ObjectiveTo assess how the level of positive end-expiratory pressure (PEEP) (antiderecruitment strategy), etiological category of diffuse lung injury, and body position of the patient modify the effect of the alveolar recruitment maneuver (ARM) in acute respiratory distress syndrome (ARDS).DesignProspective clinical trial.SettingMedical intensive care unit at a tertiary hospital.PatientsForty-seven patients with early ARDS, including 19 patients from our preliminary study.InterventionFrom baseline ventilation at a tidal volume of 8 mL/kg and PEEP of 10 cm H2O, the ARM (a stepwise increase in the level of PEEP up to 30 cm H2O with a concomitant decrease in the magnitude of tidal volume down to 2 mL/kg) was given with (ARM + PEEP, n = 20) or without (ARM only, n = 19) subsequent increase of PEEP to 15 cm H2O. In eight other patients, PEEP was increased to 15 cm H2O without a preceding ARM (PEEP only).Measurements and ResultsIn all three groups, Pao2was increased by the respective intervention (allp< .05). In the ARM-only group, Pao2at 15 mins after intervention was lower than Pao2immediate after intervention (p= .046). In the ARM + PEEP group, no such decrease in Pao2was observed, and Pao2at 15, 30, 45, and 60 mins after intervention was higher than in the ARM-only group (allp< .05). Compared with the PEEP-only group, Pao2of the ARM + PEEP group was higher immediately after intervention and at the later time points (allp< .05). Compared with patients with ARDS associated with direct lung injury (pulmonary ARDS), patients with ARDS associated with indirect lung injury (extrapulmonary ARDS) showed a greater increase in Pao2(27 ± 21% vs. 130 ± 112%;p= .002) and a greater decrease in radiologic scores (1.0 ± 2.4 vs. 3.4 ± 1.5;p= .005) after the ARM. The increase in Pao2induced by the ARM was greater for patients in the supine position than for patients in the prone position (61 ± 82% vs. 21 ± 14%;p= .028). Consequently, Pao2immediately after the ARM was similar in the two groups of patients in different positions.ConclusionsAfter the ARM, a sufficient level of PEEP is required as an antiderecruitment strategy. Pulmonary ARDS and extrapulmonary ARDS may be different pathophysiologic entities. An effective ARM may obviate the need for the prone position in ARDS at least in terms of oxygenation.