 Acute lung injury ALI and the acute respiratory distress syndrome ARDS represent a spectrum of clinical syndromes of rapid respiratory system deterioration that are associated with both pulmonary and systemic illness. These syndromes are associated with 30-40 mortality with our current standard of care and are responsible for approximately 75,000 deaths in the US yearly. The current evidence-based care consists of a strategy of mechanical ventilation utilizing low lung volumes ARDSNet ventilation intended to limit further lung injury from overstretch of the lung induced by the ventilator. However, this strategy has been shown to be associated with continued lung injury in some studies and still is associated with about a 30 mortality rate. Airway pressure release ventilation APRV is a different, nonexperimental strategy of mechanical ventilation currently in routine clinical use. APRV allows a patient a greater degree of autonomy in controlling hisher breathing while achieving a higher mean airway pressure at similar plateau pressures than that typically achieved with ARDSNet. APRV has been associated with less ventilator-associated pneumonia, better oxygenation, and less sedative usage in small studies when compared with other methods of ventilation. However, debate exists over net effects of APRV with regard to ventilator-associated lung injury. Additionally, we recently completed a study showing that APRV was associated with lower ventilator associated pneumonia VAP rates, but this benefit did not appear to be mediated by sedation differences. We hypothesized that the VAP benefits might be mediated by greater lung recruitment and possibly less ventilator-induced lung injury with APRV. We propose a randomized, crossover study looking at biomarkers of lung injury in patients with acute lung injury ventilated with APRV and ARDSNet. Our hypothesis is that airway pressure release ventilation is associated with lower levels of lung injury biomarkers than ARDSNet ventilation. 