Effect of Sevoflurane and Isoflurane on Hypoxic Pulmonary Vasoconstriction in the Isolated Rabbit Lung

Kim, Chong Sung; Kim, Seong Deok

Abstract

BACKGROUND
In vitro and in vivo studies have shown that inhalation anesthetics inhibit hypoxic pulmonary vasoconstriction (HPV). The aim of this study was to investigate the effect of isoflurane and sevoflurane on HPV in the isolated rabbit lungs.
METHODS
Isolated constant-flow perfused lungs from New Zealand white rabbit were randomly allocated to treatment with either isoflurane (n=8) or sevoflurane (n=8). HPV, defined as an increase in pulmonary arterial pressure at constant flow, was elicited by decreasing inspiratory oxygen concentration from 95% to 3% for 5 min. This effect was determined without and with increasing concentration of anesthetics (at 0.5, 1.0, and 2.0 MAC of isoflurane, and at 0.6, 0.9, and 1.2 MAC of sevoflurane). The HPV response in the presence of anesthetics was expressed as a percentage of the pressor response in the absence of anesthetics and dose-response relationship were calculated using the nonlinear least-squares method.
RESULTS
The percent hypoxic pressor response (%deltaP) of isoflurane were 100%, 78.4%, 45.1%, and 19.6% at 0, 0.5, 1.0, and 2.0 MAC, respectively. The %deltaP of sevoflurane were 100%, 66.6%, 40.0%, and 22.2% at 0, 0.6, 0.9, and 1.2 MAC, respectively. Values (mean+/-SD) for the half-inhibition values (ED50) were 0.90+/-0.14 and 0.81+/-0.15 MAC, and for the slopes were 1.97+/-0.52 and 1.84+/-0.59 for isoflurane and sevoflurane, respectively. There were no statistical difference between the values for ED50 or between the values for slope.
CONCLUSIONS
We conclude that sevoflurane and isoflurane inhibit the HPV reponse in a dose-related manner with same potency and slope.