Timing of first cannulation of arteriovenous fistula: are we waiting too long?

Rajiv Saran1,2,4, Ronald L. Pisoni3 and Eric W. Young1

1 Division of Nephrology, 2 Kidney Epidemiology and Cost Center and 3 University Renal Research and Education Association, University of Michigan and 4 Veteran Affairs Medical Center, Ann Arbor, MI, USA

Correspondence and offprint requests 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

Keywords: arteriovenous fistula; DOPPS; first cannulation; haemodialysis



   Introduction
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Timing of first cannulation of an arteriovenous (AV) fistula remains a controversial subject, but has been the subject of a few investigations reported in the literature recently [1–4]. The current K/DOQI practice guidelines pertaining to this topic [5] are based on opinion and need to be re-evaluated in the light of these recently published studies. These guidelines state that one should wait for ≥1 month, but preferably 2–3 months, before initial cannulation of an AV fistula. However, this long a wait is feasible only when there is no impending need for commencement of dialysis, which is quite often not the case. Furthermore, if it is observed that earlier cannulation practice is associated with good vascular access outcomes in some facilities, then it behoves the rest of the community to examine factors whereby earlier cannulation can be accomplished reliably and safely.



   Previous studies on vascular access practices and outcome: DOPPS
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 Introduction
 Previous studies on vascular...
 Other recent studies on...
 New DOPPS report on...
 Conclusions
 References
 
Research on vascular access practices and outcomes has remained a major focus of the international Dialysis Outcomes and Practice Patterns Study (DOPPS) [6]. Outcomes for AV fistula and AV graft survival have been superior in Europe compared with the USA [6]. In this initial detailed analysis of vascular access practices around the globe, it was postulated that these differences in vascular access outcomes could be explained, in large part, on the basis of facility-level practice patterns and factors unrelated to case-mix. Data have since emerged from DOPPS examining the issue of timing of first cannulation of AV fistulae and grafts [2,4]. A patient-level analysis by Rayner et al. [2] looked at a subcohort consisting predominantly of patients starting haemodialysis around the time of recruitment into DOPPS (n = 894) and analysed the effect of first cannulation of the AV fistulae in those patients at varying time intervals. No association was found between cannulation time ≤28 days vs >28 days with respect to patient characteristics of age, gender and 15 classes of comorbidities. These results supported the view that local policies of access surgery and fistula cannulation were more important than any of the patient characteristics examined, although prior temporary access and hospitalization was associated with a significantly higher odds of early (≤28 days) cannulation of AV fistulae [2]. No significant difference in AV fistula survival was seen for fistulae cannulated in a 15–28 day interval after creation compared with those first cannulated 43–84 days after creation. However, cannulation ≤14 days after creation was associated with a 2.1-fold increased risk of subsequent fistula failure (P = 0.006), compared with fistulae cannulated >14 days, after adjusting for case-mix, continent and facility clustering effects. The authors concluded that fistulae should preferably be left to mature for ≥14 days before first cannulation. Thus, while the study did not examine specific factors that allow for successful cannulation of an AV fistula after 14 days of creation, it suggested that certain clinical circumstances allowed for this practice and was not associated with deleterious consequences for the access.



   Other recent studies on vascular access practices and outcome
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 Introduction
 Previous studies on vascular...
 Other recent studies on...
 New DOPPS report on...
 Conclusions
 References
 
A prior study by Culp et al. [1] observed greater AV fistula failure with early cannulation within 30 days of creation compared with longer than 30 days. This study was based on 118 patients, a large proportion of whom had prior temporary catheters that are known to be associated with a variety of infective and thrombotic complications and also shortened subsequent AV fistula survival, as reported previously [6]. Moreover, a recent larger prospective, longitudinal three-centre study from northern Italy by Ravani et al. [3] has explored the issue of timing of first cannulation of AV fistulae in considerable detail in an incident cohort of dialysis patients (n = 535). A large proportion of their patients initiated dialysis with a catheter (47%) and, indeed, this subgroup cannulated their AV fistula earlier (median ‘maturation’ or first cannulation period was 0.78 months vs 1.80 months; P<0.001). Prior catheter use was the most powerful independent predictor of earlier cannulation and was also associated strongly with both primary and secondary AV fistula failure. Other important predictors of primary AV fistula failure after adjustment for confounders in this study included presence of cardiovascular disease, cannulation earlier than 1 month after placement and referral within 3 months of dialysis start. However, it is not clear whether Ravani et al. [3] adjusted for prior catheter use and did not stratify their analyses by prior catheter use. It appears that in the patient population studied, the urgency to cannulate AV fistulae for the first time is determined, in large part, by the need to eliminate initial catheter use (which has the recognized potential for complications) as well as late referral to dialysis.



   New DOPPS report on vascular access practices and outcome at facility level
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 Previous studies on vascular...
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 New DOPPS report on...
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To reduce the confounding by indication bias inherent in a patient-level analysis, DOPPS investigators recently conducted a study of fistula cannulation practices as a facility-level practice pattern [4]. The nurse managers at the dialysis facilities in DOPPS were asked for the typical time of first cannulation of AV fistulae at their facility and the response was used as the predictor variable in time to first failure of AV fistulae. A major difference between this and the two studies discussed above, in addition to the fact that this is a facility-level analysis of first cannulation practices, is the utilization of a prevalent patient cohort (that includes incident patients at the dialysis facilities). This is closer to the ‘real world’ situation where nephrologists are dealing with first cannulation both in incident and prevalent patients at the same time and need guidelines for both types of situation. The unit of observation in this study was the first AV fistula placed during the course of the study and its relationship to the facility-level practice of first cannulation. Adjustment for demographics, comorbidities, body mass index, number of prior permanent accesses, incidence to dialysis, continent and facility clustering was performed to minimize the potential for selection bias. The findings of this study suggest that facilities that typically report early cannulation (<1 month) of AV fistulae did not have worse vascular access outcomes (as measured by the relative risk of fistula failure) compared with those that delay cannulation (>1 month). In fact, despite greater lead time bias for AV fistulae with longer maturation times, the results suggest a trend to survival advantage for fistulae at facilities that typically cannulate <1 month compared with longer time periods (relative risk of fistula failure = 0.72; P = 0.08). This is strong evidence that at some facilities earlier cannulation is both achievable and not associated with worse vascular access outcomes.

Future studies should investigate factors associated with successful early cannulation, such as supervision by the nephrologists or surgeon, utilization of experienced staff for access cannulation or the proper assessment prior to first cannulation (e.g. by thorough clinical appraisal and/or objective techniques, such as Doppler ultrasound). It is generally recognized that the observational studies referred to above do not represent the final word on this issue, but merely report associations and cannot fully eliminate bias. Clearly, the ideal way to settle this issue will be a randomized clinical trial. However, it is the authors' view that such a trial, to be representative and generalizable, should include both incident and prevalent dialysis patients. However, until such a trial is undertaken we believe the following conclusions can be drawn from the observational study evidence reviewed above.



   Conclusions
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  1. Cannulation of AV fistulae <2 weeks old should be avoided.
  2. Cannulation between 2 and 4 weeks should be performed only if the fistula is deemed mature by the treating nephrologists/surgeon and under close supervision, electively and never as an ‘emergency’.
  3. It is probably safe to cannulate a fistula after 4 weeks of creation.

The importance of clinical examination prior to any cannulation is of utmost importance and if at any time it is felt that the fistula is not clinically ready, the time elapsed since its creation alone should not form the basis of the decision to cannulate. By the same token, earlier cannulation should not be eschewed simply on the basis of the time criteria, if the fistula looks clinically mature. This approach may avoid the use of central venous catheters for some patients, thereby yielding a possible benefit of longer AV fistula survival. One must remember that these are only guidelines that should not replace clinical judgment. Objective methods to evaluate fistula maturity prior to first cannulation await further study.

Conflict of interest statement. None declared.



   References
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 Introduction
 Previous studies on vascular...
 Other recent studies on...
 New DOPPS report on...
 Conclusions
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  1. Culp K, Flanigan M, Taylor L, Rothstein M. Vascular access in new hemodialysis patients. Am J Kidney Dis 1995; 26: 341–346[ISI][Medline]
  2. Rayner HC, Pisoni RL, Gillespie BM et al. Creation, cannulation and survival of arterio-venous fistulae-data from the Dialysis Outcomes and Practice Patterns Study (DOPPS). Kidney Int 2003; 63: 323–330[CrossRef][ISI][Medline]
  3. Ravani P, Brunori G, Mandolfo S et al. Cardiovascular comorbidity and late referral impact arteriovenous fistula survival a prospective multicenter study. J Am Soc Nephrol 2004; 15: 204–209[Abstract/Free Full Text]
  4. Saran R, Dykstra D, Pisoni RL et al. Timing of first cannulation and vascular access failure in haemodialysis: an analysis of practice patterns at dialysis facilities in the DOPPS. Nephrol Dial Transplant 2004; 19: 2334–2340[Abstract/Free Full Text]
  5. National Kidney Foundation. K/DOQI Clinical Practice Guidelines for Vascular Access: 2000. Am J Kidney Dis 2001; 37 [Suppl 1]: S137–S181
  6. Pisoni RL, Young EW, Dykstra DM et al. Vascular access use in Europe and the United States: results from the DOPPS. Kidney Int 2002; 61: 305–316[CrossRef][ISI][Medline]
Received for publication: 3. 1.05
Accepted in revised form: 14. 1.05