This Week In The Bmj

Extracorporeal membrane oxygenation

BMJ 1998; 317 doi: (Published 03 October 1998) Cite this as: BMJ 1998;317:916
  1. Abi Berger, Science editor
  1. BMJ

    Extracorporeal membrane oxygenation is a technique for oxygenating blood outside the body which does away with the need for gas exchange inside the lungs. It is an offshoot of cardiopulmonary bypass technology but does not require the body to be cooled down first and requires minimal heparin. This type of bypass can run for several days rather than hours. There are four extracorporeal membrane oxygenation centres in the United Kingdom, and about 120 babies are treated a year.

    The technique produces the best results in babies greater than 37 weeks' gestation. Preterm babies, under 2 kg for example, have vessels which are too fragile to withstand the damage from cannulae and are at risk of intraventricular haemorrhages from the heparinised circuits. The circumstances where extracorporeal membrane oxygenation is useful include severe meconium aspiration syndrome, where the underlying lungs are essentially healthy and the damage is potentially reversible. Thus the treatment “buys time” (usually up to 10 days) rather than offering a direct cure, allowing the lungs to be sucked out.

    Other groups of neonates can also benefit—for example, premature babies who have reached term age and develop respiratory syncitial viral bronchiolitis on top of already abnormal lungs. These babies may do well with more prolonged treatment. In the United Kingdom ventilation is usually tried first, with extracorporeal membrane oxygenation following. But if ventilation has been tried for more than one week, the chances of extracorporeal membrane oxygenation being more successful are greatly reduced because of lung damage induced by heavy ventilation.

    Two types of extracorporeal membrane oxygenation exist. In venoarterial extracorporeal oxygenation membrane blood is removed from the jugular vein by passive syphoning, pumped to an oxygenator, and passed through a warmer and back to the patient at systemic pressure through the common carotid artery. Meconium aspiration can cause myocardial damage, in addition to clogging up the lungs, and the technique allows both the lungs and the heart to be bypassed (or rested). The second and more recent type is venovenous extracorporeal membrane oxygenation, in which blood is returned to the systemic venous circulation. It is used where the lungs are damaged but cardiac function is normal.

    The oxygenator has blood passing through it countercurrent to a flow of 100% oxygen, the blood and oxygen being separated by a membrane. The rate of gas exchange is 120 ml/kg/min so the whole process in neonates (who have a blood volume of about 80 ml/kg) is very fast. Carbon dioxide is removed at the same time as oxygen is supplied.