Adult respiratory distress syndrome (ARDS) is defined as pulmonary edema with normal pulmonary capillary wedge pressures and a decrease in static pulmonary compliance. Pseudo-ARDS is used to describe patients with hypoxia who have a normal pulmonary capillary wedge pressure (PCWP) but no reduction in pulmonary compliance. This variety of ARDS is becoming more common as the techniques of enhanced oxygen delivery are increasingly used in surgical intensive care units to prevent multiple organ failure in sepsis and trauma patients. Several liters of isotonic saline may be administered to these patients without increasing the PCWP. The resultant pulmonary edema results in hypoxia treated with ventilator support and oxygen therapy. Septic patients may have significant arterial vasodilatation with increased capillary fluid leakage into the interstitial space. The vasodilated patient may have impaired renal excretion of saline, which predisposes to pulmonary edema. Dr. Schrier notes that endotoxin may induce nitric oxide (NO) synthetase in vascular smooth muscle resulting in NO-mediated vasodilatation. He alerts clinicians that such patients do not necessarily have the high mortality that is associated with bona fide ARDS and indicates that the PCWP is potentially misleading as the criterion for tolerated volume expansion. Ventilator support may be avoided by limiting volume expansion with saline and by giving diuretics to vasodilated patients that have been aggressively infused with liters of saline. Hosp. Pract. June 15, 1995, p. 19.
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