Removal of Uremic Solutes from Dialysate by Activated Carbon

Abstract

Background and objectivesAdsorption 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, & measurementsGraded 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.ResultsActivated 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.ConclusionsActivated 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.

Increasing the Clearance of Protein-Bound Solutes by Recirculating Dialysate through Activated Carbon

“…Subsequent experimental studies showed that the effect of increasing the dialysate flow can be replicated by adding a powdered sorbent to the dialysate stream or introducing a sorbent into the dialysate stream between two dialyzers. 9,22,23 This study explored a potentially superior means to increase the bound solute clearances by use of a sorbent. A sorbent introduced into a recirculating system can provide high effective dialysate flows without increasing water use.…”

“…Subsequent experimental studies showed that the effect of increasing the dialysate flow can be replicated by adding a powdered sorbent to the dialysate stream or introducing a sorbent into the dialysate stream between two dialyzers. 9,22,23…”

Novel Approaches for the Removal of Uremic Solutes

“…Mechanisms to recycle or regenerate a smaller pool of dialysate are of increasing interest, and sorbent technology utilizing activated carbon is a prominent area of focus. Lee et al (5) now show us the effect that such technology can have on the metabolome as well.…”

“…In this issue of CJASN , Lee et al . (5) expand our knowledge of the armamentarium to reduce various uremic solutes, particularly protein-bound ones, by focusing on dialysate. When solute concentrations in dialysate reach plasma-free concentrations (typically low for protein-bound substances), further removal of that solute down its concentration gradient is hindered.…”

“…Lee et al . (5) took great efforts and succeeded in adding important incremental knowledge to this field while further highlighting how daunting the task of genuinely creating “kidney replacement” through dialysis can be.…”