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Dialysis |




Departments of * Nephrology and
Vascular Surgery and
Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, and Departments of
Surgery and || Internal Medicine, St. Franciscus Gasthuis, Rotterdam, Netherlands
Correspondence: Dr. Peter J. Blankestijn, University Medical Center Utrecht, Department of Nephrology, Room F03.223, P.O. Box 85500, 3508 GA Utrecht, Netherlands. Phone: +31(0)88-7557329; Fax: +31-0-30-2543492; E-mail: P.J.Blankestijn{at}umcutrecht.nl
| Abstract |
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Design, setting, participants, & measurements: Eleven centers participated in a guidelines implementation program. All new permanent vascular accesses were included. Patency and functional patency, defined as access survival from creation and from first dialysis use, respectively, were calculated using Kaplan-Meier analysis. Risk factors for primary functional patency loss (intervention-free interval) and secondary failure (abandonment) were determined using regression models.
Results: A total of 491 arteriovenous fistulas were placed in 395 patients. Six-, 12-, and 18-mo secondary patency and functional patency were 75 ± 2.0, 70 ± 2.3, and 67 ± 2.7% and 90 ± 1.9, 88 ± 2.2, and 86 ± 2.7%, respectively. Primary failure rate was 40%. Thrombosis rate was 0.14 per patient-year. Diabetes and arteriovenous fistula surveillance were significantly associated with primary functional patency loss. Preoperative duplex was inversely related to secondary failure. The secondary failure rate per hospital varied from 0 to 39%.
Conclusions: This study showed a marked difference between patency and functional patency, likely to be explained by high primary failure rates. Hemodialysis patients with diabetes can be expected to have reduced primary functional patency rates, but if treated adequately, then arteriovenous fistula functionality can be maintained as long as in patients without diabetes.
| Introduction |
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The Dialysis Outcomes and Practice Patterns Study (DOPPS), in which the Netherlands was not included, showed large differences in both national and regional vascular access placement policies (5,9). At the start of the new millennium, prevalent AVF use in the Netherlands was approximately 60% with a wide range (31 to 91%) (10); therefore, a multicenter guidelines implementation program, Care Improvement by Multidisciplinary approach for Increase of Native vascular access Obtainment (CIMINO), was initiated to increase AVF use in a proportion of the Dutch hemodialysis population. In addition, this prospective, multicenter, observational study was designed to learn more about both early and late functionality of the AVF. Recently, our group showed that hospital-specific aspects predominantly determine primary AVF failure (11).
The purpose of the analysis in this study was to compare AVF patency rates in 11 dialysis centers with K/DOQI standards using standardized definitions in a methodologically favorable study setup. Furthermore, we aimed to obtain insight on risk factors that affect functional patency rates and late AVF functionality.
| Materials and Methods |
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Patients
Between May 2004 and July 2005, 11 vascular access centers in the middle part of the Netherlands, representing 1092 prevalent vascular accesses, started participation in this prospective, observational study (10). All hemodialysis patients or patients who had chronic renal failure and required a new permanent vascular access during this follow-up period were included.
Definitions
Coronary artery disease was defined as a history of coronary angioplasty, coronary bypass surgery, endovascular stenting, or myocardial infarction. Peripheral vascular disease (PVD) was defined as a history of angioplasty, surgical endarterectomy, endovascular stenting or bypass surgery of the iliac and/or femoral arteries, but also amputation as a result of peripheral artery occlusive disease. Cerebrovascular disease was defined as the same interventions in the carotid arteries and also included previous cerebrovascular accidents. Diabetes was defined as current use of hypoglycemic medication or use of insulin or when the diagnosis was recorded in a medical status.
Primary patency (intervention-free access survival) was defined as the interval from time of access placement to any intervention designed to maintain or reestablish patency or to access thrombosis or the time of measurement of patency (14). Assisted primary patency (thrombosis-free access survival) was defined as the interval from time of access placement to access thrombosis or time of measurement of patency, including intervening manipulations (surgical or endovascular interventions) designed to maintain the functionality of a patent access (14). Secondary patency (access survival until abandonment) was defined as the interval from time of access placement to access abandonment or time of measurement of patency, including intervening manipulations (surgical or endovascular interventions) designed to reestablish the functionality of thrombosed access (14). The word "functional" was added to patency to indicate that patency interval started at date of first successful cannulation for hemodialysis treatment instead of date of access placement (Figure 1).
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PF was defined as an AVF that did not develop to maintain dialysis or thrombosed before the first successful cannulation for hemodialysis treatment, regardless of eventual AVF abandonment. This definition includes (1) inadequate maturation, (2) early thrombosis, (3) failure of first cannulation, and (4) other complications such as ischemia or infection. Secondary failure (SF) was defined as permanent failure of the AVF, after it had achieved adequacy for hemodialysis.
In the CIMINO program, vascular access teams were encouraged to perform regular access blood flow measurements for vascular access surveillance. For analyses in this study, vascular access surveillance was scored as positive when three or more access flow measurements were performed per access year.
Statistical Analyses
Results are shown as means ± SEM unless otherwise described. Kaplan-Meier survival analysis and the life-table method were used to calculate patency rates, and the log-rank test was used to compare patency rates.
Only the first created AVF per patient in this data set was used to determine relations between possible risk factors and AVF outcome. Risk factors for primary functional patency loss and for SF were determined using multivariate Cox proportional hazards models. The comparison of AVF failure rates across hospitals was done using a Cox proportional hazards model with dummy variables in which the largest hospital was considered as reference. Results are presented as hazard ratios (HR) with corresponding 95% confidence intervals (CI). Statistical significance was assumed at two-sided P < 0.05. Analyses were carried out using SPSS 12.0 (SPSS, Chicago, IL) and SigmaStat 3.11 (Systat Software, San Jose, CA) for Windows.
| Results |
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Patency
Three-, 6-, 12-, and 18-mo patency rates and functional patency rates are depicted in Table 2 and Figure 2.
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Risk Factors for Functional Patency Loss
In univariate analyses, female gender (HR 1.40; 95% CI 0.91 to 2.14), age
65 yr (HR 1.53; 95% CI 0.995 to 2.37), presence of PVD (HR 0.47; 95% CI 0.17 to 1.28), diabetes (HR 1.56; 95% CI 1.01 to 2.40), and AVF surveillance (HR 2.33; 95% CI 1.51 to 3.60) were related to primary functional patency loss. P values of renal replacement therapy before access cannulation, coronary artery disease, ethnicity, body mass index
30 kg/m2, and fistula location were >0.15 in univariate analyses. Only preoperative duplex examination was associated with SF (HR 0.33; 95% CI 0.15 to 0.72).
On multivariate survival analysis, diabetes (HR 1.66; 95% CI 1.06 to 2.59) and AVF surveillance (HR 2.35; 95% CI 1.51 to 3.65) were significantly related to primary functional patency loss. Female gender (HR 1.52; 95% CI 0.99 to 2.34) and age
65 yr (HR 1.49; 95% CI 0.96 to 2.31) were borderline significantly related to primary functional patency loss.
Dialysis Facility Factors
Primary functional patency loss varied from 14 to 69% among the centers. Primary functional patency rates were not significantly different among the 11 hospitals (P = 0.052 for 302 AVFs; P = 0.060 for 285 patients). The SF rate per hospital varied from 0 to 39% (Table 3). Secondary functional patency rates were different among the 11 hospitals (P < 0.01 for 302 AVFs; P = 0.010 for 285 patients).
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65 yr, PVD, diabetes, and AVF surveillance, the risk for primary functional patency loss was increased only for hospital 4 (HR 3.51; 95% CI 1.48 to 8.33) when compared with the largest center. | Discussion |
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The thrombosis rate at 0.14 episodes per patient-year at risk was well below current outcome goals (0.25 per patient-year) (1). Regarding the multicenter character of this study, the K/DOQI goal seems to be more than reasonable.
Patency Rates
A significant proportion of the AVFs encounter PF during the first weeks after surgery (6,11,15); however, when patency rates are calculated starting at the day of first cannulation, primary failed AVFs are not included. To prevent confusion and incorrect comparisons, we discriminated patency from functional patency as reported by Sidawy et al. (14). Functional patency started when a vascular access had been successfully used for hemodialysis treatment for the first time; patency started at the day of surgical AVF creation. Whereas primary AVF failure was extensively studied and reported previously by our group (11), we focused on aspects of functional patency in this study.
Primary functional patency was similar to rates in the current literature (16). Our 18-mo secondary functional patency was somewhat higher at 86% (median >960 d) versus 77%. The difference may be explained by the fact that more than half of the reports used in the review by Huber et al. (16) were published before the appearance of the first K/DOQI guidelines, and surveillance programs and preventive stenosis correction were not common practice yet. In contrast, 18-mo secondary patency (from creation date) was 67%. The long-term difference of approximately 20% seems to be caused by significant PF rates. In this study, 23% of the AVFs were abandoned. Thus, after adequate maturation that results in successful initiation of HD treatment, only a few fistulas are abandoned (Table 2). Consequently, reduction of PF is likely to result in greatest patency improvements. Of note, Lok et al. (17) recently developed a scoring system to stratify a patient's risk for failure of AVF maturation.
Diabetes was identified as a risk factor associated with primary functional patency loss (HR 1.66) but not with SF (18). These results indicate that patients with diabetes may encounter more complications during fistula life, but, if treated adequately, then functionality can be maintained as long as in patients without diabetes, regardless of the anatomic location of the anastomosis (19). Although a larger sample size may have resulted in a significantly increased risk for primary functional patency loss in aging or female hemodialysis patients, older patients and women were not at significantly increased risk for fistula abandonment in our population (20). All other factors including obesity or cardiovascular disease did not reduce functional AVF survival (21,22).
Adoption of access blood flow surveillance is known to result in increased intervention rates (23). Consequently, an increased risk for primary functional patency loss can be expected in patients who receive vascular access surveillance. Although surveillance led to a decreased risk for SF in univariate analyses, no significance was achieved (HR 0.73; 95% CI 0.31 to 1.74). These findings are in conformity with work of others (24).
Preoperative duplex examination may result in increased AVF prevalence and adequacy for dialysis (25); however, the relation between preoperative duplex and long-term AVF outcomes has not been reported before. High SF rates were observed in two centers where few patients received preoperative duplex examination. To what extent these center-specific outcomes reflect actual increased risk for SF remains unclear.
Dialysis Facility Factors
SF rate varied from 0 to 39% among the hospitals that participated in CIMINO, resulting in significant difference of secondary functional patency rates (log rank test P < 0.01 for 302 AVF; P = 0.010 for 285 patients). One hospital had an increased risk for primary functional patency loss, but two hospitals had an increased risk for SF. Although this study was not designed to identify dialysis facility factors of SF in detail, surgical factors are less likely to be involved. Indeed, Prischl et al. (26) suggested that the surgeon who created the fistula was involved in patency, but these differences were predominantly generated during the first months after fistula creation. In this study, only successfully used AVF were analyzed. Practice factors such as negligent shunt surveillance (dialysis unit), delayed action to detected stenoses (nephrologists), or inadequate PTA/surgery procedures (radiologist/vascular surgeon) may have contributed to these findings. Further in-center analysis can be useful to improve secondary functional patency rates, but, obviously, the multidisciplinary character of complication handling requires a well-functioning vascular access team (27).
Limitations
Fistulas are preferred over grafts because of superior long-term patency. Follow-up time in our study was limited to 18 mo. In expanded polytetrafluoroethylene grafts, 6-, 12-, and 18-mo secondary functional patencies are approximately 76, 65, and 55%, respectively (16). When primary graft failures (approximately 10%) are also included, secondary graft patency from date of creation is likely to decrease slightly, expecting fistula survival to be superior from 12 mo on (Table 2). Extra follow-up time is required to obtain further insight into long-term AVF patency, but fewer interventions can be expected in fistulas compared with grafts (28).
This study is limited in its ability to detect significant predictors of SF as a result of the small number of SF (n = 27). In addition, the number of primary functional failures is such that the magnitude of the relation between a predictor and primary functional failure should be considerable to become statistically significant as a result of restricted precision of the estimate.
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| Disclosures |
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| Acknowledgments |
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Members of the CIMINO study group include the following: Dr. Y.C. Schrama, Dr. C.H. Wittens, H. Aerts, RN, T. van Westen, RN (St. Franciscus Gasthuis, Rotterdam); Dr. J.R. Beukhof, A. de Groot, RN, S. Temmink, RN (Isala Clinics, Zwolle); E. van Wijk, RN (University Medical Center Utrecht, Utrecht); Dr. A.A. Hollander, Dr. J.G. Olsman, T. Kokx, RN, C. Boeren, RN (Jeroen Bosch Hospital,'s-Hertogenbosch); Dr. B.C. van Jaarsveld, Dr. S.K. Nagesser, M. Baars, RN (Dianet & Diakonessenhuis, Utrecht); Dr. K.J. Parlevliet, A. van de Kaaden, RN (Rijnstate Hospital, Arnhem); Prof. M.J. Nube, J. Wijnker, RN (Medical Center Alkmaar); Dr. M.G. Betjes, L. Chardon, RN, M. Konings, RN (Erasmus Medical Center, Rotterdam); Dr. C.J. Doorenbos, Dr. C.G. Vermeij, M. Voskamp, RN (Deventer Hospital, Deventer); Dr. M.A. van den Dorpel, Dr. A.A. de Smet, L. Steegman, RN (Medical Center Rijnmond Zuid, Rotterdam); Dr. M.A. ten Dam, Dr. W.B. Barendregt, Dr. P.H. Haarbrink, F. Dastnaei, RN, A. Jilisen, RN (Canisius Wilhelmina Hospital, Nijmegen).
Cees Haaring (Department of Radiology, UMC Utrecht) is gratefully acknowledged for excellent work on database setup and maintenance. We gratefully acknowledge the contribution of the CIMINO members to the project.
| Footnotes |
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Received July 19, 2007. Accepted December 28, 2007.
| References |
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This article has been cited by other articles:
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N. Knops and E. Beek Salvage of a radiocephalic fistula by the palmar arch NDT Plus, October 1, 2008; 1(5): 326 - 328. [Abstract] [Full Text] [PDF] |
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