Mechanisms of alveolar damage

There are two principal causes of diffuse alveolar damage in ARDS:

• volutrauma - in ventilator induced lung injury. An excess volume of oxygen rather than a raised inspired oxygen concentration is thought to be the critical factor
  
  
• generalised systemic acute inflammatory process in which the lung is but one target organ - associated with sepsis or traumatic shock. Microscopic examination of the lung may reveal large numbers of neutrophils, degranulated platelets and widespread endothelial damage. Activation of complement and other inflammatory mediators such as leukotrienes and prostaglandins, induce the aggregation of leukocytes and their release of injurious agents such as lysosomal enzymes