Role of Intraoperative and Postoperative Blood Glucose Concentrations in Predicting Outcomes after Cardiac Surgery

Background: Severe hyperglycemia is associated with adverse outcomes after cardiac surgery. Whether intraoperative and postoperative glucose concentrations equally impact outcomes is unknown. The objective of this investigation was to compare the ability of perioperative glucose concentrations and glycemic variability to predict adverse outcomes. Risk associated with decreasing increments of glucose concentrations, hypoglycemia, and diabetic status was also examined. Methods: This retrospective analysis of prospectively collected data included 4,302 patients who underwent cardiac surgery between October 3, 2005 and May 31, 2007 at the Cleveland Clinic. Time-weighted mean intraoperative (Glc(OR)) and postoperative (Glc(ICU)) glucose concentrations were calculated. Patients were categorized as follows: Glc more than 200, 171-200, 141-170, and less than or equal to 140 mg/dl. Coefficient of variation was used to calculate glycemic variability. Logistic regression model with backward selection assessed the relationship between glucose concentrations, variability, and adverse outcomes while adjusting for potential confounders. Another model assessed the predictability of Glc(OR) and Glc(ICU) on adverse outcomes. Results: Both Glc(OR) and Glc(ICU) predicted risk for mortality and morbidity. Increased postoperative glycemic variability was associated with increased risk for adverse outcomes. Severe hyperglycemia (Glc(OR) and Glc(ICU) > 200 mg/dl) was associated with worse outcomes; however, decreasing increments of Glc(OR) did not consistently reduce risk. Glc(OR) less than or equal to 140 mg/dl was not associated with improved outcomes compared with severe hyperglycemia, despite infrequent hypoglycemia. Diabetic status did not influence the effects of hyperglycemia. Conclusion: Perioperative glucose concentrations and glycemic variability are important in predicting outcomes after cardiac surgery. Incremental decreases of intraoperative glucose concentrations did not consistently reduce risk. Despite rare hypoglycemia, intraoperative glucose concentrations closest to normoglycemia were associated with worse outcomes.