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Therapeutic apheresis includes plasma exchange and cytapheresis, which are generally tolerated by healthy donors. However, many minor and a few major risks exist. Insertion of the large IV catheters necessary for apheresis can cause complications (eg, bleeding, infection, pneumothorax). Citrate anticoagulant may decrease serum ionized Ca. Replacement of plasma with a noncolloidal solution (eg, saline) shifts fluid from the intravascular space. Colloidal replacement solutions do not replace IgG and coagulation factors.
Most complications can be managed with close attention to the patient and manipulation of the procedure, but some severe reactions and a few deaths have occurred.
Therapeutic plasma exchange removes plasma components from blood. A blood cell separator extracts the patient’s plasma and returns RBCs and platelets in plasma or a plasma-replacing fluid; for this purpose, 5% albumin is preferred to fresh frozen plasma (except for patients with thrombotic thrombocytopenic purpura) because it causes fewer reactions and transmits no infections. Therapeutic plasma exchange resembles dialysis but, in addition, can remove protein-bound toxic substances. A one-volume exchange removes about 66% of such components.
To be of benefit, plasma exchange should be used for diseases in which the plasma contains a known pathogenic substance, and plasma exchange should remove this substance more rapidly than the body produces it. For example, in rapidly progressive autoimmune disorders, plasma exchange may be used to remove existing harmful plasma components (eg, cryoglobulins, antiglomerular basement membrane antibodies) while immunosuppressive or cytotoxic drugs suppress their future production.
There are numerous indications (see Table: Indications for Plasma Exchange According to the American Society for Apheresis). (See also Guidelines on the Use of Therapeutic Plasma Exchange.) The frequency of plasma exchange, the volume to be removed, the replacement fluid, and other variables are individualized. Low density lipoprotein cholesterol can be selectively removed from plasma by adsorption over a column (called LDL apheresis). In photopheresis, mononuclear cells are selectively removed by centrifugation and treated with photoactivatable drugs (eg, 8-methoxypsoralen) that are then activated with ultraviolet light; it is a form of chemotherapy. In immunoadsorption, an antibody or antigen is removed from plasma by combining with an antigen or antibody chosen to bind the target antibody or antigen over a column. Complications of plasma exchange are similar to those of therapeutic cytapheresis.
Indications for Plasma Exchange According to the American Society for Apheresis
Therapeutic cytapheresis removes cellular components from blood, returning plasma. It is most often used to remove defective RBCs and substitute normal ones in patients with sickle cell anemia who have the following conditions: acute chest syndrome, stroke, pregnancy, or frequent, severe sickle cell crises. RBC exchange achieves Hb S levels of < 30% without the risk of increased viscosity that can occur because of increased Hct with simple transfusion.
Therapeutic cytapheresis may also be used to reduce severe thrombocytosis or leukocytosis (cytoreduction) in acute leukemia or in accelerated or blast crisis phase of chronic myelogenous leukemia when there is risk of hemorrhage, thrombosis, or pulmonary or cerebral complications of extreme leukocytosis (leukostasis). Cytapheresis is effective in thrombocytosis because platelets are not replaced as rapidly as WBCs. One or 2 procedures may reduce platelet counts to safe levels. Therapeutic WBC removal (leukapheresis) can remove kilograms of buffy coat in a few procedures, and it often relieves leukostasis. However, the reduction in WBC count itself may be mild and only temporary.
Other uses of cytapheresis include collection of peripheral blood stem cells for autologous or allogeneic bone marrow reconstitution (an alternative to bone marrow transplantation) and collection of lymphocytes for use in immune modulation cancer therapy (adoptive immunotherapy).
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