Evaluation of Hygiene and Safety Controls for On-Line Paired Hemodiafiltration (PHF)

Convection-enhanced High-Flux Hemodialysis

Internal filtration contributes to convective clearance in high-flux hemodialysis but its contribution is limited by low pressure gradients. Therefore, a modification using a conventional dialyzer was conceived to enhance internal filtration and backfiltration (BF) rates. The modified dialyzer includes two longitudinal independent regions for blood flow, which were created by redesigning dialyzer caps. Blood pressures remained higher than dialysate pressures in one region and lower in the other region, allowing continuous internal filtration and BF in these respective regions. Modified and conventional dialyzers were compared in terms of pressure gradients and solute clearances. Thus, our experiments involved two groups: the modified dialyzer group and the conventional dialyzer group. A renal failure model was established using a dog weighing 25-30 kg by renal artery and vein ligation. With the exception of the dialyzers, experimental conditions were identical in the two groups. The pressure gradients between blood and dialysate were much higher for the modified dialyzer than for the conventional dialyzer. No significant differences were observed with respect to small solute clearances between the two groups, but mid-range solute clearances were significantly higher in the modified group. More optimization is required before the devised unit can be used clinically. However, the devised unit offers a straightforward means of regulating internal filtration and BF rates.

Hemodiafiltration history, technology, and clinical results

Hemodiafiltration (HDF) is an extracorporeal renal-replacement technique using a highly permeable membrane, in which diffusion and convection are conveniently combined to enhance solute removal in a wide spectrum of molecular weights. In this modality, ultrafiltration exceeds the desired fluid loss in the patient, and replacement fluid must be administered to achieve the target fluid balance. Over the years, various HDF variants have emerged, including acetate-free biofiltration, high-volume HDF, internal HDF, paired-filtration dialysis, middilution HDF, double high-flux HDF, push-pull HDF, and online HDF. Recent technology has allowed online production of large volumes of microbiologically ultrapure fluid for reinfusion, greatly simplifying the practice of HDF. Several advantages of HDF over purely diffusive hemodialysis techniques have been described in the literature, including a greater clearance of urea, phosphate, beta(2)-microglobulin and other larger solutes, reduction in dialysis hypotension, and improved anemia management. Although randomized controlled trials have failed to show a survival benefit of HDF, recent data from large observational studies suggest a positive effect of HDF on survival. This article provides a brief review of the history of HDF, the various HDF techniques, and summary of their clinical effects.