Effect of Dialysate and Plasma Sodium on Mortality in a Global Historical Hemodialysis Cohort

Abstract

Significance statement: This large observational cohort study aimed to investigate the relationship between dialysate and plasma sodium concentrations and mortality among maintenance hemodialysis patients. Using a large multinational cohort of 68,196 patients, we found that lower dialysate sodium concentrations (≤138 mmol/L) were independently associated with higher mortality compared with higher dialysate sodium concentrations (>138 mmol/L). The risk of death was lower among patients exposed to higher dialysate sodium concentrations, regardless of plasma sodium levels. These results challenge the prevailing assumption that lower dialysate sodium concentrations improve outcomes in hemodialysis patients. The study confirms that until robust evidence from randomized trials that are underway is available, nephrologists should remain cautious in reconsideration of dialysate sodium prescribing practices to optimize cardiovascular outcomes and reduce mortality in this population.

Background: Excess mortality in hemodialysis (HD) patients is largely due to cardiovascular disease and is associated with abnormal fluid status and plasma sodium concentrations. Ultrafiltration facilitates the removal of fluid and sodium, whereas diffusive exchange of sodium plays a pivotal role in sodium removal and tonicity adjustment. Lower dialysate sodium may increase sodium removal at the expense of hypotonicity, reduced blood volume refilling, and intradialytic hypotension risk. Higher dialysate sodium preserves blood volume and hemodynamic stability but reduces sodium removal. In this retrospective cohort, we aimed to assess whether prescribing a dialysate sodium ≤138 mmol/L has an effect on survival outcomes compared with dialysate sodium >138 mmol/L after adjusting for plasma sodium concentration.

Methods: The study population included incident HD patients from 875 Fresenius Medical Care Nephrocare clinics in 25 countries between 2010 and 2019. Baseline dialysate sodium (≤138 or >138 mmol/L) and plasma sodium (<135, 135-142, >142 mmol/L) concentrations defined exposure status. We used multivariable Cox regression model stratified by country to model the association between time-varying dialysate and plasma sodium exposure and all-cause mortality, adjusted for demographic and treatment variables, including bioimpedance measures of fluid status.

Results: In 2,123,957 patient-months from 68,196 incident HD patients with on average three HD sessions per week dialysate sodium of 138 mmol/L was prescribed in 63.2%, 139 mmol/L in 15.8%, 140 mmol/L in 20.7%, and other concentrations in 0.4% of patients. Most clinical centers (78.6%) used a standardized concentration. During a median follow-up of 40 months, one third of patients ( n =21,644) died. Dialysate sodium ≤138 mmol/L was associated with higher mortality (multivariate hazard ratio for the total population (1.57, 95% confidence interval, 1.25 to 1.98), adjusted for plasma sodium concentrations and other confounding variables. Subgroup analysis did not show any evidence of effect modification by plasma sodium concentrations or other patient-specific variables.

Conclusions: These observational findings stress the need for randomized evidence to reliably define optimal standard dialysate sodium prescribing practices.

Graphical abstract

Figure 1

Mortality risk association of dialysate sodium concentration (≤138> mmol/l) in hyponatremia, isonatremia, and hypernatremia. Hazard ratios (HR) along y-axis are shown with 95% confidence intervals (95% CI, Whisker) in relation to the reference category with the lowest risk estimates. Hazard ratios in red: dialysate sodium ≤138 mmol/L; Hazard ratios in blue: dialysate sodium >138 mmol/L. X-axis categorized in hyponatremia (plasma sodium <135 mmol/L), isonatremia (plasma sodium=135–142 mmol/L), and hypernatremia (plasma sodium >142 mmol/L).^– Estimates are adjusted for age, sex, body mass index, ethnicity, and concomitant diseases (diabetes mellitus, liver disease, chronic heart failure, cardiovascular disease, cancer, dementia, connective tissue disease, chronic lung disease, serum creatinine, leukocytes, ferritin, hemoglobin, vascular access, and Kt/V [dialysis efficacy]).

Figure 2

Forest plot showing the effect of low dialysate sodium (≤138 mmol/L) in different strata of the study population. HD, hemodialysis. HD, hemodialysis. Figure 2 can be viewed in color online at www.jasn.org.