Acute respiratory distress syndrome (ARDS) is caused by the increased permeability of alveolar capillaries leading to fluid accumulation in the alveoli, i.e. non-cardiogenic pulmonary oedema. It is a serious condition that has a mortality of around 40% and is associated with significant morbidity in those who survive.


  • Incidence: 20.00 cases per 100,000 person-years
  • Peak incidence: 60-70 years
  • Sex ratio: 1:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+


  • infection: sepsis, pneumonia
  • massive blood transfusion
  • trauma
  • smoke inhalation
  • acute pancreatitis
  • cardio-pulmonary bypass

Clinical features

Clinical features are typically of an acute onset and severe:


A chest x-ray and arterial blood gases are the key investigations.


Criteria (American-European Consensus Conference)
  • acute onset (within 1 week of a known risk factor)
  • pulmonary oedema: bilateral infiltrates on chest x-ray ('not fully explained by effusions, lobar/lung collapse or nodules)
  • non-cardiogenic (pulmonary artery wedge pressure needed if doubt)
  • pO2/FiO2 < 40kPa (200 mmHg)


  • due to the severity of the condition patients are generally managed in ITU
  • oxygenation/ventilation to treat the hypoxaemia
  • general organ support e.g. vasopressors as needed
  • treatment of the underlying cause e.g. antibiotics for sepsis
  • certain strategies such as prone positioning and muscle relaxation have been shown to improve outcome in ARDS