ECMO cannulation is the process of inserting large tubes (called cannulas) into major blood vessels so a machine can take over the work of the heart, the lungs, or both. Blood drains out of the body through one cannula, passes through a pump and an artificial lung that removes carbon dioxide and adds oxygen, then returns through a second cannula. It’s used when someone’s heart or lungs are failing so severely that conventional treatments can’t keep them alive.
How the Circuit Works
The basic concept is straightforward. A drainage cannula pulls oxygen-poor, carbon dioxide-rich blood out of a large vein. A mechanical pump pushes that blood through an oxygenator, a device packed with thousands of tiny hollow fibers. As blood flows past these fibers, oxygen crosses into the red blood cells while carbon dioxide passes in the opposite direction and is vented away. The now oxygen-rich blood travels back into the body through a return cannula.
The oxygenator functions as an artificial lung, and the pump replaces the heart’s ability to circulate blood. Depending on which organs need support, the return cannula goes into either a vein or an artery, which is what distinguishes the two main types of ECMO.
VV-ECMO vs. VA-ECMO
The two configurations are venovenous (VV) and venoarterial (VA), and the difference comes down to where the return cannula is placed and what kind of organ support is needed.
Venovenous (VV) ECMO supports the lungs only. Both the drainage and return cannulas sit in major veins. Blood is pulled from one vein, oxygenated, and returned to another vein (or a different spot in the same vein). The heart still does all the pumping on its own. This is the typical setup for severe respiratory failure, such as acute respiratory distress syndrome (ARDS).
Venoarterial (VA) ECMO supports both the heart and the lungs. Blood drains from a large vein, but the oxygenated blood returns through a large artery, effectively bypassing the heart. This configuration is used when the heart is too weak to maintain circulation, whether from cardiac arrest, severe heart failure, or complications after heart surgery.
Where the Cannulas Are Placed
The specific blood vessels used depend on the patient’s age, size, and clinical situation. In adults receiving VA-ECMO, the most common approach is peripheral cannulation through the femoral vessels in the groin: the drainage cannula goes into the femoral vein, and the return cannula goes into the femoral artery. In some cases, particularly after open-heart surgery, a surgeon performs central cannulation by opening the chest and placing cannulas directly into the right atrium and the ascending aorta.
For VV-ECMO, there are two main options. A single dual-lumen cannula can be placed through the right internal jugular vein in the neck, which drains and returns blood through one insertion site. Alternatively, two separate cannulas are used: typically one in a femoral vein for drainage and one in the internal jugular vein for return. The single-site neck approach has a practical advantage because it leaves the patient’s legs free, making it easier to reposition them in bed or place them face-down (prone positioning), which improves outcomes in severe lung failure.
In newborns, the right side of the neck is the standard cannulation site because their femoral vessels are too small, generally unusable below about 10 kg of body weight. Children older than two and weighing more than 10 kg can typically be cannulated through the femoral vessels, similar to adults.
How the Cannulas Are Inserted
There are two broad approaches to getting the cannulas into position: percutaneous insertion and open surgical cutdown.
Percutaneous insertion uses a technique where a needle punctures the skin and enters the blood vessel directly, guided by ultrasound. A thin guidewire is threaded through the needle, the needle is removed, and progressively larger tubes are passed over the wire until the final cannula is in place. This is faster. In one study comparing the two methods during emergency cardiac support, percutaneous insertion took an average of about 10 minutes compared to 21 minutes for the surgical approach.
Open surgical cutdown involves making an incision over the target vessel, dissecting through tissue to expose the artery or vein directly, and then inserting the cannula under direct vision. It takes longer but gives the surgical team a clear view of the vessels, which can be important when anatomy is difficult or when emergency chest compressions are happening simultaneously. A hybrid approach, sometimes called the semi-Seldinger technique, combines elements of both: the vessel is surgically exposed, but the cannula is placed using the guidewire method.
Confirming Correct Placement
Placing a large cannula into the right spot inside the body requires real-time imaging. Several tools are used, and the choice depends on what’s available and the patient’s condition.
Echocardiography (ultrasound of the heart) is widely preferred because it shows the cannula tip’s exact position relative to the heart chambers in real time. Transesophageal echocardiography, where the ultrasound probe sits in the esophagus behind the heart, provides higher-resolution images than standard chest ultrasound, which can be inadequate in roughly 60% of patients on mechanical ventilation due to poor imaging windows. With echocardiography, clinicians can verify that the drainage cannula tip sits just above the junction of the large vein and the right atrium, confirm that the return port directs blood flow toward the correct valve, and check for complications like fluid accumulating around the heart.
Fluoroscopy (real-time X-ray) is another option, though it requires transporting the patient to a specialized suite and involves radiation exposure. Newer dual-lumen cannulas are designed with multiple radiopaque markers so that their position, orientation, and the location of drainage and return ports can all be verified on imaging.
Risks and Complications
ECMO cannulation carries significant risks. Vascular complications occur in roughly 10 to 30% of adults placed on ECMO, with VA-ECMO carrying a higher complication rate than VV-ECMO.
The most common issue is limb ischemia, where the arterial cannula partially or fully blocks blood flow to the leg below the insertion site. This affects around 12.6% of patients in pooled data. To prevent it, a smaller catheter is often placed downstream in the leg artery to maintain blood supply to the foot and lower leg. Other early complications include blood clots forming around the cannula (about 6.8%), compartment syndrome from swelling in the leg (4.2%), and in severe cases, amputation (0.6%).
Bleeding at the cannula site and blood pooling under the skin are common throughout the time a patient is on ECMO. More serious vascular injuries, including vessel tears, punctures, or dissection of the artery wall, can happen during insertion and may cause internal bleeding. Later on, groin complications such as fluid collections, infections, and the formation of false aneurysms at the puncture site are the most frequently reported problems after decannulation.
Removing the Cannulas
When a patient’s heart or lungs have recovered enough to function independently, the ECMO team performs decannulation. Venous cannula removal is relatively straightforward: after the cannula is pulled, firm pressure on the site is usually enough to stop bleeding.
Arterial decannulation is more involved because the hole left in a large artery needs reliable repair. The traditional method is surgical removal, where a surgeon opens the site, pulls the cannula, and stitches the artery closed. This has a high success rate (about 96%) but carries a notable risk of wound infection.
A newer alternative uses small suture-based closure devices placed around the artery, either before the cannula is inserted (pre-closure) or at the time of removal (post-closure). The pre-closure technique in particular has shown significantly lower infection rates compared to surgical removal. If these devices fail to achieve a seal, surgical repair serves as the backup. Overall, both methods are effective, with technical success rates above 90%.
Dual-Lumen Cannula Technology
One of the more important advances in VV-ECMO has been the development of dual-lumen cannulas that drain and return blood through a single insertion site in the neck. These devices, available in sizes ranging from 13 to 32 French (roughly 4 to 11 millimeters in diameter), are inserted percutaneously into the right internal jugular vein. The cannula spans from the upper to the lower large veins, with drainage holes at both ends pulling in blood while a return port in the middle directs oxygenated blood toward the heart’s tricuspid valve.
The practical benefits are meaningful for patients. A single neck site reduces the number of puncture wounds and associated bleeding risks. It also frees the lower body entirely, allowing patients to be turned prone for better lung function or even to begin physical rehabilitation while still on ECMO support. Newer designs feature reinforced construction to prevent kinking and crescent-shaped internal channels that optimize blood flow at lower pressures, reducing stress on blood cells as they pass through.