Original Article Comparison of Glycemic Variability Indices Blood Glucose Risk Index and Coefficient of Variation in Predicting Adverse Outcomes for Patients Undergoing Cardiac Surgery Valluvan Rangasamy, MD, DESA, Xinling Xu, PhD, Ammu Thampi Susheela, MD, Balachundhar Subramaniam, MD, MPH, FASA 1 Center for Anesthesia Research Excellence, Department of Anesthesia, Critical Care, and Pain Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA Objectives: Fluctuations in blood glucose (glycemic variability) increase the risk of adverse outcomes. No universally accepted tool for glyce- mic variability exists during the perioperative period. The authors compared 2 measures of glycemic variability—(1) coefficient of variation (CV) and (2) the Blood Glucose Risk Index (BGRI)—in predicting adverse outcomes after cardiac surgery. Design: Prospective, observational study. Setting: Single-center, teaching hospital. Participants: A total of 1,963 adult patients undergoing cardiac surgery. Interventions: None. Measurements and Main Results: Postoperative blood glucose levels were measured hourly for the first 24 hours and averaged every 4 hours (4, 8, 12, 16, 20, and 24 hours). Glycemic variability was measured by CV and the BGRI. The primary outcome, major adverse events (MAEs), was a predefined composite of postoperative complications (death, reoperation, deep sternal infection, stroke, pneumonia, renal failure, tamponade, and myocardial infarction). Logistic regression models were constructed to evaluate the association. Predictive ability was measured using C-sta- tistics. Major adverse events were seen in 170 (8.7%) patients. Only the fourth quartile of CV showed association (odds ratio [OR] 1.91; 95% confidence interval [CI] [1.19-3.14]; p = 0.01), whereas BGRI was related significantly to MAE (OR 1.20; 95% CI [1.10-1.32]; p < 0.0001). The predictive ability of CV and BGRI increased on adding the standard Society of Thoracic Surgeons (STS) risk index. The C-statistic for STS was 0.68, whereas STS + CV was 0.70 (p = 0.012) and STS + BGRI was 0.70 (p = 0.012). Conclusion: Both CV and the BGRI had good predictive ability. The BGRI being a continuous variable could be a preferred measure of glyce- mic variability in predicting adverse outcomes (cutoff value 2.24) after cardiac surgery. Ó 2020 Published by Elsevier Inc. Key Words: glycemic variability; cardiac surgeries; adverse outcomes; coefficient of variation; Blood Glucose Risk Index BY 2035, 1 in 10 individuals is predicted to be affected by diabetes mellitus. 1 Patients with diabetes frequently undergo cardiac surgeries and were reported to have a higher incidence of morbidity and mortality. 2,3 Perioperative changes in blood glucose levels increase the risk of postoperative complica- tions. 4,5 Hemoglobin A1c (HbA1c), an established marker for glycemic control, has several limitations and has been reported to express the degree of glycemia incompletely. 6,7 Glycemic variability, defined as the fluctuations of blood glucose by amplitude, frequency, and duration, is an emerging target for diabetes management. 1 It causes more endothelial damage and 1 Address reprint requests to Balachundhar Subramaniam, MD, MPH, FASA, Beth Israel Deaconess Medical Center, One Deaconess Road, CC-650, Boston, MA 02215. E-mail address: bsubrama@bidmc.harvard.edu (B. Subramaniam). https://doi.org/10.1053/j.jvca.2019.12.032 1053-0770/Ó 2020 Published by Elsevier Inc. ARTICLE IN PRESS Journal of Cardiothoracic and Vascular Anesthesia 000 (2020) 19 Contents lists available at ScienceDirect Journal of Cardiothoracic and Vascular Anesthesia journal homepage: www.jcvaonline.com