An Evaluation of the “Obesity Paradox” in Isolated Blunt Abdominal Trauma in the United States

Background The obesity paradox theorizes a survival benefit in trauma patients secondary to the cushioning effect of adiposity. We aim to evaluate the impact of body mass index (BMI) on abdominal injury severity, morbidity, and mortality in adults with isolated, blunt abdominal trauma in the United States. Methods We reviewed the National Trauma Data Bank (2013-2021) for adults sustaining isolated, blunt abdominal trauma stratified by BMI. We performed a doubly robust, augmented inverse-propensity weighted multivariable logistic regression to estimate the average treatment effect (ATE) of BMI on mortality and the presence of abdominal organ injury. Results 36,350 patients met the inclusion criteria. In our study, 41.4% of patients were normal-weight (BMI 18.5-24.9), 20.6% were obese (BMI 30-39.9), and 4.7% were severely obese (BMI≥40). In these cohorts, the abdominal abbreviated injury scale (AIS) was 2 (2 -3). Obese and severely obese patients had significantly reduced presence of pancreas, spleen, liver, kidney, and small bowel injuries. The predicted probability of abdominal AIS severity decreased significantly with increasing BMI. Crude mortality was significantly higher in obese (1.3%) and severely obese patients (1.3%) compared to normal-weight patients (0.7%). Obese and severely obese patients demonstrated non-statistically significant changes in the mortality of +26.4% (ATE 0.264, 95%CI -0.108–0.637, p=0.164) and +55.5% (ATE 0.555, 95%CI -0.284–1.394, p=0.195) respectively, compared to normal weight patients. Conclusion BMI may protect against abdominal injury in adults with isolated, blunt abdominal trauma. Mortality did not decrease in association with increasing BMI, as this may be offset by the increase in co-morbidities in this population.