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*Duke Institute of Renal Outcomes Research and Health Policy, Duke University Medical Center, Durham, North Carolina;
Division of Nephrology, Duke University Medical Center, Durham, North Carolina;
Center for Beneficiary Choices, the Centers for Medicare & Medicaid Services (CMS), formerly the Health Care Financing Administration (HCFA), Baltimore, Maryland; and
Division of Nephrology, Wake Forest University School of Medicine, Winston-Salem, North Carolina.
Correspondence to Dr. Donal Reddan, Duke Institute of Renal Outcomes Research and Health Policy, Box 3646, Duke University Medical Center, Durham, North Carolina 27710. Phone: 919-668-8008; Fax: 919-668-7128; E-mail: redda001{at}mc.duke.edu
| Abstract |
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| Introduction |
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Several patient-specific factors appear to influence the choice of angioaccess for hemodialysis patients. These include the patients gender, race, age, presence of diabetes mellitus, anthropometric attributes, and duration of renal replacement therapy (13,14). In 1993, a profile of angioaccess type in the United States developed from Medicare billing data observed that fewer than 30% of maintenance hemodialysis patients were dialyzed using an AVF (13). Moreover, at a time several years before the release of the DOQI clinical practice guidelines on vascular access for hemodialysis, significant geographic variation was observed in the ratio of AVF to AVG that could not be explained by differences in patient demographic characteristics (13). Information on the use of dialysis catheters was not reported. However, in a recent analysis involving fewer subjects, significant variation among dialysis units was observed for the chronic use of central vein catheters (14). The observation of substantial variability in the choice of angioaccess after controlling for baseline patient variables suggests that physician practice patterns may play a substantial role in angioaccess selection. Substantial variability in choice of angioaccess has also been noted in comparisons of vascular access epidemiology between Europe and the United States (15). Among patients enrolled in the HEMO Study, substantial variations in the prevalence of fistulas were evident, even among dialysis units in single metropolitan areas. Central venous catheter and AVG use have also been associated with increased mortality when compared with AVF (16).
In 1999 and 2000, the Centers for Medicare & Medicaid Services (CMS), formerly the Health Care Financing Administration (HCFA), sponsored the National ESRD Clinical Performance Measures (CPM) Project to collect information on clinical practices regarding vascular access in ambulatory hemodialysis patients. In comparison with previous studies, this nationally representative sample of adult Medicare-eligible beneficiaries with ESRD is contemporary. The following analysis was performed to examine clinical practice profiles for vascular access since the release of the DOQI clinical practice guidelines on vascular access. Also, the size and greater data collection offered by CMSs ESRD CPM Project permitted us to examine the effect of vascular access type on other relevant processes of ESRD patient care, such as the amount of hemodialysis provided to patients.
| Materials and Methods |
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18 yr old) ESRD patients receiving hemodialysis in a hemodialysis clinic on the last day of December 1999 were eligible for inclusion in the sample. A random sample of ESRD patients, stratified by the eighteen regional ESRD networks was drawn. The sample size (n = 8697) provided a 95% confidence interval (CI) of ±205% for ESRD network-specific estimates. The sample size was selected to allow estimation of a proportion with a 95% CI around that estimate no larger than 10 percentage points for network-specific estimates of the key hemodialysis clinical performance measures. A 30% over-sample was obtained to compensate for an anticipated nonresponse rate and to assure a large enough sample of hemodialysis patients who were dialyzing at least 6 mo before October 1, 1999. Patient demographics, clinical information, and current access type were collected for the months of October 1999 to December 1999. Current hemodialysis vascular access type was defined as the vascular access used at the last hemodialysis session on or between October 1, 1999, and December 31, 1999. The reporting strategy did not allow capture of multiple vascular access types; accesses that were maturing but not in use were not captured. The first monthly pre- and post-hemodialysis blood urea nitrogen concentration (BUN) and pre- and post-hemodialysis body weight (kg) were used to calculate the amount of urea removed as a measure of the effectiveness of solute clearance (urea reduction ratio [URR] and single pool Kt/V using the second-generation formula of Daugirdas [20]). The delivered hemodialysis time at the session at which the BUN measurements were drawn and first monthly serum albumin concentration measured by the bromcresol green (BCG) or purple (BCP) assay were obtained. ESRD network personnel validated abstracted data by review of a 5% patient sample of the medical charts. No significant differences were found in the abstraction of the data for any clinical measure (21).
Statistical Analyses
Univariate and multivariable analyses were conducted to examine associations of access type with demographic, laboratory, and geographic variables. Differences in continuous variables were tested by two-tailed t test. Associations of access type with categorical variables were tested by
2 analysis. Mean values are presented as mean ± SD. A two-tailed P < 0.05 was considered significant. Patients who initiated hemodialysis between January 1, 1999, and August 31, 1999, were considered incident. Duration of dialysis was calculated as the time since dialysis initiation. Multivariable logistic regression analyses were performed to adjust for potential confounding variables and to identify independent variables associated with access type. The first analysis included all patients and had current use of a percutaneous, central vein catheter as the dependent variable. The second analysis was limited to patients currently receiving dialysis through either an AVF or AVG (synthetic or bovine), and the dependent variable was current use of an AVG. Both analyses were repeated with patients stratified by incident/prevalent status. Potential predictor variables were entered into the model in a formal, stepwise manner with an entry criterion of 0.05. The variables included in the stepwise selection process included all demographic variables, albumin (BCG measured values only), hemoglobin, duration of dialysis, a variable indicative of the patients categorization as incident or prevalent, and BMI. Appropriate interactions were tested. Final models were subsequently generated using the variables noted to be significant in the stepwise analysis and other variables thought to be clinically relevant. Finally, separate variables for each ESRD network were added to the final model. The ESRD network that was ranked tenth on the basis of univariate analysis was used as the referent group, and odds ratios (OR) were determined for each ESRD network for each analysis. Data analyses were performed using SAS software (version 8.1; SAS Institute Inc., Cary, NC).
| Results |
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Significant variation for the use of catheters and AVG was observed among regions of the United States. Figures 1 and 2 illustrate unadjusted distribution by ESRD networks with regard to proportions of hemodialysis catheters and AVG, respectively. Figures 3 and 4 tabulate ESRD network-specific odds ratios of percutaneous catheters or AVG controlled for the predictors identified in the earlier analyses. They demonstrate that substantial geographic variability persists in angioaccess type, even when controlled for other significant variables.
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| Discussion |
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The current study demonstrates on the basis of a national sample of maintenance hemodialysis patients substantial shortfalls in vascular access performance in the United States. Two years after the public release of the DOQI CPG on vascular access for hemodialysis and the beginning of a national CPM initiative, almost half of the patients receive hemodialysis using an AVG. A small minority of patients is treated using an autologous fistula. In turn, a substantial number of hemodialysis patients are dialyzing using a percutaneous catheter. It is likely that some patients receive a tunneled, cuffed catheter as a temporary angioaccess because they present too late for the establishment of an internal angioaccess. However, using a liberal definition of 8 mo to categorize incident patients, and so to allow adequate time for bridge accesses like catheters to be replaced, little difference was observed in catheter use between incident and prevalent hemodialysis patients. This explanation alone appears inadequate to account for the preponderance of catheter use.
The establishment of a non-catheter (internal) angioaccess requires adequate venous vasculature, especially for AVF. The anatomic challenges are greatest for the generation of an autologous fistula, which requires intact peripheral arterial and venous vasculature. Patients who are older, diabetic, obese, and/or female may have relatively smaller or even compromised vascular anatomy and so require an AVG. Patients who are new to dialysis may have presented too late for the establishment of an AVF before the need for dialysis. As anticipated, female gender and decreased time since the initiation of hemodialysis were independently associated with increased catheter use. For AVG placement, incident status, female gender, and black race were significant predictors. The strong association of female gender with AVG use was consistently present across all regions of the United States. This finding is consistent with the findings of many others (3,4,13,24) and may reflect the higher failure rates for AVF in women compared with men (25). Vessel diameter has been shown to be an important predictor of AVF survival (26), and it has been suggested that increased access related morbidity in women can be attributed to disadvantageous differences in vessel diameter (27). The finding of an association between diabetes and catheter use among incident patients is probably a consequence of increased AVG use and less of a need for a "bridge" toward permanent access functionality with AVGs. The disquieting finding of black race being strongly associated with AVG placement, even in the multivariable analysis, suggests that undescribed racial differences in vascular anatomy or subconscious bias in vascular access care processes exist. The observation that blacks with ESRD are usually of lower socioeconomic status than whites may be relevant (28). Indigent patients may have limited access to health care, resulting in later referral to a nephrologist. In this situation for both blacks and whites, a catheter would precede an AVG and would be placed for expediency in establishing an access. However, the less strong association between race and catheter use suggests that late referral for vascular access alone is an inadequate explanation. Another possible explanation for this racial disparity in the use of AVG is an increased failure rate for AVF in blacks.
In the unadjusted and adjusted analyses, significant geographic variation was observed in choice of vascular access. The ability to identify regions of the United States with lower and higher fistula placement rates facilitates further focused scrutiny of patients and care processes in those areas. This will in turn assist in identifying strategies used by high performing areas, which may be imported to assist regions with lower hemodialysis vascular access performance. Local success in altering clinical practice by implementing clinical practice guidelines in vascular access has been described (29). Also, CMS billing data suggests that some improvement in clinical practice may be occurring, as gauged by an increased fistula placement rate (30). However, in the 2 yr between release of the DOQI clinical practice guidelines and the practice profiles for hemodialysis vascular access described herein, approximately 40% of incident ESRD patients in the United States have died and been replaced. Therefore, ample opportunity was available for greater improvement in hemodialysis vascular access management. Why such variability persists is not clear, but it may reflect varying facility and provider preferences and approaches to vascular access practice as well as differences in available resources to optimize care.
In comparing the performance of catheters versus internal hemodialysis vascular accesses, these data set illustrates the known association between catheter use and the increased risk of inadequate hemodialysis delivery because of compromised blood flow (19). The growing percentage of patients receiving hemodialysis chronically by percutaneous catheters (19) and the substantially lower blood flows and dialysis doses associated with catheter use may compromise the results of quality improvement initiatives for hemodialysis doses.
Just as this analysis may underestimate AVF attempt rates in women and older patients because of increased failure rates in these populations, the increased percentage of AVG in blacks could also reflect higher AVF failure rates. The cross-sectional nature of this data set is a limitation in that it does not permit an analysis of complications associated with the different hemodialysis access types. In addition, because they are cross-sectional, these data do not estimate AVF attempt rates. AVF failure rates may be increased in older patients (4) and in patients who receive brachiobasilic AVF as opposed to brachiocephalic AVF (31). Analyzing AVF rates by considering current access type alone does not therefore necessarily reflect secular trends in access placement and may underrepresent trends toward increased AVF attempts.
There are several justifiable reasons for protracted catheter use. Examples include patients awaiting living kidney donor transplantation or awaiting maturation of a fistula. Indeed, the latter is suggested by the observation that some of the ESRD networks with low AVG rates also have high catheter rates. Catheters may also be used as salvage for patients with no other potential form of access. However, although these heroic uses are increasing, they are still relatively uncommon. The reason(s) for the continued high prevalence of AVG is unclear. Possible explanations include greater reimbursement for the work in placing an AVG when compared with AVF (32), decreased expertise with autologous fistulae generation within the surgical community, misconceptions of unique complications (like high-output congestive heart failure) associated with fistulae, absence of profiling for vascular access types and inadequate self-scrutiny of performance, and deliberate selection of AVG because of relative ease of placement and convenience for managing late patient referrals (33). It has been suggested that earlier nephrology referral can facilitate autologous fistula placement by providing time for fistula maturation (34). Late patient referral has been found to be independently predictive of placement of AVG (35), as well as of increased costs and adverse outcomes.
The aforementioned confounders of best vascular access outcomes may be reduced with appropriate national quality improvement efforts through CMS, the Forum of ESRD networks, stakeholder professional societies, and the dialysis provider companies. However, vascular access quality improvement initiatives must also recognize the need to increase involvement of the vascular surgery community; neither the dialysis units nor their nephrologists can serve as surrogates for greater surgical involvement and performance.
| Acknowledgments |
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| Footnotes |
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| References |
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