Pulmonary Administration of Vasoactive Substances by Perfluorochemical Ventilation

Abstract

Objectives. Therapeutic management of respiratory distress syndrome, pneumonia, and pulmonary hypertension includes delivery of biologically active agents to the neonatal lung. However, mechanical abnormalities of the lung, intrapulmonary shunting, ventilation-perfusion mismatching, and elevated surface tension impede effective systemic or intratracheal delivery of agents to the lung during conventional gas ventilation. The objective of this study was to test the hypothesis that perfluorochemical (PFC) liquid ventilation can be used for pulmonary administration of vasoactive drugs (PAD) and to compare these responses to those elicited with intravascular (IV) administration during tidal liquid ventilation.

Methods. Cardiovascular responses of 16 preterm and neonatal lambs to randomized doses of acetylcholine, epinephrine, and priscoline were studied. Physiologic gas exchange and acid-base balance were maintained using previously described tidal liquid ventilation techniques. In subgroups of animals, the distribution pattern of carbon 1- and choline 14-labeled dipalmitoylphos-phatidylcholine (¹⁴C-DPPC) in saline and the responses to priscoline after hypoxia-induced pulmonary hypertension and hypoxemia administered during liquid ventilation were studied.

Results. Dose-response curves for PAD and IV administration demonstrated progressive, dose-dependent, cholinergic responses to acetylcholine (decreased mean systemic arterial pressure [MAP] and heart rate), sympathomimetic responses to epinephrine (increased MAP and heart rate), and α-adrenergic blockade responses to priscoline (decreased MAP and mean pulmonary arterial pressure). Compared with IV administration, PAD of priscoline resulted in a significantly greater decrease in pulmonary relative to systemic arterial pressure; this response was potentiated by hypoxia, reduced pulmonary pressures to near normal values, and improved oxygenation. The ¹⁴C-DPPC in saline was distributed relatively homogeneously throughout the lung by PAD, with 80% of the lung pieces receiving amounts of ¹⁴C-DPPC with ±20% of the mean value.

Conclusions. This study demonstrates that vasoactive agents can be delivered to the lung directly by PAD during PFC liquid ventilation. The inherent advantages of this method relate to the physical properties of PFC liquid ventilation as a vehicle (respiratory gas solublity, low surface tension-enhancing distribution, and inertness precluding interaction) and physiological properties of the lung as an exchanger.