Mechanisms of acute respiratory distress syndrome: role of surfactant changes and mechanical ventilation.

Acute respiratory distress syndrome (ARDS) is a condition characterized by a high permeability oedema due to loss of the integrity of the alveolo-capillary barrier with impairment of normal surfactant function, resulting in an increased collapse tendency of the alveoli. Mechanical ventilation on such alveoli with repeated alveolar collapse and subsequent reexpansion results in severe lung parenchymal injury and may induce further surfactant impairment. This cam be prevented by maintaining alveolar volume at end-expiration by means of sufficient levels of positive end-expiratory pressure (PEEP). Recent evidence from experimental studies has shown that ventilator modes which allow end-expiratory collapse can induce bacterial translocation from the lung into the bloodstream and trigger the release of inflammatory mediators, which can also be presented by maintaining end-expiratory alveolar volume. These data suggest that the interaction between surfactant changes and mechanical ventilation may play a role in the transition of ARDS into the systematic inflammatory disease process of multiple system organ failure (MSOF).