Pulmonary edema: pathophysiology, methods of measurement, and clinical importance in acute respiratory failure.

Pulmonary edema is a common component of adult respiratory failure. The edema process is much more complex than simply excess water and/or protein crossing the microvascular membrane. The interstitial space itself is an active component of pulmonary edema, as are the alveolar type I and type II cells. Changes in the interstitium are particularly important in increased permeability edema. The clinical measurement of lung water can be performed by a number of methods, each with its own specific advantages and disadvantages. The role of edema itself in lung failure is variable. Depending on the disease, water content correlates well with impaired oxygenation in cardiogenic edema and relatively poorly in increased permeability edema, especially established adult respiratory distress syndrome. Recognition of the mechanisms, measurements, and relevance of lung edema is of considerable importance in the critical care setting.