Blood purification by ultrafiltration and fluid replacement (diafiltration)

Abstract

Conventional extracorporeal dialysis relies on diffusion down concentration gradients for the removal of undesirable solutes from the blood. Removal of a solute by diffusion depends on its size; this gives rise to the familiar observation that small solutes such as urea are removed by dialysis more readily than larger solutes such as creatinine and uric acid. The work of Teschan et al.(1) on isolation of toxic substances from uremic blood suggests that these large molecular weight solutes contribute to uremic symptomatology. In addition, with diffusion, the rate of solute removal falls exponentially with time following a first order decay curve. As a result dialysis efficiency is low at low plasma solute concentrations. The limit approached by techniques to improve dialysis efficiency for a solute is the rate of free diffusion in water for the solute in question, and for large toxic solutes such as glutethimide and kanamycin, this maximum rate of removal may be too slow for clinical success.With these limitations for conventional dialysis in mind the present study was undertaken to evaluate a familiar process (2-5) heretofore unexploited as a means to remove toxic solutes, namely ultrafiltration. Such a process would have the advantage of removing solutes small enough to pass through the ultrafilter in proportion to their plasma concentration rather than their concentration gradient, as with diffusion. With the driving force being a pressure gradient rather than a concentration gradient there would not be a sharp a reduction in solute removal at low plasma concentrations as seen with diffusion. In addition the rate of solute removal would be proportional to the applied pressure gradient and this could be adjusted to meet the needs of the clinical situation. MATERIALSA new series of membranes composed of the precipitated polyelectrolytes sodium polystyrene sulfonate and polyvinylbenzyltriemnthyl ammonium chloride in stoichiometric proportions was selected for evaluation. These new membranes, henceforth designated by the trade name Diaflo, can be synthesized in such a way as to provide a family of membranes with a net neutral charge and a wide range of permeabilities to water when a pressure gradient is applied. Figure 1 shows a diagrammatic sketch of the membrane which in itself is only 1-2 mils thick and quite fragile. For greater strength it has been cast on a stout backing of highly porous polyester felt. The overall thickness of membrane and backing is 6-10 mils. Essentially all properties of discrimination and resistance to water flow reside in the membrane skin. EXPERIMENTAL STUDIES AND RESULTSDiaflo membranes were initally studied from the standpoint of traditional diffusive transport in order to see if a significant contribution from diffusion would be present in their subsequent evaluation with ultrafiltration. Figure 2 is a photograph of the Leonard-Bluemle batch dialyzer (6) . A membrane disc is clamped between 2 hemichambers by a metal coupler. Each chamber is stirred at constant temperature by a magne...

Recent developments in the properties and applications of polyelectrolyte multilayers

“…Hence, polyelectrolyte complexes have been used to produce non-immunogenic subcutaneous implants and high dialysis coefficient artificial kidney membranes [18,19]. The record of PECs as biocompatible materials stimulated efforts to employ PEMUs, which can be applied to virtually any surface, in biomedical applications [20,21].…”

Purification of hemoglobin by tangential flow filtration with diafiltration

“…Diafiltration should increase transmission of impurities through ultrafiltration membranes by continuously or intermittently adding buffer to maintain the retentate volume, thereby lengthening the total filtration time. It has been previously used to remove impurities from blood as an alternative to dialysis21 and can be used in other industrial applications22. In this study, diafiltration was applied during stage III to enhance transmission of any residual SMWIs through the 100 kDa HF membrane and further increase the purity of the bHb product.…”

Ultrafiltration in Patients with Hypervolemia and Congestive Heart Failure

“…More recently, solute removal in conjunction with ultrafiltration has been exploited as an alternative to diffusion as a mean of cleaning uremic blood [1]. The clinical application of ultrafiltration for fluid removal dated from the advent of dialysis therapy.…”