Lowering postdialysis plasma sodium (conductivity) to increase sodium removal in volume-expanded hemodialysis patients: a pilot study using a biofeedback software system

Feedback control in hemodialysis

A number of systems of feedback control during dialysis have been developed, which have the shared characteristic of prospectively measuring physiological parameters and then automatically altering dialysis parameters in real time according to a pre-specified dialysis prescription. These include feedback systems aimed at reducing intradialytic hypotension based on relative blood volume monitoring linked to adjustments in ultrafiltration and dialysate conductivity, and blood temperature monitoring linked to alterations in dialysate temperature. Feedback systems also exist that manipulate sodium balance during dialysis by assessing and adjusting dialysate conductivity. In this review article, we discuss the rationale for automated feedback systems during dialysis, describe how the different feedback systems work, and provide a review of the current evidence on their clinical effectiveness.

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.

Intradialysis hypertension, a diagnosis to be discovered

INTRODUCTION

Intradialytic hypertension (IDH) is a poorly understood phenomenon with no consensus on its definition, etiology, or related factors, and there is limited evidence on its consequences.

OBJECTIVE

To determine the prevalence of IDH according to different definitions in hemodialysis (HD) units, with different clinical practices and assessment of possible events after 18 months have passed.

MATERIALS AND METHODS

A cross-sectional observational study was conducted in 2 HD units, including all prevalent patients from March 2021 to September 2022. We established 3 definitions of IDH: IDH was considered present if the criterion was met in more than 50% of the 6 consecutive sessions (2 weeks) of follow-up. Personal history, medications, dialysis characteristics, and pre- and post-HD biochemical data were collected. Residual renal function (RRF) was considered as urine output >250 ml/24 h. At 18 months, the possible events of the group were analyzed.

RESULTS

We included 169 patients (68% men) with a mean age of 67.9 (14.2) years and a median HD duration of 34.5 (IQR 17.5-67.5) months. Of these, 94 come from one unit and 75 from the other. The prevalence of IDH was 8.3% according to Def 1, 27.2% according to Def 2, and 29.6% according to Def 3. Def 2 showed an association with a history of previous hypertension, use of renin-angiotensin system inhibitors (RASIs), and furosemide, as well as with patients with RRF. Def 3 showed an association only with coronary artery disease. There was an association with different prescriptions of dialysis fluids. Catecholaminergic hormones and aldosterone did not increase in patients with hypertension during the HD session. They did not present a higher incidence of cardiovascular events or mortality at 18 months.

CONCLUSIONS

IDH has different prevalence rates depending on the definition used and the studied center. The future poses an important challenge: to determine which definition correlates with higher morbidity and mortality and the role of differences found in different HD units.

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.

Dialysate sodium management in hemodialysis and on-line hemodiafiltration: the single-pool kinetic model revisited

BACKGROUND

Determining the optimal dialysate sodium remains one of the challenges of hemodialysis prescription. Several arguments suggest that the dialysate sodium should be individually adjusted according to the patient's natremia. This strategy is greatly facilitated by using an algorithm. Only three such algorithms have been embedded in hemodialysis machines for the widespread generalization of this strategy in clinical routine: the Diacontrol (Hospal-Baxter Healthcare Corp., Deerfield, IL, USA), the HFR-Aequilibrium (Bellco-Medtronic, Dublin, Ireland) and the Na-control (Fresenius Medical Care, Bad-Homburg, Germany).

METHODS

Model the solute mass-transfer across the dialyzer membrane in online hemodiafiltration and adapt the Diacontrol algorithm based on a single-pool kinetic model of sodium balance for quantifying ionic balance and managing tonicity.

RESULTS

1) Substituting sodium measurements with conductivity measurements allows the control of tonicity which is a more physiological parameter than natremia. 2) Consideration of all ion exchanges as a whole and not just sodium exchange avoids some of the assumptions required by kinetic modeling of sodium balance. 3) Equations provided by the model are applicable to both hemodialysis and online hemodiafiltration. 4) The differences between this model used by Diacontrol and the models on which the other two software's (HFR-Aequilibrium and Na-control) are based are highlighted.

CONCLUSIONS

The single-pool kinetic model validated for the management of natremia in hemodialysis is also valid for the management of tonicity for both conventional hemodialysis and all online hemodiafiltration procedures.

Routine online assessment of dialysis dose: Ionic dialysance or UV-absorbance monitoring?

For three-weekly hemodialysis, a single-pool Kt/V target of at least 1.4 together with a minimal dialysis dose Kt at 45 L for men and 40 L for women per each session is currently recommended. Fully automatic online calculation of Kt and Kt/V from conductivity or UV-absorbance measurements in the dialysate is standardly implemented on some hemodialysis monitors and makes it possible to estimate the dialysis dose without the need for blood or dialysate samples. Monitoring the UV-absorbance of the spent dialysate is the most direct method for estimating Kt/V as it does not require an estimate of V. Calculation of ionic dialysance from conductivity measurements is the most direct method for estimating Kt and BSA-scaled dialysis dose. Both ionic dialysance monitoring and UV-absorbance monitoring may help detect a change in urea clearance occurring during the session, but this change must be interpreted differently depending on the monitoring being considered. An abrupt decrease in urea clearance results in a decrease in ionic dialysance but, paradoxically, a sudden increase in estimated urea clearance provided by dialysate UV-absorbance monitoring. Healthcare teams who monitor both ionic dialysance and UV-absorbance in their hemodialysis units must be clearly informed of this difficulty.

Volume overload in hemodialysis: diagnosis, cardiovascular consequences, and management

Volume overload in haemodialysis (HD) patients associates with hypertension and cardiac dysfunction and is a major risk factor for all-cause and cardiovascular mortality in this population. The diagnosis of volume excess and estimation of dry weight is based largely on clinical criteria and has a notoriously poor diagnostic accuracy. The search for accurate and objective methods to evaluate dry weight and to diagnose subclinical volume overload has been intensively pursued over the last 3 decades. Most methods have not been tested in appropriate clinical trials and their usefulness in clinical practice remains uncertain, except for bioimpedance spectroscopy and lung ultrasound (US). Bioimpedance spectroscopy is possibly the most widely used method to subjectively quantify fluid distributions over body compartments and produces reliable and reproducible results. Lung US provides reliable estimates of extravascular water in the lung, a critical parameter of the central circulation that in large part reflects the left ventricular end-diastolic pressure. To maximize cardiovascular tolerance, fluid removal in volume-expanded HD patients should be gradual and distributed over a sufficiently long time window. This review summarizes current knowledge about the diagnosis, prognosis and treatment of volume overload in HD patients.

Blood pressure targets and pharmacotherapy for hypertensive patients on hemodialysis

INTRODUCTION

Hypertension is highly prevalent in patients with end-stage kidney disease on hemodialysis and is often not well controlled. Blood pressure (BP) levels before and after hemodialysis have a U-shaped relationship with cardiovascular and all-cause mortality. Although antihypertensive drugs are recommended for patients in whom BP cannot be controlled appropriately by non-pharmacological interventions, large-scale randomized controlled clinical trials are lacking.

AREAS COVERED

The authors review the pharmacotherapy used in hypertensive patients on dialysis, primarily focusing on reports published since 2000. An electronic search of MEDLINE was conducted using relevant key search terms, including 'hypertension', 'pharmacotherapy', 'dialysis', 'kidney disease', and 'antihypertensive drug'. Systematic and narrative reviews and original investigations were retrieved in our research.

EXPERT OPINION

When a drug is administered to patients on dialysis, the comorbidities and characteristics of each drug, including its dialyzability, should be considered. Pharmacological lowering of BP in hypertensive patients on hemodialysis is associated with improvements in mortality. β-blockers should be considered first-line agents and calcium channel blockers as second-line therapy. Renin-angiotensin-aldosterone system inhibitors have not shown superiority to other antihypertensive drugs for patients on hemodialysis.

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.

Negative Dialysate to Sodium Gradient Does not Lead to Intracellular Volume Expansion Post Hemodialysis

Introduction

Intradialytic hypotension remains the most common complication of routine outpatient hemodialysis treatments. There is debate as to the optimum dialysate sodium concentration, with hypotonic dialysates potentially causing intracellular swelling and hypertonic ones intracellular dehydration.

Methods

Multi-frequency bioimpedance was used to assess extracellular and intracellular fluid volumes in 53 adult hemodialysis patients. Dialysate sodium was checked by ion electrophoresis.

Results

The mean decrease in extracellular volume and intracellular volumes were 1.01 ±0.09 and 0.88 ±0.18 kg, respectively. The median dialysate to sodium gradient was −3 mmol/L (−1 to −6), with a median dialysate sodium of 136 mmol/L (136–138). There was no association between changes in body fluid composition and sodium concentrations, or gradients. The mean difference between dialysate sodium prescribed and delivered was 2.4 ±0.8 mmol/L.

Conclusions

In this study we were unable to demonstrate a relationship between predialysis serum sodium and the dialysate sodium prescribed and changes in extracellular or intracellular fluid volumes. However this study showed that using a negative sodium gradient, patients can be successfully ultrafiltrated without setting up intracompartmental fluid gradients. The caveat is that the prescribed dialysate to serum sodium gradient may differ from the actual gradient.

Setting the dry weight and its cardiovascular implications

Volume overload is common and associated with adverse outcomes in the hemodialysis population including systemic hypertension, pulmonary hypertension, left ventricular hypertrophy, and mortality. Since the beginning of the era of maintenance dialysis, prescribing and maintaining a dry weight remains the standard of care for managing volume overload on hemodialysis. Reducing dry weight even by relatively small amounts has been shown to improve blood pressure and has been associated with reductions in left ventricular hypertrophy. Maintaining an adequately low dry weight requires attention to sodium intake and adequate time on dialysis, as well as a high index of suspicion for volume overload. Reducing dry weight can provoke decreased cardiac chamber filling and is associated with risks including intradialytic hypotension. The ideal method to minimize intradialytic morbidity is unknown, but more frequent dialysis should be considered. Experimental methods of assessing volume status may allow identification of patients most likely both to tolerate and to benefit from dry weight reduction, but further study is needed.

Assessment and management of hypertension in patients on dialysis

Hypertension is common, difficult to diagnose, and poorly controlled among patients with ESRD. However, controversy surrounds the diagnosis and treatment of hypertension. Here, we describe the diagnosis, epidemiology, and management of hypertension in dialysis patients, and examine the data sparking debate over appropriate methods for diagnosing and treating hypertension. Furthermore, we consider the issues uniquely related to hypertension in pediatric dialysis patients. Future clinical trials designed to clarify the controversial results discussed here should lead to the implementation of diagnostic and therapeutic techniques that improve long-term cardiovascular outcomes in patients with ESRD.

[Fluid overload and arterial hypertension in hemodialysis patients]

The water sodium overload is a factor of morbi-mortality and its treatment is one of the markers of adequacy of the hemodialysis treatment. Its first clinical assessment was improved by tools such as echocardiography and ultrasonography of the inferior vena cava, the per-dialytic curve of plasma volume, measuring BNP or proBNP and by impedancemetry. The combination of the evaluation of these parameters and of the clinical situation allows one to assess the extracellular overload, the state of the blood volume and the potential of plasma refilling. The latter is a key factor of the per-dialytic hemodynamic tolerance. It is itself a determining factor in weight can be achieved at the end of the session. Getting the "dry" weight can require modifications of the prescriptions of the hemodialysis sessions, a filling by albumin even a drugs support. Finally, the overload treatment is the central part of the treatment of arterial hypertension, which has to benefit however often from antihypertensive treatment the profit of which is demonstrated.

Rationale and design of the Sodium Lowering In Dialysate (SoLID) trial: a randomised controlled trial of low versus standard dialysate sodium concentration during hemodialysis for regression of left ventricular mass

BACKGROUND

The current literature recognises that left ventricular hypertrophy makes a key contribution to the high rate of premature cardiovascular mortality in dialysis patients. Determining how we might intervene to ameliorate left ventricular hypertrophy in dialysis populations has become a research priority. Reducing sodium exposure through lower dialysate sodium may be a promising intervention in this regard. However there is clinical equipoise around this intervention because the benefit has not yet been demonstrated in a robust prospective clinical trial, and several observational studies have suggested sodium lowering interventions may be deleterious in some dialysis patients.

METHODS/DESIGN

The Sodium Lowering in Dialysate (SoLID) study is funded by the Health Research Council of New Zealand. It is a multi-centre, prospective, randomised, single-blind (outcomes assessor), controlled parallel assignment 3-year clinical trial. The SoLID study is designed to study what impact low dialysate sodium has upon cardiovascular risk in dialysis patients. The study intends to enrol 118 home hemodialysis patients from 6 sites in New Zealand over 24 months and follow up each participant over 12 months. Key exclusion criteria are: patients who dialyse more frequently than 3.5 times per week, pre-dialysis serum sodium of <135 mM, and maintenance hemodiafiltration. In addition, some medical conditions, treatments or participation in other dialysis trials, which contraindicate the SoLID study intervention or confound its effects, will be exclusion criteria. The intervention and control groups will be dialysed using dialysate sodium 135 mM and 140 mM respectively, for 12 months. The primary outcome measure is left ventricular mass index, as measured by cardiac magnetic resonance imaging, after 12 months of intervention. Eleven or more secondary outcomes will be studied in an attempt to better understand the physiologic and clinical mechanisms by which lower dialysate sodium alters the primary end point.

DISCUSSION

The SoLID study is designed to clarify the effect of low dialysate sodium upon the cardiovascular outcomes of dialysis patients. The study results will provide much needed information about the efficacy of a cost effective, economically sustainable solution to a condition which is curtailing the lives of so many dialysis patients.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry number: ACTRN12611000975998.

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.

Modifiable variables affecting interdialytic weight gain include dialysis time, frequency, and dialysate sodium

Interdialytic weight gain (IDWG) is associated with hypertension, left ventricular hypertrophy, and all-cause mortality. Dialysate sodium concentration may cause diffusion gradients with plasma sodium and influence subsequent IDWG. Dialysis time and frequency may also influence the outcomes of this Na(+) gradient; these have been overlooked. Our objective was to identify modifiable factors influencing IDWG. We performed a retrospective multivariable regression analyses of data from 86 home hemodialysis patients treated by hemodialysis modalities differing in frequency and session duration to determine factors involved that predict IDWG. Age, diabetic status, and residual renal function did not correlate with IDWG in the univariable analysis. However, using a combination of backwards selection and Akaike information criterion to build our model, we created an equation that predicted IDWG on the basis of serum albumin, age, patient sex, dialysis frequency, and the diffusive balance of sodium, represented by the product of the duration of dialysis and the patient plasma to dialysate Na(+) gradient. This equation was internally validated using bootstrapping, and externally validated in a temporally distinct patient population. We have created an equation to predict IDWG on the basis of independent factors readily available before a dialysis session. The modifiable factors include dialysis time and frequency, and dialysate sodium. Patient sex, age, and serum albumin are also correlated with IDWG. Further work is required to establish how improvements in IDWG influence cardiovascular and other clinical outcomes.

Individualized reduction in dialysate sodium in conventional in-center hemodialysis

Recent studies have focused on the association between dialysate sodium (Na(+)) prescriptions and interdialytic weight gain (IDWG). We report on a case series of 13 patients undergoing conventional, thrice-weekly in-center hemodialysis with an individualized dialysate Na(+) prescription. Individualized dialysate Na(+) was achieved in all patients through a stepwise weekly reduction of the standard dialysate Na(+) prescription (140 mEq/L) by 2-3 mEq/L until reaching a Na(+) gradient of -2 mEq/L (dialysate Na(+) minus average plasma Na(+) over the preceding 3 months). Interdialytic weight gain, with and without indexing to dry weight (IDWG%), blood pressure, and the proportion of treatments with cramps, intradialytic hypotension (drop in systolic blood pressure >30 mmHg) and intradialytic hypotension requiring an intervention were reviewed. At the beginning of the observation period, the pre-hemodialysis (HD) plasma Na(+) concentration ranged from 130 to 141 mEq/L. When switched from the standard to the individualized dialysate Na(+) concentration, IDWG% decreased from 3.4% ± 1.6% to 2.5% ± 1.0% (P = 0.003) with no change in pre- or post-HD systolic or diastolic blood pressures (all P > 0.05). We found no significant change in the proportion of treatments with cramps (6% vs. 13%), intradialytic hypotension (62% vs. 65%), or intradialytic hypotension requiring an intervention (29% vs. 33%). Individualized reduction of dialysate Na(+) reduces IDWG% without significantly increasing the frequency of cramps or hypotension.

Systolic blood pressure and mortality in patients on hemodialysis

Hypertension is extremely common in patients with end-stage renal disease who are receiving hemodialysis, and cardiovascular disease remains the leading cause of death in these patients. However, optimal blood pressure management strategies in this high-risk population are still controversial. This review first discusses the complex association of systolic blood pressure with clinical outcomes in patients on hemodialysis, with a focus on several recent studies. Next, it updates the reader on issues related to optimal timing and methods of blood pressure measurement, appropriate blood pressure targets, and pharmacologic and nonpharmacologic hypertension treatment strategies for patients on hemodialysis.

Dialysate sodium concentration and the association with interdialytic weight gain, hospitalization, and mortality

BACKGROUND AND OBJECTIVES

Recommendations to decrease the dialysate sodium (DNa) prescription demand analyses of patient outcomes. We analyzed morbidity and mortality at various levels of DNa, simultaneously accounting for interdialytic weight gain (IDWG) and for the mortality risk associated with lower predialysis serum sodium (SNa) levels.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We used multiply-adjusted linear mixed models to evaluate the magnitude of IDWG and Cox proportional hazards models to assess hospitalizations and deaths in 29,593 patients from the Dialysis Outcomes and Practice Patterns Study with baseline DNa and SNa as predictors, categorized according to lowest to highest levels.

RESULTS

IDWG increased with higher DNa across all SNa categories, by 0.17% of body weight per 2 mEq/L higher DNa; however, higher DNa was not associated with higher mortality in a fully adjusted model (also adjusted for SNa; hazard ratio [HR]=0.98 per 2 mEq/L higher DNa, 95% confidence interval [CI] 0.95-1.02). Instead, higher DNa was associated with lower hospitalization risk (HR=0.97 per 2 mEq/L higher DNa, 95% CI 0.95-1.00, P=0.04). Additional adjustments for IDWG did not change these results. In sensitivity analyses restricted to study facilities, in which 90%-100% of patients have the same DNa (56%), the adjusted HR for mortality was 0.88 per 2 mEq/L higher DNa (95% CI 0.83-0.94). These analyses represented a pseudo-randomized experiment in which the association between DNa and mortality is unlikely to have been confounded by indication.

CONCLUSIONS

In the absence of randomized prospective studies, the benefit of reducing IDWG by decreasing DNa prescriptions should be carefully weighed against an increased risk for adverse outcomes.

Effect of lowering dialysate sodium concentration on interdialytic weight gain and blood pressure in patients undergoing thrice-weekly in-center nocturnal hemodialysis: a quality improvement study

BACKGROUND

Patients on in-center nocturnal hemodialysis therapy typically experience higher interdialytic weight gain (IDWG) than patients on conventional hemodialysis therapy. We determined the safety and effects of decreasing dialysate sodium concentration on IDWG and blood pressure in patients on thrice-weekly in-center nocturnal hemodialysis therapy.

STUDY DESIGN

Quality improvement, pre-post intervention.

SETTINGS & PARTICIPANTS

15 participants in a single facility.

QUALITY IMPROVEMENT PLAN

Participants underwent three 12-week treatment phases, each with different dialysate sodium concentrations, as follows: phase A, 140 mEq/L; phase B, 136 or 134 mEq/L; and phase A(+), 140 mEq/L. Participants were blinded to the exact timing of the intervention.

OUTCOMES

IDWG, IDWG/dry weight (IDWG%), and blood pressure.

MEASUREMENTS

Outcome data were obtained during the last 2 weeks of each phase and compared with mixed models. The fraction of sessions with adverse events (eg, cramping and hypotension) also was reported.

RESULTS

IDWG, IDWG%, and predialysis systolic blood pressure decreased significantly by 0.6 ± 0.6 kg, 0.6% ± 0.8%, and 8.3 ± 14.9 mm Hg, respectively, in phase B compared with phase A (P < 0.05 for all comparisons). No differences in predialysis diastolic and mean arterial or postdialysis blood pressures were found (P > 0.05 for all comparisons). The proportion of treatments with intradialytic hypotension was low and similar in each phase (P = 0.9). In phase B compared with phase A, predialysis plasma sodium concentration was unchanged (P > 0.05), whereas postdialysis plasma sodium concentration decreased by 3.7 ± 1.9 mEq/L (P < 0.05).

LIMITATIONS

Modest sample size.

CONCLUSION

Decreasing dialysate sodium concentrations in patients undergoing thrice-weekly in-center nocturnal hemodialysis resulted in a clinical and statistically significant decrease in IDWG, IDWG%, postdialysis plasma sodium concentration, and predialysis systolic blood pressure without increasing adverse events. Prolonged exposure to higher than required dialysate sodium concentrations may drive IDWG and counteract some of the purported benefits of "go-slow" (longer session length) hemodialysis.

Blood pressure management in hemodialysis: what have we learned?

PURPOSE OF REVIEW

To review recent developments in the field of hypertension in hemodialysis patients.

RECENT FINDINGS

Despite the fact that hypertension is the most common complication of end-stage kidney disease, no evidence-based blood pressure (BP) targets exist for hemodialysis patients. There is growing evidence that outcomes are better predicted by out-of-office BP values, such as home or ambulatory BP monitoring. Intradialytic hypertension is associated with increased risk of death or hospitalization, and is probably mediated by volume overload. BP management should focus on volume control: dry weight 'probing' is well tolerated and effective in lowering BP, as are other strategies that minimize expansion of the extracellular fluid volume, such as avoidance of hypernatric dialysate. We discuss each of these issues in our review.

SUMMARY

Modest advances in the understanding of hypertension have occurred in the past 2 years. Clinical trials that focus on BP targets and treatment choices are essential to guide future practice.

The measurement of hemodialysis access blood flow by a conductivity step method

BACKGROUND AND OBJECTIVES

Measurement of blood flow rate (Qa) is used to monitor dialysis access, AV fistulas, and grafts. Indicator dilution measurements of the recirculation (R) induced by reversal of hemodialysis blood lines are commonly used. This plus the dialysis circuit flow (Qb) allows calculation of Qa. R also changes the conductivity, which can be measured by a conductivity cell in the spent dialysate. The change in conductivity caused by line reversal should vary with Qa. A methodology for Qa measurement utilizing this conductivity step is proposed. This study compares conductivity step methodology against the reference method of ultrasound dilution (Qa-Trans).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was an open diagnostic test study in a single academic hospital setting involving 15 hemodialysis-dependent patients. Each was studied over four hemodialysis treatments. During each treatment, two pairs of Qa measurements (conductivity step and Trans) were made. Pre- and postdialysis sodium levels were also measured.

RESULTS

Average Qa-conductivity step was 1040 ml/min. Average Qa-Trans was 1030 ml/min. The difference was NS. The data pairs showed mean difference of 1.3 +/- 17% (SD). The SD indicates a relatively large variation between data pairs. There was significant linear correlation between the Qa-conductivity step and Qa-Trans results (r = 0.91, P < 0.001). Serum sodium rose slightly but significantly over dialysis (P < 0.001).

CONCLUSIONS

Qa measurement by conductivity step may be an acceptable alternative to ultrasound dilution methodology. Care must be taken to prevent salt loading when the conductivity step is used.