Change in plasma electrolyte concentrations during hemodialysis following a controlled step-up in dialysate bicarbonate concentration.

Background: The concentration of bicarbonate in dialysis fluid (Dbic) that regulates acid-base balance in dialyzed patients is individually adjusted and may be modified during a hemodialysis session. We evaluated the impact of modifications of Dbic on plasma electrolytes.

Methods: Two midweek hemodialysis sessions were monitored in 25 anuric, prevalent hemodialysis patients (67.9 ± 9.3 years old, 32% females). During the first session (treatment A) Dbic was constant at 33.6 ± 1.7 mmol/L, while for the second week (treatment B) it was on average 30.8 ± 2.3 mmol/L for the initial 2 h and 34.0 ± 2.5 mmol/L for the last 2 h.

Results: During treatments A and B plasma bicarbonate (Pbic) increased during the sessions and was lower for treatment B than A at 60 and 120 min of dialysis. Plasma chloride decreased during treatments A and B and was significantly higher at 60 and 120 min of dialysis in treatment B than in treatment A. An increase of plasma calcium was observed during both treatments and it was higher for treatment B than A at 60 and 120 min. A similar profile of plasma sodium and potassium was observed during treatments A and B. The difference in Pbic correlated positively, whereas the differences in plasma chloride and calcium correlated negatively, with the difference in Dbic between treatments B and A.

Conclusion: Modifications of dialysate bicarbonate may influence the concentrations of some other electrolytes in plasma; for each percent of Dbic increase one may expect -0.27 and -0.16% change in plasma chloride and calcium, respectively.