The European Society for Vascular Surgery (ESVS) guidelines on vascular access recommend minimal diameters of 2mm in the forearm and 3mm in the upper arm in vessels selected for the creation of an arteriovenous fistula (AVF). Whether this recommendation leads to better AVF-related outcomes, however, has been called into question by the publication of secondary analysis data from the Shunt Simulation Study, led by Letty V Van Vliet (Maastricht University Medical Centre, Maastricht, The Netherlands) in the Journal of Vascular Access (JVA).
Van Vliet et al make the case that the minimal blood vessel diameters considered appropriate for AVF creation “vary between dialysis units”. And it is not only individual units—there is variation even between the recommendations of different international guidelines, they say, pointing to the Kidney Disease Outcomes Quality Initiative (KDOQI) 2019 update, which offers only “a weak recommendation to use blood vessels smaller than 2mm only after critical assessment of their quality,” in divergence from the ESVS.
The Shunt Simulation Study is uniquely positioned to provide meaningful data on the issue, Van Vliet and colleagues say, given that all patients enrolled were operated on before the ESVS guidelines’ publication in June 2018. This, they suggest, eliminates the possibility of bias “resulting from deliberate deviation from published guidelines”.
The study was a randomised controlled trial (RCT) assessing the accuracy of a personalised computational model in predicting postoperative fistula flow. This secondary analysis, meanwhile, compared outcomes of patients treated as part of the study either in accordance with the ESVS recommendations or outside of them. The latter group was defined as when the smallest segment of the artery or vein of the AVF was smaller than the 2mm for forearm and 3mm for upper arm fistulas.
Fistula maturation was assessed using duplex ultrasound, and was defined as a flow of ⩾500ml/min and a vein diameter of ⩾4mm at six weeks post-surgery. A fistula was defined as functional if it was “cannulated with two needles for six sessions of haemodialysis at the prescribed access circuit flow within thirty days”. Predialysis patients were considered to have a functional access when the fistula could be used without first needing a central venous catheter upon dialysis initiation.
Of the patients who received fistulas in the study, 160 were available for analysis at one year post-fistula creation. A total of 72 (45%) of those patients received an AVF created outside of the clinical guidelines, with the remaining 88 (55%) doing so within them.
Van Vliet et al found that 82% of fistulas created within guideline recommendations had reached maturation by six weeks, compared with 71% of the fistulas with smaller vessel diameters. They also performed a multivariable regression analysis which found that guideline concordance in AVF creation was “not associated with improvements in obtaining a timely functional vascular access” (odds ratio [OR] 0.77, 95% confidence interval [CI]: 0.38–1.56) or in decreasing the rate of access-related interventions.
During the maturation process, the authors say, the outside-the-guideline vessels increased in size, becoming as large as the fistulas created in agreement with the guidelines. They do note, however, that only 52% of the subset of forearm fistulas with blood vessel diameters smaller than 2mm became functional.
Reviewing the evidence beyond their study, the authors state: “The scientific evidence indicates that although the chance of successful fistula maturation increases with greater blood vessel diameters, there is no strict diameter cut-off that consistently differentiates between fistulas with good and bad clinical outcomes.”
On their study’s contribution to that evidence, Van Vliet et al suggest finally that their results support the assertion that “clinical decision-making should be guided by an individual approach” which considers other factors, including blood vessel quality, other access options, and patient preferences, “instead of by strictly adhering to diameter cut-off values”.