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.

Pathophysiology

• Adult respiratory distress syndrome (ARDS), also known as acute respiratory distress syndrome, is an acute respiratory failure occurring within 7 days of the onset of a lung injury.
• ARDS involves a diffuse bilateral alveolar injury, as a result of inflammation mediated by inflammatory mediators such as TNF-α, IL-1 and IL-8.
• The resulting endothelial injury activates neutrophils in the pulmonary capillaries, releasing reactive oxygen species and proteases that damage the alveolar endothelium and type 2 alveolar cells.
• As a result, the vascular permeability increases and the lung surfactant is lost. Fluid accumulation in the alveoli causes pulmonary oedema and subsequently hypoxaemia.
• It is not secondary to cardiogenic pulmonary oedema, pleural effusion or atelectasis.
• ARDS is not the same as neonatal respiratory distress syndrome, which is due to inadequate lung surfactant production caused by prematurity.

Causes

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

Clinical features