Kinetics of β2-Microglobulin and Phosphate during Hemodialysis: Effects of Treatment Frequency and Duration

Impact of intradialytic fiber clotting on dialyzer extraction and solute removal: a randomized cross-over study

Previous studies revealed the importance of biocompatibility, anticoagulation strategy, and dialysis mode and duration on fiber blocking at the end of a hemodialysis session. The present study was set up in ten hemodialysis patients to relate fiber patency to dialyzer extraction and removal of small and middle molecules. With only 1/4th of the regular anticoagulation dose, and using a Solacea 19H and FX800 CorDiax dialyzer, fiber patency was quantified using 3D micro-CT scanning for different dialysis durations (i.e. 60, 120 and 240 min). While Solacea showed enhanced fiber patency in all test sessions, fiber blocking in the FX800 CorDiax did not follow a linear process during dialysis, but was rather accelerated near the end of dialysis. Dialyzer extraction ratios were correlated with the percentages of open fibers. While the fiber blocking process affected extraction ratios (i.e. for phosphorus and myoglobin in the FX800 CorDiax), it had only minor impact on the removal of toxins up to at least 12 kDa.

Excessive elevation of serum phosphate during tumor lysis syndrome: Lessons from a particularly challenging case

Burkitt’s lymphoma is a common cause of tumor lysis syndrome (TLS) and, in the era of aggressive utilization of prophylactic allopurinol and recombinant uricase enzyme, nephrologists are increasingly witnessing monovalent or divalent cation abnormalities without marked uric acid elevation. An 18-year-old male received his 1^st cycle of intensive chemotherapy for Burkitt’s lymphoma and developed TLS as defined by the Cairo Bishop criteria. Lactate dehydrogenase peaked at 9,105 U/L (range: 130 – 250) and was accompanied by acute kidney injury, including serum creatinine 2.2 mg/dL on the 4^th day with oliguria, hyperkalemia, extreme hyperphosphatemia (21.4 mg/dL), hypermagnesemia, and hypocalcemia. Renal replacement therapy decision was made based on life-threatening electrolyte disturbances. The competing necessity to effectively control hyperphosphatemia and avoid the complication of dialysis disequilibrium syndrome prompted us to perform an initial intermittent hemodialysis with simultaneous intravenous mannitol administration, followed by continuous hemodialysis to manage the continued production of phosphorus from cell lysis. Osmotic stability during the therapy session was affirmatively demonstrated (322, 319 mOsm/kg, respectively). The patient showed excellent tolerance for these therapies and eventually recovered renal function as demonstrated during follow-up visits.

Modification and Validation of the Phosphate Removal Model: A Multicenter Study

BACKGROUND

Our research group has previously reported a noninvasive model that estimates phosphate removal within a 4-h hemodialysis (HD) treatment. The aim of this study was to modify the original model and validate the accuracy of the new model of phosphate removal for HD and hemodiafiltration (HDF) treatment.

METHODS

A total of 109 HD patients from 3 HD centers were enrolled. The actual phosphate removal amount was calculated using the area under the dialysate phosphate concentration time curve. Model modification was executed using second-order multivariable polynomial regression analysis to obtain a new parameter for dialyzer phosphate clearance. Bias, precision, and accuracy were measured in the internal and external validation to determine the performance of the modified model.

RESULTS

Mean age of the enrolled patients was 63 ± 12 years, and 67 (61.5%) were male. Phosphate removal was 19.06 ± 8.12 mmol and 17.38 ± 6.75 mmol in 4-h HD and HDF treatments, respectively, with no significant difference. The modified phosphate removal model was expressed as Tpo4 = 80.3 × C45 - 0.024 × age + 0.07 × weight + β × clearance - 8.14 (β = 6.231 × 10-3 × clearance - 1.886 × 10-5 × clearance2 - 0.467), where C45 was the phosphate concentration in the spent dialysate measured at the 45th minute of HD and clearance was the phosphate clearance of the dialyzer. Internal validation indicated that the new model was superior to the original model with a significantly smaller bias and higher accuracy. External validation showed that R2, bias, and accuracy were not significantly different than those of internal validation.

CONCLUSIONS

A new model was generated to quantify phosphate removal by 4-h HD and HDF with a dialyzer surface area of 1.3-1.8 m2. This modified model would contribute to the evaluation of phosphate balance and individualized therapy of hyperphosphatemia.

Beta-2 Microglobulin Amyloidosis: Past, Present, and Future

Almost half a century has elapsed since the first description of dialysis-related amyloidosis (DRA), a disorder caused by excessive accumulation of β-2 microglobulin (B2M). Within that period, substantial advances in RRT occurred. These improvements have led to a decrease in the incidence of DRA. In many countries, DRA is considered a "disappearing act" or complication. Although the prevalence of patients living with RRT increases, not all will have access to kidney transplantation. Consequently, the number of patients requiring interventions for treatment of DRA is postulated to increase. This postulate has been borne out in Japan, where the number of patients with ESKD requiring surgery for carpal tunnel continues to increase. Clinicians treating patients with ESKD have treatment options to improve B2M clearance; however, there is a need to identify ways to translate improved B2M clearance into improved quality of life for patients undergoing long-term dialysis.

Asymmetric dimethylarginine compartmental behavior during high-flux hemodialysis

Aim

The accumulation of uremic toxins, such as asymmetric dimethylarginine (ADMA), has emerged as one of the major cardiovascular disease-related risk factors in patients with end-stage renal disease (ESRD). Based on the low molecular weight of ADMA, hemodialysis (HD) should theoretically effectively remove ADMA. In this study, we investigated the clearance behavior of ADMA during high-flux HD.

Methods

Eight HD patients without residual renal function were included. Blood samples were collected at 0, 30, 60, 120 and 240 min after dialysis started, as well as 1 h and 48 h after dialysis. ADMA level was detected by HPLC-MS/MS. Herein, the ADMA level in blood cells and the ADMA protein binding rate were measured. Accordingly, the dialyzer extraction ratio was also determined.

Results

The reduction ratio (RR) of ADMA (corrected for hemoconcentration) was significantly lower, at only 37.21 ± 6.44%, than that of urea and creatinine (p < .05). Interestingly, its clearance from plasma was precipitous early in dialysis and became slowly from 60 to 240 min. Additionally, a greater inlet erythrocyte than plasma concentration was found for ADMA. The dialyzer extraction ratio was comparable between ADMA and creatinine or urea (83 ± 5% for ADMA vs. 84 ± 3% and 88 ± 2% for creatinine and urea, respectively; both p>.05). Urea and creatinine had a slight rebound ratio of less than 10% at 1 h after the completion of HD. In contrast, considerable rebound of approximately 30% was detected in ADMA.

Conclusion

This study suggests that ADMA may present a multicompartmental distribution that cannot be representatively reflected by the urea kinetics model.

Hemodialysis Product and Hip Fracture in Hemodialysis Patients: A Nationwide Cohort Study in Japan

Some have raised concerns that longer and more frequent hemodialysis (HD) would be associated with bone fractures due to excess phosphate removal. We examined the effects of hemodialysis product (HDP) on hip fracture incidence among Japanese HD patients using registry data of the Japanese Society for Dialysis Therapy. During a 1-year study period, 1411 hip fractures occurred among 135 984 patients. After adjusting for demographic and clinical factors, patients with a high HDP did not show a significant risk of hip fracture. Interestingly, patients with polycystic kidney disease had a lower risk of hip fracture. Our findings did not support the hypothesis that patients undergoing longer and more frequent HD would face a higher risk of hip fracture than those undergoing shorter and less frequent HD. Polycystic kidney disease was identified as a new significant factor for hip fracture; relative to glomerulonephritis, this condition was associated with a lower risk of hip fracture.

The effects of intradialytic exercise on hemodialysis adequacy: A systematic review

Dialysis adequacy is an independent predictor of high mortality rates in hemodialysis patients. Intradialytic exercise is a potential strategy to increase uremic solute removal by increasing blood flow to low perfusion tissue beds. The purpose of this review is to establish the efficacy of intradialytic exercise for hemodialysis adequacy. Additionally, this review aims to provide practical information to aid health care professionals implement intradialytic exercise for dialysis adequacy. Database and hand searches identified 15 published interventional studies that implemented intradialytic exercise for dialysis adequacy as a primary outcome measure in adult maintenance hemodialysis patients. Data pertaining to dialytic solute clearance of urea, creatinine, beta₂ microglobulin, phosphate, and potassium were extracted. Mean differences, normalized to percentages, and effect sizes were calculated and reported. The current data pertaining to the use of intradialytic exercise for improving dialysis adequacy in terms of Kt/V_urea or small molecule uremic toxin clearance are equivocal. Limited data showed that intradialytic exercise has no effect middle molecule toxin (beta₂ - microglobulin) clearance. Intradialytic exercise favored increased phosphate removal showing medium to large effects for reduced serum concentrations, reduced rebound and increased clearance. In summary, supervised light to moderate intradialytic aerobic cycling appears to be beneficial for increasing phosphate removal and may be an adjunct therapy for patients failing to meet clinical phosphate targets. Further work is required to establish the effect of intradialytic exercise on Kt/V_urea and other middle molecule and protein bound solutes. Research aimed at establishing the most effective exercise prescription for improved solute clearance is warranted.

Boundaries of frequency and treatment time in conventional hemodialysis: Balancing convenience, economics, and health outcomes

Since the inception of hemodialysis (HD) for patients with chronic kidney disease, the "perfect" dialysis prescription has remained elusive. Part of this may relate to the heterogeneity among populations, individual patients, and differences in access to health provision. The optimal balance between dialysis frequency and duration to achieve reductions in patient morbidity and mortality continues to be debated. The concept of dialysis adequacy originated from a post hoc mathematical analysis of the National Cooperative Study and has evolved to become a way of calculating dialysis dose and standardizing the dialysis prescription. In contrast, in its originally conceived sense, dialysis adequacy referred to the effective clearance of small solutes. Given the evolution of dialysis practice, we now aim to consider dialysis adequacy in a broader and more holistic manner particularly in view of our aging population and focus toward important patient-centered outcomes. While the traditional thrice weekly, HD regimen remains the default renal replacement modality, alternative strategies including short daily HD, long conventional HD, and long nocturnal HD are being widely implemented. We aim for optimal solute clearance, effective ultrafiltration to achieve normotension (while avoiding intradialytic symptoms) and maintenance of nutritional parameters all within the caveat that quality of life and autonomy are preserved.

Phosphate-control adherence in hemodialysis patients: current perspectives

OBJECTIVES

This review summarizes factors relevant for adherence to phosphate-control strategies in dialysis patients, and discusses interventions to overcome related challenges.

METHODS

A literature search including the terms "phosphorus", "phosphorus control", "hemo-dialysis", "phosphate binder medications", "phosphorus diet", "adherence", and "nonadherence" was undertaken using PubMed, PsycInfo, CINAHL, and Embase.

RESULTS

Hyperphosphatemia is associated with cardiovascular and all-cause mortality in dialysis patients. Management of hyperphosphatemia depends on phosphate binder medication therapy, a low-phosphorus diet, and dialysis. Phosphate binder therapy is associated with a survival benefit. Dietary restriction is complex because of the need to maintain adequate protein intake and, alone, is insufficient for phosphorus control. Similarly, conventional hemodialysis alone is insufficient for phosphorus control due to the kinetics of dialytic phosphorus removal. Thus, all three treatment approaches are important contributors, with dietary restriction and dialysis as adjuncts to the requisite phosphate binder therapy. Phosphate-control adherence rates are suboptimal and are influenced directly by patient, provider, and phosphorus-control strategy-related factors. Psychosocial factors have been implicated as influential "drivers" of adherence behaviors in dialysis patients, and factors based on self-motivation associate directly with adherence behavior. Higher-risk subgroups of nonadherent patients include younger dialysis patients and non-whites. Provider attitudes may be important - yet unaddressed - determinants of adherence behaviors of dialysis patients.

CONCLUSION

Adherence to phosphate binders, low-phosphorus diet, and dialysis prescription is suboptimal. Multicomponent strategies that concurrently address therapy-related factors such as side effects, patient factors targeting self-motivation, and provider factors to improve attitudes and delivery of culturally sensitive care show the most promise for long-term control of phosphorus levels. Moreover, it will be important to identify patients at highest risk for lack of control, and for programs to be ready to deliver flexible person-centered strategies through training and dedicated resources to align with the needs of all patients.

When is more frequent hemodialysis beneficial?

The use of frequent hemodialysis (HD) is growing, with the hope of improving outcomes in end-stage renal disease. We narratively review the three randomized trials, 15 comparative cohort studies, and several case series of frequent HD that empirically demonstrate the potential efficacy and adverse effects of these regimens. Taken together, the randomized studies suggest frequent HD may result in left ventricular mass regression. This effect is most pronounced when left ventricular mass is abnormal, but attenuated by significant residual urine output. Both frequent short and long HD consistently improved blood pressure control and reduced antihypertensive use, despite greater weekly interdialytic weight gains. Serum phosphate was lowered. Frequent short daytime HD improved health-related quality of life, while frequent long overnight HD did not. Regarding adverse effects, frequent HD patients underwent significantly more procedures to salvage arteriovenous vascular accesses. An absolute increase in hypotensive episodes was observed with frequent short HD, while frequent long HD accelerated residual renal function loss and increased perceived caregiver burden. The effect of frequent HD on mortality is controversial, due to conflicting results and limitations of published studies. Finally, pregnancy outcomes may be substantially better with frequent long HD. On the basis of these data, we suggest frequent HD is most likely to benefit patients with left ventricular hypertrophy particularly if there is minimal urine output, those unable to attain dry weight on a thrice weekly schedule, and pregnant women. All patients receiving frequent HD should be advised of and monitored for potential risks.

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.

Impact of using two dialyzers in parallel on phosphate clearance in hemodialysis patients: a randomized trial

Background

Dietary restriction and phosphate binders are the main interventions used to manage hyperphosphatemia in people on hemodialysis, but have limited efficacy. Modifying conventional dialysis regimens to enhance phosphate clearance as an alternative approach remains relatively unstudied.

Methods

This was a 10-week, 2-arm, randomized crossover study. Participants were prevalent dialysis patients ( n = 32) with consecutive serum phosphate levels >1.6 mmol/L and on stable doses of a phosphate binder. Following a 2-week run-in period, participants were randomized to initiate dialysis using two high flux dialyzers in parallel (blood flow ≥350 mL/min, dialysate flow 800 mL/min) or standard dialysis using one high flux dialyzer (blood flow ≥350 mL/min, dialysate flow of 800 mL/min). Each regimen was 3 weeks in duration. After a 2-week washout period, participants received the alternate regimen. The primary outcome was the mean difference in phosphate clearance by dialyzer strategy. Secondary outcomes were phosphate removal and pre-dialysis serum phosphate.

Results

Phosphate clearance for the double dialyzer strategy did not differ significantly from the single dialyzer strategy [mean difference 7.5 mL/min (95% confidence interval, 95% CI, -6.1, 21.0), P = 0.28]. There was no difference in total phosphate removal and pre-dialysis phosphate between the double and single dialyzer strategies [total phosphate removal mean difference -0.2 mmol (95% CI -4.1, 3.7), P = 0.93; pre-dialysis mean difference 0.01 mmol/L (95% CI -0.18, 0.21), P = 0.88]. There was no difference in the proportion of participants who experienced at least one episode of intradialytic hypotension (32 versus 47%, P = 0.13). A limitation of the study was frequent protocol deviations in the dialysis prescription.

Conclusions

In this study, the use of two dialyzers in parallel did not increase phosphate clearance, phosphate removal or pre-dialysis serum phosphorus when compared with a standard dialysis treatment strategy. Future studies should continue to evaluate novel methods of phosphate removal using conventional hemodialysis.

Dialyzer Reuse and Outcomes of High Flux Dialysis

Background

The bulk of randomized trial evidence for the expanding use of High Flux (HF) hemodialysis worldwide comes from two randomized controlled trials, one of which (HEMODIALYSIS, HEMO) allowed, while the other (Membrane Outcomes Permeability, MPO) excluded, the reuse of membranes. It is not known whether dialyzer reuse has a differential impact on outcomes with HF vs low flyx (LF) dialyzers.

Methods

Proportional Hazards Models and Joint Models for longitudinal measures and survival outcomes were used in HEMO to analyze the relationship between β2-microglobulin (β2M) concentration, flux, and reuse. Meta-analysis and regression techniques were used to synthesize the evidence for HF dialysis from HEMO and MPO.

Findings

In HEMO, minimally reused (< 6 times) HF dialyzers were associated with a hazard ratio (HR) of 0.67 (95% confidence interval, 95%CI: 0.48–0.92, p = 0.015), 0.64 (95%CI: 0.44 – 0.95, p = 0.03), 0.61 (95%CI: 0.41 – 0.90, p = 0.012), 0.53 (95%CI: 0.28 – 1.02, p = 0.057) relative to minimally reused LF ones for all cause, cardiovascular, cardiac and infectious mortality respectively. These relationships reversed for extensively reused membranes (p for interaction between reuse and flux < 0.001, p = 0.005) for death from all cause and cardiovascular causes, while similar trends were noted for cardiac and infectious mortality (p of interaction between reuse and flux of 0.10 and 0.08 respectively). Reduction of β2M explained only 1/3 of the effect of minimally reused HF dialyzers on all cause mortality, while non-β2M related factors explained the apparent attenuation of the benefit with more extensively reused dialyzers. Meta-regression of HEMO and MPO estimated an adjusted HR of 0.63 (95% CI: 0.51–0.78) for non-reused HF dialyzers compared with non-reused LF membranes.

Conclusions

This secondary analysis and synthesis of two large hemodialysis trials supports the widespread use of HF dialyzers in clinical hemodialysis over the last decade. A mechanistic understanding of the effects of HF dialysis and the reuse process on dialyzers may suggest novel biomarkers for uremic toxicity and may accelerate membrane technology innovations that will improve patient outcomes.

Comparison of cystatin C and Beta-2-microglobulin kinetics in children on maintenance hemodialysis

Middle-molecules (MM) are not monitored in children on hemodialysis (HD), but are accumulated and increase the risk of cardiovascular disease and mortality. Molecular properties of Cystatin C (CyC), 13 kDa, potentially make it a preferred MM marker over Beta-2-Microglobulin (B2M), 12 kDa. We compared CyC and B2M kinetics to investigate if CyC can be used as preferred MM marker. CyC (mg/L) and B2M (μg/mL) were measured in 21 low-flux HD sessions in seven children. Blood samples were taken at HD start (pre), 1 and 2 hours into HD and at end of HD (post) for all sessions and 60 minutes after the first HD (Eq). PreCyC (9.85 ± 2.15) did not differ (P > 0.05) from postCyC (10.04 ± 2.83). PostB2M (38.87 ± 7.12) was higher (P < 0.05) than preHD B2M (33.27 ± 7.41). There was no change in CyC at 1 and 2 hours into HD, while B2M progressively increased. CyC or B2M changes did not significantly correlate with spKt/V (2.09 ± 0.86), ultrafiltration (4.61 ± 1.98%) or HD duration (218 ± 20 minutes). EqCyC was not different from postCyC (11.07 ± 3.14 vs. 10.71 ± 2.85, P > 0.05), while EqB2M was lower than postB2M (36.48 ± 7.68 vs. 41.09 ± 8.99, P < 0.05). MMs as represented by B2M and CyC are elevated in children on standard HD. Intensified HD modalities would be needed for their removal. B2M is affected by the dialytic process with a rise during HD independent of ultrafiltration and decrease 1 hour after, while CyC remains unchanged. We suggest that CyC be used as preferred marker of MM removal and as a marker of adequacy of intensified HD regimens.

Managing serum phosphate in haemodialysis patients: time for an innovative approach?

BACKGROUND/OBJECTIVES

Hyperphosphataemia, a common biochemical abnormality in chronic kidney disease, poses significant management challenges. This study aims to determine whether the reasons for this are multifactorial; including poor dietary knowledge, poor adherence to a low phosphate diet and phosphate-binding medications and the impact of age on these parameters.

SUBJECTS/METHODS

In order to compare serum phosphate and other associated parameters to the UK Renal Association Clinical Practice Guidelines 2010 an audit and service evaluation questionnaire was carried out in May 2011 on 130 haemodialysis outpatients attending the Plymouth Dialysis Unit.

RESULTS

Fifty-three percent of patients had serum phosphate within the target range of 1.1-1.7 mmol/l, 77% and 85% had serum calcium and parathyroid hormone within target ranges, respectively. Younger patients (18-45 years) were significantly less likely to have serum phosphate within range χ(2) (2, n=124)=18.77, P<0.001. Despite better knowledge of their own phosphate levels (P=0.005), phosphorus-rich foods (P<0.001), symptoms of hyperphosphataemia (P<0.001) and increased use of Renal Patient View (P=0.002), <65 years old had significantly higher phosphate levels than those >65 years (P<0.001). No significant associations were found between phosphate control and the following factors: gender, timing of dialysis shift, years on dialysis or dialysis adequacy.

CONCLUSIONS

In this population, despite better knowledge, younger patients have worse phosphate control than older patients. Using the same dietary education techniques may not be suitable for all ages, more innovative approaches supported by skilled health professionals are needed to motivate and engage with younger patients to promote self-management and adherence.

Interaction between intradialytic exercise and hemodialysis adequacy

BACKGROUND/AIMS

According to mathematical modeling, intradialytic exercise of sufficient intensity and duration implemented in the second half of dialysis should be as efficacious as increasing dialysis time for dialysis adequacy. This assumption has not been tested in vivo.

METHODS

In this controlled trial, 11 hemodialysis (HD) patients (mean (SD) age 56 (13) years) were recruited. Each patient completed three trial arms in a randomized order: routine care (CONT), increased HD time of 30 min (TIME), and intradialytic exercise (EXER), 60 min of cycling at 90% of the lactate threshold in the last 90 min of HD. The primary outcome was eKt/Vurea. Secondary outcomes included reduction and rebound ratios of urea, creatinine, phosphate and β2-microglobulin. Outcomes were calculated from blood sampling collected pre-, post- and 30 min post-HD and confirmed with dialysate sampling.

RESULTS

Exercise was not as efficacious as increased HD time for eKt/Vurea (EXER vs. CONT, mean change (95% CI): 0.03 (-0.05 to 0.12); TIME vs. CONT: 0.15 (0.05-0.26)). Exercise was less efficacious at improving reduction ratios of urea and creatinine. However, exercise was more efficacious than increased dialysis time for phosphate reduction ratio (EXER vs. CONT: 8.6% (0.5-16.7); TIME vs. CONT: 5.0% (-1.0 to 11.1)).

CONCLUSION

This study utilized a rigorously controlled in vivo design to test mathematical models and assumptions regarding dialysis adequacy. Intradialytic exercise towards the end of HD cannot replace the prescription of increased HD time for dialysis adequacy, but may be an adjunctive therapy for serum phosphate control.

Patient education for phosphorus management in chronic kidney disease

OBJECTIVES

This review explores the challenges and solutions in educating patients with chronic kidney disease (CKD) to lower serum phosphorus while avoiding protein insufficiency and hypercalcemia.

METHODS

A literature search including terms "hyperphosphatemia," "patient education," "food fatigue," "hypercalcemia," and "phosphorus-protein ratio" was undertaken using PubMed.

RESULTS

Hyperphosphatemia is a strong predictor of mortality in advanced CKD and is remediated via diet, phosphorus binders, and dialysis. Dietary counseling should encourage the consumption of foods with the least amount of inorganic or absorbable phosphorus, low phosphorus-to-protein ratios, and adequate protein content, and discourage excessive calcium intake in high-risk patients. Emerging educational initiatives include food labeling using a "traffic light" scheme, motivational interviewing techniques, and the Phosphate Education Program - whereby patients no longer have to memorize the phosphorus content of each individual food component, but only a "phosphorus unit" value for a limited number of food groups. Phosphorus binders are associated with a clear survival advantage in CKD patients, overcome the limitations associated with dietary phosphorus restriction, and permit a more flexible approach to achieving normalization of phosphorus levels.

CONCLUSION

Patient education on phosphorus and calcium management can improve concordance and adherence and empower patients to collaborate actively for optimal control of mineral metabolism.

Evaluation of Alternatives for Dysfunctional Double Lumen Central Venous Catheters Using a Two-Compartmental Mathematical Model for Different Solutes

Double lumen (DL) central venous catheters (CVC) often suffer from thrombosis, fibrin sheet formation, and/or suction towards the vessel wall, resulting in insufficient blood flow during hemodialysis. Reversing the catheter connection often restores blood flows, but will lead to higher recirculation. Single lumen (SL) CVCs have often fewer flow problems, but they inherently have some degree of recirculation. To assist bedside clinical decision making on optimal catheter application, we investigated mathematically the differences in dialysis adequacy using different modes of access with CVCs.

A mathematical model was developed to calculate reduction ratio (RR) and total solute removal (TSR) of urea, methylguanidine (MG), beta-2-microglobulin (β2M), and phosphate (P) during different dialysis scenarios: 4-h dialysis with a well-functioning DL CVC (DL-normal, blood flow QB 350 ml/min), dysfunctional DL CVC (DL-low flow, QB 250), reversed DL CVC (DL-reversed, QB 350, recirculation R = 10%) and 12 Fr SL CVC (effective QB273).

With DL-normal as reference, urea RR was decreased by 3.5% (DL-reversed), 13.0% (SL), and 15.6% (DL-low flow), while urea TSR was decreased by 3.3% (DL-reversed), 13.2% (SL), and 13.5% (DL-low flow). The same trend was found for MG and P. However, β2M RR decreased only 1.5% with SL CVC although TSR decrease was 17.2%, while RR decreased 21.1% with DL-low flow although TSR decrease was only 4.9%.

In the case of dysfunctional DL CVCs, reversing the catheter connection and restoring the blood flow did not impair TSR, with 10% recirculation. The SL CVC showed suboptimal TSR results that were similar to those of the dysfunctional DL CVC.

Phosphate removal model: an observational study of low-flux dialyzers in conventional hemodialysis therapy

Precise assessing phosphate removal by hemodialysis (HD) is important to improve phosphate control in patients on maintenance HD. We reported a simple noninvasive model to estimate phosphate removal within a 4-hour HD. One hundred sixty-five patients who underwent HD 4 hours per session using low-flux dialyzers made of polysulfone (1.2 m(2)) or triacetate (1.3 m(2)) were enrolled. Blood flows varied from 180 to 300 mL/min. Effluent dialysate samples were collected during the 4-hour HD treatment to measure the total phosphate removal. Predialysis levels of serum phosphate, potassium, hematocrit, intact parathyroid hormone, total carbon dioxide (TCO(2)), alkaline phosphatase, clinical and dialysis characteristics were obtained. One hundred thirty-five observations were randomly selected for model building and the remaining 30 for model validation. Total amount of phosphate removal within the 4-hour HD was mostly 15-30 mmol. A primary model (model 1) predicting total phosphate removal was Tpo(4)  = 79.6 × C(45) (mmol/L) - 0.023 × age (years) + 0.065 × weight (kg) - 0.12 × TCO(2) (mmol/L) + 0.05 × clearance (mL/min) - 3.44, where C(45) was phosphate concentration in spent dialysate measured at the 45 minute of HD and clearance was phosphate clearance of dialyzer in vitro conditions offered by manufacturer's data sheet. Since the parameter TCO(2) needed serum sample for measurement, we further derived a noninvasive model (model 2):Tpo(4)  = 80.3 × C(45)  - 0.024 × age + 0.07 × weight + 0.06 × clearance - 8.14. Coefficient of determination, root mean square error, and residual plots showed the appropriateness of two models. Model validation further suggested good and similar predictive ability of them. This study derived a noninvasive model to predict phosphate removal. It applies to patients treated by 4-hour HD under similar conditions.

The effect of dialysis modality on phosphate control : haemodialysis compared to haemodiafiltration. The Pan Thames Renal Audit

BACKGROUND AND OBJECTIVES

Hyperphosphataemia is a primary risk factor for patients with end-stage kidney failure. Phosphate clearance by traditional thrice-weekly standard haemodialysis is inadequate for patients achieving recommended dietary protein goals. We investigated whether phosphate control was improved by adding convective clearance with haemodiafiltration.

METHODS

We audited pre-midweek session calcium and phosphate levels in 5366 adult patients, 4515 treated by haemodialysis and 851 by on-line haemodiafiltration.

RESULTS

The cohorts were similar for age, sex and dialysis vintage. Serum phosphate was lower in the haemodiafiltration cohort (1.42 +/- 0.61 mmol/l) compared to the haemodialysis cohort (1.53 +/- 0.53 mmol/l; P < 0.001), as was the calcium-phosphate product (3.31 +/- 1.53 vs 3.5 +/- 1.33 mmol(2)/l(2), respectively; P < 0.001) despite a shorter treatment session time (3.68 +/- 0.44 vs 3.92 +/- 0.49 h; P < 0.001). Parathyroid hormone levels were similar.

CONCLUSIONS

The results of this audit suggest that haemodiafiltration offers improved phosphate control compared to standard intermittent haemodialysis.

Solute kinetics with short-daily home hemodialysis using slow dialysate flow rate

"NxStage System One()" is increasingly used for daily home hemodialysis. The ultrapure dialysate volumes are typically between 15 L and 30 L per dialysis, substantially smaller than the volumes used in conventional dialysis. In this study, the impact of the use of low dialysate volumes on the removal rates of solutes of different molecular weights and volumes of distribution was evaluated. Serum measurements before and after dialysis and total dialysate collection were performed over 30 times in 5 functionally anephric patients undergoing short-daily home hemodialysis (6 d/wk) over the course of 8 to 16 months. Measured solutes included beta(2) microglobulin (beta(2)M), phosphorus, urea nitrogen, and potassium. The average spent dialysate volume (dialysate plus ultrafiltrate) was 25.4+/-4.7 L and the dialysis duration was 175+/-15 min. beta(2) microglobulin clearance of the polyethersulfone dialyzer averaged 53+/-14 mL/min. Total beta(2)M recovered in the dialysate was 106+/-42 mg per treatment (n=38). Predialysis serum beta(2)M levels remained stable over the observation period. Phosphorus removal averaged 694+/-343 mg per treatment with a mean predialysis serum phosphorus of 5.2+/-1.8 mg/dL (n=34). Standard Kt/V averaged 2.5+/-0.3 per week and correlated with the dialysate-based weekly Kt/V. Weekly beta(2)M, phosphorus, and urea nitrogen removal in patients dialyzing 6 d/wk with these relatively low dialysate volumes compared favorably with values published for thrice weekly conventional and with short-daily hemodialysis performed with machines using much higher dialysate flow rates. Results of the present study were achieved, however, with an average of 17.5 hours of dialysis per week.

Oral phosphate binders: history and prospects

The use of an oral phosphate binder is a promising and most practical strategy for the prevention of vascular calcification in patients with chronic kidney disease (CKD). To secure the safety: 1) the oral phosphate binder must not cause adverse effects in the gastrointestinal tract; 2) the oral phosphate binder should be non-absorbable or barely absorbable through the gastrointestinal tract, or 3) if partially absorbed through the gastrointestinal tract, it must be eliminated from circulation through a pathway other than urinary excretion, and 4) even if it accumulates in the body, it should not cause organ dysfunctions. Metal salt type oral phosphate binder is the most classical type of oral phosphate binders that includes aluminum hydroxide gel and lanthanum carbonate. These oral phosphate binders effectively adsorb phosphate ions, however, have a potential risk for accumulation and intoxication. Calcium salt type oral phosphate binder was the most widely prescribed oral phosphate binder in the last decade but is now believed to exert potential harm, favoring progression of vascular calcification through excessive intestinal calcium load. However, recent studies failed to detect an inferiority of calcium salt type oral phosphate binders as compared to non-calcium salt type oral phosphate binders in terms of mortality and/or morbidity of hemodialysis patients. Polymerized resin type is a safe and relatively effective oral phosphate binder, which is supported by many clinical evidences. However, it sometimes causes severe constipation, especially in Japanese patients. Among metal compound type oral phosphate binder, other promising compounds include boehmite-type aluminum and hydrotalcite-like compounds but they are not yet available in the clinical setting.

[Physical principles of renal replacement therapy applied to end stage renal disease patients]

"Hemodialysis" is the generic term that refers to all forms of renal replacement therapy (RRT) able to restore periodically the "internal milieu" composition in end stage renal disease patients (ESRD). RRT includes several modalities (hemodialysis, hemofiltration, hemodiafiltration) that induce basic physical principles (diffusion, convection, adsorption) via an exchange module (dialyser) and an electrolytic exchange solution (dialysis fluid). The cleansing property of the RRT depends on different factors: the treatment modality itself, the uremic toxin considered, patient's characteristic and the operational conditions (duration of treatment, session frequency, blood and dialysate flow rates). Solute instantaneous clearances reflect the dialyser's performances used in optimal conditions but not necessarily the body clearance. The effective solute body clearance is more difficult to assess in clinical practice since it includes some variables such as the treatment duration, the biological complexity of internal milieu and the variability of the patient/dialysis system interaction. The "dialysis adequacy" concept that governs the treatment efficacy in ESRD patients could not be reduced to the urea Kt/V ratio. It must integrate a selection of pertinent clinical and biological markers covering the complete spectrum of uremic abnormalities. Adequate knowledge of those basic physical principles that control the solute exchange in hemodialysis patient is highly recommended to any nephrologist who looks forward to improve treatment efficacy and reduce mortality in ESRD patients.

Management of hyperphosphatemia in patients with end-stage renal disease: focus on lanthanum carbonate

Elevated serum phosphate levels as a consequence of chronic kidney disease (CKD) contribute to the increased cardiovascular risk observed in dialysis patients. Protein restriction and dialysis fail to adequately prevent hyperphosphatemia, and in general treatment with oral phosphate binding agents is necessary in patients with advanced CKD. Phosphate plays a pivotal role in the development of vascular calcification, one of the factors contributing to increased cardiovascular risk in CKD patients. Treatment of hyperphosphatemia with standard calcium-based phosphate binders and vitamin D compounds can induce hypercalcemic episodes, increase the Ca × PO₄ product and thus add to the risk of ectopic mineralization. In this review, recent clinical as well as experimental data on lanthanum carbonate, a novel, non-calcium, non-resin phosphate binding agent are summarized. Although lanthanum is a metal cation no aluminium-like toxicity is observed since the bioavailability of lanthanum is extremely low and its metabolism differs from that of aluminium. Clinical studies now document the absence of toxic effects of lanthanum for up to 6 years of follow-up. The effects of lanthanum on bone, vasculature and brain are discussed and put in perspective with lanthanum pharmacokinetics.

Serum beta2-microglobulin level is a significant predictor of mortality in maintenance haemodialysis patients

BACKGROUND

Beta(2)-microglobulin (beta(2)-M) is recognized as a surrogate marker of middle-molecule uraemic toxins and is a key component in the genesis of dialysis-associated amyloidosis. Few studies have evaluated the association of beta(2)-M levels with clinical outcome in dialyzed patients.

METHODS

The prognostic implication of serum beta(2)-M levels for the survival of haemodialysis patients was examined in 490 prevalent haemodialysis patients (60.1 +/- 11.8 years, haemodialysis duration of 87.4 +/- 75.7 months, 288 males and 202 females; 24% diabetics). The patients were divided into two groups according to their serum beta(2)-M levels: lower beta(2)-M group (n = 245) with serum beta(2)-M <32.2 mg/L (the median serum beta(2)-M) and higher beta(2)-M group (n = 245) with that >or=32.2 mg/L.

RESULTS

During the follow-up period of 40 +/- 15 months, there were 91 all-cause deaths, and out of them, 36 were from cardiovascular diseases. Kaplan-Meier analysis revealed that all-cause mortality in the higher beta(2)-M group was significantly higher compared to that in the lower beta(2)-M group (P < 0.001). Multivariate Cox proportional hazards analyses showed that serum beta(2)-M level was a significant predictor for all-cause mortality (hazard ratio, 1.05; 95% CI, 1.01-1.08; P = 0.005), and for non-cardiovascular mortality (hazard ratio, 1.06; 95% CI, 1.02-1.10; P = 0.006), after adjustment for age, gender, haemodialysis duration, the presence of diabetes, serum albumin and serum C-reactive protein.

CONCLUSION

These results demonstrate that the serum beta(2)-M level is a significant predictor of mortality in haemodialysis patients, independent of haemodialysis duration, diabetes, malnutrition and chronic inflammation, suggesting the clinical importance of lowering serum beta(2)-M in these patients.

Phosphate is a uremic toxin

Hyperphosphatemia is one of the more prevalent metabolic disturbances in kidney failure. Phosphate can be considered a uremic toxin based on the accumulation of phosphate during chronic kidney disease, the effects of phosphate on biological systems, and the adverse effects of hyperphosphatemia. The renal clearance of phosphate is maintained until later stages of chronic kidney disease, when the remaining nephrons are no longer able to excrete sufficient phosphate to offset dietary phosphate absorption. Clearance of phosphate by conventional forms of dialysis is insufficient to prevent hyperphosphatemia in most endstage kidney-disease patients. Phosphate contributes to metabolic disturbances such as hyperparathyroidism, vitamin D resistance, and hypocalemia. In combination with these and other factors, hyperphosphatemia damages many organs, including the parathyroid glands, bones, and most importantly the cardiovascular system. Elevated phosphorus is associated with arterial and valvular calcification, arteriosclerosis, and an increased risk of cardiovascular death. Importantly, the adverse effects of hyperphosphatemia are partially preventable with the effective treatments available today.

Dialysis-related amyloidosis: late finding or hidden epidemic?

Dialysis-related amyloidosis is a complication of end-stage renal disease (ESRD) that results from retention of beta2-microglobulin (beta2M) and its deposition as amyloid fibrils into osteoarticular tissue. The clinical manifestations usually develop after several years of dialysis dependence and include carpal tunnel syndrome, destructive arthropathy, and bone cysts and fractures. High-flux membranes, daily dialysis, and hemofiltration all would be expected to delay the onset of dialysis-related amyloidosis because, to varying degrees, each increases the clearance of beta2M from the plasma. Thus what is currently a late complication of ESRD might become an even later complication as dialysis practices change. The significance of histologically evident but clinically silent beta2M amyloid, detectable not only in osteoarticular tissue but also in blood vessels, is unclear. Accumulating evidence that amyloidogenic proteins have direct and specific effects on cell processes irrespective of the extent of amyloid deposition raises the possibility that early, clinically silent beta2M amyloid deposits have unrecognized importance.

Beta2-microglobulin, a uremic toxin with a double meaning

beta(2)M is a strong and independent indicator of hemodialysis patient outcomes and an excellent surrogate for middle molecules, and deserves to be routinely monitored and incorporated into dialysis adequacy targets. beta(2)M has a double meaning, reflecting both dialysis efficacy in terms of solute mass transfer and patient bioactivity. The work of Ward et al. in this issue warrants a study to test the hypothesis that long daily hemodiafiltration treatment would be the optimal renal replacement modality to improve dialysis patient outcomes.