Driving pressure of respiratory system and lung stress in mechanically ventilated patients with active breathing

During control mechanical ventilation (CMV), the driving pressure of the respiratory system (ΔP ) serves as a surrogate of transpulmonary driving pressure (ΔP ). Expiratory muscle activity that decreases end-expiratory lung volume may impair the validity of ΔP to reflect ΔP . This prospective observational study in patients with acute respiratory distress syndrome (ARDS) ventilated with proportional assist ventilation (PAV+), aimed to investigate: (1) the prevalence of elevated ΔP , (2) the ΔP -ΔP relationship, and (3) whether dynamic transpulmonary pressure (Plung ) and effort indices (transdiaphragmatic and respiratory muscle pressure swings) remain within safe limits. Thirty-one patients instrumented with esophageal and gastric catheters (n = 22) were switched from CMV to PAV+ and respiratory variables were recorded, over a maximum of 24 h. To decrease the contribution of random breaths with irregular characteristics, a 7-breath moving average technique was applied. In each patient, measurements were also analyzed per deciles of increasing lung elastance (E ). Patients were divided into Group A, if end-inspiratory transpulmonary pressure (P ) increased as E increased, and Group B, which showed a decrease or no change in P with E increase. In 44,836 occluded breaths, ΔP ≥ 12 cmH O was infrequently observed [0.0% (0.0-16.9%) of measurements]. End-expiratory lung volume decrease, due to active expiration, was associated with underestimation of ΔP by ΔP , as suggested by a negative linear relationship between transpulmonary pressure at end-expiration (P ) and ΔP /ΔP . Group A included 17 and Group B 14 patients. As E increased, ΔP increased mainly due to P increase in Group A, and P decrease in Group B. Although ΔP had an area receiver operating characteristic curve (AUC) of 0.87 (95% confidence intervals 0.82-0.92, P