Dose-related cardiovascular effects of amrinone during enflurane anesthesia in the dog

Abstract

The dose-related cardiovascular effects of amrinone, a synthetic cardiotonic and vasodilating drug, were investigated in dogs anesthetized with enflurane (2.2-2.4% end-tidal concentration). Twelve mongrel dogs were divided into two groups of six animals: an enflurane group (E) that received only enflurane, and an amrinone group (A). In the latter group each dog received the following sequential boluses and 30-min infusions: 1) the amrinone solvent alone; 2) amrinone, 1 mg/kg + 5 micrograms X kg-1 X min-1; 3) amrinone, 2 mg/kg + 10 micrograms X kg-1 X min-1; 4) amrinone, 4 mg/kg + 20 micrograms X kg-1 X min-1. Over the course of the experiment, 2.2-2.4% end-tidal enflurane alone resulted in a gradual decrease in cardiac index (CI), stroke volume index (SVI), and the maximum left ventricular dP/dt (LV dP/dtmax), without changes in heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), or pulmonary capillary wedge pressure (PCWP) in group E. Significant differences from group E after 30 min of the lowest dose of amrinone included higher CI and SVI with lower systemic vascular resistance (SVR). The medium dose of amrinone, in addition to the effects already observed with the lowest dose of amrinone, decreased MAP and pulmonary vascular resistance (PVR), and increased LV dP/dtmax, when compared to group E only. Furthermore, the highest dose of amrinone caused lower pulmonary artery mean pressure (PAM), PCWP, and higher HR with shortened PR interval. The differences in MAP, CI, LV dP/dtmax, PCWP, PAM, PR interval, SVR, and PVR compared to E were still significant 30 min after the cessation of the highest dose. This study shows that the myocardial depressant effects of enflurane in an unstimulated canine model with a previously healthy heart can be overcome in a dose-related manner by amrinone. In contrast to other vasodilators, no reflex increase in plasma catecholamines was seen.(ABSTRACT TRUNCATED AT 250 WORDS)