A55-16 The Association of Elevated Pleural Pressures, Airway Opening Pressure and Expiratory Flow Limitation

Background & Aims In mechanically ventilated patients, airway collapse can happen both during inspiration, leading to airway opening pressure (AOP) and expiration, leading to expiratory flow limitation (EFL). This may impact pulmonary mechanics, pressure and resistance measurements, and possibly clinical outcomes. We hypothesized that elevated pleural pressures are associated with inspiratory and expiratory airway collapse. Methods Mechanically ventilated patients with hypoxemic respiratory failure were included. After a long washout, we obtained slow-flow PV curves. Subsequently, we increased the PEEP by 2cmH2O increments until a PEEP of 22cmH2O was reached, followed by 2cmH2O decrements until PEEP of 0cmH2O. The slow-flow PV curves were used to detect the AOP, while the EFL was detected by visual inspection of the flow and volume curves, PEEP absorber behavior and by the Rex method performed in each level of PEEP. We also assessed EFL resolution at each PEEP level. Results Twenty patients were included. The median age was 66 (IQR 57.8-72.5) years, and most patients were male (65%). ARDS was present in 15 (75%) patients. AOP occurred in 12 patients, while 9 patients experienced EFL. Of the 12 patients with AOP, 8 also had EFL, while among the 8 patients with no AOP, only 1 had EFL (p = 0.028). In patients with AOP, airway opening occurred at 5.9 (IQR 3.1-7.2) cmH2O. In patients with EFL, resolution occurred at mean set PEEP of 7.4±1.9cmH2O. The median Pes after a washout was 11.3±4.3cmH2O in the AOP group versus 7.0±5.5cmH2O in the non-AOP group (p = 0.061). The Pes after a washout was 12.4±4.3cmH2O in the EFL group versus 7.3±4.9cmH2O in the non-EFL group (p = 0.024). The mean expiratory resistance calculated by Rex method was higher in the EFL group: 55.02±37.20 cmH2O/L/s versus 12.43±2.85 cmH2O/L/s, p < 0.001. Among the 9 patients with EFL, 4 (44.4%) had complete resolution, 3 (33.3%) had partial resolution and 2 (22.2%) had no resolution of the EFL at 80% of auto-PEEP. Among the 8 patients with both AOP and EFL, when the PEEP was set at AOP, 4 (50.0%) patients had complete resolution and 2 (28.6%) had partial resolution of the EFL. Results available in Table 1. Conclusions Elevated pleural pressure is a potential etiology for EFL and AOP. Measuring EFL, AOP and the pressures set on the ventilator to overcome inspiratory and expiratory collapse could help improve ventilator support in critically ill patients. Further studies are needed to comprehensively understand these phenomena and their clinical implications This abstract is funded by: None