Intensive Care Med. 2004 Mar;30(3):437-43. Epub  2004 Feb 6.

Body mass index. An additional prognostic factor in ICU patients.

 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.   

 INTERVENTIONS: None.   

 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.