In vitro efficacy and safety of a system for sorbent-assisted peritoneal dialysis

The Revival of Sorbents in Chronic Dialysis Treatment

Interest in the use of sorbents in chronic dialysis treatment has undergone a revival in the last decades, for which two major factors are responsible. The first is the potential of sorbents as adjunct therapy for the removal of substances that are difficult to remove by conventional dialysis therapies. The second is their use in regeneration of dialysate, which is of pivotal importance in the design of portable or even wearable treatments, next to the potential for reducing water use during conventional dialysis treatment. Sorbent-enhanced dialysis with synthetic polymers was associated with a reduction in inflammatory parameters as compared to hemodialysis and even associated with improved survival in smaller studies, although this needs to be confirmed in large randomized trials. Incorporation of sorbents within a dialysis membrane (mixed matrix membrane) appears a promising way forward to reduce the complexity and costs of a dual therapy but needs to be tested in vivo. For regeneration of dialysate, at present, a combination of urease, zirconium-based sorbents, and activated charcoal is used. Next to sodium release by the sorbent in exchange for ammonium and the CO2 release by the hydrolysis of urea has been a bottleneck in the design of wearable devices, although short-term trials have been performed. Still, for widespread and flexible application of sorbent-assisted portable or wearable devices, a direct urea sorbent would be a major asset. In the near future, it will likely become apparent whether sorbent-assisted dialysis techniques are feasible for routine implementation in clinical practice.

Removal of Uremic Solutes from Dialysate by Activated Carbon

BACKGROUND AND OBJECTIVES

Adsorption of uremic solutes to activated carbon provides a potential means to limit dialysate volumes required for new dialysis systems. The ability of activated carbon to take up uremic solutes has, however, not been adequately assessed.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Graded volumes of waste dialysate collected from clinical hemodialysis treatments were passed through activated carbon blocks. Metabolomic analysis assessed the adsorption by activated carbon of a wide range of uremic solutes. Additional experiments tested the ability of the activated carbon to increase the clearance of selected solutes at low dialysate flow rates.

RESULTS

Activated carbon initially adsorbed the majority, but not all, of 264 uremic solutes examined. Solute adsorption fell, however, as increasing volumes of dialysate were processed. Moreover, activated carbon added some uremic solutes to the dialysate, including methylguanidine. Activated carbon was particularly effective in adsorbing uremic solutes that bind to plasma proteins. In vitro dialysis experiments showed that introduction of activated carbon into the dialysate stream increased the clearance of the protein-bound solutes indoxyl sulfate and p-cresol sulfate by 77%±12% (mean±SD) and 73%±12%, respectively, at a dialysate flow rate of 200 ml/min, but had a much lesser effect on the clearance of the unbound solute phenylacetylglutamine.

CONCLUSIONS

Activated carbon adsorbs many but not all uremic solutes. Introduction of activated carbon into the dialysate stream increased the clearance of those solutes that it does adsorb.

Artificial Kidney Engineering: The Development of Dialysis Membranes for Blood Purification

The artificial kidney, one of the greatest medical inventions in the 20th century, has saved innumerable lives with end stage renal disease. Designs of artificial kidney evolved dramatically in decades of development. A hollow-fibered membrane with well controlled blood and dialysate flow became the major design of the modern artificial kidney. Although they have been well established to prolong patients’ lives, the modern blood purification system is still imperfect. Patient’s quality of life, complications, and lack of metabolic functions are shortcomings of current blood purification treatment. The direction of future artificial kidneys is toward miniaturization, better biocompatibility, and providing metabolic functions. Studies and trials of silicon nanopore membranes, tissue engineering for renal cell bioreactors, and dialysate regeneration are all under development to overcome the shortcomings of current artificial kidneys. With all these advancements, wearable or implantable artificial kidneys will be achievable.

Innovationen in der Peritonealdialyse

Die Peritonealdialyse (PD) war früher eine geläufige Behandlung beim akuten dialysepflichtigen Nierenversagen. Zugunsten kontinuierlicher, extrakorporaler Nierenersatzverfahren verschwand sie von der Bildfläche der westlichen Welt, wohingegen sie in strukturarmen Ländern aufgrund ihrer Simplizität und geringen Ressourcenintensität weiter eingesetzt wird. Die Engpässe in der medizinischen Versorgung im Rahmen der COVID-19(„coronavirus disease 2019“)-Pandemie führten kürzlich zu erneuter weltweiter Beachtung der PD als sichere Option beim akuten dialysepflichtigen Nierenversagen. Von der Einführung biokompatibler Lösungen vor 20 Jahren war eine Reduktion von Mortalität oder technischem Versagen erwartet worden. Leider konnten Studien dieses bisher allenfalls andeuten, nicht aber beweisen. Eine innovative Option stellen immunmodulatorische Adjuvanzien dar, die die lokale Immunkompetenz verbessern und den Verlust der Funktion des Peritoneums verhindern sollen. Derzeit rückt die Vision einer tragbaren künstlichen Niere immer näher. Auch eine Intensivierung der Dialysedosis erscheint mit minimaler Dialysatmenge erreichbar. In Zeiten der globalen Erderwärmung könnten durch die Regeneration von Dialysat nicht nur relevante Mengen an Wasser eingespart, sondern auch die CO₂-Bilanz günstig beeinflusst werden. Zusammenfassend erlebt die PD derzeit einen zweiten Frühling. Dieser Artikel beschreibt die derzeitigen und zukünftigen Entwicklungen dieses Verfahrens.

Evaluation of a system for sorbent-assisted peritoneal dialysis in a uremic pig model

A system for sorbent-assisted peritoneal dialysis (SAPD) has been developed that continuously recirculates dialysate via a tidal mode using a single-lumen peritoneal catheter with the regeneration of spent dialysate by means of sorbents. SAPD treatment may improve plasma clearance by the maintenance of a high plasma-to-dialysate concentration gradient and by increasing the mass transfer area coefficient (MTAC) of solutes. The system is designed for daily 8-hr treatment (12 kg, nighttime system). A wearable system (2.3 kg, daytime system) may further enhance the clearance of phosphate and organic waste solutes during the day. Uremic pigs (n = 3) were treated with the day- (n = 3) and nighttime system (n = 15) for 4-8 hr per treatment. Plasma clearance (Cl), MTAC, and total mass transport (MT) of urea, creatinine, phosphate, and potassium were compared with a static dwell (n = 28). Cl, MTAC, and MT of urea, creatinine, phosphate, and potassium were low in the pig as compared to humans due to the pig's low peritoneal transport status and could be enhanced only to a limited extent by SAPD treatment compared with a static dwell (nighttime system: Cl urea: ×1.5 (p = .029), Cl creatinine: ×1.7 (p = .054), Cl phosphate: ×1.5 (p = .158), Cl potassium: ×1.6 (p = .011); daytime system: Cl creatinine: ×2.7 (p = .040), Cl phosphate: ×2.2 (p = .039)). Sorbent-assisted peritoneal dialysis treatment in a uremic pig model is safe and enhances small solute clearance as compared to a static dwell. Future studies in humans or animal species with higher peritoneal transport should elucidate whether our SAPD system enhances clearance to a clinically relevant extent as compared to conventional PD.