Surveillance for hemodialysis access stenosis: usefulness of ultrasound vector volume flow

Purpose: To investigate if ultrasound vector-flow imaging (VFI) is equal to the reference method ultrasound dilution technique (UDT) in estimating volume flow and changes over time in arteriovenous fistulas (AVFs) for hemodialysis. Materials and methods: From January 2014 to January 2015, patients with end-stage renal disease and matured functional AVFs were consecutively solicited to participate in this prospective study. All patients were included after written informed consent and approval by the National Committee on Biomedical Research Ethics and the local Ethics Committee (journal no. H-4-2014-FSP). VFI and UDT measurements were performed monthly over a six-month period. Nineteen patients were included in the study. VFI measurements were performed before dialysis, and UDT measurements after. Statistical analyses were performed with Bland-Altman plot, Student's t-test, four-quadrant plot, and regression analysis. Repeated measurements and precision analysis were used for reproducibility determination. Results: Precision measurements for UDT and VFI were 32% and 20%, respectively (p = 0.33). Average volume flow measured with UDT and VFI were 1161 mL/min (+/- 778 mL/min) and 1213 mL/min (+/- 980 mL/(min), respectively (p = 0.3). The mean difference was -51 mL/min (CI: -150 mL/min to 46 mL/min) with limits of agreement from -35% to 54%, with a strong correlation (r(2) = 0.87). A large change in volume flow between dialysis sessions detected by UDT was confirmed by VFI (p = 0.0001), but the concordance rate was poor (0.72). Conclusions: VFI is an acceptable method for volume flow estimation and volume flow changes over time in AVFs.