Dobutamine, isoprenaline and dopamine in patients after open heart surgery.

Dobutamine, a new synthetic catecholamine, has been developed as a more specific inotrope and is reported to have less effect on heart rate and peripheral vascular resistance than other catecholamines. Reports of its effects after cardiotomy have cast doubt on this idea. We have compared the haemodynamic effects of dobutamine with isoprenaline (Group I) and with dopamine (Group II) in early postcardiotomy patients. In both groups a dose response curve was evaluated (dopamine and dobutamine were given at 1.25, 2.5, 5.0 and 10.0 microgram/kg/min; isoprenaline at 0.005, 0.01, 0.02 and 0.04 microgram/kg/min). In Group I both drugs caused significant increases in cardiac index at the highest dose level only. At that level isoprenaline was associated with a significantly higher heart rate than dobutamine and a significantly lower systemic vascular resistance. Similarly, in Group II, both drugs caused significant increases in the cardiac index only at the highest dose level. However, the heart rate at this dose was significantly higher with dobutamine. Dopamine caused no changes in heart rate at any dose level. Neither drug was associated with any alteration of systemic vascular resistance. No changes in stroke volume, left atrial pressure or pulmonary vascular resistance were found in either group. The rise in cardiac output was caused mainly by tachycardia.