A COMPARISON OF CORONARY HEMODYNAMICS DURING ISOFLURANE AND SEVOFLURANE ANESTHESIA IN DOGS

We studied the effects of sevoflurane and isoflurane on coronary hemod ynamics in relation to myocardial oxygen supply and demand. Dogs were anesthetized with pentobarbital and fentanyl and received isoflurane o r sevoflurane. An electromagnetic flow probe and a pair of piezoelectr ic crystals were placed on the left circumflex coronary artery (CX) to measure CX flow and diameter. The dogs were randomly assigned to rece ive isoflurane or sevoflurane at a dose of 0.75 and 1.5 minimum alveol ar anesthetic concentration (MAC). The CX diameter decreased in parall el with the decrease in mean arterial pressure during both anesthetics . The CX blood flow decreased in parallel with the decrease in myocard ial oxygen consumption (MVo(2)) during sevoflurane, whereas it did not change in spite of the decrease in MVo(2) during isoflurane. The CX v ascular resistance decreased significantly during isoflurane but not d uring sevoflurane. Moreover, the myocardial oxygen extraction ratio (M o(2)exr) decreased at 0.75 and 1.5 MAC isoflurane and at 1.5 MAC sevof lurane, and the decrease in Mo(2)exr was significantly greater during isoflurane than during sevoflurane. The results suggest that sevoflura ne is a less potent coronary arteriolar dilator than isoflurane, and t hat neither sevoflurane or isoflurane has a direct effect on the diame ter of large coronary arteries.