Extracorporeal membrane oxygenation (ECMO) is a life-saving medical technique that provides temporary respiratory and/or circulatory support to patients with severe respiratory or cardiac failure.
This advanced therapy acts as a bridge, allowing the lungs or heart to rest and heal while providing oxygenation and circulation externally. ECMO involves the use of a sophisticated medical device that mimics the function of the lungs and/or heart, providing oxygenation and circulation to the patient’s body outside of their natural physiology. It consists of several key components, including a pump, oxygenator, tubing, and cannulas. The patient’s blood is diverted from the body through these cannulas to the ECMO circuit, where it is oxygenated and returned to the body, bypassing the lungs and/or heart temporarily. This allows the lungs or heart to rest and heal, while the ECMO system supports vital oxygenation and circulation.
Pathophysiology
Understanding the underlying pathophysiology of conditions that warrant ECMO is crucial for comprehending its application. Respiratory failure, often due to acute respiratory distress syndrome (ARDS) or severe pneumonia, and cardiac failure, such as cardiogenic shock or post-cardiotomy syndrome, are the primary indications for ECMO. These conditions result in impaired gas exchange or inadequate cardiac output, leading to severe hypoxemia or haemodynamic instability. ECMO provides a means to temporarily bypass the lungs or heart, allowing for optimal oxygenation and circulatory support until the underlying condition can be resolved.
Types of ECMO
ECMO can be classified into two main types: venoarterial (VA) ECMO and venovenous (VV) ECMO. Each type serves different purposes and is utilised based on the specific clinical scenario and the level of support required.
Venoarterial ECMO (VA ECMO)
Venoarterial ECMO (VA ECMO) provides both cardiac and respiratory support. It involves the cannulation of a large central vein and artery. Blood is drained from the right atrium or superior/inferior vena cava, passed through an oxygenator, and then returned to the arterial system, bypassing the heart and lungs.
VA ECMO is primarily utilised in patients with severe cardiac and/or respiratory failure. It helps to maintain adequate oxygenation and perfusion by bypassing the failing heart and lungs. This type of ECMO is commonly used in conditions such as cardiogenic shock, post-cardiotomy syndrome or severe myocarditis.
One advantage of VA ECMO is its ability to support both the heart and lungs simultaneously. However, it also carries the risk of increased left ventricular afterload, potentially leading to pulmonary oedema or left ventricular distension. Careful monitoring and adjustment of ECMO flow rates are necessary to optimise cardiac output and prevent complications.
Venovenous ECMO (VV ECMO)
Venovenous ECMO (VV ECMO) is primarily focused on respiratory support. It involves cannulation of two large central veins, usually the femoral vein or internal jugular vein. Blood is drained from one vein, passed through an oxygenator, and then returned to the other vein, providing enhanced gas exchange while leaving the native cardiac function intact.
VV ECMO is commonly used in patients with severe respiratory failure, such as those with acute respiratory distress syndrome (ARDS) or refractory hypoxemia. It allows the lungs to rest and heal while providing sufficient oxygenation. VV ECMO can also facilitate other lung-protective strategies, such as low tidal volume ventilation or prone positioning.
One advantage of VV ECMO is its ability to provide oxygenation and decarboxylation support without directly affecting the cardiac function. However, it does not offer direct circulatory support, so patients with significant cardiac dysfunction may require additional interventions.
Hybrid Configurations
In some complex cases, a hybrid configuration of ECMO may be employed. This involves the combination of VA and VV ECMO to provide tailored support based on the patient’s specific needs. Hybrid configurations allow for more individualised therapy, with the ability to provide simultaneous cardiac and respiratory support while minimising complications.
The selection of the appropriate ECMO configuration depends on various factors, including the underlying condition, the extent of cardiac and respiratory failure and the availability of cannulation sites.
By tailoring ECMO support to individual patient needs, both VA and VV ECMO play vital roles in providing life-saving assistance to patients with severe respiratory or cardiac failure. The specific type of ECMO employed depends on the clinical context, allowing for personalised care and improved chances of recovery.
Complications and Risks
While ECMO can be life-saving, it is not without risks. Some potential complications and risks associated with ECMO include.
- Bleeding: The use of anticoagulants to prevent blood clotting in the ECMO circuit can increase the risk of bleeding. Close monitoring of coagulation parameters is essential to strike a balance between preventing clotting and minimising bleeding.
- Infection: The presence of indwelling catheters and prolonged exposure to the ECMO circuit can increase the risk of bloodstream infections. Strict adherence to infection control measures and vigilant monitoring are crucial to minimise this risk.
- Vascular complications: Cannulation sites may develop complications such as bleeding, haematoma or limb ischaemia. Regular assessment and prompt management of these complications are necessary to ensure patient safety.
- Organ dysfunction: Despite ECMO support, patients may still experience organ dysfunction. This could be due to underlying disease processes, prolonged critical illness, or complications arising from ECMO support. Close monitoring and appropriate interventions are necessary to manage organ dysfunction effectively.