The demonstration of an individual osmolar setpoint in hemodialysis (HD) is crucial to individualize dialysate sodium concentration. Furthermore, the diffusive gradient between plasma and dialysate sodium is important in the “fine tuning” of intradialytic sodium mass balance (MB).


The design of the study includes A: retrospective analysis of pre-dialysis plasma sodium concentrations extracted from a 6-year database in our HD population (147 prevalent Caucasian anuric patients) (Table); B: intradialytic sodium kinetics in 48 patients, undergoing one 4-hour bicarbonate HD session (Table). Direct potentiometry with an ion-selective electrode was used for sodium measurements.


Study A: the mean number of plasma sodium measurements per patient was 16.06 + 14.03 in a mean follow-up of 3.55 + 1.76 years. The averaged pre-dialysis plasma sodium levels of 147 HD patients were normally distributed (Table; Figure 2). The mean of the averaged plasma sodium concentrations was 136.7 + 2.1 mmol/L with a low mean intraindividual coefficient of variation (1.39 + 0.4) (Table; Figure 3).

Study B: mean pre- and post-dialysis plasma sodium concentrations were 135.8 + 0.9 and 138.0 + 0.9 mmol/L (P < 0.001) (Table; Figure 4). Mean inlet dialyzer sodium concentration was 138.7 + 1.1 mmol/L; The hourly diffusion concentration gradients showed a statistically significant transfer from dialysate to plasma (Wilks λ < 0.0001) (Figure 5). A statistically significant relationship was found between sodium MBs and diffusion gradients (Fig. 6A, P < 0.02) and between sodium MBs and ultrafiltration volume (Fig. 6B, P < 0.01).


The existence of a relatively “fixed” and individual osmolar setpoint in HD patients is shown for the first time in the long-term follow-up. A dialysate sodium concentration of 140 mmol/L determines a dialysate to plasma sodium gradient in the setting of our patients.