NKF K/DOQI GUIDELINES 2000
GUIDELINES FOR HEMODIALYSIS ADEQUACY
IV. Hemodialyzer Reprocessing and Reuse
Use of the Association for the Advancement of Medical Instrumentation (AAMI) Standards and Recommended Practices for Hemodialyzer Reprocessing (Opinion)
When hemodialyzers are reused, they should be reprocessed following the Association for the Advancement of Medical Instrumentation (AAMI) Standards and Recommended Practices for reuse of hemodialyzers,76 with the exception of the AAMI guideline regarding baseline measurement of the total cell volume (see Guideline 11: Baseline Measurement of Total Cell Volume).
Rationale For economic reasons, reuse of hemodialyzers is a prevalent practice in the United States.12,66,70,71 Seventy-three percent of the hemodialysis units in the United States reprocessed dialyzers in 1995. Among dialysis units that reprocess dialyzers, the median of the average number of reuses has increased from 9 in 1986 to 14 in 1994. The median of the maximum number of reported reuses has increased from 23 to 30 over the same interval.71 Data describing the prevalence of dialyzer reuse among pediatric hemodialysis patients are not available. Recent retrospective information about the impact of dialyzer reuse on the mortality of dialysis patients has been published.15,200 These data report a 10% increase in the risk of death among patients who used hemodialyzers reprocessed in selected hemodialysis settings and with the use of certain germicides.15 It is noteworthy that this report did not control for differences in patient comorbidity or hemodialysis adequacy. Furthermore, this reported finding of increased risk of death has not been observed consistently, even with uniform data set extraction and risk modelling.200-203 To date, no prospective, randomized controlled trial of hemodialyzer reuse has been performed.
A thorough examination of the data concerning the impact of reused dialyzers on patient safety was beyond the scope of the HD Adequacy Work Group. Therefore, the Work Group cannot endorse or condemn the practice of hemodialyzer reuse. However, the impact of reprocessing on dialyzer performance was evaluated and addressed. The Work Group found evidence that hemodialyzer performance, measured as blood side urea clearance,204-206 and the delivered dose of dialysis may decline as a result of dialyzer reuse.72 Urea clearance decreased as the number of reuses increased. An extreme example is offered in a study examining polysulfone high flux hemodialyzers reprocessed with formaldehyde and bleach in which urea clearance decreased at least 20% by 10 reuses, even though conventional AAMI dialyzer practices were followed.204 This finding has not been observed universally.205 Furthermore, in a prospective survey of 34 hemodialysis facilities, a correlation was found between the number of dialyzer reuses and the delivered Kt/V. Although the prescribed Kt/V was identical for the high reuse (mean of 13.8) and low reuse (mean of 3.8) groups, the delivered Kt/V for each of the two groups was 1.05 and 1.1, respectively. The Work Group was particularly concerned by the apparent dialysis center-specific effect of reuse on delivered Kt/V, suggesting that the process of hemodialyzer reuse and/or its monitoring may be problematic.
Therefore, the Work Group recommends that hemodialysis facilities who choose to reuse hemodialyzers follow the AAMI recommendations for reprocessing, with the exception of the AAMI recommendation regarding baseline measurement of total cell volume (see Guideline 11: Baseline Measurement of Total Cell Volume). They should remain alert to the possibility that reuse may adversely affect adequacy of the delivered hemodialysis dose. The AAMI recommendations describe practical reuse procedures that have been adopted by the Health Care Financing Administration (HCFA).76,207 These recommendations were prepared by a panel of experts and represent the best guidance available on dialyzer reuse procedures.
Baseline Measurement of Total Cell Volume (Evidence)
If a hollow fiber dialyzer is to be reused, the total cell volume (TCV) of that hemodialyzer should be measured prior to its first use. Batch testing and/or use of an average TCV for a group of hemodialyzers is not an acceptable practice.
Rationale The essential function of a hemodialyzer is to permit the mass transfer of solutes from the patients blood into the dialysate in order to deliver the prescribed hemodialysis treatment. The solute transport capacity or clearance of a hemodialyzer is a critical variable in writing a hemodialysis prescription and in delivering an adequate treatment. For this reason, the dialysis care team needs an accurate assessment of the solute clearance of the hemodialyzer. In the absence of direct measures of solute clearance, changes in the TCV, also described as the fiber bundle volume (FBV), have been shown to be an adequate index of changes in solute transport characteristics for hollow fiber dialyzers74,75,208 (see Guideline 13: Minimum Required Total Cell Volume). The TCV is equal to the volume of saline necessary to fill the blood compartment of the hemodialyzer.
There is considerable variability between the in vitro and in vivo urea clearance of hemodialyzers.130 The TCV can vary by 8% to 10% from the TCV stated by the manufacturers.131 In addition, there is lot-to-lot variability and hemodialyzer-to-hemodialyzer variability within a single lot. Therefore, the HD Adequacy Work Group considered it inappropriate to rely only upon the manufacturers published TCV alone. The alternative practice recommended by AAMI of averaging the pre-processing volume of approximately 10 hemodialyzers and using this value for the TCV is also unacceptable. For example, if an individual hemodialyzer has a relatively large preprocessing TCV, and this is unappreciated because of the use of a lot average TCV that is lower than the true value for this dialyzer, use of the dialyzer may not be discontinued at the appropriate time. Measurement of TCV prior to hemodialyzer use is recommended in order to provide a baseline value for subsequent monitoring and evaluation of the performance of each individual dialyzer. The Work Group suggests that the actual TCV of each dialyzer be measured. Thus, although the AAMI recommendations permit batch testing and/or the use of an average TCV for a group of dialyzers, it is the opinion of the Work Group that these practices are not acceptable.
Monitoring Total Cell Volume (Evidence)
During each reprocessing, the total cell volume (TCV) of reused dialyzers should be checked.
Rationale Because of the clotting of individual hollow fibers within a dialyzer, TCV may decline after use. Assuming no change in the geometry and/or permeability of the dialyzers membrane, a reduction in the TCV may be associated with reduced solute clearance and a decline in the delivered dose of hemodialysis.72,204-206,209 Although routine monitoring of the delivered dose of hemodialysis is the gold standard for assessing the performance of a hemodialyzer, it is likely that the solute clearance rate (KoA) of a hemodialyzer could decline significantly in the interval between measures of hemodialysis adequacy and therefore go unrecognized. The use of a surrogate measure for the hemodialyzers potential performance, such as the TCV, after each use and reprocessing will help clarify the safety of continuing to reuse the hemodialyzer.73
It is noteworthy that a case report describes that careful monitoring of TCV did not preclude the reuse of hemodialyzers having unacceptable clearance characteristics.209 This situation may arise because the in vitro measure of TCV may mask the intradialytic loss of fibers secondary to thrombosis. The procedure sequence for dialyzer reprocessing mandates flushing the dialyzer with a pressurized solution to displace any clots from the lumen of the fibers. Because the TCV is measured thereafter, the loss of fibers during hemodialysis will not be appreciated. Using a novel dilution technique for in vivo determination of FBV, conventional volumetric measurements of TCV were observed to be substantially greater.210
Minimum Required Total Cell Volume (Opinion)
Dialyzers having a total cell volume (TCV) <80% of original measured value should not be reused.
Rationale Solute clearance must be maintained within acceptable limits to ensure that hemodialysis is adequate. The use of a hemodialyzer with reduced clearance without appropriate compensatory changes in other components of the dialysis prescription (such as increasing dialysis time) will reduce the delivered dose of hemodialysis. Therefore, it is necessary to monitor the TCV and define a threshold TCV at which use of reprocessed dialyzers is discontinued.
Because the relationship between the decline in TCV and solute clearance is nonlinear, the decrease in TCV must be evaluated relative to the original volume of the hemodialyzer. Small reductions in TCV may not significantly reduce dialyzer clearance. If the residual TCV of a hollow-fiber dialyzer is 80% of the hemodialyzers original TCV, it is estimated that the relative decrease in urea clearance will be approximately 10%.73 Reductions in TCV of more than 20% from the original baseline TCV compromises the effectiveness of the hemodialyzer and, thus, may affect the adequacy of the hemodialysis treatments.*,208
RECOMMENDATIONS FOR RESEARCH
1. With continued economic pressure to reuse hemodialyzers, more research needs to be done regarding the association between dialyzer reuse, hemodialyzer performance, and patient safety. The HD Adequacy Work Group believes that an observational analysis that controls for comorbid factors, the delivered dose of hemodialysis, and reprocessing techniques would be useful to clarify the safety of current hemodialyzer reuse procedures. Such an analysis is currently underway by the USRDS, and results are expected to be available soon.
2. The HD Adequacy Work Group recommends that further studies be performed to develop a better measure of dialyzer performance than TCV.
3. Data on the rate of hemodialyzer performance failure as a cause of inadequate dialysis dose should be collected, specifically:
Frequency of hemodialyzer performance failure as a cause of inadequate dialysis dose.
Effect of reductions in TCV on the solute clearance of hemodialyzers made by various manufacturers.
Clarification of the relationship between the number of reuses and dialyzer clearance, by brand.
Impact of reduced TCV on the clearance of high-flux hemodialyzers.
* Pages 106-107 of The Association for the Advancement of Medical Instrumentation (AAMI) Standards and Recommended Practices for reuse of hemodialyzers detail the relationship between TCV and dialyzer clearance.76
© 2001 National Kidney Foundation, Inc