Cardiovascular effects of and interaction between calcium blocking drugs and anesthetics in chronically instrumented dogs. III. Nicardipine and isoflurane.

Abstract

To assess the interaction between isoflurane and the new calcium channel blocker, nicardipine, mongrel dogs were chronically instrumented to allow the following measurements: aortic, left ventricular and left atrial pressures; heart rate; cardiac output; and carotid, coronary, and renal blood flows. The hemodynamic effects of intravenous nicardipine 5, 10, 30, and 50 micrograms/kg were measured in awake dogs and during 1.6 and 3.0 per cent (end-tidal) isoflurane anesthesia. Nicardipine induced a dose-dependent fall in mean arterial pressure in both awake dogs and during 1.6 and 3.0 per cent isoflurane anesthesia. Heart rate and cardiac output were increased in proportion to the nicardipine dose in the awake dogs and, to a lesser degree, in the dogs anesthetized with 1.6 per cent isoflurane, but did not change during 3.0 per cent isoflurane anesthesia. Left atrial pressure was unchanged by nicardipine in awake dogs and during anesthesia. Left ventricular maximum rate of tension development (dP/dt) increased in awake dogs and decreased during anesthesia. Coronary blood flow increased dose dependently without anesthesia, and, to a smaller degree, during anesthesia. Nicardipine increased carotid blood flow without anesthesia, whereas it was unchanged during anesthesia. Renal blood flow was unchanged in awake dogs and decreased during anesthesia. The authors conclude that nicardipine is a potent vasodilator that minimally affects cardiac function and regional blood flow in the presence of isoflurane. The interactions between nicardipine and isoflurane are mainly the result of the isoflurane-induced inhibition of the reflex tachycardia elicited by nicardipine.