Early Ultrasound Surveillance of Newly-Created Hemodialysis Arteriovenous Fistula

Abstract

Introduction: We assess if ultrasound surveillance of newly-created arteriovenous fistulas (AVFs) can predict nonmaturation sufficiently reliably to justify randomized controlled trial (RCT) evaluation of ultrasound-directed salvage intervention.

Methods: Consenting adults underwent blinded fortnightly ultrasound scanning of their AVF after creation, with scan characteristics that predicted AVF nonmaturation identified by logistic regression modeling.

Results: Of 333 AVFs created, 65.8% matured by 10 weeks. Serial scanning revealed that maturation occurred rapidly, whereas consistently lower fistula flow rates and venous diameters were observed in those that did not mature. Wrist and elbow AVF nonmaturation could be optimally modeled from week 4 ultrasound parameters alone, but with only moderate positive predictive values (PPVs) (wrist, 60.6% [95% confidence interval, CI: 43.9-77.3]; elbow, 66.7% [48.9-84.4]). Moreover, 40 (70.2%) of the 57 AVFs that thrombosed by week 10 had already failed by the week 4 scan, thus limiting the potential of salvage procedures initiated by that scan's findings to alter overall maturation rates. Modeling of the early ultrasound characteristics could also predict primary patency failure at 6 months; however, that model performed poorly at predicting assisted primary failure (those AVFs that failed despite a salvage attempt), partly because patency of at-risk AVFs was maintained by successful salvage performed without recourse to the early scan data.

Conclusion: Early ultrasound surveillance may predict fistula maturation, but is likely, at best, to result in only very modest improvements in fistula patency. Power calculations suggest that an impractically large number of participants (>1700) would be required for formal RCT evaluation.

Keywords: Doppler ultrasonography; arteriovenous fistula; hemodialysis; surveillance; vascular access surgery.

Graphical abstract

Figure 1

Representative fistula venous diameter (a and b) and fistula volume flow rate (c and d) for elbow (a and c) and wrist (b and d) according to maturation status at week 10. Box and whisker plot shows minimum value (after excluding outliers), 25th centile, median, 75th centile and maximum value (after excluding outliers) without imputation of primary outcome. Fistulas that failed before week 10 (thrombosis or abandonment after a failure) were excluded from the analysis. Stacked 100% bar charts showing the proportion of (e) elbow and (f) wrist fistulas, with the following outcomes at each of weeks 2, 4, 6, and 10: died, withdrawn, abandoned, thrombosed, mature by ultrasound parameters (at that scan), not mature by ultrasound parameters (at that scan), unknown (did not attend scan or where missing data from the scan prevented determination of maturity). (g) and (h): as for (e) and (f) but for all fistulas, presented as numbers and including arrows depicting status at next scan of those fistulas mature (g) or immature (h) at previous scan.

Figure 2

Scatter plot of representative venous diameter by average volume flow at 2, 4, and 6 weeks (a, b, and c, respectively) with different symbols for matured/not matured fistulas at week 10 (as per primary outcome with no imputation).

Figure 3

Standard receiver operating characteristic curves for the optimum models established for predicting week 10 fistula nonmaturation from week 4 ultrasound findings for (a) elbow, and (b) wrist fistulas, with 1-specificity (x-axis) plotted against sensitivity (y-axis), and each point on the graph generated by using a different threshold point. The optimal threshold point chosen in our study is shown in the plot (Youden index, symbol “Y”); the threshold value is the number on the far left to the “Y”.

Figure 4

Summary of week 4 ultrasound modeling on identifying 10-week fistula status.

Figure 5

Kaplan Meier analysis of primary, assisted primary, and secondary patency rates to 12 months for (a) elbow and (b) wrist AVFs. Numbers in brackets represent 12 month (+ 95% confidence interval) patency rates.

Figure 6

Standard receiver operating characteristic curve analysis for the optimum models established for predicting 6-month fistula nonpatency from (a) week 6 ultrasound findings for wrist and (b) week 4 ultrasound findings for elbow fistula, with 1-specificity (x-axis) plotted against sensitivity (y-axis), and each point on the graph generated by using a different threshold point. The optimal threshold point chosen in our study is shown in the plot (Youden index, symbol “Y”); the threshold value is the number on the far left to the “Y”.