Body Mass Index and Mortality in Subjects With ARDS: Post-hoc Analysis of the OSCILLATE Trial

Background: Studies on the association of obesity with mortality in subjects with ARDS have yielded inconsistent results.

Methods: In a sub-analysis of the Oscillation for ARDS Treated Early (OSCILLATE) randomized controlled trial, 451 subjects were divided into 5 strata based on their body mass index (BMI) using the World Health Organization definitions: underweight < 18.5 kg/m²; normal weight 18.5-24.99 kg/m²; overweight 25-29.99 kg/m²; obese 30-39.99 kg/m²; severely obese > 40 kg/m². The primary outcome was all-cause hospital mortality across BMI strata for all subjects and for the 2 study arms (high-frequency oscillatory ventilation [HFOV] vs conventional ventilation) separately using multivariable logistic regression adjusting for potential confounding variables.

Results: Hospital mortality was not different across the BMI strata for all subjects (P = .86), for the HFOV arm (P = .94) or for the conventional ventilation arm (P = .59). After risk adjustment, BMI was not associated with increased risk for hospital mortality (odds ratio 1.01, 95% CI 0.97-1.04, P = .67), whereas HFOV was independently associated with increased mortality (odds ratio 1.74, 95% CI 1.11-2.72, P = .02) with no effect modification by BMI strata (for this interaction, P = .56). Although there was no difference in the use of rescue therapies or in the number of days on sedation or analgesia, higher daily doses of fentanyl and midazolam were administered as BMI increased.

Conclusion: There was no difference in adjusted hospital mortality across BMI strata in subjects with moderate to severe ARDS. Processes of care were not different across BMI strata except for higher daily doses of fentanyl as BMI increased. (ClinicalTrials.gov registration NCT0150640).