Is obesity protective during critical illness? An analysis of a national ICU database

Background: Obesity is a major health care problem worldwide. By current estimates 64% of the adult population in the US are overweight. Excess body weight substantially increases the risk of morbidity and death from many chronic diseases. There is, however, limited data on the impact of obesity during critical illness. Objective: To determine the extent to which increasing body mass index (BMI) affects hospital length of stay (LOS) and mortality in a heterogenous group of ICU patients. Patients, setting and design: Forty eight thousand one hundred and seventy six patients from 101 ICUs participating in Project IMPACT, the comprehensive database system developed by the Society of Critical Care Medicine to measure and describe the care of ICU patients in the USA. Over 100 patient defined data elements including demographic information, admission diagnoses, severity of illness scores, body mass index (BMI) and outcome were prospectively collected. Main outcome measures: The Odds Ratio (OR) of hospital death for six strata of BMI as determined by stepwise logistic regression analysis and hospital LOS. Results: Thirty-eight percent of patients had a normal BMI, 7.1% of the patients were underweight, 54.1 % were overweight with 5.5% being morbidly obese. Hospital LOS was significantly longer at the extremes of BMI. By multivariate analysis the SAPS II Score, a nonmedical admission, sepsis on admission and BMI group were independent predictors of hospital mortality. The adjusted OR of death was 1.26 (95% CI, 1.14 to 1.40) in underweight patients, 0.86 (95% CI, 0.80 to 0.92) in overweight patients, 0.85 (95% CI, 0.78 to 0.93) in patients with Class I obesity, 0.76 (95% CI, 0.66 to 0.87) in patients with Class II obesity and 0.97 (0.85 to 1.11) in patients with Class III (morbid) obesity. Conclusion: The analysis of this large cohort of critically ill patients suggests that obesity may be protective in overweight and obese critically ill patients, while morbid obesity appears to have little effect on outcome. While obesity may improve the outcome following critical illness, obesity increases the overall burden of disease and reduces life expectancy.