PORCINE REGIONAL BRAIN AND MYOCARDIAL BLOOD FLOWS DURING HALOTHANE-O2 AND HALOTHANE-NITROUS OXIDE ANESTHESIA - COMPARISONS WITH EQUIPOTENT ISOFLURANE ANESTHESIA

  • 1 January 1984
    • journal article
    • research article
    • Vol. 45  (3) , 465-473
Abstract
Regional distribution of brain and myocardial blood flow were examined in 9 instrumented isocapnic normothermic swine, using 15-.mu.m diameter radionuclide-labeled microspheres injected into the left atrium. Minimal alveolar concentration (MAC) of halothane [HAL] required to prevent gross purposeful movement in responses to a noxious stimulus in 50% of the pigs was 0.70%. Measurements were made on each animal during nonanesthetized control state, 1.0 and 1.5 MAC HAL anesthesia and the equivalent of 1.0 and 1.5 MAC HAL anesthesia using 50% N2O. The order of anesthetized steps was randomized for each pig. Recovery periods of 60 min were interposed between the anesthetic tratments. During HAL + 50% N2O anesthesia, heart rate, cardiac output, mean aortic pressure and rate-pressure product were higher than comparable levels of halothane-O2 anesthesia. HAL caused dose-dependent vasodilatation in all regions of the brain. Cerebral, cerebellar and brain-stem blood flows at 1.5 MAC HAL were 135, 135 and 115% of respective control values. Substitution of 50% N2O to maintain same MAC dose markedly exaggerated the increment in porcine cerebral and brainstem blood flows, especially at 1.0 MAC when perfusions in these regions were 204 and 128% of respective control values. At 1.5 MAC anesthesia produced by HAL + 50% N2O, the cerebral, cerebellar and brain stem perfusions were 153, 146 and 129%, respectively, of control values. Transmural myocardial blood flow decreased from control value with both levels of HAL anesthesia, but with equivalent MAC anesthesia produced by HAL + 50% N2O, myocardial perfusion remained near awake values. Subendocardial:subepicardial perfusion ratio remained unchanged from control value throughout the study, indicating that O2 delivery in the inner layers probably kept pace with O2 demand. Substitution of 50% N2O for halothane to maintain equipotent anesthesia resulted in a marked increase in regional brain blood flow while myocardial perfusion was maintained near awake values.