Randomized, fixed sample. Patients were stratified by age (under and over 40 years) and by the presence or absence of trauma. Patients were assigned to conventional positive pressure ventilation therapy or to a three-step therapeutic program employing pressure-controlled-inverted-ratio-ventilation, continuous positive airway pressure, and low-frequency positive pressure ventilation-extracorporeal CO2 removal. The main outcome measure was survival at 30 days after randomization. Secondary outcome measures included hospital costs, physiologic data, length of hospital stay, and blood product consumption. Follow-up took place during the year after hospital discharge.