Effect of nitric oxide on the survival rate and incidence of lung injury in newborn lambs with persistent pulmonary hypertension.

We previously showed that inhaling nitric oxide (NO) for up to 30 minutes selectively dilates the pulmonary circulation and improves oxygenation in newborn lambs with persistent pulmonary hypertension. In the current study we determined whether inhaling NO for 23 hours increased the survival rate of newborn lambs with persistent pulmonary hypertension, oxidized hemoglobin to methemoglobin, or damaged the lungs. Persistent pulmonary hypertension was created in newborn lambs by ligating the ductus arteriosus 13 days before delivery. Six lambs were randomly selected to breathe NO at 80 parts per million for 23 hours, and 7 control lambs were untreated. Each lamb was delivered at 135 days of gestation (term is 146 days), and the lungs were ventilated at a fraction of inspired oxygen of 0.92. Each of the control lambs died before the end of the study, whereas only one of the NO-treated lambs died (p < or = 0.05). Arterial oxygen tension was greater in the NO-treated lambs by 15 minutes after delivery (63 +/- 17 vs 14 +/- 4 mm Hg). Oxygen tension increased with time in the NO-treated lambs. Inhaled NO increased the concentration of methemoglobin, but this concentration reached a plateau at 3.0% +/- 0.4%. There was evidence of early airway damage in both groups of lambs but no difference between the groups. We conclude that inhaled NO increased survival rates without increasing the incidence of acute lung injury in newborn lambs with persistent pulmonary hypertension.