Objectives: Fluctuations in blood glucose (glycemic variability) increase the risk of adverse outcomes. No universally accepted tool for glycemic 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.
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-statistics. 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 glycemic variability in predicting adverse outcomes (cutoff value 2.24) after cardiac surgery.
Keywords: Blood Glucose Risk Index; adverse outcomes; cardiac surgeries; coefficient of variation; glycemic variability.