Extracorporeal membrane oxygenation (ECMO) can only be as good as its cannulation. The cannulae are the interface between the patient's circulation and the circuit: they set the achievable blood flow, determine whether the configuration supports the lungs, the heart, or both, and are the source of many of ECMO's most serious complications. This article reviews the two principal configurations — venovenous (VV) and venoarterial (VA) — the logic of cannula selection, and the often-underestimated step of decannulation.
The Two Configurations
VV ECMO supports the lungs. Deoxygenated blood is drained from the venous system, oxygenated and decarboxylated across the membrane, and returned to the venous system — the patient's own heart still pumps. It is the configuration for severe respiratory failure (for example ARDS) with preserved cardiac function. VA ECMO supports the heart and lungs together: blood is drained from the venous system and returned to the arterial system, bypassing both. It is used in cardiogenic shock and cardiac arrest. The single most consequential decision in cannulation is choosing the configuration that matches the failing organ — and recognizing when a patient must be converted from one to the other.
Cannula Selection: Flow Follows Geometry
Achievable flow is governed by cannula geometry — described by the Hagen–Poiseuille relationship, flow rises steeply with radius and falls with length. The drainage (venous) cannula is the usual flow-limiting element: it must be large enough to feed the circuit without excessive negative pressure and "chatter." The return cannula is sized to its target (venous in VV, arterial in VA). Access routes are femoral, jugular, or, for VV, a dual-lumen single-site cannula that drains and returns through one vein — freeing a limb and easing mobilization. INVAMED's Nexus venous and arterial cannula line sits within the broader cardiac surgery instrumentation portfolio; selection of size, length, and route is the clinical team's decision per the Instructions for Use.
Insertion: Percutaneous vs Surgical
Most cannulation today is percutaneous by Seldinger technique under ultrasound and fluoroscopic guidance — faster, and lower wound burden than open cutdown. Surgical cutdown and central cannulation retain roles in specific anatomies and intraoperative scenarios. Whatever the route, wire and dilator positioning must be image-confirmed: the classic catastrophes — vessel back-walling, malposition, and dissection — happen at this step.
The Complications That Matter
Cannulation-related problems dominate ECMO morbidity: bleeding at the access site, limb ischemia distal to a femoral arterial cannula in VA ECMO (which is why a distal perfusion cannula is often placed prophylactically), vessel injury and dissection, and — in peripheral VA ECMO — the North–South (Harlequin) syndrome, where poorly oxygenated native output competes with retrograde oxygenated circuit flow, leaving the upper body hypoxemic. Recognizing and pre-empting these is part of cannula strategy, not an afterthought.
Decannulation
Removing the cannulae is a procedure in its own right. Venous cannulae are usually withdrawn with a period of manual compression or a purse-string suture. Arterial decannulation after VA ECMO more often requires open surgical repair of the artery, since percutaneously placed large-bore arterial cannulae leave a defect that primary compression may not reliably close — though closure devices have expanded the percutaneous option. Timing follows weaning: demonstrated native organ recovery on trial-off, with careful attention to hemostasis and, on the arterial side, distal perfusion after removal.
Frequently Asked Questions
What is the difference between VV and VA ECMO cannulation?
VV drains and returns within the venous system to support the lungs, relying on the patient's own heart; VA returns to the arterial system to support heart and lungs together. The configuration follows the organ that is failing.
How is cannula size chosen for ECMO?
By the flow target and the vessel: the drainage cannula is usually the flow-limiting component and is sized as large as the vein safely allows, while the return cannula is matched to its venous or arterial target.
What is a dual-lumen ECMO cannula?
A single cannula placed in one vein that both drains and returns blood for VV ECMO, allowing single-site access that can free a limb and facilitate patient mobilization.
Why can VA ECMO cause limb ischemia?
A large arterial cannula in the femoral artery can obstruct forward flow to the leg; a distal perfusion cannula is frequently placed to protect the limb.
Related on INVAMED
Portfolio: cardiac surgery instruments, including venous and arterial cannulae for cardiopulmonary bypass and ECMO.
Device availability and regulatory status vary by country. Please contact INVAMED or your authorized local distributor for current regulatory information applicable to your region.