General Anesthetics and Regional Hypoxic Pulmonary Vasoconstriction

Abstract

Administration of N2O, fluroxene and isoflurane to the left lower lobe (LLL) of dogs anesthetized with pentobarbital was previously shown to inhibit LLL hypoxic pulmonary vasoconstriction (HPV). Using the same experimental model, the present study examined the effect of whole-lung administration of N2O, fluroxene, isoflurane, halothane, and enflurane on left-lower-lobe HPV. Selective ventilation of the LLL with N2 alone caused blood flow to the lobe to decrease 53.3 +/- 3.0 per cent. Responses to LLL hypoxia were remeasured during administration of inhalation anesthetics at 1 and 2 MAC to both the LLL and the rest of the lung. Isoflurane and fluroxene progressively inhibited and at 2 MAC halved lobar HPV. N2O (one third MAC) caused slight but significant inhibition, while halothane and enflurane caused slight and nonsignificant changes in lobar HPV. These effects of whole-lung administration of anesthetics on HPV were almost identical to those obtained when the administration was confined to the test lobe alone. It is concluded that N2O, isoflurane, and fluroxene locally inhibit regional HPV and via this mechanism increase total venous admixture, while halothane and enflurane do not have this effect.