Local Effects of Anesthetics on Regional Hypoxic Pulmonary Vasoconstriction

The hypothesis that halogenated anesthetics and N2O locally inhibit hypoxic pulmonary vasoconstriction (HPV) was tested. Selective ventilation of the left lower lobe of the lung with N2 in dogs anesthetized with pentobarbital caused blood flow to the lobe to decrease 55.5 +/- 2.0 per cent and lobar vascular resistance to increase 148 +/- 8 per cent. Responses to hypoxia were remeasured during administration of various MAC multiples of inhalation anesthetics to the left lower lobe and following systemic administration of intravenous anesthetics. Isoflurane and fluorexene progressively inhibited and finally almost extinguished the vasoconstriction response as anesthetic concentration increased to 3 MAC. N2O moderately diminished HPV. Halothane had little, and intravenous anesthetics had no, significant effect on HPV. It is concluded that N2O, isoflurane, and fluroxene locally inhibit regional HPV and via this mechanism may increase total venous admixture.