How Extracorporeal Life Support (ECMO) Works

Although we're far from the development of a Darth Vader-esque life support system, ECMO or extracorporeal membrane oxygenation has come a long way in recent years. Although initially a means of therapy used to help newborn babies, an increasing number of adults are receiving ECMO, and ECMO centers are popping up all over the world. 

According to the Extracorporeal Life Support Organization (ELSO), which keeps running tabs on ECMO, ever since 1990, ECMO has been used to help 58,842 people throughout the world, with that number increasing every year. Although nearly half of these cases involve neonates with respiratory problems, a combined 10,426 cases involve adults with respiratory and cardiac problems or in need of pulmonary resuscitation.

Overview

ECMO (AKA extracorporeal life support or ECLS) is a short-term means of providing life support in people who are seriously ill (think lung or heart failure). Specifically, ECMO infuses oxygen into the blood and removes carbon dioxide. It can also provide hemodynamic (blood pressure) support. ECMO is a means of partial cardiopulmonary bypass and is used outside the operating room. Full cardiopulmonary bypass machines (heart-lung machines) are used only for a few hours during surgery.

ECMO is often used to take stress off the lungs and heart for several days, which theoretically promotes healing. It's used in patients who, if emergently treated, their chances of survival are good, and who would otherwise probably die without ECMO.

As far back as 1944, researchers recognized that blood passing through semipermeable membranes became oxygenated. This observation became the basis for cardiopulmonary bypass. At first, cardiopulmonary bypass relied on bubble or disk oxygenators which exposed blood directly to air. An adverse effect of this early form of bypass involved hemolysis or the destruction of blood cells which limited its benefit to a few hours at most. In 1956, the development of a membrane oxygenator fixed this problem and set the foundation for more prolonged use of ECMO.

Here are the components of a typical ECMO:

• heat exchanger
• membrane oxygenator
• roller or centrifugal pump
• circuit tubing
• catheters specific to the site of access (VV ECMO returns blood to the venous system via the superior vena cava or right atrium, and VA ECMO returns blood to the arterial system via the aorta or common carotid artery)

In some set-ups, a parallel circuit containing another pump and oxygenator is used to help with oxygenation and carbon-dioxide removal. Flow rates are adjusted based on close monitoring of the patient homeostasis: blood pressure, acid-base status, end-organ function, and mixed venous status. Of note, only VA ECMO provides hemodynamic or blood pressure support. Finally, although full cardiopulmonary bypass is hooked up in the operating room under general anesthesia, ECMO is typically set up using local anesthesia.

Patients who are on ECMO are usually very sick, and not everyone survives the experience. In 2013, ELSO reported that worldwide only 72 percent of people survived ECMO with this statistic being heavily weighed in favor of neonates who have limited lung injury going into the procedure. (Keep in mind that babies have new lungs and thus often enter ECMO without the comorbidity or accompanying lung damage typical of adults.) Moreover, although 72 percent of all people survived ECMO, only 60 percent made it to discharge or transfer; again this statistic was weighed in favor of newborns. Specifically, only 56 percent of adults with respiratory problems made it ​to discharge or transfer.

Adverse effects of ECMO include severe internal and external bleeding, infection, thrombosis (life-threatening blood clots inside blood vessels) and pump failure. In order to mitigate the threat of thrombosis, components of ECMO are coated in heparin, a blood thinner.

When It's Used

Here are some situations where ECMO is used in newborns:

• persistent pulmonary hypertension of the newborn (PPHN)
• neonatal meconium aspiration syndrome
• Pneumonia or other severe infection
• congenital diaphragmatic hernia
• congenital heart disease

Here are some situations where ECMO is used in older children:

• post-op cardiac repair
• aspiration pneumonia
• pneumonia
• sepsis
• poisoning
• near-drowning
• severe asthma
• poisoning

The use of ECMO is finding its way into adult medicine. Although there's a paucity of evidence supporting its universal use (namely we need large randomized-control trials in order to come up with universal guidelines), case reports, retrospective studies and so forth are emerging which suggest ECMO may be useful in a wide range of conditions. Of note, although there are no absolute contraindications for its use, some relative contraindications, in part based on expert opinion, have been suggested including a weakened immune system (immunosuppression), severe bleeding risk (marked coagulopathy), advanced age and high BMI.

Here are some situations in which ECMO is used in adults:

• cardiac arrest secondary to acute myocardial infarction or pulmonary embolism
• heart failure
• respiratory failure secondary to acute respiratory distress symptom (ARDS) or H1N1 virus

Two more bits of information on ECMO as it pertains to adults. First, unlike ventilators, ECMO avoids damaging the lungs through trauma (barotrauma) or atelectasis (lung collapse). Second, meta-analysis (pooled research) shows that ECMO may be of limited benefit in those receiving heart transplants, those with viral cardiomyopathy (a viral infection of the heart) and those with arrhythmias that have failed to respond to conventional treatment.

On a final note, ECMO is probably a treatment you will never have to encounter in either your life or the lives of your loved ones which is fortunate; ECMO is serious and reserved for those who are very ill. Nevertheless, ECMO represents a promising new way to help many more people. Although we may never develop a life support system that doubles as a suit of armor fitting of Darth Vader, we are further refining our understanding of stationary land short-term life support.