Systemic and regional blood flow distribution in unanesthetized swine and swine anesthetized with halothane + nitrous...

In order to study the distribution of cardiac output during various anesthetic regimens, we measured regional organ blood flow using 15 micrometers diameter radionuclide-labeled microspheres injected into the left atrium. Studies were carried out in nine pigs during resting unanesthetized state (control), during halothane (inspired concentration = 1.25 per cent) + nitrous oxide (50 per cent) anesthesia, during halothane (inspired concentration = 2.25 per cent) anesthesia, and during enflurane (inspired concentration = 4.0 per cent) anesthesia. The order of the last two treatments [halothane (2.25 per cent) and enflurane (4.0 per cent)] was randomized among the nine pigs. All anesthetic steps employed intermittent positive-pressure ventilation to maintain PaCO2 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. In unanesthetized resting swine blood flow received by brain, cardiac ventricles, kidneys, liver (via hepatic artery), gastrointestinal tract, and skeletal muscle was 63.70 +/- 5.56, 128.56 +/- 14.92, 280.89 +/- 19.72, 21.95 +/- 3.25, 148.55 +/- 15.29 and 13.76 +/- 4.12 ml . min-1 . 100 g-1, respectively (mean +/- SEM). Corresponding values for the percentage of cardiac output received by the brain, cardiac ventricles, kidneys, liver (via hepatic artery), and gastrointestinal tract were 1.13 +/- .08, 3.04 +/- 0.13, 12.95 +/- 1.54, 4.27 +/- 0.76, and 18.71 +/- 0.91 per cent, respectively. Cardiac output and mean arterial blood pressure decreased significantly from control values with each of the three anesthetized steps. The decrease in cardiac output was greatest with the halothane anesthesia 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. Thus, the per cent cardiac output received by the brain had increased with halothane (119 per cent) and enflurane (102 per cent) anesthesia while it was unaltered from the heart, renal, and splanchnic organs. Percentage of total cardiac output received by liver via the hepatic artery increased by 162 per cent during halothane anesthesia and 133 per cent during enflurane anesthesia, when compared to control values. During halothane + nitrous oxide anesthesia, the per cent of cardiac output going to the brain was not increased significantly. It is concluded that cardiac output as well as individual organ/tissue blood flow was better maintained during halothane + nitrous oxide anesthesia in comparison to halothane or enflurane anesthesia.