The obesity paradox in surgical intensive care unit patients

Abstract

To investigate the possible impact of obesity, as assessed by body mass index (BMI), on outcome in surgical intensive care unit (ICU) patients. Prospectively collected data from all consecutive adult patients admitted to our ICU between January 2004 and January 2009 were analysed retrospectively. BMI was calculated using the formula: BMI = body weight/height(2) (kg/m(2)), and patients were grouped as underweight (<18.5 kg/m(2)), normal weight (18.5-24.9 kg/m(2)), overweight (25-29.9 kg/m(2)), obese (30-39.9 kg/m(2)) and very obese (≥40 kg/m(2)). Among the 12,938 patients who were admitted to our ICU during the study period, 9,935 (76.8%) had complete height and weight data and constituted the study group. The mean BMI was 27.1 ± 5.0 kg/m(2). Overall, 34.4% of the study population had normal BMI, 1.8% were underweight, 41.2% were overweight, 20.8% were obese and 1.8% were very obese. The ICU mortality rate was similar among BMI subgroups, but hospital mortality was higher in underweight patients than in patients with normal BMI (17.8% versus 11.1%, P = 0.006). On multivariate Cox regression analysis, being overweight [hazard ratio (HR) 0.86, 95% confidence interval (CI) 0.74-0.99, P = 0.047] or obese (HR = 0.83, 95% CI = 0.69-0.99, P = 0.047) was independently associated with lower 60-day in-hospital mortality, with normal BMI as the reference category. Risk of death increased in very obese patients, especially after neurosurgical procedures (HR = 0.3, 95% CI = 1.06-8.48, P = 0.039). In this cohort of surgical ICU patients, being overweight or obese was associated with decreased risk of 60-day in-hospital mortality.