acute lung injury (ALI)

What are the definitions of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS)?

ALI and ARDS both reflect permeability pulmonary edema secondary to an insult to the alveolar-capillary unit. The inciting insult is more typically at the level of the vascular endothelium and is mediated via a neutrophil-dependent inflammatory cascade. There is a long list of causes that includes both intrathoracic (e.g., pneumonia, inhalational injury) and extrathoracic (e.g., pancreatitis, sepsis) etiologies.

From a clinical standpoint, ALI is defined as an acute lung disease with bilateral pulmonary opacities on a chest radiograph, a pulmonary wedge pressure of 18 mm Hg or less, and a ratio of arterial oxygen to the fraction of inspired oxygen (PaO 2 /FiO 2 ) of 300 mm Hg or less. ARDS is a more severe form of ALI and is defined by a PaO 2 /FiO 2 ratio of 200 mm Hg or less.

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