Haemodynamic Comparison of Dopamine and Dobutamine in Normovolaemic and Hypovolaemic Dogs

The haemodynamic effects of dopamine and dobutamine in doses of 1-106 micrograms/kg/min were compared in dogs, first in the normovolaemic state and then after bleeding (10 ml/kg). In normovolaemia, dopamine caused a dose-dependent rise in systolic, mean and diastolic aortic pressures, while dobutamine caused a rise only in systolic pressure. In hypovolaemia, a rise in all three aortic pressures, was caused by both drugs, but to a lesser extent by dobutamine. Heart rate and cardiac output were similarly increased by both drugs, as was pulmonary artery pressure with high doses, in both states. Renal blood flow and diuresis increased in the middle-dose area. Both inotropic drugs caused an elevation in Paco2 and a drop in Pao2 and O2-saturation in both normovolaemia and hypovolaemia. The results agree with current opinion on the dose-dependent alpha-sympathomimetic action of dopamine and the relatively pure beta-action of dobutamine.