An Introduction to Extracorporeal Membrane Oxygenation

Educational Objectives

The goal of this program is to improve extracorporeal membrane oxygenation (ECMO). After hearing and assimilating this program, the clinician will be better able to:

1. Select patients who are good candidates for ECMO.
2. Utilize appropriate cannulation strategies in patients receiving ECMO.

Summary

Extracorporeal membrane oxygenation (ECMO): an adaptation of cardiopulmonary bypass, adjusted to be used in the long term rather than for short-term operating room cases; the 2 types are venovenous (VV) ECMO and venoarterial (VA) ECMO

Bypass vs ECMO: bypass has an open volume reservoir, whereas ECMO is closed; bypass can handle a large volume of air, and ECMO does not handle air well; the venous drainage and arterial inflow are directly coupled in ECMO but not in bypass; reservoir blood is very stagnant in bypass, requiring high doses of heparin; ECMO — has a continuously flowing circuit (less need for anticoagulation); similar to heart-lung dialysis; replaces function of the lungs in VV ECMO and replaces functions of heart and lungs in VA ECMO

ECMO circuit: VA ECMO system contains flow meters, pressure monitors, and the membrane oxygenator; some components can be adjusted (eg, blender); blender adjusts the amount of oxygen (O₂) entering the airflow, which is regulated by the flow meter at the top; there is also a heat exchanger; oxygenator is a diamond-shaped piece; the flow in pump can be adjusted with a revolutions per minute (RPM) setting; the set speed, blood viscosity, patient vasculature, and oxygenator determine the flow; measuring pressures pre- and postoxygenator can indicate thrombosis in the oxygenator and help to monitor flow

Goals of ECMO: to give organs (ie, heart, lungs) time to recover and minimize the need for high-dose ionotropic and vasopressor support as well as the need for ventilators and related injuries (eg, barotrauma)

Indications: waiting too long for ECMO is not effective; it is important to identify when the patient is sick enough that they are not able to heal on their own; for VA — cardiogenic shock is a common indication; consider in postmyocardial infarction, postcardiotomy cardiac surgery, viral myocarditis, metformin toxicity myocarditis, pulmonary embolism, and ventricular tachycardia storms (if the patient cannot come off bypass); can be used for septic shock; extracorporeal cardiopulmonary resuscitation (CPR; ECMO combined with CPR) is used in some cases for patient support; for VV — used for severe respiratory diseases, eg, acute respiratory distress syndrome (ARDS); pneumonia from viruses (eg, anthrax, COVID-19) and traumas are also indications; considered now in pre- and post-lung transplant (especially for graft failure)

Murray Score: helps to identify appropriate candidates for VV ECMO and estimate mortality; according to Extracorporeal Life Support Organization, the governing body of ECMO, 50% mortality of ARDS is associated with Murray score of 2 to 3 and 80% mortality with score 3 to 4; patients with score of 2 to 3 should be considered for ECMO and those with score of 3 to 4 are clinically indicated

Contraindications: for nonrecovery, ECMO is not helpful; ECMO allows time for a plan, transplant, or spontaneous recovery; no reason to put a patient on ECMO without any possible recovery; if patient has multiorgan failure because of COVID-19 infection, lungs can be fixed but other organs cannot; patients with stage 4 cancer who are dying are not good candidates; advanced age should be considered; morbid obesity is difficult to cannulate, with insufficient cardiac output; VA-specific contraindications include profound aortic insufficiency

Components of the circuit: include an arterial inflow cannula and a venous drainage cannula; other major parts include pump, oxygenator, cannulas, and the heat exchanger; pump — previously, rollerball pumps (preload-dependent, afterload-sensitive, and could cause hemolysis and thrombosis) were used; currently, centrifugal pumps are mostly used, with fewer complications; issue with pumps (eg, pump chattering, dropping flows, not enough preload going through the pump) can be adjusted by increasing the preload, giving some volume, or changing the RPMs; oxygenator — Maquet QUADROX oxygenator is commonly used; large bioactive surface; use diffusion to exchange gas (“sweep” or “sweep gas”); can set 1 to 11 L of sweep and adjust carbon dioxide (CO₂); it is easy to clear CO₂ using sweep; a percentage of oxygenation can be set (determines the O₂ amount in the sweep gas); helpful in VV ECMO, where patients need extra oxygen

Cannulation: estimate cannula size using ultrasound guidance and surgeon’s expertise; bigger cannulas improve drainage and determine flow; sequestration of medications (especially sedatives) in cannula is an issue; lipophilic drugs are absorbed in cannula, making long-term sedation challenging; fentanyl is well absorbed; propofol is absorbed and also clots oxygenators; care must be taken with medications being used; consider oral sedation, including phenobarbital, as an alternative to fentanyl

Cannulation strategies: VA has peripheral and central cannulas; VV can have multiple cannulas (eg, Avalon, Crescent) or single site; central cannulation for VA-A version ECMO (cannulas inside the heart) is performed after bypass; VA-B version ECMO is used in patients with viral myocarditis; putting a cannula in the femoral artery causes retrograde flow into the aorta, and there is a drainage canal in inferior vena cava (IVC); the ECMO pump does not have pulsatile flow; pulsatility may be limited on VA in acute heart failure and increases as the heart begin to recover; in VV, heart function is normal, ie, pulsatility is fine; to most clinicians, inflow cannulas refer to inflowing to the patient and outflow cannulas are outflowing away from the patient; perfusionists are pump-oriented, ie, inflow cannula is an inflow into the pump (outflow from the patient); care should be taken while talking to a perfusionist

Cannula positions: transesophageal echocardiography 4 chamber view, gastric view (eg, 65° view) can be used to confirm the cannula placement; daily x-rays also helps checking cannula positions (eg, distance between cannulas); recirculation can be a problem in VV ECMO; if cannulas are too close, oxygenated blood enters the drainage cannula rather than the patient (9 cm probably the closest); one single cannula (eg, Avalon, Crescent) — great if positioned correctly; no recirculation; inflow oxygenated blood is pointed directly across the tricuspid valve, and there is drainage from the superior vena cava and IVC; designed for long-term lung transplant patients; allow ambulation

Venoarterial-venous (VAV) ECMO vs veno-venoarterial (VVA) ECMO: if a patient with lung problems who is on VV ECMO experiences right heart failure or cardiogenic shock, VAV arterial cannula is needed; if a patient on VA ECMO needs more pulmonary support, add a venous inflow cannula to achieve better oxygenation; VA ECMO requires another cannula to help increase drainage

Patient management: VV lacks cardiac support and requires ionotropic and vasopressor medications; consider ventilator settings, eg, fraction of inspired O₂<40%, positive end-expiratory pressure should be <25% to not cause barotrauma; reducing dead space, and increasing patient comfort are helpful in tracheostomy; if the patient cannot be oxygenated even at maximum O₂ delivery, use sedation to decrease O₂ consumption (paralytics can be used); volume management is crucial; patients are often volume-overloaded in the first 24 to 48 hr; provide resuscitation often; when stabilized for ECMO, start diuretics (prophylactic antibiotics not required); treat only known infections; for VA reasons, flow may drop, leading to hypovolemia; cannula may be mispositioned (especially if not directing across the tricuspid valve); intrathoracic pressure changes are important; in pneumothorax or pericardial tamponade, blood takes path of least resistance (mostly out of drainage cannula); goal of VV ECMO is a 3:1 ratio to oxygenate patients

Complications: bleeding is common; pulmonary hemorrhage (mostly in VA); include gastrointestinal bleeding is extremely common; hemorrhagic stroke, thrombus, deep vein thrombosis, and embolic strokes; COVID-19 infection (hypercoagulable) adds more risk to bleeding and clotting; VA-specific complication is left ventricular volume overload (decompress with medications or mechanically, using a balloon pump or an impeller)

Harlequin syndrome: in VA ECMO, the heart recovers but lungs do not; the heart pumps deoxygenated blood into the right side, but retrograde flow from ECMO cannot compete with it; one side becomes deoxygenated

Readings

Appelt H, Philipp A, Mueller T, et al. Factors associated with hemolysis during extracorporeal membrane oxygenation (ECMO)-Comparison of VA- versus VV ECMO. PLoS One. 2020 Jan 27;15(1):e0227793; Chung M, Shiloh AL, Carlese A. Monitoring of the adult patient on venoarterial extracorporeal membrane oxygenation. The Scientific World Journal. 2014;Article ID 393258; Pavlushkov E, Berman M, Valchanov K. Cannulation techniques for extracorporeal life support. Ann Transl Med. 2017 Feb;5(4):70; Makdisi G, Wang I. Extra corporeal membrane oxygenation (ECMO) review of a lifesaving technology. J Thorac Dis. 2015 Jul;7(7):E166–E176; Santos RS, Silva PL, Rocco JR, et al. A mortality score for acute respiratory distress syndrome: predicting the future without a crystal ball. Journal of Thoracic Disease. 2016 August;8(8); Wilson J, Fisher R, Caetano F, et al. Managing Harlequin syndrome in VA-ECMO - do not forget the right ventricle. Perfusion. 2022 Jul;37(5):526-529.

Disclosures

Members of the faculty and planning committee reported nothing relevant to disclose.

Acknowledgements

Dr. Short was recorded at the 71st Annual Postgraduate Symposium on Anesthesiology, held in Kansas City, KS, on April 9, 2022, and presented by University of Kansas Medical Center. For information on future CME activities from this presenter, please visit kumcce.ku.edu. Audio Digest thanks the speakers and presenters for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0.75 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0.75 CE contact hours.

Lecture ID:

AN643402

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.