Amrinone Blunts Cardiac Depression Caused by Enflurane or Isoflurane Anesthesia in the Dog

Abstract

The effects of two infusion rates of amrinone, a positive inotrope and vasodilator, were studied during high and low concentrations of either enflurane or isoflurane anesthesia in a canine model. The anesthetic concentrations used were: "low" = 2.1-2.2% enflurane or 1.7-1.8% isoflurane, and "high" = 3.4-3.5% enflurane or 3.0-3.1% isoflurane. The two infusion rates of amrinone were: "low" = 2 mg/kg plus 30 micrograms X kg-1 X min-1 and "high" = 4 mg/kg plus 100 micrograms X kg-1 X min-1. In the present study, amrinone, in sufficient doses, blunted the deleterious effects of enflurane or isoflurane on myocardial function, reduced systemic vascular resistance (SVR) and pulmonary capillary wedge pressure, restored left ventricular dP/dtmax (LVdP/dtmax), and maintained cardiac index, even at the high concentrations of enflurane or isoflurane that caused marked cardiac depression. However, with reduced SVR, mean arterial pressure remained low. With lower enflurane or isoflurane, high concentrations of amrinone elevated LVdP/dtmax and heart rate above baseline, which might be of concern if myocardial oxygen supply were limited. No arrhythmias were observed at any time in this study. Amrinone did not increase plasma catecholamine levels with either anesthetic. Elevated amrinone plasma concentrations persisted for at least 1 hr after cessation of the high amrinone infusion and continued stimulatory effects on the cardiovascular system were observed. These results suggest that in selected patients amrinone may be beneficial in the short-term treatment of perioperative depression of cardiac performance.