Various conditions can predispose a patient to ARDS, but they usually represent a sudden catastrophic situation. These conditions can be classified into two categories: direct lung injury and indirect lung injury. Direct injury occurs from situations such as gastric aspiration, near drowning, chemical inhalation, and oxygen toxicity. Indirect injury occurs from mediators released during sepsis, multiple trauma, thermal injury, hypoperfusion or hemorrhagic shock, disseminated intravascular coagulation, drug overdose, and massive blood transfusions. The most common risk factor for ARDS is sepsis from an abdominal source. Approximately 150,000 new cases of ARDS occur each year. Mortality rates vary and have been estimated to be between 40% and 50%, but older patients and patients with severe infections have a higher rate. Survivors generally have almost normal lung function a year after the acute illness.