Analysis of Mortality in Traumatically Injured Patients Based on Body Mass Index and Mechanism Reveals Highest Mortality among the Underweight in Comparison with the Ideal Weight Patients

The purpose of this study was to evaluate the effect of body mass index (BMI) on mortality after traumatic injury. The records of patients from 2012 to 2015 were retrospectively reviewed. The patients were stratified into the following groups based on admission BMI (kg/m2): underweight (UW) (BMI <19), ideal weight (IW) (BMI = 19-24.9), overweight (OW) (BMI = 25-29.9), obese (OB) (BMI = 30-39.9), and morbid obese (MO) (BMI >40). The groups were well matched with no significant differences in demographics and Injury Severity Score. Morality for the IW group was compared with the remaining BMI groups. A total of 6049 patients were identified. In comparison with IW group, the UW mortality was significantly higher (IW vs UW, 4.1% vs 8.8%, P = 0.001); however, the there was no significant difference with remaining groups. There was also no significant difference in mortality between IW and the remaining groups for patients that went directly to the operating room or for patients that had penetrating trauma (stab wounds and gunshot wounds). However, for blunt trauma, the mortality was significantly higher for UW (IW vs UW, 4.3% vs 9.4%, P = 0.001), no different for IW vs OW (4.3% vs 3.7%, P = 0.3), and significantly lower for IW vs OB (4.3% vs 2.8%, P = 0.04) and for IW vs MO (4.3% vs 1.0%, P = 0.03). After traumatic injuries, it is the underweight patients (BMI <19) and not the obese, that are at a significantly higher risk for overall mortality; this difference is especially evident after blunt trauma where obesity may actually confer a protective role.