Manual of Extracorporeal Membrane Oxygenation (ECMO) in the ICU Poonam Malhotra Kapoor
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1Basics of Extracorporeal Membrane Oxygenation
CHAPTERS
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Introduction to Extracorporeal Membrane Oxygenation1

Poonam Malhotra Kapoor,
BS Sethi
CHAPTER OUTLINE
  • History of Extracorporeal Membrane Oxygenation
  • Venovenous Extracorporeal Membrane Oxygenation
  • Venoarterial Extracorporeal Membrane Oxygenation
  • Low Flow Venoarterial Extracorporeal Membrane Oxygenation
Extracorporeal membrane oxygenation (ECMO) is a form of extracorporeal life support where an external artificial circulation carries venous blood from the patient to a gas exchange device (oxygenator) where blood becomes enriched with oxygen and has carbon dioxide removed. This blood then re-enters into the patient's circulation.
Patients who are hypoxemic despite maximal conventional ventilatory support, who have significant ventilator-induced lung injury or who are in reversible cardiogenic shock may be considered for ECMO support. For respiratory failure, the basic premise is that ECMO will allow the level of ventilatory support to be reduced, which may allow time for recovery from the underlying pathology and recovery from ventilator-induced lung injury to occur.
The type of ECMO performed will depend on the patient's underlying cardiac function. Veno-venous (VV) ECMO is usually performed for isolated respiratory failure, whereas veno-arterial (VA) ECMO (full cardiopulmonary bypass) is performed for combined cardiac and respiratory failure.
The term extracorporeal membrane oxygenation (ECMO) was initially used to describe a long-term extracorporeal support that focused on the function of oxygenation. Subsequently, in some patients, the emphasis shifted to carbon dioxide removal, and the term extracorporeal carbon dioxide removal was coined. Extracorporeal support was later used for postoperative support in patients following cardiac surgery.1 Other variations of its capabilities have been tested and used over the last few years, making it an important tool in the armamentarium of life and organ support measures for clinicians. With all of these uses for extracorporeal circuitry, a new term, extracorporeal life support (ECLS), has come into vogue to describe thi technology.
The differences between ECMO and cardiopulmonary bypass are as follows:
  • Extracorporeal membrane oxygenation is frequently instituted using only cervical cannulation, which can be performed under local anesthesia; standard cardiopulmonary bypass is usually instituted by transthoracic cannulation under general anesthesia.
  • Unlike standard cardiopulmonary bypass, which is used for short-term support measured in hours, ECMO is used for a long-term support ranging from 3 to 10 days.
  • The purpose of ECMO is to allow time for intrinsic recovery of the lungs and heart; a standard cardiopulmonary bypass provides support during various types of cardiac surgical procedures.
A diagram of extracorporeal membrane oxygenation is shown in Figure 1.
 
HISTORY OF EXTRACORPOREAL MEMBRANE OXYGENATION
In May 1953, Gibbon used artificial oxygenation and perfusion support for the first successful open heart operation.2 In 1954, Lillehei developed the cross-circulation technique by using slightly anesthetized adult volunteers as live cardiopulmonary bypass apparatuses during the repair of certain congenital cardiac disorders.3 In 1955, at the Mayo clinic, Kirklin et al improved on Gibbon's device and successfully repaired an atrial septal defect4 in a baby, who was suffering from meconium aspiration.
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Fig. 1: ECMO system
In 1965, Rashkind and coworkers were the first to use a bubble oxygenator as support in a neonate dying of respiratory failure.5 In 1969, Dorson and colleagues reported the use of a membrane oxygenator for cardiopulmonary bypass in infants.6
It was in 1970, when Baffes et al reported the successful use of extracorporeal membrane oxygenation as support in infants with congenital heart defects, who were undergoing cardiac surgery.7 In 1975, Bartlett et al were the first to successfully use ECMO in neonates with severe respiratory distress.8
In 1975–1976, Bartlett et al successfully applied bedside CPB to treat a newborn with meconium aspiration, marking the beginning of ECMO in critical care. Intensive care units forming, HD becoming more widely used, positive pressure ventilation better understood—infants, children, and adults all surviving initial cardiac/pulmonary insults acute respiratory distress syndrome (ARDS) emerging as the major problem ailing intensive care unit (ICU) population. Several clinical trials published demonstrating clear survival benefit in infants suffering from severe respiratory failure randomized controlled studies in adults with ARDS demonstrated no such benefit, but smaller studies and case reports emerged with reports of 50% survival in those treated with ECMO in addition to maximal ventilatory management 1989 ELSO and ELSO registry database formed 1991 NIH conference on diffusion of ECMO technology. In 1971 the first report of bedside cardiopulmonary bypass (CPB) used for the long-term support. Prior to 1970s, attempts at long-term extracorporal support was limited by gas-exchange devices (oxygenators), which did not separate the gas from the blood and led to hemolysis, thrombocytopenia, coagulopathy if used for hours at a time as given by Kolobow T, Spragg RG, Pierce JE, Zapol WM, et al. Extended term (16 days) partial extracorporeal blood gas exchange with the spiral membrane lung in unanesthetized lambs.9
Circuit flow may be achieved using a pump (centrifugal or roller) or by the patients arteriovenous pressure gradient (pumpless). At The Royal Adelaide Hospital ECMO involves in a centrifugal pump to drive circuit flow.
 
VENOVENOUS EXTRACORPOREAL MEMBRANE OXYGENATION
Venovenous ECMO involves in venous blood from the patient being accessed from the large central veins (Via access line) and returned to the venous system near the right atrium (Via the return line) after it has passed through an oxygenator. It provides support for severe respiratory failure when no major cardiac dysfunction exists. When flow through a single access cannula is insufficient to support the high ECMO flow rate that may be required in severe respiratory failure, a second venous access cannula may be required.
Venovenous ECMO improves the patient's oxygenation by reducing the amount of blood that passes through the lung without being oxygenated and in addition, removes CO2 from the patient's blood. This allows the level of ventilatory support to be reduced, which reduces ventilator-induced lung injury.
The efficiency of oxygenation by the ECMO circuit depends on the pump flow relative to the patient's cardiac output. The patient's oxygenation should increase with increasing ECMO flow rate, if this does not occur, recirculation of blood between the inflow and outflow cannulae should be suspected (See section on instituting ECMO).
Venovenous ECMO is more efficient at removing CO2 from the blood than delivering oxygen. The amount of CO2 removal depends on the ECMO flow rate relative to the patient's cardiac output and also depends on the oxygen flow rate to the oxygenator. Increasing oxygen flow rate decreases the CO2 in the blood leaving the oxygenator (analogous to the effect that increasing minute ventilation has on arterial PCO2). The oxygen flow rate to the oxygenator should be roughly twice the ECMO flow rate. With an ECMO flow rate of approximately 2/3 the patient's cardiac output, and an oxygen flow rate of twice the pump flow, nearly all of the patient's CO2 production can be removed by the oxygenator.
 
VENOARTERIAL EXTRACORPOREAL MEMBRANE OXYGENATION
Venoarterial ECMO involves in venous blood from the patient being accessed from the large central veins and returned to a major artery after it has passed through the oxygenator. It provides support for severe cardiac failure, (Usually with associated respiratory failure), most commonly after cardiac surgery.
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Fig. 2: Venovenous ECMO circuit
 
LOW FLOW VENOARTERIAL EXTRACORPOREAL MEMBRANE OXYGENATION
Low flow venoarterial ECMO is a transitory form of ECMO support in which small cannulae (quicker to insert) are inserted percutaneously. It is an emergent resuscitative intervention (Also known as ECMO-CPR).
 
Venovenous or Venoarterial Extracorporeal Membrane Oxygenation
Here are several advantages of VV ECMO (Fig. 2) compared to VA ECMO (Fig. 3). VV ECMO avoids the risks of potentially serious arterial injury and also the consequences of air or clot embolization from the circuit are less severe. VV ECMO is a low-pressure circuit compared to venoarterial, resulting in less stress on the circuit tubing and the oxygenator and may thereby improve their longevity. VV ECMO produces less hemodynamic disturbance than venoarterial as blood is withdrawn from, and returned to the same side of the circulation. For example, increasing VV ECMO flow will not cause any change in the central venous pressure (CVP), whereas increasing VA ECMO flow will reduce the CVP (and pulmonary blood flow).
Finally, there is an animal evidence that the preservation of pulmonary blood flow that occurs with VV ECMO promotes more rapid recovery from pulmonary sepsis than does VA ECMO.
The major advantages of VA over VV ECMO is that it provides complete hemodynamic and respiratory support. It may be indicated for severe cardiac failure following cardiac surgery either as a bridge to recovery or to another destination therapy (heart transplant or to another implantable support device). Other indications for VA ECMO in an adult are cardiogenic shock associated with myocarditis, poisoning or hypothermia.
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Fig. 3: Venovenous ECMO circuit
 
SUMMARY
Extracorporeal membrane oxygenation (ECMO) is a temporary life support technique. It involves connecting the child's internal circulation to an external blood pump and artificial lung. A catheter placed in the right side of the heart carries blood to a pump, then to a membrane ‘lung’, known as the oxygenator, where gas exchange of oxygen and carbon dioxide takes place. The blood then passes through tubing back into either the venous or arterial circulation.
Patients are given a continuous infusion of an anticoagulant, normally heparin, to prevent blood clotting in the external system. Bleeding is therefore a common adverse effect. Others include blood infection and hemolysis (breaking up of blood cells).
Conventional treatment is maximal intensive care support without ECMO. Ventricular assist devices, which pump the blood externally but do not allow gas transfer, may be used in addition to standard ventilation, where circulatory rather than respiratory failure is prominent.
In randomized controlled trials, ECMO has been shown to improve survival compared with conventional management in babies under the age of 28 days with severe respiratory failure. It is argued that it would also improve survival in older children.
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REFERENCES
  1. Lowry AW, Morales DL, Graves DE, Knudson JD, Shamszad P, Mott AR, et al. Characterization of Extracorporeal Membrane Oxygenation for Pediatric Cardiac Arrest in the United States: Analysis of the Kids' Inpatient Database. Pediatr Cardiol. 2013. [Medline].
  1. Gibbon JH Jr. Application of a mechanical heart and lung apparatus to cardiac surgery. Minn Med. 1954;37:180–5.
  1. Lillehei CW. A personalized history of extracorporeal circulation. Trans Am Soc Artif Intern Organs. 1982;28:5–16.
  1. Kirklin JW, Donald DE, Harshbarger HG, Hetzel PS, Patrick RT, Swan HJ. Studies in extracorporeal circulation. I. Applicability of Gibbon-type pump-oxygenator to human intracardiac surgery: 40 cases. Ann Surg. 1956;144 (1):2–8. [Medline].
  1. Rashkind WJ, Freeman A, Klein D, Toft RW. Evaluation of a disposable plastic, low volume, pumpless oxygenator as a lung substitute. J Pediatr. 1965;66:94–102. [Medline].
  1. Dorson W Jr, Baker E, Cohen ML, Meyer B, Molthan M, Trump D. A perfusion system for infants. Trans Am Soc Artif Intern Organs. 1969;15:155–60. [Medline].
  1. Baffes TG, Fridman JL, Bicoff JP, Whitehill JL. Extracorporeal circulation for support of palliative cardiac surgery in infants. Ann Thorac Surg. 1970;10(4):354–63. [Medline].
  1. Bartlett RH, Gazzaniga AB, Jefferies MR, et al. Extracorporeal membrane oxygenation (ECMO) cardiopulmonary support in infancy. Trans Am Soc Artif Intern Organs. 1976;22:80–93.
  1. Trans Am Soc Artif. Intern Organs 1971;17:350–4.