In some diseases or poisonings, there are substances in the blood that can cause harm. Apheresis procedures can be used to rid the blood plasma of these substances – and this is done by passing the blood through a device outside the body. The term apheresis is generally used to describe medical procedures whose therapeutic effect consists in the removal of components of the blood. The removal of these components takes place outside the body in a so-called extracorporeal circuit. The patient is connected to an apheresis device.
The best-known form of apheresis, which is also called blood washing, is dialysis. In a number of diseases, special blood purification procedures can specifically remove substances from the bloodstream and thus have a positive effect on the course of the disease. One of the best-known blood purification procedures is dialysis, which is a so-called kidney replacement procedure that takes over the function of the kidneys in the event of a disorder and removes toxic substances.
How does apheresis work?
Less well known than dialysis is therapeutic apheresis, which removes outside the body (extracorporeally) pathogenic proteins, pathogenic substances bound to proteins, or cells. This is done either with the aid of a filter (membrane plasma operator) or with a centrifuge. In principle, a distinction is made between two procedures:
- In the apheresis device, the blood plasma is first separated from the blood cells (plasma separation) and only in the second step is the plasma purified from the pathogenic substances. This blood washing, in turn, can be done in several ways:
- Unselective plasma exchange (plasmapheresis): here, all the patient plasma obtained is discarded and replaced by a special nutrient solution.
- Selective plasma exchange: here, only the special disease-causing proteins (e.g., in autoimmune diseases) are removed using filtering or other methods, and the remaining plasma is returned to the patient.
- Second option: the separation of blood plasma from the blood cells is omitted, but the pathogenic substances are removed in the apheresis device directly from whole blood using activated carbon or exchange resin (whole blood apheresis). This method is also called hemoperfusion.
In all cases, the affected person receives two accesses usually through the veins – from one access, the blood is removed, then passed through the apheresis device and returned through the other vein after purification and, if necessary, addition of replacement fluid. Apheresis requires close collaboration between the physician treating the underlying condition and the one performing the apheresis. Apheresis treatments are performed on an outpatient basis, but in specialized centers. Currently, there are approximately 100 apheresis centers in the Federal Republic of Germany, where primarily treatments for lipid metabolic diseases are performed.
