Acute lung injury and the acute respiratory distress syndrome.

OBJECTIVE: To review acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) in light of recent information about the definitions, epidemiology, pathophysiology, management, and outcome of these conditions. DATA SOURCES: The author's personal files as well as the computerized MEDLINE database. STUDY SOLUTION: Studies were selected for their relevance to the conditions of ALI and ARDS. DATA EXTRACTION: The author extracted all applicable data. DATA SYNTHESIS: The diagnostic criteria for ALI and ARDS include a) acute onset; b) bilateral chest radiographic infiltrates; c) a pulmonary artery occlusion pressure of < or =18 mm Hg or no evidence of left atrial hypertension; and d) impaired oxygenation manifested by a PaO2/FIO2 ratio of < or =300 torr (< or =40 kPa) for ALI and < or =200 torr (< or =27 kPa) for ARDS. The incidence of ALI and ARDS are approximately 70 and 7 patients out of 100,000 of the total U.S. population per year, respectively. The conditions result from direct or indirect injury to the pulmonary epithelium and endothelium that causes edema, atelectasis, inflammation, and fibrosis. This "diffuse alveolar damage" is actually patchy in many patients. Therapy of ALI and ARDS is largely supportive, although new approaches in mechanical ventilation, patient positioning, and pharmacologic therapy have been introduced. The mortality rate of ARDS has improved to <50%, but the reasons for this improvement are unclear.
CONCLUSION: ALI and ARDS are better defined and understood than ever before, and their outcome has improved for unclear reasons.