A total of 2,291 patients were enrolled into the original cohort. Patients admitted to the ICU for a diagnosis other than trauma (n = 883) were excluded from the study. Of the 1,406 trauma patients, 187 (15%) were excluded for missing BMI data. The demographics and clinical characteristics of the 1,219 remaining patients by BMI group are displayed in . The majority of patients fell into the normal (35%) and overweight categories (33%), but the prevalence of obesity (23%) and severe obesity (7%) was also high. The overweight group was made up of significantly more male patients (p < 0.001), while the patients in the normal weight group were younger (p < 0.001). There was no difference among the groups according to blunt or penetrating mechanism, or acute physiology and chronic health evaluation (APACHE) II score. Anatomic injury severity (ISS) was statistically higher (p = 0.008) and the predicted survival (TRISS) was significantly lower (p = 0.006) in the normal weight group. Anatomic injury pattern did not significantly differ between the groups with the exception of head injuries. The underweight and normal weight groups had a higher AIS head and neck score than the other groups (p < 0.001). With regard to pre-ICU comorbidities, underweight patients were more likely to experience chronic renal insufficiency and dialysis dependence, while severely obese patients were more likely to experience diabetes mellitus, cardiac disease, hyperlipidemia, and hypertension. Individual comorbidities were not included in the regression models since they are summarized by the chronic health score of the APACHE II score. summarizes demographic and clinical characteristics of patients by pulmonary outcomes.
Demographic and Clinical Characteristics of Patients by BMI Group*
Demographic and Clinical Characteristics by Outcome*
Unadjusted rates of primary and secondary outcomes by BMI group are summarized in . The overall rate of ARDS was 27%. The unadjusted rate of ARDS was significantly lower in the severely obese group (11%) compared to the obese group (32%; p = 0.02). While a difference was also suggested between the severely obese group and the underweight, normal weight, and overweight groups, this difference was not statistically significant. When compared to the normal weight group, the age-, gender-, and severity-adjusted odds of ARDS remained lower in the severely obese group (odds ratio, 0.36; 95% CI, 0.13 to 0.99) . The rates of pneumonia, tracheostomy tube placement, and mortality were 37%, 10%, and 11%, respectively (). There was no difference in these rates by BMI group in either the univariate or multivariate analyses.
Clinical Outcomes by BMI Group
Adjusted Values for Pulmonary Outcomes and Death by BMI Group*
Adjusted Continuous Outcomes by BMI Group*
The median mechanical ventilation requirement of the cohort was 7 days (IQR, 4 to 12 days), and the number of days spent receiving mechanical ventilation did not differ by BMI group. These relationships did not differ when nonsurvivors were excluded. The median ICU LOS was 9 days, and the median hospital LOS was 18 days. After adjusting for age, gender, head injury severity, and predicted survival, the severely obese group had an ICU LOS that was 4.8 days (95% CI, 1.8 to 7.7) longer than the normal weight group ().
summarizes the unadjusted relationship between BMI and dichotomous outcomes with a concurrent summary of anatomic injury severity (as estimated by the ISS). The unadjusted relationships among ARDS, pneumonia, and tracheostomy tube placement closely parallel anatomic injury severity across the entire spectrum of BMI, suggesting no independent relationship between BMI and these outcomes. In contrast, for patients with a BMI of > 35 kg/m2, mortality increases while injury severity decreases. This trend was detected in the BMI group analysis, but it was not significant since patients with the highest mortality rates (ie, those with a BMI of > 50 kg/m2) represent only 26% of patients (21 of 81 patients) in the severely obese group.
Associations among BMI, mortality, and pulmonary complications after injury.