Biomodulation effects of extracorporeal circulation in apheresis

The association of biochemical and cellular abnormalities in various disease states provides the rationale for apheresis technologies. Plasmapheresis by plasma exchange has severe technical and clinical limitations due to the nonselective removal of plasma factors. Plasmapheresis methods for the more selective removal of plasma components include membrane filtration, sorption, and physico-chemical methods such as precipitation. These methods can also eliminate the need for plasma product replacement and be more specific to the clinical needs. While plasmapheresis technologies are designed primarily for solute removal, the methodology itself will have a biomodulating influence and will impact on the course of the disease state. Extracorporeal biomodulation is defined as the act of effecting changes either procedurally induced or procedurally associated in the cellular or biochemical milieu of the body. Factors to be considered in an extracorporeal procedure such as plasmapheresis include the duration of an individual treatment, the degree of solute removal selectivity, the prescribed frequency for the treatment, the type of equipment employed, the choice of anticoagulant, and the materials for blood and plasma contact. Thus, the modulatory effects of the methodology occur not only in the humoral system but also among the cells. The effects of the modulation will extend beyond the procedure time. The general direction in material research for extracorporeal circulation is to minimize the biological response. However, the modulating effects of the procedure, independent of the removal effects, suggest that the proper choice of materials in the extracorporeal circuit can benefit the patient. With the various techniques of solute removal and material availability, the clinician may chose the biomodulating system for the treatment of a given disease state.