Extracorporeal membrane oxygenation (ECMO) is an advanced form of life support used when a patient’s heart and lungs are unable to sustain life. This technology functions as an external circuit that temporarily takes over the work of these failing organs, providing time for them to rest and potentially recover. The veno-arterial (VA) mode is specifically designed for patients with profound cardiorespiratory failure. The VA circuit provides both oxygenation and circulatory support simultaneously, which is necessary when the heart’s pumping function is severely compromised.
Defining Veno-Arterial Support
Veno-Arterial Extracorporeal Membrane Oxygenation provides dual support for the lungs and the heart using a continuous circuit. The process begins by draining deoxygenated blood from a large vein, typically the inferior vena cava, through a cannula into the external circuit. Within the circuit, the blood first passes through a pump, replacing the heart’s natural pumping action. The blood then enters the oxygenator, which functions as an artificial lung, adding oxygen and removing carbon dioxide (gas exchange). The oxygenated blood is returned to the patient through a second cannula inserted into a large artery, such as the femoral or subclavian artery. This restores circulation by generating systemic blood flow and pressure that the weakened heart cannot provide.
Clinical Scenarios for Use
VA ECMO is used as a rescue maneuver for catastrophic clinical situations where the patient is at immediate risk of death due to heart failure. The primary indication is refractory cardiogenic shock, a state where the heart is failing severely and is unresponsive to standard medications. This condition is often caused by a massive heart attack, severe myocarditis, or acute decompensated chronic heart failure. The device functions as a temporary “bridge” to allow for recovery, or as a bridge to a more permanent solution like a heart transplant or a long-term mechanical assist device. Another use is for extracorporeal cardiopulmonary resuscitation (ECPR), where VA ECMO is rapidly deployed for patients in cardiac arrest who have not responded to conventional resuscitation efforts. The machine immediately restores circulation and oxygenation, giving the medical team time to treat the underlying cause.
The Treatment Process
The practical application of VA ECMO begins with the placement of cannulas, which are often inserted using the Seldinger technique or through a small surgical cut-down. For peripheral VA ECMO, the most common access sites are the femoral vein for venous drainage and the femoral artery for arterial return. The axillary or subclavian arteries may also be used for arterial return. The presence of the arterial cannula in the femoral artery can restrict blood flow to the leg, so a small additional cannula, known as a distal perfusion catheter, is often placed in the same leg to prevent limb ischemia.
Throughout the treatment, continuous monitoring is required to ensure the circuit is functioning correctly and the patient’s body is responding appropriately. This involves frequent checks of blood pressure, oxygenation levels, and the mechanical parameters of the circuit, such as blood flow and pressure.
Because the blood is circulating outside the body and coming into contact with artificial surfaces within the circuit, there is a high risk of clot formation. To mitigate this, patients require continuous systemic anticoagulation, most commonly with unfractionated heparin, to prevent thrombosis. This constant need for blood thinners introduces the most frequent and serious complication, which is bleeding, especially at the insertion sites or in the brain. The medical team must constantly adjust the dose of anticoagulation to maintain a delicate balance between preventing clots in the circuit and avoiding excessive bleeding in the patient.
Weaning and Decannulation
The goal of VA ECMO is to allow the patient’s heart to recover enough function to take over circulation, which is assessed through a process called “weaning.” Weaning begins once there are objective signs of cardiac improvement, such as better heart function on imaging and a reduced need for supportive medications. The process involves gradually decreasing the blood flow provided by the ECMO machine, which forces the native heart to handle a greater workload.
The patient’s response to this reduced support is closely monitored through changes in blood pressure, oxygen saturation, and the use of echocardiography to visually assess heart function. A common protocol is to reduce the ECMO flow to a minimum level, often between 0.5 to 1.5 liters per minute, and observe the patient’s stability. If the patient remains stable during this low-flow trial and the heart demonstrates sufficient pumping ability, the medical team will proceed to decannulation.
Decannulation is the surgical removal of the cannulas, which is typically performed in the operating room to manage any potential bleeding complications. The blood thinners are temporarily reversed, and the tubes are removed, requiring surgical repair of the arterial and venous access sites, especially the artery, to restore normal blood flow and prevent local complications. Following the procedure, the patient remains under close observation to ensure their recovered heart and lungs can sustain the body’s needs independently.