 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. Current evidence-based care of ALI consists of a strategy of mechanical ventilation utilizing low lung volumes ARDSNet ventilation intended to limit further stretch-induced lung injury exacerbated by the ventilator. However, this strategy has been shown to be associated with increased lung injury in a subset of patients and still is associated with about a 30 mortality rate. Airway pressure release ventilation APRV is a different, non-experimental strategy of mechanical ventilation currently in routine clinical use. APRV is a pressure-cycled ventilator mode that allows a patient a greater degree of autonomy in controlling his or her breathing pattern than ARDSNet ventilation. Use of APRV has been associated with better oxygenation, less sedative usage, and less ventilator-associated pneumonia in small studies compared with other ventilator modes. However, debate exists over whether APRV might result in decreased or increased ventilator-associated lung injury when compared with ARDSNet ventilation. We intend to implement a randomized, cross over study looking at biomarkers of lung injury in patients with acute lung injury during ventilation with APRV and using the ARDSNet protocol. Our hypothesis is that airway pressure release ventilation is associated with lower levels of lung injury biomarkers than ARDSNet ventilation. 