Extracorporeal membrane oxygenation in adults: A practical guide for internists

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ABSTRACTThe use of extracorporeal membrane oxygenation (ECMO) in adults has rapidly increased as the technology has evolved, although there is little definitive evidence that it is beneficial in this group. ECMO is now being used in acute respiratory distress syndrome (and was used extensively for this indication during the influenza H1N1 pandemic), as a bridge to lung or heart transplant, and in postcardiac arrest patients. We review the current evidence and indications for ECMO, focusing on its principles and practical aspects in adult patients with respiratory or cardiac failure.


  • Two basic configurations of ECMO are used in adults: venoarterial, which can provide cardiac or cardiopulmonary support; and venovenous, which provides respiratory support only.
  • ECMO is used in adults who are at very high risk of death without it.
  • Because ECMO patients must receive anticoagulation, bleeding is a common complication. Others are infection, renal failure, and thrombosis.
  • ECMO may provide “lung rest,” allowing lower tidal volumes and pressures and lower fractions of inspired oxygen to be used in mechanical ventilation, strategies associated with lower mortality rates.



Extracorporeal membrance oxygenation (ECMO) provides temporary cardiorespiratory support for patients with severe respiratory or cardiac failure refractory to conventional therapy.1 It can be configured to provide oxygen, remove carbon dioxide, support perfusion, or all of the above. It may provide a bridge to recovery in patients with acute cardiopulmonary failure or to heart or lung transplant.

Developed in the 1970s, ECMO has proven effective and is widely used in children with respiratory and cardiopulmonary failure.2 However, it remained little used in adults, as early randomized trials showed higher rates of complications in adults who received it and no survival advantage.3,4 Proponents of using it in adult patients believe that these poor outcomes were at least partially due to limited training, intensive anticoagulation, and excessive volume and pressure during mechanical ventilation. Although ECMO technology has improved substantially in the last decade and survival rates have improved (, evidence to support its routine use in adults remains limited.

Nevertheless, about 14,000 adult patients received ECMO between 1990 and 2014, with a rate of survival to discharge of 57% for those in respiratory failure and 41% for those in cardiac failure.5 Its use increased 433% in the United States from 2006 to 2011.6

A national survey of critical care physicians and trainees in the United States found they had limited knowledge about ECMO technology and wanted to include specific educational objectives about it in their training.7

This article summarizes the principles of ECMO, including practical aspects such as patient selection, monitoring, and complications.


There is limited evidence from randomized controlled trials that ECMO is beneficial in adults.

In acute respiratory failure, the first randomized trial of ECMO in adults was conducted in 1979 in multiple medical centers.3 The survival rate was no higher with ECMO than with mechanical ventilation alone, and complication rates were very high.

Similarly, Morris et al4 performed a single-center trial comparing pressure-controlled inverse-ratio ventilation and extracorporeal carbon dioxide removal in patients with acute respiratory distress syndrome, which showed no survival benefit.

After these two early trials, ECMO was largely abandoned, and not until 2009 did a multicenter randomized trial in acute respiratory distress syndrome8 rejuvenate interest in its use. Although the trial did not conclusively prove that ECMO was more effective than conventional mechanical ventilation, the findings supported early referral to tertiary care centers with ECMO expertise, and the survival rate was substantially higher than in previous studies. A concise summary of randomized trials and retrospective studies utilizing ECMO in respiratory failure is shown in Table 1.8–14

During the global pandemic of influenza H1N1 in 2009–2010, several centers reported survival benefits from ECMO in patients with severe acute respiratory distress syndrome secondary to influenza.9–12,15–19 Two retrospective case-control studies reported lower mortality rates when H1N1 patients were transferred to ECMO centers10 and among younger patients with H1N1 who received ECMO.12

Ongoing trials ( identifier NCT01470703) may provide definitive evidence for the effectiveness of ECMO as a rescue therapy in acute respiratory distress syndrome.

In cardiogenic shock, single-center retrospective and observational studies have reported better outcomes for patients who received ECMO for cardiogenic shock secondary to myocardial infarction, pulmonary embolism, sepsis-related cardiomyopathy, and even extracorporeal cardiopulmonary resuscitation.20


Figure 1. Extracorporeal membrane oxygenation (ECMO).

In ECMO, venous blood is shunted through a machine to add oxygen, remove carbon dioxide, and regulate temperature (Figure 1). The components of an ECMO circuit are as follows:

  • Blood pump
  • Membrane oxygenator
  • Gas mixer
  • Cannulas
  • Heater/cooler
  • Console.


Figure 2. Four configurations of extracorporeal membrane oxygenation (ECMO).

Two basic ECMO configurations are used in adults: venoarterial and venovenous,21 although combinations of the two—hybrid configurations—are sometimes used (Figure 2).

Venoarterial ECMO

Venoarterial ECMO provides complete or partial support to the heart and lungs and is the configuration of choice in patients with isolated cardiac failure that is refractory to other treatments. It takes deoxygenated blood from the venous system and returns oxygenated blood to the arterial circulation.

In the central venoarterial configuration, the intake cannula is most often surgically placed in the right atrium and the return cannula is placed in the proximal ascending aorta.

In the peripheral femoral configuration, the drainage cannula is placed in the femoral vein and advanced to the right atrium, and the return cannula is placed in either the ipsilateral or contralateral femoral artery. However, this configuration provides the patient with retrograde flow (against the native cardiac output), and oxygen delivery to the upper body may be impeded.

Axillary cannulation, in which the return cannula is placed directly into the axillary artery to provide antegrade flow, has been used recently in patients with pulmonary hypertension or right ventricular failure.22

Venovenous ECMO

Venovenous ECMO provides complete or partial support to the lungs and is the configuration of choice in isolated respiratory failure when cardiac function is preserved. It takes deoxygenated blood from the central venous system—either the femoral vein or internal jugular vein—and returns oxygenated blood to the venous circulation directed into the right atrium. It can be delivered by different cannula configurations based on the patient’s size and clinical requirements.

In the past, the most commonly used configuration was the femoral-atrial, in which the drainage cannula was placed in the femoral vein with the tip advanced to the level of the diaphragm in the inferior vena cava, and the return cannula was placed in the right internal jugular vein with its tip at the junction of the superior vena cava and right atrium. In this configuration, some of the oxygenated blood delivered by the superior vena cava cannula reaches the inferior vena cava cannula, creating a “shunt,” also known as “recirculation.”

Currently, a double-lumen cannula is preferred. This type of cannula is placed in the right internal jugular vein with the tip advanced to the inferior vena cava so that blood is drained through one lumen from both the inferior and superior vena cavas and returned via the other lumen with the jet directed over the tricuspid valve. Advantages of this system are that as it delivers more oxygen to the pulmonary arteries it reduces recirculation, it requires only a single cannula to be inserted, and it facilitates ambulation and rehabilitation in patients requiring long-term ECMO.

A newer double-lumen cannula designed to drain venous blood from the right atrium and reinfuse it directly into the pulmonary artery may provide an alternative for patients with right ventricular failure.

Extracorporeal removal of carbon dioxide

ECMO can remove carbon dioxide in patients with hypercapneic respiratory failure. Early technology used a variation of venovenous ECMO with very low blood flow rates through the pump, which allowed use of smaller cannulas while efficiently removing carbon dioxide.23

Since then, a pumpless extracorporeal lung-assist device has been developed that uses an arteriovenous configuration with two smaller cannulas inserted into the femoral artery and vein (Novalung, Germany).24 Lacking a pump, it avoids the complications associated with pumps such as hemolysis and clotting. It effectively removes carbon dioxide and helps reduce the frequency and intensity of mechanical ventilation. Since the flow is driven by the patient’s arteriovenous pressure gradient, good cardiac output is a prerequisite for its use.

A portable low-blood-flow machine that uses a very small (ie, 15-F) catheter in the venovenous configuration is under investigation (Hemolung RAS, Alung Technologies).


Although evidence to support the routine use of ECMO is limited, tools and guidelines have been developed to help clinicians decide if a patient might benefit from it. Indications for and contraindications to ECMO are shown in Table 2.

The Extracorporeal Life Support Organization recommends considering ECMO if the predicted risk of death is greater than 50% without it, and says ECMO is indicated if the predicted risk exceeds 80%. A scoring system has been developed to help predict the risk of death in patients on ECMO.14 This system has been validated using a historical cohort of patients, and current studies are ongoing for prospective validation.

Many centers are now using ECMO as a salvage therapy in patients with severe respiratory failure when conventional mechanical ventilation and adjunctive therapies such as neuromuscular blockade, inhaled nitric oxide, steroids, prone positioning, and high-frequency oscillation therapy fail to improve gas exchange.25,26

ECMO is also indicated in hypercapneic respiratory failure secondary to status asthmaticus and exacerbation of chronic obstructive pulmonary disease, permissive hypercapnea with a Paco2 greater than 80 mm Hg, or inability to achieve safe inflation pressures with plateau pressures of 30 cm H2O or higher, refractory to conventional therapy.27

Sometimes, delay in referral leads to irreversible ventilator-induced lung injury due to intense mechanical ventilation, thus limiting the utility of ECMO.8 Early referral should be considered if the patient does not improve after a few days on optimal ventilator settings. In centers where this technology is not available, referral to the nearest ECMO center should be considered. A list of certified ECMO centers is available at

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