Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) represent a spectrum of acute respiratory failure with diffuse, bilateral lung injury and severe hypoxemia caused by non-cardiogenic pulmonary edema. Failure may be initiated by pulmonary or extrapulmonary insults (e.g., pneumonia, sepsis, trauma, aspiration) that increase alveolar epithelial endothelial permeability, flood alveoli, and reduce lung compliance. The only treatment proven to improve survival is mechanical ventilation using a 'lung protective strategy' with tidal volume =6 mL/kg predicted body weight. Although mortality can exceed 50%, survivors have a good prognosis for recovery of lung function.