A regenerable potassium and phosphate sorbent system to enhance dialysis efficacy and device portability: an in vitro study

Background. Continuous dialysis could provide benefit by constant removal of potassium and phosphate. This study investigates the suitability of specific potassium and phosphate sorbents for incorporation in an extracorporeal device by capacity and regenerability testing. Methods. Capacity testing was performed in uraemic plasma. Regenerability was tested for potassium sorbents, with adsorption based on cationic exchange for sodium, with 0.1 M and 1.0 M NaCl. To regenerate phosphate sorbents, with adsorption based on anionic exchange, 0.1 M and 1.0 M NaHCO3 and NaOH were used. Subsequently, sodium polystyrene divinylbenzene sulphonate (RES-A) and iron oxide hydroxide (FeOOH) beads were incorporated in a cartridge for testing in bovine blood using a recirculating blood circuit and a dialysis circuit separated by a high-flux dialyzer (dynamic setup). Pre-loading was tested to assess whether this could limit calcium and magnesium adsorption. Results. In the batch-binding assays, zirconium phosphate most potently adsorbed potassium (0.44 +/- 0.05 mmol/g) and RES-A was the best regenerable potassium sorbent (92.9 +/- 5.7% with 0.1 M NaCl). Zirconium oxide hydroxide (ZIR-hydr) most potently adsorbed phosphate (0.23 +/- 0.05 mmol/g) and the polymeric amine sevelamer carbonate was the best regenerable sorbent (85.7 +/- 5.2% with 0.1 M NaHCO3). In the dynamic setup, a potassium adsorption of 10.72 +/- 2.06 mmol in 3 h was achieved using 111 g of RES-A and a phosphate adsorption of 4.73 +/- 0.53 mmol in 3 h using 55 g of FeOOH. Calcium and magnesium preloading was shown to reduce the net adsorption in 3 h from 3.57 +/- 0.91 to -0.29 +/- 1.85 and 1.02 +/- 0.05 to -0.31 +/- 0.18 mmol, respectively. Conclusion. RES-A and FeOOH are suitable, regenerizable sorbents for potassium and phosphate removal in dialysate regeneration. Use of zirconium carbonate and ZIR-hydr may further increase phosphate adsorption, but may compromise sorbent regenerability. Use of polymeric amines for phosphate adsorption may enhance sorbent regenerability. Calcium and magnesium preloading considerably reduced net adsorption of these ions.