Abstract
Airway collapse may be identified during inspiration resulting in an airway opening pressure (AOP) which needs to be overcome to initiate inspiratory flow, and during expiration may lead to expiratory flow limitation (EFL). We hypothesized that elevated pleural pressures are associated with airway collapse. Mechanically ventilated patients with respiratory failure were enrolled. Esophageal pressure (Pes) was used to estimate pleural pressure and calculate transpulmonary pressure (PL). After a long washout with zero PEEP, we obtained slow-flow pressure-volume (PV) curves. The EFL was detected by visual inspection of the curves, "PEEP absorber" behavior and by the Rex method. Twenty patients were included. Our primary outcomes were the frequency of AOP and EFL, the association of AOP and baseline Pes after washout, AOP and total PEEP after washout, EFL and Pes after washout and the association of AOP with EFL. AOP occurred in 12 patients, while nine had EFL. Of the 12 patients with AOP, eight also had EFL. Among the eight patients with no AOP, only one had EFL (p=0.028). The AOP correlated with the patients' Pes after washout at zero PEEP (R2=0.5686, p=0.005). The auto-PEEP during a washout was associated with both the Pes (R2=0.5136, p=0.009) and the AOP (R2=0.352, p=0.042). The median Pes after a washout was 11.3±4.3 cmH2O in the AOP group versus 7.0±5.5 cmH2O in the non-AOP group (p=0.061). The Pes after a washout was 12.4±4.3 cmH2O in the EFL group versus 7.3±4.9 cmH2O in the non-EFL group (p=0.024). EFL and AOP correlated with elevated Pes, suggesting that elevated pleural pressures may be an important component of airway collapse. Measuring EFL and AOP could help improve ventilator support in critically ill patients.