Plasmapheresis (from the Greek πλάσμα, plasma, something molded, and ἀφαίρεσις aphairesis, taking away) is the removal, treatment, and return or exchange of blood plasma or components thereof from and to the blood circulation. It is thus an extracorporeal therapy, a medical procedure performed outside the body. Three general types of plasmapheresis can be distinguished:
Autologous, removing blood plasma, treating it in some way, and returning it to the same person, as a therapy. This is also called cascade filtration. Exchange, a patient's blood plasma is removed, while blood products are given in replacement. This type is called plasma exchange (PE, PLEX, or PEX) or plasma exchange therapy (PET). The removed plasma is discarded and the patient receives replacement donor plasma, albumin, or a combination of albumin and saline (usually 70% albumin and 30% saline). Donation, removing blood plasma, separating its components, and returning some of them to the same person, while holding out others to become blood products that this person donates for those in need. In such a plasma donation procedure, blood is removed from the body, blood cells and plasma are separated, and the blood cells are returned, while the plasma is collected and frozen to preserve it for eventual use as fresh frozen plasma or as an ingredient in the manufacture of blood products. Plasmapheresis of the autologous and exchange types is used to treat a variety of disorders, including those of the immune system, such as Goodpasture's syndrome, Guillain–Barré syndrome, lupus, myasthenia gravis, and thrombotic thrombocytopenic purpura.
Medical uses During plasmapheresis, blood, which consists of blood cells and a clear liquid called blood plasma, is initially taken out of the body through a needle or previously implanted catheter. Plasma is then removed from the blood by a cell separator. Three procedures are commonly used to separate the plasma from the blood cells, with each method having its own advantages and disadvantages:
Discontinuous flow centrifugation: One venous catheter line is required. Typically, a 300 ml batch of blood is removed at a time and centrifuged to separate plasma from blood cells. Continuous flow centrifugation: Two venous lines are used. This method requires slightly less blood volume out of the body at any one time, as it is able to continuously spin out plasma. Plasma filtration: Two venous lines are used. The plasma is filtered using standard hemodialysis equipment. This continuous process requires that less than 100 ml of blood be outside the body at one time. After plasma separation, the blood cells are returned to the person undergoing treatment, while the plasma, which contains the antibodies, is first treated and then returned to the patient in traditional plasmapheresis. Rarely, other replacement fluids, such as hydroxyethyl starch, may be used in individuals who object to blood transfusion but these are rarely used due to severe side-effects. Medication to keep the blood from clotting (an anticoagulant) is given to the patient during the procedure. Plasmapheresis is used as a therapy in particular diseases. It is an uncommon treatment in the United States, but it is more common in Europe and particularly Japan. An important use of plasmapheresis is in the therapy of autoimmune disorders, where the rapid removal of disease-causing autoantibodies from the circulation is required in addition to other medical therapy. Plasma exchange therapy in and of itself is useful to temper the disease process, while simultaneous medical and immunosuppressive therapy is required for long-term management. Plasma exchange offers the quickest short-term answer to removing harmful autoantibodies; however, the production of autoantibodies by the immune system must also be suppressed, usually by the use of medications such as cyclophosphamide, cyclosporine, mycophenolate mofetil, prednisone, rituximab, or a mixture of these. Other uses are the removal of blood proteins where these are overly abundant and cause hyperviscosity syndrome. There is weak evidence that therapeutic plasma exchange (TPE) might be of benefit in severe cases of COVID-19.
Examples of diseases that have been treated with plasmapheresis
Complications of plasmapheresis therapy Though plasmapheresis is helpful in certain medical conditions, like any other therapy, there are potential risks and complications. Insertion of a rather large intravenous catheter can lead to bleeding, lung puncture (depending on the site of catheter insertion), and, if the catheter is left in too long, it can get infected. Aside from placing the catheter, the procedure itself has complications. When patient blood is outside of the body passing through the plasmapheresis machine, the blood has a tendency to clot. To reduce this tendency, in one common protocol, sodium citrate is infused while the blood is running through the circuit. Citrate binds to calcium in the blood, calcium being essential for blood to clot. Citrate is very effective in preventing blood from clotting; however, its use can lead to life-threateningly low calcium levels. This can be detected using the Chvostek's sign or Trousseau's sign. To prevent this complication, calcium is infused intravenously while the patient is undergoing the plasmapheresis; in addition, calcium supplementation by mouth may also be given. Other complications include:
Bleeding or hematoma from needle placement Hypotension Potential exposure to blood products, with risk of transfusion reactions or transfusion transmitted diseases Suppression of the patient's immune system
Plasma donation
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