Cardiovascular and renal haemodynamic effects of dopexamine: comparison with dopamine

We have studied the effects of dopexamine and dopamine on systemic and renal haemodynamics in 20 male patients undergoing elective coronary artery bypass surgery. Patients were allocated randomly to two groups (n = 10) who were treated with incremental doses of either dopexamine 1, 2 and 4 micrograms kg-1 min-1, or dopamine 2.5 and 5 micrograms kg-1 min-1, each dose being maintained for 15 min. Measurements were performed before administration of the drug and at the end of the infusion period at each dose. Fentanyl and midazolam were used as anaesthetic agents. Renal blood flow was measured with the argon washin technique. Dopexamine 4 micrograms kg-1 min-1 produced an increase in cardiac index of 117% caused by a 65% reduction in afterload and an increase in heart rate by 61%. Dopamine 5 micrograms kg-1 min-1 caused a 40% increase in cardiac index as a result of an increase in stroke volume. Renal vascular resistance decreased more than systemic vascular resistance with dopamine. With dopexamine, the increase in renal blood flow (66%) was less than the increase in cardiac index, while renal vascular resistance and systemic vascular resistance declined to almost the same extent. The results show that dopexamine exerts systemic and renal effects mainly via stimulation of beta 2-receptors. An action of dopexamine at renal DA1-receptors could not be demonstrated in this study.