Haemodynamic effects of diltiazem during fentanyl-nitrous oxide anaesthesia: An in vivo study in the dog

Summary: The haemodynamic effects of diltiazem were studied in six dogs during fentanyl-nitrous oxide (in oxygen) anaesthesia. A bolus of diltiazem 300 μg kg^-1 was given, followed by infusions at 30, 60 and 90 μg kg^-1 min^-1 which produced plasma diltiazem concentrations of 392±30, 908±54 and 1483±134 ng ml^-1, respectively. Diltiazem significantly reduced systemic vascular resistance index, mean arterial pressure, heart rate and PR interval. The decrease in afterload increased cardiac index, since there was little change in myocardial contractility (LV dP/dt). Five dogs developed second degree atrioventricular (AV) block in association with the highest dose. Administration of calcium chloride 20 mg kg^-1 did not reverse the haemodynamic or electrophysiological effects of diltiazem. Isoprenaline increased heart rate and restored sinus rhythm in four dogs with AV block.