Maintaining blood compartment volume in dialyzers reprocessed with peracetic acid maintains Kt/V but not beta2-microglobulin removal

Choosing a dialyzer: What clinicians need to know

The objectives of hemodialysis have moved from the diffusive clearance of small molecular weight uremic toxins and achieving dialyzer urea adequacy targets to emphasis on improving clinical outcomes in end stage renal failure patients by increasing larger sized uremic toxin clearance. Clinical emphasis in the last few decades has focused on increasing middle molecule weight toxin clearance by hemodiafiltration. Although long-term data is still lacking, short-term outcomes appear promising. Advancements in nanotechnology have now introduction a new generation of medium cut-off membrane dialyzers which allow diffusive clearance of similar middle molecular weight uremia toxin clearance as hemodiafiltration, without increased albumin losses. As these dialyzers have only recently been introduced into clinical practice, no long-term outcomes are available to determine the relative benefits or advantages of this approach. As dialyzers are now designed to maximize diffusive or convective clearance, or provide a combination, then clinicians can now choose dialyzers tailored to the individual patient needs depending on clinical circumstances. We review the key important features in choosing a dialyzer for patients with end stage renal failure and acute kidney injury.

Changes in circulating biomarkers during a single hemodialysis session

The hemodialysis (HD) procedure induces an inflammatory response potentially contributing to cardiovascular disease. Here we investigated the acute impact of HD on circulating biomarkers. Circulating biomarkers (small solutes, middle molecular-sized peptides, and proteins) related to inflammation, oxidative stress, and vascular calcification (VC) were measured before and after a single session of HD in 45 clinically stable patients. Concentrations were corrected for ultrafiltration-induced hemoconcentration. Among vascular calcification-related biomarkers, osteoprotegerin and fetuin-A remained unchanged while fibroblast growth factor-23 (FGF23) decreased by -19%. Changes of FGF23 and changes of phosphate correlated (ρ = 0.61, P < 0.001). While C-reactive protein did not change, interleukin-6 (IL-6) increased by 14% and pentraxin 3 (PTX3) increased by 45%. IL-6 and PTX3 appear to be valid biomarkers of the intradialytic inflammatory response. VC-related markers were in general not affected by the single HD session; however, the observed correlation between acute changes of FGF-23 and phosphate during HD warrants further studies.

Abandoning peracetic acid-based dialyzer reuse is associated with improved survival

BACKGROUND AND OBJECTIVES

Higher mortality risk reported with reuse versus single use of dialyzers is potentially related to reuse reagents that modify membrane surface characteristics and the blood-membrane interface. A key mechanism may involve stimulation of an inflammatory response.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a prospective crossover design, laboratory markers and mortality from 23 hemodialysis facilities abandoning reuse with peracetic acid mixture were tracked. C-reactive protein (CRP), white blood cell (WBC) count, albumin, and prealbumin were measured for 2 consecutive months before abandoning reuse and subsequently within 3 and 6 months on single use. Survival models were utilized to compare the 6-month period before abandoning reuse (baseline) and the 6-month period on single use of dialyzers after a 3-month "washout period."

RESULTS

Patients from baseline and single-use periods had a mean age of approximately 63 years; 44% were female, 54% were diabetic, 60% were white, and the mean vintage was approximately 3.2 years. The unadjusted hazard ratio for death was 0.70 and after case-mix adjustment was 0.74 for single use compared with reuse. Patients with CRP≥5 mg/L during reuse (mean CRP=26.6 mg/ml in April) declined on single use to 20.2 mg/L by August and 20.4 mg/L by November. WBC count declined slightly during single use, but nutritional markers were unchanged.

CONCLUSIONS

Abandonment of peracetic-acid-based reuse was associated with improved survival and lower levels of inflammatory but not nutritional markers. Further study is needed to evaluate a potential link between dialyzer reuse, inflammation, and mortality.

Oxidation of proteins adsorbed on hemodialysis membranes and model materials

The cleaning of cellulosic hemodialysis membrane Cuprophan and model materials (glass; polystyrene and polypropylene, as such and surface-oxidized), conditioned by adsorption of blood plasma proteins (HSA, fibrinogen, IgG) was investigated in vitro. Sodium hypochlorite (NaClO) and Renalin, a product containing hydrogen peroxide and peroxyacetic acid, were used as cleaning reagents. X-ray photoelectron spectroscopy and the use of radiolabeled fibrinogen demonstrated the presence of varying amounts of a polypeptidic residue, with sulfur brought to a high oxidation stage (sulfonate-like). The trends were the same for the three proteins regarding the effectiveness of the oxidizer and the influence of the surface properties. NaClO was much more effective than Renalin to remove the adsorbed proteins. The proteins adsorbed on Cuprophan were more sensitive to the oxidizers, when compared with proteins adsorbed on other materials. This may be due to both the lower protein-surface affinity, as indicated by radiochemical measurements, and the sensitivity of the material itself to the oxidizer, as revealed by weight loss measurements. These results support the attribution of hemocompatibility improvement after regeneration of Cuprophan with Renalin to the masking of the activating surface by a residue from previously adsorbed proteins.

Water permeability of high-flux dialyzer membranes after Renalin reprocessing

Dialysis with high-flux membranes is widely used, in part, because they are thought to increase the removal of middle molecules when compared with low-flux membranes. Dialyzer reprocessing; however, is thought to alter middle molecule clearance. Renalin, a mixture of germicidal agents, has widespread use in dialyzer reprocessing. We determined the effect of Renalin reprocessing on the water permeability of three different dialyzers of Fresenius (F80A and 200A) and Gambro (17R) manufacture using the dead-end filtration method. Two hundred and seventeen, predominantly used but some new, dialyzers were evaluated. Water permeability of the used, but not the new, dialyzers fell abruptly and dramatically with reprocessing. The permeability fell almost 70% in the F80A dialyzer after three reprocessing procedures with similar, but somewhat slower declines, seen in the other two dialyzers. We conclude that there is a decline in water permeability seen in Renalin reprocessed dialyzers. This factor and the associated change in solute clearance and ultrafiltration characteristics should be considered in assessing the effectiveness of dialyzer reprocessing.

Dialyzer Reuse-Part II: Advantages and Disadvantages

Although single dialyzer use and reuse by chemical reprocessing are both associated with some complications, there is no definitive advantage to either in this respect. Some complications occur mainly at the first use of a dialyzer: a new cellophane or cuprophane membrane may activate the complement system, or a noxious agent may be introduced to the dialyzer during production or generated during storage. These agents may not be completely removed during the routine rinsing procedure. The reuse of dialyzers is associated with environmental contamination, allergic reactions, residual chemical infusion (rebound release), inadequate concentration of disinfectants, and pyrogen reactions. Bleach used during reprocessing causes a progressive increase in dialyzer permeability to larger molecules, including albumin. Reprocessing methods without the use of bleach are associated with progressive decreases in membrane permeability, particularly to larger molecules. Most comparative studies have not shown differences in mortality between centers reusing and those not reusing dialyzers, however, the largest cluster of dialysis-related deaths occurred with single-use dialyzers due to the presence of perfluorohydrocarbon introduced during the manufacturing process and not completely removed during preparation of the dialyzers before the dialysis procedure. The cost savings associated with reuse is substantial, especially with more expensive, high-flux synthetic membrane dialyzers. With reuse, some dialysis centers can afford to utilize more efficient dialyzers that are more expensive; consequently they provide a higher dose of dialysis and reduce mortality. Some studies have shown minimally higher morbidity with chemical reuse, depending on the method. Waste disposal is definitely decreased with the reuse of dialyzers, thus environmental impacts are lessened, particularly if reprocessing is done by heat disinfection. It is safe to predict that dialyzer reuse in dialysis centers will continue because it also saves money for the providers. Saving both time for the patient and money for the provider were the main motivations to design a new machine for daily home hemodialysis. The machine, developed in the 1990s, cleans and heat disinfects the dialyzer and lines in situ so they do not need to be changed for a month. In contrast, reuse of dialyzers in home hemodialysis patients treated with other hemodialysis machines is becoming less popular and is almost extinct.

UNRESOLVED ISSUES IN DIALYSIS: Dialyzer Best Practice: Single Use or Reuse?

Outcome studies have shown either no additional risk or a small additional risk for hospitalization and mortality associated with reprocessing dialyzers. Although the risks from reprocessing dialyzers have yet to be fully elucidated, reuse can be done safely if it is performed in full compliance with the standards of Association for the Advancement of Medical Instrumentation (AAMI). Like most industrial processes, however, complete control of the reuse process in a clinical environment and full compliance with regulations at all times is difficult. Potential errors and breakdowns in the reuse process are continuing concerns. The quality controls for reprocessing of dialyzers are not equal to the rigor of the manufacturing process under the purview of the U.S. Food and Drug Administration (FDA). Therefore, if one were to determine "best practice," single use is preferable to reuse of dialyzers based on medical criteria and risk assessment. The long-term and cumulative effects of exposure to reuse reagents are unknown and there is no compelling medical indication for reprocessing of dialyzers. The major impediment when deciding to convert from reuse to single use of dialyzers is economic. The experience in Fresenius Medical Care-North America (FMCNA) facilities demonstrates that converting from a practice of reuse to single use is achievable. However, the overall economic impact of conversion to single use is provider specific. The dominance of reuse has been negated of late by a major shift in practice toward single use. Physicians and patients should be well informed in making decisions regarding the practice of single use versus reuse of dialyzers.

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 membranes as determinants of the adequacy of dialysis

Hemodialysis membranes have undergone a gradual but substantial evolution over the past few decades. Classification of modern dialyzer membranes by chemical composition bears little relationship to their functional characteristics. The fundamental properties that determine the capacity of the membrane to remove solutes and fluids are its surface area, thickness, pore size, pore density, and potential to adsorb proteins. Dialyzer membrane performance is characterized clinically by its efficiency, defined as the potential to remove urea and presented as the mass-transfer area coefficient (KoA) and ultrafiltration coefficient (K(uf) ),defined as the potential to remove water adjusted for the transmembrane pressure. The parameter K(uf) usually, but not invariably, correlates with the membrane permeability, defined as the potential to remove middle molecules, with beta2-microglobulin being the currently popular marker. The sieving coefficient reflects the membrane potential to transport solutes by convection and is particularly useful for hemofiltration. Enhancing solute clearance is accomplished clinically by increasing blood and dialysate flow rates, strategies that also are applicable to middle molecules for highly permeable membranes. Novel designs of dialyzers include the optimization of fluid flow path geometry and increasing the membrane pore selectivity for solutes by using nanotechnology.

Effect of Peracetic Acid Reprocessing on the Transport Characteristics of Polysulfone Hemodialyzers

Peracetic acid is used extensively for reprocessing hemodialyzers, despite several indications that reprocessing alters the dialyzer transport characteristics. The objective of this study was to obtain quantitative data for the effects of peracetic acid reprocessing on the clearance and sieving coefficients of urea, vitamin B12, and polydisperse dextrans using Fresenius F80A polysulfone dialyzers. Reprocessing restored the urea and vitamin B12 clearance to close to their original values. However, the reprocessed dialyzers had substantially lower clearance of the larger molecular weight dextrans, which was attributed to reductions in the effective pore size caused by residual plasma proteins within the membrane. Storage in peracetic acid provided some additional removal of residual proteins, although the clearance and sieving coefficients of the larger dextrans remained well below their original values. Peracetic acid caused no degradation of the membrane polymer, in sharp contrast to results obtained with bleach reprocessing.

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.

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.

Dialyzer reuse: what we know and what we don't know

Despite extensive clinical experience, the effects of different reuse procedures have not been fully evaluated. The available data suggest that the effect of reuse on dialyzer performance depends upon the type of chemicals employed, the membrane type, and the size of the solute whose removal is being assessed. The effect of reuse on urea clearance is essentially defined by the residual cell volume with a total cell volume of > 80% associated with a dialyzer clearance that is within 10% of its original value. The effect of reuse on large solute clearance can be dramatic, with the procedure resulting in substantial changes in the beta2-microglobulin clearance of different dialyzers. Of note is the limited data available regarding the effect of reuse procedures on dialyzers processed more than 20 times.

Effects of dialyzer reuse on the permeability of low-flux membranes

Little attention has been given to the effects of reuse on the permeability of low-flux membranes, especially regarding middle molecules. We studied two different types of low-flux membranes at reuses 0, 6, and 12 in five patients undergoing hemodialysis with the following combinations of membrane and sterilant: cellulose diacetate membrane and formaldehyde, polysulfone membrane and formaldehyde, cellulose diacetate membrane and peracetic acid, and polysulfone and peracetic acid. The permeability of the membranes was assessed through the hydraulic ultrafiltration coefficient (K(UF)), sieving coefficient for beta(2)-microglobulin (B2M), and vitamin B(12) and albumin concentrations in ultrafiltrate. After 12 reuses, total cell volume (TCV) tended to be reduced in both cellulose diacetate and polysulfone dialyzers irrespective of the sterilant used, but significance was only found for the first set of dialyzers. Cellulose diacetate dialyzers reprocessed with either formaldehyde or peracetic acid showed an important reduction in K(UF) (31% [P < 0.05] and 23% [P < 0.05], respectively). A significant elevation in K(UF) was found in polysulfone membranes reprocessed with peracetic acid (41%; P < 0.05), but no alterations in K(UF) were found in polysulfone membranes reprocessed with formaldehyde. Cellulose diacetate membranes were intrinsically more permeable to B2M than polysulfone membranes (sieving coefficient, 6. 85 +/- 2.53 versus 0.04 +/- 0.02 x 10(-2); P < 0.001), which was not modified by any of the sterilants. Vitamin B(12) levels in ultrafiltrate decreased to an undetectable level in four of five samples collected after 12 reuses in polysulfone membranes reprocessed with peracetic acid (90 +/- 71 to 3 +/- 8 pg/mL; P < 0. 05 versus reuse 0). Albumin leakage occurred in two of five samples after the 12th reuse, but only in polysulfone membranes reprocessed with peracetic acid. Our findings suggest that reuse of low-flux polysulfone dialyzers reprocessed with peracetic acid is associated with structural damage of the membrane and a reduced permeability to middle molecules.

Effects of hemodialyzer reuse on clearances of urea and beta2-microglobulin. The Hemodialysis (HEMO) Study Group

Although dialyzer reuse in chronic hemodialysis patients is commonly practiced in the United States, performance of reused dialyzers has not been extensively and critically evaluated. The present study analyzes data extracted from a multicenter clinical trial (the HEMO Study) and examines the effect of reuse on urea and beta2-microglobulin (beta2M) clearance by low-flux and high-flux dialyzers reprocessed with various germicides. The dialyzers evaluated contained either modified cellulosic or polysulfone membranes, whereas the germicides examined included peroxyacetic acid/acetic acid/hydrogen peroxide combination (Renalin), bleach in conjunction with formaldehyde, glutaraldehyde or Renalin, and heated citric acid. Clearance of beta2M decreased, remained unchanged, or increased substantially with reuse, depending on both the membrane material and the reprocessing technique. In contrast, urea clearance decreased only slightly (approximately 1 to 2% per 10 reuses), albeit statistically significantly with reuse, regardless of the porosity of the membrane and reprocessing method. Inasmuch as patient survival in the chronic hemodialysis population is influenced by clearances of small solutes and middle molecules, precise knowledge of the membrane material and reprocessing technique is important for the prescription of hemodialysis in centers practicing reuse.