To assess the effect of body mass index on ICU outcome and on the development of ICU-acquired infection.
A substudy of the Intensive Care Over Nations audit.
Seven hundred thirty ICUs in 84 countries.
All adult ICU patients admitted between May 8 and 18, 2012, except those admitted for less than 24 hours for routine postoperative monitoring (n = 10,069). In this subanalysis, only patients with complete data on height and weight (measured or estimated) on ICU admission in order to calculate the body mass index were included (n = 8,829).
Underweight was defined as body mass index less than 18.5 kg/m, normal weight as body mass index 18.5-24.9 kg/m, overweight as body mass index 25-29.9 kg/m, obese as body mass index 30-39.9 kg/m, and morbidly obese as body mass index greater than or equal to 40 kg/m. The mean body mass index was 26.4 ± 6.5 kg/m. The ICU length of stay was similar among categories, but overweight and obese patients had longer hospital lengths of stay than patients with normal body mass index (10 [interquartile range, 5-21] and 11 [5-21] vs 9 [4-19] d; p < 0.01 pairwise). ICU mortality was lower in morbidly obese than in normal body mass index patients (11.2% vs 16.6%; p = 0.015). In-hospital mortality was lower in morbidly obese and overweight patients and higher in underweight patients than in those with normal body mass index. In a multilevel Cox proportional hazard analysis, underweight was independently associated with a higher hazard of 60-day in-hospital death (hazard ratio, 1.32; 95% CI, 1.05-1.65; p = 0.018), whereas overweight was associated with a lower hazard (hazard ratio, 0.79; 95% CI, 0.71-0.89; p < 0.001). No body mass index category was associated with an increased hazard of ICU-acquired infection.
In this large cohort of critically ill patients, underweight was independently associated with a higher hazard of 60-day in-hospital death and overweight with a lower hazard. None of the body mass index categories as independently associated with an increased hazard of infection during the ICU stay.