INHALED NITRIC-OXIDE FOR HIGH-ALTITUDE PULMONARY-EDEMA

Background. Pulmonary hypertension is a hallmark of high-altitude pulm onary edema and may contribute to its pathogenesis. When administered by inhalation, nitric oxide, an endothelium-derived relaxing factor, a ttenuates the pulmonary vasoconstriction produced by short-term hypoxi a. Methods. We studied the effects of inhaled nitric oxide on pulmonar y-artery pressure and arterial oxygenation in 18 mountaineers prone to high-altitude pulmonary edema and 18 mountaineers resistant to this c ondition in a high-altitude laboratory (altitude, 4559 m). We also obt ained lung-perfusion scans before and during nitric oxide inhalation t o gain further insight into the mechanism of action of nitric oxide. R esults. In the high-altitude laboratory subjects prone to high-altitud e pulmonary edema had more pronounced pulmonary hypertension and hypox emia than subjects resistant to high-altitude pulmonary edema. Arteria l oxygen saturation was inversely related to the severity of pulmonary hypertension (r=-0.50, P=0.002). In subjects prone to high-altitude p ulmonary edema, the inhalation of nitric oxide (40 ppm for 15 minutes) produced a decrease in mean (+/-SD) systolic pulmonary-artery pressur e that was three times larger than the decrease in subjects resistant to such edema (25.9+/-8.9 vs. 8.7+/-4.8 mm Hg, P<0.001). Inhaled nitri c oxide improved arterial oxygenation in the 10 subjects who had radio graphic evidence of pulmonary edema (arterial oxygen saturation increa sed from 67+/-10 to 73+/-12 percent, P=0.047), whereas it worsened oxy genation in subjects resistant to high-altitude pulmonary edema. The n itric oxide-induced improvement in arterial oxygenation in subjects wi th high-altitude pulmonary edema was accompanied by a shift in blood f low in the lung away from edematous segments and toward nonedematous s egments. Conclusions. The inhalation of nitric oxide improves arterial oxygenation in high-altitude pulmonary edema, and this beneficial eff ect may be related to its favorable action on the distribution of bloo d flow in the lungs. A defect in nitric oxide synthesis may contribute to high-altitude pulmonary edema. (C) 1996, Massachusetts Medical Soc iety.