Extracorporeal membrane oxygenation (ECMO)


A form of cardiac or pulmonary support offered in an intensive care unit for adult and pediatric patients with organ failure refractory to conventional therapies.

ECMO uses a pump to replace the function of the heart, while an oxygenator performs the work of the lungs.
ECMO is associated with better survival rates among select critically ill patients such as though with acute respiratory failure due to Covid-19 or cardiogenic shock.

ECMO provides short-term support, giving the heart and lungs times to recover from the underlying illness.

A resource intense, complex, undertaking with many potential serious complications.

Approximately 1/2 of patients who receive ECMO will die and severe complications often arise during treatment including: bleeding, ischemia, and neurologic problems.

Frequently instituted using only cervical cannulation, which can be performed under local anesthesia.

Patients may receive cannulation either peripherally or centrally.

Requires a vascular access cannula placed in a central vein, attached to a blood pump that withdraws blood under negative pressure, and delivers it to a gas exchange device ref2242ed to as in oxygenated or membrane lungs.

Cannulation is commonly percutaneous, directly into major vessels such as the aorta, or cardiac chambers.

Most membrane lungs consist of bundles of hollow fibers with gas pumped through the hollow core and venous blood washing over the fibers.

Similarly to gas exchange at the pulmonary alveolar-capillary membrane, CO2 is removed by diffusion from the blood into the fibers and oxygen is delivered to the blood from the gas flowing through the fibers.

Blood exiting is typically fully saturated with oxygen and with a lower CO2 than when it went into the system, and is pumped back into the patient.

There are two types of ECMO: Venovenous which provides respiratory support and venoarterial which provides respiratory and hemodynamic support. 

People with ARDS who do not require cardiac support typically undergo venovenous ECMO. 

Multiple studies have shown the effectiveness of ECMO in acute respiratory failure.

The CESAR (Conventional ventilatory support versus Extracorporeal membrane oxygenation for Severe Acute Respiratory failure) trial demonstrated ECMO significantly increased survival compared to conventional management (63% to 47%).

The blood is pumped into an artery known as venoarterial, providing cardiocirculatory support and a degree of respiratory support.

The blood may be returned to, or near, the right atrium via a second vascular cannula, or a second lumen of a dual lumen cannula.

Unlike standard cardiopulmonary bypass, which is used for short-term support ECMO is used for longer-term support ranging from 3-10 days.

Blood is drained from the venous system and circulated by a pump through a semipermeable membrane to facilitate oxygenation and carbon dioxide extraction, then re-infused into the venous system or to the arterial system., depending upon indication.

In patients with a respiratory failure but an intact cardiac function may be treated with venousvenous ECMO, in which the native heart circulates oxygen rich and carbon dioxide depleted blood returned from the extracorporeal circuit.

In patients with cardiac or cardio pulmonary failure benefit from venoarterial ECMO, with circulation driven by the ECMO pump independent of underlying cardiac contractility.

Indications for ECMO:primary pulmonary hypertension of the newborn, meconium aspiration syndrome, respiratory distress syndrome, group B streptococcal sepsis, and asphyxia, and congenital diaphragmatic hernia.

ECMO is utilized in: cardiogenic shock, respiratory failure, postoperative heart failure, extracorporeal cardiopulmonary resuscitation, and those awaiting heart and lung transplant.

Criteria for neonates include: gestational age of 34 weeks or more, birth weight of 2000 g or higher, normal clotting studies, no major intracranial hemorrhage, use of mechanical ventilation for 10-14 days or less, when the infant has failed maximal ventilatory support of 100% oxygen.

Supports gas exchange independently of mechanical ventilation in patients with severe respiratory failure.

May be used as a rescue intervention or a method to minimize ventilator associated lung injury.

Improves severe disability and death in patients with severe ARDS (Peek GJ et al).

Use of ECMO in patients with H1N1 ARDS reduces mortality compared to matched non-ECMO patients (Noah M).

May allow use of low tidal volumes and lower levels of inspired oxygen, and use of higher positive end expiratory pressures and may decrease risk of regional overdistension of compromised lungs and prevent further injury.

Limitations in use as it can only be used in specialized centers, invasive procedure, requires use of anticoagulation, and is associated with complications.

An extracorporeal technique of providing both cardiac and respiratory support oxygen to patients whose heart and lungs are so severely diseased or damaged that they can no longer serve their function.

The two most common forms of ECMO are veno-arterial (VA) and veno-venous (VV).

In both modalities, blood drained from the venous system is oxygenated outside of the body.

In veno-arterial (VA) extracorporeal membrane oxygenation blood is returned to the arterial system and in veno-venous ECMO the blood is returned to the venous system.

In the veno-venous system no cardiac support is provided.

In veno-arterial ECMO system a venous cannula is usually placed in the right common femoral vein for extraction and an arterial cannula is usually placed into the right femoral artery for infusion.

In the above veno-arterial ECMO system the tip of the femoral venous cannula is maintained near the junction of the inferior vena cava and right atrium, while the tip of the femoral arterial cannula is maintained in the iliac artery.

Central veno-arterial ECMO may be used if cardiopulmonary bypass has already been established.

In Veno-venous ECMO – venous cannulae are usually placed in the right common femoral vein for drainage and right internal jugular vein for infusion.

The use of ECMO in acute respiratory failure improves survival rates, with survival rates from 50—70 percent.

In heart failure Venoarterial (VA) ECMO is a bridge to further therapy, either a ventricular assist device, transplant or recovery.

Indications for ECMO are: bridge to transplant, bridge to mechanical circulatory support, bridge to recovery, bridge to decision in patients whose prognoses are uncertain.

Initiation of ECMO include: acute severe cardiac or pulmonary failure that is potentially reversible and unresponsive to conventional management.

ECMO used for: hypoxemic respiratory failure with a ratio of arterial oxygen tension to fraction of inspired oxygen (PaO2/FiO2) of <100 mmHg despite ventilator,

hypercapnic respiratory failure with an arterial pH <7.20, refractory cardiogenic shock,

cardiac arrest, failure to wean from cardiopulmonary bypass, as a bridge to either cardiac transplantation or placement of a ventricular assist device.

Relative contraindications to ECMO: conditions incompatible with normal life if the patient recovers.

Treatment with EMCO requires anticoagulation, and placement of vascular cannulae, usually

placed percutaneously by the Seldinger technique.

VV ECMO is typically used for respiratory failure.

VA ECMO is used for cardiac failure.

Near-maximum flow rates are usually used during VV ECMO to optimize oxygen delivery.

The flow rate used during VA ECMO must provide adequate perfusion pressure and venous oxyhemoglobin saturation but low enough to provide sufficient preload to maintain left ventricular output.

Ultrafiltration can be added to ECMO circuit if patients are unable to produce sufficient urine.

Left ventricular output is monitored during VA ECMO because left ventricular output can become worse.

With respiratory failure, improvements in radiographic appearance, pulmonary compliance, and arterial oxyhemoglobin saturation indicate that the patient may be ready to be taken off of ECMO support.

For patients with cardiac failure, enhanced aortic pulsatility correlates with improved left ventricular output and indicates that the patient may be ready to be taken off of ECMO support.

Complications of ECMO include bleeding Arizona coagulase are used to prevent clots from forming in the tubing.
Strokes may occur if clots form in the ECMO circuit or body.
Leg injuries may occur when cannulas are placed in blood vessels in the leg compromising blood flow

A common complication of ECMO-treated adults is neurological injury

Neurological injury from ECMO include: subarachnoid hemorrhage, ischemic watershed infarctions, hypoxic-ischemic encephalopathy, unexplained coma, and brain death.

Complications of EMCO include: Sepsis, and bleeding.

Survival rates for EMCO are around 60%.

ECMO usefulness in adults with acute respiratory distress syndrome hAs not been proven.

In patients whose cardiac function does not recover sufficiently to be weaned from ECMO may be bridged to a ventricular assist device (VAD) or transplant.

Preterm infants are at unacceptably high risk for intraventricular hemorrhage (IVH) if administered ECMO at a gestational age less than 32 weeks.

Standard practice to ultrasound the brain prior to administering ECMO.

Complications can be direct as a result of the device or its insertion or indirectly through the use of anticoagulants.

Adverse response to extracorporeal membrane oxygenation range from trivial to devastating.

The most common complications are bleeding, 24%, infection 11%, circuit related complications 25% cardiac arrhythmias are reported and 7.9% of patients and CNS hemorrhage or infarction IN 5.2%.

Bleeding occurs in 30 to 40 percent of patients receiving ECMO and can be life-threatening.

Bleeding is due to both the necessary continuous heparin infusion and platelet dysfunction.

Heparin-induced thrombocytopenia (HIT) is common among patients receiving ECMO.

When HIT is suspected, the heparin infusion is usually replaced by a non-heparin anticoagulant.

Pulmonary hemorrhage can occur in patients receiving ECMO.

Stasis of the blood can occur if left ventricular output is not maintained, and may result in thrombosis.

During VA ECMO, saturated blood infused into the femoral artery from the ECMO circuit will perfuse the lower extremities and the abdominal viscera, while blood ejected from the heart will selectively perfuse the heart, brain, and upper extremities.

ECMO use can increase the viability rate of transplanted organs.

ECMO provides improved gas exchange allowing the decrease of intensity of mechanical ventilation, which decreased in ventilatory induced lung injury.

Among survivors of ECMO treatment there is a significant associated risk of new mental problems.

In patients with acute myocardial infarction, complicated by cardiogenic shock, and with planned early revascularization, the risk of death from any cause at the 30 day follow up, was not lower among patients who received ECLS therapy than among those who received medical therapy alone (ECLS-SHOCK Investigators).

Among patients with severe ARDS, supported by venovenous extra corporeal membrane oxygenation, prone positioning, compared with supine positioning, did not significantly reduced time to successful weaning of extracorporeal membrane oxygenation (PRONECMO, investigators).

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