Comparison of the effect of venovenous versus venoarterial extracorporeal membrane oxygenation on renal blood flow in newborn lambs

Venovenous extracorporeal membrane oxygenation (VV ECMO) using double lumen catheters is an alternative to venoarterial (VA) ECMO and allows for total blood flow using the patient's cardiac output in comparison to partial blood flow provided during VA ECMO. Objective: To compare the effects of VV versus VA ECMO on renal blood flow. Design: Prospective study. Setting: Research laboratory in a hospital. Subject: Newborn lambs 1-7 days of age (n = 15). Interventions: In anesthetized, ventilated lambs, femoral artery and vein were cannulated for monitoring and renal venous blood sampling. An ultrasonic flow probe was placed on the left renal artery for continuous renal blood flow measurements. Animals were randomly assigned to control (non-ECMO), VV ECMO and VA ECMO groups. After systemic heparinization, the animals were cannulated and studied at bypass flows of 120 mL/kg/min (partial bypass) for two hours in both ECMO groups and 200 mL/kg/min (full bypass) for an additional 30 min in the VA group. Changes in blood pressure and renal flow on ECMO and during ECMO bridge unclamping were recorded continuously. Plasma renin activity (PRA) levels were sequentially sampled. Results: Systemic blood pressure was not different in VV or VA ECMO at partial bypass flow. However, systemic blood pressure increased significantly at maximal bypass flow in the VA ECMO group. There was no change in renal flow in either VV or VA ECMO groups. PRA levels did not correlate with bypass flow change. During unclamping of the ECMO bridge, blood pressure and renal flow drop significantly in the VA group, but not in the VV group. Conclusion: VV and VA ECMO at partial bypass flows had comparable effect on blood pressure, renal blood flow and PRA level in this short-term study. However, unclamping of the ECMO bridges did differentially affect blood pressure and renal blood flow between VV and VA groups. We speculate that this repeated acute change in long-run VA ECMO support may play a role in the persistent hypertension seen in some patients.