Systemic and Regional Blood Flow Distribution in Unanesthetized Swine and Swine Anesthetized with Halothane + Nitrous Oxide, Halothane, or Enflurane

Open Access
Publisher Website
Google Scholar
Abstract
To study the distribution of cardiac output during various anesthetic regimens, regional organ blood flow was measured using 15-.mu.m-diameter radionuclide-labeled microspheres injected into the left atrium in 9 pigs during resting unanesthetized state (control), halothane (inspired concentration = 1.25%) + N2O (50%), halothane (inspired concentration = 2.25%), and enflurane (inspired concentration = 4.0%) anesthesia. The order of the last 2 treatments [halothane (2.25%) and enflurane (4.0%)] was randomized among the 9 pigs. All anesthetic steps employed intermittent positive-pressure ventilation to maintain PaCO2 [arterial partial pressure of CO2] close to control values. Animals were allowed to recover towards the control state before changing to the next anesthetic regimen. Forty-five minutes were allowed for equilibration with each anesthetic regimen before hemodynamic measurements were made. Cardiac output and mean arterial blood pressure decreased significantly from control values with each of the 3 anesthetized steps. The decrease in cardiac output was greatest with halothane and least with halothane + N2O. Blood flow per unit weight of the cardiac, renal and splanchnic tissues decreased significantly with each anesthetic regimen, whereas brain blood flow and hepatic arterial blood flow were unaltered from control values. The percent cardiac output received by the brain increased with halothane (119%) and enflurane (102%) anesthesia, while it was unaltered for the heart, renal and splanchnic organs. Percentage of total cardiac output received by liver via the hepatic artery increased by 162% during halothane and 133% during enflurane, when compared to control values. During halothane + N2O anesthesia, the percent of cardiac output going to the brain was not increased significantly. Evidently, cardiac output and individual organ/tissue blood flow was better maintained during halothane + N20 than halothane or enflurane anesthesia.