THE EFFECT OF DEXMEDETOMIDINE ON THE BALANCE OF MYOCARDIAL ENERGY REQUIREMENT AND OXYGEN-SUPPLY AND DEMAND

The effect of the alpha(2)-adrenergic agonist dexmedetomidine on the b alance between myocardial energy requirement and oxygen supply and dem and was investigated in 16 open-chest dogs anesthetized with either ch loralose/urethane (CU) or fentanyl/halothane (FH). Myocardial energy r equirement (estimated from the pressure work index), blood flow and it s transmural distribution (radioactive microspheres), as well as myoca rdial oxygen and lactate extraction, were measured before and after ad ministration of dexmedetomidine in doses ranging from 0.1 to 10 mu g/k g intravenously. Under CU anesthesia, dexmedetomidine decreased heart rate, arterial blood pressure, and cardiac output. During FH anesthesi a, dexmedetomidine reduced heart rate and cardiac output whereas arter ial blood pressure increased. Dexmedetomidine decreased myocardial ene rgy requirement only during CU anesthesia; myocardial oxygen supply an d demand decreased in parallel. At the (large) dose of 10 mu g/kg, myo cardial oxygen extraction increased during both types of anesthesia. D exmedetomidine greater than or equal to 1 mu g/kg increased endocardia l/epicardial blood flow ratio during FH anesthesia. These data indicat e that dexmedetomidine greater than or equal to 1 mu g/kg reduces myoc ardial energy requirements, especially when baseline heart rate and bl ood pressure are increased. Dexmedetomidine preserves endocardial perf usion and reduces oxygen demand in parallel with oxygen supply and ene rgy requirements.