Extracorporeal membrane oxygenation (ECMO) is a form of extracorporeal life support, operated by a perfusionist, providing prolonged cardiac and respiratory support to people whose heart and lungs are unable to provide an adequate amount of oxygen, gas exchange or blood supply (perfusion) to sustain life. The technology for ECMO is largely derived from cardiopulmonary bypass, which provides shorter-term support with arrested native circulation. The device used is a membrane oxygenator, also known as an artificial lung.
ECMO works by temporarily drawing blood from the body to allow artificial oxygenation of the red blood cells and removal of carbon dioxide. Generally, it is used either post-cardiopulmonary bypass or in late-stage treatment of a person with profound heart and/or lung failure, although it is now seeing use as a treatment for cardiac arrest in certain centers, allowing treatment of the underlying cause of arrest while circulation and oxygenation are supported. ECMO is also used to support patients with the acute viral pneumonia associated with COVID-19 in cases where artificial ventilation alone is not sufficient to sustain blood oxygenation levels.
Medical uses
Guidelines that describe the indications and practice of ECMO are published by the Extracorporeal Life Support Organization (ELSO). Criteria for the initiation of ECMO vary by institution, but generally include acute severe cardiac or pulmonary failure that is potentially reversible and unresponsive to conventional management. Examples of clinical situations that may prompt the initiation of ECMO include the following:
Hypoxemic respiratory failure with a ratio of arterial oxygen tension to fraction of inspired oxygen (PaO2/FiO2) of <100 mmHg despite optimization of the ventilator settings, including the fraction of inspired oxygen (FiO2), positive end-expiratory pressure (PEEP), and inspiratory to expiratory (I:E) ratio Hypercapnic respiratory failure with an arterial pH <7.20 Refractory cardiogenic shock Thyroid storm Cardiac arrest Failure to wean from cardiopulmonary bypass after cardiac surgery As a bridge to either heart transplantation or placement of a ventricular assist device As a bridge to lung transplantation Septic shock is a more controversial but increasingly studied use of ECMO Hypothermia, with a core temperature between 28 and 24 °C and cardiac instability, or with a core temperature below 24 °C.
In those with cardiac arrest or cardiogenic shock, it is believed to improve survival and good outcomes. However, a recent clinical trial has shown that in patients with cardiogenic shock following acute myocardial infarction, ECLS did not improve survival (as measured via 30-day mortality); on the contrary, it resulted in increased complications (e.g., major bleeding, lower limb ischemia). This finding is corroborated by a recent meta-analysis that used data from four previous clinical trials, indicating a need to reassess current guidelines for initiation of ECLS treatment.
COVID-19 Beginning in early February 2020, doctors in China increasingly used ECMO as an adjunct support for patients presenting with acute viral pneumonia associated with SARS-CoV-2 infection (COVID-19) when, with ventilation alone, the blood oxygenation levels still remain too low to sustain the patient. Initial reports indicated that it assisted in restoring patients' blood oxygen saturation and reducing fatalities among the approximately 3% of severe cases where it was utilized. For critically ill patients, the mortality rate reduced from around 59–71% with conventional therapy to approximately 46% with extracorporeal membrane oxygenation. A March 2021 Los Angeles Times cover story illustrated the efficacy of ECMO in an extremely challenging COVID patient. In February 2021, three pregnant Israeli women who had "very serious" cases of COVID-19 were given ECMO treatment and it seemed this treatment option would continue.
Outcomes Early studies had shown survival benefit with use of ECMO for people in acute respiratory failure especially in the setting of acute respiratory distress syndrome. A registry maintained by ELSO of nearly 51,000 people that have received ECMO has reported outcomes with 75% survival for neonatal respiratory failure, 56% survival for pediatric respiratory failure, and 55% survival for adult respiratory failure. Other observational and uncontrolled clinical trials have reported survival rates from 50 to 70%. These reported survival rates are better than historical survival rates. Even though ECMO is used for a range of conditions with varying mortality rates, early detection is key to prevent the progression of deterioration and increase survival outcomes.
Evidence indicates that ECMO reduces mortality compared with conventional management. No clear differences in outcomes have been observed across the different types of ECMO (VV, VA, or ECPR modalities), and data on other important outcomes, such as neurologic injury or quality of life, remain limited.
In the United Kingdom, veno-venous ECMO deployment is concentrated in designated ECMO centers to potentially improve care and promote better outcomes.
Contraindications Most contraindications are relative, balancing the risks of the procedure versus the potential benefits. The relative contraindications are: Conditions incompatible with normal life if the person recovers Preexisting conditions that affect the quality of life (CNS status, end-stage malignancy, risk of systemic bleeding with anticoagulation) Age and size Futility: those who are too sick, have been on conventional therapy too long, or have a fatal diagnosis.
Side effects and complications Neurologic A common consequence in ECMO-treated adults is neurological injury, which may include intracerebral hemorrhage, subarachnoid hemorrhage, ischemic infarctions in susceptible areas of the brain, hypoxic-ischemic encephalopathy, unexplained coma, and brain death. Bleeding occurs in 30 to 40% of those receiving ECMO and can be life-threatening. It is due to both the necessary continuous heparin infusion and platelet dysfunction. Meticulous surgical technique, maintaining platelet counts greater than 100,000/mm3, and maintaining the target activated clotting time reduce the likelihood of bleeding.
Blood ECMO is associated with an increased risk of major bleeding compared with conventional management. Heparin-induced thrombocytopenia (HIT) is increasingly common among people receiving ECMO. When HIT is suspected, the heparin infusion is usually replaced by a non-heparin anticoagulant.
There is retrograde blood flow in the descending aorta whenever the femoral artery and vein are used for VA (Veno-Arterial) ECMO. Stasis of the blood can occur if left ventricular output is not maintained, which may result in thrombosis.
Bridge-to-assist device In VA ECMO, those whose cardiac function does not recover sufficiently to be weaned from ECMO may be bridged to a ventricular assist device (VAD) or transplant. A variety of complications can occur during cannulation, including vessel perforation with bleeding, arterial dissection, distal ischemia, and incorrect location.
Children Preterm infants, having inefficiency of the heart and lungs, are at unacceptably high risk for intraventricular hemorrhage (IVH) if ECMO is performed at a gestational age less than 32 weeks.
Infections The prevalence of hospital-acquired infections during ECMO is 10-12% (higher compared to other critically ill patients). Coagulase-negative staphylococci, Candida spp., Enterobacteriaceae and Pseudomonas aeruginosa are the most frequently involved pathogens. ECMO patients display a high incidence of ventilator-associated pneumonia (24.4 cases/1000 ECMO days), with a major role played by Enterobacteriaceae. The infectious risk was shown to increase along the duration of the ECMO run, which is the most important risk factor for the development of infections. Other ECMO-specific factors predisposing to infections include the severity of illness in ECMO patients, the high risk of bacterial translocation from the gut and ECMO-related impairment of the immune system. Another important issue is the microbial colonisation of catheters, ECMO cannulae and the oxygenator.
Types
There are several forms of ECMO; the two most common are veno-arterial (VA) ECMO and veno-venous (VV) ECMO. In both modalities, blood drained from the venous system is oxygenated outside of the body. In VA ECMO, this blood is returned to the arterial system and in VV ECMO the blood is returned to the venous system. In VV ECMO, no cardiac support is provided.
Veno-arterial In veno-arterial (VA) ECMO, a venous cannula is usually placed in the right or left common femoral vein for extraction, and an arterial cannula is usually placed into the right or left femoral artery for infusion. The tip of the femoral venous cannula should be maintained near the junction of the inferior vena cava and right atrium, while the tip of the femoral arterial cannula is maintained in the iliac artery. In adults, accessing the femoral artery is preferred because the insertion is simpler. Central VA ECMO may be used if cardiopulmonary bypass has already been established or emergency re-sternotomy has been performed (with cannulae in the right atrium (or SVC/IVC for tricuspid repair) and ascending aorta).
VA ECMO is typically reserved when native cardiac function is minimal to mitigate increased cardiac stroke work associated with pumping against retrograde flow delivered by the aortic cannula.
Veno-venous In veno-venous (VV) ECMO, cannulae are usually placed in the right common femoral vein for drainage and right internal jugular vein for infusion. Alternatively, a dual-lumen catheter is inserted into the right internal jugular vein, draining blood from the superior and inferior vena cavae and returning it to the right atrium.
Initiation ECMO should be performed only by clinicians with training and experience in its initiation, maintenance, and discontinuation. ECMO insertion is typically performed in the operating room setting by a cardiothoracic surgeon. ECMO management is commonly performed by a registered nurse, respiratory therapist, or a perfusionist. Once it has been decided to inititiate ECMO, the patient is anticoagulated with intravenous heparin to prevent thrombus formation from clotting off the oxygenator. Prior to initiation, an IV bolus of heparin is given and measured to ensure that the activated clotting time (ACT) is between 300 and 350 seconds. Once the ACT is between this range, ECMO can be initiated and a heparin drip will be started after as a maintenance dose.
Cannulation Cannulae can be placed percutaneously by the Seldinger technique, a relatively straightforward and common method for obtaining access to blood vessels, or via surgical cutdown. The largest cannulae that can be placed in the vessels are used in order to maximize flow and minimize shear stress. However, limb ischemia is one of the notorious complications of ECMO but can be avoided utilizing a proper distal limb perfusion method. In addition, ECMO can be used intraoperatively during lung transplantation to stabilize the patient with excellent outcomes.
ECMO required for complications post-cardiac surgery can be placed directly into the appropriate chambers of the heart or great vessels. Peripheral (femoral or jugular) cannulation can allow patients awaiting lung transplantation to remain awake and ambulatory with improved post-transplant outcomes.
Titration Following cannulation and connection to the ECMO circuit, the appropriate amount of blood flow through the ECMO circuit is determined using hemodynamic parameters and physical exam. Goals of maintaining end-organ perfusion via ECMO circuit are balanced with sufficient physiologic blood flow through the heart to prevent stasis and subsequent formation of blood clot.
Maintenance