Dialysate Sodium

Hemodialysis is a lifesaving therapy, but it carries inherent risks. Increasing attention has focused on long-term complications, including vascular calcification, hemodynamic instability, and progressive endothelial injury. The vascular lumen is coated with the glycocalyx, a thin negatively charged mesh that maintains vascular integrity and fluid balance.1 Composed of proteoglycans, glycosaminoglycans, and glycoproteins, it regulates shear stress, nitric oxide release, permeability, and leukocyte adhesion.2 Its disruption precipitates inflammation, oxidative stress, and microvascular leak.1,2 Syndecan-1, a core proteoglycan of the glycocalyx, is shed into circulation when the glycocalyx is injured and elevated plasma syndecan-1 has been associated with worse outcomes in sepsis, trauma, ischemia-reperfusion, and cardiac surgery.3,4 In hemodialysis, repetitive glycocalyx degradation may accumulate over thousands of treatment hours, contributing to the excess cardiovascular morbidity and mortality seen in this population.5 The glycocalyx is vulnerable to hemodynamic and oncotic shifts, and its disruption during hemodialysis may link microvascular damage to long-term cardiovascular outcomes.5,6 Based on this concept, Hur et al. evaluated the effects of dialysate sodium concentration on endothelial injury and microcirculatory dysfunction in hemodialysis.7 Dialysate sodium prescription has been debated for decades. Higher sodium baths (≥145 mmol/L) are often used to minimize intradialytic hypotension, cramps, and disequilibrium by blunting osmotic shifts.8 Yet this comfort comes at a cost: increased thirst, interdialytic weight gain, and adverse cardiovascular outcomes. Similarly, lower serum sodium (<135 mmol/L) with higher sodium baths predispose chronic hemodialysis patients to increased mortality.9 This clinical conundrum has prompted strategies such as sodium modeling, in which dialysate concentrations are adjusted dynamically during hemodialysis to balance fluid and hemodynamic stability.10 However, the underlying vascular biology has remained underexplored. Hur et al. provide mechanistic evidence that sodium exposure is not merely a driver of hemodynamic shifts, but a determinant of endothelial integrity. In this issue of Kidney360, Hur et al. advance our understanding of microvascular injury during hemodialysis by using a preclinical study interrogating the role of dialysate sodium concentration in modulating glycocalyx injury and microcirculatory dysfunction. Using a small-animal hemodialysis model in healthy Wistar-Kyoto rats, the investigators exposed animals to three different dialysate sodium concentrations: low (130 mmol/L), control (140 mmol/L), and high (150 mmol/L). Through intravital microscopy, they tracked microvascular perfusion across multiple time points; baseline, sham circulation, 1-hour hemodialysis, 2-hour hemodialysis, and posthemodialysis, while simultaneously measuring syndecan-1, a biochemical marker of glycocalyx damage. The authors show that higher concentrations of sodium in the dialysate lead to decreased microcirculation and increased serum levels of syndecan-1. Their results showed that all groups demonstrated a progressive rise in syndecan-1 and a trend toward reduced perfusion, but the high-sodium group exhibited the greatest degree of endothelial injury, significantly elevated syndecan-1 at 2 hours and a marked decline in microvascular perfusion. Taken together, these findings suggest that high sodium dialysate concentration directly affects the glycocalyx and cause vascular injury that disrupts organ perfusion (Figure 1). Their findings bridge the translation gap to underscore a fundamental principle: the prescription of dialysate sodium is not merely a technical adjustment, but may induce direct injury to the endothelial glycocalyx and perpetuate vascular disease. This study highlights the need for a more personalized approach to sodium concentrations in dialysis patients.Figure 1: The effect of high sodium dialysate on the endothelial glycocalyx and systemic hemodynamics.These implications extend well beyond the laboratory. First, the study challenges the view that dialysate sodium is simply a stabilizer. While high sodium baths may improve intradialytic tolerance, they may do so at the hidden cost of endothelial injury and long-term cardiovascular harm. Second, it raises the possibility of biomarker-guided sodium personalization. If glycocalyx integrity could be monitored in real time (e.g., syndecan-1), clinicians might tailor sodium prescriptions to balance vascular protection and hemodynamic needs. Such precision dialysis could move beyond the current one-size-fits-all approach. Third, it highlights the importance of microcirculatory health in dialysis patients. Conventional adequacy metrics such as Kt/V and urea reduction ratio capture solute kinetics, but not vascular consequences. Microcirculatory dysfunction may explain why adequate dialysis by urea clearance still leaves patients at unacceptably high cardiovascular risk. Finally, the study illustrates how robust preclinical models can shape clinical perspectives by revealing mechanisms invisible at the bedside. We must recognize that there are important limitations to this study. The presented studies were performed in a rodent model with acute exposure to hemodialysis and supraphysiological dialysate sodium concentrations. Thus, comorbid conditions and complications associated with long-term hemodialysis treatments in human ESKD were not addressed. These common comorbidities found in ESKD include uremia, diabetes, hypertension, chronic inflammation, and vascular calcification. In addition, the authors do not account for contributions of dialysate electrolytes outside of sodium such as potassium, bicarbonate, and calcium concentrations. The 1-hour sham bypass period in which the animal's blood was recirculated, but not dialyzed, could lead to cytokine release and a proinflammatory state priming endothelial damage even before the initiation of the dialysis phase. Furthermore, all three study groups experienced significant drops in mean arterial pressure, bringing into question the contribution of intradialytic hypotension to endothelial damage and reduced microcirculation as a cofounding factor in this model. While the observed changes in syndecan-1 and microvascular perfusion are biologically compelling, translation to human treatment requires validation and further studies. Some of the critical questions remain unanswered. Is the higher dialysate sodium concentration leading to glycocalyx shedding linked to adverse outcomes such as cardiovascular compromise, arrhythmia, or high mortality? Can sodium-lowering strategies reduce these risks without precipitating hemodynamic instability? Does higher dialysate sodium interfere with the maturation and long-term patency of arteriovenous access (fistula or graft)? Moreover, because extremes of sodium prescription are not typically employed in clinical practice, are the observed effects on glycocalyx degradation progressive and linear with incremental sodium exposure or are they threshold dependent? Does predialysis sodium, by determining the transdialytic sodium gradient, influence this relationship? Finally, how does the uremic milieu modify these interactions and their clinical consequences? Future research could validate these findings in humans through serum biomarkers (e.g., syndecan-1) and noninvasive imaging modalities (e.g., microcirculatory assessments) to identify vulnerable patient populations at higher risk of cardiovascular disease. Such human validation could then serve as a foundation for clinical trials testing both dialysate sodium manipulation and pharmacologic strategies to preserve or restore the endothelial glycocalyx (Figure 1). Although several randomized controlled trials have demonstrated that lower dialysate sodium can mitigate adverse cardiovascular outcomes, these studies have largely emphasized on symptomatic improvements by tracking conventional clinical markers such as left ventricular size, BP control, and volume management.11 What remains lacking, however, are trials incorporating a biomarker-driven approach to assess the mechanistic effects of lowering dialysate sodium on cardiovascular outcomes. This study represents an important advancement in our understanding of how dialysis prescriptions intersect with vascular pathophysiology and provides a mechanistic rationale for re-examining sodium prescription practices. Importantly, it opens avenues for biomarker-integrated clinical trials that may refine sodium prescription strategies and advance cardiovascular risk reduction in dialysis populations. For researchers, the work highlights new opportunities to explore glycocalyx-targeted therapies and biomarker-guided precision dialysis, while for clinicians, the message is clear: dialysate sodium is more than a dial-setting, it is a biologically active determinant of vascular health with long-term implications for patient outcomes.