Effect of inhaled nitric oxide on experimentally induced pulmonary hypertension in neonatal foals

Objective-To evaluate the efficacy of inhaled nitric oxide (NO) in anesthet ized healthy newborn foals with experimentally induced pulmonary hypertensi on. Animals-Five 1- to 3-day-old foals. Procedure-Anesthesia was induced and maintained with propofol, and foals we re intubated and mechanically ventilated. Systemic pressure and pulmonary a rterial pressure (P-PA) were recorded every 30 seconds. Hypertension was in duced via a hypoxic gas mixture or chemical vasoconstriction, using the thr omboxane mimetic U46619. Nitric oxide was added at a concentration of 80 pa rts per million (ppm) for 6 minutes under baseline conditions and during pu lmonary hypertension-induced alveolar hypoxia (inspired oxygen concentratio n = 0.08). Nitric oxide (20, 40, 80, and 160 ppm) was evaluated during U466 19-induced hypertension. Samples for determination of arterial blood gas te nsions were collected before and after each NO treatment. Results-inhaled NO (approx 80 ppm) did not have an effect on baseline varia bles. Infusion of U46619 (0.35 +/- 0.04 mu g/kg of body weight/min) or alve olar hypoxia resulted in increased P-PA and decreased arterial oxygenation (Pao(2)) and hemoglobin saturation (HbSat). The increase in P-PA was attenu ated, in a dose-dependent manner, by NO during U46619 infusion and reversed by NO during induced hypoxemia. The Pao2 and HbSat were significantly impr oved at all NO doses during U44619 infusion but not during alveolar hypoxia . For all inhaled NO concentrations, nitrogen dioxide and metho-globin valu es were < 5 ppm and 3%, respectively. Conclusions and Clinical Relevance-Nitric oxide is a potent, selective vaso dilator of the pulmonary circulation in healthy newborn foals. Inhaled NO m ay have value as a therapeutic agent in foals with pulmonary hypertension.