Hemodynamic responses to alfentanil in halothane-anesthetized dogs

Alfentanil is an opioid that has been used both as a sole anesthetic and in conjunction with other inhalation anesthetics. However, its effects on myocardial performance and regional blood flow are not clearly known. Using sonomicrometry and radioactive microsphere techniques, we examined the hemodynamic responses to alfentanil when given as a loading dose (45 micrograms/kg) followed by continuous infusion (3 micrograms X kg-1 X min-1) in dogs anesthetized with halothane. Similar plasma levels of alfentanil were observed after the loading and infusion doses, and both techniques of administration produced a significant reduction in arterial pressure without change in global or regional function of the left ventricle. Although cardiac output and left ventricular end-diastolic pressure remained unchanged, heart rate and systemic vascular resistance decreased significantly after the loading dose and recovered slightly when alfentanil was infused continuously. Despite the systemic hypotension, alfentanil did not alter perfusion to the heart, brain, muscle, and skin; however, blood flow to the renal cortex and the arterial supply to the liver decreased by 25 and 60%, respectively. Reduction in blood flow to the kidneys and the liver suggests that alfentanil should be used with caution when normal function of these organs is in question.