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 balance between myocardial energy requirement and oxygen supply and demand was investigated in 16 open-chest dogs anesthetized with either chloralose/urethane (CU) or fentanyl/halothane (FH). Myocardial energy requirement (estimated from the pressure work index), blood flow and its transmural distribution (radioactive microspheres), as well as myocardial oxygen and lactate extraction, were measured before and after administration of dexmedetomidine in doses ranging from 0.1 to 10 micrograms/kg intravenously. Under CU anesthesia, dexmedetomidine decreased heart rate, arterial blood pressure, and cardiac output. During FH anesthesia, dexmedetomidine reduced heart rate and cardiac output whereas arterial blood pressure increased. Dexmedetomidine decreased myocardial energy requirement only during CU anesthesia; myocardial oxygen supply and demand decreased in parallel. At the (large) dose of 10 micrograms/kg, myocardial oxygen extraction increased during both types of anesthesia. Dexmedetomidine >/= 1 microgram/kg increased endocardial/epicardial blood flow ratio during FH anesthesia. These data indicate that dexmedetomidine >/= 1 microgram/kg reduces myocardial energy requirements, especially when baseline heart rate and blood pressure are increased. Dexmedetomidine preserves endocardial perfusion and reduces oxygen demand in parallel with oxygen supply and energy requirements.