5. Receiving conventional MV, or lung-protective ventilation (LPV), in the assist control (AC) mode with positive end-expiratory pressure (PEEP) > 5 cm H2O Criteria 1-3 must occur within a 24-hour period. "Acute onset" is defined as follows: the duration of the hypoxemia criterion (#1) and the chest radiograph criterion (#2) must be < 7 days at the time of randomization.