Noncardiogenic pulmonary edema
Section snippets
Definition
Noncardiogenic pulmonary edema also is called acute respiratory distress syndrome (ARDS). It is characterized by diffuse alveolar damage, marked increased permeability of the alveolar-capillary membrane, and accumulation of protein-rich fluid in the alveolar air sacs. This entity first was recognized and described by the military in relation to battlefield casualties in World War I and World War II. Increased understanding of the pathophysiology that produces this clinical state led to
Pathophysiology
The causes of noncardiogenic pulmonary edema are diverse and myriad. It can result from direct and indirect pathologic processes (Box 1). Some conditions injure the lung and alveolar epithelium directly, whereas others are systemic processes that produce damage through indirect mechanisms and hematogenous delivery of inflammatory mediators (Box 2). Indirect mechanisms result from the overexpression of the normal inflammatory response, resulting in an inflammatory cascade that can injury not
Clinical presentation
Noncardiogenic pulmonary edema presents with varying degrees of respiratory distress that may progress rapidly to respiratory failure. A moderate-to-severe degree of decreased oxygen saturation is evident on pulse oximetry and arterial blood gas measurement. The earliest clinical sign is increased work of breathing evidenced by tachypnea and dyspnea. Rales are evident on lung auscultation and are indistinguishable from those heard in cardiogenic pulmonary edema. Other findings consistent with a
Treatment
Treatment is largely supportive and aimed at ensuring adequate ventilation and oxygenation. There are no specific treatments to correct the underlying alveolar-capillary membrane permeability problems, or to control the inflammatory cascade once triggered, beyond mechanical ventilator management and intensive care support.
Prognosis
No single variable has been found to predict patient outcome. Even the degree of hypoxemia has not been valuable in this regard. Ongoing research measuring pulmonary dead space fraction (particularly when measured early in the course of the disease process) has been promising, with elevated values associated with an increased risk of death [20]. Mortality rates for severe noncardiogenic pulmonary edema have been reported to range from 50% to 70% in the past but now are declining with optimized
Summary
Pulmonary edema is differentiated into two categories—cardiogenic and noncardiogenic. Noncardiogenic pulmonary edema is due to changes in permeability of the pulmonary capillary membrane as a result of either a direct or an indirect pathologic process. It is a spectrum of illness ranging from the less severe form of ALI to the severe ARDS. The mainstay of treatment is mechanical ventilation with maximization of ventilation and oxygenation through the judicious use of PEEP. Newer ventilation
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