Acute respiratory distress syndrome

doi:10.1136/bmj.39293.624699.AD

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Susannah K Leaver, British Heart Foundation clinical research fellow,
Timothy W Evans, professor of critical care medicine

Department of Critical Care, Imperial College School of Medicine, Royal Brompton Hospital, London SW3 6NP

Correspondence to: T W Evanst.evans{at}rbht.nhs.uk

Summary points

• Acute lung injury and its extreme manifestation, the acute respiratory distress syndrome, complicate a variety of serious medical and surgical conditions, not all of which affect the lung directly
• Dyspnoea is the commonest presenting symptom; clinical signs are those of pulmonary oedema
• Early admission to intensive care is needed; the precipitating illness should be identified and managed aggressively
• Protective techniques of mechanical ventilatory support reduce mortality
• Rigorous application of general supportive measures is likely to improve outcome
• Non-ventilatory adjuncts to gas exchange generally improve oxygenation but do not reduce mortality
• Although death rates are falling, long term debility in survivors is considerable

Why do I need to know about acute respiratory distress syndrome?

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.

How are these conditions defined?

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:

• Radiological—New, bilateral, diffuse, patchy, or homogeneous pulmonary infiltrates on chest radiograph consistent with pulmonary oedema
• Exclusion—No clinical evidence that heart failure, fluid overload, or chronic lung disease are responsible for the infiltrates; or pulmonary artery occlusion pressure of 18 mm Hg
• Oxygenation—PaO …