ABSTRACT
Acute lung injury (ALI), first described by Ashbaugh in 1967 (1), is a disorder with
varying degrees of pulmonary cellular damage (parenchymal and vascular) that alters
alveolar capillary membrane permeability, produces accumulation of noncardiogenic
extravascular lung water, and results in hypoxic respiratory failure. Patients with this syn-
drome have dyspnea, refractory hypoxia, reduced lung compliance, and diffuse radiologic
changes. Acute respiratory distress syndrome (ARDS) is a more severe subset of ALI
characterized by dyspnea, refractory hypoxemia, decreased lung compliance, and diffuse
radiologic changes that occur in the absence of cardiac failure or chronic lung disease. The
American-European Consensus Conference on ARDS of 1994 defines ALI as “a syn-
drome 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.” It is associated most often
with sepsis syndrome, aspiration, primary pneumonia, or multiple traumas. Much less
common associations include cardiopulmonary bypass, multiple transfusions, fat embo-
lism, and pancreatitis. ALI and ARDS are acute in onset and persistent, for example,
lasting days to weeks; are associated with one or more known risk factors; are character-
ized by arterial hypoxemia resistant to oxygen therapy alone; and demonstrate diffuse
radiologic infiltrates. Chronic lung diseases such as interstitial pulmonary fibrosis and
sarcoidosis, which would technically meet the criteria for the chronicity, are excluded
by this definition (2). The criteria recommended by this consensus committee are enum-
erated in Table 1. This definition emphasizes that ALI/ARDS is not the result of primary cardiac disease as the cause of the hypoxia and radiographic findings (2), although
patients with this condition can become fluid overloaded or develop concurrent heart
failure (3).
