Partition of respiratory mechanics in patients with acute respiratory distress syndrome and association with outcome: a multicentre clinical study

Purpose In acute respiratory distress syndrome (ARDS), physiological parameters associated with outcome may help defining targets for mechanical ventilation. This study aimed to address whether transpulmonary pressures ( P L ), including transpulmonary driving pressure (DP L ), elastance-derived plateau P L , and directly-measured end-expiratory P L , are better associated with 60-day outcome than airway driving pressure (DP aw ). We also tested the combination of oxygenation and stretch index [PaO 2 /(FiO 2 *DP aw )]. Methods Prospective, observational, multicentre registry of ARDS patients. Respiratory mechanics were measured early after intubation at 6 kg/ml tidal volume. We compared the predictive power of the parameters for mortality at day-60 through receiver operating characteristic (ROC) and assessed their association with 60-day mortality through unadjusted and adjusted Cox regressions. Finally, each parameter was dichotomized, and Kaplan–Meier survival curves were compared. Results 385 patients were enrolled 2 [1–4] days from intubation (esophageal pressure and arterial blood gases in 302 and 318 patients). As continuous variables, DP aw , DP L , and oxygenation stretch index were associated with 60-day mortality after adjustment for age and Sequential Organ Failure Assessment, whereas elastance-derived plateau P L was not. DP aw and DP L performed equally in ROC analysis ( P = 0.0835). DP aw had the best-fit Cox regression model. When dichotomizing the variables, DP aw ≥ 15, DP L ≥ 12, plateau P L ≥ 24, and oxygenation stretch index < 10 exhibited lower 60-day survival probability. Directly measured end-expiratory P L ≥ 0 was associated with better outcome in obese patients. Conclusion DP L was equivalent predictor of outcome than DP aw . Our study supports the soundness of limiting lung and airway driving pressure and maintaining positive end-expiratory P L in obese patients.