Myocardial Functional and Metabolic Responses to Ischemia in Swine during Halothane and Fentanyl Anesthesia

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Abstract
The effect of 60% reduction in flow to the left anterior descending (LAD) coronary artery in young swine during N2O-pancuronium anesthesia supplemented with either halothane (0.52% end-tidal) or fentanyl (50 .mu.g/kg bolus, 100 .mu.g/kg per h-1 infusion) was compared. The presence of ischemia was assessed from coronary arterial-venous (a-v) blood content differences of O2, H+, acetate, K+ and inosine. Cardiac output and left ventricular pressure indices were used to estimate ventricular function. Before stenosis, mean aortic pressure (MAP), left ventricular systolic pressure, (LVSP) rate of rise of LVSP (dP/dt), peak contractile element velocity (Vce Peak), and systemic vascular resistance (SVR) were higher during fentanyl than during halothane. Heart rate (HR), left ventricular end-diastolic pressure (LVEDP), cardiac output (CO) and stroke volume (SV) were not significantly different. LAD coronary blood flow (CBF) and regional myocardial oxygen consumption (.ovrhdot.VO2) were also higher during fentanyl than during halothane. Significant extraction of lactate without v-a differences of K+ and inosine indicated that the hearts during both anesthetics were well-oxygenated. After 30 min of 60% reduction in LADCBF, the metabolic and functional effects were similar during both anesthetics. Lactate extraction changed to production and coronary v-a differences of H+, K+ and inosine became positive or increased. In addition, O2 extraction increased as well. There was little change in HR, SVR, MAP, LVdP/dt or Vce peak with either anesthetic, but CO and SV decreased and LVEDP increased during both anesthetics, indicating global pump dysfunction. Subsequent to 30 min of reperfusion, the metabolic indices returned towards control although lactate extraction was still lower than before stenosis with both anesthetics. CO and LVdP/dt did not recover with halothane and SV was still depressed with both halothane and fentanyl. MAP decreased further with both anesthetics and HR and SVR increased after reperfusion during fentanyl anesthesia. A 60% decrease in LADCBF resulted in equivalent depression in ventricular pump function and degree of ischemia during halothane or fentanyl supplemented N2O-pancuronium anesthesia in young swine. There was partial recovery both functionally and metabolically with both agents. Thus, the effect of significant stenosis of the LADCA was equivalent whether the hearts had a high (fentanyl) or low (halothane) O2 supply and demand before stenosis.