ObjectivePositive end-expiratory pressure (PEEP) and recruitment maneuvers (RMs) may partially reverse atelectasis and reduce ventilation-associated lung injury. The purposes of this study were to assess a) magnitude and duration of RM effects on arterial oxygenation and on requirements for oxygenation support (Fio2/PEEP) in patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS) receiving ventilation with low tidal volumes and high levels of PEEP; and b) frequency of adverse respiratory and circulatory events attributable to RMs.DesignProspective, randomized, crossover study.SettingThirty-four intensive care units at 19 hospitals.PatientsSeventy-two patients with early ALI/ARDS. Baseline PEEP and Fio2were 13.8 ± 3.0 cm H2O and 0.39 ± 0.10, respectively (mean ± sd).InterventionsWe conducted RMs by applying continuous positive airway pressure of 35–40 cm H2O for 30 secs. We conducted sham RMs on alternate days. We monitored oxyhemoglobin saturation by pulse oximetry (SpO2), Fio2/PEEP, blood pressure, and heart rate for 8 hrs after RMs and sham RMs. We examined chest radiographs for barotrauma.Measurements and Main ResultsResponses to RMs were variable. Greatest increments from baseline SpO2within 10 mins after RMs were larger than after sham RMs (1.7 ± 0.2 vs. 0.6 ± 0.3 %, mean ± sem,p< .01). Systolic blood pressure decreased more within 10 mins after RMs (9.4 ± 1.1 vs. 3.1 ± 1.1 mm Hg,p< .01). Changes in Fio2/PEEP requirements were not significantly different at any time after RMs vs. sham RMs. Barotrauma was apparent on first radiographs after one RM and one sham RM.ConclusionsIn ALI/ARDS patients receiving mechanical ventilation with low tidal volumes and high PEEP, short-term effects of RMs as conducted in this study are variable. Beneficial effects on gas exchange in responders appear to be of brief duration. More information is needed to determine the role of recruitment maneuvers in the management of ALI/ARDS.