Insulin resistance following cardiothoracic surgery in patients with and without a preoperative diagnosis of type 2 diabetes during treatment with intravenous insulin therapy for postoperative hyperglycemia

Objective: To assess insulin resistance postoperatively in patients with (DM) and without (nonDM) a prior diagnosis of diabetes. Research Design and Methods: Following cardiac surgery, 122 nonDM and 33 DM were treated with insulin infusions to obtain glucose levels <110 mg dl^-1. Glucose levels, insulin infusion rates, and insulin infusion rate/glucose ratios were calculated to assess insulin resistance. Results: The average blood glucose at insulin drip initiation (209 vs. 173 mg dl^-1; P<.001) and during the first 12 h (146 vs. 135 mg dl^-1; P<.05) was higher in DM, but during Hours 12-24 glucose levels were not different. The peak (5.7 vs. 4.1 U h^-1; P<.001) and average insulin drip rates (3.7 vs. 2.9 U h^-1; P<.01) were higher in DM. Insulin resistance (insulin drip rate/glucose ratio) was higher in DM during Hours 1-12 (0.029 vs. 0.022 U h^-1 mg^-1 dl^-1; P<.001), but not during Hours 12-24 (P=.57). To eliminate glucotoxicity as a cause of the insulin resistance, 23 DM patients were pair matched with 23 nonDM patients based first on glucose levels at drip initiation then by body mass index (BMI) and then catecholamine use to maintain blood pressure. The average blood glucose levels, insulin drip rates, and insulin resistance ratios were not significantly different between the pair-matched groups at all time points. Conclusions: When matched for initial glucose levels, insulin resistance is not different between DM and nonDM following cardiac surgery, likely due to the overwhelming stress response. Insulin drip protocols used postoperatively do not have to be modified for those with a prior diagnosis of diabetes.