Altering plasma sodium concentration rapidly changes blood pressure during haemodialysis

Sodium Management in Kidney Disease: Old Stories, New Tricks

Excessive dietary sodium intake is associated with an increased risk of hypertension, especially in the setting of chronic kidney disease (CKD). Although implementation of a low-sodium diet in patients with CKD generally is recommended, data supporting the efficacy of this practice is mostly opinion-based. Few controlled studies have investigated the specific association of dietary sodium intake and cardiovascular events and mortality in CKD. Furthermore, in epidemiologic studies, the association of sodium intake with CKD progression, cardiovascular risk, and mortality is not homogeneous, and both low- and high-sodium intake has been associated with adverse health outcomes in different studies. In general, the adverse effects of high dietary sodium intake are more apparent in the setting of advanced CKD. However, there is no established definitive target level of dietary sodium intake in different CKD stages based on glomerular filtration rate and albuminuria/proteinuria. This review discusses the current challenges regarding the rationale of sodium restriction, target levels and assessment of sodium intake, and interventions for sodium restrictions in CKD in relation to clinical outcomes.

Impact of dialysate sodium concentration on vascular refilling

BACKGROUND

Although relationship between dialysate sodium concentration and hemodynamic stability has been well studied over the years, outcomes of absolute blood volume (ABV) maintenance and vascular refilling volume (V_ref ) modifications were not included, as its analysis has not been easily accessible to direct investigation. However, recent studies report a simple and feasible methodology to assess ABV and V_ref during hemodialysis (HD) treatments. It is the aim of this study to analyze whether sodium concentration in dialysate modifies ABV drop and V_ref .

METHODS

The study was performed in 19 patients under HD. During three different sessions, sodium concentration in dialysate was randomized to three different profiles: low sodium concentration (LNa, 138 mEq/L), neutral sodium concentration (NNa, 140 mEq/L), and high sodium concentration (HNa, 143 mEq/L). ABV and V_ref were calculated using Kron et al methodology.

RESULTS

Predialysis values of the measured parameters showed similar results for the three profiles. Sodium concentration showed an effect on ABV drop, V_ref, and vascular refilling fraction (F_ref ). Pair-wise comparison revealed mean ABV decreased 0.21 L less when using HNa profile versus LNa profile (p = 0.027), a mean V_ref increase of 0.39 L (p = 0.038), and a mean F_ref increase of 9.94% (p = 0.048).

CONCLUSIONS

This study shows that the use of HNa profiles increases V_ref and F_ref and reduces ABV drop during dialysis treatments when compared to LNa profiles.

Serum sodium variation is a major determinant of peridialytic blood pressure trends in haemodialysis outpatients

Intradialytic hypotension (IDH) and peridialytic blood pressure (BP) trends are associated with morbidity and mortality in haemodialysis (HD) patients. We aimed to characterise the respective influence of volume status and small solutes variation on peridialytic systolic BP (SBP) trends during HD. We retrospectively analysed the relative peridialytic SBP decrease in 647 prevalent outpatients attending for their mid-week session with corresponding pre- and post-HD bioelectrical impedance analysis. Mean SBP decreased by 10.5 ± 23.6 mmHg. Factors positively associated with the relative decrease in SBP were: serum sodium (Na) decrease, body mass index, serum albumin, dialysis vintage, ultrafiltration rate and urea Kt/V (p < 0.05 for all). Antihypertensive medications and higher dialysate calcium were negatively associated with the relative decrease in SBP (p < 0.05 for both). Age had a quadratic relationship with SBP trends (p < 0.05). Pre-HD volume status measured by extracellular to total body water ratio was not associated with SBP variation (p = 0.216). Peridialytic SBP trends represent a continuum with serum Na variation being a major determinant while volume status has negligible influence. Middle-aged and overweight patients are particularly prone to SBP decline. Tailoring Na and calcium dialysate concentrations could influence haemodynamic stability during HD and improve patient experience and outcomes.

Effect of Low-Sodium versus Conventional Sodium Dialysate on Left Ventricular Mass in Home and Self-Care Satellite Facility Hemodialysis Patients: A Randomized Clinical Trial

BACKGROUND

Fluid overload in patients undergoing hemodialysis contributes to cardiovascular morbidity and mortality. There is a global trend to lower dialysate sodium with the goal of reducing fluid overload.

METHODS

To investigate whether lower dialysate sodium during hemodialysis reduces left ventricular mass, we conducted a randomized trial in which patients received either low-sodium dialysate (135 mM) or conventional dialysate (140 mM) for 12 months. We included participants who were aged >18 years old, had a predialysis serum sodium ≥135 mM, and were receiving hemodialysis at home or a self-care satellite facility. Exclusion criteria included hemodialysis frequency >3.5 times per week and use of sodium profiling or hemodiafiltration. The main outcome was left ventricular mass index by cardiac magnetic resonance imaging.

RESULTS

The 99 participants had a median age of 51 years old; 67 were men, 31 had diabetes mellitus, and 59 had left ventricular hypertrophy. Over 12 months of follow-up, relative to control, a dialysate sodium concentration of 135 mmol/L did not change the left ventricular mass index, despite significant reductions at 6 and 12 months in interdialytic weight gain, in extracellular fluid volume, and in plasma B-type natriuretic peptide concentration (ratio of intervention to control). The intervention increased intradialytic hypotension (odds ratio [OR], 7.5; 95% confidence interval [95% CI], 1.1 to 49.8 at 6 months and OR, 3.6; 95% CI, 0.5 to 28.8 at 12 months). Five participants in the intervention arm could not complete the trial because of hypotension. We found no effect on health-related quality of life measures, perceived thirst or xerostomia, or dietary sodium intake.

CONCLUSIONS

Dialysate sodium of 135 mmol/L did not reduce left ventricular mass relative to control, despite improving fluid status.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

The Australian New Zealand Clinical Trials Registry, ACTRN12611000975998.

Uncertainties in BP management in dialysis patients

Hypertension in dialysis patients is extremely common. In this article, we review the current evidence for blood pressure (BP) goals in hemodialysis patients, and consider the effectiveness of interventions by which BP may be lowered, including manipulation of dietary and dialysate sodium; optimization of extracellular water; prolongation of dialysis time; and antihypertensive medication. Although two meta-analyses suggest lowering BP using antihypertensive drugs might be beneficial in reducing cardiovascular events and mortality, there are insufficient rigorously designed trials in hypertensive hemodialysis populations to determine preferred antihypertensive drug classes. We suggest aiming for predialysis systolic BP between 130 and 159 mm Hg, while at the same time acknowledge the significant limitations of the data upon which it is based. We conclude by summarizing current knowledge as regards management of hypertension in the peritoneal dialysis population and make recommendations for future research in this field.

Food Products That May Cause an Increase in Blood Pressure

PURPOSE OF REVIEW

To review latest reports of the food products which might increase blood pressure and therefore might participate in the pathogenesis of hypertension.

RECENT FINDINGS

Results of clinical study suggest that consumption of high-sodium food leads to transient increase in plasma sodium concentration. This is accompanied by blood pressure increase. Results of both clinical and experimental studies suggest direct vasculotoxic effects of sodium. Increased plasma sodium concentration could mediate its effects on blood pressure by changes in endothelial cell stiffness and glycocalyx integrity. Energy drinks are non-alcoholic beverages with increasing popularity. Clinical, interventional, randomized, placebo controlled, and cross-sectional studies showed that energy drinks may increase arterial blood pressure. Blood pressure increase after exposure for the energy drinks is mainly related to the caffeine content in these drinks. Many case reports were published concerning the clinically significant increase in blood pressure caused by the consumption of liquorice root or food products containing liquorice, such as candies, tea, Pontefract cookies, and chewing gum. Liquorice contains a precursor of glycyrrhetic acid. Glycyrrhetic acid reduces the activity of the 11β-hydroxysteroid dehydrogenase type 2 (11ß-HSD2) isoenzyme, which leads to activation of the mineralocorticoid receptor by cortisol in the distal convoluted tubule resulting in hypertension, hypokalemia, and metabolic alkalosis. The relationship between chronic alcohol intake and blood pressure is well established on the basis of a diverse body of evidence including animal experiments, epidemiological studies, mendelian randomization studies, and interventional studies. Results of recent studies suggested that binge drinking (i.e., episodic consumption of a very high amount of alcohol beverages) has pronounced hypertensinogenic effects. Recently, it was documented that also low doses of alcohol may increase the risk of cardiovascular complications. Therefore, the amount of alcohol consumption that is safe is zero. High-salt food products, energy drinks, food products containing liquorice, and alcoholic beverages have hypertensinogenic properties. Patients with hypertension and other cardiovascular diseases should avoid even accidental consumption of these food products.

Serum Sodium and Pulse Pressure in SPRINT

BACKGROUND

High dietary sodium intake may induce a small, yet physiologically relevant rise in serum sodium concentration, which associates with increased systolic blood pressure. Cellular data suggest that this association is mediated by increased endothelial cell stiffness. We hypothesized that higher serum sodium levels were associated with greater arterial stiffness in participants in the Systolic Blood Pressure Intervention Trial (SPRINT).

METHODS

Multivariable linear regression was used to examine the association between baseline serum sodium level and (i) pulse pressure (PP; n = 8,813; a surrogate measure of arterial stiffness) and (ii) carotid-femoral pulse wave velocity (CFPWV; n = 591 in an ancillary study to SPRINT).

RESULTS

Baseline mean ± SD age was 68 ± 9 years and serum sodium level was 140 ± 2 mmol/L. In the PP analysis, higher serum sodium was associated with increased baseline PP in the fully adjusted model (tertile 3 [≥141 mmol] vs. tertile 2 [139-140 mmol]; β = 0.87, 95% CI = 0.32 to 1.43). Results were similar in those with and without chronic kidney disease. In the ancillary study, higher baseline serum sodium was not associated with increased baseline CFPWV in the fully adjusted model (β = 0.35, 95% CI = -0.14 to 0.84).

CONCLUSIONS

Among adults at high risk for cardiovascular events but free from diabetes, higher serum sodium was independently associated with baseline arterial stiffness in SPRINT, as measured by PP, but not by CFPWV. These results suggest that high serum sodium may be a marker of risk for increased PP, a surrogate index of arterial stiffness.

Low dialysate sodium levels for chronic haemodialysis

BACKGROUND

Cardiovascular (CV) disease is the leading cause of death in dialysis patients, and strongly associated with fluid overload and hypertension. It is plausible that low dialysate [Na+] may decrease total body sodium content, thereby reducing fluid overload and hypertension, and ultimately reducing CV morbidity and mortality.

OBJECTIVES

This review evaluated harms and benefits of using a low (< 138 mM) dialysate [Na+] for maintenance haemodialysis (HD) patients.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 7 August 2018 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

Randomised controlled trials (RCTs), both parallel and cross-over, of low (< 138 mM) versus neutral (138 to 140 mM) or high (> 140 mM) dialysate [Na+] for maintenance HD patients were included.

DATA COLLECTION AND ANALYSIS

Two investigators independently screened studies for inclusion and extracted data. Statistical analyses were performed using random effects models, and results expressed as risk ratios (RR) for dichotomous outcomes, and mean differences (MD) or standardised MD (SMD) for continuous outcomes, with 95% confidence intervals (CI). Confidence in the evidence was assessed using GRADE.

MAIN RESULTS

We included 12 studies randomising 310 patients, with data available for 266 patients after dropout. All but one study evaluated a fixed concentration of low dialysate [Na+], and one profiled dialysate [Na+]. Three studies were parallel group, and the remaining nine cross-over. Of the latter, only two used a washout between intervention and control periods. Most studies were short-term with a median (interquartile range) follow-up of 3 (3, 8.5) weeks. Two were of a single HD session, and two of a single week's HD. Half of the studies were conducted prior to 2000, and five reported use of obsolete HD practices. Risks of bias in the included studies were often high or unclear, lowering confidence in the results.Compared to neutral or high dialysate [Na+], low dialysate [Na+] had the following effects on "efficacy" endpoints: reduced interdialytic weight gain (10 studies: MD -0.35 kg, 95% CI -0.18 to -0.51; high certainty evidence); probably reduced predialysis mean arterial blood pressure (BP) (4 studies: MD -3.58 mmHg, 95% CI -5.46 to -1.69; moderate certainty evidence); probably reduced postdialysis mean arterial BP (MAP) (4 studies: MD -3.26 mmHg, 95% CI -1.70 to -4.82; moderate certainty evidence); probably reduced predialysis serum [Na+] (7 studies: MD -1.69 mM, 95% CI -2.36 to -1.02; moderate certainty evidence); may have reduced antihypertensive medication (2 studies: SMD -0.67 SD, 95% CI -1.07 to -0.28; low certainty evidence). Compared to neutral or high dialysate [Na+], low dialysate [Na+] had the following effects on "safety" endpoints: probably increased intradialytic hypotension events (9 studies: RR 1.56, 95% 1.17 to 2.07; moderate certainty evidence); probably increased intradialytic cramps (6 studies: RR 1.77, 95% 1.15 to 2.73; moderate certainty evidence).Compared to neutral or high dialysate [Na+], low dialysate [Na+] may make little or no difference to: intradialytic BP (2 studies: MD for systolic BP -3.99 mmHg, 95% CI -17.96 to 9.99; diastolic BP 1.33 mmHg, 95% CI -6.29 to 8.95; low certainty evidence); interdialytic BP (2 studies:, MD for systolic BP 0.17 mmHg, 95% CI -5.42 to 5.08; diastolic BP -2.00 mmHg, 95% CI -4.84 to 0.84; low certainty evidence); dietary salt intake (2 studies: MD -0.21g/d, 95% CI -0.48 to 0.06; low certainty evidence).Due to very low quality of evidence, it is uncertain whether low dialysate [Na+] changed extracellular fluid status, venous tone, arterial vascular resistance, left ventricular mass or volumes, thirst or fatigue. Studies did not examine cardiovascular or all-cause mortality, cardiovascular events, or hospitalisation.

AUTHORS' CONCLUSIONS

It is likely that low dialysate [Na+] reduces intradialytic weight gain and BP, which are effects directionally associated with improved outcomes. However, the intervention probably also increases intradialytic hypotension and reduces serum [Na+], effects that are associated with increased mortality risk. The effect of the intervention on overall patient health and well-being is unknown. Further evidence is needed in the form of longer-term studies in contemporary settings, evaluating end-organ effects in small-scale mechanistic studies using optimal methods, and clinical outcomes in large-scale multicentre RCTs.

Serum sodium concentration and the progression of established chronic kidney disease

Background

Higher serum sodium concentration has been reported to be a risk factor for the development of incident chronic kidney disease (CKD), but its relationship with the progression of established CKD has not been investigated. We hypothesised that increased serum sodium concentration is a risk factor for estimated glomerular filtration rate (eGFR) decline in CKD.

Methods

This was a retrospective cohort study using data collected over a 6-year period, with baseline data obtained during the first 2 years. We included patients known to our renal service who had had a minimum of three blood tests every 2 years and an eGFR of < 60 mL/min/1.73 m² at baseline. Exclusion criteria were renal replacement therapy, diabetes mellitus, heart failure and decompensated liver disease. A multiple linear regression model investigated the relationship between baseline serum sodium and eGFR decline after adjustment for confounding factors.

Results

7418 blood results from 326 patients were included. There was no relationship between serum sodium concentration and estimated glomerular filtration rate at baseline. After multivariable adjustment, a 1 mmol/L increase in baseline serum sodium was associated with a 1.5 mL/min/1.73 m² decline in eGFR during the study period (95% CI 0.9, 2.0). A reduction in eGFR was not associated with significant changes in serum sodium concentration over 6 years.

Conclusion

Higher serum sodium concentration is associated with the progression of CKD, independently of other established risk factors. Conversely, significant alterations in serum sodium concentration do not occur with declining kidney function.

Why does the choice of dialysate sodium concentration remain controversial?

The choice of the ideal dialysate sodium concentration remains controversial. Most dialysis centers have a standard dialysate concentration. In theory, choosing a dialysate sodium concentration lower than serum sodium should result in an additional loss of sodium by diffusion with a reduction in the prevalence of hypertension and interdialytic weight gains (IDWGs) on one hand, but with potential increased risk of intradialytic hypotension and cramps on the other hand, and the opposite effects may accompany the choice of dialysate sodium concentrations greater than serum concentration. Although most studies have reported a reduction in IDWG with lower dialysate sodium concentrations, the effects on blood pressure control, and adverse intradialytic events have been variable. Different outcomes between studies may be partially explained by patient selection, with differences in dietary sodium intake, urinary sodium losses, and sodium stores in the body. In addition, multicenter trials potentially introduce additional confounders, including differences in local quality control of delivered dialysate sodium concentration and sodium measurements. Although there may be advantages for lower dialysate sodium concentration, observational studies have reported a survival advantage for higher dialysate sodium concentrations for those patients with lower serum sodium concentrations pre-dialysis. As there is no current consensus for a universal dialysate sodium concentration, attention has turned to considering an individualized approach to choosing a dialysate sodium concentration.

Comparison of Prescribed and Measured Dialysate Sodium: A Quality Improvement Project

BACKGROUND

There is controversy regarding the optimal dialysate sodium concentration for hemodialysis patients. Dialysate sodium concentrations of 134 to 138 mEq/L may decrease interdialytic weight gain and improve hypertension control, whereas a higher dialysate sodium concentration may offer protection to patients with low serum sodium concentrations and hypotension. We conducted a quality improvement project to explore the hypothesis that prescribed and delivered dialysate sodium concentrations may differ significantly.

STUDY DESIGN

Cross-sectional quality improvement project.

SETTING & PARTICIPANTS

333 hemodialysis treatments in 4 facilities operated by Dialysis Clinic, Inc.

QUALITY IMPROVEMENT PLAN

Measure dialysate sodium to assess the relationships of prescribed and measured dialysate sodium concentrations.

OUTCOMES

Magnitude of differences between prescribed and measured dialysate sodium concentrations.

MEASUREMENTS

Dialysate sodium measured pre- and late dialysis.

RESULTS

The least square mean of the difference between prescribed minus measured dialysate sodium concentration was -2.48 (95% CI, -2.87 to -2.10) mEq/L. Clinics with a greater number of different dialysate sodium prescriptions (clinic 1, n=8; clinic 2, n=7) and that mixed dialysate concentrates on site had greater differences between prescribed and measured dialysate sodium concentrations. Overall, 57% of measured dialysate sodium concentrations were within ±2 mEq/L of the prescribed dialysate sodium concentration. Differences were greater at higher prescribed dialysate sodium concentrations.

LIMITATIONS

We only studied 4 facilities and dialysate delivery machines from 2 manufacturers. Because clinics using premixed dialysate used the same type of machine, we were unable to independently assess the impact of these factors. Pressures in dialysate delivery loops were not measured.

CONCLUSIONS

There were significant differences between prescribed and measured dialysate sodium concentrations. This may have beneficial or deleterious effects on clinical outcomes, as well as confound results from studies assessing the relationships of dialysate sodium concentrations to outcomes. Additional studies are needed to identify factors that contribute to differences between prescribed and measured dialysate sodium concentrations. Quality assurance and performance improvement (QAPI) programs should include measurements of dialysate sodium.

The association of serum sodium and chloride levels with blood pressure and estimated glomerular filtration rate

BACKGROUND

High serum sodium (sNa) concentrations may be associated with hypertension, which deteriorates kidney function. However, it is equivocal whether high sNa concentrations are associated with impaired kidney function independently of blood pressure (BP) or serum chloride (sCl). Therefore, we addressed this issue in an apparently healthy population.

METHODS

Clinical variables including estimated glomerular filtration rate (eGFR) were examined in 3603 men and women (aged 25-75 years) who underwent health-screening check-ups. sNa concentrations were classified into five categories.

RESULTS

Most parameters, including age and BP, increased with increasing sNa, whereas eGFR decreased. Logistic regression analysis showed that, compared with low-normal sNa (≤ 140 mEq/l), high sNa (≥ 144 mEq/l) was significantly associated with elevated BP (≥ 130/85 mmHg) even after adjustment for blood hematocrit, eGFR, serum potassium (sK) concentration and sCl. The highest sNa category was significantly associated with reduced eGFR (< 60 ml/min/1.73 m(2)) independently of elevated BP. Unlike adjustment for sK, adjustment for sCl strengthened the association between high sNa and elevated BP but attenuated the association between high sNa and reduced eGFR.

CONCLUSIONS

These results suggest that high sNa concentrations, even within the normal range, are independently associated with elevated BP and impaired kidney function. These associations may be substantially modified by sCl.

A neglected issue in dialysis practice: haemodialysate

The intended function of dialysate fluid is to correct the composition of uraemic blood to physiologic levels, both by reducing the concentration of uraemic toxins and correcting electrolyte and acid-base abnormalities. This is accomplished principally by formulating a dialysate whose constituent concentrations are set to approximate normal values in the body. Sodium balance is the cornerstone of intradialysis cardiovascular stability and good interdialytic blood pressure control; plasma potassium concentration and its intradialytic kinetics certainly play a role in the genesis of cardiac arrhythmias; calcium is related to haemodynamic stability, mineral bone disease and also cardiac arrhythmias; the role of magnesium is still controversial; lastly, acid buffering by means of base supplementation is one of the major roles of dialysis. In conclusion, learning about the art and the science of fashioning haemodialysates is one of the best ways to further the understanding of the pathophysiologic processes underlying myriad acid-base, fluid, electrolyte as well as blood pressure abnormalities of the uraemic patient on maintenance haemodialysis.

Sodium renders endothelial cells sticky for red blood cells

Negative charges in the glycocalyx of red blood cells (RBC) and vascular endothelial cells (EC) facilitate frictionless blood flow through blood vessels. Na⁺ selectively shields these charges controlling surface electronegativity. The question was addressed whether the ambient Na⁺ concentration controls RBC-EC interaction. Using atomic force microscopy (AFM) adhesion forces between RBC and endothelial glycocalyx were quantified. A single RBC, mounted on an AFM cantilever, was brought in physical contact with the endothelial surface and then pulled off. Adhesion forces were quantified (i) after enzymatic removal of negative charges in the glycocalyx, (ii) under different ambient Na⁺ and (iii) after applying the intracellular aldosterone receptor antagonist spironolactone. Removal of negative surface charges increases RBC-EC interaction forces. A stepwise increase of ambient Na⁺ from 133 to 140 mM does not affect them. However, beyond 140 mM Na⁺ adhesion forces increase sharply (10% increase of adhesion force per 1 mM increase of Na⁺). Spironolactone prevents this response. It is concluded that negative charges reduce adhesion between RBC and EC. Ambient Na⁺ concentration determines the availability of free negative charges. Na⁺ concentrations in the low physiological range (below 140 mM) allow sufficient amounts of vacant negative charges so that adhesion of RBC to the endothelial surface is small. In contrast, Na⁺ in the high physiological range (beyond 140 mM) saturates the remaining negative surface charges thus increasing adhesion. Aldosterone receptor blockade by spironolactone prevents Na⁺ induced RBC adhesion to the endothelial glycocalyx. Extrapolation of in vitro experiments to in vivo conditions leads to the hypothesis that high sodium intake is likely to increase the incidence of thrombotic events.

Salt and sugar: their effects on blood pressure

Both dietary salt and sugar are related to blood pressure (BP). The evidence for salt is much stronger, and various types of studies have consistently shown that salt is a major cause of raised BP, and a reduction from the current intake of ≈ 9-12 g/day in most countries of the world to the recommended level of 5-6 g/day lowers BP in both hypertensive and normotensive individuals, in men and women, in all age groups and in all ethnic groups. Countries such as Finland and the UK that have successfully reduced salt intake have demonstrated a reduction in population BP and cardiovascular mortality, with major cost savings to the health service. The mechanisms whereby salt raises BP are not fully understood. The traditional concepts focus on the tendency for an increase in extracellular fluid volume. Increasing evidence suggests that small increases in plasma sodium may play an important role. There are several other factors that also increase BP, one of which is added sugars. The current high intake of added sugars increases obesity which, in turn, raises BP. Recent studies also suggest that added sugars, particularly those in soft drinks, may have a direct effect on BP. However, the relationship between soft drink consumption and BP could be, at least partially, mediated by the effect of salt intake on increasing soft drink consumption. Actions to reduce salt and sugar intake across the whole population will have major beneficial effects on health along with major cost savings.

The choice of dialysate sodium is influenced by hemodialysis frequency and duration: what should it be and for what modality?

Cardiovascular disease is the leading cause of mortality in hemodialysis patients. A chronic state of volume and pressure overload contributes, and central to this is the net sodium balance over the course of a hemodialysis. Of recent interest is the contribution of the dialysate sodium concentration (Dial-Na+) to clinical outcomes. Abundant evidence confirms that in thrice-weekly conventional hemodialysis, higher Dial-Na+ associates with increased intradialytic weight gain, blood pressure, and cardiovascular morbidity and mortality. On the other hand, low Dial-Na+ associates with intradialytic hypotension in the same patient population. However, the effect of Dial-Na+ in short hours daily hemodialysis (SHD; often referred to as "quotidian" dialysis), or nocturnal dialysis (FHND) is less well studied. Increased frequency and duration of exposure to a diffusive sodium gradient modulate the way in which DPNa+ alters interdialytic weight gain, predialysis blood pressure, and intradialytic change in blood pressure. Furthermore, increased dialysis frequency appears to decrease the predialysis plasma sodium setpoint (SP), which is considered stable in conventional thrice-weekly patients. This review discusses criteria to determine optimal Dial-Na+ in conventional, SHD and FHND patients, and identifies areas for future research.

Dialysate sodium prescription and blood pressure in hemodialysis patients

BACKGROUND

Diffusive sodium removal has been recommended to control hypertension in hemodialysis patients. Recent evidence on hospitalizations and mortality, however, challenged the benefit of lower dialysate sodium prescriptions and ignited a debate in the dialysis community. We therefore studied the relationship between dialysate sodium and blood pressure over the longer term.

METHODS

We used multiply adjusted linear mixed models to estimate the association between dialysate sodium and predialysis systolic blood pressure (SBP) as well as change in SBP (delta SBP; postdialysis minus predialysis) in 23,962 patients from the international Dialysis Outcomes and Practice Patterns Study.

RESULTS

We found that 43% of hemodialysis facilities had variable (individualized) dialysate sodium prescriptions (125-155 mEq/L), whereas 57% had uniform dialysate sodium prescriptions (135-145 mEq/L) for ≥90% patients. Between-group comparisons of these 2 facility types suggested that dialysate sodium, when variably prescribed, might have been used to modify predialysis SBP (P interaction = 0.01) and perhaps delta SBP levels (P interaction = 0.08). Within facilities not prone to indication bias, because dialysate sodium was not variable, higher uniform dialysate sodium (per 2 mEq/L) was associated with slightly higher SBP (+0.9 mm Hg, 95% confidence interval (CI) = 0.1-1.6 among all patients; +1.7 mm Hg, 95% CI = 0.1-3.2 among patients not treated with blood pressure medication) and no increase in delta SBP.

CONCLUSIONS

Patients assigned to hemodialysis facilities with uniformly higher dialysate sodium do not have markedly higher predialysis SBP, providing rather limited support for lowering dialysate sodium to control hypertension, particularly in view of hospitalization and mortality risks associated with lower dialysate sodium.