Objective: To examine the association between body mass index (BMI) and mortality in adult intensive care unit (ICU) patients. DESIGN. A prospective multi-center study.
Methods: A cohort study (yielding the OUTCOMEREA database) was conducted over 2 years in 6 medical-surgical ICUs. In each participating ICU, the following were collected daily: demographic information, admission height and weight, comorbidities, severity scores (SAPS II, LOD, and SOFA), ICU and hospital lengths of stay, and ICU and hospital mortality rates.
Results: A total of 1,698 patients were examined and divided into 4 groups based on BMI: <18.5, 18.5-24.9, 25-29.9, and >30 kg/m(2). These groups differed significantly for age, gender, admission category (medical, scheduled surgery, unscheduled surgery), ICU and hospital lengths of stay, and comorbidities. Severity at admission and within the first 2 days was similar in the 4 groups, except for the SOFA score. Overall hospital mortality was 31.3% (532 out of 1,698 patients). By multivariate analysis, a BMI below 18.5 kg/m(2) was independently associated with increased mortality (odds ratio 1.63; 95% confidence intervals 1.11-2.39). None of the other BMI categories were associated with higher mortality and even a BMI>30 kg/m(2) was protective of mortality (odds ratio 0.60, 95% confidence intervals 0.40-0.88).
Conclusions: A low BMI was independently associated with higher mortality and a high BMI with lower mortality in this large cohort of critically ill patients. Since BMI is absent from currently available scoring systems, further studies are needed to determine whether adding BMI would improve the effectiveness of scores in predicting mortality.