Acute respiratory distress syndrome historical perspective

Overview
Acute respiratory distress syndrome was first observed in 1967 and has been defined progressively as a ratio of arterial partial oxygen tension as a fraction of inspirated oxygen below 200 mmHg in the presence of bilateral alveolar infiltrates.

Historical background

 * Acute respiratory distress syndrome was first described in 1967 by Ashbaugh et al. Initially there was no definition, resulting in controversy over incidence and mortality. In 1988 an expanded definition was proposed which quantified physiologic respiratory impairment.
 * In 1994 a new definition was recommended by the American-European Consensus Conference Committee. It had two advantages: 1 it recognizes that severity of pulmonary injury varies, 2 it is simple to use.
 * ARDS was defined as the ratio of arterial partial oxygen tension (PaO2) as fraction of inspired oxygen (FiO2) below 200 mmHg in the presence of bilateral alveolar infiltrates on the chest x-ray.
 * These infiltrates may appear similar to those of left ventricular failure, but the cardiac silhouette appears normal in ARDS.
 * Also, the pulmonary capillary wedge pressure is normal (less than 18 mmHg) in ARDS, but raised in left ventricular failure.
 * A PaO2/FiO2 ratio less than 300 mmHg with bilateral infiltrates indicates acute lung injury (ALI). Although formally considered different from ARDS, ALI is usually just a precursor to ARDS.

Consensus after 1967 and 1994

 * ARDS is characterized by:
 * Acute onset
 * Bilateral infiltrates on chest radiograph
 * Pulmonary artery wedge pressure < 18 mmHg (obtained by pulmonary artery catheterization), if this information is available; if unavailable, then lack of clinical evidence of left ventricular failure suffices
 * if PaO2:FiO2 < 300 mmHg acute lung injury (ALI) is considered to be present
 * if PaO2:FiO2 < 200 mmHg acute respiratory distress syndrome (ARDS) is considered to be present