Burn Outcomes at Extremes of Body Mass Index: Underweight Is as Problematic as Morbid Obesity.

Limited evidence suggests that obesity adversely affects burn outcomes. However, the impacts of body mass index (BMI) across the continuum have not been fully characterized. Therefore, we aimed to characterize outcomes after burn injury across the BMI continuum. We hypothesized that "normal" BMI (18.5-24.9) would have the lowest mortality and complication rates. The US National Trauma Data Bank (NTDB) was queried for adult burn-injured patients from 2007 to 2015. Admission BMI was calculated and grouped according to World Health Organization (WHO) classification. The primary outcome was in-hospital mortality. Secondary outcomes of time to wound closure, length of stay, and inpatient complications were similarly assessed. Of the 116,008 burn patient encounters that were identified, 7243 underwent at least one operation for wound closure. Mortality was lowest in the overweight (P = .039) and obese I cohorts (BMI 25-29.9, 30.0-34.9) at 2.9% and increased in both directions of the BMI continuum to 4.1% in the underweight (P = .032) and 5.1% in the morbidly obese (class III) group (P = .042). Time to final wound closure was longest in the two BMI extremes. BMI ≥40 was associated with increased intensive care unit days, ventilator days, renal and cardiac complications. BMI <18.5 had increased hospital days and rates of sepsis. Aberrations in metabolism associated with both increases and decreases of body weight may cause pathophysiologic changes that lead to worsened outcomes in burn-injured patients. In addition to morbidly obese patients, underweight patients also experience increased burn-related death and complications. In contrast, overweight BMI patients may have greater physiologic reserves without the burden of obesity or sarcopenia.