Pulmonary vascular responses to nitrous oxide in newborn lambs.

The hemodynamic effects of N2O and N2O plus hypoxia were studied in six lambs (0-3 days of age) that were instrumented with pulmonary artery flow probes and catheters, as well as aortic and left atrial catheters. N2O was administered to the awake lambs through a mask in mixtures of 75% N2O:25% O2 and 75% N2O:11% O2:14% N2. Pulmonary arterial pressure and resistance increased significantly upon exposure to N2O both during normoxia and hypoxia, and nitrous oxide also significantly elevated left atrial pressure and decreased pulmonary artery blood flow during normoxia. Aortic pressure was essentially unchanged by nitrous oxide. The data indicate that in newborn lambs the pulmonary vasculature responds to N2O with vasoconstriction.