Acute lung injury (ALI) is a spectrum of pulmonary insufficiency ranging from minor and easily correctable hypoxemia to severe refractory respiratory failure or acute respiratory distress syndrome (ARDS). The American-European Consensus Conference on ARDS in 1994 defined ALI as a syndrome of inflammation and increased permeability that is associated with a constellation of clinical, radiologic, and physiologic abnormalities that cannot be explained by, but may coexist with, left atrial or pulmonary capillary hypertension . The resultant pulmonary insufficiency can be an indirect result of a systemic inflammatory state (circulating inflammatory mediators causing reactivity and edema in the lung parenchyma), or a direct result of a localized release of inflammatory mediators from a process affecting the lung parenchyma such as blunt chest trauma, toxic inhalation, aspiration, or pneumonia. Factors increasing a patient's likelihood of developing ALI are those that predispose a patient to massive inflammation, as well as increasing age, preexisting need for mechanical ventilation, smoke inhalation, massive transfusion, and drug overdose.
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