CEREBRAL, RENAL, ADRENAL, INTESTINAL, AND PANCREATIC CIRCULATION IN CONSCIOUS PONIES AND DURING 1.0, 1.5, AND 2.0 MINIMAL ALVEOLAR CONCENTRATIONS OF HALOTHANE-O2 ANESTHESIA

  • 1 January 1985
    • journal article
    • research article
    • Vol. 46  (12) , 2492-2497
Abstract
Blood flow to the brain, kidneys, adrenal glands, pancreas, and small intestine was studied in 8 healthy ponies while awake (control) and during 1.0, 1.5, and 2.0 minimal alveolar concentrations (MAC) of anesthesia produced, using halothane vaporized in oxygen. During the anesthesia steps, intermittent positive-pressure ventilation was used to ensure isocapnia. Organ blood flow was determined with 15-.mu.m (diameter) radionuclide-labeled microspheres, after allowing 30 minutes of equilibration at each of the 3 preestablished end-tidal halothane concentrations. The sequence of 1.0, 1.5, and 2.0 MAC levels of anesthesia (0.90, 1.35, and 1.80% end-tidal halothane) was randomized for every animal. In the awake ponies, cerebral blood flow in the cortical (106 .+-. 15 ml/min per 100 g) and deep gray (103 .+-. 12 ml/min per 100 g) matter was approximately 5-fold of that in the white matter (22 .+-. 3 ml/min per 100 g). In the brain stem, there was a decreasing gradient of blood flow from the cranial (thalamohypothalamus: 65 .+-. 8 mil/min per 100 g) to caudal regions (medulla: 34 .+-. 5 ml/min per 100 g). Vasodilatation occurred in all regions of the brain with halothane-O2 anesthesia; the decrease in vascular resistance reached its nadir at 1.5 MAC. In the medulla and pons, blood flow increased above control values, with each of the 3 concentrations of halothane, but in the midbrain and thalamohypothalamus, it remained similar to the control value. In the cerebral white matter and cerebellum, blood flow increased with 1.0 and 1.5 MAC of halothane anesthesia, whereas mean aortic pressure decreased to 91% and 74% of the control value. Blood flow in the cerebral cortex was not different from the control value, even at 2.0 MAC of halothane, despite a 49% reduction in perfusion pressure. Renal blood flow decreased from its control value (483 .+-. 79 ml/min per 100 g) with each concentration of halothane; at 2.0 MAC, renal vascular resistance increased markedly. Marked dilatation occurred in the adrenal gland vasculature during halothane anesthesia, and at 1.0 and 1.5 MAC, adrenal blood flow was significantly increased. The pancreatic and small intestinal vasculature exhibited intense vasoconstriction during each level of halothane-O2 anesthesia. It is concluded that in ponies anesthetized with halothane-O2, vasodilation occurred in the cerebrum, cerebellum, brain stem, and adrenal glands, whereas intense vasoconstriction occurred in the pancreactic and small intestinal vasculature. Renal blood flow decreased in halothane-anesthesized ponies.