Complex ECMO Configurations

by Ahmed Zaky, MD, MSc, MPH, MBA, MSHQS, CMQ, FASA, FASE
Member, SOCCA
University of Alabama, Birmingham, AL

Volume 37 | Issue 1 | April 2026

Extracorporeal membrane oxygenations (ECMO) is a form of mechanical support used for life-threatening refractory cardiorespiratory failure. ECMO may serve as a bridge to recovery, decision on long-term mechanical support, or transplantation. In patients with isolated respiratory failure a veno-venous ECMO, or VV ECMO, is the preferred modality. In patients with isolated cardiac or combined cardiorespiratory failure, veno-arterial, or VA ECMO, is typically employed. The ECMO circuit consists of a drainage cannula, a pump, an oxygenator, and a return cannula. At many centers, peripheral VA ECMO cannulation is preferred to central VA cannulation because of ease and rapidity of deployment. 

Although in the majority of patients, conventional VV and VA femoral ECMO provides adequate support, there are certain instances where this configuration may not be feasible or may not provide the desired support. These instances may be due to patient factors such as limited vascular access and limb ischemia or to machine-related factors such as cannula size, recirculation of blood in VV ECMO, and inadequate body perfusion and the North-South (Harlequin) syndrome in VA ECMO. Under circumstances of inadequate conventional ECMO support, it is important to maximize medical management for peripheral VV and VA ECMO before changing the ECMO configuration¹. 

In this review, we will discuss the most commonly used hybrid and parallel ECMO configurations and more advanced complex configurations. 

Hybrid Configurations of ECMO

Strategy #1: Increasing venous drainage

The goal of this strategy is to increase ECMO flows by adding a venous drainage cannula. Thus, there are two draining lines and one return line in each of the subtypes of this strategy.

    1. Veno-veno-venous (VVV) ECMO

This modality is primarily used in VV ECMO. At baseline, there is a femoral venous drainage cannula and an internal jugular return cannula. Adding another drainage cannula from the contralateral femoral vein will increase ECMO flow to allow more oxygenation during VV ECMO support. Another reason to resort to the VVV configuration is to reduce the recirculation that results from close proximity of the drainage and return VV ECMO cannulas, after attempting to reduce the flows and reposition the cannulas. Adding a drainage cannula will decrease the drainage through the existing drainage cannula that is at close proximity to the return cannula - decreasing the likelihood of recirculation. 

    2. Veno-veno-arterial (VVA) ECMO

This configuration applies to VA ECMO. Adding a drainage cannula - typically from the right internal jugular vein in patients with peripheral femoral-femoral VA ECMO, will offload the heart, treat differential upper body hypoxia resulting from the heart pumping deoxygenated blood to the upper body through a failing lung (Harlequin syndrome). 

Strategy #2: Increasing oxygenated blood return from the circuit

In this strategy, an additional return cannula is added to either VV or VA ECMO. 

    1. Converting VV to VAV configuration 

This configuration is implemented in patients who develop heart failure while on VV ECMO. A return arterial cannula is added to the femoral artery to add oxygenated blood to the circulation in addition to the oxygenated blood returning through the venous cannula in the internal jugular vein. By so doing, more offloading of the failing heart occurs by pumping oxygenated blood to the peripheral circulation through the added return cannula. Overall, in this configuration we add an arterial cannula carrying oxygenated blood to provide cardiac support on top of respiratory support provided by VV ECMO.  

    2. Converting VA ECMO to VAV ECMO 

This configuration is implemented in patients on VA ECMO who develop Harlequin syndrome. In such a case, the heart function is recovering in the presence of respiratory failure. As a result, the heart pumps deoxygenated blood to the upper body - including the brain, the arms, and the coronaries. Adding a return cannula carrying oxygenated blood to the internal jugular vein will improve the oxygenation of the upper body by delivering well-oxygenated blood to the right heart. Therefore, in this situation a venous return cannula carrying oxygenated blood is added to provide respiratory support on top of cardiac support already provided by VA ECMO.

Important considerations for hybrid configuration 

When blood flow is split between 2 cannulas by a Y-connector, either on the returning or the drainage limb of the ECMO circuit, attention has to be paid to the flow across each cannula. In VVA ECMO, the flow distribution between venous drainage cannulas may be equivalent assuming similar size of the cannulae as the resistance to flow is almost the same. The condition is different in VAV ECMO where blood flow through the arterial cannula may encounter higher resistance compared to the flow through the venous cannula. This differential resistance with resulting differential flow may lead to hemolysis and thrombosis. Flow probes and throttle valves at the tubing between the Y-connector and the venous return cannula have been used successfully to monitor and control flow distribution, respectively. 

Parallel ECMO Configuration 

Parallel ECMO configuration entails the institution of two separate VV or VA ECMO circuits. The need for this configuration arises in conditions of high cardiac output (CO) in patients on VV ECMO due to sepsis, for example, after the employment of other rescue measures. The inability of a single ECMO circuit to capture adequate CO in patients with VV ECMO may lead to refractory hypoxia. In patients on VA ECMO, a parallel VA ECMO circuit is indicated when there is evidence of inadequate perfusion due to cardiorespiratory failure on a single VA ECMO circuit after employment of rescue measures and changes in VA ECMO configuration. A central VA ECMO cannulation may be a better option in these circumstances. The latter is composed of a drainage cannula that is placed in the right atrium or in a central vein and a return cannula that is placed in the ascending aorta. 

Considerations during parallel ECMO circuit configuration 

Parallel ECMO circuits are associated with the morbidity of utilizing 2 separate circuits and 4 cannulas. In parallel VA ECMO there is a risk of recirculation within each circuit as well as cross circulation between both circuits. There should be an adequate distance between the drainage and return cannulae of both circuits. In the setting of 2 peripheral VA ECMO circuits, there is always the risk of cardiac thrombus formation resulting from extended low flow state in the heart due to both circuits offloading blood return to the heart. 

More Advanced ECMO Configurations

The advent of the dual-lumen single cannula has opened new avenues for treating right and left ventricular failure in patients on VV and VA ECMO2, respectively (Table 1). 

References

1. Shah A, Dave S, Goerlich CE, Kaczorowski DJ. Hybrid and parallel extracorporeal membrane oxygenation circuits. JTCVS Tech. Aug 2021;8:77-85. doi:10.1016/j.xjtc.2021.02.024

2. Calhoun A, Szabo C, Convissar D, Pisano DV, Ortoleva J. Beyond Venoarterial and Venovenous Extracorporeal Membrane Oxygenation: Novel Cannulation Strategies. Journal of Cardiothoracic and Vascular Anesthesia. 2024;38(9):1830-1835. doi:10.1053/j.jvca.2024.04.012