The association between body-mass index and patient outcome in septic shock: a retrospective cohort study.

Background: It is unknown whether body-mass index (BMI) and commonly defined BMI categories are associated with mortality in patients with septic shock.
Methods: The database of a multidisciplinary intensive care unit (ICU) was retrospectively screened for adult patients with septic shock. BMI, demographic, clinical and laboratory variables together with outcome measures were collected in all patients. Subjects were categorized as follows: underweight, BMI < 18.5; normal weight, BMI 18.5-24.9; overweight, BMI 25-29.9; obesity, BMI >or= 30. Bivariate and multivariate logistic regression models were used to evaluate the association between BMI and outcome parameters.
Results: In total, 301 patients with septic shock were identified. BMI was bivariately associated with ICU mortality (OR 0.91; 95% CI 0.86-0.98; P = 0.007). There was no significant association between BMI and ICU mortality in the multivariate model but an increasing BMI tended to be associated with lower ICU mortality (OR 0.93; 95% CI 0.86-1.01; P = 0.09). Although overweight (OR 0.43; 95% CI 0.19-0.98; P = 0.04) and obese (OR 0.28; 95% CI 0.08-0.93; P = 0.04) patients had an independently lower risk of ICU death than those with normal weight, there was no difference in the risk of ICU death between normal weight and underweight patients (P = 0.22). A high BMI was independently associated with a lower frequency of acute delirium (P = 0.04) and a lower need for ICU re-admission (P = 0.001) but with a higher rate of ICU-acquired urinary tract infections (P = 0.02).
Conclusions: BMI up to 50 does not appear to be associated with worse ICU and hospital mortality in patients with septic shock. In contrast, a high BMI may reduce the risk of death from septic shock.