Timing of first cannulation and vascular access failure in haemodialysis: an analysis of practice patterns at dialysis facilities in the DOPPS
Rajiv Saran1,2,3,
Dawn M. Dykstra3,
Ronald L. Pisoni3,
Takashi Akiba4,
Tadao Akizawa5,
Bernard Canaud6,
Kenneth Chen7,
Luis Piera8,
Akira Saito9 and
Eric W. Young1,10
1 Division of Nephrology, Department of Internal Medicine, 2 Kidney Epidemiology and Cost Center, University of Michigan, 3 University Renal Research and Education Association, 10 Division of Nephrology, Department of Veterans Affairs Medical Center, Ann Arbor, Michigan, 6 Nephrology Department, Lapeyronie University Hospital, Montpellier, France, 7 Government Relations, Amgen Inc., Washington, DC, USA, 4 Department of Blood Purification and Internal Medicine, Kidney Center, Tokyo Women's Medical University, Tokyo, 5 Center of Blood Purification Therapy, Wakayama Medical University, Wakayama, 9 Institute of Medical Science, Tokai University School of Medicine, Kanagawa, Japan and 8 Nephrology Service, Hospital General Vall dHebron, Barcelona, Spain
Correspondence and offprint reqiuests to: Rajiv Saran, MD, MS, Kidney Epidemiology and Cost Center, University of Michigan 315 W. Huron, Suite 240, Ann Arbor, MI 48103, USA. Email: rsaran{at}umich.edu
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Abstract
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Background. Optimal waiting time before first use of vascular access is not known.
Methods. Two practicesfirst cannulation time for fistulae and grafts, and blood flow ratewere examined as potential predictors of vascular access failure in the Dialysis Outcomes and Practice Patterns Study (DOPPS). Access failure (defined as time to first failure or first salvage intervention) was modelled using Cox regression.
Results. Among 309 haemodialysis facilities, 2730 grafts and 2154 fistulae were studied. For grafts, first cannulation typically occurred within 24 weeks at 62% of US, 61% of European and 42% of Japanese facilities. For fistulae, first cannulation occurred <2 months after placement in 36% of US, 79% of European and 98% of Japanese facilities. Overall, the relative risk (RR) of graft failure in Europe was lower compared with the USA (RR = 0.69, P = 0.04). The RR of graft failure (reference group = first cannulation at 23 weeks) was 0.84 with first cannulation at <2 weeks (P = 0.11), 0.94 with first cannulation at 34 weeks (P = 0.48) and 0.93 with first cannulation at >4 weeks (P = 0.48). The RR of fistula failure was 0.72 with first cannulation at <4 weeks (P = 0.08), 0.91 at 23 months (P = 0.43) and 0.87 at >3 months (P = 0.31) (reference group = first cannulation at 12 months). Facility median blood flow rate was not a significant predictor of access failure.
Conclusions. Earlier cannulation of a newly placed vascular access at the haemodialysis facility level was not associated with increased risk of vascular access failure. Potential for confounding due to selection bias cannot be excluded, implying the importance of clinical judgement in determining time to first use of vascular access.
Keywords: access monitoring; blood flow rate; cannulation; haemodialysis; practice pattern; vascular access
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Introduction
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Vascular access failure remains the most common cause of morbidity and hospitalization among dialysis patients worldwide. Adequate delivery of prescribed haemodialysis relies on an optimally functioning vascular access. Meticulous surgical technique and selection of the autologous arteriovenous (AV) fistula (hereinafter referred to as the fistula) over a prosthetic arteriovenous graft (herein after referred to as the graft) are well-recognized strategies to ensure access longevity [1]. In addition, practices such as first cannulation timing (FCT) and blood flow rate (BFR) during haemodialysis may influence vascular access survival. Optimal waiting time to first use of vascular access is not known. A fistula typically is first cannulated when the nephrologist and/or dialysis nurse determine clinically that the vein is sufficiently developed and palpable to allow cannulation. It is common practice to postpone FCT of a fistula to allow for its adequate maturation. The prevalent concern is that early cannulation may predispose to access failure because of thrombosis, extrinsic compression by haematoma or infection. In the USA, the recommended FCT for polytetrafluoroethylene grafts is at least 2 weeks in most facilities; for newly placed fistulae, FCT in the USA is typically 68 weeks [2]. It is also uncertain whether BFR during haemodialysis has any impact on vascular access outcomes. It is possible that higher blood flow rates at dialysis (i) disrupt laminar flow, resulting in a pro-coagulative milieu; and (ii) lead to a lowered threshold for detection of vascular access dysfunction.
An analysis of first cannulation and fistula survival was published recently [3]. This type of analysis, which focuses on first cannulation practice at the patient level, while customary and useful, may be confounded by the treatment by indication bias inherent in such a model. One way to overcome this type of confounding in an observational study is to examine the average access-related practice pattern at the dialysis facility level and to use this as a predictor of access outcomes. With this in mind, the present study set out to examine the relationship, if any, of two facility-level practice patterns, namely FCT and BFR, to vascular access failure. If early cannulation were to have no negative impact on long-term access outcomes, it would permit first cannulation whenever it is determined to be clinically safe and feasible rather than being postponed to an arbitrarily defined time limit deemed necessary for access maturation. Such a finding would allow for shortened use and, in some cases, even complete avoidance of dialysis catheters, which are known to be associated with increased morbidity and mortality.
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Methods
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The Dialysis Outcomes and Practice Patterns Study (DOPPS) is a prospective, observational study of adult haemodialysis patients and facilities; data for DOPPS I were collected in seven countries (France, Germany, Italy, Japan, Spain, the UK and the USA). The DOPPS sampling plan, study methods and selection of nationally representative samples of facilities and patients have been published previously [4]. A data validation study has been carried out in all five European countries by the contracting research organization. For the US DOPPS, the values for age, diabetes mellitus as a primary cause of end-stage renal disease (ESRD), and the proportion of female and Black patients in the US DOPPS sample are very similar to the values reported by the US Renal Data System for the 1997 US population of in-centre haemodialysis patients [5], suggesting that the US DOPPS data are representative of the country's population.
The current study includes data from three continents, obtained from a sample of 144 haemodialysis facilities in the USA, 101 European facilities and 64 Japanese facilities. On average, 30 adult chronic haemodialysis patients (age >17 years) were randomly selected at each facility. Study patients who departed from a facility were replaced periodically with new patients who started haemodialysis treatment at the same facility; the sample was thus enriched continuously with incident patients on all continents. Data were collected between July 1996 and May 2001 in the USA, from June 1998 to November 2000 in Europe, and from February 1999 to March 2001 in Japan.
Longitudinal data were collected in the seven countries using identical questionnaires and a standardized chart abstraction procedure performed by coordinators based at each dialysis facility. Data included demographic characteristics, co-morbid conditions and vascular access events. At study enrolment, the current access type and the number, type and location of prior accesses were recorded. All subsequent vascular access events (e.g. thrombosis) and procedures (e.g. salvage, revisions and new access creation) were recorded prospectively. Nurse managers reported the typical time from creation to first cannulation of a new fistula or graft at their facilities. BFR data (facility median) were obtained from a random cross-section of patients in each facility at the time of study enrolment. All new haemodialysis accesses created during the course of the study recruitment period were included in this sample (n = 4884; AV graft = 2730 and AV fistula = 2154). The unit of observation was the access, rather than the patient. Time to first failure (unassisted patency) of a graft or fistula was defined as the time from surgical creation/placement to first access thrombosis or access salvage procedure.
All statistical analyses were performed using SAS version 8.0 (SAS Institute, Cary, NC). Associations between access failure and FCT or BFR were modelled separately for fistulae and grafts. Upper arm and lower arm fistula failure were modelled separately to investigate differences by site of fistula placement. Data specific to type of AV anastomosis, including basilic vein transpositions, were not collected in the DOPPS and therefore could not be analysed. Time to first failure was modelled using Cox regression analysis to determine the relative risk (RR) of access failure. Cox models enabled us to make comparisons among samples with variable length of follow-up time. Models were adjusted for continent, age, race, sex, body mass index, diabetes mellitus, congestive heart failure, coronary artery disease, peripheral vascular disease and hypertension at study entry, as well as for the number of prior accesses (catheters, grafts and fistulae), and incidence to ESRD at time of access creation (i.e. number of patients where access was created within 90 days of first-ever haemodialysis). As a subanalysis, the Cox models were adjusted for presence or absence of access monitoring protocols as predictors of unassisted access patency. This was done to examine the effects of vascular access monitoring protocols on both fistula and graft outcomes. Facility clustering effects were addressed using robust standard estimates based on the sandwich estimator [6]. Within-subject clustering effects (multiple accesses per patient) were not explicitly adjusted for, but were addressed by adjustment for number of prior permanent accesses, as described above. Proportional hazards assumptions for the model covariates were confirmed by visual inspection of the natural log of the negative log survival over time by strata. Time to first failure analyses were censored at the date of the last follow-up for the specific access. The median follow-up time among all accesses (failed or censored) was 4 months.
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Results
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Among the 309 facilities that participated in this study, 2730 grafts and 2154 fistulae were created during the study among 3686 patients. Demographics by continent are displayed in Table 1, which also shows the adjustment factors for the Cox models. It is notable that during the study period, 30% of the permanent accesses created in the USA were fistulae compared with 79.9% in Europe and 71.8% in Japan. Figure 1 shows the adjusted RR of graft and fistula failure by continents. Compared with the USA (reference RR = 1.00), the adjusted RR of graft failure in Europe was 0.69 (P = 0.04) and in Japan was 0.95 (P = 0.75). Again, compared with the USA (reference RR = 1.00), the adjusted RR of fistula failure in Europe was 0.62 (P<0.001) and in Japan was 0.72 (P = 0.06).
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Table 1. Distribution of arteriovenous grafts and fistulae, patient demographics and adjustment factors used in Cox models
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Fig. 1. Relative risk of fistula and graft failure by continent. Models were adjusted for patient age, race, sex, body mass index, diabetes mellitus, congestive heart failure, coronary artery disease, peripheral vascular disease and hypertension at study entry, as well as for the number of prior accesses and incidence to end-stage renal disease.
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First cannulation timing practices for grafts and fistulae
FCT practices are displayed in Figure 2 (grafts) and Figure 3 (fistulae) for all three continents. Europe and the USA demonstrated similar practice patterns pertaining to first cannulation of grafts: 16% of US facilities and 17% of European units typically cannulated grafts at <2 weeks, while 62% of US facilities and 61% of European units cannulated grafts between 2 and 4 weeks. However, Japanese facilities reported a shorter cannulation time for grafts: 42% of units typically cannulated grafts within 2 weeks and 65% cannulated them within 3 weeks. Fistulae, on the other hand, were first cannulated <1 month after creation in 74% of Japanese facilities, 50% of European facilities and only 2% of US facilities. In the USA, 26% of facilities first cannulated their fistulae after 3 months of placement compared with 8% of facilities in Europe and only 2% in Japan.

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Fig. 2. Number of weeks from placement to first cannulation of grafts as a facility-level practice pattern. Bar graph displaying facility typical time to first cannulation of arteriovenous grafts in US, European and Japanese haemodialysis facilities enrolled in the DOPPS.
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Fig. 3. Number of months from placement to first cannulation of fistulae as a facility-level practice pattern. Bar graph displaying facility typical time to first cannulation of arteriovenous fistulae in US, European and Japanese haemodialysis facilities enrolled in the DOPPS.
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First cannulation timing and vascular access failure
Table 2 shows the adjusted RR of graft failure and fistula failure by FCT. In the case of grafts, an RR of 1.00 was assigned to an FCT at 23 weeks (reference group). There was no significant difference in the RR of graft failure between early vs later cannulation times for grafts. For fistulae, an RR of 1.00 was assigned to an FCT at 12 months. While there was a trend for lower RR of fistula failure for the FCT category of <1 month, this did not reach statistical significance (RR = 0.72; P = 0.08). RRs for upper and lower arm fistula failure are also displayed in the same table. There were no differences in FCT practices for upper vs lower arm fistulae and no significant differences in RR of fistula failure by site of fistula in this subanalysis by FCT. A subanalysis of vascular access monitoring protocols was also performed to determine whether the use of standard clinical monitoring, venous pressure monitoring, recirculation measurements, access flow measurements or Doppler sonography reported at the facility level had an effect on vascular access outcomes. The results indicated no significant association of fistula or graft failure with the presence of various monitoring protocols (data not shown).
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Table 2. Relative risk of access failure by facility typical time of first cannulation for arteriovenous grafts (n = 2730) and fistulae (n = 2154)
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Blood flow rate distribution by continent and vascular access failure
The mean of the facility median BFR practised in Europe was 300 ml/min and in Japan was 196.5 ml/min, compared with 412 ml/min in the USA. These BFR means for the USA, Japan and Europe were significantly different from each other, P<0.0001. A trend toward increased graft failure at higher facility-level BFRs was observed, but this was not statistically significant for a large sample of grafts (RR = 1.14, P = 0.28). Overall, there were no statistically significant differences in RR of graft or fistula failure between different BFR categories (data not shown).
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Discussion
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The present study was designed to analyse data pertaining to vascular access failure and to study the relationship between access failure and both FCT and BFR practices across DOPPS countries. The results presented here suggest that the facility practice pattern of early FCT (<1 month after surgical creation) was not associated with increased risk of primary failure of fistulae. Indeed, if anything, the adjusted RR of fistula failure was lower for facilities typically cannulating fistulae <1 month after creation, even after adjustment for case mix (RR = 0.72, P = 0.08, Table 2). However, cannulation of a fistula within 2 weeks of its surgical creation would not be advisable, as suggested by Rayner et al. in a patient-level analysis of newly created fistulae in the DOPPS [3]. There are major differences between the data presented in this paper and that of Rayner et al., even though both studies are based on DOPPS data. The most important difference is that the present study is based on a facility-level practice pattern analysis, as derived from responses to questionnaires filled out by the nurse manager of the dialysis units in the DOPPS. This, in our view, is analogous to an intent to treat approach used in randomized clinical trials that avoids the treatment by indication bias that a patient-level analysis potentially could suffer from. For example, a lower fistula failure rate in a patient-level model could result from earlier cannulation of those fistulae that have matured early. This would give the false impression of the earlier cannulation practice itself being harmless, while being confounded by the state of patient vasculature or other factors that allowed earlier maturation and longer survival of the fistula in the first place. Other differences between the present study and the study of Rayner et al. include: (i) the Rayner study looked at 894 patients; the current study examined 3686 patients, with data on 2154 fistulae and 2730 grafts; (ii) only incident dialysis patients were selected for study by Rayner et al.; the present study examined a cross-section of prevalent patients who had a new access created during the study period; and, finally, (iii) only the topic of autologous fistula cannulation was addressed in the Rayner paper; the current study analysed data pertaining to both fistulae and grafts. Thus, combined evidence from these two different yet complementary DOPPS analyses suggests that, while cannulation of a fistula would not be advisable <2 weeks after its creation, first cannulation between 2 and 4 weeks could be attempted if clinically indicated and deemed feasible based on clinical assessment without necessarily increasing the risk of fistula failure.
There were no differences in RR of fistula failure when upper vs lower arm (forearm) fistulae were analysed separately (Table 2). This was contrary to the hypothesis that perhaps upper arm fistulae would be cannulated earlier in practice and would have a lower RR of failure compared with lower arm fistulae. However, detailed analysis by type of surgical AV anastomosis and nature of the fistula (e.g. transposition or not) were beyond the scope of this study, as these types of data were not collected in the DOPPS.
Results from the current study are at variance with findings of a single-centre study by Culp et al. [7], who report in a group of patients with fistulae (n = 118) that first cannulation after the first 30 days was associated with lower risk of access thrombosis when compared with those cannulated prior to 30 days. However, a large proportion of these patients had prior temporary catheters, which probably contributed significantly to subsequent primary fistula failure, as reported in previous studies [3,8]. Cannulation time/first use with respect to AV grafts has received some attention in the literature, but mostly in single-centre studies [912].
A considerable body of literature has developed pertaining to the monitoring of BFR in order to improve vascular access outcomes [13]. However, no prior study has examined the relationship between the BFR used during haemodialysis (represented by the pump speed) and vascular access failure. The current study notes that significant differences in BFR-related practices exist among countries, with Japanese facilities using the lowest and US facilities the highest mean BFR. The authors had postulated that higher BFR may be associated with greater RR of vascular access failure, because of increased platelet aggregation with increased risk of coagulation resulting from the disturbed laminar flow in the extracorporeal circuit [14]. In addition, a higher facility BFR practice is likely to lower the threshold for detection of access failure at relatively higher BFR, leading to earlier intervention (and thus reducing primary patency). While a trend toward increased graft failure at higher facility-level BFRs was observed, this was not statistically significant for a large sample of grafts (RR = 1.14, P = 0.28) and, indeed, overall, BFR was not associated with any increased risk of vascular access failure.
This study is the first report of differences in graft outcomes across the USA, Japan and five European countries (Figure 1). The RR of graft failure was 31% lower for Europe compared with the USA (P = 0.04). However, there was no significant difference between Japan and the USA in terms of graft failure. The outcomes for fistulae have been superior in Europe when compared with the USA. It has been postulated that these vascular access outcomes could be better explained by facility-level practice patterns and factors unrelated to case mix [8]. The difference in graft outcomes similarly was observed after adjustment for multiple co-morbidities, and is therefore likely to be independent from the co-morbidity difference between the patients in the two continents. It is conceivable that in Europe, only a small minority of patients receive a graft, most probably those who are technically more challenging, given their number of previous failed access procedures or the poor status of their blood vessels. Despite this potential reverse selection bias, the RR for graft failure is lower. These differences are, the authors feel, just as important as the differences in fistula failure and warrant investigation in future studies. The observation that in 42% of Japanese facilities, first cannulation of grafts took place within 2 weeks after placement (Figure 2) could possibly have resulted from the use of a higher proportion of polyurethane vascular access grafts, which are amenable to early first cannulation and are gaining favour in Japan, although this could not be confirmed with available DOPPS data.
Certain types of data are not available in the DOPPS, and their absence is a source of potential bias or residual confounding in this observational study. Examples include information about vein size at the time of cannulation (a larger vein would lend itself to earlier cannulation), type of AV anastomosis and use of the basilic vein transposition technique. Some authors have reported different actuarial survival of different types of fistulae; forearm fistulae are said to survive longer than upper arm fistulae [15]. It is conceivable that the initial failure rate is lower with upper arm fistulae, but that these accesses then fail more rapidly than do mature forearm fistulae. Bigger elbow cephalic veins typically are more readily punctured than smaller forearm veins. A higher proportion of upper arm fistulae may also imply that local surgeons have less experience with forearm fistulae and so create fistulae in the forearm only when big veins (>3 mm) and arteries (>2 mm) are available. Fistulae created under those circumstances are likely to be cannulated earlier than fistulae created with smaller arteries and veins.
The presence of access monitoring protocols as a facility-level practice pattern was not associated with significant changes in the results of primary patency of AV fistulae in a subanalysis in this study. This result is contrary to the expectation that with the use of access monitoring protocols, primary patency would be decreased (due to an increase in salvage procedure rate). The results of the current paper are consistent with the recently completed randomized controlled clinical trial comparing graft survival with standard monitoring (i.e. clinical examination combined with dynamic venous pressure monitoring compared with access blood flow surveillance in addition to standard monitoring) [16]. However, other studies have reached the opposite conclusion [1719], and the practice of formal surveillance as a means to improving access outcomes remains controversial.
While a randomized clinical trial would be the ideal method to compare the effect of early vs delayed cannulation on vascular access survival, an intent to treat approach, as detailed earlier in this Discussion, that examines the effect of the average access cannulation and BFR practice patterns on access outcomes across dialysis facilities is considered an efficient method within an observational study that avoids the treatment by indication bias inherent in a patient-based model [20].
In summary, this study has examined the association between vascular access failure and two facility-level access practices, i.e. first cannulation and blood flow rate, across the participating DOPPS I countries. This is the first published report of better AV graft outcomes for the five European countries studied in the DOPPS compared with the USA using nationally representative samples. Earlier cannulation of grafts (prior to 2 weeks) and fistulae (prior to 4 weeks) as a facility-level practice pattern was not associated with increased risk of access failure after extensive adjustments for case mix and facility clustering. These findings suggest that the reduced time required for vascular access maturation has the potential to decrease reliance on temporary vascular accesses (catheters), while not compromising long-term access survival. This conclusion should not be interpreted as undermining the primary importance of clinical judgement in the FCT. It is notable that the typical FCT for fistulae was considerably shorter in Europe than in the USA, despite the European facility practice of placing fistulae at a higher rate in patients with diabetes, peripheral vascular disease and coronary artery disease [8]. The mean BFR was lower in Japan and Europe compared with the USA. However, the RR of vascular access failure was not significantly associated with any of the BFR categories. Furthermore, the presence of access monitoring protocols at dialysis facilities was not associated with significant change in the RR of access failure. Other factors not the subject of this analysis, such as differences in staff experience, and surgical commitment, training, experience and technique, may provide an explanation for differences in vascular access outcomes across the three continents and should be explored in future studies.
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Acknowledgments
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Preliminary reports of this study have been published in abstract form [21,22]. The authors express appreciation to members of the WorldWide DOPPS Committee for contributions during the design and implementation of the DOPPS. For a full listing of committee members, please see Young et al. [4]. This study was supported by scientific grants from Amgen and Kirin without restrictions on publications.
Conflict of interest statement. None declared.
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Received for publication: 22. 5.03
Accepted in revised form: 19. 5.04