Response to Recruitment Maneuver Influences Net Alveolar Fluid Clearance in Acute Respiratory Distress Syndrome

Abstract

RECENT studies have reported improved outcome for patients with acute respiratory distress syndrome (ARDS) ventilated with tidal volumes of 6 ml/kg.1,2 A low tidal volume, by reducing ventilator-induced lung overinflation, may decrease the lung and systemic inflammatory reaction.3 ARDS is characterized by a protein-rich alveolar edema,4 the amount of which depends in part on the alveolar fluid clearance resulting from Na/K adenosine triphosphatase–dependent pumps.5 Classically, alveolar fluid clearance is considered as maintained in cardiogenic pulmonary edema, impaired in ARDS,6 and not affected by mechanical ventilation.7 A recent animal study, however, has demonstrated that a reduction of tidal volume improves alveolar fluid clearance.8 The authors hypothesized that the reduced injury of the alveolar epithelium resulting from the low tidal volume decreased lung inflammatory reaction, thereby improving alveolar fluid clearance. Protective ventilation may add to the reduction of tidal volume a recruitment maneuver (RM). An RM improves arterial oxygenation and respiratory mechanics by increasing the amount of gas in nonaerated lung areas.9 By providing alveolar recruitment, RM may reduce lung stretch and the inflammatory reaction caused by mechanical ventilation10 and therefore increase alveolar fluid clearance. As recently demonstrated,11–13 it may also induce overinflation, which, in turn, could damage the alveolar epithelium and impair net alveolar fluid clearance.