Apheresis
From Wikipedia, the free encyclopedia
- For the figure of speech, see Apheresis (linguistics).
Apheresis (Greek: "to take away") is a medical technology in which the blood of a donor or patient is passed through an apparatus that separates out one particular constituent and returns the remainder to the circulation. It is thus an extracorporeal therapy.
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[edit] Method
Depending on the substance that is being removed, different processes are employed in apheresis. If separation by weight is required, centrifugation would be the method of choice. Other methods involve absorbation onto beads coated with an absorbent material. The centrifugation method can be divided into two basic categories: A. Continuous flow centrifugation (CFC) historically required two venipunctures as the "continuous" means the blood is collected, spun, and returned simultaneously. Newer systems can use a single venipuncture. The main advantage of this system is the low extracorporeal volume (calculated by volume of the aphresis chamber, the donor's hematocrit, and total blood volume of the donor) used in the procedure, which may be advantageous in the elderly and for children. B. Intermittent flow centrifugation works in cycles, taking blood, spinning/processing it and then giving back the unnecessary parts to the donor in a bolus. To stop the blood from coagulating, the tubing is coated in anticoagulant. The main advantage is a singlevenipuncture site. The centrifugation process itself has four variables that can be controlled to selectively remove desired components. The first is spin speed and bowl diameter, the second is "sit time" in centrifuge, the third is solutes added, and the fourth is not as easily controllable: plasma volume and cellular content of the donor. The end product in most cases is the classicsedimented blod sample with the RBC's at the bottom, the "buffy coat" of platelets and WBC's (lymphocytes/granulocytes (PMN's, basophils, eosinophils)/monocytes) in the middle and the plasma on top. It is important to remember when the apheresis system is used for therapy, the system is removing relativly small amounts of fluid (not more than 10.5 mL/kg body weight), but that fluid is must be replaced to keep correct intravascular volume. The fluid replaced is different at different institutions. If a crystalloid like normal saline is used, the infusion amount should be triple what is removed as the three to one ratio of NS for plasma is needed to keep uponcotic pressure. Some institutions use normal serum albumin, but it is costly and can be difficult to find. Some advocate using FFP, but the dangers including citrate toxicity (from the anticoagulant), ABO incompatibility, bacterial infection, and cellular antigens make this choice less than desirable.
[edit] Types of apheresis
There are numerous types of apheresis. Blood taken from a healthy donor can be separated into its component parts, the needed component collected and the "unused" components returned to the donor. Fluid replacement is usually not needed in these type of collections. There are large categories of component collections:
- Plasmapheresis - blood plasma. Plasmapheresis is useful in collecting FFP (fresh frozen plasma) of a particular ABO group, most prized group being AB (as they lack anti-A and anti-B antibodies). Commercial uses aside from FFP for this procedure range from immune globulin products, plasma derivatives, and to collect rare WBC and RBC antibodies. Consult AABB standards for procedure criteria. FFP may be stored one year at -18 C and seven years at -65 C. After thawing, FFP can be stored for 24 hours at 1-6 C.
- Plateletpheresis (thrombapheresis, thrombocytapheresis) - blood platelets. Plateletpheresis, like it sounds, is the collection of platelets by aphresis; while returning the RBC's, WBC's, and component plasma. The yield is normally the equivalent of between six and ten random platelet concentrates. Quality control demands the platelets fromaphresis are equal to or greater than 3.0 x 10^11 and have a pH of equal to or greater than 6.2 in 90% of the products tested and must be used within five days. ABO compatibility is a good idea.
- Leukapheresis - leukocytes (white blood cells). Leukopheresis is the removal of PMN's, basophils, eosinophils for transfusion into patients whose PMN's are ineffective or traditional therapy has failed. There is limited data to suggest the benefit of granulocyte infusion. The complications of this procedure are the difficulty in collection and short shelf life (24 hours at 20 to 24 C). Since the "buffy coat" layer sits directly atop the RBC layer, HES, a sedimenting agent, is employed to improve yield while minimizing RBC collection. Quality control demands the resultant concentrate be 1.0 x 10^10 granulocytes in 75% of the units tested and that the product be irradiated to avoid graft-versus-host disease (inactivate lymphocytes). Irradiation does not effectPMN function. Since there is usually a small amount of RBC's collected ABO compatibility should be employed when feasible.
- Stem cell harvesting - circulating bone marrow cells are harvested to use in bone marrow transplantation
- LDL apheresis - removal of low density lipoprotein in patients with familial hypercholesterolemia
- Photopheresis
- Automated Red Cell Collection (2RBC) - removal of two units of red blood cells. Erythrocytaphersis is the collection of RBC's, either two standard units of RBC's or one unit plus either plasma or platelets. The advantage to the donor is the use of smaller needles and saline compensation. The advantage to the blood bankers is the on-line separation into standardized RBC masses with the subsequent reduction in testing, data entry and staffing.
[edit] Uses
[edit] Donation
Blood components can be separated from a collected bag of whole blood or from a donor's blood flow before collected to a blood bag. Various blood components are obtained by apheresis from donors. This includes platelets and blood plasma.
[edit] Therapy
- Please refer to the individual apheresis methods for use in diseases
The various apheresis techniques may be used whenever the removed constituent is causing severe symptoms of disease. Generally, apheresis has to be performed fairly often, and is an invasive process. It is therefore only employed if other means to control a particular disease have failed, or the symptoms are of such a nature that waiting for medication to become effective would cause suffering or risk of complications.
[edit] See also
[edit] External links
- American Society for Apheresis
- Apheresis News
- WebPath Apheresis page.
- WebPath Blood Donation and Processing
- Donating Platelet Apheresis: Facts and the FAQ
- Baxter: Automated Component Collection
- Haemonetics: PCS2 System
- Haemonetics: MCS+ 9000 Dystem
- Gambro BCT: Trima Automated Blood Collection System
