Objectives: Patients with diabetes mellitus form 23%–30% of published cohorts of critically ill patients. Conflicting published evidence links diabetes mellitus to both higher and lower mortality. Other cohort studies suggest that diabetes mellitus protects against acute lung injury. We hypothesized that diabetes mellitus is an independent risk factor for mortality. We further hypothesized that diabetes mellitus is a risk factor for cardiac overload and not for acute lung injury.
Design: Retrospective cohort study.
Setting: The intensive care unit of a tertiary referral hospital.
Patients: From November 1, 2004, to October 1, 2007, a cohort of patients admitted ≥48 hrs to the intensive care unit.
Measurements and Main Results: Of 2,013 patients, 317 had diabetes mellitus. Ninety-day mortality was higher in the diabetes mellitus patients compared to patients without diabetes mellitus (hazard ratio 1.53, 95% confidence interval 1.29–1.80). This association strengthened after adjusting for confounders and for medication (hazard ratio 1.53, 95% confidence interval 1.07–2.17).We found no association between diabetes mellitus and acute lung injury (relative risk ratio 1.01, 95% confidence interval 0.78–1.32; adjusted relative risk ratio 0.99, 95% confidence interval 0.75–1.31), but diabetes mellitus was a risk factor for cardiac overload (relative risk ratio 1.91, 95% confidence interval 1.30–2.81; adjusted relative risk ratio 1.45, 95% confidence interval 0.97–2.18). Statins were associated with both a reduced risk of mortality (hazard ratio 0.74, 95% confidence interval 0.63–0.87; adjusted hazard ratio 0.53, 95% confidence interval 0.44–0.64) and a decreased risk of developing acute lung injury (relative risk ratio 0.71, 95% confidence interval 0.56–0.89; adjusted relative risk ratio 0.61, 95% confidence interval 0.47–0.79).
Conclusions: Diabetes mellitus is an independent risk factor for mortality in critically ill patients and failure to adjust for statins underestimates the size of this association. Diabetes mellitus is not associated with acute lung injury but is associated with cardiac overload. A diagnosis of cardiac overload excludes a diagnosis of acute lung injury. Investigators who do not account for cardiac overload as a competing alternative outcome may therefore falsely conclude that diabetes mellitus protects from acute lung injury.