Seminars in respiratory and critical care medicine
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Semin Respir Crit Care Med · Aug 2006
ReviewRadiological imaging in acute lung injury and acute respiratory distress syndrome.
Computed tomography (CT) has been utilized to study acute respiratory distress syndrome (ARDS) since the middle 1980s, when it revealed the inhomogeneous pattern of the lung lesion. Its advantages rely on the strict correlation between CT density and the lung physical density, allowing a quantification of lung compartments with different degrees of aeration. By CT scans, ARDS lung appeared to be "small" rather than "stiff," leading to the "baby lung" concept. ⋯ The amount of recruitable lung varies among ARDS patients. This knowledge is necessary for a rational positive end-expiratory pressure (PEEP) setting because the amount of tissue maintained aerated by PEEP is closely associated with the amount of recruitable lung. CT scans may also help to diagnose ARDS because CT provides a good estimate of the high-permeability lung edema, the characteristic lesion of this syndrome.
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Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) describe syndromes of diffuse parenchymal lung injury resulting from a variety of inflammatory triggers. The pathophysiological consequences include stiff, low-compliance lungs with impaired gas exchange. Importantly, there is often marked heterogeneity of disease. ⋯ To this end, the goals of mechanical ventilatory support of ALI and ARDS have shifted over the last decade to providing smaller (and thus less injurious) tidal volumes and accepting consequently lower arterial values for PaO(2) and the development of respiratory acidosis. This has resulted in significant improvements in outcomes. Future developments will need to further refine this lung protective concept.
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Semin Respir Crit Care Med · Aug 2006
ReviewThe role of the coagulation cascade in the continuum of sepsis and acute lung injury and acute respiratory distress syndrome.
Sepsis is a common and life-threatening condition with a high mortality rate. Severe sepsis includes multiorgan dysfunction syndrome. The organ most often affected is the lung, with development of acute lung injury (ALI), which, in its most severe form, is referred to as acute respiratory distress syndrome (ARDS). ⋯ With this clinical success, administration of drotecogin alfa (recombinant activated protein C), the importance of coagulation in the pathogenesis of human sepsis is becoming clearer. This review summarizes the current understanding of the role of coagulation and fibrinolytic abnormalities in sepsis and the development of ALI and ARDS. Both in vitro and in vivo studies of the role of the coagulation cascade in sepsis and lung injury will be discussed, including initiation of coagulation through modulation of tissue factor and tissue factor pathway inhibitor, propagation of coagulation via protein C and thrombomodulin, inhibition of thrombin generation and resolution through thrombolysis by plasminogen activator, and plasminogen activator inhibitor-1.
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Semin Respir Crit Care Med · Aug 2006
ReviewAcute lung injury and acute respiratory distress syndrome: extracorporeal life support and liquid ventilation for severe acute respiratory distress syndrome in adults.
Acute respiratory distress syndrome (ARDS) has many underlying causes and carries an overall mortality of 40 to 60%. For those patients with severe ARDS who have a predicted mortality of 80 to 100%, extracorporeal life support (ECLS) can provide an extraordinary means of support. We recently demonstrated a survival to hospital discharge of 52% in this subset of patients. ⋯ Systemic heparinization is a mainstay of ECLS therapy because of platelet activation in the circuit. Mechanical complications and significant bleeding can occur in up to one quarter of patients, requiring close attention and prompt intervention should they occur. Although not currently in clinical practice, liquid ventilation using perfluorocarbons to provide gas exchange in the lungs is a potentially useful adjunct in the management of severe respiratory failure.
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Semin Respir Crit Care Med · Aug 2006
ReviewThe role of cytokines during the pathogenesis of ventilator-associated and ventilator-induced lung injury.
Mortality rates from acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) range from 30 to 65%. Although mechanical ventilation (MV) may delay mortality in critically ill patients with ALI/ARDS, it may also cause a lung injury that further promotes and perpetuates ALI/ARDS and multiorgan dysfunction syndrome (MODS). Recent studies have demonstrated that lung protective strategies of MV, as compared with the injurious strategy of conventional MV (CMV) can reduce absolute mortality rates during ALI/ARDS. ⋯ Both human and animal studies suggest that alveolar cell deformation from CMV leads to the release of cytokines/chemokines which orchestrate the extravasation, activation, and recruitment of leukocytes, causing ventilator-associated lung injury (VALI) and ventilator-induced lung injury (VILI). Moreover, VALI/VILI can perpetuate the chronic inflammatory response during ALI/ARDS and MODS. This article explores the role of cytokines/chemokines during the pathogenesis of VALI/VILI.