Adult respiratory distress syndrome

Adult respiratory distress syndrome (ARDS) occurs as a result of severe pulmonary injury that cause alveolar damage heterogeneously throughout the lung ¹. It can either result from a direct pulmonary source or as a response to systemic injury.

Pathology

Lung damage results in leakage of fluid into alveoli, leading to non cardiogenic pulmonary oedema and decreased arterial oxygenation. 

The diagnosis is based on mainly clinical criteria set forth by the American-European Consensus Conference ⁴.

Causes

• trauma
• septicaemia
• hypovolaemic shock
• fat embolism
• near-drowning
• burns
• viral pneumonia
• pancreatitis
• oxygen toxicity
• smoke inhalalation
• disseminated intravascular coagulopathy
• transfusion reaction
• aspiration of gastric content
• head injury

Radiographic features

Plain film

Chest radiographic findings of ARDS are non specific and resemble those of typical pulmonary oedema 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. 

Chest x ray features usually develop 12 - 24 hours after initial lung insult. 

In contrast to cardiogenic pulmonary oedema, which clears in response to diuretic therapy, ARDS persists for days to weeks. In addition, as the initial radiographic findings of ARDS clear, the underlying lung appears to have a reticular pattern ⁴.

Prognosis

ARDS carries a high mortality of around 50% ² and many survivors develop chronic lung disease, with damaged lung healing by fibrosis. A minority recover fully.