Ultrafiltration and Backfiltration during Hemodialysis

Abstract

Ultrafiltration is the pressure-driven process by which hemodialysis removes excess fluid from renal failure patients. Despite substantial improvements in hemodialysis technology, three significant problems related to ultrafiltration remain: ultrafiltration volume control, ultrafiltration rate control, and backfiltration. Ultrafiltration volume control is complicated by the effects of plasma protein adsorption, hematocrit, 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 intradialytic complications is complicated by inaccurate estimates of dry weight and patient-to-patient differences in vascular refilling rates. Continuous monitoring of circulating blood volume during hemodialysis may enable a better understanding of the role of blood volume in triggering intradialytic symptoms and allow determination of optimal ultrafiltration rate profiles for hemodialysis. Backfiltration can occur as a direct result of ultrafiltration control and results in transport of bacterial products from dialysate to blood. By examining these problems from an engineering perspective, the authors hope to clarify what can and cannot be prevented by understanding and manipulating the fluid dynamics of ultrafiltration.

Microbiologic Purity of Dialysate:Rationale and Te chnical Aspects

“…The general use of sodium bicarbonate as buffer in the dialysate, favoring bacteria proliferation, has been associated with pyrogenic reactions and water-borne bacteremia [14][15][16][17]. The combined use of highly permeable membrane with a dialysis machine equipped with an ultrafiltration controller system has enhanced the backtransport phenomenon [18] (backfiltration and/or diffusion) from dialysate to blood, enhancing the risks related to contaminant of the dialysis fluid [19,20]. Second, dialysate has been recognized as a major component of the complex hemocompatibility system in dialysis [21][22][23].…”

Pulse Push/Pull Hemodialysis in a Canine Renal Failure Model

“…However, net fluid removal is maintained at the level of desired weight loss because net filtration rates are regulated by a balance of internal filtration and backfiltration along with a dialyzer length [17][18][19] . Thus, external sterile replacement infusion is not required, which makes this modality inherently simpler than HDF.…”

Dialysis Membrane Manipulation for Endotoxin Removal

“…Backfiltration is based upon geometrical and permeability properties of the hollow fiber membrane, and cannot be avoided in high-flux hemodialysis (Ofsthun & Leypoldt, 1995). However, both physical and chemical means c a n b e u s e d t o p r o h i b i t e n d o t o x i n f r o m crossing the membrane, by removing it from solution and holding it within the dialyzer membrane.…”