A retrospective cohort study examining the association between body mass index and mortality in severe sepsis

Body mass index (BMI) is an easily calculated indicator of a patient’s body mass including muscle mass and body fat percentage and is used to classify patients as underweight or obese. This study is to determine if BMI extremes are associated with increased 28-day mortality and hospital length of stay (LOS) in emergency department (ED) patients presenting with severe sepsis. We performed a retrospective chart review at an urban, level I trauma center of adults admitted with severe sepsis between 1/2005 and 10/2007, and collected socio-demographic variables, comorbidities, initial and most severe vital signs, laboratory values, and infection sources. The primary outcome variables were mortality and LOS. We performed bivariable analysis, logistic regression and restricted cubic spline regression to determine the association between BMI, mortality, and LOS. Amongst 1,191 severe sepsis patients (median age, 57 years; male, 54.7 %; median BMI, 25.1 kg/m²), 28-day mortality was 19.9 % (95 % CI 17.8–22.4) and 60-day mortality was 24.4 % (95 % CI 21.5–26.5). Obese and morbidly obese patients were younger, less severely ill, and more likely to have soft tissue infections. There was no difference in adjusted mortality for underweight patients compared to the normal weight comparator (OR 0.74; CI 0.42–1.39; p = 0.38). The obese and morbidly obese experienced decreased mortality risk, vs. normal BMI; however, after adjustment for baseline characteristics, this was no longer significant (OR 0.66; CI 0.42–1.03; p = 0.06). There was no significant difference in LOS across BMI groups. Neither LOS nor adjusted 28-day mortality was significantly increased or decreased in underweight or obese patients with severe sepsis. Morbidly obese patients may have decreased 28-day mortality, partially due to differences in initial presentation and source of infection. Larger, prospective studies are needed to validate these findings related to BMI extremes in patients with severe sepsis.