Increasing organ blood flow during cardiopulmonary bypass in pigs: Comparison of dopamine and perfusion pressure

Objective: To determine whether low-dose dopamine infusion (5 pg/kg/min) during cardiopulmonary bypass selectively increases perfusion to the kidney, splanchnic organs, and brain at low (45 mm Hg) as well as high (90 mm Hg) perfusion pressures. Design: Randomized crossover trial. Setting: Animal research laboratory in a university medical center. Subjects: Ten female Yorkshire pigs (weight 29.9 ± 1.2 kg). Intervention: Anesthetized pigs were placed on normothermic cardiopulmonary bypass at a 100-mL/kg/min flow rate. After baseline measurements, the animal was subjected, in random sequence, to 15-min periods of low perfusion pressure (45 mm Hg), low perfusion pressure with dopamine (5 μg/kg/min), high perfusion pressure (90 mm Hg), and high perfusion pressure with dopamine. Regional perfusion (radioactive microspheres) was measured in tissue samples (2 to 10 g) from the renal cortex (outer two-third and inner one-third segments), stomach, duodenum, jejunum, ileum, colon, pancreas, and cerebral hemispheres. Measurements and Main Results: Systemic perfusion pressure was altered by adjusting pump flow rate (r² = .61; p < .05). In the kidney, cortical perfusion pressure increased from 178 ± 16 mL/min/100 g at the low perfusion pressure to 399 ± 23 mL/min/100 g at the high perfusion pressure (p < .05). Perfusion pressure augmentation increased the ratio of outer/inner renal cortical blood flow from 0.9 ± 0.1 to 1.2 ± 0.1 (p < .05). At each perfusion pressure, low- dose dopamine had no beneficial effect on renal perfusion or flow distribution. Similar results were found in the splanchnic organs, where regional perfusion was altered by perfusion pressure but not by dopamine. In contrast, neither changing perfusion pressure nor adding low-dose dopamine altered blood flow to the cerebral cortex. Conclusions: These data indicate that the lower autoregulatory limits of perfusion to the kidneys and splanchnic organs differ from those limits to the brain during normothermic bypass. Selective vasodilation from low-dose dopamine was not found in renal, splanchnic, or cerebral vascular beds. Increasing the perfusion pressure by pump flow, rather than by the addition of low-dose dopamine, enhanced renal and splanchnic but not cerebral blood flows during cardiopulmonary bypass.