Sepsis and the lung host response

Sepsis is the leading cause of death in critically ill patients and is the most common risk factor for the development of acute lung injury in medical patients. Initially investigators hypothesized that an excessive proinflammatory response contributed to the pathogenesis of sepsis. However, this hypothesis overlooked the beneficial effects of proinflammatory mediators and the detrimental effects of an excessive anti-inflammatory response. This has led to a new hypothesis where sepsis is characterized by imbalances of the pro- and anti-inflammatory responses, with tissue injury the result of an excessive proinflammatory response and impaired pulmonary host defense the result of an excessive anti-inflammatory response. This article reviews clinical studies and animal models which show that sepsis results in an impaired lung host response to bacteria. Information in this article should provide the reader with an increased understanding of the pathogenesis of sepsis and the realization that new therapeutic strategies for sepsis need to take into account the need to balance pro- and anti-inflammatory responses to maintain pulmonary host defenses and prevent the development of acute lung injury.