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

thumb|ECMO sketch

thumb|ECMO circuit

thumb|A MAQUET [[hollow fiber membrane oxygenator]]

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&nbsp;°C and cardiac instability, or with a core temperature below 24&nbsp;°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. Other observational and uncontrolled clinical trials have reported survival rates from 50 to 70%.

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.

Types

[[File:Veno-arterial (VA) ECMO for cardiac or respiratory failure.jpg|thumb|Veno-arterial (VA) ECMO for cardiac or respiratory failure. 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

thumb|A [[respiratory therapist takes a blood sample from a newborn in preparation for ECMO therapy. ]]

Once the initial respiratory and hemodynamic goals have been achieved, the blood flow is maintained at that rate. Frequent assessment and adjustments are facilitated by continuous venous oximetry, which directly measures the oxyhemoglobin saturation of the blood in the venous limb of the ECMO circuit.

Special considerations

VV ECMO is typically used for respiratory failure, while VA ECMO is used for cardiac failure. There are unique considerations for each type of ECMO, which influence management.

Blood flow

High flow rates are usually desired during VV ECMO to optimize oxygen delivery. In contrast, the flow rate used during VA ECMO must be high enough to provide adequate perfusion pressure and venous oxyhemoglobin saturation (measured on drainage blood) but low enough to provide sufficient preload to maintain left ventricular output.

Diuresis

Since most people are fluid-overloaded when ECMO is initiated, aggressive diuresis is warranted once the patient is stable on ECMO. Ultrafiltration can be easily added to the ECMO circuit if the patient has inadequate urine output. ECMO "chatter", or instability of ECMO waveforms, represents under-resuscitation and would support cessation of aggressive diuresis or ultrafiltration. There is an increased risk of acute kidney injury related to the use of ECMO and systemic inflammatory response.

Left ventricular monitoring

Left ventricular output is rigorously monitored during VA ECMO because left ventricular function can be impaired from increased afterload, which can in turn lead to formation of thrombus within the heart.

Banning Gray Lary first demonstrated that intravenous oxygen could maintain life. His results were published in Surgical Forum in November 1951. Lary commented on his initial work in a 2007 presentation wherein he writes, "Our research began by assembling an apparatus that, for the first time, kept animals alive while breathing pure nitrogen. This was accomplished with very small bubbles of oxygen injected into the blood stream. These bubbles were made by adding a 'wetting agent' to oxygen being forced through a porcelain filter into the venous blood stream. Shortly after its initial presentation to the American College of Surgeons, this apparatus was reviewed by Walton Lillehei who with DeWall made the first practical heart[–]lung machine that employed a bubble oxygenator. With variations such machines were used for the next twenty years."

Manufacturers

  • Medtronic
  • Maquet ||

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| style="text-align:left;|Canada || North America || 23 (in 2022)

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| style="text-align:left;|Brazil || South America || 21 (in 2021) ||

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| style="text-align:left;|England and Wales || Europe || 5 (in 2020)

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| style="text-align:left;|Northern Ireland || Europe || 0 (in 2020)

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| style="text-align:left;|Scotland || Europe || 1 (in 2020)

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| style="text-align:left;|Germany || Europe || 214 (in 2020) || 779 (in 2021)

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| style="text-align:left;|Poland || Europe || || 47 (in 2020)

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| style="text-align:left;|Sweden || Europe || || 7 or more (in 2020)<!--3 in Stockholm, 4 in Uppsala-->

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| style="text-align:left;|Albania || Europe || 0 (in 2020)

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| style="text-align:left;|Russia || Europe || || 124 + 17 (in 2020)

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| style="text-align:left;|Moscow || Europe || || 16 (in 2020)

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| style="text-align:left;|Saint Petersburg, Russia || Europe || 7 || 19 (in 2020)

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| style="text-align:left;|Japan || Asia || || 2208 (in 2020)

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| style="text-align:left;|Mainland China || Asia || || 400 (approx. in 2020)

2,857 (in 2023)

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| style="text-align:left;|South Korea ||Asia || ||350 (in 2023)

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|style="text-align:left;|Taiwan

|Asia

|51 (in 2016)

|105 (in 2016)

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|style="text-align:left;|Sri Lanka

|South Asia

|2 (in 2021)

|2 (in 2021) and Morris et al. were plagued by technical challenges related to the ECMO technology available in the 1970s and 1990s. The CESAR and EOLIA trials utilized modern ECMO systems and are considered the central ECMO RCTs.

CESAR Trial (2009)

The Conventional Ventilatory Support vs. Extracorporeal Membrane Oxygenation for Severe Adult Respiratory Failure (CESAR) Trial was a UK-based multicenter RCT aiming to evaluate the safety, efficacy and cost effectiveness of ECMO compared to conventional mechanical ventilation in adults with severe but reversible respiratory failure. which is known to improve mortality in ARDS patients.

The authors conclude that referral of patients with severe, potentially reversible respiratory failure to an ECMO center can significantly improve 6-month, severe disability free survival. The secondary endpoint, treatment failure, demonstrated a relative risk of 0.62 (p<0.001) in favor of the ECMO group. Results of the secondary endpoint should be interpreted cautiously due to the primary end point results. With respect to safety, the ECMO group had significantly higher rates of severe thrombocytopenia and bleeding requiring transfusion, but lower rates of ischemic stroke.

The main conclusion the study authors drew from these results is that early ECMO initiation in severe ARDS patients does not provide a mortality benefit compared to continued standard of care treatment.

References

  • Extracorporeal Education Portal