Mortality risk by hemodialyzer reuse practice and dialyzer membrane characteristics: results from the usrds dialysis morbidity and mortality study

Reduced Cytokine Induction and Removal of Complement Products with Synthetic Hemodialysis Membranes

The increasing use of high-flux membranes for hemodialysis (HD) has raised concerns that these membranes may confer a higher risk of exposure to cytokine-inducing, bacterial substances (CIS) in the dialysate. Several studies, however, reported higher transfer of CIS through low-flux cellulosic than high-flux synthetic membranes. This surprising paradox was explained by adsorption of CIS to certain high-flux membranes. In order to investigate flux and membrane type independently, we studied two synthetic Polyflux (PF) membranes of the same type but with different flux properties and compared them to a cellulosic membrane (Cuprophan). Three different approaches were employed: (1) cytokine induction in whole blood during in vitro HD contaminated with bacterial filtrates, (2) removal of recombinant C5a, and (3) transfer of purified lipopolysaccharide (LPS). After 90 min recirculation of whole blood, the appearance of IL-6-inducing substances on the blood side was lowest with high-flux PF (1.1 +/- 0.2 ng/ml), slightly higher with low-flux PF (1.9 +/- 0.7 ng/ml) and highest with Cuprophan (4.1 +/- 1 ng/ml). Recombinant C5a added to plasma on the blood side was markedly removed by high-flux PF (by 83%), to a lesser degree and only in the presence of ultrafiltration with low-flux PF (by 54%) and not significantly with Cuprophan (by 11%). Significant transfer of purified LPS from the dialysate onto the blood side was only observed with the cellulosic membrane. We conclude that in contrast to cellulosic membranes, certain synthetic membranes do not permit transfer of LPS. Cytokine induction on the blood side is further reduced by the use of high-flux membranes due to removal of activated complement factors.

The relevance of convection in clinical practice: A critical review of the literature

Convective treatments (high-flux hemodialysis (HD), hemodiafiltration and hemofiltration) are characterized by enhanced removal of middle and large molecular weight solutes compared with conventional low-flux HD. As these molecules are claimed to play an important role in the genesis of many complications of chronic HD, the availability of these techniques represented an intriguing innovation and a possible means to improve the still poor prognosis of HD patients. Here we will critically review the most important published studies comparing convective treatments with low-flux HD on chronic morbidity, preservation of residual renal function, and long-term survival.

Uremic toxins: a new focus on an old subject

The uremic syndrome is characterized by an accumulation of uremic toxins due to inadequate kidney function. The European Uremic Toxin (EUTox) Work Group has listed 90 compounds considered to be uremic toxins. Sixty-eight have a molecular weight less than 500 Da, 12 exceed 12,000 Da, and 10 have a molecular weight between 500 and 12,000 Da. Twenty-five solutes (28%) are protein bound. The kinetics of urea removal is not representative of other molecules such as protein-bound solutes or the middle molecules, making Kt/V misleading. Clearances of urea, even in well-dialyzed patients, amount to only one-sixth of physiological clearance. In contrast to native kidney function, the removal of uremic toxins in dialysis is achieved by a one-step membrane-based process and is intermittent. The resulting sawtooth plasma concentrations of uremic toxins contrast with the continuous function of native kidneys, which provides constant solute clearances and mass removal rates. Our increasing knowledge of uremic toxins will help guide future treatment strategies to remove them.

Dialyzer reuse and patient outcomes: what do we know now?

Although some hemodialysis (HD) providers in the United States have recently embarked on programs to discontinue dialyzer reprocessing, the practice of dialyzer reuse is still much more common in the United States than in many other countries. Continuation of reprocessing programs has been justified chiefly as an effort to deliver HD with biocompatible and often expensive higher flux dialysis membranes. However, this rationale is considerably less compelling with the decrease in cost for most types of HD membranes and with ongoing debates about the relative effectiveness of HD membranes according to flux and other characteristics. While it is highly likely that mandated quality control standards have limited catastrophic events, such as outbreaks of blood-borne bacterial infections that can occur due to poor dialyzer reprocessing techniques, hemodialyzer reprocessing remains vulnerable to poor implementation. Reprocessing is no longer indicated in order to improve blood-membrane biocompatibility, due to the marked decrease in first-use syndrome since the widespread adoption of synthetic dialysis membranes. Rather, the possibility exists that certain chronic inflammatory responses observed with dialyzer reuse may be deleterious, although these relationships remain speculative. While observational studies have not consistently demonstrated a large excess mortality attributable to reuse, the association of reuse to mortality remains uncertain. Evaluation of the safety of particular reprocessing techniques, germicides, and cleaners has been even harder to examine. Given the widespread availability of inexpensive biocompatible HD membranes and persistent uncertainties about the safety of dialyzer reprocessing, it is time for providers to reexamine their rationale for continuing hemodialyzer reprocessing programs.

Dialyzer membrane permeability and survival in hemodialysis patients

BACKGROUND

We previously showed that nutritional protein concentrations were predictive of outcome, whereas variables reflecting body composition and dialysis dose were not, in a 30-month prospective follow-up of 1,610 hemodialysis patients. Information on dialysis membrane and erythropoietin use had to be evaluated in an additional follow-up.

METHODS

A subset of 650 patients from the initial cohort of 1,610 was analyzed for survival in a 2-year extension of follow-up. Detailed data were collected: demographics; cause of renal failure; time on dialysis therapy; type of membrane; erythropoietin treatment; body mass index (BMI); predialysis albumin, prealbumin, and bicarbonate levels; and outcome. Normalized protein catabolic rate (nPCR), dialysis adequacy, and lean body mass were computed from predialysis and postdialysis urea and creatinine values.

RESULTS

Patient characteristics were age of 61 +/- 16 years, 58% men, BMI of 22.7 +/- 4.4 kg/m2 , time on dialysis therapy of 102 +/- 73 months, and 8.8% had diabetes. Dialysis parameters were duration of 247 +/- 31 minutes, Kt/V of 1.4 +/- 0.3, and nPCR of 1.2 +/- 0.3 g/kg/d. Albumin level was 3.73 +/- 0.53 g/dL (37.3 +/- 5.3 g/L), and prealbumin level was 31 +/- 8 mg/dL. The survival rate was 78.7% after 2 years. Survival was influenced by age, presence of diabetes, use of high-flux membrane, and serum albumin level, but not other variables, including Kt/V and prealbumin level. Two-year variations in values for urea, creatinine, and weight were predictive of survival in univariate, but not multivariate, analyses.

CONCLUSION

In patients on dialysis therapy for a long period, better survival was observed when high-flux dialysis membranes were used.

Reuse-Associated Mortality in Incident Hemodialysis Patients in the United States, 2000 to 2001

BACKGROUND

The impact of dialyzer reuse on the mortality of hemodialysis patients is debated. This study assesses reuse-associated mortality across US dialysis provider systems (for-profit, not-for-profit; hospital-based, and freestanding units) in incident patients.

METHODS

Incident Medicare hemodialysis patients who initiated dialysis therapy from January 1, 2000, to December 31, 2001, were included and followed up to December 31, 2002. A 3-month entry period was used to determine comorbidity and disease severity. Applying various analytic approaches, mortality rates for patients treated with reused (or reprocessed) or single-use dialyzers were compared. Because of differences among dialysis units, facility clustering was addressed.

RESULTS

Of 75,831 patients, 61,391 patients (81.0%) were classified as on reuse, and 14,440 patients (19.0%), as on single use, as of the start of follow-up. The overall mortality rate was 25.0/100 patient-years. No difference in mortality risk was found between patients treated with reuse compared with single use in an intent-to-treat approach (hazard ratio, 0.98; 95% confidence interval, 0.94 to 1.02; P = 0.266) after adjusting for chain affiliation, for-profit status, year of dialysis inception, age, sex, race, renal diagnosis, comorbidity, and hospitalization days. Findings were similar in an as-treated approach (hazard ratio, 0.97; 95% confidence interval, 0.93 to 1.01; P = 0.136). No survival advantage associated with single use was found for subgroups.

CONCLUSION

No overall survival advantage or disadvantage is associated with dialyzer reuse compared with single use in incident hemodialysis patients in the United States; however, continued monitoring is advised.

Epidemic of end-stage renal disease in people with diabetes in the United States population: do we know the cause?

BACKGROUND

The number of individuals initiating renal replacement therapy in the United States population grew exponentially over the past two decades. Cases of end-stage renal diseae (ESRD) attributed to diabetes accounted for most of this increase. In this report we examined factors that may account for the increase to determine whether it truly represents an epidemic of ESRD due to diabetes.

METHODS

We reviewed time trends in data of the United States Renal Data system, the Diabetes Surveillance Program of the Centers for Disease Control and Prevention, and diabetes literature.

RESULTS

Recent growth of the number of individuals with diabetes accounted for less than 10% of the increase in the number of diabetes-related ESRD. Instead, most of it was due to a threefold increase in risk of ESRD in people with diabetes and, therefore, qualifies as an epidemic. Curiously, this epidemic occurred despite widening implementation of effective renoprotective therapies. Individuals with type 2 diabetes, regardless of gender, age, or race, experienced the greatest increase in risk. There is no evidence that diabetic patients have been surviving longer, so the increased risk was not attributable to the high risk associated with long duration diabetes.

CONCLUSION

We hypothesize that an epidemic of ESRD has occurred in people with diabetes in the United States population over the last two decades. The nature of the factor responsible for the epidemic and the reasons it affects patients with type 2 diabetes particularly are unknown. Research efforts to identify the putative factor deserve high priority, as does a commitment of resources to provide care for the burgeoning number of patients with ESRD and type 2 diabetes.

Patient survival following renal transplant failure in Canada

Studies from the United States have shown that renal allograft failure is associated with a high mortality rate. The purpose of this study was to determine whether transplant failure was associated with survival in a recent cohort of kidney transplant recipients with different characteristics and a distinct health care system from the United States. Cox regression was used to model allograft loss as a time-dependent variable with patient survival as the primary outcome in 4743 kidney transplant recipients from the Canadian Organ Replacement Register. During follow-up 607 (12.8%) patients had allograft failure and 411 (8.7%) died. Patients with a functioning transplant had an unadjusted death rate of 2.06 per 100 patient years that increased to 5.14 per 100 patient years following allograft failure. After controlling for important confounding variables, allograft failure was found to increase the risk of death by over threefold compared to patients who maintained transplant function (adjusted hazard ratio, 3.39; 95% CI, 2.75-4.16; p < 0.0001). In conclusion, this analysis has shown that kidney transplant failure is an independent predictor of mortality following renal transplantation in a Canadian population. This finding supports the premise that it is the loss of transplant function, rather than patient or system-related issues, that is the main factor contributing to outcome.

Early referral as an independent predictor of clinical outcome in end-stage renal disease on hemodialysis and continuous ambulatory peritoneal dialysis

OBJECTIVES

To evaluate the influence of early nephrology referral on clinical outcome in patients on maintenance hemodialysis (HD) and peritoneal dialysis (PD).

PATIENTS AND METHODS

This study retrospectively analyzed patients entering our HD and PD program from February 2000 to June 2003. Patients who presented to a nephrologist more than 6 months before starting dialysis were defined as early referral (ER). Meanwhile, patients transferred to the nephrology department less than 6 months before initial dialysis were considered late referral (LR). RESULTS HD GROUPS: Of 78 HD patients, 37 (47.1%) qualified for the ER group and 41 (52.6%) were designated to the LR group. The demographic data were analyzed for both the HD and PD groups. No significant differences in average age at dialysis, duration of hemodialysis, and gender were noted between these two groups. The same applied for the biochemical parameters in both groups. HD patients with early referral had significantly better survival (p < .05) as plotted with the Kaplan-Meier method. In univariate analysis by cox proportional hazards mode, the early referral in HD patients [Exp (Coef) = 0.426, P < .01] significantly influenced survival. The various variables were further examined by multivariate analysis, and early referral, hemoglobin, and age still significantly impacted patient survival (P < .05). CAPD GROUPS: The survival curve related to early referral in continuous ambulatory peritoneal dialysis (CADP) patient survival rate was significantly higher for the early referral groups (P < .05). In addition, a multivariate analysis adjusting for several potential risk factors found that referral time remained significantly associated with patient survival. In additional, hemoglobin and age were significant and independent predictors of mortality.

CONCLUSION

This study demonstrates that time between referral and starting dialysis is a predictor of survival for both HD and PD patients, with early referral being associated with longer survival time. These analytical results suggest that early referral before dialysis is important in determining long-term prognosis in HD and PD patients.

Status of dialyser reuse in Korea

BACKGROUND AND AIM

Dialyser reuse treatments in Korea were first practised at a facility in 1985. Until 1999, there was only one facility practising dialyser reuse treatments, but the reuse practice has gradually increased since 1999. The purpose of this study was to gather and analyse the current (April 2002) dialyser reuse treatment data in Korea.

METHOD AND RESULTS

Data was collected via a questionnaire sent to the each hospital that reuses the dialyser, and we received a response from 26 out of 29 facilities (89.7%). Twenty-nine facilities comprised 7.7% (29 of 376) of the total nationwide haemodialysis facilities in Korea. The percentage of patients on dialyser reuse treatments was 6.2% (1234 of 20,010). All facilities used an automated reuse processing technique for dialyser reuse and 22 facilities used a peracetic acid mixture (PAM) without hypochlorite. There was one facility that used the heated citric acid method. Eighty per cent of facilities used only high flux membranes (Kuf > or = 20 mL/h per mmHg) and 12% of the facilities used both high and low flux membranes. The average number of the reuse treatments was 15-fold (range 10-22) and the average of the maximum number of reuse treatments was 20-fold (range 10-50).

CONCLUSION

Although dialyser reuse treatments are not a common practice in Korea, the reuse programs are steadily increasing. Strict quality control and further regulations regarding the reuse program should be promptly enacted to provide a better quality of haemodialysis treatment for patients in Korea.

Effects of high-flux hemodialysis on clinical outcomes: results of the HEMO study

Among the 1846 patients in the HEMO Study, chronic high-flux dialysis did not significantly affect the primary outcome of the all-cause mortality (ACM) rate or the main secondary composite outcomes, including the rates of first cardiac hospitalization or ACM, first infectious hospitalization or ACM, first 15% decrease in serum albumin levels or ACM, or all non-vascular access-related hospitalizations. The high-flux intervention, however, seemed to be associated with reduced risks of specific cardiac-related events. The relative risks (RR) for the high-flux arm, compared with the low-flux arm, were 0.80 [95% confidence interval (CI), 0.65 to 0.99] for cardiac death and 0.87 (95% CI, 0.76 to 1.00) for the composite of first cardiac hospitalization or cardiac death. Also, the effect of high-flux dialysis on ACM seemed to vary, depending on the duration of prior dialysis. This report presents secondary analyses to further explore the relationship between the flux intervention and the duration of dialysis with respect to various outcomes. The patients were stratified into a short-duration group and a long-duration group, on the basis of the mean duration of dialysis of 3.7 yr before randomization. In the subgroup that had been on dialysis for >3.7 yr, randomization to high-flux dialysis was associated with lower risks of ACM (RR, 0.68; 95% CI, 0.53 to 0.86; P = 0.001), the composite of first albumin level decrease or ACM (RR, 0.74; 95% CI, 0.60 to 0.91; P = 0.005), and cardiac deaths (RR, 0.63; 95% CI, 0.43 to 0.92; P = 0.016), compared with low-flux dialysis. No significant differences were observed in outcomes related to infection for either duration subgroup, however, and the trends for beneficial effects of high-flux dialysis on ACM rates were considerably weakened when the years of dialysis during the follow-up phase were combined with the prestudy years of dialysis in the analysis. For the subgroup of patients with <3.7 yr of dialysis before the study, assignment to high-flux dialysis had no significant effect on any of the examined clinical outcomes. These data suggest that high-flux dialysis might have a beneficial effect on cardiac outcomes. Because these results are derived from multiple statistical comparisons, however, they must be interpreted with caution. The subgroup results that demonstrate that patients with different durations of dialysis are affected differently by high-flux dialysis are interesting and require further study for confirmation.

Biochemical and Clinical Evidence for Uremic Toxicity

The uremic syndrome is a mix of clinical features resulting from multiple organ dysfunctions which develop when kidney failure progresses, and is attributed to the retention of solutes, which under normal conditions are excreted by the healthy kidneys into the urine. The most practical classification of uremic solutes is based on their physicochemical characteristics that influence their dialytic removal, in (1) small water soluble compounds, (2) the larger "middle molecules," and (3) the protein bound compounds. Hence, uremic retention is much more complex than originally believed. Among the small water soluble compounds, urea exerts not much toxic activity and is not very representative in its kinetic behavior for many other uremic solutes. Among the middle molecules, many have been recognized to exert biological activity and hence to contribute to the uremic syndrome. Specific dialysis strategies apply large pore membranes to remove those middle molecules and have a beneficial impact on uremic morbidity and mortality. A substantial number of uremic solutes are protein bound. Only recently, a relation between their concentration and clinical status could be demonstrated. Likewise, it was only recently possible to demonstrate more than standard removal with super-flux dialysis membranes. To further improve characterization of uremic solutes and to develop directed therapeutic approaches, further concerted action among various groups of researchers will be needed.

Dialyser reuse-associated mortality and hospitalization risk in incident Medicare haemodialysis patients, 1998-1999

BACKGROUND

The reuse of haemodialysers has been practiced in the United States for >20 years. We investigated mortality and hospitalization risk according to various reuse practices, testing the hypothesis that outcomes are improved in patients treated with dialysers cleaned with bleach and sterilized with formaldehyde.

METHODS

We studied 1998 and 1999 incident Medicare haemodialysis patients, with follow-up through December 31, 2000 (49 273 patients). Clinical conditions and dialysis therapy were characterized from Medicare claims data. Included were patients who could be linked to a dialysis provider. Demographic characteristics were obtained from the Centers for Medicare and Medicaid Services (CMS) Medical Evidence Report. Mortality information was obtained from the CMS ESRD Death Notification; hospitalization information, from Medicare in-patient claims files. Data on reuse practices were obtained from the annual survey of haemodialysis units conducted by the Centers for Disease Control and Prevention.

RESULTS

Cox regression analyses found no significant differences in mortality or first-hospitalization risk for patients in dialysis units not using bleach as a cleaning agent. Outcomes for patients treated in units using glutaraldehyde did not vary according to use of bleach. In the analysis of first-hospitalization risk, there was no difference according to various germicide/bleach combinations. Overall, there was no significant difference in relative risk of death or in hospitalization risk among the reuse groups (including the no-reuse group).

CONCLUSIONS

For the 1998-1999 period, reuse practices were not associated with a survival advantage or disadvantage. Our findings may reflect the National Kidney Foundation's 1997 introduction of clinical practice guidelines, the intent of which was to bring about increased consistency of care within the dialysis community in the United States.

Dialyzer membrane type and reuse practice influence polymorphonuclear leukocyte function in hemodialysis patients

BACKGROUND

Polymorphonuclear leukocyte (PMNL) production of reactive oxygen species (ROS) has been linked to hemodialysis (HD) associated morbidity. The effect of dialyzer membrane type and reuse on PMNL function has not been clearly defined.

METHODS

The present report is a cross-sectional study undertaken in a cohort of patients undergoing regular HD, at enrollment into the Hemodialysis (HEMO) Study, to study the association between patient and dialysis-related factors and PMNL function. PMNL function was assessed by measuring PMA- and N-formyl methionyl-leucyl-phenylalanine (fMLP) -induced respiratory burst, and phagocytic activity toward Staphylococcus aureus.

RESULTS

PMNL from patients dialyzed with polysulphone (PS) or cuprophane (CU) membranes showed higher PMA-induced respiratory burst activity compared with those exposed to substituted cellulose (cellulose acetate, cellulose triacetate, CA/CT) membranes, regardless of dialyzer reuse. The use of bleach as a cleansing agent during reuse was associated with higher PMA-induced PMNL superoxide production, as was the use of renalin when compared to aldehydes. In a subgroup of patients using PS dialyzers, reuse itself was associated with higher fMLP-induced superoxide production. The type of bleach-germicide combination during reuse showed that use of renalin as a germicide was also associated with higher PMNL phagocytosis index. The number of years on HD correlated inversely with PMA-induced PMNL superoxide response. Weaker PMNL response to fMLP was associated with greater comorbidity and poor functional status as quantified by Index of Coexisting Diseases (ICED) and Karnofsky scores, respectively.

CONCLUSION

Our results indicate that dialyzer membrane type and the reuse process influence the oxidative response of PMNL among HD patients. The implications of these observations on clinical morbidity need to be further evaluated in prospective studies.

Haemodialysis prescription, adherence and nutritional indicators in five European countries: results from the Dialysis Outcomes and Practice Patterns Study (DOPPS)

BACKGROUND

The Dialysis Outcomes and Practice Patterns Study (DOPPS) is a prospective, observational study designed to evaluate practice patterns in random samples of haemodialysis facilities and patients across three continents. Participating countries include France, Germany, Italy, Spain and the UK (Euro-DOPPS), Japan and the USA. DOPPS data collection has used the same questionnaires and protocols across all participating countries to assess components of dialysis therapy and outcomes. This study focuses on dialysis prescription, adherence and nutrition among the Euro-DOPPS countries.

METHODS

In each Euro-DOPPS country, patients were selected randomly from 20-21 representative facilities. Simple means and frequencies were calculated to compare relevant data elements to gain insights into differences in therapeutic aspects among nationally representative patients. Participants entering the study within 90 days of beginning dialysis therapy were excluded from these analyses.

RESULTS

Among the five countries, mean delivered dose as measured by normalized urea clearance (Kt/V) varied from 1.28 to 1.50 and was accompanied by differences in dialysis prescription components, including blood flow rates, treatment times, and dialyser membrane and flux characteristics. By country, a nearly 2-fold difference was observed in indicators of patient adherence and management (skipping and shortening dialysis, hyperkalaemia, hyperphosphataemia and high interdialytic weight gain). Indicators of malnutrition varied substantially.

CONCLUSIONS

This study demonstrates differences in the management of haemodialysis patients across Euro-DOPPS and offers opportunities for improving dialysis dose, adherence and nutrition. Correlation of differences in practice patterns at the dialysis unit level with patient outcomes will offer new insights into improving dialysis therapy.

Impact of Bleach Cleaning on the Performance of Dialyzers with Polysulfone Membranes Processed for Reuse Using Peracetic Acid

Dialyzer performance may change with reuse depending on whether or not the dialyzer is cleaned with bleach. Bleach is usually used in conjunction with formaldehyde as the germicide. Because few data are available for dialyzers cleaned with bleach and disinfected with peracetic acid, we examined dialyzer performance in a cross-over study of dialyzers containing polysulfone membranes reprocessed using bleach and peracetic acid or peracetic acid alone. Each dialyzer was used for a total of 16 treatments, or until it failed standard criteria for continued use. Urea, beta2-microglobulin, and albumin removal were determined during the first, second, seventh, and 16th use of each dialyzer. Urea removal did not differ between the two reprocessing methods and did not change with reuse. Overall, beta2-microglobulin removal remained unchanged in dialyzers reprocessed with peracetic acid alone, but tended to increase after the seventh use in dialyzers reprocessed with bleach and peracetic acid. Approximately 60% of beta2-microglobulin removal resulted from trapping of beta2-microglobulin at the dialyzer membrane. Albumin loss into the dialysate was clinically insignificant throughout the study with both reprocessing methods. These data show that the clearance of both small and large molecules by dialyzers containing polysulfone membranes is well maintained by reprocessing with peracetic acid and that additional cleaning with bleach has limited impact on performance.

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.

Beta-2 microglobulin in ESRD: an in-depth review

Beta-2 microglobulin is the most widely studied low-molecular-weight protein in end-stage renal disease. It is known to cause dialysis-related amyloidosis (DRA), by virtue of its retention when renal function fails, its deposition in tissues, its aggregation into fibrils, and its ability to become glycosylated. The onset of DRA may be protracted by the use of noncellulosic membranes, especially when high-volume hemodiafiltration is used in the treatment of renal failure. Adsorptive methods have been developed to improve the removal of beta-2 microglobulin. There seems to be a relative risk reduction in mortality when patients are treated with dialysis membranes that have a higher clearance of beta-2 microglobulin.

On-line mixed hemodiafiltration with a feedback for ultrafiltration control: effect on middle-molecule removal

BACKGROUND

Increased middle-molecular uremic toxin removal seems to favorably influence survival in dialysis patients. The aim of this study was to verify if, in on-line mixed hemodiafiltration, solute removal by convection may be enhanced by forcing the ultrafiltration rate (QUF) and optimizing the infusion technique in order to achieve the highest possible filtration fraction (FF).

METHODS

Removal of beta2-microglobulin (beta2-m), urea, creatinine, and phosphate were compared in 20 patients randomly submitted to one dialysis session (A), one postdilution hemodiafiltration session (B), and three sessions of mixed hemodiafiltration (C, D, and E) at different infusion rates (QS). In mixed hemodiafiltration, a newly developed feedback system automatically maintained the transmembrane pressure (TMP) within its highest range of safety (250 to 300 mm Hg) at constant QUF, while ensuring the maximum FF by splitting infusion between pre- and postdilution.

RESULTS

A mean QS of 134 +/- 20 mL/min (mean FF = 0.65) was attained in post-HDF, and up to 307 +/- 41 mL/min (mean FF = 0.69) in mixed hemodiafiltration. The mean dialysate clearances (KDQ) for all tested solutes and urea eKt/V were significantly higher in all hemodiafiltration sessions than in dialysis. Only in the case of urea did the infusion mode have no significant effect. KDQ for beta2-m was maximal in session D and significantly higher than in session B (90.2 +/- 11 mL/min vs. 77.5 +/- 11 mL/min; P = 0.02). KDQ for beta2-m significantly correlated with QS and the plasma water flow rate (QPW). The highest KDQ for beta2-m was found at values of QS approximately QPW. Beyond this value KDQ decreased.

CONCLUSION

The mixed infusion mode in hemodiafiltration, controlled by the TMP-ultrafiltration feedback, seems to improve the efficiency of hemodiafiltration by fully exploiting the convective mechanism of solute removal. The feedback automatically adjusted the infusion rate and site to the maximum FF taking into account flow conditions, internal pressures, and hydraulic permeability of the dialyzer and their complex interactions.

Middle molecules and small-molecular-weight proteins in ESRD: properties and strategies for their removal

Molecular weight has traditionally been the parameter most commonly used to classify uremic toxins, with a value of approximately 500 Da frequently used as a demarcation point below which the molecular weights of small nitrogenous waste products fall. This toxin group, the most extensively studied from a clinical perspective, is characterized by a high degree of water solubility and the absence of protein binding. However, uremia is mediated by the retention of a plethora of other compounds having characteristics that differ significantly from those of the previously mentioned group. As opposed to the relative homogeneity of the nitrogenous metabolite class, other uremic toxins collectively are a very heterogeneous group, not only with respect to molecular weight but also other characteristics, such as protein binding and hydrophobicity. A recently proposed classification scheme by the European Uraemic Toxin Work Group subdivides the remainder of molecules into 2 categories: protein-bound solutes and middle molecules. For the latter group, the Work Group proposes a molecular weight range (500-60,000 Da) that incorporates many toxins identified since the original middle molecule hypothesis, for which the upper molecular weight limit was approximately 2,000 Da. In fact, low-molecular-weight peptides and proteins (LMWPs) comprise nearly the entire middle molecule category in the new scheme. The purpose of this article is to provide an overview of the middle molecule class of uremic toxins, with the focus on LMWPs. A brief review of LMWP metabolism under conditions of normal (and in a few cases, abnormal) renal function will be presented. The physical characteristics of several LMWPs will also be presented, including molecular weight, conformation, and charge. Specific LMWPs to be covered will include beta 2-microglobulin, complement proteins (C3a and Factor D), leptin, and proinflammatory cytokines. The article will also include a discussion of the treatment-related factors influencing dialytic removal of middle molecules. Once these factors, which include membrane characteristics, protein-membrane interactions, and solute removal mechanisms, are discussed, an overview of the different therapeutic strategies used to enhance clearance of these compounds is provided.

In vitro performance of hemodialysis membranes after repeated processing

BACKGROUND

Dialyzers reprocessed with chlorine-based solutions have been associated with increases in ultrafiltration coefficient and middle-molecule removal. Increased pore size has been hypothesized as the mechanism for the latter phenomenon. Dialyzers exposed to Amukin-D (Amuchina Int Inc, Gaithersburg, MD), a chlorine-based reprocessing agent, were evaluated for changes in molecular weight (MW) cutoff and ultrafiltration properties.

METHODS

In vitro MW cutoff studies were performed on Fresenius F-80A (Fresenius, Lexington, MA) and Gambro Polyflux 17 (Gambro, Lakewood, CO) hemodialyzers that were reprocessed 20 times using Amukin-D. Permeability (Uf-A), defined as the area from the ultrafiltered compartment (Uf) compared with the area from the equivalent arterial compartment (A), for dextran across the hemodialyzer membrane was determined after the initial use and after reuses 1, 5, 10, 15, and 20 by using size-exclusion chromatography.

RESULTS

Uf-A for dextran increased approximately 10-fold between hemodialyzer reuses 1 and 5. Thereafter, additional reprocessing did not increase the Uf-A ratio further. MW cutoff increased during these 5 washes and did not change thereafter.

CONCLUSION

Reprocessing with Amukin-D increased the MW cutoff and permeability of both hemodialyzers between reuses 1 and 5, resulting in a greater ultrafiltration rate and greater middle-molecule removal. After reuse 5, there were no further increases in MW cutoff with additional reprocessing in either hemodialyzer. This suggests that reprocessing and storage of each hemodialyzer with Amukin-D affects the permeability of dextran in a nonlinear fashion and to a finite level, such that subsequent reprocessing has no further effect on the MW cutoff of the membrane.

Review on uremic toxins: classification, concentration, and interindividual variability

BACKGROUND

The choice of the correct concentration of potential uremic toxins for in vitro, ex vivo, and in vivo experiments remains a major area of concern; errors at this level might result in incorrect decisions regarding therpeutic correction of uremia and related clinical complications.

METHODS

An encyclopedic list of uremic retention solutes was composed, containing their mean normal concentration (CN), their highest mean/median uremic concentration (CU), their highest concentration ever reported in uremia (CMAX), and their molecular weight. A literature search of 857 publications on uremic toxicity resulted in the selection of data reported in 55 publications on 90 compounds, published between 1968 and 2002.

RESULTS

For all compounds, CU and/or CMAX exceeded CN. Molecular weight was lower than 500 D for 68 compounds; of the remaining 22 middle molecules, 12 exceeded 12,000 D. CU ranged from 32.0 ng/L (methionine-enkephalin) up to 2.3 g/L (urea). CU in the ng/L range was found especially for the middle molecules (10/22; 45.5%), compared with 2/68 (2.9%) for a molecular weight <500 D (P < 0.002). Twenty-five solutes (27.8%) were protein bound. Most of them had a molecular weight <500 D except for leptin and retinol-binding protein. The ratio CU/CN, an index of the concentration range over which toxicity is exerted, exceeded 15 in the case of 20 compounds. The highest values were registered for several guanidines, protein-bound compounds, and middle molecules, to a large extent compounds with known toxicity. A ratio of CMAX/CU <4, pointing to a Gaussian distribution, was found for the majority of the compounds (74/90; 82%). For some compounds, however, this ratio largely exceeded 4 [e.g., for leptin (6.81) or indole-3-acetic acid (10.37)], pointing to other influencing factors than renal function, such as gender, genetic predisposition, proteolytic breakdown, posttranslation modification, general condition, or nutritional status.

CONCLUSION

Concentrations of retention solutes in uremia vary over a broad range, from nanograms per liter to grams per liter. Low concentrations are found especially for the middle molecules. A substantial number of molecules are protein bound and/or middle molecules, and many of these exert toxicity and are characterized by a high range of toxic over normal concentration (CU/CN ratio). Hence, uremic retention is a complex problem that concerns many more solutes than the current markers of urea and creatinine alone. This list provides a basis for systematic analytic approaches to map the relative importance of the enlisted families of toxins.

Improvement of clinical outcome by early nephrology referral in type II diabetics on hemodialysis

OBJECTIVES

To evaluate the influence of early nephrology referral on clinical outcome in type II diabetes mellitus patients on maintenance hemodialysis dialysis.

PATIENTS AND METHODS

This study retrospectively analyzed the type II diabetic patients entering our PD program from February 1988 to June 2001. Patients who were presented to a nephrologist more than 6 months before starting dialysis were defined as early referral (ER). Patients were considered late referral (LR) if they were transferred to the nephrology department within 6 months before initial dialysis.

RESULTS

Hundred and fifteen type II diabetic patients receiving HD for at least 3 months were enrolled in this study. Sixteen of the 53 patients (46.1%) were in the ER group and 62 of the 115 (53.9%) were in the LR group. In univariate analysis by Cox proportional hazards mode, the early referral (Exp (Coef) = 0.423, p < 0.01), good glycemic control (Exp (Coef) = 0.16, p < 0.05), and age at dialysis (Exp (Coef) = 1.026, p < 0.05 (had significantly influenced the patient survival. The residual renal function in the ER group, estimated by creatinine clearance (Ccr), significantly exceeded that of the LR group (ER vs. LR: 4.46 +/- 1.56 vs. 2.51 +/- 1.70 mL/min, p < 0.001). The patients with early referral had significantly better survival (p < 0.05). Five-year survival improved significantly in the early referral group compared to the late referral group (ER: 72.4%; LR: 35.2%, p < 0.05).

CONCLUSIONS

We demonstrate that the time of referral before starting dialysis is a predictor of survival for type II diabetics on HD. Patients with early referral are associated with longer survival. The beneficial effect might be associated with the timely initiation of the chronic HD program. These results suggest that early referral before dialysis is important in determining the long-term prognosis in type II diabetics on HD.

Survival of hemodialysis patients and uremic toxin removal

Uremic toxin removal based on diffusion and/or convection allows eliminating solutes with negative metabolic impact. Uremic solutes can be classified as small and water-soluble compounds, larger "middle" molecules, or protein bound solutes. The question arises whether more removal of each of these solute classes affects patient survival. Kt/V of urea is currently used as a surrogate for small water-soluble solute removal. There is ample evidence that Kt/V and survival are correlated, but the threshold Kt/V remains a matter of debate. Probably, the actually proposed threshold of 1.2 is too low. This impact of Kt/V is in contradiction with the low toxicity of urea and points to a role for other water-soluble solutes, e.g., potassium. More removal of middle molecules results in a lower morbidity and also in a lower mortality. In addition, a relationship has been demonstrated between the use of membranes with large pore size and a decrease of inflammatory status, by itself an important factor related to mortality. One of the problems is that large pore membranes are at the same time more biocompatible and reflect more dialysate impurities, compared to many small pore membranes, whereas they also reflect more dialysate impurities. It remains uncertain which one of these factors, if any, has a predominant effect. Recent studies point to a separate effect of pore size but await confirmation. Protein bound toxins inhibit several biochemical functions. Their removal pattern is totally different from that of classical markers such as urea. In analogy with drugs, it is essentially the free unbound fraction that exerts biological action; this free fraction is inversely related to serum albumin, another inflammatory marker related to survival. In a final section of this presentation, attention will be drawn to the relationship in uremic patients between inflammation, malnutrition, cardiovascular disease, and mortality, and some of the potential culprits are discussed. Virtually all of these molecules have a high molecular weight or are protein bound. It is concluded that both small and middle molecule removal have an impact on survival, so that more than urea removal alone should be pursued.

Effect of dialysis dose and membrane flux in maintenance hemodialysis

BACKGROUND

The effects of the dose of dialysis and the level of flux of the dialyzer membrane on mortality and morbidity among patients undergoing maintenance hemodialysis are uncertain.

METHODS

We undertook a randomized clinical trial in 1846 patients undergoing thrice-weekly dialysis, using a two-by-two factorial design to assign patients randomly to a standard or high dose of dialysis and to a low-flux or high-flux dialyzer.

RESULTS

In the standard-dose group, the mean (+/-SD) urea-reduction ratio was 66.3+/-2.5 percent, the single-pool Kt/V was 1.32+/-0.09, and the equilibrated Kt/V was 1.16+/-0.08; in the high-dose group, the values were 75.2+/-2.5 percent, 1.71+/-0.11, and 1.53+/-0.09, respectively. Flux, estimated on the basis of beta2-microglobulin clearance, was 3+/-7 ml per minute in the low-flux group and 34+/-11 ml per minute in the high-flux group. The primary outcome, death from any cause, was not significantly influenced by the dose or flux assignment: the relative risk of death in the high-dose group as compared with the standard-dose group was 0.96 (95 percent confidence interval, 0.84 to 1.10; P=0.53), and the relative risk of death in the high-flux group as compared with the low-flux group was 0.92 (95 percent confidence interval, 0.81 to 1.05; P=0.23). The main secondary outcomes (first hospitalization for cardiac causes or death from any cause, first hospitalization for infection or death from any cause, first 15 percent decrease in the serum albumin level or death from any cause, and all hospitalizations not related to vascular access) also did not differ significantly between either the dose groups or the flux groups. Possible benefits of the dose or flux interventions were suggested in two of seven prespecified subgroups of patients.

CONCLUSIONS

Patients undergoing hemodialysis thrice weekly appear to have no major benefit from a higher dialysis dose than that recommended by current U.S. guidelines or from the use of a high-flux membrane.

The importance of convective transport

BACKGROUND

Despite technological advances in dialysis equipment and modalities, survival, morbidity, and quality of life of hemodialysis patients are still severely affected by acute intradialytic and long-term complications, possibly related to the treatment itself. Convective treatments, such as high-flux hemodialysis, hemodiafiltration, and hemofiltration are increasingly suggested as further improvements over standard diffusive hemodialysis. The membranes used for these techniques are high-flux semisynthetic and synthetic membranes. Characteristics of these membranes are high permeability, which allows convective removal of water and electrolytes and higher clearance of middle and large molecular weight solutes, and high biocompatibility, which minimizes the "inflammatory response" secondary to interactions between blood and the artificial material of the hemodialysis system.

METHODS

With the specific aim of verifying the superiority of convective treatments in reducing morbidity and mortality, we performed a review of the published literature.

RESULTS

Some epidemiological studies suggest that convective treatments reduce morbidity and mortality among dialysis patients. However, the results of the published prospective randomized controlled trials are conflicting. Moreover, since convective treatments are usually performed with synthetic biocompatible membranes, it is hard to separate the effect of convection from the effect of biocompatibility.

CONCLUSIONS

To finally assess the effect of high-flux membranes on morbidity and mortality, the results of two randomized, controlled clinical trials (HEMO study and MPO study) specifically designed with this aim are needed.

Daily hemodialysis: an update

The interest in daily hemodialysis in the form of short daily hemodialysis and nocturnal hemodialysis has continued to increase over the past few years. A significant number of publications support the evidence for improved outcomes in most of the study areas, including financial benefits. The increased direct cost of the provision of daily hemodialysis seems to be the main obstacle to the wider acceptance of these methods. Convincing data of improved outcomes and evidence of cost efficiency of daily hemodialysis are being generated. These data may increase the interest of the institutional payors as well as of the dialysis industry to create the proper infrastructure for the use of daily hemodialysis. These dialysis regimens promise to have a major impact on the management of end-stage renal disease.

Quo vadis dialysis membrane?

The development of dialysis membranes is closely related to the development of dialysis as a routine therapy for patients with kidney failure. Without having membranes and dialyzers available as commodity products, the treatment of more than 1 million uremic patients worldwide would be impossible. Several transition periods can be identified: a change in membrane geometry from flat sheet to capillaries, a shift in market appreciation from cellulose to synthetic polymers, and from low-flux to high-flux dialyzers. This shift is supported by the notion that convective therapies using high-flux membranes allow the removal of large-molecular-weight solutes. From a historical background, three eras of perception can be identified for both membrane and dialysis development. First, the period of survival when nephrologists had to focus on techniques for blood access and availability of membranes. Second, the period of issues dedicated to rather specific features of membranes and dialysis therapy such as dose of dialysis, reuse, sterilization, and membrane biocompatibility. And third, the period of quality tops this sequence with a complicated approach: the principal area of interest from the medical community has switched to issues such as quality of life, morbidity, mortality, therapy standards, and cost-effectiveness. New membrane developments should focus on this situation.

Savings in dialysis treatment?

The steadily increasing number of dialysis patients prompts considerations on possibilities for budget reductions with maintenance of treatment quality. A literature survey is presented concerning trends of population increase, individual treatment costs, rationing of patient intake, and consequences of delayed progress of renal insufficiency as well as of savings during both the initial and the later phases of regular dialysis therapy. Cost reduction in one area may well induce rising total budgets and influence clinical outcome. A multidisciplinary approach is suggested to obtain answers to several questions: Can the economic burden of the changing patient demography be counterbalanced by a reorganized staff structure? Will early referral, good predialysis control, and incremental dialysis start imply longer survival? Will increased dialysis doses be economically neutralized by less staff requirements, drug consumption, and patient morbidity? Should dialyzer reuse be abandoned? Can pretransplant dialysis periods be reduced or omitted by improved planning?

Cost-quality trade-offs in dialysis care: a national survey of dialysis facility administrators

Dialysis facilities face important trade-offs between cost and quality under constrained capitated reimbursement. How management at dialysis facilities makes decisions affecting cost and quality of care and views opportunities and threats is unknown. We conducted a national survey of dialysis facility administrators. We asked administrators what changes they would make in response to increases or decreases in reimbursement, their views on linking dialysis care payment to quality-of-care measures, and their views on providing patients with treatment options and outcomes information. One hundred fifty-seven of 280 dialysis facility administrators (56%) responded. If dialysis reimbursement were to increase by 20%, the five most common responses were to: improve patient education programs (62% of respondents), improve facility amenities (42%), purchase new equipment (30%), provide more money for staff salaries (28%), and increase number of nursing staff (21%). Conversely, if dialysis reimbursement were to decrease by 20%, the most common responses were to: limit staff salary (45% of respondents), decrease nursing staff (41%), not replace dialysis equipment (43%), increase dialyzer reuse (37%), and return less to investors (36%). Differences in rank order of responses were observed according to professional training of the administrator and profit status of the facility. Administrators uniformly believe that it is very acceptable to provide facility-specific outcomes data to the public, as well as information on modalities of treatment provided by facilities. However, administrators varied in their views regarding whether reimbursement should be based on quality by using a process-of-care measure, such as the average dose of dialysis, or an outcome-of-care measure, such as case-mix-adjusted mortality rates. We conclude that increases in facility reimbursement generally would be used by dialysis facility administrators for the benefit of patients, whereas decreases (or inflation erosion) in payment rates might compromise staffing. US dialysis administrators support sharing treatment options and outcomes information with patients, but appear to be ambivalent with regard to linking reimbursement to adequacy of dialysis or patient outcomes. These results have important implications regarding proposed changes in the US capitated dialysis payment rate and current efforts to empower consumers of dialysis care.

Quantification of middle molecular weight solute removal in dialysis

The pioneering work of Gotch emphasized the critical need to be quantitative with respect to treatment prescription. Through his meticulous derivations and analyses regarding Kt/V(urea), he has provided powerful insight into the standard therapy prescriptions that we now employ clinically. However, time has seen the proliferation of treatment techniques, most of which are too "young" to have been characterized with respect to clinical outcomes. Further, the relationship between removal of urea and removal of middle molecular size solutes associated with these newer techniques deviates from that associated with conventional, clinically qualified techniques. In this article we examine the solute clearance profile of some of these new methodologies and their relationship to current criteria for treatment adequacy. Our approach is to discuss components of the overall transport process and then utilize modeling of surrogate molecules over the size range of interest whose transport characteristics are known. Alteration in the solute clearance profile of these surrogate markers in response to changes in prescription variables will thus offer insight into the spectrum of toxic middle molecules that are removed when size, space of distribution, and generation rate are known.