Sepsis remains the most common condition associated with adult respiratory distress syndrome (ARDS). ARDS is a physiologic syndrome characterized acutely by lung edema resulting from increased alveolar-capillary permeability. Recently, the concept of global microcirculatory injury has won favor with many investigators. In the setting of trauma and sepsis, ARDS affects capillary beds throughout the body concurrently. The lung is a conspicuous organ because when increased microvascular permeability develops in the lung, alveolar flooding occurs, causing dyspnea, hypoxemia, and abnormal opacities on chest x-ray. The appearance of ARDS varies from minutes to hours after the onset of sepsis. Although there are no specific and sensitive markers for ARDS, diagnostic criteria for ARDS include bilateral pulmonary infiltrates, pulmonary capillary wedge pressure (PCWP) <18 mmHg, Pa o2/PAo2 ratio <0.2, and static compliance <40 mL/cm H2O. Clinically, severe refractory hypoxemia, noncompliant "heavy" lungs, and a chest radiograph showing bilateral pulmonary alveolar infiltrates should suggest the presence of ARDS. The hypoxemia is due to perfusion of the underventilated alveoli; right-to-left shunting has been reported as high as 30 to 50 percent in this syndrome. Pathogenic factors implicated in the global microcirculatory injury are endotoxin, TNFa, IL-1, IL-6, IL-8, and bacterial permeability increasing protein.
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