Inhaled nitric oxide in congenital heart disease. Circulation 87

Background. Congenital heart lesions may be complicated by pulmonary arterial smooth muscle hyperplasia, hypertrophy, and hypertension. We assessed whether inhaling low levels of nitric oxide (NO), an endothelium-derived relaxing factor, would produce selective pulmonary vasodilation in pediatric patients with congenital heart disease and pulmonary hypertension. We also compared the pulmonary vasodilator potencies of inhaled NO and oxygen in these patients. Methods and Results. In 10 sequentially presenting, spontaneously breathing patients, we determined whether inhaling 20-80 ppm by volume of NO at inspired oxygen concentrations (FIO2) of 0.21-0.3 and 0.9 would reduce the pulmonary vascular resistance index (Rp). We then compared breathing oxygen with inhaling NO. Inhaling 80 ppm NO at lIO2 0.21-0.3 reduced mean pulmonary artery pressure from 48 ± 19 to 40+14 mm Hg and Rp from 658±421 to 491±417 dyne * sec * cm ' * m-2 (mean±SD, both p<0.05). Increasing the nlO2 to 0.9 without adding NO did not reduce mean pulmonary artery pressure but reduced Rp and increased the ratio of pulmonary to systemic blood flow (Qp/Q5), primarily by increasing Qp (p<0.05). Breathing 80 ppm NO at FIO2 0.9 reduced mean pulmonary artery pressure and Rp to the lowest levels and increased Qp and Qp/Q, (all p<0.05). While breathing at FIo2 0.9, inhalation of 40 ppm NO reduced Rp (p<0.05); the maximum reduction of Rp occurred while breathing 80 ppm NO. Inhaling 8