A study of the combined haemodynamic effects of dobutamine and enoximone in patients taking beta adrenoceptor antagonists.

We conducted a randomized, double-blind investigation to determine whether enoximone affects the actions of dobutamine in patients taking beta adrenoceptor antagonists. We studied sixteen patients with good ventricular function after coronary artery bypass operations. All patients were taking a beta adrenoceptor antagonist. The patients received a standardized intravenous anaesthetic, which was maintained throughout the investigation. They received a masked infusion, containing either normal saline or enoximone. Haemodynamic data were recorded before, during, and after an infusion of dobutamine, which was given at three different rates. Patients receiving enoximone had a greater cardiac output, a higher heart rate and a lower systemic vascular resistance than patients receiving saline. They also required an average of 1500 ml more intravenous colloid in the immediate postoperative period to achieve haemodynamic stability. Dobutamine produced a consistent, significant peripheral vasoconstriction, but no inotropic or chronotropic effect. There was no significant difference in this effect between the two groups, and it was not influenced by concurrent therapy with enoximone. The alpha adrenergic action of dobutamine prevented us from using high enough rates of infusion to explore any interaction between the inotropic actions of dobutamine and enoximone.