Hypoxia‐Induced Pulmonary Vasoconstriction: Effects of Fentanyl Following Dfierent Routes of Administration

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Abstract
I.V. anesthetics, including fentanyl [FN] do not reduce the pulmonary vasoconstrictor response to alveolar hypoxia. In contrast, the response is markedly reduced or abolished by inhalation anesthetics. The route of administration [ROA] is important. Halothane, which inhibits the response when administered via the airways, behaves more like an i.v. anesthetic following administration via the blood stream, provided the alveolar concentration has been kept low. The lack of any damping effect of FN on the response could be due to the ROA rather than to a different pharmacological property. This hypothesis was tested by introducing FN in nebulized form via the airways in one group of isolated rat lungs, and via the blood stream in another group. No effect of FN on the pulmonary vasoconstrictor response to hypoxia was found, regardless of the ROA. Plasma concentrations of FN were determined by radioimmunoassay and compared with those encountered in anesthetic practice.