An ECMO machine takes over the work of your heart, your lungs, or both when they’re too damaged or weak to function on their own. ECMO stands for extracorporeal membrane oxygenation, which essentially means “oxygenating blood outside the body.” The machine draws blood out through large tubes, removes carbon dioxide, adds oxygen, warms the blood back to body temperature, and pumps it back in. It’s a last-resort life support system used when a ventilator or other treatments aren’t enough.
How the Machine Works
The core of an ECMO machine is a component called a membrane oxygenator, sometimes referred to as an artificial lung. Blood is pulled from the patient’s body through a tube (called a cannula) using a centrifugal pump that creates gentle suction. That blood flows into the oxygenator, where it passes over thousands of tiny hollow fibers. Oxygen-rich gas flows through the inside of those fibers while blood flows along the outside, and the two never actually touch directly. This separation reduces damage to blood cells.
Gas exchange happens through simple diffusion: oxygen moves from the fiber side (where concentration is high) into the blood (where it’s low), and carbon dioxide moves the opposite direction, out of the blood and into the gas stream. It’s the same principle your lungs use, just happening inside a plastic cartridge instead of your chest. After passing through the oxygenator, the blood moves through a built-in heat exchanger. Blood loses significant heat as it travels through the circuit’s tubing, so the heat exchanger warms it precisely back to body temperature before it returns to the patient.
Two Types for Different Problems
ECMO comes in two configurations depending on what the patient needs.
VV ECMO (veno-venous) supports only the lungs. Blood is pulled from a large vein, oxygenated, and returned to another large vein. The patient’s own heart still does all the pumping. This is the type used for severe respiratory failure when a mechanical ventilator can’t keep oxygen levels adequate.
VA ECMO (veno-arterial) supports both the heart and lungs. Blood is drained from a large vein but returned to a large artery, effectively bypassing the heart entirely. This makes it the option for patients in cardiogenic shock, cardiac arrest, or any situation where the heart can’t pump enough blood on its own.
When ECMO Is Used
ECMO is reserved for cases where standard treatments have failed and the underlying condition is considered potentially reversible. For lung failure, that typically means severe pneumonia, acute respiratory distress syndrome (ARDS), or complications from infections like COVID-19 or influenza where the lungs are so inflamed that even maximum ventilator settings can’t deliver enough oxygen. For heart failure, it includes massive heart attacks, post-surgical cardiac collapse, or as a bridge while waiting for a heart transplant or a more permanent support device.
The key word is “reversible.” ECMO buys time for the body to heal. It doesn’t cure the underlying disease. If the heart or lungs have no realistic chance of recovering and no transplant or further intervention is available, ECMO generally isn’t offered.
How the Tubes Are Placed
Getting connected to ECMO requires inserting large tubes into major blood vessels. In adults, the most common sites are the femoral artery and femoral vein in the groin, or the internal jugular vein in the neck. Surgeons can place these tubes at the bedside using ultrasound guidance (peripheral cannulation) or during open-chest surgery where the tubes connect directly to the heart and aorta (central cannulation). Central cannulation is typically reserved for patients who need ECMO after cardiac surgery, since their chest is already open.
The tubes are significantly larger than a standard IV line because they need to carry high volumes of blood. Placement is done under sedation or anesthesia, and once in place, the tubes are secured to prevent movement. Patients on ECMO are in an intensive care unit for the entire duration, with a specialized team monitoring the circuit around the clock.
Risks and Complications
ECMO carries substantial risks, which is one reason it’s only used when other options have been exhausted. The two biggest categories of complications are bleeding and blood clots, and they work against each other. The circuit requires blood thinners to prevent clots from forming inside the tubing and oxygenator, but those same blood thinners increase the risk of bleeding.
In a study of 358 ECMO patients, nearly 45% experienced some form of bleeding complication (about 18% of those were classified as major), and roughly 23% developed blood clots. Clots can form in the circuit itself, in the veins of the legs, or travel to the lungs or brain. Bleeding can occur at the tube insertion sites, in the gastrointestinal tract, or in the brain. The contact between blood and the artificial surfaces of the circuit can also damage red blood cells over time, a process called hemolysis.
Survival Rates
According to the Extracorporeal Life Support Organization (ELSO), which maintains an international registry of ECMO cases, survival to hospital discharge varies significantly depending on why ECMO was needed. Among adults treated for respiratory failure, 57% survived to leave the hospital. For adults with cardiac failure, the survival rate was 44%. The lowest survival rate, around 30%, was in patients who received ECMO during or after cardiac arrest, a use called ECPR (extracorporeal cardiopulmonary resuscitation).
These numbers reflect how sick ECMO patients are to begin with. A 57% survival rate for respiratory failure means that more than half of patients whose lungs had completely failed recovered enough to go home. For context, without ECMO, many of these patients would have had little to no chance of survival.
Coming Off ECMO
Patients are evaluated daily with blood tests, imaging, and heart ultrasounds to determine whether their organs are recovering enough to take over again. The weaning process differs depending on the type of ECMO.
For VA ECMO, the team gradually reduces the pump speed in small increments, pausing for at least an hour after each reduction to watch for signs that the heart can’t handle the extra workload. Flow rates aren’t dropped below a minimum threshold because blood sitting in the circuit at very low flow rates will clot. If the heart maintains adequate blood pressure and oxygen delivery as support decreases, the patient can be separated from the machine.
For VV ECMO, the weaning process focuses on the lungs. The team reduces and eventually shuts off the gas flow through the oxygenator while keeping blood circulating through the circuit. This effectively forces the patient’s own lungs to do all the oxygen and carbon dioxide exchange. About 20 minutes after the gas is turned off, a blood test confirms whether the lungs can handle it. Some centers keep this trial going for one to six hours before committing to full removal. If oxygen levels drop below 88% or the patient’s breathing rate spikes above 30 to 35 breaths per minute, the trial has failed and full support is restarted.
Once a patient successfully passes the weaning trial, the tubes are removed. Recovery after ECMO depends heavily on the original illness, how long the patient was on the machine, and whether complications occurred during the run. Patients who were on ECMO for respiratory failure and whose lungs recovered may face weeks to months of physical rehabilitation, largely because of the prolonged ICU stay and immobility rather than ECMO itself.