Airway opening pressure in mechanically ventilated patients: regional distribution and impact of body position

Background: Airway Opening Pressure (AOP) refers to the pressure level needed to reopen previously collapsed airways. Its underlying mechanisms remain debated. This study aimed to assess its regional distribution and the effect of body position. Methods: Global AOP (AOPGLOBAL) was assessed by the low-flow inflation maneuver. Electrical impedance tomography allowed to assess regional AOP (ventral and dorsal). Measurements were performed in the semi-recumbent position (SR30°) in all patients and repeated in supine position (SP0°) in a subgroup of patients to explore the effect of body position. As a proof of concept, AOP was also evaluated in four Thiel cadavers in both SR30° and SP0°, with and without the adjunction of a 3 kg saline bag on the abdomen. Results: 46 mechanically ventilated patients were analyzed. In SR30°, AOPGLOBAL was detected in 10 patients (22%) (median level 8.4 [6.3–12.0] cmH2O), while AOPVENTRAL and AOPDORSAL occurred in 11 (24%) and 16 (35%) patients, respectively. The lowest regional AOP correlated with the AOPGLOBAL (r2 = 0.993, p < 0.001). In the subgroup of 23 patients with position analysis, the highest regional AOP increased from SR30° to SP0°. Cadavers’ experiments showed that the increase in end-expiratory esophageal pressure associated with SP0° or increased abdominal pressure correlated with the increase in AOPGLOBAL (r2 = 0.908, p < 0.001). Conclusion: Bedside AOP detection based on the low-flow insufflation method may miss regional AOP, leading to an underestimation of the minimal positive end-expiratory pressure which may be required to avoid tidal opening and closing in some lung regions. The level of regional AOP increases in SP0° compared to SR30° position.