Lessons from the Hemodialysis (HEMO) Study: an improved measure of the actual hemodialysis dose

Reporting of "dialysis adequacy" as an outcome in randomised trials conducted in adults on haemodialysis

Background

Clinical trials are most informative for evidence-based decision-making when they consistently measure and report outcomes of relevance to stakeholders, especially patients, clinicians, and policy makers. However, sometimes terminology used is interpreted differently by different stakeholders, which might lead to confusion during shared decision making. The construct dialysis adequacy is frequently used, suggesting it is an important outcome both for health care professionals as for patients.

Objective

To assess the scope and consistency of the construct dialysis adequacy as reported in randomised controlled trials in hemodialysis, and evaluate whether these align to the insights and understanding of this construct by patients.

Methods

To assess scope and consistency of dialysis adequacy by professionals, we performed a systematic review searching the Cochrane Central Register of Controlled Trials (CENTRAL) up to July 2017. We identified all randomised controlled trails (RCT) including patients on hemodialysis and reporting dialysis adequacy, adequacy or adequacy of dialysis and extracted and classified all reported outcomes. To explore interpretation and meaning of the construct of adequacy by patients, we conducted 11 semi-structured interviews with HD patients using thematic analysis. Belgian registration number B670201731001.

Findings

From the 31 included trials, we extracted and classified 98 outcome measures defined by the authors as adequacy of dialysis, of which 94 (95%) were biochemical, 3 (3%) non-biochemical surrogate and 2 (2%) patient-relevant. The three most commonly reported measures were all biochemical. None of the studies defined adequacy of dialysis as a patient relevant outcome such as survival or quality of life. Patients had a substantially different understanding of the construct dialysis adequacy than the biochemical interpretation reported in the literature. Being alive, time spent while being on dialysis, fatigue and friendliness of staff were the most prominent themes that patients linked to the construct of dialysis adequacy.

Conclusion

Adequacy of dialysis as reported in the literature refers to biochemical outcome measures, most of which are not related with patient relevant outcomes. For patients, adequate dialysis is a dialysis that enables them to spend as much quality time in their life as possible.

Effect of Adequacy of Dialysis and Nutrition on Morbidity and Working Rehabilitation of Patients Treated by Maintenance Hemodialysis

Numerous studies have demonstrated a correlation between adequacy of hemodialysis (HD) and patient mortality. In this study we evaluated the effect of adequacy of dialysis and nutrition on morbidity and working rehabilitation. Single center experience carried out in 1998 in an outpatient university-affiliated dialysis facility was presented. A total of 181 patients, on HD over 3 months, was included in the study; mean age 54.5 years, mean duration of HD 5.4 years. Thirthy-two patients were hospitalized in 1998. Patients with an eKt/V < 0.8 had significantly more frequent and extended hospitalizations than patients with eKt/V > 1.2. In the regression model eKt/V had a significant effect on hospital days. Serum albumin, as an index of nutrition, was also found to significantly influence hospitalizations. Patients with a BMI < 20.0 kg/m2 were found to have significantly more frequent hospitalizations, more hospital days/patient, and hospital days/hospitalized patient/year than those with a BMI > 25.0 kg/m2. BMI < 20.0 kg/m2 was associated with a significantly lower dialysis adequacy (eKt/V and URR) and more severe anemia. However, regression model failed to confirm a statistically significant association of BMI with hospital days. The best working rehabilitation (stage 1), according to the EDTA criteria, was obtained in patients with significantly (p<0.05) higher eKt/V, URR, albumin, nPNA, and body fat than in patients at stage 6 (not able to work, and not able to take care of themselves).

This study has established that dialysis adequacy and nutrition have an effect on morbidity (estimated through hospitalizations) and patient rehabilitation. (Int J Artif Organs 2000; 23: 83–9)

Comparative Survival Analysis of Urea Kinetic Based Indices

Background

Although urea kinetic modeling indices for measuring dialysis dose are recommended by world expert groups, it is not quite clear whether some of these are superior in predicting the outcome over others. This prospective, single-center study was carried out with the aim to compare predictive value of different indices and methods of measuring dialysis dose.

Methods

The analysis included 93 anuric patients having been on hemodialysis for at least 2 years who were followed-up for 75-months. The dialysis dose was measured by Kt/V (formal UKM, 3 and 2 urea samples), Kt/V (Daugirdas), Kt/V (Lowrie), eKt/V (Daugirdas), URR and TAC urea.

Results

Correlations between dialysis indices and survival time were significant for all indices (p<0.01) except for TAC. All indices, except for TAC urea, were significant predictors of mortality (multivariate Cox regression analysis; p<0.01) and differences of significant levels among these colinear parameters were small.

Conclusion

All examined indices except for TAC urea were highly predictive of patient mortality. Daugirdas and Lowrie simplified Kt/V indices are as predictive of all-cause mortality as more complex formal UKM methods in long-term patients on a 3×4h/week schedule.

Inflammatory and Angiogenic Factors Linked to Longitudinal Microvascular Changes in Hemodialysis Patients Irrespective of Treatment Dose Intensity

BACKGROUND

Cardiovascular disease is a major contributor to the poor outcomes observed in hemodialysis. We investigated the relationship between hemodialysis intensity and vascular parameters in high-dose (HDHD; >12hrs/week) and Conventional (CHD; ≤12hrs/week) hemodialysis intensity over a 6-month period.

METHODS

We present the 6-month longitudinal analysis of a 2-year multicenter study investigating the effects of HDHD on cardiovascular parameters. We used pulse wave velocity, 24hr ambulatory blood pressure and sublingual dark field capillaroscopy measurements to assess macro- and microcirculation on 6-monthly basis. Pro-inflammatory and endothelial biomarkers were also measured at 6-monthly intervals.

RESULTS

47 participants (21 HDHD, 26 CHD) were studied. CHD were older (63.5±14.2 vs 53.7±12.6 yr; p=0.018), with shorter dialysis vintage (median 23 vs 61 months; p=0.001). There was considerable variability in the degree and direction of change of circulatory measurements over a 6-month period. Hemodialysis intensity (hrs/week) did not correlate to these changes, when adjusted for age, dialysis vintage and comorbidity. Higher levels of Interleukin (IL)-8 measured at baseline independently predicted an increase in the Perfused Boundary Region (5-25μm) of the endothelial glycocalyx (p=0.010) whilst higher levels of soluble Flt-1 had a significant inverse effect (p=0.002) in an adjusted linear model.

CONCLUSION

Hemodialysis intensity did not predict changes in either macro- or microvascular parameters. Inflammation mediated through the IL-8 pathway predicted microvascular injury while Flt-1, a potential marker of angiogenesis and endothelial repair, might have a significant protective role. Further understanding of these pathways will be necessary to improve dialysis outcomes.

Elevation of Interleukin-18 Correlates With Cardiovascular, Cerebrovascular, and Peripheral Vascular Events: A Cohort Study of Hemodialysis Patients

Cardiocerebral vascular events are the major cause of mortality among patients with end-stage renal disease (ESRD). Subclinical inflammation and atherosclerosis have been implicated in the pathophysiology of ESRD. Evidence has shown the crucial role of interleukin-18 (IL-18) in inflammation. Interleukin-18 has been markedly upregulated in ESRD patients. Nevertheless, the ability of the IL-18 level to predict cardiocerebral vascular events and the correlation between IL-18 levels and cardiocerebral vascular events have not been established in hemodialysis patients.To determine whether the serum IL-18 level predicts cardiocerebral vascular events, the authors studied 171 ESRD patients. Samples were collected and patients were followed for 24 months. Demographic data, the duration of hemodialysis, nutrition status, inflammatory parameters, dialysis adequacy, and lipid profiles were analyzed to predict the outcome by using multivariate logistic regression. Cutoff points were calculated by acquiring the highest Youden index. The Kaplan-Meier method was used to scrutinize the cumulative proportion of events.The multivariate logistic regression model revealed that serum creatinine, C-reactive protein, and IL-18 levels were independent predictors for cardiocerebral vascular events. The odds ratio of events for each increase in IL-18 (pg/mL) was 1.008 for cardiocerebral vascular events. The area under the receiver operating characteristic curve of IL-18 was 0.779 ± 0.039, the overall correctness was 73%, and the Youden index was highest at a cutoff of 463 pg/mL. In the Kaplan-Meier model, patients with an IL-18 level higher than 463 pg/mL exhibited the highest probability of experiencing an adverse event during the entire follow-up period.Increased serum IL-18 could be considered as a predictor of cardiocerebral vascular events in dialysis patients. It is noteworthy that various comorbidities might interfere the expression of IL-18; therefore, further validation study is required to incorporate IL-18 in clinical use.

Effects of pyrophosphate delivery in a peritoneal dialysis solution on bone tissue of apolipoprotein-E knockout mice with chronic kidney disease

Vascular calcification (VC) is a risk factor for cardiovascular mortality in the setting of chronic kidney disease (CKD). Pyrophosphate (PPi), an endogenous molecule that inhibits hydroxyapatite crystal formation, has been shown to prevent the development of VC in animal models of CKD. However, the possibility of harmful effects of exogenous administration of PPi on bone requires further investigation. To this end, we examined by histomorphometry the bone of CKD mice after intraperitoneal PPi administration. After CKD creation or sham surgery, 10-week-old female apolipoprotein-E knockout (apoE(-/-)) mice were randomized to one non-CKD group or 4 CKD groups (n = 10-35/group) treated with placebo or three distinct doses of PPi, and fed with standard diet. Eight weeks later, the animals were killed. Serum and femurs were sampled. Femurs were processed for bone histomorphometry. Placebo-treated CKD mice had significantly higher values of osteoid volume, osteoid surface and bone formation rate than sham-placebo mice with normal renal function. Slightly higher osteoid values were observed in CKD mice in response to very low PPi dose (OV/BV, O.Th and ObS/BS) and, for one parameter measured, to high PPi dose (O.Th), compared to placebo-treated CKD mice. Treatment with PPi did not modify any other structural parameters. Mineral apposition rates, and other parameters of bone formation and resorption were not significantly different among the treated animal groups or control CKD placebo group. In conclusion, PPi does not appear to be deleterious to bone tissue in apoE(-/-) mice with CKD, although a possible stimulatory PPi effect on osteoid formation may be worth further investigation.

Carbamylation of serum albumin as a risk factor for mortality in patients with kidney failure

Urea, the toxic end product of protein catabolism, is elevated in end-stage renal disease (ESRD), although it is unclear whether or how it contributes to disease. Urea can promote the carbamylation of proteins on multiple lysine side chains, including human albumin, which has a predominant carbamylation site on Lys(549). The proportion of serum albumin carbamylated on Lys(549) (%C-Alb) correlated with time-averaged blood urea concentrations and was twice as high in ESRD patients than in non-uremic subjects (0.90% versus 0.42%). Baseline %C-Alb was higher in ESRD subjects who died within 1 year than in those who survived longer than 1 year (1.01% versus 0.77%) and was associated with an increased risk of death within 1 year (hazard ratio, 3.76). These findings were validated in an independent cohort of diabetic ESRD subjects (hazard ratio, 3.73). Decreased concentrations of serum amino acids correlated with higher %C-Alb in ESRD patients, and mice with diet-induced amino acid deficiencies exhibited greater susceptibility to albumin carbamylation than did chow-fed mice. In vitro studies showed that amino acids such as cysteine, histidine, arginine, and lysine, as well as other nucleophiles such as taurine, inhibited cyanate-induced C-Alb formation at physiologic pH and temperature. Together, these results suggest that chronically elevated urea promotes carbamylation of proteins in ESRD and that serum amino acid concentrations may modulate this protein modification. In summary, we have identified serum %C-Alb as a risk factor for mortality in patients with ESRD and propose that this risk factor may be modifiable with supplemental amino acid therapy.

High-flux versus low-flux membranes for end-stage kidney disease

BACKGROUND

Clinical practice guidelines regarding the use of high-flux haemodialysis membranes vary widely.

OBJECTIVES

We aimed to analyse the current evidence reported for the benefits and harms of high-flux and low-flux haemodialysis.

SEARCH METHODS

We searched Cochrane Renal Group's specialised register (July 2012), the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1948 to March 2011), and EMBASE (1947 to March 2011) without language restriction.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared high-flux haemodialysis with low-flux haemodialysis in people with end-stage kidney disease (ESKD) who required long-term haemodialysis.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two authors for study characteristics (participants and interventions), risks of bias, and outcomes (all-cause mortality and cause-specific mortality, hospitalisation, health-related quality of life, carpal tunnel syndrome, dialysis-related arthropathy, kidney function, and symptoms) among people on haemodialysis. Treatment effects were expressed as a risk ratio (RR) or mean difference (MD), with 95% confidence intervals (CI) using the random-effects model.

MAIN RESULTS

We included 33 studies that involved 3820 participants with ESKD. High-flux membranes reduced cardiovascular mortality (5 studies, 2612 participants: RR 0.83, 95% CI 0.70 to 0.99) but not all-cause mortality (10 studies, 2915 participants: RR 0.95, 95% CI 0.87 to 1.04) or infection-related mortality (3 studies, 2547 participants: RR 0.91, 95% CI 0.71 to 1.14). In absolute terms, high-flux membranes may prevent three cardiovascular deaths in 100 people treated with haemodialysis for two years. While high-flux membranes reduced predialysis beta-2 microglobulin levels (MD -12.17 mg/L, 95% CI -15.83 to -8.51 mg/L), insufficient data were available to reliably estimate the effects of membrane flux on hospitalisation, carpal tunnel syndrome, or amyloid-related arthropathy. Evidence for effects of high-flux membranes was limited by selective reporting in a few studies. Insufficient numbers of studies limited our ability to conduct subgroup analyses for membrane type, biocompatibility, or reuse. In general, the risk of bias was either high or unclear in the majority of studies.

AUTHORS' CONCLUSIONS

High-flux haemodialysis may reduce cardiovascular mortality in people requiring haemodialysis by about 15%. A large well-designed RCT is now required to confirm this finding.

Dialysis cannot be dosed

Adequate dialysis is difficult to define because we have not identified the toxic solutes that contribute most to uremic illness. Dialysis prescriptions therefore cannot be adjusted to control the levels of these solutes. The current solution to this problem is to define an adequate dose of dialysis on the basis of fraction of urea removed from the body. This has provided a practical guide to treatment as the dialysis population has grown over the past 25 years. Indeed, a lower limit to Kt/V(urea) (or the related urea reduction ratio) is now established as a quality indicator by the Centers for Medicare and Medicaid for chronic hemodialysis patients in the United States. For the present, this urea-based standard provides a useful tool to avoid grossly inadequate dialysis. Dialysis dosing, however, based on measurement of a single, relatively nontoxic solute can provide only a very limited guide toward improved treatment. Prescriptions which have similar effects on the index solute can have widely different effects on other solutes. The dose concept discourages attempts to increase the removal of such solutes independent of the index solute. The dose concept further assumes that important solutes are produced at a constant rate relative to body size, and discourages attempts to augment dialysis treatment by reducing solute production. Identification of toxic solutes would provide a more rational basis for the prescription of dialysis and ultimately for improved treatment of patients with renal failure.

Assessment of Hemodialysis Adequacy by Ionic Dialysance: Comparison to Standard Method of Urea Removal

BACKGROUND

The hemodialysis adequacy is one of the most important issues influencing the survival of patients on maintenance hemodialysis (HD). Assessment of measuring the delivered dialysis dose using clearance x time/volume (Kt/V) index requires multiple blood sampling. New methods for assessment of dialysis dose based on ionic dialysance (ID) have been suggested. Online conductivity monitoring (using sodium flux as a surrogate for urea) allows the repeated noninvasive measurement of Kt/V on each HD treatment. In this study we have compared this method with the standard method of estimating Kt/V.

METHODS

We studied 24 established HD patients over a 4 week time period. Patients were dialyzed using Fresenius 4008S dialysis monitors, equipped with modules to measure ID. Data were manually collected and analyzed using the appropriate statistical software. Urea removal (UR) was measured once a week by a two-pool calculation, estimating an eKt/V.

RESULTS

The Kt/V measured by ID highly correlated with the one derived from the measurement of the UR (r=0.8959, p< 0.0001). The ID underestimated UR by the mean of 6%. The ID varied greatly within individual patients with a median of 1.29 +/- 0.22. If the eKt/V > or = 1.2 is considered adequate, 33% of the patients would have been inadequately dialyzed. The mean HD duration to achieve an adequate dialysis was 4 hours and 47 minutes with high interpatient variability.

CONCLUSION

The ID seems to be an easily obtained measure of the delivered dialysis dose, correlating well with standard UR method. Substantial individual variations imply that repeated measures (ideally for all treatments) are necessary to obtain a real answer to the mean treatment dose being delivered to the patients.

C-reactive Protein Is a Strong Predictor of Mortality in Hemodialysis Patients

BACKGROUND

To establish the baseline cutoff value of C-reactive protein (CRP) that would predict increased overall and cardiovascular mortality in patients with end-stage renal disease (ESRD).

METHODS

A cohort of 270 prevalent hemodialysis patients treated at Rijeka University Hospital was eligible for the study. Monthly CRP measurements were performed for three consecutive months. Only the patients with CRP values varying <20% were included (n=256). During the follow-up, 24 patients were transplanted and therefore excluded from the analysis. The CRP cutoff point of 6.2 mg/L was established by Receiver Operating Characteristic curve. The patients were divided into four groups according to their CRP values. Group 1 included 80 (34.5%) patients with CRP <3.0 mg/L, group 2 included 23 (9.9%) patients with CRP 3.0-6.1 mg/L, group 3 consisted of 18 (7.7%) patients with CRP 6.2-10.0 mg/L, and group 4 included 111 (47.9%) patients with CRP >10.0 mg/L. The survival was evaluated by Kaplan-Meier curve.

RESULTS

During the two-year follow-up, 59 patients died. The major cause of death was cardiovascular disease (64%). Significantly higher overall and cardiovascular mortality was observed in group 3 when compared with groups 1 and 2 (chi2=11.97; P < 0.001) and in group 4 when compared with groups 1 and 2 (chi2=14.40; P<0.001). Compared with survivors, non-survivors had a higher median CRP value (19.0 [1.5-99.7] mg/L vs. 2.3 [0.1-49.1] mg/L, respectively; P<0.001).

CONCLUSION

Serum concentration of CRP above 6.2 mg/L is a strong predictor of overall and cardiovascular mortality in patients with ESRD.

Haemoglobin and haematocrit targets for the anaemia of chronic kidney disease

BACKGROUND

Anaemia affects 60% to 80% of patients with chronic kidney disease (CKD) reduces quality of life and is a risk factor for early death. Treatment options are blood transfusion, erythropoietin (EPO) and darbepoetin alfa. Recently higher haemoglobin (Hb) and haematocrit (HCT) targets have been widely advocated because of positive associations with improved survival and quality of life from observational studies.

OBJECTIVES

To assess the benefits and harms of different Hb or HCT targets in CKD patients receiving any treatment for anaemia.

SEARCH STRATEGY

We searched The Cochrane Renal Group's specialised register, Cochrane Central Register of Controlled Trials (CENTRAL, in The Cochrane Library) MEDLINE (from 1966), EMBASE (from 1980) and reference lists of retrieved articles. Date of most recent search: April 2006

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs comparing different Hb/HCT targets in patients with the anaemia of CKD.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. Statistical analyses were performed using the random effects model and results expressed as relative risks (RR) for dichotomous outcomes and weighted mean difference (MD) for continuous outcomes, with 95% confidence intervals (CI).

MAIN RESULTS

Twenty two trials (3707 patients) were included. Hb > or = 133 g/L was not associated with a reduction in the risk of all-cause mortality compared with 120 g/L in dialysis and pre-dialysis patients. In pre-dialysis patients, there was a significantly lower end of treatment creatinine clearance with Hb < 120 g/L compared to > 130 g/L (MD -4.17, 95% CI -6.33 to -2.02) but no significant difference in the risk of end-stage kidney disease (ESKD) (RR 1.05, 95% CI 0.50 to 2.22). Lower Hb targets resulted in an increased risk for seizures (RR 5.25, 95% CI 1.13 to 24.34) and a reduced risk of hypertensive episodes (RR 0.50, 95% CI 0.33 to 0.76). There were no significant differences in the risk of vascular access thrombosis.

AUTHORS' CONCLUSIONS

There was no significant difference in the risk of death for low (< 120 g/L) versus higher Hb targets (>133 g/L). Lower Hb targets were significantly associated with an increased risk for seizures but a reduced risk of hypertension. In general study quality was poor. There is a need for more adequately powered, well-designed and reported trials. Trials should be pragmatic, focusing on hard end-points (mortality, ESKD, major side effects) or outcomes which were previously not studied adequately (e.g. seizures, quality of life).

UNRESOLVED ISSUES IN DIALYSIS: Revisiting the Hemodialysis Dose

An adequate dose of hemodialysis is currently defined by the Kidney Disease Outcomes Quality Initiative (K/DOQI) and European guidelines as a delivered single-pool urea Kt/V (spKt/V) of 1.2 and 1.4, respectively. Results from several studies, in particular the Hemodialysis (HEMO) study, have largely supported the legitimacy of these guidelines, although they may need to be altered or amended for certain patient subgroups. This review discusses several potential changes to current guidelines based on recent clinical outcome studies. The following questions are addressed: 1) Should the dialysis dose for low molecular weight water-soluble solutes (i.e., urea) be normalized by the body distribution volume for urea? 2) Should spKt/V or equilibrated Kt/V (eKt/V) be used for routine monitoring of the hemodialysis dose? 3) Should the dialysis dose for small solutes be dependent on gender? 4) Should the dialysis dose for middle molecules be used in clinical practice? 5) What should be the dialysis dose when using hemodialysis treatment strategies that are more frequent than thrice weekly?

Double target comparison of blood-side methods for measuring the hemodialysis dose

BACKGROUND

Despite the fact that urea kinetic modelling has been successfully applied to quantify the hemodialysis since the beginning of the 1980s, there is not a consensus yet concerning which is the most proper dialysis dose index and the method for calculating it. In this work, we propose that a combined measurement of the dialysis dose from two complementary perspectives of the removal process should provide a more complete description of dialysis than a measurement alone. This hypothesis is reviewed and the measuring methods are compared.

METHODS

A cross-sectional randomized clinical study over 98 stable ESRD patients submitted to thrice-weekly hemodialysis was carried out with the aim of comparing 16 blood-side methods for measuring the hemodialysis dose from patient and dialyzer perspectives. The availability of urea rebound measurements and computational resources have been taken into account.

RESULTS

The outcomes point to four novel blood-side methods as the most accurate for measuring the effective dialysis system Kt/V (mKt/V) in clinical conditions. Their limits of agreement (mean +/- 2.SD) range from 1.93 +/- 2.09% for a non-iterative method without the urea rebound measurement (BUN3) to -0.08 +/- 0.58% for an iterative method with BUN3. The best non-iterative blood-side method for measuring the equilibrated Kt/V (eKt/V) is the second generation formula of Daugirdas (-2.42 +/- 1.05%) when BUN3 is available and the rate equation of Daugirdas and Schneditz (-1.74 +/- 7.91%) when BUN3 is not available. The difference mKt/V-eKt/V is significant and positive, and increases with the dialysis dose in a personalized manner.

CONCLUSION

We have confirmed the arguments that support the hypothesis of the study. The best blood-side methods for the combined measurement of dialysis dose as a function of the available resources have been determined.

Indices for assessment of hemodialysis adequacy: A comparison of different formulae

Of the various indices used in the assessment of dialysis adequacy, fractional urea clearance controlled for volume of distribution "Kt/V" remains the most widely used. Its determination is best performed by formal urea kinetic modeling (UKM), which is laborious and cumbersome, and the computational softwares are largely unavailable, particularly in developing countries. Consequently, different equations have been developed that approximate the formal UKM determination. Of the available formulae, that from second-generation logarithmic equation have been found to approximate values derived from formal UKM closely. We set out to determine the clinical utility of percent reduction of urea and Kt/V formulae derived from it, using the logarithmic equation as the standard.

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

Current understanding of beta2-microglobulin (beta2M) and phosphate (or inorganic phosphorus) kinetics during hemodialysis is reviewed. The postdialysis:predialysis concentration ratio for beta2M is determined by dialyzer clearance for beta2M, treatment time, patient body size (specifically, extracellular fluid volume), and total ultrafiltration volume during the treatment. Evaluation of these treatment parameters can be used to calculate dialyzer clearance for beta2M; however, such calculated values are only approximations, since they neglect intradialytic generation, nonrenal (nondialyzer) clearance, and postdialysis rebound of beta2M. The detailed kinetics of beta2M during hemodialysis are best described using a two-compartment model. Theoretical predictions from such two-compartment models suggest that the product of dialyzer clearance for beta2M and weekly treatment duration, independent of treatment frequency, is the main determinant of plasma beta2M concentrations. The kinetics of phosphate removal during hemodialysis are incompletely understood. Phosphate is removed from both extracellular and intracellular compartments during hemodialysis; the plasma phosphate concentration levels off after the first 1 or 2 hours of treatment and plasma concentrations can rebound even before therapy is complete. Increases in dialyzer clearance of phosphate have been previously achieved only by increasing dialysis membrane surface area or by the use of hemodiafiltration. A four-compartment model of phosphate kinetics proposed recently by Spalding et al. suggests that the major barrier to phosphate removal is limited transfer of phosphate between the intracellular and extracellular compartments, although other complex factors also play important roles. Theoretical predictions using the model of Spalding et al. suggest that increasing either treatment frequency or treatment duration can increase phosphate removal. The kinetics of beta2M are representative of middle molecules whose removal during hemodialysis is governed predominantly by clearance at the dialyzer. In contrast, phosphate removal is limited primarily by its sequestration in the intracellular compartment (and possibly other compartments), not by its clearance at the dialyzer. The kinetics of phosphate may therefore be representative of uremic toxins whose removal is limited by sequestration into compartments or by protein binding. Enhanced removal of both of these uremic toxins using a given therapy will require treatments of increased frequency and longer duration.

An update of irbesartan and renin-angiotensin system blockade in diabetic nephropathy

Type 2 diabetes is a chief cause of pathologies such as cardiovascular disease, nephropathy and retinopathy, and its prevalence is increasing worldwide. Development of renal disease can be slowed by tight glycaemic control and treatment of associated hypertension with angiotensin-converting enzyme inhibition, as The Diabetes Control and Complications Trial and the UK Prospective Diabetes Study have demonstrated. Recent clinical trials have supported the use of angiotensin II receptor antagonists in the treatment of diabetic nephropathy, resulting in the approval of new therapeutic indications in the US and Europe. The main goal of this review is to demonstrate how results from the Programme for Irbesartan Mortality and Morbidity Evaluation and other recent studies, based on the effects of renin-angiotensin system blockade, can be appropriate in clinical practice, thus displaying benefits of irbesartan therapy at any stage of renal disease in diabetics.

Cellulose, modified cellulose and synthetic membranes in the haemodialysis of patients with end-stage renal disease

BACKGROUND

When the kidney fails the blood-borne metabolites of protein breakdown and water cannot be excreted. The principle of haemodialysis is that such substances can be removed when blood is passed over a semipermeable membrane. Natural membrane materials include cellulose or modified cellulose, more recently various synthetic membranes have been developed. Synthetic membranes are regarded as being more "biocompatible" in that they incite less of an immune response than cellulose-based membranes.

OBJECTIVES

To assess the effects of different haemodialysis membrane material in patients with end-stage renal disease (ESRD).

SEARCH STRATEGY

We searched MEDLINE, EMBASE, PreMEDLINE, HealthStar CINAHL, the Cochrane Central Register of Controlled Trials (CENTRAL), Biosis, SIGLE, CRIB, UK National Research Register and reference lists of relevant articles. We contacted biomedical companies, known investigators and handsearched selected journals and conference proceedings. Date of most recent search: June 2004.

SELECTION CRITERIA

All randomised controlled trials (RCTs) or quasi-RCTs comparing different haemodialysis membrane material in patients with ESRD.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the methodological quality of studies. Data was abstracted onto a standard form by one reviewer and checked by another. Relative Risk (RR) and weighted mean difference (WMD) with 95% confidence intervals (CI)) MAIN RESULTS: Thirty two studies were identified. Pre-dialysis ss(2) microglobulin concentrations were not significantly lower in patients treated with synthetic membranes (WMD -14.67, 95% CI -33.10 to 4.05). When analysed for change in ss(2) microglobulin, a fall was only noted with high-flux membranes. The incidence of amyloid was less in patients who were dialysed for six years with high-flux synthetic membranes (one study, RR 0.03, 95% CI 0.00 to 0.54). There was a significant difference in favour of the synthetic (high-flux) membrane in comparison to cellulose membranes for triglycerides (WMD -0.66; 95% CI -1.18 to -0.14) but not for modified cellulose membranes. Dialysis adequacy measured by Kt/V was marginally higher when cellulose membranes were used (WMD -0.10; 95% CI -0.16 to 0.04), whereas synthetic membranes achieved significantly higher Kt/V values when compared with modified cellulose membranes (WMD 0.20, 95% 0.11 to 0.29) . There were no data on quality of life measures.

AUTHORS' CONCLUSIONS

We found no evidence of benefit when synthetic membranes were compared with cellulose/modified cellulose membranes in terms of reduced mortality no reduction in dialysis-related adverse symptoms. Despite the relatively large number of RCTs undertaken in this area none of the included studies reported any measures of quality of life.

Kinetics of urea and β2-microglobulin during and after short hemodialysis treatments

BACKGROUND

Daily short hemodialysis (HD) is often prescribed by simply doubling treatment frequency and halving treatment time; however, the effect of this prescription approach on the equilibrated HD dose (urea eKt/V) and whole body clearance for beta(2)-microglobulin has not been established.

METHODS

We compared urea and beta(2)-microglobulin kinetics during and 60 minutes after a short HD treatment and a conventional HD treatment in a crossover study on 22 maintenance HD patients: 16 male and 6 female, 61 +/- 18 (mean +/- standard deviation) years of age. One patient in each treatment modality was excluded from certain analyses because of missing data. Short and conventional HD treatments were essentially identical, except for treatment times, which were 116 +/- 14 and 241 +/- 27 minutes, respectively. Blood samples were collected at regular intervals during and after treatments, and additional blood and dialysate samples were collected at 60 minutes of treatment to evaluate dialyzer clearances.

RESULTS

Plasma water urea clearances measured directly across the dialyzer during short and conventional HD treatments were not different (255 +/- 23 mL/min and 255 +/- 28 mL/min, respectively). The 60-minute postdialysis blood urea nitrogen concentration rebounded more (P < 0.01) after short HD than conventional HD (5.9 +/- 3.1 vs. 4.0 +/- 1.5 mg/dL, respectively). Calculated urea eKt/V values using the Daugirdas-Schneditz rate equation were not different from those measured during conventional HD using the 60-minute postdialysis concentration but significantly overestimated measured urea eKt/V values during short HD. Postdialysis rebound of beta(2)-microglobulin concentrations was variable but similar after short and conventional HD treatments (0.1 +/- 3.4 vs. 0.7 +/- 1.8 mg/L, respectively). Whole body clearances of beta(2)-microglobulin calculated from predialysis and immediate (10-second) postdialysis serum concentrations during short and conventional HD treatments were not different from each other (42.9 +/- 24.1 vs. 41.9 +/- 22.4 mL/min, respectively).

CONCLUSION

These observations show that the Daugirdas-Schneditz rate equation is accurate in predicting urea eKt/V during conventional, but not during short, HD. In contrast, whole body clearances of beta(2)-microglobulin during short and conventional HD treatments were similar. We conclude that calculation of accurate estimates of urea eKt/V, but not clearances of beta(2)-microglobulin, differ during short and conventional HD treatments.

A novel mathematical method based on urea kinetic modeling for computing the dialysis dose

A novel normalized single pool urea kinetic model (nspUKM) for the quantification of the urea removal, dialyzer urea clearance and urea generation rate during a dialysis session, is presented. Its major goal is the computation of an accurate estimate of the fractional dialyzer urea clearance (dKt/V), which is denoted nKt/V, in contrast to the equilibrated Kt/V (eKt/V). This work clarifies the significance of dKt/V as a complement to eKt/V in hemodialysis (HD) prescription and quantification. This new model emerges from a generalization of the standard single pool urea kinetic model (spUKM) of the US National Cooperative Dialysis Study (NCDS), identified as gspUKM. Due to their significance, the standard single pool Kt/V (spKt/V) and the eKt/V are also analyzed from gspUKM in this work, with the aim of achieving a better interpretation of the results. Indices nKt/V, eKt/V and spKt/V have been compared with the dKt/V computed from a published and validated two-pool urea kinetic model (2pUKM). We present the results obtained from a clinical study carried out on a group of 30 end stage renal disease (ESRD) patients. The limits of agreement (mean+/-2S.D. (standard deviation) of the difference) between nKt/V and 2pKt/V were -0.077+/-0.72% (percentage of the dKt/V mean), while between eKt/V and 2pKt/V were -13.75+/-17.39% and between spKt/V and 2pKt/V were -1.61+/-6.54%. These scores prove that the nspUKM model is able to provide a very accurate estimate of 2pKt/V and thus dKt/V, even with high flux (HF) HD. The presented method joins the simplicity of single-pool models to the accuracy of double-pool models, when the target is the identification of the dialyzer urea clearance, urea removal and urea generation rate, although it does not provide a good prediction of the urea dynamics. Finally, we think that our analytical and experimental findings throw light on the behavior and applicability of the different Kt/V indices analyzed.

What is the impact of PRIME on real-life diabetic nephropathy?

Type 2 diabetes is increasing globally and is a major cause of conditions such as cardiovascular disease, retinopathy and nephropathy. The Diabetes Control and Complications Trial and the UK Prospective Diabetes Study demonstrated that the progression of renal disease could be slowed by tight glycaemic control and treating any associated hypertension with angiotensin-converting enzyme inhibition. Recent clinical trials have supported the use of angiotensin II receptor antagonists in the treatment of diabetic nephropathy, resulting in the approval of new therapeutic indications in the United States and Europe. The objective of this review is to demonstrate how results from the Program for Irbesartan Mortality and morbidity Evaluation studies apply to clinical practice, and to show how the benefits of irbesartan therapy can be realised at any stage of renal disease in patients with diabetes.

Dialyzer Performance in the HEMO Study:In Vivo K 0 A and True Blood Flow Determined from a Model of Cross-Dialyzer Urea Extraction

Inlet and outlet blood urea concentrations (Cin and Cout) can be used to directly measure dialyzer performance if simultaneous blood flow measurements (Qb) are available. Dialyzer clearance, for example, is the product of the urea extraction ratio [ER = (Cin - Cout)/Cin] and Qb. Urea concentrations are measured routinely in all hemodialysis clinics, but Qb is usually reported as the product of the pump rotational speed and pump segment stroke volume, which can be inaccurate at high flow rates. Dialyzer urea extraction is also a function of Qb, dialysate flow (Qd), and the membrane permeability-area coefficient (K0A) for urea. To determine true in vivo values for Qb and K0A in the absence of direct flow measurements, we developed a model based on an existing mathematical equation for hemodialyzer ER under conditions of countercurrent flow. Qb, K0A, and other variables were adjusted to fit the modeled ER to ER measured in 1,285 patients treated with Qb that ranged from 200 to 450 ml/min during the HEMO Study. Fitting was performed by least squares nonlinear regression using parametric and nonparametric methods for estimating true flow. As Qb rose above 250 ml/min, both methods for estimating actual Qb showed increasing deviations from the flow reported by the blood pump meter. Modeled values for K0A differed significantly among dialyzer models, ranging from 71% to 96% of the in vitro values. The previously described 14% increase in K0A, as Qd increased in vitro from 500 to 800 ml/min, was much less in vivo, averaging only 5.5 +/- 1.5% higher. Dialyzer reprocessing was associated with a 6.3 +/- 1.0% reduction in K0A and an approximate 2% fall in urea clearance per 10 reuses (p < 0.001). Multiple regression analysis showed a small but significant dialysis center effect on ER but no independent effects of other variables, including the ultrafiltration rate, diabetic status, race, ethnicity, sex, method of reuse, treatment time, access recirculation, and use of central venous accesses. The new algorithm allowed a more accurate determination of true Qb and in vivo K0A in the absence of direct flow measurements in a large population treated with a wide range of blood flow rates. Application of this technique for more than 1000 patients in the HEMO Study confirmed that in vitro measurements using simple crystalloid solutions cannot readily substitute for in vivo measurements of dialyzer function, and permitted a more accurate calculation of each patient's prescribed dialysis dose and urea volume.

The HEMO study - where do we go from here?

PURPOSE OF REVIEW

The HEMO study is a randomized clinical trial using a 2x2 factorial design to assign patients to a standard or high dose of dialysis and to a low flux or a high flux dialyzer. This study is the largest, most comprehensive, randomized clinical trial ever performed in the maintenance hemodialysis population. This review analyzes the results of the study and discusses how the HEMO study results affect efforts to lower morbidity and mortality in the hemodialysis population.

RECENT FINDINGS

The primary outcome of the HEMO study was death from any cause. This outcome was not significantly influenced by treatment assignment for the dose of dialysis or for the flux of the dialysis membranes used. The main secondary outcomes also did not differ significantly in either the dose groups or the flux groups.

SUMMARY

The results of the HEMO study support current clinical practice guidelines for the delivery of thrice-weekly dialysis, but the results do not support conventional attempts to lower the high morbidity and mortality in hemodialysis patients. Current efforts are being focused on increasing dialysis time and/or frequency, improving phosphate control, and lowering traditional and nontraditional risk factors for adverse cardiovascular events in this patient population.

Haemoglobin and haematocrit targets for the anaemia of chronic renal disease

BACKGROUND

Anaemia affects 60-80% of patients with renal impairment, reduces quality of life and is a risk factor for early death. Treatment options are blood transfusion, erythropoietin (EPO) alpha or beta and darbepoetin alfa. Recently higher haemoglobin (Hb) and haematocrit targets have been widely advocated because of positive data from observational studies. However, higher targets may lead to access thrombosis and hypertension and are costly.

OBJECTIVES

This review assesses the benefits and harms of low (Hb </= 100 g/L or HCT </= 30%) and high (Hb > 100 g/L or HCT > 30%) targets in pre- and post-dialysis patients receiving any treatment for anaemia.

SEARCH STRATEGY

We searched The Cochrane Renal Group specialised register (September 2002), Cochrane Controlled Trials Register (The Cochrane Library, Issue 3, 2002) MEDLINE (1966 - September 2002), EMBASE (1988 - September 2002) and reference lists of retrieved articles.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs comparing low Hb/HCT targets (Hb</- 100 g/L) with high Hb/HCT targets (Hb > 100 g/dL) in patients with anaemia of chronic renal disease.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. Statistical analyses were performed using the random effects model and the results expressed as relative risk (RR) for dichotomous outcomes and weighted mean difference (WMD) for continuous outcomes, with 95% confidence intervals (95% CI).

MAIN RESULTS

Fifteen trials were identified in which 2096 patients were included. Twelve trials (673 patients) compared placebo with EPO and three trials (1423 patients) compared two doses of EPO. Hb values of 100 g/L (obtained with low EPO doses) were associated with lower mortality compared to Hb values of 140 g/L or more (obtained with high EPO doses) in the population with chronic renal disease and cardiovascular impairment (two trials, 1379 patients: RR 0.82; 95% CI 0.68 to 0.99). Lower targets obtained with a placebo resulted in an increased risk for seizures (four trials, 219 patients: RR 5.25; 95% CI 1.13 to 24.34) as compared to higher targets reached with EPO treatment. Finally, there was a reduced risk for hypertensive episodes with lower Hb targets reached with a placebo as compared to higher targets reached with EPO (six trials, 387 patients: RR 0.50; 95% CI 0.33 to 0.76). Quality of life was not adequately evaluated in the studies.

REVIEWER'S CONCLUSIONS

Lower Hb targets of 100 g/L were associated with a lower risk of death in the population with cardiovascular impairment and chronic renal disease as compared to Hb 140 g/L. Lower Hb targets (Hb < 100 g/L) were also significantly associated with an increased risk for seizures and a reduced risk of hypertension compared to Hb > 100 g/L. There is a need of more adequately powered, well-designed and reported trials in this area. In particular, randomised controlled trials comparing the benefits and harms of low (Hb < 100 g/L) versus intermediate (Hb 130 g/L) and high (Hb 140 g/L) targets in the pre-dialysis population with chronic renal disease are necessary. In fact, there is a large deficiency of trials in the pre-dialysis population. The new trials should focus on hard outcomes and also look at outcomes which were previously not studied adequately, such as seizures and quality of life, which is to be assessed with validated measures.

Computer simulation of small-solute and middle-molecule removal during short daily and long thrice-weekly hemodialysis

BACKGROUND

More intensive hemodialysis (HD) regimens (short daily and long thrice-weekly HD) provide potential opportunities for improved patient outcome. An adequate dialysis dose for these regimens cannot be established from the existing literature.

METHODS

Using computer simulation, we compared conventional HD with short daily HD and long thrice-weekly HD using two dose measures of solute clearance: equivalent renal clearance (EKR) and a generalized standard Kt/V (stdKt/V) for urea, creatinine, vitamin B12, inulin, and beta2-microglobulin. Solute kinetics were simulated using a variable-volume two-compartment mathematical model.

RESULTS

Calculated EKR values were greater during short daily HD compared with those during conventional HD by 16.9%, 15.5%, 16.1%, 5.2%, and 2.5% for urea, creatinine, vitamin B12, inulin, and beta(2)-microglobulin, respectively. Calculated stdKt/V values predicted more substantial increases in dose for all solutes. Increasing the time of dialysis from 4 to 8 hours three times weekly resulted in substantially greater stdKt/V and EKR values compared with both conventional and short daily HD. Solute clearances during short daily HD could be enhanced to approach those during long HD if treatment time was increased or very high surface area dialyzers were used with very high blood flow rates.

CONCLUSION

Dose measures for all molecules larger than urea increase with either increased frequency or, even more so, increased duration of dialysis. Prediction results of these models require confirmation in clinical studies. Furthermore, the relationship between increased dialysis dose and long-term clinical outcome during more intensive HD regimens requires examination in clinical trials.

New empiric expressions to calculate single pool Kt/V and equilibriated Kt/V

Most formulae used for Kt/V computations are cumbersome and require variables that are not always available. Even the simplest models involve urea distribution volume or patient postdialysis weight. Calculating urea reduction ratio (URR) is easier and does not require additional variables, but it fails to account for residual renal function or for the removal of urea when urea levels do not change, e.g., during ultrafiltration. The goal of this study was to derive new expressions to calculate Kt/V based on URR using bivariate and multivariate linear and nonlinear models, with the URR adjusted for ultrafiltration volume and time on dialysis. Models were derived from a database of 598 dialysis records with a mean spKt/V of 1.6 (range 0.74-2.8). Models were validated on the same dataset that they were derived from and a separate dataset consisting of 17,190 dialysis records. The validation was made by comparing the empirically derived models with the Gotch and Daugirdas formulae. Among our empirically derived expressions, the closest approximation of the "gold standard," Kt/V, is the multivariate linear model of URR adjusted for ultrafiltration volume. When information about ultrafiltration is not available, the bivariate exponential formula can be successfully used to estimate Kt/V.

Dissociation between dialysis adequacy and Kt/V

Since the initiation of dialysis, nephrologists have sought an index (or indices) for the adequacy of toxic solute removal. This quest has been characterized by a gradual shift in thinking, ending with a preference for dynamic parameters such as clearances normalized for body size (Kt/V). The threshold Kt/V, however, has changed over the years. While present guidelines suggest 1.2 with single-pool kinetics, higher levels might be proposed in the future. In spite of the known relation between Kt/V and survival, the accuracy of this parameter as a representative of the removal of the whole spectrum of compounds that are responsible for uremia is problematic. Kt/V only assesses the removal of a water-soluble compound from the body water through mostly hydrophilic membranes to the dialysate water. Furthermore, the small size of urea means that convective and/or diffusive transfer through a given semipermeable membrane is unlikely to be representative of larger molecules, especially if dialyzers with a small pore size are applied. Urea kinetics are also poorly representative of the removal of small protein-bound molecules and intracellular solutes with cell membrane-limited clearance. Finally, it should be realized that the Kt/V concept has been developed in a specific population, that is, a group of renal failure patients with few comorbidities, submitted to short intermittent hemodialysis with small-pore bioincompatible membranes very likely using dialysate of lower quality than that used today. Kt/V might well become less accurate and useful in predicting outcomes as different dialysis conditions are pursued, such as dialysis with biocompatible and/or large-pore membranes, (ultra) pure dialysate, alternative time frames, high levels of convection, and/or in populations with a different distribution of body mass.

Comparison of causes of death using HEMO Study and HCFA end-stage renal disease death notification classification systems. The National Institutes of Health-funded Hemodialysis. Health Care Financing Administration

Few data are available on the accuracy of death classification in patients with end-stage renal disease (ESRD). The National Institutes of Health-funded Hemodialysis (HEMO) Study allows the opportunity to compare cause of death recorded on the Health Care Financing Administration (HCFA) Death Notification Form 2746 with death classified by the HEMO Study. The HEMO Study cause of death is determined by trained HEMO Study Outcome Review Committee physicians. In this interim analysis, there were 220 deaths coded by both classification systems. Using the HEMO Study classification system, the most common cause of death was ischemic heart disease (20.4%), followed by arrhythmia and conduction problems (10.4%), cerebrovascular disease (8.6%), and non-access-related infections (7.7%). Using the HEMO Study final death classification as the reference standard, most differences in the two classification systems were related to coding of heart disease. Sensitivity for the HCFA classification ranged from 9.1% for congestive heart failure to 91.7% for malignancy, whereas specificity values were all greater than 78%. Positive predictive values ranged from 11.8% for other heart disease and conditions to 100% for malignancy and hepatobiliary disease, whereas negative predictive values were all greater than 85%. The kappa statistic between the two death classification systems ranged from 0.12 for congestive heart failure to 0.95 for malignancy. Studies using death classification from the HCFA ESRD death notification form for deaths secondary to either cardiovascular diseases or unknown causes should be interpreted cautiously.

HEMO equilibrated Kt/V goals are difficult to achieve in large male patients

The long-term outcome of chronic hemodialysis patients is influenced by the adequacy of dialysis treatment. A major objective of the ongoing US HEMO Study is to determine if a higher target value of treatment as measured by the equilibrated Kt/V (eKt/V), a calculation of dialysis adequacy developed for the study, of 1.45 results in a better outcome than the presently accepted target value for eKt/V of 1.05 (approximately equal to spKt/V of 1.2). eKt/V corrects for urea rebound and gives a better estimate of actual treatment received. To examine the feasibility of achieving the higher eKt/V in large hemodialysis patients, a retrospective analysis of 389 monthly eKt/V values from 65 men on chronic hemodialysis of larger than average size dialyzed at high blood and dialysate flows (QB 400, QD 800 ml/min) with large dialyzers (1.8-2.2 m2) for longer than 4 hours three times weekly was performed. A total of 278 treatments considered optimal by a blood water urea clearance estimate were included in the final analyses. The mean body weight and Chertow water volume were 84.3+/-16.5 kgm and 50.0+/-6.7 L, respectively. The mean sp Kt/V was 1.29+/-0.17. The mean eKt/V was 1.16+/-0.14 and was inversely correlated with weight and water volume (p < 0.0001). Despite the large dialyzers and high blood and dialysate flow rates, no patient weighing more than 80 kgm or with body water volume exceeding 46 liters achieved an eKt/V of 1.45. This study suggests that creative dialyses will be required to achieve the HEMO "high arm" target in large patients.

Daily hemodialysis: a dialysis provider perspective

Regardless of size, ownership or corporate structure, the goal of the dialysis provider is to deliver the best renal substitution therapy in the safest and most convenient manner, at a cost commensurate with reimbursement. This paper reviews the available data on daily hemodialysis, focusing on its ability to satisfy this goal. In addition, it examines the potential influence of frequency, time, and dose of dialysis on clinical outcomes of various series over the last 3 decades. The available data strongly suggest the clinical benefits of daily hemodialysis, but are not sufficient to show statistically better outcomes. Under the present reimbursement system, daily hemodialysis is not economically feasible in the United States. Prospective clinical trials designed to prove the benefits of these therapies and justify their reimbursement are needed.

Daily hemodialysis efficiency: an analysis of solute kinetics

Increasing the frequency of hemodialysis increases its efficiency, which causes the popular dialysis yardstick, single-pool Kt/V, to underestimate the dose just as it overestimates the dose of less frequent dialysis. The frequency dependence of hemodialysis can be explained by examining solute kinetics. Several factors, including the logarithmic fall in solute concentration and solute disequilibrium within the patient, account for the improved efficiency of both daily hemodialysis and continuous peritoneal dialysis, but to fully explain the marked difference in clinical targets for dosing peritoneal versus hemodialysis, one must go outside the realm of urea kinetics. Solutes that dialyze easily, such as urea, but diffuse less readily within the patient, require a 2-compartment model to accurately predict their concentration profiles and to measure efficiency. When applied to appropriately selected solutes, the model can account for the difference in clinical targets and can explain the failure of other indices, such as middle molecule clearance, eKt/V, and EKR, to account for the differences. A cumulative toxic effect of these relatively secluded compounds might offer a better explanation of uremic toxicity and an objective rationale for increasing dialysis frequency and time. Simplified methods for measuring the dose of dialysis fail when the patient is treated more often than 3 times per week, but 2 new and independently derived methods that include parameters to account for the improved efficiency have been developed for measuring frequent dialysis. The new expressions of dose as a weekly analog of urea clearance are similar in magnitude and independent of frequency, giving present-day clinicians a choice of methods to compare 2 to 7 treatments per week. The kinetic behavior of solutes removed by dialysis and the new expressions of dose support the subjective improvement reported by patients, many of whom have embraced a transition to more frequent and prolonged hemodialysis.

The end-stage renal disease program. Experience with a chronic disease capitated health plan

The ESRD program has demonstrated the potential for a capitated, disease-oriented, total care method of patient support. Given both the increasing age and complexity of the patient population, not only has the cost per patient decreased over the life of the program, but the standardized mortality rates have also declined. Technology has bridged the gap and made the relative cost per treatment more affordable and science has developed medications and techniques that have enhanced both patient comfort and longevity. As more complex patients enter the fold of the ESRD program, an increased awareness of enhanced coordination of care needs to be recognized.

The role of the dietitian in a multicenter clinical trial of dialysis therapy: the Hemodialysis (HEMO) Study

The Hemodialysis (HEMO) Study is a randomized multicenter prospective clinical trial, supported by the National Institute of Diabetes, Digestive, and Kidney Diseases of the National Institutes of Health. The trial is designed to assess the effects of a standard versus higher dialysis dose and low versus high dialysis membrane flux on morbidity and mortality of chronic hemodialysis patients. The role of the dietitian in the HEMO Study is to support and maintain the nutritional status of randomized participants. To ensure participant safety, nutritional status is closely monitored by a variety of biochemical and participant-reported parameters. Serum albumin and equilibrated normalized protein catabolic rates are obtained monthly. Appetite assessment and dietary energy and protein intakes using a 2-day diet diary assisted recall are ascertained at baseline and on a yearly basis. Consumption of vitamins, minerals, and nutritional supplements, including oral enterals, tube feedings, and parenteral nutrition, is obtained at least once a year. In addition, anthropometry is performed at baseline and on a yearly basis. Prespecified changes in serum albumin level or body weight trigger action by the dietitian to prevent protein calorie malnutrition. The HEMO Study dietitians play a vital role in carrying out the nutrition program for the trial. The HEMO Study should provide important information about the natural history of the nutritional status of chronic hemodialysis patients and the impact of dialysis dose and dialysis membrane flux on these parameters.

Multicompartment urea kinetics in well-dialyzed children

BACKGROUND

We have reported catch-up growth with hemodialysis (HD) of approximately 15 hours/week. Without an equilibrated post-treatment blood urea nitrogen, the variable-volume single-pool (VVSP) model will not account for urea rebound, inflating the estimated HD dose (K(d)t/V). A two-pool model (FVDP) predicts rebound, but requires fixed compartment volumes for the equations to be solvable in closed form, also inflating K(d)t/V.

METHODS

We developed an approximate perturbation solution (WKB method) to a variable volume, two-pool (VVDP) model. Estimated model parameters were compared with the results of equilibrated kinetic studies using measured clearance K(d) (N = 17). Once the model was validated, we re-analyzed 292 kinetic studies from our earlier cohort, which was considered well-dialyzed on the basis of growth rates (N = 12, mean annual change in height standard deviation score +0.31, mean follow-up of 26 months).

RESULTS

For the VVSP, FVDP, and VVDP models, respectively, the mean errors were (1) K(d)t/V, 0.22 +/- 0.07, 0.29 +/- 0.17, 0.06 +/- 0.07 (ANOVA, P < 0.001); (2) urea distribution volume vol/wt (%), -8.2 +/- 4.2, -9.1 +/- 3.0, -2.2 +/- 3.6 (P < 0.001). Sequential studies confirmed reproducibility, with a coefficient of variation < or = 5%. In the earlier cohort, a comparison of the VVSP and VVDP models yielded the following: (1) K(d)t/V, 1.91 +/- 0.35 vs. 1.76 +/- 0.33 (P < 0.001); (2) normalized protein catabolic rate (nPCR, g/kg/day), 1.56 +/- 0.39 vs. 1.52 +/- 0.38 (P < 0.001); and (3) K(d) (whole blood, mL/kg/min), 4.8 +/- 0.9 vs. 4.4 +/- 0.8 (P < 0.001).

CONCLUSION

This VVDP model yields reliable estimates of K(d)t/V and other kinetic parameters using standard blood urea nitrogen sampling. Analysis of patients previously characterized as well-dialyzed on the basis of growth rates clarifies the HD dose needed to sustain normal growth.

Design and statistical issues of the hemodialysis (HEMO) study

The Hemodialysis Study is a multicenter clinical trial of hemodialysis prescriptions for patients with end stage renal disease. Participants from over 65 dialysis facilities associated with 15 clinical centers in the United States are randomized in a 2 x 2 factorial design to dialysis prescriptions targeted to a standard dose or a high dose, and to either low or high flux membranes. The primary outcome variable is mortality; major secondary outcomes are defined based on hospitalizations due to cardiovascular or infectious complications, and on the decline of serum albumin. The Outcome Committee, consisting of study investigators, uses a blinded review system to classify causes of death and hospitalizations related to the major secondary outcomes. The dialysis dose intervention is directed by the Data Coordinating Center using urea kinetic modeling programs that analyze results from dialysis treatments to monitor adherence to the study targets, adjust suggested dialysis prescriptions, and assist in trouble-shooting problems with the delivery of dialysis. The study design has adequate power to detect reductions in mortality rate equal to 25% of the projected baseline mortality rate for both of the interventions.

Trends in end-stage renal disease. Epidemiology, morbidity, and mortality

ESRD is always fatal unless recognized and treated appropriately. In the United States, the incidence of ESRD is increasing. Fortunately, both mortality among dialysis patients and the rate at which ESRD has been increasing over the past decade are declining. Obviously, the primary goal should be prevention of ESRD. Aggressive treatment of hypertension and hyperglycemia is likely to reduce the incidence of ESRD. Screening for diabetes and hypertension may be a fruitful approach to reduction in ESRD rates, because many patients present with renal failure after prolonged periods of undiagnosed hypertension or type 2 diabetes.

In vivo effects of dialysate flow rate on Kt/V in maintenance hemodialysis patients

It is generally assumed that hemodialysis adequacy is only minimally affected by increasing the dialysate flow rate (Qd). Recent in vitro studies showed that dialyzer urea clearance (Kd(urea)) may increase substantially more than expected in response to an increase in Qd. Because these studies implied that dialysis efficacy may benefit from greater Qds, we studied in vivo the effects of various Qds on the delivered dose of dialysis in 23 maintenance hemodialysis (MHD) patients. Hemodialysis was performed at Qds of 300, 500, and 800 mL/min for at least 3 weeks each, whereas specific dialysis prescriptions (treatment time, blood flow rate [Qb], ultrafiltration volume, and type and size of dialyzer) were kept constant. Delivered dose of dialysis, assessed by single-pool Kt/V (Kt/V(sp)) and double-pool Kt/V (Kt/ V(dp)), was measured at least three times for each Qd (218 measurements). Mean +/- SEM Kt/V(sp) was 1.19 +/- 0.03 at Qd of 300 mL/min, 1.32 +/- 0.04 at 500 mL/min, and 1.45 +/- 0.04 at 800 mL/min. The relative gains in Kt/V(sp) for increasing Qd from 300 to 500 mL/min and 500 to 800 mL/min were 11.7% +/- 8.7% and 9.9% +/- 5.1%, respectively. Kt/V(dp) increased at a similar percentage (11.2% +/- 8.9% and 10.3% +/- 5.1%, respectively). The observed gain in urea clearance by increasing Qd from 500 to 800 mL/min was significantly greater than the increase in Kd(urea) predicted from mathematical modeling (5.7% +/- 0.4%; P = 0.0008). Removal ratios for creatinine and the high-molecular-weight marker, beta(2)-microglobulin, were not affected by increasing Qd from 500 to 800 mL/min. The proportion of patients not achieving adequacy (Kt/V(sp) >/= 1.2) was reduced from 56% at Qd of 300 mL/min to 30% at 500 mL/min and further to 13% at 800 mL/min. It is concluded that increasing Qd from 500 to 800 mL/min is associated with a significant increase in Kt/V. Hemodialysis with Qd of 800 mL/min should be considered in selected patients not achieving adequacy despite extended treatment times and optimized Qbs.