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Author: Tim Montrief, MD, MPH
Emergency Medicine Resident, PGY-2
Jackson Memorial Hospital
Extra Corporeal Membrane Oxygenation (ECMO), more accurately known as Extracorporeal Life Support (ECLS) is a type of prolonged mechanical cardiopulmonary support that began in the 1970s. Its technology, indications, and usage have rapidly evolved over the last two decades; it has now become an essential tool in the care of critically ill adults and children refractory to conventional management who have potentially reversible causes of respiratory/cardiac failure. With the development of ECMO programs across the nation, this technology is making its way to an emergency department (ED) near you.
ECMO’s basic principle is to replace cardiac function. ECMO passes blood through an oxygenator to allow for gas exchange. The blood is driven by a pump that generates a pressure that may augment or replace cardiac function. The actual ECMO circuit can be conceptualized like the actual human circulatory system. Components include: a pump (heart), a membrane oxygenator (lung), a heat exchanger, and tubing and cannulas (blood vessels). ECMO can be used in a variety of cases, including cardiac arrest, intractable arrhythmias with hemodynamic instability, pulmonary embolism, massive hemoptysis, acute respiratory distress syndrome (ARDS),[3,4] cardiotoxic drug overdose, as a bridge to organ transplant, and oxygenation during difficult airway management. Although originally an inpatient therapeutic option, several hospitals have successfully integrated ECMO cannulation into their ED practice models.
There are two major configurations of the ECMO circuit: Veno-arterial (VA) and Veno-venous (VV).
- In this type of ECMO, the patient’s blood is taken from a major vein and returned via an artery (peripheral artery or the aorta)
- It provides both circulatory support and oxygenation.
- This system can support a failed heart (by providing pump support), a failed lung (by providing gas exchange), or both.
- This type of ECMO requires access to two major veins or the use of a double-lumen catheter to access one major vein.
- Advantages over VA ECMO include lower risk for ischemic injury or thromboembolic complications, as well as decreased risk of arterial injury due to vein cannulation.
- Does not provide circulatory support.
- Best used to support a failed lung.
Indications and Contraindications
ECMO is not a strategy to correct a medical condition, but rather a bridge to definitive therapy, and thus requires strict inclusion and exclusion criteria. Therefore, selection of the right patients is crucial to avoid harm and inappropriate use of resources. Guidelines that describe the indications and contraindications of ECMO are published by the Extracorporeal Life Support Organization (ELSO). As per the ELSO, indications for ECMO include, “acute severe heart or lung failure with high mortality risk despite optimal conventional therapy. ECLS is considered at 50% mortality risk, and indicated in most circumstances at 80% mortality risk. Severity of illness and mortality risk is measured as precisely as possible using measurements for the appropriate age group and organ failure.” While contraindications for ECMO are relative, there are some generally accepted contraindications, including conditions which are incompatible with recovery (i.e. severe neurologic injury), or severe preexisting conditions which affect quality of life (i.e. poor baseline mental status, end-stage malignancy, or high risk of systemic bleeding with anticoagulation). Likewise, relative contraindications include patient age, size, and medical futility. Medical futility extends to include patients who are moribund, have been on conventional therapy for a prolonged period of time, or have a universally fatal diagnosis.
Starting a Patient on ECMO
The procedure of placing a patient on ECMO is similar to obtaining central venous and arterial access; however, there is an additional step of serial dilation in order to fit the larger ECMO cannulae in the vessels. The most widely publicized algorithm comes from the ED ECMO Project that consists of three stages:
- Stage 1: Placement of femoral artery and venous catheters
- Stage 2: Serial dilation and placement of ECMO cannulas
- Stage 3: Transitioning the patient to the ECMO pump.
Complications of ECMO
The major complications can be divided into several groups, including hemorrhage, thromboembolism, and cannula-related complications. ECMO-related hemorrhage is most commonly due to continued anticoagulation, vessel cannulation, and underlying platelet dysfunction. Bleeding occurs in 30 to 50 percent of patients who receive ECMO and can be life threatening. Systemic thromboembolism due to thrombus formation within the ECMO circuit can occur, with reported rates as high as 16 percent. Thromboembolism has a greater clinical impact in VA configurations than VV configurations due to the thromboembolism having a direct route into systemic circulation. Cannulation-related complications include hemorrhage, arterial dissection, distal ischemia, and incorrect location of cannulae (e.g. inserting the venous cannula into the artery). Fortunately, these occurrences are relatively rare, accounting for less than 5% of all ECMO-related complications. Finally, there are VA ECMO-specific complications, including pulmonary hemorrhage, cardiac thrombosis, coronary or cerebral ischemia, and neurologic injury.
- ECMO is a type of prolonged mechanical cardiopulmonary support designed to replace oxygenation and cardiac function.
- There are two major configurations for the ECMO circuit: VA and VV ECMO. VV ECMO is used primarily in patients with respiratory failure, while VA ECMO is used in patients with cardiac failure
- Patients who have severe, but potentially reversible, acute respiratory or cardiac failure that is refractory to conventional management may be candidates for ECMO.
- Placing a patient on ECMO is similar to obtaining central arterial and venous access, with the additional steps of serial dilation and connecting to the ECMO machine.
- Bleeding is the most common complication of ECMO, while thromboembolism and cannula complications are rare.
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