Insulin resistance heralds positive cultures after severe injury

Insulin resistance and hyperglycemia are common in acutely injured patients, and associated with poor outcomes. In the era of tight glucose control, measures of insulin responsiveness (IR) may provide a better indicator of patient status than does the serum glucose concentration. We hypothesized that measures of IR during tight glycemic control protocols are associated with infection and may be more predictive than the serum glucose concentration.

All critically injured, mechanically ventilated patients undergo protocolized tight glycemic control with the aid of a computer-based system that calculates the insulin dose using an adapting multiplier (insulin dose = [blood glucose - 60) x M). Consecutive patients on protocol were studied to identify the incidence of positive sterile-site or quantitative bronchoalveolar lavage cultures (>10(4) colony-forming units/mL). Patients were stratified by presence and number of positive cultures and analyzed by both serum glucose measures and measures of IR (average multiplier and average insulin infusion rate).

During the six-month study period, 356 patients were placed on the tight glycemic control protocol. Of these, 101 patients had 192 positive cultures. Patients with positive cultures required significantly more hourly insulin than those without a positive culture (3.7 vs. 2.8 units/h; p = or<0.001). Logistic regression showed the insulin dose (odds ratio 2.1; 95% confidence interval 1.6, 3.0; p = <0.001) and the adapting multiplier to be independent predictors of the patient having a positive culture among other factors associated with nosocomial infection.

Insulin resistance, quantified by hourly insulin dose and median multiplier, confers a higher risk of systemic nosocomial infection. Patients with positive cultures actually had lower admission and median blood glucose values over their intensive care unit stays, highlighting the decreased value of this measure as a predictor of outcome in the setting of tight glucose control. A greater insulin requirement suggesting resistance may be used as a marker of a higher risk of nosocomial infection.