The Association of Perioperative Glycemic control with Post-operative wound Infection after Coronary Artery Bypass Grafting in Veterans with Diabetes Mellitus

Introduction: After coronary artery bypass (CABG), diabetes mellitus is associated with increased risk of infection. We model the inter-relationship of pre- and post-operative glycemic control and their composite influence on post-operative wound infection. Methods: 2,899 Veterans that underwent isolated CABG were stratified (Group I: < 8%, Group II: 8 - 10%, Group III: > 10%) according to preoperative HbA1c levels. We obtained the median blood sugar level (BSL) on post-operative days 0 - 4 (POD) and compared trends in BSL readings according to HbA1c groups. We fit a multi-variable random effects mixed model to understand the odds (OR) of developing postoperative mediastinitis. A two-stage joint model was fit to evaluate the adjusted hazard (HR) of pre-operative HbA1c, post-operative BSL and clinical factors on 90-day readmission for infection. Results: In groups I, II, and III had 66%, 25% and 9% patients respectively. In 148,810 post-operative BSL readings, median BSL values peaked at POD 2 (145 mg/dl). In group III, 29% BSL reading was above the recommended limit (< 180 mg/dl). Group III (OR 3.5; p < 0.01) and COPD (OR 2.51; p < 0.01) were associated with higher rates of mediastinitis. Groups II (HR 1.4; p = 0.01) and III (HR 1.5; p = 0.04) were associated with increased risk for 90-day readmission for infection. Post-operative blood sugar levels (p = 0.5) were not associated with increased risk for wound infection at 90 days. Conclusion: Among Veterans undergoing coronary artery bypass, a large proportion had HbA1c levels > 8%. In the post-operative period, 22% of the blood sugar readings are higher than 180 mg/dl. Preoperative HbA1c (rather than postoperative glycemic control) is associated with higher rates of deep sternal wound infection.