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

Abstract

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 [PaO₂/(FiO₂*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.

Keywords: Acute respiratory distress syndrome; Artificial respiration; Mechanical ventilation; Positive-pressure respiration; Respiratory mechanics.