Revisiting the dialysate sodium prescription as a tool for better blood pressure and interdialytic weight gain management in hemodialysis patients

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.

Management of hypertension in the hemodialysis population: a review of the literature

OBJECTIVE

The objective of this paper was to propose an algorithm for approaching hypertensive hemodialysis patients admitted to the hospital for hypertensive urgency.

METHODS

A literature search was conducted using PubMed (Medline). Articles selected were limited to humans and the English language.

RESULTS

WE IDENTIFIED EIGHT MANAGEMENT MODALITIES INCLUDING: short-daily and nocturnal dialysis, sodium restriction, sodium profiling, antihypertensive medications, sympathetic denervation, bilateral nephrectomy, and bioimpedance spectroscopy. The benefits and drawbacks of each were investigated and discussed before implementation into the algorithm.

DISCUSSION

The algorithm presented suggests a linear approach to patient care, but treatment modalities may not be mutually exclusive, and additional factors, such as patient compliance and individual health status, should be taken into account to provide patients with optimum care.

General anesthesia soon after dialysis may increase postoperative hypotension - A pilot study

INTRODUCTION

Pilot study associating hemodialysis-to-general-anesthesia time interval and post-operative complications in hemodialysis patients to better define a more optimal pre-anesthetic waiting period.

METHODS

Pre-anesthetic and 48-hours post-anesthetic parameters (age, gender, body-mass-index, pre-operative ultrafiltrate, potassium, renal disease etiology, hemodialysis sessions per week, Acute Physiology and Chronic Health Evaluation-II score, Portsmouth-Physiologic and Operative Severity Score for the Enumeration of Mortality and Morbidity, American Society of Anesthesiologists physical status, Johns Hopkins Surgical Classification System Category, surgical urgency, intra-operative fluids, estimated blood loss, post-operative complications) were collected on chronic hemodialysis patients between 11/2009-12/2010. Continuous data were analyzed by Analysis of Variance or t-test. Bivariate data were analyzed by Fisher's Exact Test. Relative Risks/Confidence Intervals were calculated for statistically significant comparisons (p=0.05). Exclusion criteria were incomplete records, peritoneal dialysis, intra-operative hemodialysis, liver transplant, and cardiopulmonary bypass.

RESULTS

Patients were grouped by dialysis to anesthesia time interval: Group 1 >24 hours, Group 2 7-23.9 hours, Group 3 < 7 hours. Among Surgical Category 3-5 patients, hypotension was more common in Group 3 than Group 1 (63.6% vs 9.2%, p<0.0001, relative risk=6.9, confidence interval=3.0-15.7) or Group 2 (63.6% vs 17.3%, p=0.0002, relative risk=3.7, confidence interval=1.9-7.2). Other complications rates were not statistically significant. Disease and surgical severity scores, preoperative ultrafiltrate, and intra-operative fluids were not different.

CONCLUSIONS

Post-anesthetic hypotension within 48 hours was more common in those with < 7 hours interval between dialysis and anesthesia. Therefore, if surgical urgency permits, a delay of ≥7 hours may limit postoperative hypotension. More precise associations should be obtained through a prospective study.

Vascular endothelium: a vulnerable transit zone for merciless sodium

In humans, when plasma sodium concentration rises slightly beyond 140 mM, vascular endothelium sharply stiffens and nitric oxide release declines. In search of a vascular sodium sensor, the endothelial glycocalyx was identified as being a negatively charged biopolymer capable of selectively buffering sodium ions. Sodium excess damages the glycocalyx and renders vascular endothelium increasingly permeable for sodium. In the long term, sodium accumulates in the interstitium and gradually damages the organism. It was discovered that circulating red blood cells (RBC) 'report' surface properties of the vascular endothelium. To some extent, the RBC glycocalyx mirrors the endothelial glycocalyx. A poor (charge-deprived) endothelial glycocalyx causes a poor RBC glycocalyx and vice versa. This observation led to the assumption that the current state of an individual's vascular endothelium in terms of electrical surface charges and sodium-buffering capabilities could be read simply from a blood sample. Recently, a so-called salt blood test was introduced that quantifies the RBC sodium buffer capacity and thus characterizes the endothelial function. The arguments are outlined in this article spanning a bridge from cellular nano-mechanics to clinical application.

Analytical solution of multicompartment solute kinetics for hemodialysis

Objective. To provide an exact solution for variable-volume multicompartment kinetic models with linear volume change, and to apply this solution to a 4-compartment diffusion-adjusted regional blood flow model for both urea and creatinine kinetics in hemodialysis. Methods. A matrix-based approach applicable to linear models encompassing any number of compartments is presented. The procedure requires the inversion of a square matrix and the computation of its eigenvalues λ, assuming they are all distinct. This novel approach bypasses the evaluation of the definite integral to solve the inhomogeneous ordinary differential equation. Results. For urea two out of four eigenvalues describing the changes of concentrations in time are about 10⁵ times larger than the other eigenvalues indicating that the 4-compartment model essentially reduces to the 2-compartment regional blood flow model. In case of creatinine, however, the distribution of eigenvalues is more balanced (a factor of 10² between the largest and the smallest eigenvalue) indicating that all four compartments contribute to creatinine kinetics in hemodialysis. Interpretation. Apart from providing an exact analytic solution for practical applications such as the identification of relevant model and treatment parameters, the matrix-based approach reveals characteristic details on model symmetry and complexity for different solutes.

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 concentration measurement during hemodialysis through ion-exchange resin and conductivity measure approach: in vitro experiments

Sodium measurement during hemodialysis treatment is important to preserve the patient from clinical events related to hypo- or hyper-natremia Usually, sodium measurement is performed through laboratory equipment which is typically expensive, and requires manual intervention. We propose a new method, based on conductivity measurement after treatment of dialysate solution through ion-exchange resin. To test this method, we performed in vitro experiments. We prepared 40 ml sodium chloride (NaCl) samples at 280, 140, 70, 35, 17.5, 8.75, 4.375 mEq/l, and some “mixed samples”, i.e., with added potassium chloride (KCl) at different concentrations (4.375-17.5 mEq/l), to simulate the confounding factors in a conductivity-based sodium measurement. We measured the conductivity of all samples. Afterwards, each sample was treated for 1 min with 1 g of Dowex G-26 resin, and conductivity was measured again. On average, the difference in the conductivity between mixed samples and corresponding pure NaCl samples (at the same NaCl concentration) was 20.9%. After treatment with the exchange resin, it was 14.7%, i.e., 42% lower. Similar experiments were performed with calcium chloride and magnesium chloride as confounding factors, with similar results. We also performed some experiments on actual dialysate solution during hemodialysis sessions in 15 patients, and found that the correlation between conductivity measures and sodium concentration improved after resin treatment (R=0.839 before treatment, R=0.924 after treatment, P<0.0001). We conclude that ion-exchange resin treatment coupled with conductivity measures may improve the measurement of sodium compared to conductivity measures alone, and may become a possible simple approach for continuous and automatic sodium measurement during hemodialysis.

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.

An emerging concept of vascular salt sensitivity

Excessive amounts of salt in food, as usually consumed worldwide, affect the vascular system, leading to high blood pressure and premature disabilities. Salt entering the vascular bed after a salty meal is transiently bound to the endothelial glycocalyx, a negatively charged biopolymer lining the inner surface of the blood vessels. This barrier protects the endothelium against salt overload. A poorly-developed glycocalyx increases the salt permeability of the vascular system and the amount of salt being deposited in the body, which affects organ function. A simple test system is now available that evaluates vascular salt sensitivity in humans and identifies individuals who are at risk of salt-induced hypertension. This short review aims to discuss how the underlying basic research can be translated into medical practice and, thus, meaningful health outcomes.

Blood pressure and blood volume: acute and chronic considerations in hemodialysis

Hypertension is highly prevalent yet poorly controlled in the majority of dialysis patients and represents a significant burden of disease, with rates of morbidity and mortality greater than those in the general population. In dialysis, blood volume plays a critical role in the pathogenesis of hypertension, with expansion of extracellular volume increasingly recognized as an independent risk factor for morbidity and mortality. Within the current paradigm of dialysis prescription the majority of patients remain chronically volume expanded. However, management of blood pressure and volume state is difficult for clinicians with a paucity of randomized evidence adding to the complexity of nonlinear morbidity and mortality associations. With dialysis itself as a significant cardiac stressor, control of volume state is critical to minimize intradialytic hemodynamic instability, aid in preservation of cardiac anatomy and prevent progression to cardiovascular morbidity and mortality. This review explores the relationship of blood volume to blood pressure and potential targets for management in this at risk population.

Does a reduction in dialysate sodium improve blood pressure control in haemodialysis patients?

INTRODUCTION

There has been debate as to the value of lower sodium dialysates to control blood pressure in haemodialysis patients, as sodium is predominantly removed by ultrafiltration.

METHODS

Re-audit of clinical practice following reduction in dialysate sodium concentration.

RESULTS

Overall dialysate sodium concentration decreased from 138.9 ± 1.7 to 137.8 ± 1.7 mmol/L (mean ± standard deviation), resulting in a reduction in pre- and post-dialysis mean arterial pressure (MAP) of 4 mmHg (from 100.6 ± 15.6 to 97.1 ± 15.6, P < 0.01 and from 91.7 ± 15.6 to 87.1 ± 14.6, P < 0.001 respectively), yet fewer patients were prescribed antihypertensives (49.6 vs 60.6%), and less antihypertensive medications/patient (mean 0.86 vs 1.05), ultrafiltration requirements (2.8% vs 3.2% body weight, P < 0.001), and symptomatic intradialytic hypotension (0.19 vs 0.28 episodes per week, P < 0.001). A multivariable model showed that for a dialysate sodium of 136 mmol/L, younger patients had higher MAP than older patients (0.35 mmHg lower MAP/year older; but with a dialysate sodium of 140 mmol/L, there was minimal association of MAP with age (0.07 mmHg higher MAP/year older).

CONCLUSION

Change in clinical practice, amounting to a modest reduction in dialysate sodium was associated with a reduction not only in pre- and post-dialysis blood pressures, but also ultrafiltration requirements and symptomatic intradialytic hypotension. However, this effect on blood pressure was most marked for older patients and women, within minimal effects for younger patients, and lesser effects for men, suggesting that dialysate sodium reduction alone may help improve blood pressure control, but requires additional factors such as dietary sodium restriction to be effective in younger male patients.

Absolute interdialytic weight gain is more important than percent weight gain for intradialytic hypotension in heavy patients

AIM

Few published reports have mentioned the difference between absolute interdialytic weight gain (IDWG) and IDWG/DW (IDWG%), and subsequent effects on daily dialysis. The aim of present study was to evaluate the difference between absolute IDWG and IDWG% in new haemodialysis patients.

METHOD

We retrospectively reviewed the records of 255 patients who recently received conventional haemodialysis for at least 1 year at the same centre from 1997 to 2008. The first 4 weeks after starting haemodialysis was defined as the pre-study period. Data were collected for 5-56 weeks.

RESULTS

IDWG% value remained relatively constant in the first year of haemodialysis despite most patients having certain residual renal function. For haemodialysis outcomes, both absolute IDWG and IDWG% were significantly correlated with intradialytic hypotension (IDH) in men and heavy women. After dividing patients into four strata, which according to the gender and the median dry weight, stepwise multivariate linear regression analysis showed that absolute IDWG, rather than IDWG%, was an independent risk factor for IDH in heavy men (Beta = 0.585, P < 0.001) and heavy women (Beta= 0.458, P < 0.001).

CONCLUSIONS

Absolute IDWG, rather than IDWG%, is an independent risk factor for IDH in heavy haemodialysis patients. Therefore, higher absolute IDWG needs to be strictly controlled despite the corresponding IDWG% possibly being relatively small in heavy haemodialysis patients.

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.

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.

Hypertension and hemodialysis: pathophysiology and outcomes in adult and pediatric populations

Hypertension is prevalent in adult and pediatric end-stage renal disease patients on hemodialysis. Volume overload is a primary factor contributing to hypertension, and attaining true dry weight remains a priority for nephrologists. Other contributing factors to hypertension include activation of the sympathetic and renin-angiotensin-aldosterone systems, endothelial cell dysfunction, arterial stiffness, exposure to hypertensinogenic drugs, and electrolyte imbalances during hemodialysis. Epidemiologic studies in adults show that uncontrolled hypertension results in cardiovascular morbidity, but reveal increased mortality risk at low blood pressure, so that it remains unclear what the target blood pressure should be. Despite the lack of a definitive BP target, gradual dry weight reduction should be the first intervention for BP control. Renin-angiotensin-aldosterone system inhibitors have been shown to improve cardiovascular morbidity and mortality and are recommended as the initial pharmacologic therapy for hypertensive hemodialysis patients. Short-daily or nocturnal hemodialysis are also good therapeutic options for these patients. It is already established that hypertension in pediatric hemodialysis patients is associated with adverse cardiovascular outcomes, and there is emerging evidence that the mechanisms causing hypertension are similar to adults. Hypertension in adult and pediatric hemodialysis patients warrants aggressive management, although clinical trial evidence of a target BP that improves mortality does not currently exist.

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.

Predialysis serum sodium level, dialysate sodium, and mortality in maintenance hemodialysis patients: the Dialysis Outcomes and Practice Patterns Study (DOPPS)

BACKGROUND

Predialysis serum sodium concentrations recently have been linked to patient characteristics and outcomes in hemodialysis patients and may have implications for the dialysate sodium prescription.

STUDY DESIGN

Prospective cohort study.

PARTICIPANTS

11,555 patients from 12 countries in the Dialysis Outcomes and Practice Patterns Study (DOPPS), phases I (1996-2001) and III (2005-2008).

PREDICTORS

Demographics, comorbid conditions, laboratory measurements (model 1); mean serum sodium level, dialysate sodium concentration (model 2).

OUTCOMES

Serum sodium level, using adjusted linear mixed models (model 1); all-cause mortality, using Cox proportional hazards models (model 2).

RESULTS

Median follow-up was 12 months, with 1,727 deaths (15%) occurring during the study period (12,274 patient-years). Mean serum sodium level in the DOPPS countries was 138.5 ± 2.8 mEq/L. Japan had the highest (139.1 ± 2.6 mEq/L) and Australia/New Zealand had the lowest mean serum sodium level (137.4 ± 2.8 mEq/L). Serum sodium level was associated positively with male sex, black race, body mass index, serum albumin level, and creatinine level and negatively with neurologic and psychiatric disease, white blood cell count, and intradialytic weight loss (0.16 mEq/L lower per 1% loss). Higher serum sodium level was associated with lower adjusted all-cause mortality in a continuous model (HR, 0.95 per 1 mEq/L higher; 95% CI, 0.93-0.97). Dialysate sodium prescription was not associated with serum sodium level. Mortality analyses restricted to the serum sodium tertile with the highest mortality (serum sodium <137 mEq/L) showed lower mortality risk in patients with dialysate sodium prescriptions >140 mEq/L.

LIMITATIONS

Causality cannot be established in this observational study, which does not consider potential effects of dialysate sodium level on postdialysis thirst, dietary salt and water intake, interdialytic weight gain, and cardiovascular stability.

CONCLUSIONS

Lower serum sodium levels are associated with certain hemodialysis patient characteristics and higher adjusted risk of death. The lower mortality observed in our adjusted analyses in patients with serum sodium levels <137 mEq/L dialyzed against dialysate sodium prescriptions >140 mEq/L is intriguing, may be related to intradialytic cardiovascular stability, and deserves further study.

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.

Dialysate sodium and sodium gradient in maintenance hemodialysis: a neglected sodium restriction approach?

BACKGROUND

A higher sodium gradient (dialysate sodium minus pre-dialysis plasma sodium) during hemodialysis (HD) has been associated with sodium loading; however, its role is not well studied. We hypothesized that a sodium dialysate prescription resulting in a higher sodium gradient is associated with increases in interdialytic weight gain (IDWG), blood pressure (BP) and thirst.

METHODS

We conducted a cross-sectional study on 1084 clinically stable patients on HD. A descriptive analysis of the sodium prescription was performed and clinical associations with sodium gradient were analyzed.

RESULTS

The dialysate sodium prescription varied widely across dialysis facilities, ranging from 136 to 149 mEq/L, with a median of 140 mEq/L. The mean pre-HD plasma sodium was 136.7 ± 2.9 mEq/L, resulting in the majority of subjects (n = 904, 83%) being dialyzed against a positive sodium gradient, while the mean sodium gradient was 4.6 ± 4.4 mEq/L. After HD, the plasma sodium increased in nearly all patients (91%), reaching a mean post-HD plasma sodium of 141.3 ± 2.5 mEq/L. We found a direct correlation between IDWG and sodium gradient (r = 0.21, P < 0.0001). After adjustment for confounders and clustering by facilities, the sodium gradient was independently associated with IDWG (70 g/mEq/L, P < 0.0001). There were no significant associations among sodium gradient and BP, whether measured as pre-HD systolic (r = -0.02), diastolic (r = -0.06) or mean arterial pressure (r = -0.04). Post-HD thirst was directly correlated with sodium gradient (r = 0.11, P = 0.02).

CONCLUSION

Sodium gradient is associated with statistically significant and clinically meaningful differences in IDWG in stable patients on HD.

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.

Mortality associated with low serum sodium concentration in maintenance hemodialysis

BACKGROUND

low serum sodium concentrations are associated with an increased risk of death in the general population, but causality is uncertain due to confounding from clinical conditions such as congestive heart failure and cirrhosis, in which hyponatremia results from elevated levels of arginine vasopressin.

METHODS

to examine the association between predialysis serum sodium concentration and mortality in patients undergoing hemodialysis for end-stage renal disease, a condition in which arginine vasopressin does not affect water excretion and osmoregulation, we studied 1549 oligoanuric participants in the HEMO study, a randomized controlled trial of hemodialysis patients examining the effect of hemodialysis dose and flux. We used proportional hazards models to compare the risk of death according to predialysis serum sodium concentration.

RESULTS

considered as a continuous variable, each 4-mEq/L increment in baseline predialysis serum sodium concentration was associated with a hazard ratio for all-cause mortality of 0.84 (95% confidence interval (CI), 0.78-0.90). Multivariable adjustment for demographic, clinical, laboratory, and dialysis-specific covariates, including ultrafiltration volume, did not appreciably change the results (hazard ratio for all-cause mortality of 0.89; 95% CI, 0.82-0.96). the results also were consistent in time-updated analyses using repeated measures of serum sodium and other relevant covariates.

CONCLUSION

Lower predialysis serum sodium concentration is associated with an increased risk of death. Considering the unique physiology in the dialysis population, these findings raise the possibility that hyponatremia itself may be a causal determinant of mortality in the broader population.

Did 20 years of technological innovations in hemodialysis contribute to better patient outcomes?

During the past two decades, impressive technological innovations have been introduced in the field of hemodialysis. This review analyzes whether these have been translated into better patient survival. The potential impacts of an increase in dialysis dosage, the preference of high-flux versus low-flux membranes, the choice between convection and diffusion as dialysis strategy, the chemical composition and biologic purity of dialysate, the effect of sodium, potassium, volume profiling, and the intradialytic volume monitoring aiming at improving hemodynamic stability are explored. Studies in which the dialysis dosage was increased were not associated with increased patient survival, whereas the superiority of high-flux over low-flux membranes is not convincingly demonstrated. Although strict evidence is lacking, observational data suggest an advantage of convective over pure diffusive strategies. Longer duration of the dialysis sessions and/or higher frequency of dialysis is probably beneficial, but the results of powerful randomized, controlled trials should be awaited. Sodium profiling has more disadvantages than advantages, whereas potassium profiling mainly in arrhythmia-prone patients with ventricular hypertrophy should be considered. Intradialytic blood volume monitoring has reduced intradialytic hypotension episodes, but hard evidence for improving patient survival is lacking. Overall, the major technological advances in dialysis have not yet been translated into longer patient survival. Optimal predialysis care in preventing the cardiovascular damage that accumulates before the start of dialysis and timely creation of an arteriovenous fistula as vascular access is a more effective and more economic strategy in the long-term outcome of the dialysis patient.

Dialysis unphysiology and sodium balance

Dialysis unphysiology was first discussed by Carl Kjellstrand in 1975 for the possible negative effects of the unphysiology of intermittent dialysis treatment. Current hemodialysis practices are still unphysiologic because they cannot keep blood chemistries within normal limits, both before and after dialysis. In addition, the discontinuous nature of hemodialysis causes saw-tooth volume fluctuations, and the extracellular fluid volume expansion during the interdialytic period may lead to hypertension and adverse cardiovascular consequences. Sodium, which is accumulated over the interdialytic period, may be divided into two fractions. The one is the fraction of osmotically active sodium which is mainly confined to the extracellular space, and the other is that of water-free (osmotically inactive) sodium which diffuses into the intracellular space. Both contribute to the pathogenesis of hypertension because the former may act to expand extracellular fluid volume and the latter may cause vasoconstriction in the long run by increasing cytosolic concentration of calcium in the vascular smooth muscle cells. Even in intensive hemodialysis, it may take several weeks to months for water-free sodium storage in the vascular smooth muscle cells to be relieved. This may be an explanation for the lag phenomenon, i.e., the delay of blood pressure decrease after normalization of extracellular fluid volume shown in the Tassin experience. Modest restriction of dietary sodium intake, the dialytic session length long enough to maintain a high ultrafiltration volume, and the reasonably low dialysate sodium concentration are required to avoid unphysiology of positive sodium balance in current hemodialysis practice.

The growing problem of intradialytic hypertension

Intradialytic hypertension is not a rare complication of dialysis, with a prevalence of 5-15% among hemodialysis patients, and it seems to be associated with adverse outcomes. This complex phenomenon is not well understood, and many uncertainties exist regarding its pathophysiologic mechanisms and appropriate treatment strategies. Mechanisms that might be involved in the pathogenesis of intradialytic hypertension include extracellular volume overload, increased cardiac output, changes in electrolyte levels (particularly sodium), activation of the renin-angiotensin-aldosterone system, overactivity of the sympathetic nervous system, and endothelial cell dysfunction. Most current treatment strategies are based only on expert opinion and not on the results of randomized clinical trials, as very little data on the therapy of intradialytic hypertension are available. The most important treatment is adequate sodium and water removal, but reducing sympathetic hyperactivity and reducing endothelin-1 levels should also be considered. Well-designed, randomized clinical trials are urgently needed to better understand the pathophysiologic mechanisms of this complex phenomenon and to improve its diagnosis, prognosis and treatment.

Prescription of antihypertensive agents to haemodialysis patients: time trends and associations with patient characteristics, country and survival in the DOPPS

BACKGROUND

Haemodialysis patients were studied in 12 countries to identify practice patterns of prescription of antihypertensive agents (AHA) associated with survival.

METHODS

The sample included 28 513 patients enrolled in DOPPS I and II. The classes of AHA studied were beta blocker (BB), angiotensin-converting enzyme inhibitor (ACEI), angiotensin receptor blocker (ARB), peripheral blocker, central antagonist, vasodilator, long-acting dihydropyridine calcium channel blocker (CCB), short-acting dihydropyridine CCB and non-dihydropyridine CCB. To reduce bias due to unmeasured confounders, the associations with mortality were assessed by separate Cox models based on patient-level prescription and facility prescription practice.

RESULTS

An increase in prescription of ARBs (9.5%) and BBs (9.1%) was observed from DOPPS I to II. Prescription of AHA classes varied significantly by country, ranging for BBs from 9.7% in Japan to 52.7% in Sweden and for ARBs from 5.5% in Italy to 21.3% in Japan in DOPPS II. Facilities that treated 10% more patients with ARBs had, on average, 7% lower all-cause mortality, independent of patient characteristics and the prescription patterns of other antihypertensive medications (P = 0.05). Significant and independent associations with reduction in cardiovascular mortality were observed for ARBs (RR = 0.79; P = 0.005) and BBs (RR = 0.87, P = 0.004) in analyses of patient-level prescriptions. These associations in the facility-level model followed the same direction.

CONCLUSIONS

DOPPS data show large variations across countries in AHA prescription for haemodialysis patients. The data suggest an association between ARB use and reduction in all-cause mortality, as well as with the use of BBs and reduction in cardiovascular mortality among haemodialysis patients.

Hypertension in dialysis and kidney transplant patients

For the first time, the Canadian Hypertension Education Program has studied the evidence supporting blood pressure control in people requiring renal replacement therapy for end-stage kidney disease, including those on dialysis and with renal transplants. According to the Canadian Organ Replacement Registry's 2008 annual report, there were an estimated 33,832 people with end-stage renal disease in Canada at the end of 2006, an increase of 69.7% since 1997. Of these, 20,465 were on dialysis and 13,367 were living with a functioning kidney transplant. Thus, it is becoming more likely that primary care practitioners will be helping to care for these complex patients. With the lack of large controlled clinical trials, the consensus recommendation based on interpretation of the existing literature is that blood pressure should be lowered to below 140/90 mmHg in hypertensive patients on renal replacement therapy and to below 130/80 mmHg for renal transplant patients with diabetes or chronic kidney disease.