Selective reduction of pulmonary artery pressure (PAP) in the context of pulmonary hypertension is oft desired but rarely achieved. Inhaled nitric oxide (iNO) has been shown to produce this desirable effect, but is relatively difficult to administer or monitor. We wondered whether NP, chemically related to NO but more stable in solution, would produce similar physiologic effects when administered in the convenient modality of nebulization.

Methods: 9 piglets were anesthetized, mechanically ventilated, and surgically instrumented. Systemic blood pressure (BP), PAP, and cardiac output (CO) were monitored continuously. After post-operative stabilization, 0.9% NaCl nebulization was begun, and pulmonary hypertension was induced by reducing FiO2 from 0.30 to 0.07. The piglets were monitored for 15 minutes during this hypoxic phase. Next, without altering FiO2 or ventilator settings, NP (10 mg/ml, dissolved in 0.9% NaCl, flow 4 lpm) was substitued for 0.9% NaCl saline in the nebulizer circuit. NP was nebulized continuously for 15 minutes.

Results: During hypoxia, PaO2 fell from 150 to 29 mm Hg. PAP rose during hypoxia from 14 to 31 torr (p< 0.01), while BP and CO did not change significantly. PAP fell during nebulized NP in each piglet, (mean ΔPAP = 31 to 21 torr; p< 0.01; mean reduction of hypoxia-induced rise in PAP = 61%; range: 36 to 78%; p < 0.01). PVR/SVR fell by 28% during NP nebulization (p< 0.01), while BP and CO did not fall significantly (90 to 86 torr; 653 to 636 mL/kg-min). The reduction in PAP began within 2 minutes of the onset of nebulized NP, and appeared to reach a plateau by 15 minutes. No tachyphylaxis to nebulized NP was noted. Nebulized NP did not significantly affect PAP, BP, or CO under normoxic conditions.

Conclusions: 1) Like NO, NP selectively reduced hypoxia-induced pulmonary hypertension without altering systemic BP. 2) Unlike NO, NP can be administered by nebulizer, a technique familiar to virtually all health-care providers, and potentially adaptable to both intubated and non-intubated patients. 3) Nebulized NP may be beneficial in clinical contexts where inhaled NO is impractical.