Extracorporeal circulation is a medical procedure where blood is pumped out of the body, cleaned or treated and them pumped back in again. This way, the medical devices used act as an extra piece of circulation outside of the body. Such actions are usually taken because of kidney failure, immune system disorders and heart failure. Circulation can be continuous, as in dialysis, or interrupted, where blood is taken out, treated and then put back in.
Dialysis is where a machine is used to pump blood in a continuous cycle and is linked to renal failure. Hemodialysis is an extracorporeal circulation treatment aimed at removing waste from blood. Waste usually takes the form of creatinine, urea or free water. Hemodialysis can take place at home, but is more likely to be performed in a clinic or hospital. It uses hydrostatic pressure to force the blood against a semipermeable membrane, the waste passes through the membrane and is separated, the blood continues on and back into the body.
Hemofiltration is used in an intensive care situation and is a slow, long and continuous process, taking between 12 and 24 hours. The procedure needs to be done once a day. Hemofiltration is otherwise the same as hemodialysis.
Apheresis is an extracorporeal circulation treatment where one element is removed from the blood, is treated or destroyed and the rest of the blood is put back into the body. Plasmapheresis is where blood and plasma are removed by injection or by a catheter and then separated using centrifugal force. The blood is put back into the body and the plasma treated. The procedure is used to treat immune system disorders like lupus.
Extracorporeal Membrane Oxygenation (ECMO) is an extracorporeal circulation method used to offer respite to damaged hearts and lungs. Blood is taken from a vein or artery and treated with an anticoagulant. It is then passed through a membrane oxygenator that replicates lung function and converts carbon dioxide into oxygen. Once oxygenated, the blood passes back into the body. There are two types of ECMO: one that pumps blood back into a vein and one that pumps it back into an artery.
A cardiopulmonary bypass is only used during an operation on the heart. This extracorporeal circulation technique allows surgeons to work on a still heart. It is difficult for doctors to make precise incisions and to open up heart chambers when it is still beating. The technique was first performed by Dr. Clarence Dennis of Minnesota in 1951. It uses a mechanical heart-lung machine to pump blood out of the body, oxygenate it and pump it back in again.
