Dialysate sodium, serum sodium and mortality in maintenance hemodialysis

Abstract

Background: Individuals with end-stage kidney disease appear to have stable pre-dialysis serum sodium concentrations over time, with lower values associating with increased mortality. Dialysate sodium concentrations have increased over many years in response to shorter treatments, but the relationship between serum sodium, dialysate sodium and outcomes in chronic hemodialysis patients has not yet been systematically examined.

Methods: We studied a cohort of 2272 individuals receiving thrice-weekly hemodialysis treatment. Available data included demographics, laboratory and clinical measures, details of the dialysis prescription and 30-month follow-up. We examined the distribution of serum and dialysate sodium among subjects and compared mortality according to dialysate and serum sodium concentrations using Cox regression models.

Results: Dialysate sodium concentration varied within and among dialysis centers. The pre-dialysis serum sodium concentration (mean 136.1 mmol/L) did not differ across dialysate sodium concentrations. There was evidence for effect modification for mortality according to differing serum sodium and dialysate sodium concentrations (P=0.05). For each 4 mmol/L increment in serum sodium, the hazard ratio for death was 0.72 [95% confidence interval (CI) 0.63-0.81] with lower dialysate sodium compared to 0.86 (95% CI 0.75-0.99) for higher dialysate sodium. Higher dialysate sodium concentration was associated with mortality at higher, but not lower, pre-dialysis serum sodium concentrations.

Conclusions: The pre-dialysis serum sodium concentration appears to be unaffected by the dialysate sodium concentration. The relationship between serum and dialysate sodium and mortality appears to be variable. Further research is warranted to determine the biological mechanisms of these associations and to re-examine total body sodium handling in hemodialysis.

Fig. 1.

Distribution of dialysate sodium concentrations according to dialysis center.

Fig. 2.

Distribution of the pre-dialysis serum sodium according to subgroup of dialysate sodium concentration. The plus corresponds to the mean; upper edge corresponds to the upper quartile; middle line corresponds to the median; lower edge corresponds to the lower quartile; upper whisker is the maximum value; lower whisker is the minimum value.

Fig. 3.

Adjusted hazard ratios (log scale) for all-cause mortality associated with pre-dialysis serum sodium [Na] concentration, according to the use of higher (>140 mmol/L or modeling; dashed line) versus lower (≤140 mmol/L; solid line) dialysate sodium concentration. The histogram of the pre-dialysis serum sodium concentration is shown in the background. Adjusted effect estimates were stratified on clinical center and adjusted for sex, race (black versus non-black), age, diabetes, CHF status, vintage (<12, 12–24, 24–48, >48 months), albumin, hemoglobin, phosphorus and Kt/V; two-way time interaction terms were included for albumin and hemoglobin due to non-proportional hazards.

Fig. 4.

Adjusted hazard ratios (log scale) for all-cause mortality associated with higher (>140 mmol/L or modeling; gray bars) versus lower (≤140 mmol/L: reference; black bars) dialysate sodium concentration evaluated at varying pre-dialysis serum sodium concentrations. Adjusted effect estimates were stratified on clinical center and adjusted for sex, race (black versus non-black), age, diabetes, CHF status, vintage (<12, 12–24, 24–48, >48 months), albumin, hemoglobin, phosphorus and Kt/V; two-way time interaction terms were included for albumin and hemoglobin due to non-proportional hazards.