Accuracy of the Dexcom G6 Continuous Glucose Monitoring System Following Cardiac Surgery
Phase: NA
Conditions: Surgery--Complications
Sponsor: The Cleveland Clinic

Version Date: 01-12-2024 
1 
 
 
 
Title: Accuracy of the Dexcom G6 continuous glucose monitoring system following cardiac 
surgery  
Investigators 
PI: M. Cecilia Lansang, MD, MPH – endocrinology 
Co-PI: Steven Insler, DO – cardiothoracic anesthesiology 
Other investigators: 
Dr. Moheb Gohar  
Dr. Brett Wakefield 
CRU nurses 
• 
Melanie Ramos, RN 
• 
Kim Hopkins, RN 
• 
Victoria Rowney, RN 
• 
Kaitlyn Kubec, RN 
• 
Natalie Grenier, RN 
• 
Teresa Schaffer, RN 
• 
Becky Perry, RN 
• 
Lisa Minotas, RN  
• 
Velma Stephens, LPN 
• 
Jaclyn Grayson, RN 
 
 
Statistician 
James Bena – Quantitative Health Sciences 
 
 
Background 
Maintaining tight blood glucose control following surgery is imperative to reducing infections and 
neurologic dysfunction. This requires frequent blood sampling while in the intensive care unit, 
leading to increased waste of blood and utilizing time and resources to collect samples and wait 
for results. Additionally, when on the regular floors, frequent point of care fingersticks for 
glucose levels are needed for therapeutic intervention.  
 
Continuous glucose monitoring systems (CGMS) are now available for ambulatory use in 
patients with diabetes. The potential of using such a system in the hospital, including during the 
postoperative critical care setting and upon transfer to the regular floor, may reduce personnel 
burden, produce rapid results, and decrease blood waste. 
 
However, these systems have not yet been validated for hospital use. 
 
 
Objectives 
To assess the accuracy of the continuous glucose monitor Dexcom G6 (or similar device) on 
patients with hyperglycemia, with or without known diagnosis of diabetes, after cardiovascular 
surgery.  
 
To calculate potential cost savings, time savings, and blood waste compared to current care 
(point of care glucose through blood gas)  

Version Date: 01-12-2024 
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Methods 
All patients following cardio-thoracic surgery are required to have tight control of blood glucose, 
thus requiring multiple blood draws as part of the Surgical Care Improvement Project (SCIP). 
Patients 
Patients will be identified and consented preoperatively  
 
Inclusion criteria for consenting patients: 
Age 18 years old and above 
Planned Cardiovascular surgery 
Planned admission to Cleveland Clinic Main Campus J5 or J6 or Q5 cardiovascular ICU 
(CVICU) post-operatively  
With or without known diabetes (as 75% of patients entering the CVICU have hyperglycemia 
requiring intravenous insulin infusion) 
If with known diagnosis of diabetes, diabetes can be type 1, type 2, or secondary (such as due 
to glucocorticoids or pancreatitis 
 
 
Exclusion criteria: 
Allergy to the material of the CGMS or the adhesive to be used  
Skin conditions precluding the use of the CGMS 
Pregnancy  
Other conditions that the investigators deem inappropriate for the study 
 
Consent: 
Consent will be performed pre-operatively at the TCI (To Come In) unit.   
 
Procedure: 
Dexcom G6 has a sensor (see photo below) that goes underneath the skin to sense interstitial 
glucose. 
It is attached to a transmitter. 
The third component is a receiver. The receiver has to be within 10-15 feet from the patient. We 
will place this in a well-marked pouch/bag.  
In the photo below, the purple is the sensor and the gray oval on top of it is the transmitter. The 
sensor is inserted first, then the transmitter is attached to it. 
 
 
 

Version Date: 01-12-2024 
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The sensor/transmitter will be applied pre-operatively in the preop holding area or in the 
operating room (before anesthesia induction) to the upper outer arm by a physician, nurse, 
nurse practitioner or physician’s assistant. The insertion area can be cleaned with alcohol of 
betadine. 
 
The glucose readings on the device will not be visible to the ICU/regular floor staff nor the 
patients. 
At the end of 10 days or upon discharge from the hospital, which ever comes first, the 
sensor/transmitter will be removed. 
 
Time-stamped data from the CGMS software will be compared with the correlated ABG or 
venous of Accu-check Inform II glucose reading 
 
The data transmission occurs via Blue-Tooth from sensor to the receiver. 
 
 
The data have do be downloaded within 2 weeks. 
 
The sensor has an adhesive so that it can stick to the skin. Skin Tac can be used to increase 
the adhesion to the skin. An adhesive overpatch specifically coming from/approved by Dexcom 
can be used over the sensor as needed to increase adhesion. NOTE: OpSite or Tegaderm 
CANNOT be used over the sensor as this will decrease reliability.  
 
 
Sanitation 
We requested for enough sensors and transmitters for 30 patients. 
Should the transmitters fall short for some reason, they can be cleansed with bleach or alcohol 

Version Date: 01-12-2024 
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The sensors can only be used for one person each. 
The receivers will come with sterile shields which wil be changed in-between patients. 
 
 
 
Safety: 
The CGMS will be inserted on the outer arm after the site is cleaned. The insertion site will be 
inspected daily for signs of infection, or of allergy from the sensor, adhesive, or overpatch.  
 
 
Study Design 
This is a prospective longitudinal study to study the agreement between a novel continuous 
glucose monitoring system (CGMS) versus current blood glucose monitoring.   
Subjects in this study will have their blood glucose measured regularly every 1-3 hours with current 
methods in the CVICU, and by point of care glucose using the Accuchek Inform II on the regular 
floors, and the CGMS at the same time will be captured.  Subjects will have measurements taken 
throughout their stay in the CVICU and on the regular floors.  Agreement and correlation between 
systems will be calculated, and error will be classified using the Surveillance Error grid.  The 
proportion of errors of at least moderate risk will be calculated. 
 
 
Subject compensation 
There is no subject compensation for this study. 
 
Statistical Methods 
Subject characteristics including demographics, comorbidities and baseline disease severity will be 
summarized using means and standard deviations for continuous measures and frequencies and 
percentages for categorical factors.  To evaluate agreement between methods, concordance 
correlation coefficients will be calculated, using the method that adjusts for repeated measures as 
described by King et al. (2007) and implemented in software by Carrasco et al. (2013).  Analysis 
will be performed overall, and then stratifying by type of current measure, if the type of 
measurement varies across settings.  Correlations will be calculated using the methods described 
by Bland and Altman (1995) and implemented by Bakdash and Marusich (2017).  Differences will 
also be evaluated for errors according to the Surveillance Error Grid (Klonoff et al, 2014).  Rates of 
moderate or more severe errors will be calculated.  For each measure above, 95% confidence 
intervals will be calculated, accounting for the clustering within subject..  Analyses will be performed 
using SAS software (version 9.4; Cary, NC) and R software (version 3.5; Vienna Austria). 
 
Sample Size 
Sample size calculations were performed based on the precision of the moderate error rate as 
based on the surveillance error grid calculations.  Given the goal to estimate the error rate to within 
5% based on 95% confidence intervals, assuming 10 samples per patient and a moderate 
intraclass correlation coefficient (ICC) of 0.3, if the observed error rate is 5%, then 28 subjects (at 
least 271 paired samples) will be required to achieve this level of precision.  Note that if you wish to 
estimate these levels with this precision for subgroups of your population, each subgroup will need 
to have this many subjects.  Table 1 shows the number of samples required for different levels of 
precision and error rates under similar assumptions.  Sample size calculations were performed 
using the online calculator by Dhand, N. K., & Khatkar, M. S. (2014).   

Version Date: 01-12-2024 
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Table 1.  Samples required to achieve precision as described assuming 95% confidence, an ICC of 
0.3, and 10 paired samples per subject.  Number is subjects would be the number below divided 
by 10. 
 
 
Absolute precision 
Error Rate 
0.03 
0.04 
0.05 0.06 0.07 0.08 0.09 0.10 
20% 
2527 1422 
910 
632 
465 
356 
281 
228 
15% 
2014 1133 
725 
504 
370 
284 
224 
182 
10% 
1422 
800 
512 
356 
262 
200 
158 
128 
5% 
751 
422 
271 
188 
138 
106 
84 
68 
 
 
Primary outcome: 
To address accuracy, glucose readings obtained from the CGMS will be compared with 
1) blood glucose from the arterial blood gas (ABG) or peripheral/central venous catheter if 
arterial catheter not in use (standard of care in CVICU) while patients are in the CVICU 
2) fingerstick point of care (POC) glucose when patients are on the regular floors 
 
 
 
Other outcomes: 
The following can be derived based on the average length of stay (LOS) of the study patients in 
the CVICU and the regular floors (current average of 24-36 hours, and a total hospital LOS of 4-
5 days) 
 
Cost savings: cost of CGMS device including sensor, transmitter versus cost of doing an ABG to 
obtain glucose levels (CVICU stay), and versus the cost of Accu-chek Inform II meter, test 
strips, and lancets 
 
Time savings: time it takes to perform and time it takes to have results based on an ABG or 
fingerstick POC on Accu-check Inform II 
 
Blood waste: blood sample amount for an ABG or fingerstick POC on Accu-chek Inform II 
 
 
Variables: 
Age 
Gender 
Race 
Weight 
Height 
BMI 
Systolic blood pressures 
Diastolic blood pressures 
Temperatures 
Diabetes status (no known diagnosis, known diagnosis) 
Type of diabetes 
Type of cardiothoracic surgery 
Presence of peripheral vascular disease 

Version Date: 01-12-2024 
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Presence of peripheral edema 
Presence of medications/substances that might interfere with the CGMS  
Glucose readings (lab, point of care, CGMS) 
Serume creatinine 
Intravenous insulin infusion rate 
Subcutaneous insulin doses 
Use of pressors/vascoconstrictors/vasodilators 
Intravenous fluids 
Medications administered in the hospital 
 
 
Data 
Because the data are blinded to the nurses and ICU staff, we need to use the web-based Clarity 
program to be able to download data. 
The endocrine department already has an existing Clarity account for clinic patients. Dexcom 
has given us instructions since they have studies with other institutions. For our study, there will 
be an account in Clarity. Subject ID can be entered. Clarity can then export data as an Excel file 
to be imported into RedCap. 
The Dexcom G6 gives glucose readings every 5 minutes. The closest glucose reading to the 
time and date of the blood gas or point of care blood glucose will be matched. 
 
Other info 
CDA already executed with Dr Lansang, Dr. Insler and Dexcom