REGIONAL VASODILATING PROPERTIES OF ISOFLURANE IN NORMAL SWINE MYOCARDIUM

Background. Studies of the coronary vasodilating properties of isoflur ane have produced inconsistent results. Isoflurane has been reported t o cause minimal or no coronary vasodilation, mild dose-related vasodil ation, or even near-maximal coronary vasodilation. The current study w as performed to clarify the direct coronary vasodilating potency of is oflurane. Methods. We determined the vasodilating properties of isoflu rane in regionally perfused swine myocardium. Six domestic swine were anesthetized with pentobarbital and fentanyl. The left anterior descen ding artery (LAD) was cannulated and perfused with blood drawn from th e carotid artery and passed thorough a membrane oxygenator. LAD arteri al flow was controlled by a calibrated roller pump with continuous dig ital readout, and LAD arterial pressure was measured directly. The ant erior interventricular vein was cannulated and dimension crystals plac ed in the LAD-perfused myocardium. The vasodilation response to 0, 1, 2, and 3% isoflurane administered via the membrane oxygenator was dete rmined and compared to maximal vasodilation produced by regional intra coronary administration of adenosine. Results: Systemic blood pressure and heart rate remained constant throughout the experiment. With 3% i soflurane, systolic shortening and regional myocardial oxygen consumpt ion decreased by 60 and 20%, respectively. The same concentration incr eased coronary blood flow by 51 +/- 34% and reduced coronary vascular resistance by 32.9 +/- 11.0%. Neither coronary blood flow nor coronary vascular resistance was affected with 1% isoflurane. Regional coronar y administration of adenosine produced much greater changes in both co ronary blood flow (+591%) and coronary vascular resistance (-92.5%). I soflurane increased the venous oxygen content of the anterior interven tricular vein in a dose-dependent fashion from 4.85 vol% at control to 6.17, 7.01, and 8.63 vol% at 1, 2, and 3% isoflurane, respectively. C onclusions: We conclude that isoflurane is a mild dose-dependent coron ary vasodilator. At a 1% concentration, the coronary vasodilating prop erties of isoflurane are minimal.