A survey of blood purification techniques

Apheresis may be performed with many different techniques. The basis for different therapeutic approaches lies in the pathophysiological processes present in the diseases that have to be treated. Over the years more sophisticated devices have been developed. The most frequent treatment is plasma exchange (plasmapheresis) using centrifugation or single filtration techniques. In addition cascade filtration and subsequent adsorption from plasma is done. Thereby removal is done by adsorption of molecules such as bilirubin, immunoglobulins (immunoadsorption), circulating immune complexes, various antibodies including those against blood types. Such adsorption technologies have also been developed to allow adsorption directly from a column perfused by whole blood (hemoperfusion). By combining various techniques, systems are available that allow bridging of patients with hepatic failure to transplantation (MARS, Prometheus). By adding e.g., hepatic cells to such systems, besides dialysis and adsorption, cells will help to degrade toxic molecules. Such bioreactors are in clinical use. Apheresis includes also the removal or retrieval of cells from blood for e.g., stemcell transplantation, polycythaemia or hemochromatosis. Removal of leukocytes from blood using leukocyte filters is indicated in inflammatory bowel diseases. By specifically irradiating lymphocytes and monocytes with UV light using the technique of extra corporeal photochemotherapy (ECTP) various immunological diseases are treated. On the other hand, various alternative techniques may be used for the same disorder. Thus for patients with high plasma LDL-cholesterol not responding to other lipid lowering strategic treatment, alternative therapy may be done either by cascade filtration, adsorption technology from plasma, heparin precipitation (HELP-system) or hemoperfusion. This article describes various techniques in clinical use.