Whole-body distribution of radioactivity labelled microspheres in the rat during anesthesia with halothane, enflurane, or ketamine

Cardiac output and distribution of blood flow using 15-μm radioactively labelled microspheres were determined in 25 Wistar rats. In seven awake control animals, first and second injections of microspheres did not change cardiac output (137±8 ml/min) or result in alteration in apparent blood flow to the various organs studied. Halothane anesthesia (n=6) (1.3 per cent inspired) resulted in a decrease in cardiac output, with increases in the percentages of cardiac output going to the brain, kidney, liver and large intestine. Enflurane anesthesia (n=6) (2.2 per cent inspired) did not decrease cardiac output. The percentages of cardiac output going to the liver, lung, spleen, and large intestine increased. Both halothane and enflurane caused decreases in the percentages of cardiac output going to the heart and skeletal muscle. Ketamine anesthesia (n=6) (125 mg/kg, im) differed from the other two agents in that few changes occurred from the awake state except in brain, lung and muscle. Microspheres that were trapped after the first injection were released from muscle and skin ketamine anesthesia, resulting in an apparent decrease in the distribution of cardiac output to muscle in the controls and an apparent increase in 'flow' to the lung. The microsphere method gives reliable information about cardiac output and distribution of flow in rats anesthetized with halothane or enflurane. Further studies are necessary to determine whether microsphere studies are valid indicators of organ flow during ketamine anesthesia in the rat.