Introduction: Acute lung injury and its more severe form, acute respiratory distress syndrome (ARDS), cause respiratory failure, the most common organ failure leading to intensive care. Airway pressure release ventilation (APRV, also known as Bi-Level and Bi-phasic) is a timecycled, time triggered, pressure-targeted form of ventilatory support. Specifically, conventional pressure-targeted SIMV uses a "physiological" inspiratory time with I:E ratio less than 1:1.