Acute respiratory distress syndrome

#### Summary points Acute respiratory distress syndrome is the extreme manifestation of acute lung injury. Both these conditions complicate many medical and surgical conditions, not all of which affect the lung directly and are therefore encountered by clinicians working outside the critical care setting with varying frequency. Early recognition is important in determining outcome, as prognosis is usually dependent partly on the nature and prompt management of the precipitating condition. Acute lung injury and acute respiratory distress syndrome are defined by refractory hypoxaemia (using the PaO2 to FiO2 ratio) in association with bilateral lung infiltrates on chest radiography, in the absence of left atrial hypertension (thereby excluding hydrostatic pulmonary oedema as a cause) but in the presence of a clinical condition known to precipitate the syndrome (box 1). #### Box 1 Definition criteria for acute lung injury and acute respiratory distress syndrome1 In the appropriate clinical setting with one or more recognised risk factors, three criteria are required: