ObjectiveTo determine the hemodynamic responses to dopamine and epinephrine infusions in newborn piglets during normoxia and hypoxia.DesignProspective, randomized, blind cross-over study.SubjectsNewborn piglets (n = 7).InterventionsAnimals were acutely instrumented for measurements of cardiac output, pulmonary and systemic pressures, carotid and coronary artery blood flow, and coronary artery oxygen consumption. Dopamine at infusion rates of 2 to 16 micro gram/kg/min and epinephrine 0.2 to 1.6 micro gram/kg/min were administered during normoxia. Six piglets were similarly prepared and were then made hypoxic to an arterial O2saturation of 45% to 50%. Epinephrine at infusion rates of 0.2 to 3.2 micro gram/kg/min and dopamine at rates of 2 to 32 micro gram/kg/min were administered in random order during hypoxia.Measurements and Main Results0.4 and 4 micro gram/kg/min, respectively. Increases of both variables were greater with epinephrine than with dopamine. Myocardial extraction ratio was unaffected by dopamine and reduced at 0.2 and 1.6 micro gram/kg/min of epinephrine.Hypoxia caused significant increases in cardiac index, systemic blood pressure, pulmonary arterial pressure, carotid artery blood flow, coronary artery blood flow, coronary oxygen consumption, coronary oxygen extraction ratio, and the pulmonary/systemic vascular resistance ratio.Mean systemic arterial blood pressure increased significantly with 1.6 and 3.2 micro gram/kg/min of epinephrine, but was not significantly affected by dopamine at any infusion rate. Cardiac index was not affected significantly by either of the medications. Thus, there was a significant increase in the calculated systemic vascular resistance index with the highest dose of epinephrine, in contrast to the slight, statistically significant, decrease in calculated systemic vascular resistance index with the highest dose of dopamine. Epinephrine significantly reduced pulmonary arterial pressures at 0.2, 0.4, and 0.8 micro gram/kg/min. Dopamine had no effect on this variable. The pulmonary/systemic vascular resistance ratio was significantly reduced by epinephrine at doses of 0.2 and 3.2 micro gram/kg/min, whereas the highest dose of dopamine caused a significant increase in the pulmonary/systemic vascular resistance ratio.Conclusionsor=to8 micro gram/kg/min, and furthermore, produces a more appropriate hemodynamic profile in the presence of hypoxic pulmonary hypertension than dopamine infusion, in the acutely operated anesthetized piglet.(Crit Care Med 1995; 23:740-748)