A Process for Enhancing Selectivity and Limiting Plugging in Plasmafractionation for Apob Removal

A new process using pressure and flow pulsations was investigated in the second stage of cascade filtration for ApoB removal. Due to enhanced filtration by the pulsations, the retentate flow vanished naturally without clamping the line, which reduced albumin and ApoA1 losses. The performance of Eval 4A and cellulose PF100 filters in this case were compared with that of classical dead end mode at a plasma flux of 18 ml/(min m2). The apparent sieving coefficient for small proteins (albumin, ApoA1) under pulsed conditions increased with increasing pressure instead of dropping as in dead end mode. In both cases the ApoB sieving coefficients remained below 0.02. These encouraging results were accompanied by a slower rise of transmembrane pressure showing a decrease of membrane plugging. Thus, the recovery of albumin and ApoA1 is increased while ApoB removal remains constant, which improves the selectivity of the fractionation stage.

Membrane-based Therapeutic Plasma Exchange: A New Frontier for Nephrologists

Therapeutic plasma exchange has long been utilized to manage a variety of immune-mediated diseases. The underlying principle is the removal of a circulating pathogenic substance from the plasma and substitution with a replacement fluid. Different methodologies of plasma separation include the use of centrifuge, which relies on the variation in the specific gravity of blood components, and membrane-based separation, which relies on particle size. With advancements in technology and clinical insight into disease pathophysiology, membrane technology has become more biocompatible, safer, and more adaptable to conventional hemodialysis and hemofiltration machines. As such, nephrologists, who are familiar with management of extracorporeal blood purification systems, are increasingly involved with membrane-based plasma separation. This review aims to highlight the technical aspects of membrane-based separation, review the prescription for therapy, and draw comparisons with the centrifuge-based technique when applicable.

Effects of operating conditions on selectivity of a plasma fractionator in double filtration plasmapheresis

In a typical double filtration plasmapheresis treatment, plasma fractionation between albumin and some immunoglobulins associated with toxins is limited because none of the currently available plasma fractionators has a strict cutoff property for these proteins. Selectivity of immunoglobulins over albumin depends not only on the cutoff properties of the membrane but on the operating conditions such as the flow rate of the supplied plasma (Q(P)) and retained plasma to be discarded (Q(D)) in the plasma fractionator. We carried out an in vitro study using human plasma harvested by single plasma exchange treatments to assess the selectivity of a plasma fractionator, Evaflux 2A-F (Kawasumi Laboratories, Inc., Tokyo, Japan), under various operating conditions. The results of rate-constant filtration experiments showed that the concentrations in the feed tank and the sieving coefficient (SC) values of every protein were decreased slightly within 2 h after the start of the experiment because of membrane trapping, adsorption, and/or plugging. The time-averaged SC value of albumin increased with flow rate ratio (Q(P)/Q(D)) due to increasing filtration fraction (FF), but relative removal efficiency (mD/mP*) for albumin decreased with Q(P)/ Q(D) due to decreasing Q(D). For immunoglobulins, on the other hand, the SC values were almost unchanged, and the mD/mP* values increased with Q(P)/Q(D) due to an increase in FF. Both increasing Q(P) and decreasing Q(D) are effective means of improving selectivity between these proteins in the plasma fractionator. Membrane fouling is, however, obvious beyond a Q(P)/Q(D) value that is thought to be a critical point. Operation should be conducted below the critical Q(P)/Q(D) value, which depends on the patient's plasma components and the cutoff property of the membrane.

Membrane plasmapheresis in the United States: a review over the last 20 years

Plasmapheresis is a general term involving extracorporeal plasma separation by centrifugation or primary membrane plasma separator (MPS). Further plasma processing can be accomplished by the use of secondary membrane plasma fractionation (PF), as in double filtration plasmapheresis, also called cascade filtration, low-density lipoprotein pheresis, thermofiltration, and cryofiltration apheresis. Otherwise, the separated plasma is replaced by colloid solution as in plasma exchange (PE). PE is used, unselectively, to treat patients with immunological, neurological, hematological, renal, and metabolic disorders. Secondary PF may be a more selective alternative. In general, the primary MPS and secondary PF are safe, effective, and biocompatible. The advantages of the primary MPS include its simplicity to use with blood pumps and no observed white blood cell or platelet loss, compared with centrifugation. The disadvantages are lack of versatility, the need to monitor transmembrane pressure to prevent hemolysis, and possible biocompatibility issues such as use of polyvinyl alcohol membranes. The advantages of secondary PF, compared with PE, include selective removal of macromolecules according to molecular weight and filter pore size. No deficiency syndromes or sepsis are observed, nor is replacement solution required. More than 1 plasma volume may be processed, and it is less expensive than PE. Cryofiltration apheresis, using the cryoglobulin filter, selectively removes cryoproteins and is a specific treatment for cryoprecipitate-induced diseases. The disadvantages of PF include biocompatibility, especially with concomitant ACE inhibitor use, and membrane plugging. An important disadvantage is that most PFs are investigational in the United States. This article reviews the availability, safety, efficacy, and biocompatibility of primary MPSs and secondary PF in the United States.