Impact of the driving pressure on mortality in obese and non-obese ARDS patients: a retrospective study of 362 cases.

Purpose: The relation between driving pressure (plateau pressure-positive end-expiratory pressure) and mortality has never been studied in obese ARDS patients. The main objective of this study was to evaluate the relationship between 90-day mortality and driving pressure in an ARDS population ventilated in the intensive care unit (ICU) according to obesity status.
Methods: We conducted a retrospective single-center study of prospectively collected data of all ARDS patients admitted consecutively to a mixed medical-surgical adult ICU from January 2009 to May 2017. Plateau pressure, compliance of the respiratory system (Crs) and driving pressure of the respiratory system within 24 h of ARDS diagnosis were compared between survivors and non-survivors at day 90 and between obese (body mass index ≥ 30 kg/m ² ) and non-obese patients. Cox proportional hazard modeling was used for mortality at day 90.
Results: Three hundred sixty-two ARDS patients were included, 262 (72%) non-obese and 100 (28%) obese patients. Mortality rate at day 90 was respectively 47% (95% CI, 40-53) in the non-obese and 46% (95% CI, 36-56) in the obese patients. Driving pressure at day 1 in the non-obese patients was significantly lower in survivors at day 90 (11.9 ± 4.2 cmH ₂ O) than in non-survivors (15.2 ± 5.2 cmH ₂ O, p < 0.001). Contrarily, in obese patients, driving pressure at day 1 was not significantly different between survivors (13.7 ± 4.5 cmH ₂ O) and non-survivors (13.2 ± 5.1 cmH ₂ O, p = 0.41) at day 90. After three multivariate Cox analyses, plateau pressure [HR = 1.04 (95% CI 1.01-1.07) for each point of increase], Crs [HR = 0.97 (95% CI 0.96-0.99) for each point of increase] and driving pressure [HR = 1.07 (95% CI 1.04-1.10) for each point of increase], respectively, were independently associated with 90-day mortality in non-obese patients, but not in obese patients.
Conclusions: Contrary to non-obese ARDS patients, driving pressure was not associated with mortality in obese ARDS patients.