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

Abstract

Background 

Conventional hemodialysis provides limited clearance of uremic solutes that bind to plasma proteins. No studies however have tested testing whether increasing the clearance of bound solutes provides clinical benefit. Practical means to increase the dialytic clearance of bound solutes are required to perform such studies.

Methods 

Artificial plasma was dialyzed using two dialysis systems in series. In the first recirculating system a fixed small volume of dialysate flowed rapidly through an activated carbon block before passing through two large dialyzers. In a second conventional system a lower flow of fresh dialysate was passed through a single dialyzer. Chemical measurements tested the ability of the recirculating system to increase the clearance of selected solutes. Mathematical modeling predicted the dependence of solute clearances on the extent to which solutes were taken up by the carbon block and were bound to plasma proteins.

Results 

By itself, the conventional system provided clearances of the tightly bound solutes p-cresol sulfate (PCS) and indoxyl sulfate (IS) of only 18±10 and 19±11 ml/min, respectively (mean±sd). Because these solutes were effectively adsorbed by the carbon block, the recirculating system by itself provided PCS and IS clearances of 45±11 and 53±16 ml/min. It further raised their clearances to 54±12 ml/min and 61±17 ml/min when operating in series with the conventional system (p < 0.002 vs conventional clearance both solutes). Modeling predicted that the recirculating system would increase the clearances of bound solute even if their uptake by the carbon block was incomplete.

Conclusions 

When added to a conventional dialysis system, a recirculating system employing a carbon block sorbent, a single pump, and standard dialyzers can greatly increase the clearance of protein-bound uremic solutes.