Differential effects of sustained inflation recruitment maneuvers on alveolar epithelial and lung endothelial injury*

Objective: The role of recruitment maneuvers in mechanical ventilation for patients with the acute respiratory distress syndrome and acute lung injury remains uncertain in part due to a lack of data on the effects of specific recruitment maneuvers on lung injury severity. The primary objective of this study was to determine the effect of one type of recruitment maneuver—sustained inflation—on alveolar epithelial and lung endothelial injury in experimental acute lung injury. Design: Randomized experimental study. Setting: Academic research laboratory. Subjects: Forty-nine Sprague-Dawley rats. Interventions: Lung injury was induced in anesthetized, ventilated rats by instillation of acid (pH 1.5) into the airspaces. Rats were ventilated with a tidal volume of 6 mL/kg and a positive end-expiratory pressure of 5 cm H2O with or without a sustained inflation recruitment maneuver repeated every 30 mins. Each recruitment maneuver consisted of two 30-sec inflations to total lung capacity (30 cm H2O) 1 min apart. Measurements and Main Results: The use of recruitment maneuvers significantly improved oxygenation, compliance, end-expiratory lung volume, functional residual capacity, and deadspace fraction. Recruitment maneuvers reduced extravascular lung water and lung endothelial injury as measured by protein permeability (217 ± 28 vs. 314 ± 70 extravascular plasma equivalents [μL], p < .05). However, recruitment maneuvers did not prevent alveolar epithelial injury. Epithelial permeability and bronchoalveolar lavage RTI40 levels, a marker of type I cell injury, were similar with or without recruitment maneuvers. Recruitment maneuvers decreased epithelial fluid transport, a functional marker of epithelial injury. Recruitment maneuvers did not reduce markers of airspace inflammation. Conclusions: Sustained inflation recruitment maneuvers improve respiratory mechanics and oxygenation and may protect the lung endothelium but do not reduce alveolar epithelial injury. Because of the differential effects of recruitment maneuvers on the lung endothelium and alveolar epithelium, the net effect in clinical acute lung injury may not be beneficial. Additional clinical studies will be needed to assess the net impact of recruitment maneuvers in patients with acute lung injury.