Acute respiratory distress syndrome

Adult respiratory distress syndrome (ARDS) occurs as a result of severe pulmonary injury (see table below) that cause alveolar damage heterogeneously throughout the lung (Artigas et al, 1998). This damage results in leakage of edema fluid into alveoli, leading to noncardiogenic pulmonary edema and decreased arterial oxygenation. Diagnosis is based on mainly clinical criteria set forth by the American-European Consensus Conference (Bernard et al, 1994).

Chest radiographic findings of ARDS are nonspecific and resemble those of typical pulmonary edema or pulmonary haemorrhage: diffuse bilateral coalescent opacities (the only radiologic criterion defined by the Consensus Conference). The time course of ARDS may help in differentiating it from typical pulmonary edema. ARDS, in contrast to cardiogenic pulmonary edema, which clears in response to diuretic therapy, persists for days to weeks. In addition, as the initial radiographic findings of ARDS clear, the underlying lung appears to have a reticular pattern (Reed, 2003).

The causes of ARDS include:

• Trauma
• Septicaemia
• Hypovolaemic shock
• Fat embolism
• Near-drowning
• Burns
• Viral pneumonia
• Pancreatitis
• Oxygen toxicity
• Disseminated intravascular coagulopathy
• Transfusion reaction

ARDS mortality is high--around 50% (Artigas et al, 1991)--and many survivors develop chronic lung disease, with damaged lung healing by fibrosis. A minority recover fully.