CORONARY VASODILATION BY ISOFLURANE - ABRUPT VERSUS GRADUAL ADMINISTRATION

Background: Under certain circumstances, isoflurane is associated with coronary artery vasodilation. The objective of the current study was to ascertain whether the rate of administration of isoflurane influenc es its vasodilating effect in the coronary circulation. Methods: Seven open-chest dogs anesthetized with fentanyl and midazolam were studied . The left anterior descending coronary artery was perfused via either of two pressurized (80 mmHg) reservoirs; reservoir 1 (control) was su pplied with arterial blood free of isoflurane, and reservoir 2 was sup plied with blood from an extracorporeal oxygenator, which was provided with 95% O-2/5% CO2 gas that passed through calibrated vaporizer. Cor onary blood flow (CBF) was measured with Doppler flow transducer. In e ach dog, isoflurane was administered according to two protocols; abrup t (isoflurane-A) or gradual (isoflurane-G). In isoflurane-A, the left anterior descending coronary artery was switched from reservoir 1 to r eservoir 2 after the latter was filled with blood previously equilibra ted with 1.4% (1 MAC) isoflurane. In isoflurane-G, the left anterior d escending coronary artery was switched to reservoir 2 with vaporizer s et at 0% isoflurane; then the vaporizer was adjusted to 1.4% isofluran e, which produced a gradual increase in isoflurane concentration withi n reservoir 2 that reached a level equivalent to that in isoflurane-A (as evaluated by gas chromatography) by 30 min. CBF during maximally d ilating, intracoronary infusion of adenosine served as a reference to assess effects of isoflurane. Results: Isoflurane-A caused marked incr eases in CBF, which, at constant perfusion pressure, reflected pronoun ced reductions in vascular resistance, These increases in CBF were 80% of those with adenosine. Although isoflurane-G also caused increases in CBF, the increases were only 45% of those caused by isoflurane-A. C onclusions: The current findings demonstrate that the extent of corona ry vasodilation by isoflurane was not dependent only on its blood conc entration but also on the rate at which this blood concentration was a chieved; a gradual increase in blood concentration blunted the vasodil ator effect, Differences in the rate of administration of isoflurane l ikely contributed to its widely variable coronary vasodilating effects in previous studies,