Effect of dialysate sodium concentration on interdialytic increase of potassium

Abstract

To evaluate the role of plasma tonicity in the postdialysis increment of plasma potassium (p[K+]), the outcome of two hemodiafiltration treatments that differed only in the Na+ level in dialysate (Na(D) - 143 mmol/L (high dialysate sodium concentration [H-Na(D)]) and 138 mmol/L (low dialysate sodium concentration [L-Na(D)]) - were compared in the same group of uremic patients from the end of treatment (T0) to the subsequent 30 to 120 min and up to 68 h. Kt/V and intradialytic K+ removal were comparable. At T0, plasma [Na+] was 145 ± 1 and 137 ± 1 mmol/L after H-Na(D) and L-Na(D), respectively (P < 0.001). The difference in plasma tonicity persisted from T0 to T68 h. At T120, p[K+] was increased from the T0 value of 3.7 ± 0.2 to 4.7 ± 0.2 mmol/L (P < 0.05) after H-Na(D), whereas it was unchanged after L-Na(D). The change of p[K+] was still different after 68 h (+76 ± 10% and +50 ± 7% in H-Na(D) and L-Na(D), respectively; P < 0.05). Of note, in the first 2 h after the end of treatment, bioimpedance analysis revealed only in H-Na(D) a significant 11 ± 3% decrement of phase angle that is compatible with a decrease of intracellular fluid volume at the expense of the extracellular volume. Similarly, within the same time frame, in H-Na(D), a significant reduction of mean corpuscular volume of red cells, associated with a 2 ± 1% decrease of the intracellular [K+], was observed. In contrast, mean corpuscular volume of red cells did not change and erythrocyte [K+] increased by 6 ± 1% after L-Na(D) (P < 0.005 versus H-Na(D)). Thus, hypertonicity significantly contributes to the increase of p[K+] throughout the whole interdialytic period by determining intracellular fluid volume/extracellular volume redistribution of water and K+.