To use all functions of this page, please activate cookies in your browser.
With an accout for my.bionity.com you can always see everything at a glance – and you can configure your own website and individual newsletter.
- My watch list
- My saved searches
- My saved topics
- My newsletter
Additional recommended knowledge
Depending on the substance that is being removed, different processes are employed in apheresis. If separation by weight is required, centrifugation is the most common method. Other methods involve absorption onto beads coated with an absorbent material and filtration.
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 apheresis 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. The main advantage is a single venipuncture site. To stop the blood from coagulating, anticoagulant is automatically mixed with the blood as it is pumped from the body into the apheresis machine. 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 classic sedimented blood 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 that when the apheresis system is used for therapy the system is removing relatively small amounts of fluid (not more than 10.5 mL/kg body weight). That fluid 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 up oncotic pressure. Some institutions use normal serum albumin, but it is costly and can be difficult to find. Some advocate using FFP or a similar blood product, but there are dangers including citrate toxicity (from the anticoagulant), ABO incompatibility, infection, and cellular antigens.
Types of apheresis
There are numerous types of apheresis. Blood taken from a healthy donor can be separated into its component parts, where the needed component is collected and the "unused" components are returned to the donor. Fluid replacement is usually not needed in these type of collections. There are large categories of component collections:
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.
Intravenous immunoglobulin (IVIG) is a blood product administered intravenously. It contains the pooled IgG immunoglobulins (antibodies extracted from the plasma of thousands of blood donors). IVIG is given as a protein replacement therapy for immune deficient patients which have decreased or abolished antibody production capabilities. IVIG is administered to maintain adequate antibodies levels to prevent infections and confers a passive immunity. IVIG effects last between 2 weeks and 3 months. It is mainly used as treatment in three major categories:
Immune deficiencies - Immune deficiencies such as X-linked agammaglobulinemia, hypogammaglobulinemia (Primary immune deficiencies), and acquired compromised immunity conditions (secondary immune deficiencies), featuring low antibody levels. Inflammatory and autoimmune diseases. Acute infections.
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.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Apheresis". A list of authors is available in Wikipedia.|