Acute lung injury: Etiologies and basic features

Acute lung injury is characterized by the rapid onset of a severe inflammatory response that contributes to cell and tissue injury, abnormal lung compliance, and impaired gas exchange. This chapter describes the multiple etiologies and clinical relevance of acute lung injury, with an emphasis on basic pathophysiological principles, processes, and pathways. Basic concepts of pulmonary epithelial, endothelial, and interstitial injury are presented and discussed. Pathophysiological processes such as lung edema formation, vascular abnormalities, and surfactant dysfunction in acute injury are also introduced, with more detailed discussion on these phenomena given later in Chapters 7-9. A conceptual overview of inflam- matory mediators important in acute lung injury is also provided, with addi- tional details on mediator activity and cell recruitment discussed in the following chapter. In addition to summarizing basic concepts of acute lung injury and inflammation, the present chapter defines clinical acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). These clinical syndromes are associated with severe acute respiratory failure in patients of all ages (infants to adults). Coverage here focuses primarily on the etiologies, pathological features, and clinical course of ALI=ARDS. Therapeutic considerations for ALI=ARDS are also noted, withmore detailed discussion about lung-injury therapies given later in Chapters 13-19.