Comparison of Resistive Index and Volume Flow in Ultrasound of Arteriovenous Fistula for Dialysis Access

INTRODUCTION: Despite extensive investigation, the optimal method of assessing arteriovenous fistula (AV fistula) function remains elusive. Ultrasound is an important tool in the assessment of AV fistula, with a wide range of protocols and flow criteria used across the literature. However, the operator dependency of ultrasound has the potential to impact the quality of the acquired measurements, particularly volume flow, and has been poorly reported. Therefore, incorporating other measurements such as resistive indices may increase the robustness of the ultrasound findings. METHODS: This retrospective cohort study reviewed ultrasound and clinical data from two vascular ultrasound practices in Australia. All patients presenting with an upper limb AV fistula between January 2017 and October 2021 were included, stratified by indication for referral. The relationship between volume flow and resistive index was analyzed and predictive values were determined for two cutoff levels of resistive index (≤ 0.65 and ≤ 0.75) for a volume flow of ≥ 500 mL/min. FINDINGS: Eight types of AV fistula were noted in the 1988 ultrasound examinations conducted by 9 sonographers. Analysis was based on the three major AV fistula types: radio-cephalic (1267), brachiocephalic (491) and brachio-basilic (193). There were significant differences in the median values for both resistive index and volume flow between AV fistula type and indication for study. At an resistive index of ≤ 0.65 or 0.75, the positive predictive value in the group referred for surveillance was 96.8% and 95.4% respectively for a volume flow ≥ 500 mL/min, while in the group referred for problematic AV fistula it was 92.5% and 83.8%. CONCLUSION: The addition of resistive index values can support confidence in the technically difficult volume flow measures, especially for sonographers with non-specialized vascular skills.