Pressure-volume curve–derived recruitability indices are protocol-dependent in lavage-induced lung injury

Background Bedside assessments of lung recruitability using the static pressure-volume (PV) curve are crucial in managing acute respiratory distress syndrome (ARDS). We hypothesized that quantitative recruitability indices, such as the hysteresis ratio (HR) and normalized maximal distance (NMD), are inherently influenced by the peak airway pressure used during the measurement maneuver. Methods We conducted a secondary analysis of data from 17 sheep with lavage-induced ARDS. Static PV curves were generated using the super-syringe method at peak airway pressures of 40 and 60 cm H 2 O. HR and NMD were calculated and compared between the two pressure conditions using a two-tailed paired t-test. Results Both indices were significantly higher at a peak pressure of 60 cm H 2 O compared to 40 cm H 2 O. The mean HR increased from 0.18 ± 0.05 at 40 cm H 2 O to 0.22 ± 0.06 at 60 cm H 2 O ( P = .01). Similarly, the mean NMD increased significantly from 0.33 ± 0.08 at 40 cm H 2 O to 0.39 ± 0.07 at 60 cm H 2 O ( P = .008). Conclusions Lung recruitability quantified by HR and NMD increased significantly when higher airway pressures were used during the assessment. Clinicians must cautiously interpret PV curve-based assessments, recognizing that assessments performed at lower pressures may underestimate the lung’s true recruitment potential.