group 1: PM colonoscopy; 4 

different regimens 8-10 H before colonoscopy 

(n=287); included PEG, NaP, PicoSalax+magnesium citrate

NPO status group 2: AM colonoscopy; 4 

different prep regimens 10-14 h before 

colonoscopy (n=491) 

All patients; clear liquid diet the day before 

colonoscopy; hydrate liberally with water or 

clear electrolyte replacement solution until 2 hrs 

before procedure

Sedation: NR

Study withdrawals: None

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: single blinded

Incomplete outcome data: 

no 

Selective outcome 

reporting: no 

Risk of bias: Low

64
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Kastenberg 2001, 

200734,35

Location: 

Multiple sites, 

USA

Study design: 

RCT

Funding source: 

Pharmaceutical 

Industry

Inclusion Criteria: either 

gender, at least 18 years old, 

scheduled for colonoscopy, 

able to swallow tablets 

without difficulty, and gave 

written informed consent 

Exclusion Criteria: evidence

of acute or chronic renal 

insufficiency; cardiovascular 

disease (uncontrolled

congestive heart failure, 

unstable angina pectoris, or,

within past 3 months, PTCA, 

MI, or CABG); ascites; 

electrolyte imbalance 

(hyponatremia, 

hyperphosphatemia, or 

hypocalcemia); colon disease 

(acute exacerbation of 

chronic IBD, chronic 

constipation [<2 bowel 

movements per week for >1

year], ileus and/or acute 

obstruction, ileostomy, right 

or transverse colostomy, 

subtotal colectomy [≥50% of 

colon removed] with 

ileosigmoidostomy [patients 

with right or left 

hemicolectomy alone were 

eligible], hypomotility

syndrome, megacolon, or 

idiopathic pseudoobstruction

N=886 randomized (859 

received study product) 

Age (yr): 56

Gender (Male %): 48

Race (%): white 87, AfricanAmerican 8, Hispanic 5

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: 20 tablets NaP at 6 pm 

evening before and repeat 3-5 hrs before 

colonoscopy (n=420) 

 

NPO status group 2: 4L PEG evening before 

colonoscopy (n=425)

Sedation: NR

Study withdrawals: 1.6% (14 patients) 

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: single blinded

Incomplete outcome data: 

no 

Selective outcome 

reporting: no 

Risk of bias: Low

65
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Khan 201036

Location: USA

Study design: 

CCT

Funding source: 

Not reported

Inclusion Criteria: adults, 

scheduled for outpatient 

colonoscopy

Exclusion Criteria: NR

N=412

Age (yr): NR

Gender (Male %): NR

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: NaP tablets (n=93) or 2L 

PEG + ascorbic acid (n=64) administered by 

split-dose (exact timing unknown) (total n=157) 

NPO status group 2: 4L PEG the evening 

before (exact timing unknown) (n=255) 

Sedation: NR

Study withdrawals (%): bowel preparation 

scoring incomplete for 49/412 (12%)

For RCTs and CCTs

Sequence generation: not 

applicable

Allocation concealment: 

not described

Blinding: unclear

Incomplete outcome data: 

yes

Selective outcome 

reporting: no

Risk of bias: High

Koh 201137

Location: Korea

Study design: 

RCT

Funding source: 

University 

research fund

Inclusion Criteria: NR

Exclusion Criteria: diabetes 

mellitus, hyperthyroidism or 

hypothyroidism, taking 

prokinetic or antispasmotic 

medication, history of bowel 

resection

N=80

Age (yr): 53

Gender (Male %): 66

Race (%): NR

BMI: NR

Co-existing conditions (%): 

chronic disease 23; previous 

abdominal surgery 11

Indications for colonoscopy 

(%) 

Screening: 48

Altered bowel habit: 28

Bowel symptoms: 18

Anemia: 8

NPO status group 1: 4L PEG between 6 and 8 

am; ate lunch between 12 and 12:30 pm (n=40)

NPO status group 2: 4L PEG between 6 and 8 

am; no lunch (n=40)

All colonoscopies between 2 and 4 pm

Sedation: conscious sedation/analgesia with IV 

midazolam and pethidine titrated as required

For RCTs and CCTs

Sequence generation: 

inadequate (odd and even 

days)

Allocation concealment: 

inadequate

Blinding: endoscopists 

were blinded

Incomplete outcome data: 

no

Selective outcome 

reporting: no

Risk of bias: High

66
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Kolts 199338

Location: USA

Study design: 

RCT

Funding source: 

University 

research fund

Inclusion Criteria: consecutive 

outpatients requiring an 

elective colonoscopy

Exclusion Criteria: acute 

diverticulitis, active IBD, 

unstable cardiovascular or 

respiratory status, allergies to 

all available conscious 

sedation medications, MI or 

cerebrovascular accident in 

last 2 months, serum 

creatinine > 2.0 mg/dl, 

massive ascites, delayed 

gastric emptying

N=113

Age (yr): 54

Gender (Male %): 39 (lower % 

male in NPO group 1)

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%) 

GI bleed: 36

Polyps: 39

Anemia: 4 

Diarrhea: 9 

Constipation: 3

NPO status group 1: NaP (90ml fluid) at 6 pm 

and 6 am plus at least 36oz water 1 hour after 6 

pm dose (n=34)

NPO status group 2: 4L GoLYTELY (PEG) at 6 

pm day before (n=38)

NPO status group 3: Castor oil (60ml fluid) at 6 

pm plus at least 36oz water 1 hour after (n=41)

All patients: liquid diet day before with NPO 

after midnight

Sedation: IV sedation

For RCTs and CCTs

Sequence generation: 

unclear

Allocation concealment: 

pharmacist distributed 

preparations

Blinding: endoscopists 

were blinded

Incomplete outcome data: 

no

Selective outcome 

reporting: no

Risk of bias: Moderate

Kössi 200739

Location: USA

Study design: 

Prospective 

observational

Funding source: 

Not reported

Inclusion Criteria: consecutive 

outpatients

Exclusion Criteria: None 

reported

N=214 enrolled; demographic 

data for 204 analyzed

Age (yr): 54

Gender (Male %): 45

Race (%): NR

BMI: NR

Co-existing conditions (%)

Diverticulosis (moderate to 

severe): 11

Indications for colonoscopy 

(%): NR

Morning colonoscopies: 45 ml NaP at 7 am and 

7 pm day before colonoscopy

Afternoon colonoscopies: 45 ml NaP at 6 pm 

day before and 6 am on day of colonoscopy

Created 3 groups:

NPO status group 1: 6 hours or less between 

2nd dose of prep and colonoscopy (n=53) 

NPO status group 2: 6 to 12 hours between 2nd

dose of prep and colonoscopy (n=90)

NPO status group 3: 12 hours or more between 

2nd dose of prep and colonoscopy (n=61) 

All patients: instructed to not eat vegetables, 

berries, fruits, or bread containing seeds for 1 

wk before colonoscopy; encouraged to drink 2-3 

liters of clear liquids during bowel prep

Sedation: NR

Study withdrawals: 5% (10/214) 

1) Study design: 

prospective 

2) Population: consecutive 

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

yes

b. Were the 

characteristics of the

different NPO groups 

similar? yes

Risk of bias: Low

67
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

LongcroftWheaton 201240

Location: UK

Study design: 

Obsersvational 

(Prospective 

Cohort)

Funding source: 

None reported

Inclusion Criteria: receiving 

colonoscopy under National

Bowel Cancer Screening

Programme; age 59 to 70 

years

Exclusion Criteria: known 

renal impairment (CKD grade 

3, Creatinine>150; 

eGFR<40); congestive 

cardiac failure; sodium <130

N=227

Age (yr): median 65 (range: 

60-71)

Gender (Male %): 75

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: same-day regimen, 2 

sachets of sodium picosulphate at 7 and 10 am 

on morning of afternoon procedure; NPO <3 

hours (n=132)

NPO status group 2: 2-day regimen, pts used 3 

sachets of sodium picosulphate at noon and 5 

pm on day before and 1 at 8am on day of 

afternoon procedure; NPO 4-8 hours (n=95) 

All patients: light diet day before procedure (no 

vegetables/fruit); increase fluid intake for 24 hrs 

leading up to procedure

Sedation: NPO Status 1: 1.27, NPO Status 2: 

1.20 (Mean sedation level where 1=awake, 

2=drowsy, 3=asleep)

Study withdrawals: NR

1) Study design: 

prospective 

2) Population: consecutive 

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

appears all were included

b. Were the 

characteristics of the 

different NPO groups 

similar? yes

Note: endoscopist and 

screening nurse were 

blinded to the

preparation regimen. 

Risk of bias: Low

Manno 201241

Location: Italy

Study design: 

RCT

Funding source: 

None reported

Inclusion Criteria: 18 years of 

age or older, either a positive 

FOBT or in surveillance postpolypectomy with elective 

colonoscopy scheduled 

between 9:00 am and 1:00 

pm

Exclusion Criteria: presence 

of severe cardiac, renal or

hepatic impairment; known 

allergy or hypersensitivity to

any constituent of preparation

N=336

Age (yr): 61

Gender (Male %): 71

Race (%): NR

BMI: NR

Co-existing conditions (%) 

Prior abdominal surgery: 21

Constipation: 10

Diabetes: 4

Indications for colonoscopy 

(%) 

Positive FOBT: 70

Polypectomy follow-up: 30

NPO status group 1: 3L PEG starting at 3 pm

day before and 1L PEG over 1 hr starting 3 hrs 

before procedure (n=168)

NPO status group 2: 4L PEG over 4 hrs starting 

at 3 pm day before colonoscopy (n=168)

All patients: low fiber diet for 3 days before 

procedure

Sedation: conscious sedation

Study withdrawals: None

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: investigator 

Incomplete outcome data: 

no

Selective outcome 

reporting: no 

Risk of bias: Low

68
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Marmo 201042

Location: Italy

Study design: 

RCT

Funding source: 

None reported

Inclusion Criteria: 

“appropriate indication” to 

colonoscopy

Exclusion Criteria: pregnant 

or lactating women; age <18 

years; significant 

gastroparesis or gastric outlet 

obstruction or ileus; known or 

suspected bowel obstruction 

or perforation; 

phenylketonuria or glucose-6-

phosphate dehydrogenase 

deficiency; severe chronic 

renal failure (creatinine 

clearance <30 mL/minute); 

severe congestive heart 

failure (New York Heart 

Association class III or IV); 

dehydration; severe acute 

inflammatory disease; 

compromised swallowing 

reflex or mental status; 

uncontrolled hypertension 

(SBP >170 mm Hg, DBP

>100 mm Hg); toxic colitis; or 

megacolon

N=randomized 895 (ITT 

includes 868)

Age (yr): 58

Gender (Male %): 58 

Race (%): NR

BMI: NR

Co-existing conditions (%):

Diabetes: 5

Indications for colonoscopy 

(%): 

Symptoms: 41

Screening: 13

Surveillance: 16

Polypectomy/resection: 8

NPO status group 1: High volume (4L PEG-ES) 

or low volume (2L PEG-ES + ascorbic acid); 

half taken afternoon before, half early morning 

on day of colonoscopy (n=435) 

NPO status group 2: Same as above with doses

taken 2 hours apart starting around 6:30 pm 

evening before colonoscopy (n=433) 

All patients: low fiber diet for 3 days before 

procedure; light breakfast and lunch plus 

semiliquid dinner day before taking bowel prep; 

NPO after midnight before procedure

Sedation: NR

Study withdrawals (%):

Type of prep unknown:18 (2)

Incorrect prep 9 (1)

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: single-blind

Incomplete outcome data: 

yes (3%)

Selective outcome 

reporting: no 

Risk of bias: Low

69
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Mathus-Vliegen 

201343

Location: 

Netherlands

Study design: 

RCT

Funding source: 

NR

Inclusion Criteria: consecutive 

ambulant patients referred for 

colonoscopy; age ≥ 18; 

physically able to take bowel 

preparation at home

Exclusion Criteria: pregnant 

or lactating, inpatient, heart 

failure, severe dehydration, 

GI ulcers, hypersensitivity to 

PEG< ileus, (partial) 

colectomy, colostomy, 

phenylketonuria, glucose-6-

phosphate deficiency, 

enrolled in populationscreening program

N=200 randomized (12 did not 

receive allocated intervention); 

patients were randomized to 

PEG or PEG+ascorbate 

solution and then completed 

split-dose or single-dose prep 

based colonoscopy time

Age (yr): 60

Gender (Male %): 48

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): 

Polyp surveillance: 37

GI bleeding: 21

Changed stool pattern: 21

Familiar 

screening/surveillance: 12

Anemia: 5

IBD: 4 

NPO status group 1 (afternoon colonoscopies):

2L PEG or PEG+ascorbate solution starting at 6 

pm day before and 2L morning of procedure 

(exact time not reported) (n=89)

NPO status group 2 (morning colonoscopies):

4L PEG or PEG+ascorbate solution starting at 6 

pm evening before (n=99)

All patients: 2-day low-fiber diet recommended

Sedation: NR

Study withdrawals (%):

Did not receive allocated intervention: 6%

For efficacy outcome:

a. Failed examination: 6% of those receiving 

intervention

b. Missing data: 9% of those receiving 

intervention

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: endoscopists 

were blinded

Incomplete outcome data: 

yes (efficacy data missing 

for 20%, safety data 

missing for 6%) 

Selective outcome 

reporting: no 

Risk of bias: Moderate

70
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Matro 201044

Location: USA

Study design: 

RCT

Funding source: 

Industry

Inclusion Criteria: age ≥ 18; 

scheduled for elective, 

outpatient afternoon (12 pm 

or later) colonoscopy

Exclusion Criteria: pregnancy, 

breast feeding, known or 

suspected gastroparesis, 

chronic nausea or vomiting, 

bowel obstruction, 

hypomotility syndrome, 

severe constipation, >50% 

colon resection, known 

glucose-6-phosphate 

dehydrogenase deficiency, 

PEG allergy, significant 

psychiatric illness

N=125 randomized (9 

withdrew prior to taking prep; 1 

additional patient in AM group 

did not undergo colonoscopy) 

Age (yr): 52

Gender (Male %): 46

Race (%): NR

BMI: NR

Co-existing conditions (%): 

Diabetes: 8

Thyroid disease: 7

Hypertension: 30

GERD: 9

IBD: 4

Pulmonary disease: 4

Cardiovascular disease: 24

Indications for colonoscopy 

(%): 

Screening: 51

Surveillance: 17

Symptoms: 32

NPO status group 1 (AM prep): 1L PEG 7 hours 

before procedure and 1L 4 hours before 

procedure (n=65)

NPO status group 2 (PM/AM prep): 1L PEG + 

250 ml clear liquid at 6 pm and 1L 4 hours 

before procedure (n=60) 

All patients: low-residue breakfast before 10 am 

day before then clear liquids until 2.5 hours 

before colonoscopy (medications with sips of 

water allowed within 2.5 hours of procedure)

Sedation: monitored anesthesia with propofolbased sedation 

Study withdrawals (%): 7% did not take prep

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

adequate

Blinding: endoscopists 

were blinded

Incomplete outcome data: 

7%

Selective outcome 

reporting: no 

Risk of bias: Low

Paoluzi 199345

Location: Italy

Study design: 

RCT

Funding source: 

NR

Inclusion Criteria: NR

Exclusion Criteria: presence 

of stenosis, suspected 

perforation of the gut, colonic 

resection, pregnancy

N=160 randomized; data for 

132

Age (yr): 51

Gender (Male %): 60

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): 

IBD: 46

Cancer: 4

Polyps: 17

Haematochezia: 19

NPO status group 1: 2L PEG at 6 to 8 pm 

evening before; 1L PEG at 6 to 7 am; fast or 

clear liquids after starting prep (n=80)

NPO status group 2: 35g castor oil at 4 pm day 

before; cleansing enema evening before and 

morning of procedure; low residual semi-liquid 

diet for 2 days before exam with fast from eve 

of exam (n=80)

Colonoscopies performed 8-9:30 am

Sedation: NR

Study withdrawals: 24/160 (15%) did not 

present on day of examination; additional 4 

patients in PEG group did not complete solution 

because of side effects and did not complete 

adequacy of prep outcomes

For RCTs

Sequence generation: 

unclear

Allocation concealment: 

unclear

Blinding: endoscopists 

were blinded

Incomplete outcome data: 

17.5%

Selective outcome 

reporting: no 

Risk of bias: Moderate

71
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Park 200746

Location: Korea 

Study design: 

RCT

Funding source: 

None reported

Inclusion Criteria: consecutive 

individuals undergoing 

medical check−up 

colonoscopy at 

university−affiliated medical 

center

Exclusion Criteria: age < 18

years; serious medical 

conditions such as severe 

cardiac, renal, or metabolic 

disease; active alcoholism, 

drug addiction, or major 

psychiatric illness; known 

allergy to PEG; previous 

surgical bowel resection or 

gynecologic surgery; refusal 

of consent to participate in 

study

N=303

Age (yr): 49

Gender (Male %): 81 

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: 3L PEG between 8 and 11 

pm evening before procedure; 1L PEG early 

morning (at least 2 hours prior to procedure)

(n=152)

NPO status group 2: 4L PEG between 8 and 11 

pm evening before procedure (n=151)

Colonoscopies performed 8-9:30 am

Sedation: NR

Study withdrawals: None

For RCTs

Sequence generation: not 

described

Allocation concealment: 

not described

Blinding: Colonoscopists 

blinded, groups evenly 

allocated

Incomplete outcome data: 

no

Selective outcome 

reporting: no

Risk of bias: Low

Park 201047

Location: Korea

Study design: 

RCT

Funding source: 

No funding

Inclusion Criteria: men and 

women >18 years of age 

scheduled for colonoscopy in 

the morning

Exclusion Criteria: serious 

medical conditions such as 

severe cardiac, renal, 

hepatic, or metabolic 

diseases; active alcoholism, 

drug addiction, or major 

psychiatric illness; known 

allergy to PEG; history of 

prior colon or rectal surgery

N=285randomized (analyzed 

232)

Age (yr): 52

Gender (Male %): 63

Race (%): NR

BMI: 24

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: 2L PEG 8 pm evening 

before procedure, 2L PEG 5 am day of 

procedure (n=80)

NPO status group 2: 250 ml magnesium citrate 

8 pm evening before procedure, 2L PEG 5 am 

day of procedure (n=73)

NPO status group 3: 4L PEG 10 pm evening

before procedure (n=79) 

All patients: thick liquid diet at dinner evening 

before procedure; NPO after 6 pm

Sedation: NR

Study withdrawals: 19% (postponed or 

canceled procedure or changed to pm)

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

inadequate (an 

investigator managed the 

printed allocation 

schedule)

Blinding: investigator 

Incomplete outcome data: 

yes

Selective outcome 

reporting: no 

Risk of bias: High

72
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Parra-Blanco 

200648

Location: Spain 

Study design: 

RCT

Funding source: 

Government, 

Education

Inclusion Criteria: consecutive 

outpatients, scheduled for 

elective colonoscopy 

(morning or afternoon), age 

18-85

Exclusion Criteria:

Pregnancy, partial or total 

colectomy, IBD (known or 

suspected)

N=197 randomized, 177 

included in analysis

Age (yr): 54 

Gender (Male %): 48 

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%) 

Chronic constipation: 24

Polyp surveillance: 13

NPO status group 1: 3L PEG-ELS starting at 6 

am day of colonoscopy (n=43) (NOTE: 39.5% 

had morning colonoscopy)

NPO status group 2: 45 mL NaP 8 pm evening 

before and 45 mL 6 am day of colonoscopy

(n=45)a (NOTE: 53.3% had morning 

colonoscopy)

NPO status group 3: 3L PEG-ELS starting at 8 

pm evening before colonoscopy (n=45) (NOTE: 

68.9% had morning colonoscopy)

NPO status group 4: 45mL NaP at 3 pm and 8 

pm day before colonoscopy (n=44)a (NOTE: 

77.3% had morning colonoscopy)

Colonoscopies: 9 am to 3 pm

Patients NaP groups encouraged to drink fluids 

liberally (at least 2L) during cleansing period

All patients: received Bysacodyl (15 mg) day 

before colonoscopy and low-fiber diet 

recommended; allowed clear fluids after 

completing bowel preparation

Sedation: NR

Study withdrawals: 10 (20/197 consecutive 

outpatients initially included in the study)

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

unclear

Blinding: endoscopists 

and attending nurse 

blinded to prep regimen

Incomplete outcome data: 

yes

Selective outcome 

reporting: no

Risk of bias: Moderate

73
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Rex 201349

(SEE CLEAR I 

study)

Location: USA

Study design: 

RCT

Funding source: 

Industry

Inclusion Criteria: men and 

women, 18 to 80 years, at 

least 3 spontaneous bowel 

movements/week for 1 month 

before colonoscopy

Exclusion Criteria: acute 

abdominal conditions; active 

IBD; colon disease (including 

toxic megacolon, toxic colitis, 

idiopathic pseudo-obstruction, 

hypomotility syndrome); 

ascites; GI disorders (such as 

active ulcers, gastric outlet 

obstruction, retention, 

gastroparesis, and ileus); 

uncontrolled angina and/or MI 

within past 3 months; CHF or 

uncontrolled hypertension; 

known renal insufficiency with 

abnormal creatinine or serum 

potassium levels at 

screening; history of 

colorectal surgery or upper GI 

surgery 

Use of lithium, laxatives, 

constipating drugs, 

antidiarrheal agents, or oral 

iron preparations not allowed 

during the study

N=608 randomized; 

demographic data for 603

Age (yr): 55 (median)

Gender (Male %): 41

Race (%): white 88; 

black/African American 11

BMI: 29.5

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: P/MC; first dose in 5 oz 

water between 5 and 9 pm evening before 

followed by 40 oz clear liquid over next several 

hours; second dose in 5 oz water 5 to 9 hours 

before procedure followed by 24 oz clear liquid 

(n=305) 

NPO status group 2: 2 5-mg bisacodyl tablets 

taken in afternoon before colonoscopy; after 

first bowel movement or 6 hours 2L PEG-3550 

(n=298)

All patients limited to clear liquid diet 24 hours 

before procedure

Sedation: NR

Study withdrawals: 0.8% not treated and 

excluded; 0.7% did not complete study

For RCTs

Sequence generation: 

unclear

Allocation concealment: 

adequate

Blinding: 

gastroenterologists and 

assistants were blinded

Incomplete outcome data: 

yes (1%)

Selective outcome 

reporting: no

Risk of bias: Low

74
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Seo 201250

Location: Korea

Study design: 

Prospective 

observational 

Funding source: 

NR

Inclusion Criteria: 18 to 85 

years, outpatients

Exclusion Criteria: pregnancy, 

breastfeeding, history of 

surgical large-bowel 

resection, severe renal 

failure, drug addiction or 

major psychiatric illness, 

allergy to PEG, refusal to 

participate in study

N=366

Age (yr): 55

Gender (Male %): 48

Race (%): NR

BMI: 23

Co-existing conditions (%)

Hypertension: 14

Diabetes: 7

Stroke: 1

Liver cirrhosis: 2

Constipation: 20

Indications for colonoscopy 

(%) 

Screening: 40

Surveillance: 17

Symptoms: 43

NPO status group 1: 2L PEG at 6 pm on day 

before, 2L PEG at least 2 hours before 

procedure (n=366) 

NPO status group 2: N/A

All patients instructed to start low fiber diet 3 

days before colonoscopy; regular diet for 

breakfast and lunch and soft diet for dinner the 

day before colonoscopy; allowed only clear 

liquids until 2 hours before colonoscopy

Sedation: NR

Study withdrawals: None

1) Study design: 

prospective 

2) Population: consecutive 

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

appears all were included

b. Were the 

characteristics the 

different NPO groups 

similar? unclear

Risk of bias: Moderate

Vanner 201151

Location: Canada

Study design: 

Prospective 

observational

Funding source: 

Internal funding 

only

Inclusion Criteria:

colonoscopy for routine 

clinical indication

Exclusion Criteria: congestive 

heart failure, renal 

insufficiency, ileus or bowel 

obstruction, previous 

colorectal surgery, ascites, 

active IBD, recent (<6 mo) MI 

or unstable angina

N=100

Age (yr): 60 

Gender (Male %): 42

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): NR

NPO status group 1: PSLX, 1st dose at 7 pm, 

2nd dose at 6 am before colonoscopy scheduled 

after 11 am (interval >5 hrs) (n=32)

NPO status group 2: PSLX 1st dose at 5 pm, 2nd

dose at 10 pm evening before colonoscopy 

scheduled before 11 am (interval >9 hrs) (n=68) 

All patients: 10 mg bisacodyl tablet at 6 pm 

days 3 and 2 before colonoscopy; low fiber diet 

5 days before colonoscopy; clear fluid diet day 

before colonoscopy; encouraged to drink 4L of 

carbohydrate electrolye sports drink on day of 

clear fluids and until leaving home for procedure

Sedation: NR

Study withdrawals: unclear; 5 incomplete 

colonoscopies (4 abdominal discomfort, 1 poor 

preparation and sigmoid stricture)

1) Study design: 

prospective 

2) Population: unclear if 

consecutive 

3) Analysis of findings 

a. Was the method for 

handling missing data 

reported and appropriate?

appears all were included

b. Were the 

characteristics the 

different NPO groups 

similar? unclear

Risk of bias: Moderate

75
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study/Region/

Funding Source Inclusion/Exclusion Criteria

Patient Characteristics 

(expressed in means unless 

otherwise noted)

NPO status groups Risk of Bias

Varughese 201052

Location: USA

Study design: 

RCT

Funding source: 

No funding

Inclusion Criteria: age > 19 

years, elective colonoscopy 

scheduled from 1 pm onward

Exclusion Criteria: history of 

colon resection, suspicion of 

bowel obstruction

N=136 randomized

Age (yr): 52

Gender (Male %): 52

Race (%): white 45; Hispanic 

49; other 6

BMI: 28.5

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): 

CRC screening: 54

Diagnostic/therapeutic: 46

NOTE: study terminated early 

- interim analysis showed 

larger effect size than 

anticipated

NPO status group 1: 1 gallon PEG between 6 

am and 10 am day of colonoscopy (interval >3 

hrs) (n=68) 

NPO status group 2: 1 gallon PEG between 5 

pm and 9 pm day before colonoscopy (interval 

>16 hrs) (n=68)

Group 1 was allowed breakfast on day before 

colonoscopy followed by clear liquids for lunch 

and dinner; Group 2 advised to take only clear 

liquid on day before colonoscopy

Both groups allowed clear liquids the morning of 

the procedure with NPO after 10 am

Sedation: Meperidine+midazolam (32%); 

monitored anesthesia care (68%)

Study withdrawals: None

For RCTs

Sequence generation: 

adequate

Allocation concealment: 

unclear

Blinding: yes, 

endoscopists were blinded

Incomplete outcome data: 

no 

Selective outcome 

reporting: no

Risk of bias: Moderate

Voiosu 201353

Location: 

Romania

Study design: 

RCT 

Funding source: 

NR

Inclusion Criteria: clear 

indication for colonoscopy, 

age >18 years

Exclusion Criteria: refusal to 

sign consent or preference for 

a specific bowel prep product, 

stenosing colorectal cancer or 

intestinal obstruction, 

previous colonic resection, 

severe concomitant disease 

(heart, renal or liver failure; 

pulmonary disease; 

electrolyte imbalance; 

neuropsychiatric conditions)

N=181 randomized (patient 

characteristics for n=165)

Age (yr): 60

Gender (Male %): 54

Race (%): NR

BMI: NR

Co-existing conditions (%): NR

Indications for colonoscopy 

(%): 

Rectal bleeding: 24

CRC screening: 18

Diarrhea: 14

Anemia: 10

Constipation: 7

Abdominal pain: 7

Referral for polypectomy: 6

Other: 16

NPO status group 1: 2L PEG at 5 to 7 pm day 

before and 2L PEG at 5 to 7 am day of 

colonoscopy (n=94 randomized, 95 analyzed) 

NPO status group 2: P/MC 1st dose at 1 pm, 2nd

dose at 7 pm day before colonoscopy (plus 250 

ml fluid/hour between1 and 11 pm) (n=87 

randomized, 80 analyzed)

Colonoscopies: 8 am to 2 pm

Sedation: propofol at 1 center, midazolam at 1 

center

Study withdrawals: 9.6% of group 1, 8.0% of 

group 2 

For RCTs

Sequence generation: 

unclear

Allocation concealment: 

adequate

Blinding: endoscopists 

were blinded 

Incomplete outcome data: 

yes 

Selective outcome 

reporting: no

Risk of bias: Moderate

76
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

AE = adverse event; CRC = colorectal cancer; DBP = diastolic blood pressure; FOBT = fecal occult blood test; hrs = hours; IBD = inflammatory bowel disease; L 

= liter(s); MI = myocardial infarction; CHF = congestive heart failure; NaP = sodium phosphate; PEG = polyethylene glycol; PEG-E or PEG-ELS = polyethylene 

glycol electrolyte solution; P/MC or PSLX = sodium picosulfate and magnesium citrate; SBP = systolic blood pressure

a Patients with co-morbid conditions (chronic renal failure, symptomatic ischemic heart disease, congestive heart failure, hypertension with poor pharmacological 

control) allocated to NaP groups were given PEG-ELS instead (Group 2 followed Group 1 protocol, Group 4 followed Group 3 protocol) and evaluated on an 

intention-to-treat analysis

77
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Table 2. Primary Outcomes

Study

NPO Status 

(Intervention/

Control)

Aspiration,

n/N (%)

Rescheduled colonoscopies,

n/N (%)

NPO group 1 NPO group 2 NPO group 1 NPO group 2 

Gurudu 201029

NPO status 1: ≥ 4 

hours

NPO status 2: > 8 

hours

No episodes of bronchoaspiration were 

recorded, including in the procedures 

performed in patients taking same-day bowel 

preparation

NR NR

Huffman 201031

NPO status 1: ≥ 2 

hours 

NPO status 2: > 8

hours

None of the patients in any group had clinical 

evidence of aspiration during their procedures NR NR

Kolts 199338

NPO status 1:

Hours unclear (last 

dose 6 am)

NPO status 2: 

> 8 hours

NPO status 3: 

> 8 hours

NR 1/34 (3%)

Group 2: 3/38 (8%) 

Group 3: 10/41 

(24%) 

(P = .011)

Manno 201241

NPO status 1: 2 

hours

NPO status 2: 

> 8 hours

No major complications related to sedation NR NR

Mathus-Vliegen 

201343

NPO status 1: 

Hours unclear (Splitdose, PM exam)

NPO status 2: 

> 8 hours

No events during 30-day period (from charts of 

patients and a complication database) NR NR

Matro 201044

NPO status 1: 

4 hours (am prep 

only)

NPO status 2:

4 hours (pm/am prep)

1.6 (1/62)

Aspirated during 

procedure

0/54 NR NR

Varughese 201052

NPO status 1: ≥ 3 

hours

NPO status 2: > 8 

hours

No sedation complications NN NR

NPO = nil per os; NR = not reported

Bowel preparation completed the day before colonoscopy designated as NPO status > 8 hours

78
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Table 3. Procedural Outcomes

Study

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Abdul-Baki 

200813

NPO status 1: 

≥ 1.5 hours 

NPO status 2: 

> 8 hours

Excellent

45 (90/199)

Excellent/Good

89 (177/199)

(Sharma et al.)

Excellent

9 (16/183)

Excellent/Good

43 (78/183);

P < .001

NR NR NR NR NR NR NR NR

Aoun 200514

NPO status 1:

≥ 1.5 hours

NPO status 2: 

> 8 hours

Excellent

44 (30/68)

Excellent/Good

76 (52/68)

(Sharma et al.)

Excellent

6 (4/73) 

P < .001

Excellent/Good

56 (41/73) 

P = .01

NR NR NR NR NR NR NR NR

Arya 201315

NPO status 1: 

≥ 2 hours

NPO status 2: 

> 8 hours 

Success 

(Grade A+B)

91 (59/65)

Grade A

57 (37/65)

(Author scale)

Success 

(Grade A+B)

97 (66/68)

P = NS

Grade A

72 (49/68)

NR NR NR NR NR NR NR NR

Athreya 201116

NPO status 1: 

5-9 hours 

NPO status 2: 

> 8 hours 

Satisfactory

Rectum

91 (136/150)

Sigmoid

87 (130/150)

Descending

68 (102/150)

Transverse

57 (86/150)

Ascending

47 (70/150)

(Author scale)

Satisfactory

Rectum

92 (161/175)

P = .52

Sigmoid

92 (161/175)

P = .15

Descending

82 (143/175)

P = .005

Transverse

73 (128/175)

P = .002

Ascending

62 (108/175)

P = .007

NR NR NR NR NR NR NR NR

79
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Barclay 200417

NPO status 1: 

< 3 hours 

NPO status 2:

≥ 5 hours

Excellent/Good

89

(116/130)

(Author scale)

Excellent/Good

morning

60 (n NR)

P < .0001 vs

NPO status 1 

Excellent/Good

afternoon (split)

76 (n NR)

P = .03 vs.NPO 

status 1

NR NR NR NR NR NR NR NR

Bryant 201318

NPO status 1: 

5-7.5 hours

NPO status 2: 

> 8 hours 

Satisfactory/

good 

preparation

89 (684/768)

(Author scale)

Satisfactory/

good 

preparation

86 (873/1017)

P = .04

NR NR NR NR NR NR NR NR

80
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Chiu 201119

NPO status 1: 

5-9 hours 

NPO status 2: 

> 8 hours

Excellent

13 (197/1552)

Good

60 (930/1552)

(Aronchick et 

al.)

Excellent

3 (38/1527)

P < .001

Good

32 (481/1527)

P < .001

NR NR NR NR

Overall

17

(270/1552

) 

proximal

11

(175/1552

) 

Advanced

overall

4 

(68/1552)

proximal

2 

(34/1552)

Nonpolypoid

overall

6 

(98/1552)

Proximal

5 

(71/1552)

Advanced

2 

(25/1552)

Overall

15

(233/1527)

P = .11

proximal

9 

(138/1527)

P = .04

Advanced

overall

3 (46/1527)

P = .04

proximal

2 (25/1527)

Nonpolypoid

overall

4 (67/1527)

P = .02

Proximal

3 (40/1527)

P = .004

Advanced

1 (12/1527

NR NR

Chiu 200620

NPO status 1: 

6-8 hours 

NPO status 2: 

> 8 hours

Note: lesions 

detected in first 

and second 

colonoscopies

Adequate

93 (56/60)

(Sharma et al.)

Adequate

72 (42/58)

P < .0001

Total 

lesions

2.78 (0.29)

Proximal 

1.52 (0.22)

Advanced

0.87 (0.13)

Total 

lesions

1.90 (0.27)

P = .028

Proximal 

0.97 (0.24)

P = .094

Advanced

0.55 (0.10)

P = .056

100

(60/60)

100

(58/58) NR NR NR NR

81
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Church 199821

NPO status 1: 

5-8 hours

NPO status 2:

> 8 hours

Excellent

Cecum

62 (97/157)

Ascending

66 (103/157)

Transverse

65 (102/157)

Left colon

59 (93/157)

Excellent/Good

Cecum

90 (142/157)

Ascending

93 (148/157)

Transverse

97 (152/157)

Left colon

93 (148/157)

(Author scale)

Excellent

Cecum

9 (14/160)

Ascending

9 (14/160)

Transverse

9 (15/160)

Left colon

11 (18/160)

Excellent/Good

Cecum

73 (117/160)

Ascending

76 (121/160)

Transverse

82 (131/160)

Left colon

83 (132/160)

P < .01 for all 

groups

NR NR 97

(152/157)

99

(159/160)

P = NS

NR NR NR NR

De Salvo 200622

NPO status 1: 

5-8 hours (NaP) 

NPO status 2a: 

> 8 hours 

(MgSO4) 

NPO status 2b:

> 8 hours (PEG) 

Good

67 (53/79)

(Author scale)

Good

MgSO4

39 (35/90)

P < .001

PEG 

50 (48/96)

P = .02

NR NR 98

(77/79)

MgSO4

97

(86/90)

PEG 

96

(92/96)

P = NS

NR NR NR NR

Di Palma 201123

NPO status 1: 

3-9 hours; 2 arms, 

sulfate and PEGEA

NPO status 2: 

> 8 hours; 2 arms, 

sulfate and PEGEA)

Success

Sulfate

97 (175/181)

PEG-EA 

97 (175/183)

Excellent

Sulfate

63 (114/181)

PEG-EA 

53 (96/53)

(Author scale)

Success

Sulfate

82 (159/194)

PEG-EA 

80 (155/193)

P < .001 for 

both arms

Excellent

Sulfate

45 (86/194)

PEG-EA 

37 (72/193)

NR NR NR NR NR NR NR NR

82
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

El Sayed 200324

NPO status 1: 

≥ 2 hours

NPO status 2: 

> 8 hours

Excellent

39 (35/91)

Satisfactory

83 (75/91)

(Church)

Excellent

19 (18/96)

P = .005 

Satisfactory

69 (66/96)

P < .05

NR NR NR NR NR NR NR NR

Eun 201125

NPO status 1: 

≤ 4 hours

NPO status 2: 

> 4 hours 

(Analysis by PC 

time with hourly 

intervals from ≤2 

hours to >7 hours)

Ottawa

3.49 (2.11) 

(Rostom et al.)

Ottawa

4.10 (2.45) 

P = .02

NR NR NR NR NR NR NR NR

Flemming 201226

NPO status 1: 

≥ 4 hours

NPO status 2: 

> 8 hours 

Ottawa

4.05 (2.37) 

(Rostom et al.)

Excellent/good

94 (107/114)

(Aronchick et 

al.)

Ottawa

5.51 (2.74)

P < .001

Excellent/good 

67 (74/110)

P < .001

NR NR 96

(114/119) 

95 

(111/117) 

P = NS

NR NR NR NR

Frommer 199727

NPO status 1: 

3-9 hours

NPO status 2: 

> 8 hours, 2 arms 

Cleanliness/

Visibility Score

4.11 (0.67)

(Author scale)

Arm 1:

3.34 (0.97)

Arm 2: 

3.22 (0.85) 

Both P < .0005 

vs NPO 1

NR NR NR NR NR NR NR NR

Gupta 200728

NPO status 1:

≥ 5 hours 

(morning)

NPO status 2: 

> 8 hours

(evening before)

Ottawa

4.7 (2.8)

(Rostom et al.)

Excellent/good

36 (37/102)

(Aronchick et 

al.)

Ottawa

4.7 (2.9)

P = .87

Excellent/good

35 (35/99)

NR NR NR NR NR NR NR NR

Gurudu 201029

NPO status 1: 

≥ 4 hours

NPO status 2: 

> 8 hours 

Good or excellent cleansing for 

same day preps (NPO status 1)

compared to previous day (NPO 

status 2):

OR 3.42 (1.81, 6.47); P < .001

(Aronchick et al., modified)

NR NR NR NR

OR 1.17 [95%CI 0.94, 

1.45] for same day vs

prior day prep dosing NR NR

83
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Gurudu 201230

NPO status 1: 

≥ 4 hours

NPO status 2: 

> 8 hours 

Excellent/good

54 (871/1615)

(Aronchick et 

al., modified)

Excellent/good

35 (1241/3560)

P < .001

NR NR

96

(1542/

1615)

94

(3346/

3560)

P = .008

32

(514/

1615)

27

(951/

3560)

P < .001

NR NR

Huffman 201031

NPO status 1: 

≥ 2 hours

NPO status 2: 

> 8 hours

NR NR NR NR NR NR NR NR NR NR

Johanson 200732

NPO status 1: 

2.5-4.5 hours

NPO status 2: 

> 8 hours

Excellent

64 (132/205)

Excellent/good

90 (184/205)

Overall score

1.5 (0.74)

(Aronchick et 

al.)

Excellent

39 (80/206)

Excellent/good

82 (169/206)

Overall score

1.8 (0.76)

P < .0001

NR NR NR NR NR NR NR NR

Kao 201133

NPO status 1: 

4-8 hours

NPO status 2: 

> 8 hours 

Total Score: 

PEG 4L 2.59

PEG+B 3.08;

NaP 3.51

PSMC+M 2.82

(Rostom et al.)

Total scorePEG 4.14

PEG+B 3.51 

NaP 5.37

PSMC+M 3.84

NR NR NR NR NR NR NR NR

Kastenberg 2001, 

200734,35

NPO status 1: 

2-4 hours

NPO status 2: 

> 8 hours

Mean score

1.75 (0.75)

Excellent/Good

84 (354/420)

(Aronchick et 

al.)

Mean score

1.81 (0.82)

P = .1175

Excellent/Good

77 (326/425)

P = .006

NR NR 98 

(420/427)

98 

(425/432) NR NR NR NR

Khan 201036

NPO status 1: 

Hours unclear 

(Split-dose) 

NPO status 2: 

> 8 hours 

No bowel 

content seen or 

clear lavage 

and >50% 

visualization

89%

(Lai et al.)

70% 

P < .0001 NR NR NR NR NR NR NR NR

84
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Koh 201137

NPO status 1: 

1.5-3.5 hours

NPO status 2: 

6-8 hours

Ottawa Scale 

(mean)

5.61 (2.54)

Ottawa Fluid

0.72 (0.58)

Ottawa Scale 

(mean)

5.08 (2.31)

P = .58

Ottawa Fluid 

0.58 (0.67)

P = .55

NR NR NR NR NR NR NR NR

Kolts 199338

NPO status 1:

Hours unclear 

(last dose 6 am)

NPO status 2: 

> 8 hours

NPO status 3: 

> 8 hours

Excellent or 

Good: 80%

(Author scale)

Group 2

Excellent or 

Good: 64% 

P < .05

Group 3

Excellent or 

Good: 32%

P < .05

NR NR NR NR NR NR NR NR

Kössi 200739

NPO status 1: 

≤ 6 hours 

NPO status 2: 

6-12 hours 

NPO status 3: 

≥ 12 hours 

Group 1

4.00 (0.12)

(Frommer) 

Group 2

3.56 (0.12)

P= .023 vs Gr 1

Group 3

2.64 (0.14)

P = .0001 vs

Gr 1 and Gr 2

NR NR

95.8% completion; no 

failure was related to 

bowel cleansing

NR NR NR NR

LongcroftWheaton 201240

NPO status 1: 

> 3 hours

NPO status 2: 

> 5 hours

Excellent

46.9

(38.7-55.5)

Overall better 

cleansing in 

NPO group 1 

(P = .0046)

(Chilton et al.)

Excellent

49.5

(39.6-59.4)

NR NR NR NR 71

(94/132)

62(59/95)

P = .2 NR NR

Manno 201241

NPO status 1: 

2 hours

NPO status 2: 

> 8 hours

Excellent

68 (115/168)

Excellent/good 

(Adequate)

95 (160/168)

(Di Palma et 

al.)

Excellent

38 (63/168)

P < .001

Excellent/good 

(Adequate)

98 (156/168)

NR NR NR NR NR NR NR NR

85
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Marmo 201042

NPO status 1: 

≤ 2 hours

NPO status 2:

> 8 hours

Excellent/ 

Good

75 (327/435)

(Rostom et al.)

Excellent/ 

Good

43 (186/433)

P < .001

NR NR

Overall 

completion: 

95%

Aborted 

procedures

93 

(402/432)

Aborted 

procedures

79 

(339/430)

P < .0001

NR NR NR NR

Mathus-Vliegen 

201343

NPO status 1: 

Hours unclear 

(Split-dose, PM 

exam)

NPO status 2: 

> 8 hours

Adequate

98%

(Aronchick ≤2)

93%

(Ottawa ≤7)

Adequate

99%; P = NS

(Aronchick ≤2)

87%; P = NS

(Ottawa ≤7)

NR NR NR NR NR NR NR NR

Matro 201044

NPO status 1: 

4 hours (am prep 

only)

NPO status 2:

4 hours (pm/am 

prep)

Excellent/good

92%

Fair/poor

8%

(Author scale)

Excellent/good

94%

Fair/poor

6%

P = .01 for noninferiority

“Findings” 

per patient

0.70 (1.3)

“Findings” 

per patient

0.46 (1.0)

P = .047

98

(60/61) 100 (54/54)

Low risk

adenoma

23 (14/60)

High risk

adenoma

12 (7/60)

Cancer 

2 (1/60)

Low risk

15 (8/54)

High risk

9 (5/54)

Cancer 

2 (1/54)

P = .038 

overall

NR NR

Paoluzi 199345

NPO status 1: 

1-2.5 hours

NPO status 2: 

> 8 hours

Excellent/

adequate

84 (51/61)

(Author scale)

Excellent/

adequate

63 (45/71)

P < .05

NR NR NR NR NR NR NR NR

Park 200746

NPO status 1:

≥ 2 hours

NPO status 2:

> 8 hours

Ottawa Scale

Good

5.9 (2.6)

79 (119/151)

(Rostom et al.)

Ottawa Scale

Good

8.5 (2.5)

76 (116/152)

P = .60

NR NR NR NR NR NR NR NR

86
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Park 201047

NPO status 1: 

2-5 hours (PEG)

NPO status 2: 

2-5 hours (Mg 

citrate

NPO status 3: 

> 8 hours 

Excellent

PEG 

25 (20/80)

Mg citrate

34 (25/73)

Excellent/good

PEG 

76 (61/80)

Mg citrate

75 (55/73)

(Aronchick et 

al.)

Excellent

18 (14/79)

Excellent/good

51 (40/79

P < .01 versus 

both groups

NR NR NR NR NR NR NR NR

Parra-Blanco 

200648

NPO status 1: 

1.5-7 hours (PEG) 

NPO status 2: 

1.5-7 hours (NaP) 

NPO status 3: 

> 8 hours (PEG)

NPO status 4: 

> 8 hours (NaP)

Excellent/Good

PEG 

79 (33/43)

NaP

80 (36/45)

(Author scale)

Excellent/Good

PEG 

27 (12/45)

P < .001

NaP

7 (3/44)

P < .001

Groups

1 & 2

Any polyp 

52 (46/88)

Flat lesions

22 (19/88)

Protruding 

polyps

40 (35/88)

Groups

3 & 4

Any polyp 

45 (40/89)

Flat lesions

9 (8/89)

P = .02

Protruding 

polyps

42 (37/89)

NR NR

Histological confirmation 

for 83 (152/183) polyps

70 (107/152) were 

adenomas

NR NR

Rex 201349

NPO status 1: 

5-9 hours

NPO status 2: 

> 8 hours

Successful

84 (256/304)

(Aronchick et 

al., modified)

Ottawa scale

87 (264/304)

(Rostom et al.)

Successful

74 (221/297)

P = .003

Ottawa scale

75 (224/297)

P < .01

NR NR Overall completion rate 

was 98.7% NR NR NR NR

87
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Quality of bowel preparationa

% (n/N) or Mean (±SD)

Diagnostic yield

% (n/N) or Mean (±SD)

Completion rate

% (n/N)

Adenoma detection 

rate % (n/N)

False negative 

colonoscopies % (n/N)

NPO group 1 NPO group 2 NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO 

group 2

NPO 

group 1

NPO group 

2

NPO 

group 1

NPO 

group 2

Seo 201250

NPO status 1:

≤ 3 hours / 

NPO status 2:

> 3 hours 

Analysis by PC 

time with hourly 

intervals from ≤3 

hours to >8 hours

Ottawa Scale 

5.08 (2.17)

(0 = perfect,

14 = solid stool 

and fluid)

(Rostom et al.)

Ottawa Scale

NPO status

3-4 hrs:

4.25 (1.85)

4-5 hrs:

4.70 (2.12)

5-6 hrs:

5.11 (2.34)

6-7 hrs:

4.86 (1.85)

7-8 hrs

5.20*(1.79)

>8 hrs

5.92 (2.01)

P < .05 vs

3-4 hour mean

NR NR NR NR NR NR NR NR

Vanner 201151

NPO status 1:

> 5 hours

NPO status 2:

> 8 hours 

Ottawa Scale

5.03 (2.8)

(Rostom et al.)

Aronchick 

no significant 

differences 

between 

groups 

(Aronchick et 

al.)

Ottawa Scale

5.22 (3.1)

P = .77

NR NR Overall completion rate 

95% (95/100) NR NR NR NR

Varughese 

201052

NPO status 1: 

≥ 3 hours

NPO status 2:

> 8 hours

Ottawa Scale

4.7 (2.4)

(Rostom et al.)

Ottawa Scale

7.1 (2.7)

P < .01

NR NR NR NR 24 (16/68) 24(15/68)

P = NS NR NR

Voiosu 201353

NPO status 1: 

1-7 hours

NPO status 2: 

> 8 hours

Excellent (4)

30 (25/85)

(Rex et al.)

Excellent (4)

21 (17/80)

P = .23

NR NR NR NR NR NR NR NR

NaP = sodium phosphate; NPO = nil per os; NR = not reported; NS = not statistically significant; PC = preparation-to-colonoscopy; PEG = polyethylene glycol; 

P/MC = sodium picosulfate and magnesium citrate; SD = standard deviation

Bowel preparation completed the day before colonoscopy designated as NPO status > 8 hours

88
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

a Rating system references (“Author scale” indicates scale was developed by study authors and is described in the study reference) 

Sharma VK et al. Gastrointest Endosc. 1998;47:167-71.

Arya V et al. Dig Dis Sci. 2013;58:2156-66.

Aronchick CA et al. Gastrointest Endosc. 2000;52:346-52.

Church JM. Dis Colon Rectum. 1998;41:1223-5.

Rostom A et al. (Ottawa). Gastrointest Endosc. 2004;59:482-6.

Lai EJ et al. (Boston). Gastrointest Endosc. 2009;69(Suppl 3);620-5.

Frommer D. Dis Colon Rectum. 1997;40:100-4.

Chilton A et al. Quality assurance guidelines for colonoscopy. Sheffield: NHS Cancer Screening Programmes; 2010.

Di Palma JA et al. Gastrointest Endosc. 1990;36:285-9.

Rex DK et al. Am J Gastroenterol. 2006;101:873-85.

89
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Table 4. Time and Patient Outcomes

Study 

NPO Status 

(Intervention/

Control)

Total procedure time,

mean (SD)

Cecal intubation time, 

mean (SD)

Withdrawal time, 

mean (SD) a

Patient adherence to 

preparation or 

colonoscopy, % (n/N)

Patient satisfaction, 

preparation or

colonoscopy, % (n/N)

NPO group 

1

NPO 

group 2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

Abdul-Baki 

200813

NPO status 1:

≥ 1.5 hours 

NPO status 2: 

> 8 hours)

NR NR NR NR NR NR Adherence

91%

Adherence

69%

P < .001

Work/school 

missed

10 (20/199)

Sleep 

disturbed

15 (30/199)

Work/school 

missed

13 (23/183)

P = NS

Sleep 

disturbed

21 (38/183)

P = NS

Aoun 200514

NPO status 1:

≥ 1.5 hours

NPO status 2: 

> 8 hours)

NR NR NR NR NR NR

Drank as 

instructed

90 (61/68)

Drank as 

instructed

78 (57/73)

P = .06

Work/school 

missed

12 (8/68)

Sleep 

disturbed

20 (29/68)

Willingness 

to take again

84 (57/68)

Work/school 

missed

21 (15/73)

P = NS

Sleep 

disturbed

24 (33/73)

P = NS

Willingness 

to take again

75 (55/73)

P = .21

Athreya 201116

NPO status 1: 

5-9 hours

NPO status 2: 

> 8 hours

n=150

11.40 min

(SD NR)

n=175

11.16 min

(SD NR) 

P=0.40

n=150

6.58 min

(SD NR)

n=175

7.05 min

(SD NR)

P=0.78

n=150

4.42 min

(SD NR)

n=175

4.11 min

(SD NR)

P=0.10

NR NR NR NR

Barclay 200417

NPO status 1: 

< 3 hours 

NPO status 2:

≥ 5 hours

NR NR NR NR NR NR

Completed

95 

(117/123)a 

Completed

88 

(114/130)a

P = .04

Prefer 

alternative in 

future

34 (44/130)a 

Prefer 

alternative in 

future

15 (19/123)a 

P < .001

Church 199821

NPO status 1: 

5-8 hours

NPO status 2: 

>8 hours

NR NR

n=157

19.5 min 

(2.2)

n=160

20.0 min 

(1.6)

n=157

11.9 min 

(0.8)

n=160

13.1 min 

(0.7)

NR NR NR NR

90
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Total procedure time,

mean (SD)

Cecal intubation time, 

mean (SD)

Withdrawal time, 

mean (SD) a

Patient adherence to 

preparation or 

colonoscopy, % (n/N)

Patient satisfaction, 

preparation or

colonoscopy, % (n/N)

NPO group 

1

NPO 

group 2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

Eun 201125

NPO status 1: 

< 4 hours 

NPO status 2: 

> 4 hours 

(Analysis by PC 

time; hourly 

intervals from ≤

2 hours to > 7 

hours)

NR NR NR NR NR NR Completed

81 (120/149)

Completed

85 

(129/151)

P = .51

NR NR

Gupta, 200728

NPO status 1: 

≥ 5 hours 

NPO status 2: 

> 8 hours 

NR NR NR NR NR NR NR NR

Work hrs 

lost

8.0 (2.1) hrs

Sleep 

disturbed

15 (15/102) 

Work hrs 

lost

10.2 (3.9)

hrs

P < .001

Sleep 

disturbed

42 (42/99) 

P < .001

Gurudu 201230

NPO status 1: 

≥ 4 hours

NPO status 2: 

> 8 hours 

NR NR NR NR 11.6 (7.7) 15.3 (11.1) 

(p=<.001) NR NR NR NR

Kössi 200738

NPO status 1: 

≤ 6 hours 

NPO status 2: 

6-12 hours 

NPO status 3: 

≥ 12 hours

NR NR NR NR NR NR NR NR

Difficulty traveling to 

colonoscopy

≤ 6 hours: 3.8%

6-12 hours: 5.6%

≥ 12 hours: 4.9%

P = NS

91
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Total procedure time,

mean (SD)

Cecal intubation time, 

mean (SD)

Withdrawal time, 

mean (SD) a

Patient adherence to 

preparation or 

colonoscopy, % (n/N)

Patient satisfaction, 

preparation or

colonoscopy, % (n/N)

NPO group 

1

NPO 

group 2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

LongcroftWheaton 

201240

NPO status 1: 

> 3 hours

NPO status 2: 

> 5 hours

NR NR NR NR NR NR

N=47

Completed

98%

N=58

Completed 

95%

P = NS

Interruption 

of work

0 (median)b 

Sleep 

disturbed

11 (5/47)

Preferred 

same prep 

for future

81% (N=NR)

Interruption 

of work

4 (median)b

Sleep 

disturbed

29 (17/58)

P = .03

Preferred 

same prep 

for future

40% (N=NR)

Manno 201241

NPO status 1: 

2 hours

NPO status 2: 

> 8 hours

NR NR NR NR NR NR

Completed

≥ 75% of 

prep

96 

(162/168)

Completed

≥ 75% of 

prep

95 

(159/168)

P = .70

Preferred 

same prep 

for future 

69 (116/168)

Preferred 

same prep 

for future 

31 (52/168)

P < .001

Matro 201044

NPO status 1: 

4 hours (am 

prep only)

NPO status 2:

4 hours (pm/am 

prep)

Median

12.8 min 

Median

12.4 min 

P = .147

NR NR Median

8.0 min

Median

7.3 min

P = .637

Completed 

> 90% of 

prep

84 (52/62)

Completed 

> 90% of 

prep

72 (39/54)

P = .175

No 

interference 

with work 

day before 

procedure 

(only if went 

to work)

85 (23/27)

Slept > 80% 

of usual 

hours 

71 (44/62) 

Repeat 

same prep in 

future 

82 (51/62)

No 

interference 

with work 

day before 

procedure 

55 (12/22)

P = .019

Slept > 80% 

of usual 

hours 

76 (41/54)

P = .675

Repeat 

same prep in 

future 

80 (43/54)

P = .814

92
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Study 

NPO Status 

(Intervention/

Control)

Total procedure time,

mean (SD)

Cecal intubation time, 

mean (SD)

Withdrawal time, 

mean (SD) a

Patient adherence to 

preparation or 

colonoscopy, % (n/N)

Patient satisfaction, 

preparation or

colonoscopy, % (n/N)

NPO group 

1

NPO 

group 2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

Park 200746

NPO status 1: 

2 hours

NPO status 2: 

> 8 hours

NR NR

Good 

compliancec

8.0 (5.6)

min

n=119

Poor 

Compliance

9.4 (5.8)

min

n=32

Good 

compliancec

13.0 (7.8)

min

n=116

P < .01

Poor 

Compliance

12.7 (5.1)

min

n=36

P < .05

NR NR

Good 

compliance 

with prep

79 (119/151)

Good 

compliance 

with prep

76

(116/152)

P > .05

Sleep 

disturbed

11 (16/151)

Overall 

tolerance of 

prep

1.01 (1.03)d 

Sleep 

disturbed

12 (18/152)

P = NS

Overall 

tolerance of 

prep

1.05 (0.86)d

P = NS

Park 201047

NPO status 1: 

2-5 hours 

NPO status 2: 

> 8 hours 

NR NR NR NR NR NR

Compliance

> 80%

91 (73/80) 

Compliance

> 80%

92 (73/79) 

Sleep 

disturbed

28 (22/80)

Willing to 

repeat prep

48 (38/80)

Sleep 

disturbed

32 (25/79)

Willing to 

repeat prep

62 (49/79)

P = .08

Rex 201349

NPO status 1: 

5-9 hours

NPO status 2: 

> 8 hours

NR NR NR NR NR NR

Treatmentemergent 

adverse 

event 

leading to 

discontinuation

0 (0/305)

Treatmentemergent 

adverse 

event 

leading to 

discontinuation

0.7 (2/298)

NR NR

Varughese 

201052

NPO status 1: 

≥ 3 hours

NPO status 2: 

> 8 hours

n=68

19.2 (7.2) 

min

n=68

18.7 (7.2) 

min

P = .73

n=68

8.5 (5.5)

min

n=68

7.4 (4.5) min

P = .27

n=68

10.6 (5.0)

min

n=68

11.3 (4.8)

min

P = .49

Quantity 

consumed 

3.7 (0.5) L 

(of 4L 

regimen)

Quantity 

consumed 

3.7 (0.6) L 

(of 4L 

regimen)

P = .61

Sleep loss

16 (11/68)

Sleep loss

31 (21/68)

P = .04

NPO = nil per os; NR = not reported; PC = preparation to colonoscopy; SD = standard deviation

Bowel preparation completed the day before colonoscopy designated as NPO status > 8 hours a Group with shorter NPO status was required to take 3 doses while group with longer NPO status took 2 doses

b 5-point Likert scale with 0 = completely unimpaired, 4 = major impact effectively preventing an activity c Study reports time to cecal intubation in minutes (SD) by compliance with preparation (good versus poor) d 4-point scale with 0 = not at all distressing, 3 = severely distressing

93
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

Table 5. Hospitalizations, Costs, and Adverse Events 

Study

NPO Status 

(Intervention/

Control)

Hospitalizations

% (n/N) Costs Bowel perforation% (n/N)

Other adverse eventsa (describe) % 

(n/N)

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2

NPO group 

1

NPO group 

2 NPO group 1 NPO group 2

Barclay 200417

NPO status 1: < 3 hours 

NPO status 2: ≥ 5 hours

NR NR NR NR NR NR

Interview 2 days after colonoscopy – no 

patient in either group developed 

clinically significant neurologic, cardiac, 

or other adverse events that were thought 

to be attributable to colonic purgation

Church 199821

NPO status 1: 5-8 hours

NPO status 2: >8 hours

NR NR NR NR NR NR No complications of colonoscopy in either 

group

Flemming 201226

NPO status 1: ≥ 4 hours 

NPO status 2: > 8 hours

NR NR NR NR

No documented 

complications of 

perforation on discharge 

from endoscopy unit

No documented complications of 

bleeding on discharge from endoscopy 

unit

Johanson 200732

NPO status 1: 2.5-4.5

hours

NPO status 2: > 8 hours

NR NR NR NR NR NR 0/207

0.5 (1/208) 

Lower GI bleeding 

post-colonoscopy

Mathus-Vliegen 201343

NPO status 1: 

Hours unclear (Splitdose, PM exam) 

NPO status 2: 

> 8 hours

NR NR NR NR NR NR None reported

1 (1/99)

Severe retrosternal 

pain 3 hours after 

colonoscopy; 

anteroseptal infarction 

diagnosed

Rex 201349

NPO status 1: 5-9 hours

NPO status 2: > 8 hours

NR NR NR NR NR NR

Acute 

pancreatitisb 

0.3 (1/305)

Non-cardiac chest 

painb

0.3 (1/298)

Colon cancer 

0.3 (1/298)

Voiosu 201353

NPO status 1: 1-7 hours

NPO status 2: > 8 hours

NR NR NR NR NR NR Reported no serious adverse events 

throughout the study

GI = gastrointestinal; NPO = nil per os; NR = not reported

Bowel preparation completed the day before colonoscopy designated as NPO status > 8 hours

a Anesthesia-related b Unclear whether event occurred during preparation or colonoscopy

94
NPO Status Prior to Colonoscopy

Table 6. Gastric Contents Outcomes

Study

NPO Status 

(Intervention/

Control)

Volume of gastric contents, 

Mean (SD)

pH of gastric contents, 

Mean (SD)

NPO group 1 NPO group 2 NPO group 1 NPO group 2

Aoun 200514

NPO status 1: ≥ 1.5 

hours 

NPO status 2: > 8 hours 

No notable difference in the amount of 

residual gastric fluid between groups NR NR

Huffman 201031

NPO status 1: ≥ 2 hours 

NPO status 2: > 8 hours

19.7 (19.1) mL 20.2 (22.4) mL NR NR

NPO = nil per os; NR = not reported; SD = standard deviation 

Bowel preparation completed the day before colonoscopy designated as NPO status > 8 hours

95

Evidence-based Synthesis Program
NPO Status Prior to Colonoscopy Evidence-based Synthesis Program

APPENDIX D. STRENGTH OF EVIDENCE 

Outcome

Category

Outcome (# of 

Studies 

Reporting)

Results, Shorter NPO status vs Longer NPO 

status Risk of Bias Consistency Directness Precision Strength of 

Evidence

Primary

Aspiration, RCTs 

(3) 

Three moderate sized trials (n=672)

a reported no 

aspiration events or no major complications 

related to sedation

moderate consistent direct imprecise Low

Aspiration, Obs. (2)

Two studies (n=1,646), one large and one 

moderately sized, reported no episodes of

aspiration were observed

moderate consistent direct imprecise Insufficient

Rescheduled 

colonoscopies (1) 

One moderate sized RCT reported fewer 

rescheduled colonoscopies with shorter NPO 

status

moderate unknown direct imprecise Insufficient

Secondary

Completion rate, 

RCTs (6)

Pooled results from 5 trialsa,b (n=1,795) found no 

difference between NPO status groups (RR 1.00 

[95%CI 0.98, 1.01])

moderate consistent direct precise Moderate

Completion rate, 

Obs. (1)

One large retrospective study (n=5175) reported a 

greater completion rate with a shorter NPO status 

(OR 1.35 [95%CI 1.03, 1.77])

high unknown direct precise Insufficient

Adenoma detection 

rate, RCTs (1)

A single small trial (n=136)a found no difference 

between NPO status groups moderate unknown direct imprecise Insufficient

Adenoma detection 

rate, Obs. (3)

Pooled results from 3 studies (n=8,481) found 

improved adenoma detection rates with a shorter 

NPO status (OR 1.25 [95%CI 1.13, 1.39])

moderate consistent direct precise Low

Diagnostic yield, 

RCTs (2)

Two moderate sized trialsa,b (n=254) reported 

inconsistent results in diagnostic yield of all polyps 

or lesions

moderate inconsistent direct imprecise Insufficient

Bowel perforation, 

RCT (1)

A single moderate sized trial (n=250) reported no 

documented complications of perforation moderate unknown direct imprecise Insufficient

False negative 

colonoscopy (0)

No eligible studies Insufficient

Obs. = observational studies; RCTs = randomized controlled trials; OR = odds ratio; RR = risk ratio a One additional RCT (n=125) (Matro 2010)44 of morning-only versus evening before/morning of colonoscopy bowel preparation (all patients NPO for 4 hours 

with clear liquids allowed until 2.5 hours before colonoscopy) reported one aspiration event requiring 24 hour hospitalization for observations, no significant 

difference in completion rate, and significantly better adenoma detection rate and diagnostic yield in the morning-only preparation group. b One study (Chiu 2006)20 was of patients getting follow-up colonoscopy

96