Ketamine Preserves and Propofol Potentiates Hypoxic Pulmonary Vasoconstriction Compared with the Conscious State in Chronically Instrumented Dogs

Abstract

Background The authors tested the hypothesis that ketamine and propofol anesthesia would alter the magnitude of hypoxic pulmonary vasoconstriction compared with the conscious state. In addition, they assessed the extent to which cyclooxygenase pathway inhibition and adenosine triphosphate-sensitive potassium channel inhibition modulate hypoxic pulmonary vasoconstriction in the conscious state, and whether these pathways are altered during propofol anesthesia. Methods Twenty conditioned, male mongrel dogs were chronically instrumented to measure the left pulmonary vascular pressure-flow relationship. Pressure-flow plots were measured during normoxia and hypoxia (systemic arterial PO2 reduced to about 60 and about 50 mm Hg) on separate days in the conscious state, during ketamine anesthesia, and during propofol anesthesia. The effects of indomethacin and glibenclamide on the magnitude of hypoxic pulmonary vasoconstriction were also assessed in the conscious and propofol-anesthetized states. Results Neither ketamine nor propofol had an effect on the baseline pressure-flow relationship during normoxia compared with the conscious state. Hypoxia resulted in stimulus-dependent pulmonary vasoconstriction (P<0.01) in the conscious state. Compared with the conscious state, the magnitude of hypoxic pulmonary vasoconstriction was preserved during ketamine but was potentiated (P<0.01) during propofol anesthesia. Indomethacin enhanced (P<0.01) hypoxic pulmonary vasoconstriction in both the conscious and propofol-anesthetized states. In contrast, glibenclamide only enhanced (P<0.01) hypoxic pulmonary vasoconstriction in the conscious state and had no effect during propofol anesthesia. Conclusion Hypoxic pulmonary vasoconstriction is preserved during ketamine anesthesia but is potentiated during propofol anesthesia. The potentiated response during propofol anesthesia appears to be caused by inhibition of adenosine triphosphate-sensitive potassium channel-mediated pulmonary vasodilation.