Extracorporeal Membrane Oxygenation (ECMO)

Extracorporeal membrane oxygenation (ECMO) provides cardiopulmonary support for patients with acute severe heart or respiratory failure despite conventional therapy. The ECMO system consists of a membrane oxygenator to perform gas diffusion, a roller or centrifugal pump to achieve blood flow through the system, heat exchanger, pressure and temperature sensors, and a drainage system. Vascular accesses are provided by cannulation of large peripheral vessels (the femoral or internal jugular vein and femoral, axillary, or subclavian artery). Cannulation can be performed using a percutaneous or surgical technique.

Types of ECMO systems: Figure 1.

1. Venovenous ECMO (VV-ECMO) allows for collection of deoxygenated blood from the venous system and transfer of oxygenated blood to the right atrium. Double-lumen cannulas are most commonly used to collect and transfuse blood through a single vascular access site (eg, the internal jugular vein).

2. Venoarterial ECMO (VA-ECMO) allows for collection of deoxygenated blood from the venous system and transfer of oxygenated blood directly into the arterial system. This can be achieved through central or peripheral cannulation via a large peripheral artery (eg, femoral, axillary, or subclavian).

VV-ECMO enables extracorporeal oxygenation of the patient's blood, while VA-ECMO ensures simultaneous extracorporeal oxygenation of the patient's blood and adequate blood flow through the arterial system. In cases of biventricular failure, VA-ECMO is the mechanical circulatory support (MCS) of choice for patients with cardiogenic shock and impaired oxygenation, since it provides full cardiopulmonary support. With peripheral VA-ECMO, because of the retrograde flow support, blood travels in the direction opposite to normal (ie, from the femoral artery back toward the thoracic aorta), which may increase left ventricular afterload.

It is important to note that, since VV-ECMO relies on the patient’s native cardiac function for circulation, it does not provide any hemodynamic support.

The scope of cardiac support depends on the predetermined flow generated by VA-ECMO and can be individually adjusted to the patient's needs. Anticoagulation is required during therapy, usually with IV unfractionated heparin, controlled with activated clotting time (ACT) and/or activated partial thromboplastin time (aPTT) (usually measured ≥3 times a day).

IndicationsTop

Indications for VA-ECMO:

1) Cardiogenic shock.

2) Acute heart failure (HF) (INTERMACS 1 and 2).

3) Low cardiac output syndrome following cardiac surgery.

4) Extracorporeal cardiopulmonary resuscitation (ECPR).

VA-ECMO can be used as a bridge to decision (BTD), bridge to bridge (BTB), bridge to transplant (BTT), as well as bridge to recovery (BTR).

As stated in the 2021 European Resuscitation Council (ERC) guidelines, ECMO for ECPR may be considered as a rescue therapy in selected patients with cardiac arrest when conventional cardiopulmonary resuscitation (CPR) is failing. Commonly used criteria include witnessed cardiac arrest with bystander CPR, short time to establishing ECPR (<60 min from CPR onset), young age and no major comorbidities, and a known or suspected treatable cause of cardiac arrest. ECPR should be considered particularly in hypothermic cardiac arrest and patients with hypothermia and risk factors for imminent cardiac arrest (ie, core temperature <30 degrees Celsius, ventricular arrhythmia, systolic blood pressure <90 mm Hg); however, prognostic evaluation of successful rewarming should be assessed whenever possible based on the Hypothermia Outcome Prediction after Extracorporeal Life Support (HOPE; www.hypothermiascore.org).

According to the 2017 Extracorporeal Life Support Organization (ELSO) guidelines for respiratory failure in adults, the use of VV-ECMO should be considered in severe isolated respiratory failure without HF, with a high risk of death (see Acute Respiratory Failure). The use of ECMO in the treatment of coronavirus disease 2019 (COVID-19)–related respiratory failure became the dominant use of this approach during the pandemic. At that time VA-ECMO continued to be used as both respiratory and cardiac output support or replacement.

ContraindicationsTop

ECMO is used in emergent cases as a rescue therapy; therefore, contraindications include irreversibility of the underlying disease, absolute contraindications to anticoagulation, and severe immunosuppression. In the case of VV-ECMO used for isolated respiratory support, contraindications in our own setting include intensive mechanical ventilation for ≥7 days (high fraction of inspired oxygen [FiO2] and high airway pressures, eg, plateau pressure >30 cm H2O). In addition, the risk of severe complications significantly increases with age.

ComplicationsTop

1. Injury to the vessel and bleeding from cannulation sites.

2. Neurologic complications (seizure, hemorrhagic or ischemic stroke).

3. Complications of anticoagulation (bleeding, heparin-induced thrombocytopenia), and transfusion reactions.

4. Blood clotting in the ECMO circuit resulting in consumption of clotting factors and platelets.

5. Mechanical damage to blood components (hemolysis, anemia, thrombocytopenia).

6. Renal failure requiring renal replacement therapy.

7. Bloodstream infections, sepsis.

8. Systemic inflammatory response syndrome (SIRS) due to contact of blood with the surface of the ECMO circuit (which may cause acute respiratory distress syndrome [ARDS]).

9. Altered pharmacokinetics of drugs (increased elimination due to binding in the ECMO circuit).

10. Other VA-ECMO complications: Limb ischemia (due to insertion of an arterial cannula; can be managed with insertion of an additional reperfusion cannula), hypoxia of the upper body (Harlequin syndrome may occur when a cannula that provides oxygenated blood is inserted through the femoral artery in a patient with respiratory failure; can be managed with insertion of an additional cannula to provide oxygenated blood from the ECMO circuit through the internal jugular vein [venoarterial-venous ECMO, or VAV-ECMO]), worsening of left ventricular failure and pulmonary edema (eg, with too high blood flow through the ECMO circuit), pulmonary hypoxia.

FigureSTop

Figure 21.10-1.

Scheme of extracorporeal membrane oxygenation (ECMO). A, venoarterial system (VA-ECMO). B, venovenous system (VV-ECMO).