Acute Respiratory Distress Syndrome (ARDS) is a condition marked by sudden and severe lung failure. The lungs fill with fluid, which obstructs the transfer of oxygen into the bloodstream. For the most severe cases, a form of life support known as Extracorporeal Membrane Oxygenation (ECMO) may be used. This technology functions as an artificial lung, performing gas exchange outside the body for patients when conventional treatments, like mechanical ventilation, are insufficient.
When ECMO is Considered for ARDS
The decision to initiate ECMO is made after a patient with ARDS fails to respond to standard intensive care therapies. These include optimized mechanical ventilation and prone positioning, where the patient is placed on their stomach to improve lung function. The medical team will consider more invasive options if these methods are not effective.
Key indicators for starting ECMO are severe hypoxemia, a state of dangerously low oxygen in the blood that does not improve with 100% oxygen delivery, and uncompensated hypercapnia, where the body cannot effectively clear carbon dioxide, leading to acidic blood. Physicians may use scoring systems, like the Murray score or the RESP score, to help standardize the decision-making process and assess mortality risk.
However, not every patient with severe ARDS is a candidate for ECMO. Contraindications, or factors that make the treatment too risky, are carefully considered. These can include irreversible brain damage, a terminal illness, or severe bleeding disorders that cannot be managed. Prolonged use of high-pressure mechanical ventilation for more than a week is also a relative contraindication, as it may suggest that lung injury has become irreversible.
The ECMO Procedure for ARDS Patients
Starting ECMO involves a surgical procedure to connect the patient to the external circuit through cannulation. Large, flexible tubes called cannulas are inserted into major veins, such as the internal jugular vein in the neck and the femoral vein in the groin.
For ARDS, the specific type of ECMO used is almost always Veno-Venous (VV) ECMO. In this configuration, deoxygenated blood is drained from a large vein through one cannula and pumped through the ECMO circuit. The circuit contains a specialized device called an oxygenator, which is made of thousands of tiny hollow microfibers. As blood flows over these fibers, oxygen is added and carbon dioxide is removed, and the newly oxygenated blood is then warmed and returned to the body through the second cannula.
VV ECMO only provides respiratory assistance; the patient’s own heart continues to circulate blood. The procedure and management of the ECMO machine are handled by a specialized team. This team includes critical care physicians, surgeons, nurses, and perfusionists trained to operate the circuit and monitor the patient.
Patient Management During ECMO
The primary objective of using ECMO for ARDS is to provide “lung rest.” By taking over gas exchange, ECMO allows mechanical ventilator settings to be turned down to minimal levels. This reduction in pressure and oxygen, known as “ultra-protective” ventilation, helps prevent further lung injury and gives the inflamed lungs a chance to heal.
Patients on ECMO are kept under deep sedation, especially in the initial phase, to ensure comfort and tolerance of the breathing tube and cannulas. Neuromuscular blocking agents, or paralytics, may also be used to prevent spontaneous breathing efforts that could interfere with the resting strategy.
While the lungs rest, the medical team provides comprehensive supportive care. This involves continuous monitoring of vital signs, regular blood tests, and nutritional support through a feeding tube. As patients stabilize, sedation can be lightened, and they may participate in physical therapy to prevent muscle weakness.
Potential Complications and Weaning Off Support
ECMO is a life-sustaining intervention, but it carries substantial risks. One of the most significant complications is bleeding. To prevent clots from forming within the external circuit, patients must receive anticoagulants, or blood thinners. This necessary treatment increases the risk of serious bleeding, either at the cannula insertion sites or internally, such as in the brain or gastrointestinal tract.
Despite the use of anticoagulants, blood clots can still form. These clots, a condition known as thrombosis, can develop within the ECMO circuit, potentially leading to equipment failure. Clots can also form within the patient’s own blood vessels, which could travel to the brain and cause a stroke. Because the large cannulas create a direct path into the bloodstream, there is also a heightened risk of serious infections.
The process of discontinuing ECMO support is known as weaning. This begins when there are clear signs of lung recovery, such as improvements on chest X-rays and the ability of the lungs to oxygenate the blood with minimal help from the ventilator. Doctors perform weaning trials by gradually reducing support from the ECMO machine, forcing the patient’s lungs to take on more of the work.
If the patient successfully tolerates these trials while maintaining stable oxygen and carbon dioxide levels, they are considered ready to come off the machine. The final step is decannulation, a procedure to surgically remove the cannulas. Following this, the patient will continue to recover, often still requiring some support from a mechanical ventilator at much lower settings.