Sodium Balance in Maintenance Hemodialysis

I Brazilian guideline on hypertension in dialysis of the Brazilian Society of Nephrology

Hypertension in dialysis patients (HTND) has a high prevalence, affecting at least 80% or more of patients, and its management in the nephrology practice is heterogeneous and often empirical. Knowing how to define, understand the pathophysiology, diagnose, monitor and treat with lifestyle changes, and adjust antihypertensive drugs to achieve the recommended blood pressure (BP) target - to reduce morbidity and mortality - requires specific knowl-edge and approaches within the contexts of hemodialysis (HD) and peritoneal dialysis (PD). This document is the first guideline of the Brazilian Society of Nephrology, developed by the departments of Hypertension and Dialysis. It aims to guide physicians who provide care in dialysis centers on how to manage patients with HTND, in a comprehensive and individualized manner, based on the critical appraisal of the best available scientific evidence. When such evidence is scarce or unavailable, the opinion of specialists should be recommended. The different topics covered include HTND definition (pre-HD BP ≥ 140/90 mmHg and post-HD BP ≥ 130/80 mmHg), epidemiology, and pathophysiology; diagnosis of HTND preferably with BP measurements outside the dialysis setting (BP ≥ 130/80 mmHg); complementary assessment; blood pressure targets; non-pharmacological treatment; use of the most appropriate antihypertensive medications; special situations; and complications of HTND, predominantly cardiovascular ones.

Low dialysate sodium levels for chronic haemodialysis

BACKGROUND

Cardiovascular (CV) disease is the leading cause of death in dialysis patients and is strongly associated with fluid overload and hypertension. It is plausible that low dialysate sodium ion concentration [Na+] may decrease total body sodium content, thereby reducing fluid overload and hypertension and ultimately reducing CV morbidity and death. This is an update of a review first published in 2019.

OBJECTIVES

This review evaluated the 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 1 October 2024 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 Registry Platform (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 authors independently screened studies for inclusion and extracted data. Statistical analyses were performed using the random-effects model, 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 Grades of Recommendation, Assessment, Development and Evaluation (GRADE).

MAIN RESULTS

We included 17 studies randomising 509 patients, with data available for 452 patients after dropouts. All but three studies evaluated a fixed concentration of low dialysate [Na+], with one using profiled dialysate [Na+] and two using individualised dialysate [Na+]. Five were parallel group studies, and 12 were cross-over studies. Of the latter, only six used a washout between intervention and control periods. Most studies were short-term with a median (interquartile range) follow-up of 4 (4 to 16) weeks. Two were of a single HD session and two of a single week's HD. Seven studies were conducted prior to 2000, and six reported the use of obsolete HD practices. Other than for indirectness arising from older studies, risks of bias in the included studies were generally low. Compared to neutral or high dialysate [Na+] (≥ 138 mM), low dialysate [Na+] (< 138 mM) reduces interdialytic weight gain (14 studies, 515 participants: MD -0.36 kg, 95% CI -0.50 to -0.22; high certainty evidence) and antihypertensive medication use (5 studies, 241 participants: SMD -0.37, 95% CI -0.64 to -0.1; high certainty evidence), and probably reduces left ventricular mass index (2 studies, 143 participants: MD -7.65 g/m2, 95% CI -14.48 to -0.83; moderate certainty evidence), predialysis mean arterial pressure (MAP) (5 studies, 232 participants: MD -3.39 mm Hg, 95% CI -5.17 to -1.61; moderate certainty evidence), postdialysis MAP (5 studies, 226 participants: MD -3.17 mm Hg, 95% CI -4.68 to 1.67; moderate certainty evidence), predialysis serum [Na+] (11 studies, 435 participants: MD -1.26 mM, 95% CI -1.81 to -0.72; moderate certainty evidence) and postdialysis serum [Na+] (6 studies, 188 participants: MD -3.09 mM, 95% CI -4.29 to -1.88; moderate certainty evidence). Compared to neutral or high dialysate [Na+], low dialysate [Na+] probably increases intradialytic hypotension events (13 studies, 15,764 HD sessions: RR 1.58, 95% 1.25 to 2.01; moderate certainty evidence) and intradialytic cramps (10 studies, 14,559 HD sessions: RR 1.84, 95% 1.29 to 2.64; moderate certainty evidence). Effect size for important outcomes were generally greater with low dialysate [Na+] compared to high compared with neutral dialysate [Na+], although formal hypothesis testing identifies that the difference was only certain for postdialysis serum [Na+]. Compared to neutral or high dialysate [Na+], it is uncertain whether low dialysate [Na+] affects intradialytic or interdialytic MAP, and dietary salt intake. It is also uncertain whether low dialysate [Na+] changed extracellular fluid status, venous tone, arterial vascular resistance, left ventricular volumes, or fatigue. Studies did not examine CV or all-cause death, CV events, or hospitalisation.

AUTHORS' CONCLUSIONS

Low dialysate [Na+] reduces intradialytic weight gain and probably blood pressure, which are effects directionally associated with improved outcomes. However, the intervention probably increases intradialytic hypotension and probably reduces serum [Na+], effects that are associated with an increased risk of death. 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.

Can the response to dialysis treatment be predicted by using patient-specific modeling of fluid and solute exchanges? A multicentric evaluation

BACKGROUND

Parametric multipool kinetic models were used to describe the intradialytic trends of electrolytes, breakdown products, and body fluids volumes during hemodialysis. Therapy customization can be achieved by the identification of parameters, allowing patient-specific modulation of mass and fluid balance across dialyzer, capillary, and cell membranes. This study wants to evaluate the possibility to use this approach to predict the patient's intradialytic response.

METHODS

6 sessions of 68 patients (DialysIS© project) were considered. Data from the first three sessions were used to train the model, identifying the patient-specific parameters, that, together with the treatment settings and the patient's data at the session start, could be used for predicting the patient's specific time course of solutes and fluids along the sessions. Na+ , K+ , Cl- , Ca2+ , HCO3 - , and urea plasmatic concentrations and hematic volume deviations from clinical data were evaluated.

RESULTS

nRMSE predictive error is on average equal to 4.76% when describing the training sessions, and only increases by 0.97 percentage points on average in independent sessions of the same patient.

CONCLUSIONS

The proposed predictive approach represents a first step in the development of tools to support the clinician in tailoring the patient's prescription.

Automated adjustment of dialysate sodium by the hemodialysis monitor: Rationale, implementation, and clinical benefits

Prescribing dialysate sodium is the responsibility of the physician, but there are currently no clear guidelines for this prescription. Furthermore, there is quite frequently a significant difference between prescribed and measured dialysate sodium. Several arguments, both theoretical and experimental, suggest that dialysate sodium should be adjusted individually in such a way as to result in a decreasing sodium profile that takes into account the patient's predialytic natremia. The generalization in clinical routine of this strategy requires the integration into the hemodialysis monitor of software making the machine capable to automatically adjust the dialysate sodium at each session. The only three such softwares that have been integrated into hemodialysis machines for routine clinical use are discussed. All three work with conductivity measurements as a surrogate for sodium concentrations. Although there are only a few publications on the use of these softwares in clinical practice, they appear to result in improved intradialytic tolerance to the dialysis treatment, better control of hypertension, and reduced thirst, leading to decreased interdialytic weight gain.

Salt, Not Always a Cardiovascular Enemy? A Mini-Review and Modern Perspective

Dietary salt intake is a long-debated issue. Increased sodium intake is associated with high blood pressure, leading to salt-sensitive hypertension. Excessive salt intake leads to arterial stiffness in susceptible individuals via impaired nitric oxide action and increased endothelin-1 expression, overactivity of the renal sympathetic nervous system and also via aldosterone-independent activation of the mineralocorticoid receptor. Salt restriction in such individuals reduces blood pressure (BP) values. The optimal level of salt restriction that leads to improved cardiovascular outcomes is still under debate. Current BP and dietary guidelines recommend low sodium intake for the general population. However, a specific category of patients does not develop arterial hypertension in response to sodium loading. In addition, recent research demonstrates the deleterious effects of aggressive sodium restriction, even in heart failure patients. This mini review discusses current literature data regarding the advantages and disadvantages of salt restriction and how it impacts the overall health status.

Tissue Sodium Storage in Patients With Heart Failure: A New Therapeutic Target?

BACKGROUND

Preclinical data suggest sodium deposited (without water) in tissues may lead to aberrant remodeling and systemic inflammation, independently of fluid overload in patients with heart failure (HF). Tissue salt storage can be measured noninvasively and quantitatively with ²³Na-magnetic resonance imaging. We aimed to investigate the possibility that patients with HF complicated by renal dysfunction are subject to higher tissue sodium concentration exposure than patients with chronic kidney disease alone.

METHODS

We conducted an exploratory study including 18 patients with HF, 34 hemodialysis patients (with no meaningful renal clearance of sodium), and 31 patients with chronic kidney disease, with glomerular filtration rate matched to the patients with HF. Every patient underwent ²³Na-magnetic resonance imaging of the calf, to quantify tissue sodium and allow comparison among the 3 patient groups.

RESULTS

There were no differences in age, sex, and body mass index between groups. Median (interquartile range) skin sodium content in HF (31 [23-37] mmol/L) was very high and indistinguishable from skin sodium content in hemodialysis patients (30 [22-35] mmol/L), P=0.6. Patients with HF exhibited significantly higher skin sodium content than matched estimated glomerular filtration rate chronic kidney disease patients (22 [19-26] mmol/L), P=0.005. Median muscle sodium content in patients with HF was significantly higher than in patients with chronic kidney disease, P=0.002. There was no relationship with estimated glomerular filtration rate in patients with HF. We report a significant correlation between skin sodium and urinary sodium (P=0.04) but no correlation with muscle sodium. Patients who were assessed as being volume depleted (sodium excretion fraction <1%) had lower skin sodium content than patients with sodium excretion fraction >1% (P=0.03).

CONCLUSIONS

We have demonstrated that patients with HF characteristically have very high levels of skin sodium storage, comparable to well-characterized extreme levels seen in patients with end-stage kidney disease requiring hemodialysis. ²³Na-magnetic resonance imaging may allow precision medicine in the management of this challenging group of patients with HF. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03004547.

Concentration-Responsive Soft Valve for Osmotic Flow Control

We propose a novel osmotic soft valve consisting of an osmosis membrane and hydrogel films. In our osmotic valve system, material selectivity is determined by the osmosis membrane, and the hydrogel film, which deforms depending on the ion concentration of the surrounding solution, controls the passage area of the membrane. Independently controlling the material selectivity and permeability allowed us to design an osmotic soft valve with an osmotic flow rate that increases with osmotic pressure at low pressures but decreases with osmotic pressure at high pressures. We demonstrate a representative application of our hydrogel valve system in a portable power generator utilizing reverse electrodialysis (RED). As the permeability varied with concentration, the hydrogel valve was able to maintain the electric power of the RED for 30 min with only an ∼10% change. Our study provides techniques to build osmotic soft valves that can serve as gating membranes in various osmosis and dialysis systems.

A new approach to individualize dialysis fluid sodium concentration using a four-stream, bicarbonate-based fluid delivery system

We propose a new 45X, four-stream, triple-concentrate, bicarbonate-based dialysis fluid delivery system, allowing a wide range of dialysis fluid sodium concentrations\\ (DF_Na ) without affecting the concentrations of other crucial solutes. The four streams consist of product water (W), and concentrates with sodium chloride (S), acid (A), and sodium bicarbonate (B). An adjustment in the DF_Na in this new system requires changes only in the W and S concentrate streams. The ingredients in A and B concentrates do not change.

Dyselectrolytemia-management and implications in hemodialysis (Review)

Hemodialysis is a method for the renal replacement therapy followed by series of acute and chronic complications. Dyselectrolytemia appears in patients undergoing dialysis through mechanisms related to the chronic kidney disease and/or to the dialysis therapy and for this group of patients it is associated with an increase of morbidity and mortality. The dialysate has a standard composition, which can be modified according to the patient's characteristics. During hemodialysis patients are exposed to 18,000-36.000 litres of water/year, and the water purity along with the biochemical composition of the dialysate are essential. The individualization of the dialysis prescription is recommended for each patient and it has an important role in preventing the occurrence of dyselectrolyemia. The individualization of the treatment prescription according to the blood constants of each patient is the prerogative of the nephrologist and the association of the electrolyte imbalances with the patients cardiovascular mortality explains the importance of paying special attention to them.

Fluid and hemodynamic management in hemodialysis patients: challenges and opportunities

Fluid volume and hemodynamic management in hemodialysis patients is an essential component of dialysis adequacy. Restoring salt and water homeostasis in hemodialysis patients has been a permanent quest by nephrologists summarized by the ‘dry weight’ probing approach. Although this clinical approach has been associated with benefits on cardiovascular outcome, it is now challenged by recent studies showing that intensity or aggressiveness to remove fluid during intermittent dialysis is associated with cardiovascular stress and potential organ damage. A more precise approach is required to improve cardiovascular outcome in this high-risk population. Fluid status assessment and monitoring rely on four components: clinical assessment, non-invasive instrumental tools (e.g., US, bioimpedance, blood volume monitoring), cardiac biomarkers (e.g. natriuretic peptides), and algorithm and sodium modeling to estimate mass transfer. Optimal management of fluid and sodium imbalance in dialysis patients consist in adjusting salt and fluid removal by dialysis (ultrafiltration, dialysate sodium) and by restricting salt intake and fluid gain between dialysis sessions. Modern technology using biosensors and feedback control tools embarked on dialysis machine, with sophisticated analytics will provide direct handling of sodium and water in a more precise and personalized way. It is envisaged in the near future that these tools will support physician decision making with high potential of improving cardiovascular outcome.

Sodium and water handling during hemodialysis: new pathophysiologic insights and management approaches for improving outcomes in end-stage kidney disease

Space medicine and new technology such as magnetic resonance imaging of tissue sodium stores (²³NaMRI) have changed our understanding of human sodium homeostasis and pathophysiology. It has become evident that body sodium comprises 3 main components. Two compartments have been traditionally recognized, namely one that is circulating and systemically active via its osmotic action, and one slowly exchangeable pool located in the bones. The third, recently described pool represents sodium stored in skin and muscle interstitium, and it is implicated in cell and biologic activities via local hypertonicity and sodium clearance mechanisms. This in-depth review provides a comprehensive view on the pathophysiology and existing knowledge gaps of systemic hemodynamic and tissue sodium accumulation in dialysis patients. Furthermore, we discuss how the combination of novel technologies to quantitate tissue salt accumulation (e.g., ²³NaMRI) with devices to facilitate the precise attainment of a prescribed hemodialytic sodium mass balance (e.g., sodium and water balancing modules) will improve our therapeutic approach to sodium management in dialysis patients. While prospective studies are required, we think that these new diagnostic and sodium balancing tools will enhance our ability to pursue more personalized therapeutic interventions on sodium and water management, with the eventual goal of improving dialysis patient outcomes.

Influence of Hemofiltration on Intradialytic Plasma Volume Decrease

BACKGROUND/AIMS

Compared with hemodialysis (HD), hemodiafiltration (HDF) reduces the frequency of episodes of intradialytic hypotension. Intradialytic plasma volume decrease (IPVD) induced by ultrafiltration is a leading cause of the episodes, and hemofiltration might have a preventive effect on IPVD. This study examined whether online HDF (ol-HDF) prevented IPVD compared with HD.

METHODS

Online HDF of pre-dilution mode (pre-ol-HDF) and post-dilution mode (post-ol-HDF) and HD were performed in 22 patients on maintenance dialysis. In each session, IPVD was calculated by using an intradialytic change in hematocrit, and IPVD in pre-ol-HDF and post-ol-HDF was compared with that in HD in a crossover manner.

RESULTS

While the ratios of intradialytic body weight loss to post-dialysis BW (IBWL/BW) in ol-HDF were generally smaller than those in HD, the levels of IPVD and IPVD/IBWL/BW were generally larger than those in HD; the IPVD levels were 0.108 ± 0.058, 0.113 ± 0.053, and 0.101 ± 0.057 (P = 0.67), and those of IPVD/IWL/BW were 2.21 ± 0.97, 2.32 ± 0.91, and 1.98 ± 1.14 (P = 0.21) in pre-ol-HDF, post-ol-HDF, and HD, respectively.

CONCLUSION

Online mode hemofiltration, in either pre-dilution mode or post-dilution mode, performed in combination with hemodialysis has no preventive effect on IPVD.

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.

[The different modalities of isonatric hemodialysis]

Setting dialysate sodium allows to adequately adjust sodium balance and plasma sodium at the end of dialysis session. In accordance with the set-point theory based on the concept of restoring cellular hydration, an adequate target for plasma sodium at the end of the session could be the value of predialysis plasma sodium concentration (isonatric hemodialysis). Some recently available dialysis monitors provide an on-line value of plasma-water conductivity usually converted in on-line natremia. There are different modalities of isonatric hemodialysis depending on whether the online value of natremia is used or not. By reviewing the few studies concerning the isonatric hemodialysis, it seems logical to set a target of postdialysis on-line natremia (or plasma-water conductivity) slightly lower than its predialysis value. However this strategy requires specifically designed software not yet available in clinical routine.

A Bayesian approach for the identification of patient-specific parameters in a dialysis kinetic model

Hemodialysis is the most common therapy to treat renal insufficiency. However, notwithstanding the recent improvements, hemodialysis is still associated with a non-negligible rate of comorbidities, which could be reduced by customizing the treatment. Many differential compartment models have been developed to describe the mass balance of blood electrolytes and catabolites during hemodialysis, with the goal of improving and controlling hemodialysis sessions. However, these models often refer to an average uremic patient, while on the contrary the clinical need for customization requires patient-specific models. In this work, we assume that the customization can be obtained by means of patient-specific model parameters. We propose and validate a Bayesian approach to estimate the patient-specific parameters of a multi-compartment model, and to predict the single patient's response to the treatment, in order to prevent intra-dialysis complications. The likelihood function is obtained by means of a discretized version of the multi-compartment model, where the discretization is in terms of a Runge-Kutta method to guarantee convergence, and the posterior densities of model parameters are obtained through Markov Chain Monte Carlo simulation. Results show fair estimations and the applicability in the clinical practice.

Sodium Prescription in the Prevention of Intradialytic Hypotension: New Insights into an Old Concept

Background: Sodium prescription in patients with intradialytic hypotension remains a challenge for the attending nephrologist, as it increases dialysate conductivity in hypotension-prone patients, thereby adding to dietary sodium levels. Methods: New sodium prescription strategies are now available, including the use of a mathematical model to compute the sodium mass to be removed during dialysis as a physiological controller. Results: This review describes the sodium load of patients with end-stage renal disease on chronic hemodialysis (HD) and discusses 2 strategies to remove excess sodium in patients prone to intradialytic hypotension, namely, Profiled HD and the hemodiafiltration Aequilibrium System. Conclusion: The Profiled HD and Aequilibrium System trial both proved effective in counteracting intradialytic hypotension.

The Dialysis Sodium Gradient: A Modifiable Risk Factor for Fluid Overload

Background

Fluid overload in patients on conventional hemodialysis is a frequent complication, associated with increased cardiovascular morbidity and mortality. The dialysate sodium prescription is a potential modifiable risk factor. Our primary objective was to describe associations between dialysate-to-serum sodium gradient and parameters of fluid status. A secondary objective was to evaluate the 6-month risk of hospitalization and mortality in relation to sodium gradient.

Methods

We performed a cross-sectional study of 110 prevalent conventional hemodialysis patients at a single center. The associations of sodium gradient with interdialytic weight gain index (IDWG%), ultrafiltration (UF) rate, and blood pressure (BP) were analyzed.

Results

The mean serum sodium gradient was 4.6 ± 3.6 mEq/L. There was a direct correlation between sodium gradient and IDWG% (r = 0.48, p < 0.01) as well as UF rate (r = 0.44, p < 0.01). In a logistic regression model, a 1 mEq/L higher sodium gradient was associated with increased risk of IDWG% >3% (OR 1.33, p < 0.01) and increased risk of UF rate >10 mL/kg/h (OR 1.16, p = 0.03), but there were no associations with intradialytic hypotension, intradialytic hypertension or BP. No significant differences were found with 6-month hospitalization or mortality risk in relation to sodium gradient.

Conclusion

A higher sodium gradient was associated with significant increases in IDWG and UF rates, known to be associated with poor outcomes, but was not associated with intradialytic hypotension. Individualizing the dialysate sodium prescription to minimize sodium gap may lead to less fluid overload in conventional hemodialysis patients.

Patient-Specific Modeling of Multicompartmental Fluid and Mass Exchange during Dialysis

Background

Dialysis is associated with a non-negligible rate of morbidity, requiring treatment customization. Many mathematical models have been developed describing solute kinetics during hemodialysis (HD) for an average uremic patient. The clinical need can be more adequately addressed by developing a patient-specific, multicompartmental model.

Materials and Methods

The data from 148 sessions (20 patients), recorded at the Regional Hospital of Lugano, Switzerland, were used to develop and validate the mathematical model. Diffusive and convective interactions among patient, dialysate and substitution fluid were considered. Three parameters, related to mass transfer efficiency at the cell membrane, at the dialyzer and at the capillary wall, were used to tune the model. The ability of the model to describe the clinical evolution of a specific HD session was evaluated by comparing model outputs with clinically acquired data on solutes and catabolite concentrations.

Results

The model developed in this study allows electrolyte and catabolite concentration trends during each HD session to be described. The errors obtained before the estimation of the patient-specific parameters drastically decrease after their identification. With the optimized model, plasmatic concentration trends can be described with an average percent error lower than 2.1% for Na+, CI-, Ca2+ and HCO3-, lower than 5% for K+ and lower than 8% for urea.

Conclusions

The peculiarity of the proposed model is the possibility it offers to perform a real-time simulation enabling quantitative appraisal of hematochemical quantities whose direct measurement is prohibitive. These will be beneficial to dialysis therapy planning, reducing intradialysis complications and improving patients’ quality of life.

Hyponatremia and Cognitive Impairment in Patients Treated with Peritoneal Dialysis

BACKGROUND AND OBJECTIVES

Hyponatremia has been identified as a relevant factor for cognitive impairment but has not been investigated in patients receiving peritoneal dialysis (PD). This study investigated the relationship between hyponatremia and cognitive functions in PD patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A total of 476 clinically stable patients from five PD units who were older than 18 years of age and had undergone PD for at least 3 months between March 2013 and March 2014 were enrolled in this multicenter cross-sectional study. Global cognitive function was measured using the Modified Mini-Mental State Examination (3MS); executive function, by trail making tests A (trails A) and B (trails B); and immediate memory, delayed memory, and language ability, by subtests of Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Hyponatremia was defined as serum sodium level ≤135 mmol/L, which was calculated as the mean of measurements taken over the preceding 3 months.

RESULTS

Fifty patients (10.5%) had hyponatremia; these patients tended to be older and less educated, to have less inflammation, and to have the higher prevalence of cognitive impairment. They also had lower scores on RBANS subtests. After adjustment for demographic and clinical confounders, hyponatremia was independently associated with lower 3MS score (coefficient, -5.28; 95% confidence interval [CI], -8.44 to -2.13) and longer completion time of trials A (coefficient, 22.68; 95% CI, 3.44 to 41.92) and B (coefficient, 45.56; 95% CI, 1.30 to 89.81). After additional adjustment for laboratory measures, hyponatremia was still associated with 3MS score and completion time of trails A. Hyponatremia was independently associated with CI (odds ratio, 2.17; 95% CI, 1.02 to 4.94) and executive dysfunction (odds ratio, 2.43; 95% CI, 1.01 to 5.87) using multivariate logistic regression analysis. Sensitivity analyses with multivariable models that included propensity score still supported the association between hyponatremia and cognitive impairment.

CONCLUSIONS

Hyponatremia was associated with global and specific cognitive impairment in PD patients.

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.

Home Hemodialysis Dose: Balancing Patient Needs and Preferences

<b><i>Background:</i></b> The aim in defining the dose of HHD is to provide sufficient dialysis required to possibly ‘normalize' all abnormalities associated with renal failure in order improve patient survival and quality of life. Much progress has been made in defining the dose required to accomplish this goal, but the evidence is still far from robust. The main limitations are incomplete understanding of uremic toxins, their relative importance in causing uremic symptoms, and our inability to comprehensively assess dry weight. <b><i>Summary:</i></b> This review provides guidance on realistic dosing of dialysis for the HHD patient based on the available evidence, where available, and alternative regimens that suit the individual's lifestyle and preferences. <b><i>Key Messages:</i></b> HHD can easily accommodate alternative, intensive HD prescriptions, including daily and nocturnal HD. HHD provides prescription flexibility to fulfill patient needs while taking their preferences into account.

Effect of dialysate sodium concentration on sodium gradient and hemodialysis parameters

This retrospective study was performed to determine the ranges of the sodium gradient (SG) between the dialysate sodium concentration (DNa) and serum sodium concentration (SNa) in hemodialysis (HD) patients and to examine the relationships between HD parameters over a 1 year period. Fifty-five clinically stable HD patients, who had been on HD >2 years were enrolled. Monthly HD [ultrafiltration (UF) amount, systolic blood pressure (SBP), frequency of intradialytic hypotension (IDH)] and laboratory data were collected and 12-month means were subjected to analysis. The SG was calculated by subtracting SNa from prescribed DNa. Mean SG values were 1.5±3.3 (range -5.6~9.1). SG was positively related to DNa and the frequency of IDH. A higher SG was associated with larger UF amounts and SBP reduction during HD. The percentages of patients with a SG ≥3mEq/L increased as DNa increased. On the other hand, SG was not found to be associated with SNa or pre-HD SBP. DNa appears to cause a significant increase in SG, and this seems to be related to HD parameters, such as, UF amount and IDH.

Optimizing peritoneal dialysis prescription for volume control: the importance of varying dwell time and dwell volume

Not only adequate uremic toxin removal but also volume control is essential in peritoneal dialysis (PD) to improve patient outcome. Modification of dwell time impacts on both ultrafiltration (UF) and purification. A short dwell favors UF but preferentially removes small solutes such as urea. A long dwell favors uremic toxin removal but also peritoneal fluid reabsorption due to the time-dependent loss of the crystalloid osmotic gradient. In particular, the long daytime dwell in automated PD may result in significant water and sodium reabsorption, and in such cases icodextrin should be considered. Increasing dwell volume favors the removal of solutes such as sodium due to the increased volume of diffusion and the recruitment of peritoneal surface area. A very large fill volume with too high an intraperitoneal pressure (IPP) may, however, result in back-filtration and thus reduced UF and sodium clearance. Based on these principles and the individual transport and pressure kinetics obtained from peritoneal equilibration tests and IPP measurements, we suggest combining short dwells with a low fill volume to favor UF with long dwells and a large fill volume to favor solute removal. Results from a recent randomized cross-over trial and earlier observational data in children support this concept: the absolute UF and UF relative to the administered glucose increased and solute removal and blood pressure improved.

Inadvertent sodium loading with renal replacement therapy in critically ill patients

BACKGROUND

Inadvertent sodium (Na(+)) flux may occur during renal replacement therapy (RRT) in ICU. The objective of this study was to estimate sodium flux during RRT.

METHODS

Between September 2011 to December 2012 we studied 60 ICU patients receiving extended daily dialysis (EDD, Fresenius 4008S) or continuous renal replacement technique (CRRT, Aquarius 6.01). CRRT was categorized as dialysis with continuous veno-venous haemofiltration (CVVH) or haemodiafiltration (CVVHDF). Sodium balance was calculated as the difference between affluent and effluent fluid sodium concentration corrected for volume. The duration of study was either the duration of a single EDD session or 24 h of CRRT.

RESULTS

Both EDD and CRRT contributed to a positive Na(+) flux. Despite similar demographics, CRRT patients had a greater positive sodium flux (p < 0.001). At multivariate analysis, factors [exp(b) (SE), p] which significantly affected sodium flux in each mode of RRT were: (1) EDD (R(2) = 0.42): gradient between RRT Na(+) and serum Na(+) [20.9 (5.8), p < 0.02], and total litres of exchange [1.5 (0.68), p < 0.04]; (2) CVVH (R(2) = 0.77): gradient between RRT Na(+) and serum Na(+) [21.8 (4.7), p < 0.001], dialysis day [-20.9 (9.8), p < 0.05], and total litres of exchange [5.2 (0.96), p < 0.001]; (3) CVVHDF (R(2) = 0.73): gradient between RRT Na(+) and serum Na(+) [23.8 (3.7), p < 0.001], and total fluid removal [-18.5 (3.26), p < 0.001].

CONCLUSION

RRT may inadvertently contribute to sodium load in critically ill patients and is affected by multiple factors including gradient between RRT Na(+) and serum Na(+).

Optimal dialysate sodium-what is the evidence?

Oligo-anuric patients with end-stage kidney disease are dependent on hemodialysis to achieve and maintain the desired goal of euvolemia. The dialysis prescription, in addition to sodium and fluid restriction, is therefore a critically important factor in the care of hemodialysis patients. Various dialysate sodium concentrations have been favored throughout the history of dialysis, but the "optimal" concentration remains unclear. In this manuscript, we examine the historical context of changes to the dialysate sodium prescription, review the evidence of its associated effects, discuss 'individualization' of dialysate sodium, and highlight the need for definitive trials that are powered for important clinical outcomes.

Lower serum potassium combined with lower sodium concentrations predict long-term mortality risk in hemodialysis patients

BACKGROUND

The purpose of this study was to evaluate the combined effect of different pre-hemodialysis (HD) serum sodium (S[Na]) and potassium (S[K]) concentrations on the long-term prognosis of HD patients.

METHODS

A cohort of 424 maintenance HD patients (age: 58 ± 13 years, male: 47%, diabetes: 39%) from a single center were divided into four groups based on both medians of S[Na] (138.4 mmol/L) and S[K] (4.4 mmol/L): Group 1: lower S[Na] & lower S[K]: n = 92; Group 2: lower S[Na] & higher S[K]: n =113; Group 3: higher S[Na] & lower S[K]: n =123; Group 4: higher S[Na] & higher S[K]: n =96. The median observation period was 21 months.

RESULT

By multivariate logistic regression analysis, Group 1 was characterized by hypoalbuminemia (OR = 0.37, 95%CI = 0.20-0.67), and lower normalized protein catabolism rate (nPCR) (OR = 0.37, 95% CI = 0.16-0.83). In contrast, Group 4 was characterized by higher nPCR (OR = 2.26, 95% CI = 1.05-4.86) and albumin level (OR = 2.26, 95% CI = 1.17-4.39). As compared to the reference (group 1), the HR for long-term mortality was significantly lower in Groups 3 (HR = 0.54, 95% CI = 0.34- 0.86) and 4 (HR = 0.49, 95% CI = 0.28-0.84). By multivariate Cox proportional analysis, Group 1 was an independent factor (HR = 1.74, 95% CI = 1.18-2.58) associated with long-term mortality.

CONCLUSION

HD patients combined with lower S[K] and lower S[Na] were characterized by hypoalbuminemia, lower nPCR and a high prevalence of co-morbidity. They were associated with long-term mortality risk. On the other hand, those patients with higher levels of S[Na] and S[K] tended to have better clinical outcomes.

Hydration measurement by bioimpedance spectroscopy and blood pressure management in children on hemodialysis

BACKGROUND

Hypertension is frequent in chronic hemodialyzed patients and usually treated by reducing extracellular fluid. Probing dry weight only based on a clinical evaluation may be hazardous, especially in case of volume independent hypertension.

METHODS

We performed a 1-year retrospective study in three pediatric centers to define the relation between blood pressure (BP) and hydration status, assessed by whole-body bioimpedance spectroscopy (BIS). We analyzed 463 concomitant measurements of BP, relative overhydration (rel.OH), and plasma sodium (Napl) in 23 children (mean age 13.9 ± 5.1 years).

RESULTS

Pre-dialytic under-hydration (rel.OH < -7%) was present in 5.4% of the sessions, out of which 24% showed hypertension. Normohydration (rel.OH -7 - +7%) was observed in 62.4% of the sessions, 45.3% of them revealed hypertension. Moderate OH (rel.OH +7 - +15%) was present in 21% of the sessions, 47.4% of them showed normal BP. In 11.2% of the sessions, severe overhydration (rel.OH > +15%) was assessed, however, the majority (73%) showed normal BP. Patient-specific Napl setpoint could not be described. Mean dialysate sodium concentration was higher than mean Napl.

CONCLUSIONS

Hypertension is not always related to overhydration. Therefore, BIS should restrict the practice of "probing dry weight" in hypertensive children. Moreover, sodium dialytic balance needs to be considered to improve BP management.

Significance of interdialytic weight gain versus chronic volume overload: consensus opinion

Predialysis volume overload is the sum of interdialytic weight gain (IDWG) and residual postdialysis volume overload. It results mostly from failure to achieve an adequate volume status at the end of the dialysis session. Recent developments in bioimpedance spectroscopy and possibly relative plasma volume monitoring permit noninvasive volume status assessment in hemodialysis patients. A large proportion of patients have previously been shown to be chronically volume overloaded predialysis (defined as >15% above 'normal' extracellular fluid volume, equivalent to >2.5 liters on average), and to exhibit a more than twofold increased mortality risk. By contrast, the magnitude of the mortality risk associated with IDWG is much smaller and only evident with very large weight gains. Here we review the available evidence on volume overload and IDWG, and question the use of IDWG as an indicator of 'nonadherence' by describing its association with postdialysis volume depletion. We also demonstrate the relationship between IDWG, volume overload and predialysis serum sodium concentration, and comment on salt intake. Discriminating between volume overload and IDWG will likely lead to a more appropriate management of fluid withdrawal during dialysis. Consensually, the present authors agree that this discrimination should be among the primary goals for dialysis caretakers today. In consequence, we recommend objective measures of volume status beyond mere evaluations of IDWG.

Sodium balance in maintenance hemodialysis

Sodium is the principal solute in the extracellular compartment and the major component of serum osmolality. In normal persons in the steady state, sodium homeostasis is achieved by a balance between the dietary intake and the urinary output of sodium, whereas in intermittent hemodialysis patients, sodium balance depends on dietary intake and sodium removal during hemodialysis. Thus, the main goal of hemodialysis is to remove precisely the amount of sodium that has accumulated during the interdialytic period. Sodium removal during hemodialysis occurs via convective (~78%) and diffusive losses (~22%) between dialysate and plasma sodium concentration. The latter (the sodium gradient) is an important factor in the 'fine tuning' of sodium balance during intermittent hemodialysis. Most use fixed dialysate sodium concentrations, but each patient has his/her own plasma sodium concentrations pre-hemodialysis, which are quite reproducible and stable in the long-term. Thus, in many patients, a fixed dialysate sodium concentration will cause a persistent positive sodium balance during dialysis, which could possibly cause increased thirst, interdialytic weight gain, and mortality. Several methods will be discussed to reduce positive sodium balance, including sodium alignment.

The dual blockade of the renin-angiotensin system in hemodialysis patients requires decreased dialysate sodium concentration

Purpose

The study evaluated whether the dual blockade of the renin–angiotensin system may influence the sodium balance in hemodialysis.

Methods

The study involved 148 hemodialysis patients (male 85, female 63), mean age 59.6 ± 12.9 years. Participants were randomly selected to receive either angiotensin-converting enzyme inhibitor (ACEI)—subgroup A—or dual blockade ACEI and angiotensin receptor blocker (ARB)—subgroup AA.

Results

At baseline, in the A versus AA subgroups, the pre-dialysis sodium concentrations (mmol/l) were 137.7 ± 0.5 versus 137.9 ± 0.8, the sodium gradients 2.6 ± 0.5 versus 2.9 ± 0.4, interdialytic weight gain (IWG) (kg) 3.1 ± 0.2 versus 3.0 ± 0.3, and thirst inventory score (points) 18.1 ± 1.0 versus 19.0 ± 1.7, respectively. After 3 months of therapy, a decrease in sodium concentration to 134.5 ± 0.5 and the increase of its gradient to 5.5 ± 0.5 were noted in the AA subgroup. An elevation of mean interdialytic weight gain to 3.47 ± 0.2 and thirst score to 21.3 ± 2.1 was observed. No significant changes in subgroup A were found. One month of the dialysate sodium concentration being lowered from 140 mmol/l to 138 mmol/l was associated with reduced serum sodium concentration and gradient, decreased IWG and restored moderate thirst score in the AA subgroup (137.5 ± 0.6 and 2.9 ± 0.6, 3.0 ± 0.5 and 19.2 ± 1.3, respectively).

Conclusions

The dual blockade of the renin–angiotensin system affects sodium balance, increasing the sodium gradient, thus elevating thirst sensation and enhancing interdialytic weight gain. In maintenance hemodialysis patients treated with both ACEI and ARB, lowered dialysate sodium levels should be prescribed.

Prevention of intradialytic hypotension in patients with acute kidney injury submitted to sustained low-efficiency dialysis

OBJECTIVES

This study evaluated the effects of a protocol aiming to reduce hypotension in acute kidney injury (AKI) patients submitted to sustained low-efficiency dialysis (SLED).

METHODS

Patients were randomly assigned to two SLED prescriptions-control group, dialysate temperature was 37.0°C with a fixed sodium concentration [138 mEq/L] and ultrafiltration (UF) rate; and profiling group, dialysate temperature was 35.5°C with a variable sodium concentration [150-138 mEq/L] and UF rate.

RESULTS

Sixty-two SLED sessions were evaluated (34 in profiling and 28 in control). Patients (n = 31) were similar in terms of gender, age, and Sequential Organ Failure Assessment (SOFA) score. Dialysis time, dialysis dose, and post-dialysis serum sodium were similar in both groups. The profiling group had significantly less hypotension episodes (23% vs. 57% in control, p = 0.009) and achieved higher UF volume (2.23 ± 1.25 L vs. 1.59 ± 1.03 L in control, p = 0.04) when compared with control group.

CONCLUSIONS

SLED protocol with modulation of dialysate temperature, sodium, and UF profiling showed similar efficacy but less intradialytic hypotension when compared with a standard SLED prescription.

Avoiding harm and achieving optimal dialysis outcomes--the dialysate component

Appropriate dialysate composition is critical for effective and safe hemodialysis. Unfortunately, there are few randomized trials to guide practice, and although solute clearance is well understood, there is a limited understanding of balance in dialysis patients. The current practice of simply trying to normalize serum electrolyte and mineral concentrations measured predialysis may not provide optimal care. More thought should be given to normalizing balance with respect to sodium, bicarbonate, magnesium, and potassium and minimizing wide swings in serum concentrations that may have adverse effects. In practice, this would require longer or more frequent dialysis with less steep chemical gradients. With respect to calcium, the goal should be to optimize bone and vascular health. Clinicians should also be mindful that the dialysis procedure itself exposes patients to potential toxins, and efforts to minimize these risks should be stressed.

How should we manage adverse intradialytic blood pressure changes?

Variations in intradialytic blood pressure (BP) are a common and predictable occurrence in ESRD patients. These are caused by a decrease in blood volume provoked by ultrafiltration, lack of normal compensatory responses to fluid removal, underlying cardiac disease, and electrolyte changes that may adversely affect cardiovascular function. Intradialytic hypotension is the most frequent complication of the hemodialysis (HD) procedure and is fundamentally a consequence of an ultrafiltration rate that surpasses mechanisms activated to avert a decline in BP. Intradialytic hypertension is a less well-understood problem that has been recently associated with increased mortality. Fundamental patient characteristics and components of the HD procedure are involved in the pathophysiology of intradialytic hypotension and intradialytic hypertension. Correction of patient factors, modulation of HD prescription, and management of pharmacologic agents are the strategies to deal with adverse intradialytic BP changes.

Minerals in dialysis therapy: an introduction

The 180 l of glomerular filtrate formed each day contain some 1100 g (2.5 pounds) of sodium chloride, of which only 5-10 g are excreted in the urine--95% is reabsorbed by the tubules. Some 425 g (nearly a pound) of sodium bicarbonate and 145 g of glucose are filtered, and more than 99% of both are reabsorbed. Also filtered, only to be reabsorbed, are substantial quantities of potassium, calcium, magnesium, phosphate, sulfate, amino acids, vitamins, and many other substances valuable to the body. It is no exaggeration to say that the composition of the blood is determined not by what the mouth takes in but by what the kidneys keep: they are the master chemists of our internal environment, which, so to speak, they manufacture in reverse by working it over completely some fifteen times a day…Our bones, muscles, glands, even our brains are called upon to do only one kind of physiological work, but our kidneys are called upon to perform an innumerable variety of operations. Bones can break, muscles can atrophy, glands can loaf, even the brain can go to sleep, without immediately endangering our survival; but should the kidneys fail to manufacture the proper kind of blood neither bone, muscle, gland nor brain could carry on (1).