Extracorporeal membrane oxygenation

In intensive care medicine, extracorporeal membrane oxygenation (ECMO) is 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.

Uses

ECMO is most commonly used in neonatal intensive-care units, for newborns in pulmonary distress , but it is also used for adults that, even with the use of a ventilator, need to be oxygenated until they are able to do the job without assistance. One of the new uses is in adults and children with the H1N1 flu. It is also used with children who have respiratory syncytial virus infections. ECMO treatment provides oxygenation until their lung function has sufficiently recovered to maintain appropriate O2 saturation. It is often a last resort.

It is around 75% effective in saving the newborn's life. Newborns cannot be placed on ECMO if they are under 4.5 pounds (2 kg), because they have extremely small vessels for cannulation, thus hindering adequate flow because of limitations from cannula size and subsequent higher resistance to blood flow (compare with vascular resistance). Therefore, the device cannot be used for most premature newborns. Newborn infants are occasionally placed on ECMO due to the lack of a fully functioning respiratory system or other birth defect, but the survival rates drops to roughly 33%.

ECMO has proven to be useful in treating some severe trauma/polytrauma patients.

ECMO use on cadavers can increase the viability rate of transplanted organs.

Procedure

ECMO schema

An ECMO machine is similar to a heart-lung machine. To initiate ECMO, cannulae are placed in large blood vessels to provide access to the patient's blood. Anticoagulant drugs, usually heparin, are given to prevent blood clotting. The ECMO machine continuously pumps blood from the patient through a membrane oxygenator that imitates the gas exchange process of the lungs, i.e. it removes carbon dioxide and adds oxygen. Oxygenated blood is then returned to the patient. Management of the ECMO circuit is done by a team of ECMO specialists that includes intensive care unit (ICU) physicians,physician assistants, perfusionists, Registered Nurses,respiratory therapists, and Medical Laboratory Technologists that have received training in this specialty.

ECMO in H1N1 patient

Types

There are several forms of ECMO, the two most common of which are veno-arterial (VA) and veno-venous (VV). In both modalities, blood drained from the venous system is oxygenated outside of the body. In VA ECMO, this blood is returned to the arterial system and in VV ECMO the blood is returned to the venous system. In VV ECMO, no cardiac support is provided.

Duration

VV ECMO can provide sufficient oxygenation for several weeks, allowing diseased lungs to heal while the potential additional injury of aggressive mechanical ventilation is avoided. It may therefore be life-saving for some patients. However, due to the high technical demands, cost, and risk of complications, such as bleeding under anticoagulant medication, ECMO is usually only considered as a last resort.

The time limit for a newborn on ECMO is usually around 21 days. Dr. Thomas Krummel, Chairman of General Surgery at Stanford University, held the record for the longest survivor on ECMO at 62 days. This record was in turn broken recently on January 30, 2008, when a patient at NTU hospital, Taiwan survived a drowning accident after 117 days of ECMO application.

Complications

Fatal sepsis may occur when the large catheters inserted in the neck provide fertile field for infection. Additional risks include bleeding. In adults, ECMO survival rates are around 60%, and there are reports of patients being supported for over ten weeks. ECMO has yet to have proven survival benefit in adults with acute respiratory distress syndrome (ARDS). In VA ECMO, patients whose cardiac function does not recover sufficiently to be weaned from ECMO may be bridged to a ventricular assist device (VAD) or transplant.

In infants aged less than 34 weeks of gestation several physiologic systems are not well-developed, specially the cerebral vasculature and germinal matrix, resulting in high sensitivity to slight changes in pH, PaO₂, and intracranial pressure. Subsequently, preterm infants are at unacceptably high risk for intraventricular hemorrhage (IVH) if administered ECMO at a gestational age less than 32 weeks. Also later, given the risk of IVH, it has become standard practice to ultrasound the brain prior to administering ECMO.

External links

• Flow Measurement for ECMO Applications
• ECMO Simulation Site

See also

• Extracorporeal therapy