[Evaluation of inhibitory effect of isoflurane on the hypoxic pulmonary vasoconstriction response in dogs].

The effect of isoflurane on hypoxic pulmonary vasoconstriction (HPV) was examined using the separately ventilated left lower lobe lung model in dogs. When the HPV was induced with anoxic gas ventilation of the left lower lobe, the magnitude of HPV inhibition by isoflurane of 2 MAC was predominant, as assessed by the index of pressure-flow curve which is a novel indicator of pulmonary vascular tone in the left lower lobe. However, isoflurane 2 MAC attenuated the HPV by only 16%, as assessed by indices of the changes in left lower lobe blood flow rate and PaO2. This weak HPV inhibition, as shown by the latter parameters, may result from the net effect of isoflurane-induced HPV inhibition and secondary HPV enhancement due to decreases in cardiac output and pulmonary arterial pressure by isoflurane. However, none of the parameters showed inhibition of HPV when the HPV was induced by collapse of the left lower lobe. This discrepancy in the results may be caused by a lack of isoflurane reaching the hypoxic lobe when the HPV is induced with atelectasis. These results show that potency of HPV inhibition with isoflurane depends on the method of induction or evaluation of HPV, and that inhibition of HPV response with isoflurane at clinical concentrations is negligible in an atelectasis-induced HPV, in which no isoflurane is directly reaching the hypoxic lobe.