Blood glucose concentration and outcome of critical illness: The impact of diabetes

Objective. To study the impact of diabetes mellitus on the relationship between glycemia and mortality in critically ill patients. Design. Retrospective observational study. Setting. Intensive care units of two university hospitals. Patients. Cohort of 4946 critically ill patients including 728 patients with diabetes mellitus. Intervention: None. Measurements and Main Results: We assessed and compared the relationship between glycemia during intensive care unit stay and mortality in diabetic and nondiabetic patients. There were 125,036 blood glucose measurements (5.7 measurements/day on average). Intensive care unit mortality increased significantly with increasing mean blood glucose concentration in nondiabetes mellitus patients but not in diabetes mellitus patients. Nondiabetes mellitus patients with a time-weighted glucose concentration (Glu(Tw)) between 8.0 and 10.0 mmol/L were found to be 1.74 times more likely to die in intensive care unit as diabetes mellitus patients in the same range (odds ratio = 1.74 [1.13-2.68] p = 0.01). They were also more than three times more likely to die in the intensive care unit compared with diabetes mellitus patients when the Glu(tw) was between 10.0 and 11.1 mmol/L (odds ratio = 3.34 [1.35-8.23] p = 0.009). Using multivariate logistic regression analysis, hyperglycemia was strongly and independently associated with outcome in nondiabetic patients (p < 0.001) but showed no significant association with outcome in diabetic patients. Conclusions: Unlike nondiabetic patients, diabetic patients show no clear association between hyperglycemia during intensive care unit stay and mortality and markedly lower odds ratios of death at all levels of hyperglycemia. These findings suggest that, in critically patients with diabetes mellitus, hyperglycemia may have different biological and/or clinical implications.