Extracorporeal Membrane Oxygenation (ECMO)
'ECMO' is an acronym for 'extracorporeal membrane oxygenation'.As the name implies, it refers to the delivery of oxygen by "extracorporeal" measures, and literally means by mechanical bypass that takes place outside of the body. Toward that end, an ECMO machine is a medical device that performs this task. In fact, it is very similar to a heart-lung machine that is used to continue the supply of blood and oxygen while the heart is stopped, such as during open heart surgery. ECMO therapy, however, is intended for patients whose heart and lungs cannot normally function on their own.
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, perfusionists, respiratory therapists and registered nurses that have received training in this specialty.
ECMO is most commonly used in neonatal intensive-care units, for newborns in pulmonary distress. 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 drop to roughly 33%.
Europe's largest Extracorporeal Membrane Oxygenation (ECMO) centre is based at Glenfield Hospital in Leicester. Babies, children and adults are treated at the centre for reversible acute respiratory or cardio-respiratory disease. There are four ECMO centres in the UK: Glenfield Hospital, Leicester, the Freeman Hospital, Newcastle, the Royal Hospital for Sick Children, Glasgow and Great Ormond Street Hospital, London. The units work in co-operation to provide a national co-ordinated service. Glenfield Hospital is the only ECMO centre in the UK which offers treatment to adults. The hospital is registered with Extracorporeal Life Support Organisation (ELSO), is part of the CESAR Trial and is one of the world's most experienced hospitals in using ECMO.
VV and VA ECMO
The additional acronyms of VV and VA are used to differentiate between the two main methods of administering ECMO therapy. VV stands for veno-venous and indicates that the mode of entry into the body is a vein. This is usually the preferred method when the patient has suffered the loss of lung function exclusively. In contrast, veno-arterial, or VA, means that dual access by a vein and the carotid artery is necessary, and usually applies to patients with both lung and heart impairment.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.
While many patients receive ECMO therapy due to advance disease or damage to the heart and/or lungs, it also has an application in neonatal emergency medicine. In fact, use of the EMCO machine in children's hospitals has saved many full-term infants with pulmonary or respiratory distress that fails to respond to other interventions. On occasion, EMCO therapy may also be given to premature infants born with underdeveloped lungs or other birth defect. 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
While ECMO is indeed lifesaving in many cases, there are certain risks associated with this therapy. ECMO can have dangerous side effects. The large catheters inserted in the baby's neck can provide a fertile field for infection, resulting in fatal sepsis. There is always a risk of infection at the access site, which may necessitate a regimen of antibiotics. The formation of air bubbles or blood clots in the tubing also presents a risk. Also, the fact that anticoagulant drugs are given to prevent clotting poses an additional risk of excessive bleeding. Finally, patients who undergo VA ECMO may have an increased risk of stroke.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. There is a risk of intraventricular haemorrhages, it has become standard practice to ultrasound the brain prior to administering ECMO.
Sources:
http://www.uhl-tr.nhs.uk/index.asp?pgid=6923
http://www.wisegeek.com/what-is-an-ecmo-machine.htm
http://en.wikipedia.org/wiki/Extracorporeal_membrane_oxygenation
September 2009