Parallel Venous Extracorporeal Membrane Oxygenation Circuits During Bridge-to-Lung Transplantation

VV ECMO is commonly used to support patients with isolated respiratory failure as a bridge to recovery or lung transplantation. While percutaneous peripheral cannulation is preferred, refractory hypoxia can occur and can limit essential physical therapy and mobilization during bridging. Patients with severe respiratory disease may develop right ventricular failure, leading to cardiogenic shock and refractory hypoxia that sometimes necessitates RVAD or VA ECMO. Increasing oxygen delivery and reducing oxygen extraction are key goals in managing refractory hypoxia on VV ECMO. The authors present a case in which a patient with refractory hypoxia after cardiac arrest was supported with parallel, independent VV ECMO circuits to allow continued PT and successful bridging to lung transplantation.

Prior literature supports ECMO as a bridge to lung transplantation and highlights the evolution toward awake ECMO with active rehabilitation to improve pretransplant conditioning and posttransplant recovery. Early PT during ECMO is associated with faster return to function, reduced delirium, and shorter ICU stays, and ambulation can be safely achieved even with femoral cannulation when managed by an experienced multidisciplinary team. Parallel ECMO circuits have been described in contexts such as sepsis, necrotizing lung infections, and RV failure to augment oxygenation when single-circuit VV ECMO is inadequate. The manuscript references studies on ECMO as a bridge to transplant, outcomes with additional drainage during VV ECMO, definitions and management of RV injury on ECMO, hybrid/parallel circuits, early mobilization on ECMO, the adverse impact of mechanical ventilation during ECMO bridging, and rehabilitation strategies for lung transplant candidates and recipients.

Case report of a 34-year-old male with recurrent respiratory infections presenting with cyanosis and refractory hypoxemia requiring VV ECMO via 20 Fr right internal jugular drainage/return and 25 Fr multistage right femoral venous cannula. After extubation on hospital day 13, the patient engaged in PT. Persistent ECMO dependency and irreversible lung damage led to transplant evaluation. The course was complicated by RV failure and cardiac arrest on hospital day 57, prompting temporary V-AV ECMO with an additional 16 Fr left femoral arterial reinfusion cannula and a 6 Fr distal perfusion cannula. Following stabilization, the patient was transitioned to a single-site dual-lumen left subclavian Protek Duo RVAD cannula (31 Fr) for veno-pulmonary ECMO support, remaining extubated and ambulatory while on ECMO. On ECMO day 110, after a PT session, the patient developed acute hypoxia and shock refractory to noninvasive ventilation, vasopressors, sedation, circuit exchange, and transfusions. Differential diagnoses included worsening RV failure due to pulmonary hypertension and valve insufficiency from the RVAD, intracardiac shunt, or aspiration-induced hyperdynamic state and acute lung injury. Echo demonstrated preserved LV function with severe RV volume/pressure overload and markedly reduced RV systolic function; right atrium was severely dilated. Right heart catheterization before listing suggested pulmonary hypertension and cannula-associated valvular regurgitation driving RV dysfunction. With inadequate response to inotropy or increased ECMO flows, a multidisciplinary team opted for parallel, independent circuits using peripheral cannulation: dual-lumen veno-pulmonary ECMO via left subclavian site plus an added RFem multistage venous drainage cannula connected to an additional VV circuit (dl) VP/VV ECMO. This approach aimed to improve the ECMO flow-to-native cardiac output ratio, mitigate intracardiac shunt effects, avoid arterial or central cannulation, prevent intubation, and preserve capacity for PT. Post-conversion management targeted flow settings to minimize hemolysis, transfusions, and organ hypoxemia while maintaining oxygenation sufficient for mobilization.

• Immediate improvement in hypoxia and resolution of hemodynamic instability after initiating parallel, independent VV ECMO circuits.
• Before parallelization: RVAD ECMO flows 4.75–4.98 L/min at 4,300–4,400 RPM.
• After parallelization: RIJ–RFem circuit flows 4.25 L/min at 3,100 RPM; VP ECMO reduced to 3.5 L/min at 3,485 RPM; no further transfusion needs during the ECMO run.
• Resumed and escalated ambulation the day after reconfiguration, walking daily for three days on parallel circuits up to 1,250 ft (380 m), exceeding prior 110-day record.
• Underwent successful bilateral lung transplantation 9 days after conversion to parallel circuits.
• Discharged home after 203 hospital days, including 119 days on ECMO, spanning four circuit configurations with seven total cannulae.
• Strategy enabled maintenance of extubation and continued PT throughout prolonged support, despite complications including subarachnoid hemorrhage, bloodstream infections, and thrombosis.

This case demonstrates that adding a parallel, independent VV ECMO circuit can safely and effectively augment oxygenation in the setting of refractory hypoxia when single-circuit VV ECMO is inadequate, particularly in the context of suspected intracardiac shunt, high cardiac output, or high oxygen extraction states. The approach stabilized gas exchange and hemodynamics without interrupting ECMO support, intubating, or resorting to arterial or central cannulation, thereby enabling ongoing PT and functional conditioning critical for transplant candidacy and recovery. Compared with alternatives such as reconfiguration requiring circuit clamping, VA or central cannulation, or sedation and intubation, the parallel circuit provided a less invasive, continuously supportive option. Cross-circuit recirculation is a recognized risk; in this case, the subclavian dual-lumen RVAD configuration likely routed any recirculated flow into the pulmonary artery, mitigating systemic desaturation. These findings support multidisciplinary decision-making to tailor ECMO configurations that prioritize oxygen delivery, minimize complications, and maintain mobility in bridge-to-transplant patients.

Parallel, independent VV ECMO circuits can preserve end-organ function and support ongoing rehabilitation in severe refractory respiratory failure during bridge-to-lung transplantation. In selected patients, this strategy offers a feasible, less invasive alternative to arterial or central cannulation and avoids interruption of ECMO support and the need for intubation, while facilitating continued mobility. Multidisciplinary evaluation is essential to balance risks, including potential cross-circuit recirculation, against benefits in oxygenation and functional status.

Single-patient case report limits generalizability. Although the strategy was successful here, risks inherent to additional cannulation and parallel circuits remain, including potential cross-circuit recirculation and thrombotic or bleeding complications. The report does not provide comparative outcomes versus alternative configurations, and exact criteria for patient selection require further study.