(p. 496) Acute respiratory distress syndrome 

The acute respiratory distress syndrome (ARDS) is a syndrome of acute respiratory failure characterized by the acute onset of non-cardiogenic pulmonary oedema due to increased lung endothelial and alveolar epithelial permeability. Common predisposing clinical conditions include sepsis, pneumonia, severe traumatic injury, and aspiration of gastric contents. Environmental factors, such as alcohol abuse and cigarette smoke exposure may increase the risk of developing ARDS in those at risk. Pathologically, ARDS is characterized by diffuse alveolar damage with neutrophilic alveolitis, haemorrhage, hyaline membrane formation, and pulmonary oedema. A variety of cellular and molecular mechanisms contribute to the pathophysiology of ARDS, including exuberant inflammation, neutrophil recruitment and activation, oxidant injury, endothelial activation and injury, lung epithelial injury and/or necrosis, and activation of coagulation in the airspace. Mechanical ventilation can exacerbate lung inflammation and injury, particularly if delivered with high tidal volumes and/or pressures. Resolution of ARDS is complex and requires coordinated activation of multiple resolution pathways that include alveolar epithelial repair, clearance of pulmonary oedema through active ion transport, apoptosis, and clearance of intra-alveolar neutrophils, resolution of inflammation and fibrinolysis of fibrin-rich hyaline membranes. In some patients, activation of profibrotic pathways leads to significant lung fibrosis with resultant prolonged respiratory failure and failure of resolution.