EFFECT OF DOPAMINE ON RENAL BLOOD-FLOW AND CARDIAC-OUTPUT

Objective: To characterize the relationship between changes in renal b lood flow and cardiac output induced by dopamine, hypothesizing that a t low doses renal blood flow changes more than cardiac output. Design: Anesthetized swine had renal blood now and cardiac output measured du ring either continuous dopamine infusions (2 to 8 mu g/kg per minute) or bolus dosing (1 to 16 mu g/kg), and increases in both were compared . Two different fluid protocols were compared using constant dopamine infusions. In the constant pulmonary capillary wedge pressure protocol , intravenous fluids were titrated to keep this parameter constant. In the other protocol, fluid therapy was held constant at 10 mL/kg per h our. Results: With infusions, mean increases in renal blood flow and c ardiac output were relatively equal. The maximum increase was 35% at 8 mu g/kg per minute under the constant pulmonary capillary wedge press ure protocol, with no significant differences (P>.1) found between the change in renal blood flow and cardiac output at any dose in either p rotocol. With bolus dosing, renal blood flow increased significantly m ore than cardiac output at 1, 4, and 8 mu g/kg (P<.05). Conclusion: Di sproportionate increases in renal blood flow compared with cardiac out put at low bolus doses show initial renal responses to be independent of cardiac output. The infusion data suggest that renal responses exhi bit tachyphylaxis or that cardiac output slowly accommodates to decrea sed total peripheral resistance.