Abstract 53

Background: Inhaled nitric oxide (iNO) decreases pulmonary vascular resistance and improves oxygenation in babies with PPHN. We compared nebulized nitroprusside (Neb-NP), a NO-donor, to iNO during hypoxic pulmonary vasoconstriction. Materials: Newborn piglets (n=5) were anesthetized, ventilated and instrumented to measure systemic (SAP) and pulmonary (PAP) arterial pressures, and cardiac output (CO). Interventions: Hypoxia was induced. After stabilization, treatment (randomly assigned) with either Neb-NP (5 mg/ml @ 4L/min) or iNO (20ppm) was begun. Between treatments, piglets recovered in FiO2 0.05. Hypoxia was again induced, the other treatment instituted and measurements recorded. Results: Hypoxia prior to treatment was similar (PaO2: 31.6 torr prior to Neb-NP and 29.2 torr prior to iNO). PAP elevation following hypoxia was similar (Neb-NP:18 to 33 vs iNO: 18 to 32 mmHg). SAP and CO were not altered by hypoxia. Neb-NP during hypoxia significantly reduced PAP (33±2 [SEM] to 23±2 mmHg; p<0.01) without altering SAP (91 to 87 mmHg) or CO (918 to 848 ml/min). Inhaled NO also significantly reduced PAP (32±2 to 21±1 mmHg; p<0.01) without altering SAP (96 to 91 mmHg) or CO (861 to 833 ml/min). The PAP decrease following Neb-NP (9.2±0.9 mmHg; p<0.0004) was comparable to iNO (11.0±1.1 mmHg; p<0.0006). Conclusions: Neb-NP significantly attenuates hypoxic pulmonary vasoconstriction in newborn piglets. The effect of Neb-NP was comparable to iNO. Neb-NP may be a useful adjunct to iNO in conditions associated with PPHN.