A modified algorithm of the single pool urea kinetic model

Toward an individualized determination of dialysis adequacy: a narrative review with special emphasis on incremental hemodialysis

INTRODUCTION

The search for the 'perfect' renal replacement therapy has been paralleled by the search for the perfect biomarkers for assessing dialysis adequacy. Three main families of markers have been assessed: small molecules (prototype: urea); middle molecules (prototype β2-microglobulin); comprehensive and nutritional markers (prototype of the simplified assessment, albumin levels; composite indexes as malnutrition-inflammation score). After an era of standardization of dialysis treatment, personalized dialysis schedules are increasingly proposed, challenging the dogma of thrice-weekly hemodialysis.

AREAS COVERED

In this review, we describe the advantages and limitations of the approaches mentioned above, focusing on the open questions regarding personalized schedules and incremental hemodialysis.

EXPERT OPINION

In the era of personalized dialysis, the assessment of dialysis adequacy should be likewise personalized, due to the limits of 'one size fits all' approaches. We have tried to summarize some of the relevant issues regarding the determination of dialysis adequacy, attempting to adapt them to an elderly, highly comorbidity population, which would probably benefit from tailor-made dialysis prescriptions. While no single biomarker allows precisely tailoring the dialysis dose, we suggest using a combination of clinical and biological markers to prescribe dialysis according to comorbidity, life expectancy, residual kidney function, and small and medium-size molecule depuration.

What volume to choose to assess online Kt/V?

INTRODUCTION

Urea distribution volume (V) can be assessed in different ways, among them the anthropometric Watson Volume (V_W). However, many studies have shown that V_W does not coincide with V and that the latter can be more accurately estimated with other methods. The present multicentre study was designed to answer the question: what V to choose to assess online Kt/V?

MATERIALS AND METHODS

Pre- and postdialysis blood urea nitrogen concentrations and the usual input data set for urea kinetic modelling were obtained for a single dialysis session in 201 Caucasian patients treated in 9 Italian dialysis units. Only dialysis machines measuring ionic dialysance (ID) were utilized. ID reflects very accurately the mean effective dialyser urea clearance (Kd). Six different V values were obtained: the first one was V_W; the second one was computed from the equation established by the HEMO Study to predict the single pool-adjusted modelled V from V_W (V_H) (Daugirdas JT et al. KI 64: 1108, 2003); the others were estimated kinetically as: 1. V_ID, in which ID is direct input in the in the double pool variable volume (dpVV) calculation by means of the Solute-solver software; 2. V_Kd, in which the estimated Kd is direct input in the dpVV calculation by means of the Solute-solver software; 3. V_KTV, in which V is calculated by means of the second generation Daugirdas equation; 4. V_SPEEDY, in which ID is direct input in the dpVV calculation by means of the SPEEDY software able to provide results quite similar to those provided by Solute-solver.

RESULTS

Mean± SD of the main data are reported: measured ID was 190.6 ± 29.6 mL/min, estimated Kd was 211.6 ± 29.0 mL/min. The relationship between paired data was poor (R² = 0.34) and their difference at the Bland-Altman plot was large (21 ± 27 mL/min). V_W was 35.3 ± 6.3 L, V_H 29.5 ± 5.5, V_{_}ID 28.99 ± 7.6 L, V_{_}SPEEDY 29.4 ± 7.6 L, V_KTV 29.7 ± 7.0 L. The mean ratio V_W/V_ID was 1.22, (i.e. V_W overestimated V_ID by about 22%). The mean ratio V_H/V_ID was 1.02 (i.e. V_H overestimated V_ID by only 2%). The relationship between paired data of V_ID and V_W was poor (R² = 0.48) and their mean difference at the Bland-Altman plot was very large (-  6.39 ± 5.59 L). The relationship between paired data of V_ID and V_H was poor (R² = 47) and their mean difference was small but with a large SD (- 0.59 ± 5.53 L). The relationship between paired data of V_ID and V_SPEEDY was excellent (R² = 0.993) and their mean difference at the Bland-Altman plot was very small (- 0.54 ± 0.64 L). The relationship between paired data of V_ID and V_KTV was excellent (R² = 0.985) and their mean difference at the Bland-Altman plot was small (- 0.85 ± 1.06 L).

CONCLUSIONS

V_ID can be considered the reference method to estimate the modelled V and then the first choice to assess Kt/V. V_SPEEDY is a valuable alternative to V_ID. V_KTV can be utilized in the daily practice, taking also into account its simple way of calculation. V_W is not advisable because it leads to underestimation of Kt/V by about 20%.

Eliminating the need for routine monthly postdialysis serum urea nitrogen measurement: A method for monitoring Kt/V and normalized protein catabolic rate using conductivity determined dialyzer clearance

Many dialysis machines can compute dialyzer sodium clearances at multiple time points during a dialysis treatment using conductivity. For a given treatment, the average dialyzer sodium clearance (K), when combined with treatment time (t), and the estimated urea distribution volume (V, usually based on either anthropometry or bioimpedance), can be used to estimate Kt/V, an important measure of hemodialysis adequacy. While this conductivity-derived value for Kt/V correlates moderately with Kt/V calculated from predialysis and postdialysis serum urea nitrogen (SUN) values (urea reduction ratio, URR), the ultrafiltration volume, and session length it is, unfortunately, not sufficiently accurate to replace URR-based Kt/V. Here we underline the potential utility of an alternative method to estimate Kt/V (a variant of a technique originally proposed by Gotch and Levin and their colleagues) using conductivity-derived sodium clearance (K) that does not require routine measurement of the postdialysis SUN but which should closely track Kt/V computed in the usual fashion. The increased accuracy with the new method is explained by the use of a patient-specific value of V, which is an average value calculated from several dialysis sessions where both conductivity dialyzer clearance and predialysis and postdialysis SUN have been measured. Once this patient-specific conductivity/URR-based value for V has been determined, it can be used to calculate Kt/V for subsequent treatments in which conductivity-based dialyzer clearances are measured, but around which predialysis and postdialysis SUN values have not been obtained. (If the predialysis SUN values for such a subsequent treatment are also measured, then a normalized protein catabolic rate that closely tracks the value from conventional urea modeling, can also be determined.) By reducing the number of postdialysis SUN measurements needed to monitor hemodialysis adequacy this new method of estimating Kt/V by conductivity should save staff time and laboratory costs, increase patient and staff safety, and decrease error rates associated with improper postdialysis blood sampling technique.

On-Line Dialysate Urea Monitor: Comparison with Urea Kinetics

The outputs of a new on-line dialysate urea monitor (UM) were compared to a urea kinetic model (UKM) and to dialysis direct quantification (DDO) in 13 patients. As for urea extraction and predialysis urea level, a good degree of correspondence was found between UM and laboratory data. Kt/VUM (1.21) is intermediate between Kt/VUKM (1.28) and Kt/VuKM using the post-rebound urea value (1.14) or Kt/VDDQ (1.14). Passing and Bablok regression analysis indicated no systematic error between Kt/VUM and Kt/VDDQ. The percentage differences in nPCR by UM, UKM and DDQ were not significant, but the standard deviations were wide. The UM approach is very simple and practical, avoiding blood sampling, laboratory analysis and data handling. It is reliable enough for clinical practice. Compared with traditional urea kinetics, Kt/V computation by a mathematical elaboration of the dialysate urea profile drawn from several points theoretically invites fewer errors due to the analytical procedure.

Factors Affecting Npcr in Hemodialysed Patients

The determination of dialysis adequacy is difficult and definitions are in a state of flux (Lindsay). In fact, after fifteen years from the introduction of urea kinetics into clinical practice, nephrologists still do not agree on recognizing the real utility of it. Gotch and Sargent in their mechanistic analysis of the NCDS indicated that the dose of small molecules removal could be defined by Kt/V urea. The results of the NCDS were depicted in a three-variable plot in which six domains could be seen. Several reports have documented malnutrition as being frequently present in patients on maintenance hemodialysis. It is generally accepted that a suboptimal nutritional status is associated with an increased morbidity and may adversely affect rehabilitation and the quality of life. In 1989 Lindsay et al showed that low levels of Kt/V corresponded with low levels of nPCR and found a direct correlation between the two parameters. On this basis, they suggested the hypothesis of nPCR dependence on Kt/V. The Authors showed a good correlation (r=0.73) between nPCR and Kt/V in 55 patients. This work aims to evaluate the correlation between Kt/V and nPCR, real age and dialytic age in a dialytic population in Southern Italy, during a long period of observation (six years, follow up 2,692 months). One hundred and thirty-four patients were studied in six years of observation. Follow up: 2692 months. Twenty-six patients died during the observation period. The simple regression analysis of nPCR vs. Kt/V, real age and dialytic age was performed in 63 anuric patients. nPCR showed a statistical difference (p<0.01) versus reall age, but no difference versus dialytic age and Kt/V. Our research data show that increasing Kt/V administration does not modify the nPCR of patients with initial and steady low protein intake over a medium time of observation. The same happens in patients with initial and steady high protein intake, when decreasing Kt/V administration in a short period of observation. We confirm that nPCR and Kt/V do not show any mathematical correlation in short and medium times of observation. It is also stressed by the simple regression analysis of data for a selected population of anuric uremics on dialysis thrice weekly for long observation times (between three and six years). Variance analysis (in 8 patients who had used all the membranes) showed differences between Kt/V and dialytic age, but not nPCR and real age. Kt/V and biocompatibility do not appear to be correlated directly with nPCR, because other factors are important in determining the general well-being in uremic patients. Such factors have to be considered when prescribing the dialytic “dose” and in clinically evaluating a uremic patient.

Prescription and Surveillance of the Acetate-Free Biofiltration Sessions: The Bicarbonate Cycle

A computerized system, structured by 4 different models concerning urea depuration, and bicarbonate and sodium handling in acetate-free hemodiafiltration has been conceived for integrated use covering each step of the therapeutic cycle, from a) the prescription of the session to b) its delivery, up to c) the dose - response analysis: the system, now fully developed for the bicarbonate cycle, covers both working areas; the medical one, with a program implemented on a Personal Computer, called Skipper which deals with steps a) and c), and the nursing area, with a program built into the dialytic equipment software. The Skipper program supports the prescription step (a) testing the session schedule by bicarbonate, sodium and urea kinetics. The dialytic equipment, (step(b)) using a different program, on the basis of the scheduled parameters memorizes the end-session plasma bicarbonate level and reacts to any modifications of the parameters regarding blood flow and fluid reinfusion flow suggesting opposite changes in order to reach the scheduled results. Finally (step (c)), the Skipper system statistically evaluates the observed end session bicarbonate plasma level with an expected value with upper and lower confidence bounds obtained by a multiple regression analysis performed on a large population of patients.

A Modified Two-Bun Method for Routine Urea Modeling: Clinical Validation in 120 Patients on a Free Diet

Recently, a modified algorithm of the Two-BUN method (MA2p), avoiding dialyzer clearance measurement, was presented for routine assessment of Kt/V and NPCR. To validate MA2p in patients on a free diet (FDP), we studied 120 stable dialysis FDP by measuring Kt/V and NPCR with both MA2p and a modified version of the standard Three-BUN method (MA3p), for the 3 weekly sessions. The NPCR values (g/kg/day), calculated by MA3p for the 3 interdialyses were: 1.286∓0.274, 1.256∓0.276, and 1.116∓0.230, respectively. The correlation coefficient (r) for averaged Kt/V values obtained by the two methods was 0.999 and the percent error (Error%) for MA2p vs. MA3p results ranged from -1.5 to +0.78%. The respective results for NPCR were: r=0.967, Error% range from -11.7 to +13.9%. In conclusion, MA2p can be safely used in patients on a free diet. The lowest NPCR values were observed during the long interdialysis.

The variable target model: a paradigm shift in the incremental haemodialysis prescription

Background

The recent interest in incremental haemodialysis (HD) is hindered by the current prescription based on a fixed target model (FTM) for the total (dialytic + renal) equivalent continuous clearance (ECC). The latter is expressed either as standard Kt/V (stdKt/V), i.e. the pre-dialysis averaged concentration of urea-based ECC, or EKRc, i.e. the time averaged concentration-based ECC, corrected for volume (V) = 40 L. Accordingly, there are two different targets: stdKt/V = 2.3 volumes per week (v/wk) and EKRc = 13 mL/min/40 L. However, fixing the total ECC necessarily implies perfect equivalence of its components-the residual renal urea clearance (Kru) and dialysis clearance (Kd). This assumption is wrong because Kru has much greater clinical weight than Kd. Here we propose that the ECC target varies as an inverse function of Kru, from a maximum value in anuria to a minimum value at Kru levels not yet requiring dialysis. The aim of the present study was to compare the current FTM with the proposed variable target model (VTM).

Methods

The double pool urea kinetic model was used to model dialysis sessions for 360 virtual patients and establish equations predicting the ECC as a function of Kd, Kru and the number of sessions per week. An end-dialysis urea distribution V of 35 L (corresponding to a body surface area of 1.73 m 2 ) was used, so that the current EKRc target of 13 mL/min/40 L could be recalculated at an EKRc 35 value of 12 mL/min/35 L equal to 12 mL/min/1.73 m 2 . The latter also coincides with the maximum value of the EKRc 35 variable target in anuria. The minimum target value of EKRc 35 was assumed to coincide with Kru corrected for V = 35 L (i.e. Krc 35 = 6 mL/min/1.73 m 2 ). The corresponding target for stdKt/V was assumed to vary from 2.3 v/wk at Krc 35 = 0 to 1.7 v/wk at Krc 35 = 6 mL/min/1.73 m 2 . On this basis, the variable target values can be obtained from the following linear equations: target EKRc 35 = 12 - Krc 35 ; target stdKt/V = 2.3 - 0.1 × Krc 35 . Two versions of stdKt/V were considered: the classic version (stdKt/V Gotch ) with Kru at 70%, and the current version (stdKt/V Daug ) with Kru at 100%.

Results

The VTM with stdKt/V Gotch produces results very close to those using the FTM with stdKt/V Daug . Once-weekly HD is virtually not allowed by the FTM. In contrast, the VTM allows dialysis to start at Krc 35 ∼5 mL/min/1.73 m 2 on a once-weekly HD schedule, at least in relatively healthy patients; this schedule can be maintained until Krc 35 falls below 4 mL/min/1.73 m 2 , at which point the schedule should be changed to a twice-weekly HD schedule, that, in turn, could be maintained until Krc 35 falls below 2 mL/min/1.73 m 2 .

Conclusions

A paradigm shift from the FTM to the VTM in the prescription of incremental HD is proposed, whereby the VTM would allow less frequent treatments at lower Kru, with important clinical and economic implications. This approach is likely to be safe but needs to be confirmed by randomized controlled trials.

Kt/V (and especially its modifications) remains a useful measure of hemodialysis dose

Removal of small molecular weight solutes shows a strong relationship to hemodialysis outcomes. In contrast, survival with high-flux dialysis or hemodiafiltration is only slightly better than with low-flux hemodialysis. Despite laboratory evidence regarding toxicity of protein-bound uremic solutes, few data exist showing that increased removal of this class of molecules impacts outcomes. In the FHN trials, there was no effect of frequent dialysis, including frequent and long dialysis, on nutrition or control of anemia, outcomes expected to be sensitive to uremic toxin removal; the main benefit appeared to be better volume control. Scaling of hemodialysis dose to total body water may not be optimal. Kt/V scaling to body surface area and use of a continuous measure such as standard Kt/V reduces the likelihood of underdialysis of small patients, including children, and women. Minimum hemodialysis time may best be considered in respect to ultrafiltration rate, and a maximum target ultrafiltration rate unscaled to body size may be optimal. Intensive, extended dialysis may cause adverse effects to residual kidney function, and more information needs to be collected to better understand how urine volume modifies dose requirements, and how to maximize the chances of preserving residual kidney function.

Dialysis dosing for chronic hemodialysis: beyond Kt/V

Current views regarding hemodialysis adequacy reach beyond indices of small solute removal such as Kt/V. Nevertheless, new Kt/V-based constructs such as the standard Kt/V, which adjusts not only for dialysis frequency, but which also represents removal of sequestered solutes rather than easily removed urea, continue to be useful. The scaling of dialysis dose to measures of size other than body water results in higher recommended doses of dialysis for children, small patients, and women, compared with the current body water-based scaling approach. Aside from small solute removal, increasing weekly time on dialysis results in slower removal of fluid with better tolerance and with increased removal of phosphorus, although both salt and water and phosphorus control often respond to efforts to reduce intake. The intermediate term benefits of removing larger middle molecules such as beta-2-microglobulin appear to be modest, and the benefits of removal of protein-bound uremic toxins remain to be proved in controlled trials.

Dialysis dose scaled to body surface area and size-adjusted, sex-specific patient mortality

BACKGROUND AND OBJECTIVES

When hemodialysis dose is scaled to body water (V), women typically receive a greater dose than men, but their survival is not better given a similar dose. This study sought to determine whether rescaling dose to body surface area (SA) might reveal different associations among dose, sex, and mortality.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Single-pool Kt/V (spKt/V), equilibrated Kt/V, and standard Kt/V (stdKt/V) were computed using urea kinetic modeling on a prevalent cohort of 7229 patients undergoing thrice-weekly hemodialysis. Data were obtained from the Centers for Medicare & Medicaid Services 2008 ESRD Clinical Performance Measures Project. SA-normalized stdKt/V (SAN-stdKt/V) was calculated as stdKt/V × ratio of anthropometric volume to SA/17.5. Patients were grouped into sex-specific dose quintiles (reference: quintile 1 for men). Adjusted hazard ratios (HRs) for 1-year mortality were calculated using Cox regression.

RESULTS

spKt/V was higher in women (1.7 ± 0.3) than in men (1.5 ± 0.2; P<0.001), but SAN-stdKt/V was lower (women: 2.3 ± 0.2; men: 2.5 ± 0.3; P<0.001). For both sexes, mortality decreased as spKt/V increased, until spKt/V was 1.6-1.7 (quintile 4 for men: HR, 0.62; quintile 3 for women: HR, 0.64); no benefit was observed with higher spKt/V. HR for mortality decreased further at higher SAN-stdKt/V in both sexes (quintile 5 for men: HR, 0.69; quintile 5 for women: HR, 0.60).

CONCLUSIONS

SA-based dialysis dose results in dose-mortality relationships substantially different from those with volume-based dosing. SAN-stdKt/V analyses suggest women may be relatively underdosed when treated by V-based dosing. SAN-stdKt/V as a measure for dialysis dose may warrant further study.

Cholesterol Crystal Embolism Syndrome in Dialysis Patients: An Emerging Clinical Diagnosis?

BACKGROUND

Cholesterol crystal embolism syndrome (CCE) is an increasing end-stage renal disease cause. Few cases have been described on dialysis, despite the high prevalence of the predisposing factors.

METHODS

The diagnostic criteria of the present study were: skin lesions, myalgia, fatigue, fever and acute inflammatory serologic signs, in the presence of severe vasculopathy. The precipitating factors were: anticoagulation, endovascular intervention and ulcerated atherosclerotic plaque.

RESULTS

Between October 2003 and September 2005, CCE was diagnosed in 6 dialysis patients (of 200-210 on chronic treatment): 5 males, 1 female, median age 59.5 years (47-70) and end-stage renal disease follow-up 11.5 years (3-25). All had severe vasculopathy, 5 cardiopathy, and 4 were failed graft recipients. The treatment included: peritoneal dialysis, daily dialysis, 'conventional' hemodialysis (2 cases) and hemodiafiltration. The diagnosis was based on the clinical-laboratory picture in 1 patient. In the 5 others clues were present (dicumarol therapy, angioplasty, femoral artery thrombosis, CCE predialysis and ulcerated aortic plaque). The therapeutic approach consisted of corticosteroids (5 cases), statins (4 cases) and prostaglandin analogues (4 cases).

CONCLUSION

The differential diagnosis of CCE should also be considered in dialysis patients (necrotic lesions, limb pain and vasculitis-like signs).

A high body mass index and female gender are associated with an increased risk of nodular hyperplasia of parathyroid glands in chronic uraemia

BACKGROUND

A persistent hyperphosphataemia represents one of the most important factors in the development of secondary hyperparathyroidism (sHPTH). The present prospective study was designed in order to test the hypothesis that a higher body mass index (BMI) may predispose to a larger body burden of phosphate (P), influencing by that way the severity of sHPTH.

METHODS

Histological studies were performed on 168 parathyroid glands of 42 consecutive adult Caucasian haemodialysis patients (20 males and 22 females) referred for first parathyroidectomy (PTx): each parathyroid gland was graded as 0, when only or mainly diffuse hyperplasia was found, or as 1, when only or mainly nodular hyperplasia was found. Thus, parathyroid histology was scored on a 5-point scale: 0 = diffuse hyperplasia in the four glands; 1 = nodular hyperplasia in one gland; 2 = nodular hyperplasia in two glands; 3 = nodular hyperplasia in three glands; 4 = nodular hyperplasia in the four glands. For sake of simplicity, the three less severe histological gradings, i.e. scores 0-2 were grouped together and indicated as score group 2.

RESULTS

The distribution of the patients was the following: 28.6% were in the score group 2, 23.8% in the score group 3 and 47.6% in the score group 4 (20 patients, 14 of whom were females). The output of the one-way ANOVA with the histological scores as grouping variable and age, dialysis duration, BMI and pre-PTx serum iPTH, alkaline phosphatase (ALP), calcium (Ca) and P as predictors showed that only BMI was different among the three histological scores (P = 0.001). By stratifying the analysis by gender, the relationship between BMI and histological scores was confirmed only in females (P = 0.006). The stratification of the entire cohort into two groups according to the cut-off value of BMI = 25 kg/m(2) showed that: (i) score 4 was more prevalent in the high-BMI group and score 2 in the normal-BMI group (P = 0.01); (ii) female gender was more represented in the high-BMI group (12 out of 18 patients, P = 0.04); and (iii) the pre-PTx serum P levels were significantly higher in the high-BMI group (P = 0.008). The output of the linear multiple regression analysis with pre-PTx serum P as dependent variable and BMI, pre-PTx serum ALP and Ca as independent variables (selected according to the statistical significance in the bivariate correlations) showed that only serum Ca and BMI were statistically significant predictors of serum P levels.

CONCLUSIONS

A high BMI and female gender are associated with an increased risk of nodular hyperplasia of parathyroid glands in adult Caucasian haemodialysis patients. The two risk factors, above all if combined in the same patient, appear to predispose to a larger body burden of P, increasing by that way the severity of sHPTH.

Simple and accurate quantification of dialysis in acute renal failure patients during either urea non-steady state or treatment with irregular or continuous schedules

BACKGROUND

The quantification of dialysis in critically ill acute renal failure (ARF) patients requires a unifying expression that can establish kinetic equivalence amongst patients treated with irregular or frequent intermittent haemodialysis (IHD) schedules or with differing renal replacement therapies. EKRjc is a generalized form of the equivalent urea renal clearance (EKRc), and represents the equivalent continuous urea clearance that will result in the given time-averaged concentration of urea, for the given amount of urea removal. The suitability of EKRjc for the measurement of dialysis dose in this setting is examined.

SUBJECTS AND METHODS

420 weeks of renal replacement therapy (IHD and continuous renal replacement therapy) were simulated in 15 virtual 'patients' using a variable volume double pool urea kinetic model. Additional data from eight ARF patients were used to exemplify calculations. 1260 EKRjc values were calculated using both formal urea kinetic modelling, as well as a simplified method that requires input of changes in patient fluid state and blood urea nitrogen concentrations over a period of observation, in addition to an initial estimate of patient post-dialysis urea distribution volume (V(T)).

RESULTS

EKRjc is shown to provide a unifying expression of dialysis dose irrespective of IHD schedule or renal replacement therapy. EKRjc is shown to be independent from the assumption of the urea steady state, and intrinsically normalized to patient urea distribution volume to allow dose comparisons between patients of different size. Residual renal urea clearance is easily incorporated where present. EKRjc is easily calculated using the simplified method without the need for iterative urea kinetic modelling. The accuracy of this simplified method is maintained when the initial estimation of V(T) is both 25% greater or smaller than the true value. Calculation of EKRjc is exemplified using the clinical data.

CONCLUSIONS

EKRjc is the most suitable urea kinetic expression for the quantification of dialysis in critically ill ARF patients.

Vascular access surgery managed by renal physicians: the choice of native arteriovenous fistulas for hemodialysis

BACKGROUND

After decades of success in dialysis research and treatment, prompt availability of a well-functioning vascular access for dialysis remains a disturbing problem. On the basis of a single-center experience in which nephrologists are responsible for access surgery, we sought to identify predictors of catheter use at the start of hemodialysis (HD) therapy and risk factors affecting first permanent access survival.

METHODS

Demographics, comorbid conditions, predialysis follow-up, and access-related procedures of the 197 consecutive patients beginning extracorporeal treatment between 1995 and 2001 were prospectively entered into our database.

RESULTS

Despite the high prevalence of comorbidities (diabetes, 22%; cardiovascular disease, 50%; neoplasm, 15%), all subjects received a native fistula as a first permanent access, but almost 60% initiated HD therapy using a catheter. The latter showed more comorbidities and were referred later. According to the Kaplan-Meier method, median primary and secondary survivals of the first fistula were 38.1 months and more than 70 months, respectively. The Cox model indicated that diabetes and previous catheter use were independently associated with 85% and 63% greater relative risks for first failure, but only diabetes led to a greater risk for final failure (relative risk, 2.38; P = 0.05).

CONCLUSION

Both the absence of predialysis care and presence of comorbidity influence access type at HD therapy initiation and fistula survival. Earlier intervention strategies can increase the use and durability of a native fistula for HD. Direct involvement of nephrologists in the management of access surgery can be helpful in this respect.

Behavior of non-protein-bound and protein-bound uremic solutes during daily hemodialysis

BACKGROUND

In the last few years, renewed interest in daily short hemodialysis (DHD; six 2-hour sessions per week) has become apparent as a consequence of the better clinical outcome of patients treated by this schedule. Uremic syndrome is characterized by the retention of a large number of toxins with different molecular masses and chemical properties. Some toxins are water soluble and non-protein bound, whereas others are partially lipophilic and protein bound. There is increased evidence that protein-bound toxins are responsible for the biochemical and functional alterations present in uremic syndrome, and the kinetics of urea is not applicable to these substances for their removal. The aim of this study is to investigate whether DHD is accompanied by increased removal of non-protein-bound and protein-bound toxins and a decrease in their prehemodialysis (pre-HD) serum levels.

PATIENTS AND METHODS

We studied 14 patients with end-stage renal disease treated by standard HD (SHD; three 4-hour sessions per week) for at least 6 months and randomly assigned them to a two-period crossover study (SHD to DHD and DHD to SHD). Patients maintained the same dialyzer, dialysate, and Kt/V during the entire study. At the end of 6 months of SHD and 6 months of DHD, we evaluated hemoglobin levels, hematocrits, recombinant human erythropoietin doses, and pre-HD and post-HD concentrations of serum urea, creatinine, uric acid, and the following protein-bound toxins: 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid, p-cresol, indole-3-acetic acid, indoxyl sulfate, and hippuric acid.

RESULTS

Values for hemoglobin, hematocrit, and recombinant human erythropoietin dose did not change during the two study periods. Pre-HD concentrations of creatinine, urea, and uric acid decreased on DHD (creatinine, from 8.7 +/- 1.9 to 7.8 +/- 1.6 mg/dL; P < 0.05; urea, from 149.4 +/- 28.8 to 132.7 +/- 40 mg/dL; P = 0.05; uric acid, from 9.14 +/- 1.49 to 8.16 +/- 1.98 mg/dL; P = 0.06). Concerning protein-bound toxins, lower pre-HD levels during DHD were reported for indole-3-acetic acid (SHD, 0.16 +/- 0.04 mg/dL; DHD, 0.13 +/- 0.03 mg/dL; P = 0.01), indoxyl sulfate (SHD, 3.35 +/- 1.68 mg/dL; DHD, 2.85 +/- 1.08 mg/dL; P = 0.02), and p-cresol at the borderline of significance (SHD, 0.96 +/- 0.59 mg/dL; DHD, 0.78 +/- 0.33 mg/dL; P = 0.07).

CONCLUSION

Such non-protein-bound compounds as uric acid, creatinine, and urea were removed significantly better by DHD, and pre-HD serum levels were reduced. Furthermore, pre-HD concentrations of some protein-bound solutes, such as indole-3-acetic acid, indoxyl sulfate, and p-cresol, also were lower during DHD.

Effect of acetate-free biofiltration on the anaemia of haemodialysis patients: a prospective cross-over study

BACKGROUND

The discussion about the pathogenesis of renal anaemia, whether it is primarily due to relative erythropoietin (Epo) deficiency or to uraemic inhibition of erythropoiesis, is still open. Although it has so far not been possible to identify or isolate a substance retained in uraemia with a suppressive action directed specifically against red-cell production, dialysis therapy can improve the effect of both residual endogenous Epo and exogenous rHuEpo. To what extent the mode and/or the dose of dialysis influence Epo efficacy is as yet poorly understood.

METHODS

This study was performed as a single-centre trial. The protocol included a run-in period of 4 months followed by a prospective cross-over study including 6 months each of acetate-free biofiltration (AFB) with a high-flux biocompatible membrane and standard bicarbonate dialysis (BD) with a low-flux cellulosic membrane in a random sequence. AFB is a haemodiafiltration technique based on a continuous post-dilution infusion of a sterile isotonic bicarbonate solution. At the start of the run-in period (and for the entire length of the study), rHuEpo administration was withdrawn; patients whose haemoglobin (Hb) levels dropped at a level <8.0 g/dl at one single monthly check, had to be withdrawn from the study. A blood sample was collected every month for the blood gas analysis and for the determination of blood urea nitrogen, serum creatinine, sodium, potassium, calcium, phosphorus, Hb, erythrocyte, reticulocyte, leukocyte and thrombocyte cell counts, mean globular volume and haematocrit. An equilibrated single pool Kt/V(urea)>1.2 was mandatory in both treatment modalities. Serum iron, total iron-binding capacity, and ferritin were checked every 3 months.

RESULTS

Twenty-three of 137 haemodialysis patients were considered eligible for the trial on the basis of the entry criteria. Of these, 15 volunteered and only 10 completed the study. No significant differences in the haematological indices, in the biochemical parameters assessing body iron stores, or in i.v. iron dosage was observed when comparing AFB with BD treatments. The equilibrated single pool Kt/V(urea) was always >1.2 and in no case was a significant difference observed when comparing AFB with BD treatments. Treatment time was significantly different between the two treatments (262+/-2 min in BD and 249+/-1 in AFB, P<0.0001). Neither pre- nor post-dialysis systolic and diastolic blood pressures, pre-dialysis serum bicarbonate and pH, pre-dialysis serum sodium, potassium, calcium, or phosphorus were significantly different when comparing the two treatment modalities. All 10 patients completed the 1-year follow-up without any major side-effects.

CONCLUSIONS

Our study did not show any improvement of anaemia when treating a highly selected patient group, in the absence of any Epo therapy, with AFB compared with standard BD. Even though these conclusions cannot be extended in toto to the entire dialysis population, in which there is a large proportion of Epo-treated patients with Hb levels around 11 g/dl, we may nevertheless conclude that when patients are well selected, adequately dialysed, and not iron- and/or vitamin-depleted, the effect of a haemodiafiltration technique with a high-flux biocompatible membrane is less than might be expected from the results of uncontrolled studies.

Efficacy and safety of haemodialysis treatment with the Hemocontrol biofeedback system: a prospective medium-term study

BACKGROUND

Hypovolaemia has been implicated as a major causal factor of morbidity during haemodialysis (HD). A model biofeedback control system for intra-HD blood volume (BV) changes modelling has been developed (Hemocontrol), Hospal Italy) to prevent destabilizing hypovolaemia. It is based on an adaptive controller incorporated in a HD machine (Integra), Hospal Italy). The Hemocontrol biofeedback system (HBS) monitors BV contraction during HD with an optical device. HBS modulates BV contraction rates by adjusting the ultrafiltration rate (UFR) and the refilling rate by adjusting dialysate conductivity (DC) in order to obtain the desired pre-determined BV trajectories.

METHODS

Nineteen hypotension-prone uraemic patients (seven males, 12 females; mean age 64.5+/-3.0 SEM years; on maintenance HD for 80.5+/-13.2 months) volunteered for the present prospective study that compared the efficacy and safety of bicarbonate HD treatment equipped with HBS, as a whole, with the gold-standard bicarbonate treatment equipped with a constant UFR and DC (BD). The study included three phases: Medium-term studies started with one period of 6 months of BD and always had a follow-up period of HBS treatment ranging from 14 to 30 months (mean 24.0+/-1.6); short-term studies started in September 1999, when all patients went back to BD treatment for a wash-out period of 4 weeks and a short-term study period of a further 3 weeks (phase A). Afterwards, they once again started HBS treatment for a wash-out period of 4 weeks and a short-term study period of a further 3 weeks (phase B). Every patient underwent acute studies during a single HD run, once during phase A and once in phase B. Resistance (R) and reactance (Xc) measurements were obtained utilizing a single-frequency (50 kHz) tetrapolar bioimpedance analysis (BIA). Extracellular fluid volume (ECV) was calculated from R, Xc, and height and body weight measurements using the conventional BIA regression equations.

RESULTS

The overall occurrence of symptomatic hypotension and muscle cramps was significantly less in HBS treatment in both medium- and short-term studies. Self-evaluation of intra- and inter-HD symptoms (worst score=0, best score=10) revealed a statistically significant difference, as far as post-HD asthenia was concerned (6.2+/-0.2 in HBS treatment vs 4.3+/-0.1 in BD treatment, P<0.0001). No difference was observed between the two treatments when comparing pre- and post-HD lying blood pressure, heart rate, body weights and body weight changes in medium- and short-term studies. The residual BV%/ Delta ECV% ratio, expression of the vascular refilling, was significantly higher during HBS treatment in acute studies.

CONCLUSIONS

HBS treatment is effective in lowering hypovolaemia-associated morbidity compared with BD treatment; this could be related to a greater ECV stability. Furthermore, HBS is a safe treatment in the medium-term because these results are not achieved through potentially harmful changes in blood pressure, body weight, and serum sodium concentration.

Erythrocyte calcium influx is related to severity of ventricular arrhythmias in uraemic patients

BACKGROUND

Myocardial disorders are a remarkable cause of morbidity and mortality in chronic haemodialysed patients (HD). They could be favoured by alteration of cell Ca(2+) handling. In previous studies we characterized an erythrocyte Ca(2+) influx, sensitive to membrane potential and inhibited by Ca(2+) antagonists. Since its maximal influx rate was decreased in HD patients, this study investigates if Ca(2+) influx alterations are related to myocardial disorders in HD patients.

METHODS

Voltage-sensitive erythrocyte Ca(2+) influx was measured in 30 healthy controls and in 53 patients (47 HD patients and six patients with left ventricular hypertrophy and normal kidney function), using fura 2. In 29 HD patients and in six healthy subjects Ca(2+) influx was also determined in the presence of parathyroid hormone (PTH) in vitro. Patients were classified according to Lown's ventricular arrhythmias classification after 24-h Holter electrocardiograph (ECG) monitoring. Forty-six patients underwent echocardiography.

RESULTS

Voltage-sensitive erythrocyte Ca(2+) influx was significantly reduced in HD patients. Maximal influx rate was significantly higher in HD patients of Lown's classes 3 and 4 (0.789 +/- 0.156 nmol/s, n = 8; P < 0.01) than in patients of classes 1 and 2 (0.499 +/- 0.055 nmol/s, n=15), or without ventricular arrhythmias (0.400 +/- 0.041 nmol/s, n = 24). Maximal influx rate was directly correlated to left ventricular mass index (LVM) (r = 0.353, P < 0.05). Subjects with left ventricular hypertrophy and normal kidney function displayed erythrocyte Ca(2+) influx similar to that of normal subjects. Multiple regression indicates that LVM and Ca(2+) influx were independently related to severity of arrhythmias. When added to the influx assay, PTH increased the maximal influx rate only in patients with ventricular arrhythmias.

CONCLUSION

Myocardial dysfunction and altered ventricular excitability could be related in uraemic HD patients to alterations of calcium transport, as found in the erythrocyte model. Reduced resistance to PTH could contribute to this phenomenon.