The extra-corporal membrane oxygenation machine is one of
the wonders of 20th and 21st century medicine, as it acts as an artificial lung
outside of the body, oxygenating the blood and pumping it round.
ECMO was first used
successfully in the USA in 1976 and was introduced in the UK in 1989. It was
first set up in a paediatric setting at Great Ormond Street Hospital in 1992
and to date they have supported over 850 babies and children. This is of vital
significance as ECMO machines are mostly used on children and babies, but are
sometimes used in adults with cardiac and respiratory failure.
There are two main types of ECMO: veno-arterial and veno-venous.
In both types, 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 this typr of ECMO there is
no cardiac support.
In
veno-arterial ECMO, a venous cannula is placed in the right common femoral vein
for extraction and an arterial cannula is placed into the right femoral artery
for infusion. The tip of the femoral venous cannula should be kept near the
junction of the inferior vena cava and right atrium, while the tip of the
femoral arterial cannula should be kept in the iliac artery. Central VA ECMO
may be used if cardiopulmonary bypass has already been established (with
cannulae in the right atrium and ascending aorta).
In
veno-venous ECMO cannulae are usually placed in the right common femoral vein
for drainage and right internal jugular vein for infusion. Alternatively, a
dual-lumen catheter is inserted into the right internal jugular vein, draining
blood from the superior and inferior vena cava and returning it to the right
atrium
ECMO can be used in the operating theatre straight after
surgery or on one of the intensive care units. If a patient is going through ECMO after cardiac surgery,
the surgeon will usually insert the cannulae (tubes) during the operation,
directly into the heart through the chest. Whereas, if ECMO is started in the
intensive care unit, the cannulae connecting the patient to the ECMO circuit
are placed directly into the blood vessels on the side of the neck.
Once in place, the cannulae are then connected to the ECMO circuit.
Dark deoxygenated blood drains from the patient through the tube in the vein
and is pumped through the membrane oxygenator where carbon dioxide is removed
and oxygen added. The blood is then re-warmed and returned to the body. This
process goes on continuously while the patient is on ECMO. Additionally, they
will also stay on a ventilator but on very gentle settings which allow the
lungs to rest.
