A Lifeline When The Heart Or Lungs Fail: ECMO

By Asst Prof Mathew Jose Chakaramakkil, Senior Consultant, Cardiothoracic Surgery 

When the heart or lungs fail suddenly and severely, conventional treatments such as ventilators and medications may not be enough to keep a patient alive. In such extreme situations, doctors may turn to Extracorporeal Membrane Oxygenation (ECMO). This is an advanced, temporary mechanical circulatory support system designed to sustain patients while their underlying condition is treated or while recovery takes place.

The system takes over the function of the heart, the lungs, or both. It is used in critically ill patients whose own organs cannot maintain adequate oxygen delivery to the body. This happens despite maximal conventional therapy. In simple terms, ECMO removes venous blood from the body, adds oxygen and removes carbon dioxide from the blood using an artificial lung called an oxygenator. It then pumps the oxygenated blood back into the body using a mechanical pump.

ECMO is not a treatment for the underlying condition causing heart or lung failure. Instead, it buys time. It provides time for antibiotics to work, for inflammation to settle, for damaged heart muscle to recover, or for a patient to undergo further interventions such as surgery or transplantation.

How ECMO Works

An ECMO circuit, as shown in Figure 1, consists of several key components. These include large cannulas (tubes) inserted into major blood vessels. There is a centrifugal pump that circulates blood. A membrane oxygenator performs gas exchange. A heat exchanger keeps blood at body temperature and finally, there is a monitoring system for pressure, oxygenation, and flow rates.

Blood is drained from the patient through a cannula placed in a large vein. It travels through the ECMO circuit, where it is oxygenated and cleared of carbon dioxide. The blood is then returned to the body through either a vein or an artery, depending on the type of ECMO used.

However, because blood circulates outside the body, it has a tendency to clot. To prevent dangerous clots from forming in the circuit, patients must receive anticoagulation (blood thinners). This treatment carries bleeding risks but is necessary for safe ECMO operation.

Figure 1: A close-up of the ECMO circuit.

Two Types of ECMO Support

A. Veno-Arterial (VA) ECMO – Heart and Lung Support

VA ECMO supports both cardiac and respiratory function. Blood is drained from a vein and returned to an artery, effectively bypassing both the heart and lungs. It is typically used in cases such as:

• Severe heart attack (acute myocardial infarction)
• Cardiogenic shock (when the heart becomes too weak to pump enough blood)
• Cardiac arrest
• Heart muscle inflammation (myocarditis)• Heart muscle disease (cardiomyopathy)
• Large, life-threatening blood clots in the lungs (massive pulmonary embolism)
• Post-cardiac surgery cardiogenic shock

VA ECMO reduces the workload of the heart by diverting blood flow through the external circuit. It is often used for 5 to 10 days, although duration varies depending on recovery.

B. Veno-Venous (VV) ECMO – Lung Support Only

VV ECMO supports respiratory function alone. Blood is drained from a vein and returned to a vein, typically into a chamber of the heart (right atrium). The patient’s heart must still function adequately to pump blood to the body. It is most commonly used in severe lung failure due to:

• Acute respiratory distress syndrome
• Severe pneumonia
• Influenza
• COVID-19
• Other conditions such as refractory hypoxemia, hypercarbia and air-leak syndromes (serious breathing problems that do not respond to standard treatments)

VV ECMO allows the lungs to rest while minimising damage that can occur from mechanical ventilators. Patients are often supported for 10 to 14 days, though longer periods are possible.

When ECMO Is Considered

Other than being used as temporary support for heart and lung failure, ECMO is reserved for patients in whom all conventional therapies such as mechanical ventilation, strong heart medications and other advanced life-support treatments, have failed. It is also increasingly being used in other critical situations, including trauma, drug overdose, burns, sepsis, severe hormone-related (endocrine) emergencies, severe allergic reactions (anaphylaxis), and to support high-risk airway, chest and heart procedures.

As with any invasive, intensive therapy, ECMO carries significant risks. Patients may experience complications including bleeding, stroke, blood clots, infection, and reduced blood flow to limbs. Other potential issues may include kidney failure and mechanical problems with the ECMO circuit. Because of these risks, ECMO should only be considered after careful evaluation by a multidisciplinary team including cardiothoracic surgeons, perfusionists, nurses, intensivists, cardiologists, and pulmonologists.

Each patient is assessed individually, but ECMO is generally not suitable for patients with:

• Advanced multi-organ failure
• Severe chronic organ dysfunction (e.g., end-stage liver or kidney disease)
• Advanced cancer
• Severe irreversible brain injury
• Advanced age (typically above 65 years, depending on context)

NHCS launched Singapore's first ECMO service in 2001. For 25 years, the centre has performed more than 1,000 ECMO procedures and has become the largest ECMO provider in the country, with approximately 80 procedures performed annually. The centre also operates a mobile ECMO service which allows the team to begin treatment at other hospitals before transferring patients to NHCS for continued care.