The ARDSnet protocol is the current, standard of care for ARDS. Mechanical ventilation is managed using low tidal volumes, relatively high respiratory rates, with oxygenation managed according to PEEP and FIO2 relationships as defined in a table. This study compares the ARDSnet protocol with an open lung approach to mechanical ventilation. The open lung approach uses a technique to recruit collapsed lung areas and then uses the lowest PEEP level that prevents recollapse of recruited lung units. The best PEEP level is determined by a decremental PEEP trial involving a series of pressure measurements taken after the recruitment maneuver. Both the ARDSnet protocol and the open lung approach require low tidal volumes and plateau pressures.