Obesity and traumatic brain injury

Background: As obesity continues to run rampant in our society, an understanding of its adverse effect after traumatic injury is starting to unfold. We hypothesize that obesity negatively impacts head-injured patients, and the current study intends to compare obese and lean patients with traumatic brain injury (TBI). Methods: This is a retrospective study evaluating all blunt trauma patients with TBI admitted to the intensive care unit (ICU) in our urban, Level I trauma center from 1998 until 2003. Body mass index (BMI) was used to categorize patients as either lean (BMI < 30 kg/m(2)) or obese (BMI >= 30 kg/m(2)). Admission demographics, type and severity of head injury, and associated injuries were recorded for each patient. Primary outcome was mortality, while secondary outcomes were cause of death, complications, and for survivors, days of mechanical ventilation, ICU length of stay, and hospital length of stay. Obese and lean patients were compared using univariate analysis and multivariate stepwise logistic regression. In addition, a subgroup analysis of patients with isolated head injury was performed. Results:There were 690 patients with TBI admitted to the ICU during the study period, with 129 (19%) obese patients (BMI = 34 +/- 5 kg/m(2)) and 561 (81%) lean patients (BMI = 24 +/- 4 kg/m(2)). The two groups were similar with the exceptions that obese patients were older (46 +/- 20 years versus 39 years, p < 0.01), had lower admission systolic blood pressure (125 +/- 38 mm Hg versus 134 +/- 30 mm Hg,p = 0.01), and more often sustained an associated chest injury (46% versus 35%, p = 0.03). Obese patients with TBI had a trend toward more complications (34% versus 28%, p = 0.17) and a higher mortality (36% versus 25%, p = 0.02). However, stepwise logistic regression failed to identify obesity as an independent risk factor for either morbidity or mortality. In addition, obese patients with isolated head injury had no increase in complications or death. Conclusions: Although obese patients suffer more complications and higher mortality than lean patients after TBI, this adverse effect seems to be due to age, lower admission blood pressure, and more associated chest injury, rather than a direct result of the obese state.