ARDS is characterized by pulmonary hypertension and impaired gas exchange. Inhalation of nitric oxide (NO) or NO analogs has been suggested as a technique capabable of ameliorating one or both of these pathologies. We investigated the effects of inhalation of an NO analog, sodium nitroprusside, administered by nebulization in a piglet model of ARDS.

Methods: 5 piglets were anesthetized and mechanically ventilated with 50% FiO2. Systemic blood pressure (BP), pulmonary artery pressure (PAP), and cardiac output (CO) were monitored continuously. Serial lung lavages (10 mL/kg of 0.9% NaCl) were performed until significant hypoxia was stably observed (O2 sat < 75% in 50% FiO2). At that point, Neb-NP was introduced into the ventilator circuit, and changes in hemodynamics and gas exchange were monitored for 15 minutes.

Results: After lung lavage, PAP rose (17 ± 3 [s.d.] to 23± 5 torr) and O2 sat fell (98 ± 4 to 64 ± 10%)(both p< 0.05), while BP and CO were not significantly affected. After Neb-NP, PAP fell significantly (23 ± 5 to 17 ± 4 torr) as did PVR/SVR (-22± 15%) (both p < 0.05), while BP and CO were not significantly affected. Neither PaO2 (45 ± 9 to 43 ± 11 torr) nor PaCO2 (48± 11 to 43 ± 11 torr) improved or worsened during Neb-NP.

Conclusions: 1) Neb-NP significantly ameliorated pulmonary hypertension in a piglet model of ARDS. 2) This effect was likely mediated by direct smooth muscle relaxation, as it was not associated with any improvement in gas exchange. 3) Neb-NP may be a useful adjunct to inhaled NO in clinical conditions associated with pathologic pulmonary hypertension.