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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.
Ankit Vyas ; Michael A. Bishop .
Last Update: June 21, 2023 .
Extracorporeal membrane oxygenation (ECMO) is used for cardiac or respiratory failure where conventional management, including CPR, is not successful. ECMO is a circuit comprised of a draining cannula that drains blood from the body that is circulated in the machine and returns back to the body through a returning cannula. Traditionally veno-venous and veno-arterial ECMO are used. During this circulation of blood, anticoagulation monitoring is essential to maintain the balance between clotting or bleeding. Also, heparin-induced thrombocytopenia, neurologic complications, sepsis complications should be taken into account. Survival after ECMO usage has improved in cases of cardiac arrest, cardiogenic shock, and ARDS, including COVID-19 infection. This activity includes indications and the use of ECMO by the interprofessional team.
Describe the indications for using ECMO circuits. Outline the various types of ECMO circuits. Explain the monitoring of anticoagulation and weaning off ECMO pertaining to ECMO. Review the importance of coordination among the interprofessional team members in a patient on ECMO.Extracorporeal membrane oxygenation (ECMO), a life support system, is an invaluable tool to treat adults and children with life-threatening cardiac and pulmonary dysfunction that is refractory to the conventional management or when cardiopulmonary resuscitation (CPR) measures are not successful in achieving the return of spontaneous circulation (ROSC).[1][2] An ECMO machine consists of a pump with an oxygenator that replaces the function of the heart and lung, respectively. The primary purpose of ECMO is performed by replacing the function of the heart and lungs, which gives these organs considerable time to recover.[2]
According to the Extracorporeal Life Support Organization (ELSO) registry, ECMO has been used on 151,683 patients through 2020, including 45,205 neonates, 30,743 children, and 75,735 adults. In 1990 ECMO was initially started in 83 centers; those numbers increased to 492 centers in 2020. Veno-venous ECMO (VV ECMO) provides respiratory support, whereas veno-arterial ECMO (VA ECMO) provides cardio-respiratory support.[3][4]
ECMO is supportive therapy, not a disease-modifying treatment. In 1944 Kolff and Berk reported oxygenation of the blood when passing through cellophane chambers of the artificial kidney. In 1953 Gibbon used this concept of artificial oxygenation and perfusion for the first successful open-heart operation. Before 1956 either a film oxygenator or bubble oxygenator was used. In a film oxygenator, blood flows through multiple vertical discs, and in a bubble oxygenator, oxygen is bubbled through the deoxygenated blood.[5]
The major drawbacks of these devices were intravascular hemolysis, systemic inflammation, platelet destruction, and embolization. In 1956, Clows and Basler invented and used the prototype member of a membrane oxygenator that was suitable for cardiopulmonary bypass surgery.[6] The first use of a bubble oxygenator was performed by Rashkind in 1965 on a neonate with respiratory failure. Dorson et al. reported in 1969 using a membrane oxygenator for cardiopulmonary bypass in infants. Baffes et al. in 1970 mentioned the use of extracorporeal membrane oxygenation in infants undergoing cardiac surgery. In 1972, Hill et al. reported the first-time use of ECMO for respiratory support in an adult patient with a post-traumatic severe respiratory failure.[7] Bartlett et al. reported of first successful use of ECMO in neonates with severe respiratory distress in 1975.
From the 1980s to the early 2000s, either silicone membrane or polypropylene hollow fiber oxygenators were used in the ECMO circuits.[8] However, due to plasma leakage in these units, a new generation of oxygenators has been developed, made from polymethylpentene (PMP). The latest generation oxygenators are easy to use, durable, and provide better gas exchange and less blood trauma.[9][10]
Kolobow and his team analyzed the ECMO experience in the National Institute of Health trial in 1981. Gattanoni et al. showed in 1981 the first successful use of ECMO in a large population of ARDS patients. In 1987, Gattanoni et al. reported an approximately 50% survival rate.[11]
In 1994, a randomized control trial published by Morris et al. failed to show the advantage of using additional extracorporeal support in acute respiratory distress syndrome compared to conventional management with mechanical ventilation. The survival rate with mechanical ventilation was 42% compared to 33% in the low-flow VV ECMO group. The use of ECMO flourished after the conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure (CESAR) trial published in 2009. This trial randomized 180 patients in 68 centers. In this study, the outcome was significantly higher with ECMO than conventional management and showed marked improvement in death rate and severe disability with severe respiratory failure treated with extracorporeal support. Thereafter, ECMO support applications have remarkably increased.[12]
Extracorporeal membrane oxygenation consists of a circuit where blood is drained through a catheter from the venous vascular system, circulated in a pump outside the body, and reinfused into the other venous or arterial vascular system depending on the ECMO circuit type for circulation in the body.[13]
Cannulas made of plastic tubes are placed in veins or arteries in the groins, neck, or chest. A catheter withdraws blood from the cannula through veins that consist of high carbon dioxide (CO2) and low oxygen (O2) content. Deoxygenated blood extracted from the venous catheter gets transferred to the oxygenator with the help of a pump. An oxygenator works as an artificial lung that maintains the CO2 extraction and oxygenation flow rate. Air and oxygen flow through the hollow fibers in the oxygenator. As the blood passes through tiny fibers, oxygen leaves the fibers and replaces carbon dioxide in the red blood cells (RBCs). CO2 then enters the fiber and is removed in the exhaust gas. Oxygenated blood is delivered through the catheter back to the patient.[2]
Two basic types of ECMO exist, VV ECMO and VA ECMO. VV ECMO provides respiratory support only, and VA ECMO bypasses the heart and lungs; therefore is a choice in patients with cardiogenic shock or patients with cardiac arrest with failed therapies.[3]
Veno-Venous (VV) ECMO
Types of Cannula
Single Venous Cannula: Extraction of blood from the vena cava or right atrium transferred to the ECMO circuit, which is returned to the right atrium. Seldinger technique is used via a right jugular vein to place cannula percutaneously. A single venous cannula allows many pros for the patient: one cannula site in the patient's neck, the patient does not have groin lines. Therefore, they can be out of bed to ambulate once they are extubated, the cannulas are very flexible, and most are kink-resistant. There are also several cons to using a single venous cannula: patient positioning is much more sensitive to movement, and these changes can affect flows through the cannula, single venous cannulas often have smaller Fr sizes and therefore reduce the peak flows of the circuit, single venous cannulas require the cannula to be placed under transesophageal echo guidance so that the SVC and IVC catheters can be placed in the proper positions, and significant concern is recirculation of the newly oxygenated blood to be withdrawn back through the drainage catheter instead of going through the systemic circulation to oxygenate the rest of the patient's body. The displacement of the cannulas can cause this recirculation phenomenon.
Double Venous Cannula: One cannula for drainage is placed in the common femoral vein, and blood infusion through the cannula is placed in either the right internal jugular or femoral vein. Two cannulas venous ECMO can allow flow direction to be from the right atrium to the inferior vena cava or opposite flow from the inferior vena cava to the right atrium. Most centers use multistage catheters with drainage from the right internal jugular vein with the return of oxygenated blood via the femoral vein cannula. This technique does allow much less change for recirculation.
ECMO circuit is connected in series to the heart and lungs.[14]Veno-Arterial (VA) ECMO
Types of Cannula
Peripheral Cannula: Blood drainage from the right atrium or vena cava and infusion of blood to either femoral, axillary, or carotid arteries.
Central Cannula: Blood drainage from the right atrium or vena cava and infusion of blood to the ascending aorta.
Central cannulation is preferred in postcardiotomy patients where cannulas used for cardiopulmonary bypass can be transferred to the ECMO circuit.
In the case of a Right ventricular assisted device, oxygenated blood from ECMO is infused into the pulmonary artery, and blood bypasses the right heart.
In case of emergency or cardiogenic shock, femoral access is preferred. To decrease the ischemia to ipsilateral lower extremity, insertion of cannula distal to the femoral artery or posterior tibial artery to perfuse distal extremity or for retrograde flow to the extremity.
In the case of peripheral artery disease or prior femoral reconstruction, femoral arterial cannulation is unsuitable. Therefore, the right common carotid artery or axillary artery should be considered.
In addition to respiratory support, VA ECMO provides hemodynamic support as well. ECMO circuit is connected in parallel to the heart and lungs.
Inclusion criteria for Extracorporeal Cardiopulmonary Resuscitation
Age <70 years Cardiopulmonary arrest to first CPR <5 minutes Witnessed arrestVentricular fibrillation (VF) or paroxysmal ventricular tachycardia (pVT) or pulseless electrical activity (PEA) as initial cardiac rhythm
Recurrent VF or intermittent ROSCAbsence of comorbidities like end-stage heart failure/chronic obstructive pulmonary disease/liver failure/end-stage renal failure or terminal irreversible illness
No known aortic valve incompetenceECMO use has been extended to more prolonged use in intensive care units. Extracorporeal cardiopulmonary resuscitation: As a part of CPR in cardiac arrest, ECMO is started in several specialized centers.[2]
Indications for VA ECMO
VA ECMO is used to provide both respiratory and cardiac support.[15]Cardiac conditions with low cardiac output (cardiac index < 2L/min/m) and hypotension (systolic blood pressure
Cardiogenic shock secondary to either acute coronary syndrome, refractory cardiac arrhythmia, sepsis leading to cardiac depression, myocarditis, pulmonary embolism, drug toxicity, cardiac trauma, anaphylaxis, acute decompensated heart failure, septic shock; where cardiac activity is compromised and unable to pump out the adequate blood to meet the body’s demand.
Periprocedural for high-risk cardiac interventionsPostoperative heart failure: Inability to wean from cardiopulmonary bypass after cardiac surgery; ECMO is very useful post-operatively to provide rest for the heart and helps in recovery after the surgery.
Post heart transplant: after heart or lung-heart transplantation in cases of primary graft failure Bridge to long-term VAD support or bridge to heart/lung transplant.Indications for VV ECMO
VV ECMO is used for respiratory support in those who do not respond to mechanical ventilation or any acute potentially reversible respiratory failure.[15]
Acute respiratory distress syndrome secondary to either severe bacterial or viral pneumonia, including COVID-19 or aspiration pneumonitis. ECMO bypasses the compromised activity of the lungs and maintains oxygenation and ventilation with the removal of CO2.[2]
Covid-19 Severe Respiratory Failure: ARDS due to SARS-CoV-2 infection when prolonged mechanical ventilatory support fails. In some cases, when ventilation fails, ECMO support (venovenous ECMO) has been initiated.[5]
Extracorporeal assistance to support lung in cases of airway obstruction, pulmonary contusion (barotrauma), smoke inhalation, drowning, air leak syndrome, hypercapnia, or hypoxic respiratory failure
Status asthmaticus Massive hemoptysis or pulmonary hemorrhage Bridge to lung transplant Support for lung resections in unstable patients.Pulmonary hypertension (mean pulmonary artery pressure >50 mmHg) or cardiogenic failure: VV ECMO is contraindicated
Advanced age Pre-existing chronic illness with long term poor prognosis Prolonged mechanical ventilation >14 daysVeno-venous (VV) ECMO and Veno-arterial (VA) ECMO comparison[1][3]:
ECMO circuit basically consists of drainage and return cannula, pump, heat/gas exchanger.[4]
Pump: Roller and centrifugal are two types of the driving force (pump) of ECMO. Centrifugal pumps contain plastic cones or impellers that rotate around 3000 revolutions per minute. This generates up to 900 mmHg of forwarding pressure that propels the blood in a centrifugal pump. The negative pressure of around 400 to500 mmHg is responsible for fewer microemboli and fewer cavitations. Blood flow in the pump is preload and afterload dependent, but in the case of hypovolemia, the inlet pressure becomes more negative to maintain the speed of the pump; however, the rate of the blood flow decreases. Systemic vascular resistance changes the circuit flow and the speed of the pump in VA ECMO.[16]
The roller pump consists of tubing compressed by rollers. The rotating arm has rollers that compress the tube and propel the blood. In the case of hypovolemia, pump speed, and flow rate decrease. Roller pumps are not controlled by the afterload, therefore in VA ECMO, changes in the systemic vascular resistance do not influence blood pumping. Roller pumps are less expensive, safer, and more reliable, but microembolization shedding can occur due to the production of high negative pressure.
Oxygenators: Membrane oxygenators are similar to the lungs, having the characteristic of either microporous polypropylene hollow fiber or non-microporous silicone rubber. Less particulate and gas embolization by membrane oxygenators compared to bubbles also allows superior control of blood gases.[17][18] During cardiopulmonary bypass, polypropylene hollow fiber oxygenators are used. Compared to silicone membrane oxygenators, polypropylene hollow fiber oxygenators are superior due to small priming volume, higher gas transfer, and low resistance. A new generation of oxygenators developed of polymethyl pentene has shown improved gas exchange, reduced red cell and platelet transfusion.[10][19]
Cannulae and Tubing: The drainage cannula is suggested to be 23 F to 25 F, and the return cannula should be 17 F to 21 F. 25 F multi-stage femoral venous cannula was suggested by Sidebotham et al., which has numerous side holes that provide drainage for both VV and VA ECMO, which is useful in many patients who require a flow of more than 6 L/min.[16] In the ECMO circuit, polyvinyl tubing and polycarbonated connectors are used. Medical grade polyvinyl tubing is popular due to its compatibility with blood, flexibility, smoothness and transparency, resistance to kinking, and collapse characteristics. Cannulation in VA ECMO can be central, or it can be peripheral in VA and VV ECMO. Central access through sternotomy is performed by a cardiothoracic surgeon, and peripheral access can be performed percutaneously in the intensive care unit or cardiac catheterization laboratory.[20]
In ECMO circuits, heparin can be coated through ionic or covalent bonds, but effectiveness is not very well established. Heparin/platelet factor 4 antibodies are considered for the development of heparin-induced thrombocytopenia type II.[21] Activation of inflammatory mediators like the complement activation pathway can be activated due to direct contact of blood with the ECMO circuit. Few reports showed a reduction of C3a and C5b-9 complements through heparin coating, but the inflammatory response is not reduced, and no convincing answer for the use of heparin coating and decrease in inflammatory response has been established yet.[22]
Anticoagulation for ECMO: Monitoring anticoagulation is essential for ECMO management. The balance between reducing the platelet and thrombin activation to prevent thrombosis and providing sufficient clotting to prevent bleeding is the goal of anticoagulation.[23] Activated clotting time (ACT) is the most widely used test to monitor anticoagulation.[24][25] Accuracy of the ACT result varies by age, sample size, temperature, hemodilution, degree of hypothermia, antithrombin level, platelet dysfunction, maturity of the coagulation system, coagulopathy, and ongoing synthesis of thrombin.[26][27] The suggested range for ACT during ECMO is 180 to 220s. Baird et al. mentioned a mean ACT of 227 +/- 50s on 604 pediatric patients, but the range was very broad of 158 to 620s. Another option to measure anticoagulation is to obtain the heparin concentration. The use of heparin concentration is less sensitive to the changes of clotting factors and platelet changes. The number of studies to compare the monitoring the anticoagulation by heparin concentration is less as compared to the ACT measurement.[28]
Thromboelastography (TEG) has been used by several medical centers that help to check the coagulation profile, including the measurement of strength and dissolution of clots in case of fibrinolysis. To monitor anticoagulation through heparin, activated partial thromboplastin time (APTT) is most widely used except in the case of cardiopulmonary bypass when high heparin dose is required. But in ECMO high heparin dose is not required; therefore, APTT is considered a valuable tool for anticoagulation assessment. In comparison to APTT, ACT has been found to poorly correlate with APTT as ACT could not delineate between low and moderate levels of anticoagulation.[23][29]
The first choice for anticoagulation for ECMO, heparin, is most widely used because it is easily available, has a rapid onset of action, is easily reversible, and is well tolerated by pediatric and adult patients. For ECMO, 20 to 70 U/kg/h of heparin dosage is recommended. Dosage varies in adult and pediatric patients based on metabolic rates and thrombin generation. With prolonged use of ECMO, consumption of antithrombin can reduce heparin responsiveness. Argatroban is an alternative anticoagulant in those with heparin allergies or a history of HIT. The starting dose of Argatroban ranges between 0.2 to 0.5 mcg/kg/min. Koster et al. mentioned of successful use of bivalirudin, a direct thrombin inhibitor like Argatroban, for a patient of myocardial failure who developed heparin-induced thrombocytopenia during ECMO.[30] The dose of bivalirudin is 0.025 to 0.05 mg/kg/min.
The ECMO team consists of a cardiothoracic/vascular surgeon or interventional cardiologists who perform the cannulation and an intensivist, perfusionist, ECMO specialist, respiratory therapist, and bedside nurse.[31] An ECMO specialist is a technical specialist trained to handle the ECMO circuit per the patient's clinical needs under the guidance and supervision of an ECMO-trained physician.
The preparation consists of the following steps:
