ULTRAFILTRATION AND BACKFILTRATION DURING HEMODIALYSIS

Ultrafiltration is the pressure-driven process by which hemodialysis r emoves excess fluid from renal failure patients. Despite substantial i mprovements in hemodialysis technology, three significant problems rel ated to ultrafiltration remain: ultrafiltration volume control, ultraf iltration rate control, and backfiltration. Ultrafiltration volume con trol is complicated by the effects of plasma protein adsorption, hemat ocrit, and coagulation parameters on membrane performance. Furthermore , previously developed equations relating the ultrafiltration rate and the transmembrane pressure are not applicable to high-flux dialyzers, high blood flow rates, and erythropoietin therapy. Regulation of the ultrafiltration rate to avoid hypotension, cramps and other intradialy tic complications is complicated by inaccurate estimates of dry weight and patient-to-patient differences in vascular refilling rates. Conti nuous monitoring of circulating blood volume during hemodialysis may e nable a better understanding of the role of blood volume in triggering intradialytic symptoms and allow determination of optimal ultrafiltra tion rate profiles for hemodialysis. Backfiltration can occur as a dir ect result of ultrafiltration control and results in transport of bact erial products from dialysate to blood. By examining these problems fr om an engineering perspective, the authors hope to clarify what can an d cannot be prevented by understanding and manipulating the fluid dyna mics of ultrafiltration.