Extracorporeal Membrane Oxygenation Demystified

Educational Objectives

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

1. Recognize the indications and contraindications for using ECMO.

2. Describe different configurations of ECMO.

3. Adjust ECMO parameters to optimize maintenance and weaning.

Summary

Indications for extracorporeal membrane oxygenation (ECMO): to support end-organ perfusion until decision made or recovery attained; takes over much, but not all, oxygenation, ventilation, and circulatory functions of body

Contraindications: include hemolysis, coagulopathy, disseminated intravascular coagulation (DIC), morbid obesity, incurable processes, metabolic diseases without correction, and chronic end-stage heart failure without possibility of durable device or transplantation

Configurations: veno-venous (VV) provides intravenous oxygen (O2) and removal of carbon dioxide (CO2); veno-arterial (VA) provides respiratory and hemodynamic support with central cannulation (like cardiopulmonary bypass); VA ECMO used for postcardiotomy shock, failure of graft after transplantation of heart, myocarditis, and septic cardiomyopathy when source of sepsis can be controlled

Configurations of VA ECMO: central cannulation involves taking blood from right atrium and returning it to aorta; peripheral cannulation (eg, femoral-femoral) involves removal of blood from vein and return to artery

Configurations of VV ECMO: involve vein-to-vein transfer of blood; most common configurations include femoral vein to internal jugular and femoral-femoral venous; additional option involves single cannula with 3 holes (Avalon catheter) placed under guidance from transesophageal echocardiography; blood removed from inferior vena cava and superior vena cava, processed through ECMO machine, and returned to tricuspid valve

Drawbacks of VV and VA ECMO: VV does not provide support for cardiac function; problems with mixing can occur with VA; VA provides less rest for lungs than VV; afterload increased; complications of cannulation of artery include ischemia, arterial embolism, and hemorrhage; patients require anticoagulation; pseudoaneurysms common; preferable to avoid cannulation of artery if possible

Parts of ECMO machine: centrifugal pump dependent on gravity (like machine for cardiopulmonary bypass in operating room); ECMO machine sits low to facilitate drainage of blood into machine by gravity; sweep controls removal of CO2; lower levels of sweep correspond to increased use of lungs and increased requirement for ventilation; sweep of 10 eliminates need for ventilator if oxygenator functioning properly; inspired device O2 sets fraction of inspired O2; oxygenator receives venous blood and uses blender to oxygenate blood and remove CO2; blood then heated and returned to patient

Peek et al (2009): published findings of CESAR trial; led to increased popularity of ECMO; speaker considers it poor trial; trial conducted as intention to treat, in which all patients who met criteria and transferred to ECMO center included in ECMO arm; only ≈75% of patients in ECMO arm received ECMO, but all included in analysis; ventilation not standardized in either ventilator or ECMO arm

Changes to pump on ECMO machine: roller pump caused hemolysis and stress; risked rupture of tubing; pump changed to centrifugal pump before 2009, and survivability improved; change of membrane used on oxygenator resulted in less blood shearing, less clotting, and less hemolysis

Physiology on ECMO: VV ECMO not associated with hemodynamic derangements because of intravenous oxygenation and removal of CO2; VA ECMO decreases cardiac output (CO); heart tends to rest while machine performs work; afterload increases (particularly with peripheral cannulation); contractility decreases; systemic blood pressure increases because of output of ECMO machine; pulmonary arterial pressure decreases because of decreased pulmonary blood flow; removal of CO2 decreases pulmonary vascular resistance, leading to further decrease in pulmonary arterial pressure

Effects of sweep titration: more CO2 removed as sweep increased; highest setting for sweep 10; less CO2 removed as sweep decreases; CO2 potent pulmonary vasoconstrictor; as sweep decreases, levels of CO2 increase and pulmonary arterial pressures increase; change in CO2 not linearly related to change in sweep; increases in CO2 small when sweep changes from 10 to 8 to 6 to 4; CO2 then increases exponentially from 4 to 2 and from 2 to 1; partial pressure of O2 not affected by sweep; necessary to maintain vigilance about CO2 when weaning sweep; increasing pulmonary resistance affects right ventricle (RV); patients requiring VA ECMO likely to have dysfunction of RV

Afterload: important to monitor pulsatility on arterial line as afterload increases and cardiac index decreases; very low CO can lead to pulmonary edema, left ventricular ischemia (because of decreased coronary perfusion), and ventricular thrombus (because of low movement of blood); maintenance of mean arterial pressure between 65 mm Hg and 90 mm Hg suggested; speaker uses inotropes; decreasing flow of ECMO results in placement of less arterial blood in left ventricle (LV) and decreased pulmonary edema; increasing flow of ECMO might hurt patient with low CO; surgical solution left ventricular vent (vent in LV draining directly back into ECMO machine)

Cardiac output: ECMO can increase CO to body (as opposed to ventricular CO); excessive use of inotropes and excessive CO undesirable with peripheral cannulation because high CO can lead to deoxygenation; high ventricular CO leads to pumping of blood from lungs (not oxygenated during peripheral cannulation); increasing flow of ECMO increases oxygenation because of increased work of ECMO machine relative to heart; desirable to avoid both extremes of CO

Delivery of O2: function of flow; decreases with decreased flow; if oxygenation becomes issue, rule out malfunction of oxygenator by increasing O2 to 100% and checking blood gases upstream and downstream from oxygenator; minimize recirculation; recirculation returns oxygenated blood to ECMO machine; can occur with Avalon catheter if patient repositioned

Hypovolemia: indicated by signs of “chugging” (cannula bounces up and down); important to correct; risk factor for hemolysis; large cannulas helpful for maximizing flow of ECMO; large cannulas increase drainage out and infusion in but can cause arterial complications; transfusion of red blood cells can increase volume; beneficial to maintain higher than normal hemoglobin because of ongoing risk of bleeding and ability of hemoglobin to deliver O2

Mixing: physiologic consequence of ECMO in which oxygenated blood meets patient’s deoxygenated blood; retrograde flow competes with anterograde flow; beneficial to decrease flow through lungs if lungs not working; central cannulation solves problem but creates increased risk compared with peripheral cannulation; point of mixing varies depending on function of patient’s heart, rate of flow of ECMO, and location of tip of arterial cannula

North-south syndrome (harlequin syndrome): poor pulmonary function combined with good myocardial function and femoral-femoral cannulation leads to hypoxemia of upper body because native heart pumps poorly oxygenated blood from lungs; placement of cannula in internal jugular vein can provide oxygenated blood to head

Measurement of arterial blood gas (ABG): affected by mixing; with peripheral cannulation, measure ABG in artery farthest from infusion cannula; speaker typically uses right wrist with femoral-femoral cannulation; location less critical when patient centrally cannulated

Complications: include hemorrhage (patients anticoagulated to maintain partial thromboplastin time between 60 and 80 sec), DIC, consumption or dysfunction of platelets, hemolysis (higher risk at lower flows; assessed by plasma free hemoglobin, lactate dehydrogenase, and color of urine), hypovolemia, infection, and issues with cannulas (eg, clotting, neurovascular damage, ischemia of limb, compartment syndrome); important to regularly assess pulses in extremity with cannula

Weaning: guided by mixed venous data, lactate, continuous ABGs, and total body balance of O2; involves fractions of O2 and sweep; increase ventilation as ECMO weaned; echocardiography helpful; important to assess RV; avoid prolonged periods of low flow because of risk for thrombosis; ensure adequate anticoagulation before trial of weaning

Readings

Aissaoui N et al: How to wean a patient from veno-arterial extracorporeal membrane oxygenation. Intensive Care Med 2015 May;41(5):902-5; Allen S et al: A review of the fundamental principles and evidence base in the use of extracorporeal membrane oxygenation (ECMO) in critically ill adult patients. J Intensive Care Med 2011 Jan-Feb;26(1):13-26; Cavarocchi NC et al: Weaning of extracorporeal membrane oxygenation using continuous hemodynamic transesophageal echocardiography. J Thorac Cardiovasc Surg 2013 Dec;146(6):1474-9; Makdisi G et al: Extra corporeal membrane oxygenation (ECMO) review of a lifesaving technology. J Thorac Dis 2015 Jul;7(7):E166-76; Peek GJ et al: Efficacy and economic assessment of conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure (CESAR): a multicentre randomised controlled trial. Lancet 2009 Oct 17;374(9698):1351-63; Rehder KJ et al: State of the art: strategies for extracorporeal membrane oxygenation in respiratory failure. Expert Rev Respir Med 2012 Nov;6(5):513-21; Zangrillo A et al: Extracorporeal membrane oxygenation (ECMO) in patients with H1N1 influenza infection: a systematic review and meta-analysis including 8 studies and 266 patients receiving ECMO. Crit Care 2013 Feb 13;17(1):R30; Zapol WM et al: Extracorporeal membrane oxygenation in severe acute respiratory failure. A randomized prospective study. JAMA 1979 Nov 16;242(20):2193-6.

Disclosures

For this program, members of the faculty and planning committee reported nothing to disclose.

Acknowledgements

Dr. Flynn was recorded at the 67th Annual Postgraduate Symposium on Anesthesiology, held April 28-30, 2017, in Kansas City, MO, and presented by the University of Kansas Medical Center Department of Anesthesiology and the Department of Continuing Education and Professional Development. For information about upcoming CME opportunities from the University of Kansas Medical Center, please visit www.kumc.edu. The Audio Digest Foundation thanks the speakers and the University of Kansas Medical Center 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 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 CE contact hours.

Lecture ID:

AN600102

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.