Abstract
Purpose
Arteriovenous fistula (AVF) stenosis is a major cause of vascular access dysfunction in hemodialysis patients. This study evaluated the associations between Doppler ultrasound-derived blood flow parameters measured at different AVF sites and Doppler-defined significant AVF stenosis.
Methods
This retrospective cohort study included adult hemodialysis patients with native AVFs who underwent Doppler ultrasound evaluation at Cho Ray Hospital, Vietnam. Blood flow parameters were measured at the brachial artery, anastomosis, 5 cm from the anastomosis, and 10 cm from the anastomosis. Doppler-defined significant stenosis was defined as ≥50% luminal narrowing compared with the adjacent normal vessel segment. Univariable and multivariable logistic regression analyses were performed to evaluate associations between Doppler flow parameters and significant stenosis.
Results
Among 1,541 patients, 585 (38.0%) had Doppler-defined significant AVF stenosis. Patients with significant stenosis had lower blood flow values at all evaluated sites, including Qmin and Qmean (all p<0.001). After adjustment for demographic and AVF characteristics, higher blood flow values remained associated with lower odds of significant stenosis. The adjusted odds ratios (95% confidence intervals) per 500 mL/min increase were 0.73 (0.67–0.79) for brachial artery flow, 0.76 (0.71–0.83) for anastomosis flow, 0.83 (0.78–0.89) for flow measured 5 cm from the anastomosis, 0.81 (0.75–0.87) for flow measured 10 cm from the anastomosis, 0.63 (0.56–0.71) for Qmin, and 0.76 (0.70–0.82) for Qmean. Significant stenosis was still observed in some patients with relatively high flow values.
Conclusion
Lower Doppler ultrasound-derived blood flow values at multiple AVF sites were associated with Doppler-defined significant AVF stenosis and may support comprehensive vascular access assessment. Further prospective studies using independent reference standards and clinically relevant outcomes are needed before these parameters can be used as validated predictive tools.
Keywords: AVF stenosis, doppler ultrasound, hemodialysis, vascular access, blood flow parameters
Introduction
Arteriovenous fistulas (AVF) are the preferred vascular access for maintenance hemodialysis due to their superior long-term patency and lower complication rates compared with other vascular access modalities.1,2 A recent nationwide cohort study also demonstrated that AVF use was associated with lower risks of infection-related, cardiovascular, and all-cause mortality compared with other vascular access types among patients undergoing maintenance hemodialysis.3 Despite these advantages, AVF dysfunction remains a major clinical problem among hemodialysis patients, with stenosis representing the most common underlying cause of access failure.4,5 Progressive AVF stenosis may lead to thrombosis, inadequate dialysis delivery, repeated interventions, hospitalization, and eventual loss of vascular access.5 Early identification of clinically significant stenosis is therefore essential to maintain AVF function and improve long-term dialysis outcomes.
Doppler ultrasound is among the most widely used non-invasive techniques for evaluating AVF dysfunction and monitoring vascular access blood flow.6,7 Measurements of blood flow volume, particularly brachial artery flow, are commonly employed in clinical practice to assess stenosis risk and guide subsequent investigations or interventions.8 However, the diagnostic performance of Doppler-derived flow parameters exhibits considerable variability across studies.6 For example, reported access flow cutoffs for stenosis detection have ranged from <400 mL/min to <900 mL/min, with sensitivities ranging from 59% to 95%.9,10 Moreover, although routine Doppler surveillance has been proposed for early stenosis detection, whether it prevents thrombosis or improves long-term access survival remains uncertain.6,11 Furthermore, comparative evidence regarding the associations between blood flow measurements obtained at different AVF sites and significant stenosis remains limited.
The hemodynamic consequences of AVF stenosis depend on the anatomical location and severity of the lesion. Stenoses at the inflow artery, anastomosis, or venous outflow tract can differentially influence local blood flow, thereby affecting Doppler measurements obtained at different sites along the vascular access circuit.12,13 Thus, Doppler-derived flow parameters measured beyond the conventional brachial artery Qa may provide additional clinically relevant information for identifying significant stenosis.6,8 However, comparative data on associations between blood flow measurements at different AVF sites and significant stenosis remain limited, particularly in Asian populations and resource-limited hemodialysis settings.
Vietnam is experiencing a rapid increase in the number of patients requiring long-term hemodialysis, with approximately 30,000 on maintenance hemodialysis (310 per million population) thereby placing substantial demands on vascular access surveillance and management in resource-limited settings.14,15 Our research group previously reported the diagnostic performance of bedside physical examination findings for detecting AVF stenosis in a sample of 325 Vietnamese hemodialysis patients.16 However, that study primarily focused on clinical examination-based screening and did not evaluate Doppler ultrasound-derived hemodynamic parameters or blood flow measurements at multiple AVF locations. Large-scale studies evaluating Doppler ultrasound-derived blood flow parameters for identifying AVF stenosis, particularly at multiple sites, remain scarce in Vietnamese patients. Therefore, this study aimed to evaluate the associations between Doppler ultrasound-derived blood flow parameters measured at different AVF locations and Doppler-defined significant AVF stenosis in a large Vietnamese hemodialysis cohort. We hypothesized that lower blood flow values measured at the brachial artery, anastomosis, and venous segments 5 cm and 10 cm from the anastomosis, as well as lower Qmin and Qmean, would be associated with higher odds of significant AVF stenosis.
Materials and Methods
Setting and Participants
This retrospective cohort study was conducted based on existing medical records and AVF Doppler ultrasound data at the Hemodialysis Department of Cho Ray hospital, one of the largest tertiary referral hospitals in southern Vietnam, between 2020 and 2022. The study was reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement.17 The data included adult patients receiving maintenance hemodialysis through native arteriovenous fistulas (AVFs) who underwent Doppler ultrasound evaluation of vascular access during routine clinical care or because of suspected AVF dysfunction. Eligible participants were patients with AVFs created at least three months before enrollment to ensure adequate AVF maturation and to minimize the influence of immediate postoperative changes. Because the study used retrospectively available hospital data and a large number of eligible patients were identified during the study period, all eligible cases were included, and no formal sample size calculation was performed.
Study Procedures
Demographic data, dialysis vintage, AVF characteristics, and other relevant clinical parameters were retrieved from electronic hospital records and ultrasound reports. Doppler ultrasound examinations were performed on non-dialysis days by a single experienced physician using a color Doppler ultrasound system (Vinno E10, VINNO, China) equipped with a high-frequency linear-array transducer. The same standardized examination protocol was applied to all patients. The entire vascular access circuit was systematically evaluated from the feeding artery through the anastomosis to the venous outflow tract. The study protocol was approved by the Biomedical Research Ethics Committee of Cho Ray Hospital (Approval No. 146–25/CN-HĐĐĐ). The requirement for informed consent was waived by the ethics committee because this retrospective study used existing clinical records and imaging data and involved no additional procedures or direct contact with patients. Patient information was kept strictly confidential, and data used for analysis did not contain direct patient identifiers. The study was conducted in accordance with the principles of the Declaration of Helsinki.
Measurements
The primary outcome was significant AVF stenosis, defined as a reduction of at least 50% in luminal diameter on Doppler ultrasound compared with the adjacent normal vessel segment, according to KDOQI recommendations and previous literature.6,18 Vessel diameter was measured on a transverse image obtained perpendicular to the vessel, from the inner wall to the inner wall. Spectral Doppler waveforms were obtained according to standard vascular Doppler principles, with the Doppler angle consistently maintained below 60°. The velocity measurement was repeated twice, and the higher of the two measurements was recorded. Blood flow volume was calculated using the formula: volume flow = cross-sectional area x mean velocity x 60. Doppler ultrasound-derived blood flow parameters were measured at four predefined locations: the brachial artery, the anastomosis, 5 cm from the anastomosis, and 10 cm from the anastomosis. Two composite flow parameters were subsequently calculated: Qmean, defined as the mean flow across the four measurement sites, and Qmin, defined as the minimum flow value among the four sites.
Data Analysis
Data were complete for all primary study variables and most covariates. AVF location was unavailable for 16 of 1,541 patients (1.0%). Because AVF location is an anatomical characteristic that could not be reliably inferred from the available data, no imputation was performed. Continuous variables were presented as mean ± standard deviation or median and interquartile range. Categorical variables were presented as frequencies and percentages. Comparisons between groups were performed using the Chi-square test or Fisher’s exact test for categorical variables, and the independent t-test or Mann–Whitney U-test for continuous variables, as appropriate. Univariable and multivariable logistic regression analyses were conducted to evaluate associations between Doppler-derived flow parameters and significant AVF stenosis. Adjusted models included sex, age, AVF side, AVF location, inflow artery, and outflow vein. Statistical significance was defined as a two-sided p value <0.05. All data analyses were conducted using Stata version 17.
Results
Among 1,541 hemodialysis patients, 53.0% were female and the mean age was 55.3 ± 15.1 years. Most AVFs were located on the left arm (69.1%) and at the wrist level (63.3%). The cephalic vein was the predominant outflow vein (88.2%), while the radial artery was the most common inflow artery (63.3%). Significant AVF stenosis was identified in 585 patients (38.0%). The proportion of stenosis differed significantly according to AVF characteristics. Wrist AVFs demonstrated a higher prevalence of stenosis compared with elbow AVFs (43.5% vs 27.9%, p < 0.001). Similarly, AVFs using the radial artery as the inflow artery showed a substantially higher proportion of stenosis than those using the brachial artery (43.6% vs 28.3%, p < 0.001). A significant association was also observed according to outflow vein type (p = 0.018), whereas stenosis prevalence did not differ significantly by sex, age group, or AVF side (Table 1).
Table 1.
Baseline Characteristics and Association with AVF Stenosis Among Hemodialysis Patients (n = 1541)
| Arteriovenous Fistula Stenosis | p value | |||
|---|---|---|---|---|
| Total | Yes n = 585, 38.0% |
No n = 956, 62.0% |
||
| Sex | ||||
| Male | 725 (47.0) | 271 (37.4) | 454 (62.6) | 0.657 |
| Female | 816 (53.0) | 314 (38.5) | 502 (61.5) | |
| Age (years) M (SD) | 55.3 (15.1) | 55.3 (15.1) | 55.3 (15.2) | 0.940 |
| Age (years) | ||||
| <50 | 514 (33.4) | 193 (37.5) | 321 (62.5) | 0.355 |
| 50–59 | 326 (21.2) | 118 (36.2) | 208 (63.8) | |
| 60–69 | 441 (28.6) | 182 (41.3) | 259 (58.7) | |
| ≥70 | 260 (16.9) | 92 (35.4) | 168 (64.6) | |
| Arteriovenous fistula side | ||||
| Left | 1065 (69.1) | 410 (38.5) | 655 (61.5) | 0.517 |
| Right | 476 (30.9) | 175 (36.8) | 301 (63.2) | |
| Arteriovenous fistula location (n = 1525) | ||||
| Wrist | 965 (63.3) | 420 (43.5) | 545 (56.5) | <0.001 |
| Elbow | 560 (36.7) | 156 (27.9) | 404 (72.1) | |
| Outflow vein | ||||
| Cephalic vein | 1359 (88.2) | 518 (38.1) | 841 (61.9) | 0.018 |
| Basilic vein | 166 (10.8) | 66 (39.8) | 100 (60.2) | |
| Other vein | 16 (1.0) | 1 (6.3) | 15 (93.8) | |
| Inflow artery | ||||
| Brachial artery | 566 (36.7) | 160 (28.3) | 406 (71.7) | <0.001 |
| Radial artery | 975 (63.3) | 425 (43.6) | 550 (56.4) | |
The distributions of all Doppler ultrasound-derived blood flow parameters were right-skewed, as shown in Supplemental Figure S1. Median brachial artery flow in the study population was 780.0 mL/min (IQR 377.0–1351.0), while median flow at the anastomosis, 5 cm from the anastomosis, and 10 cm from the anastomosis were 651.0 mL/min (IQR 300.0–1287.0), 498.0 mL/min (IQR 204.0–1104.0), and 394.0 mL/min (IQR 140.0–918.0), respectively. The median Qmin and Qmean values were 354.0 mL/min (IQR 129.0–817.0) and 605.3 mL/min (IQR 272.8–1182.3), respectively. Patients with significant AVF stenosis consistently demonstrated substantially lower blood flow parameters across all measured sites, including Qmin and Qmean, compared with those without stenosis (all p < 0.001) (Table 2).
Table 2.
Arterial and AVF Characteristics Associated with Stenosis Among Hemodialysis Patients (n = 1541)
| Arteriovenous Fistula Stenosis | p value | |||
|---|---|---|---|---|
| Total Median (IQR) |
Yes n = 585, 38.0% Median (IQR) |
No n = 956, 62.0% Median (IQR) |
||
| Brachial artery flow (mL/min) | 780.0 (377.0–1351.0) | 628.0 (349.0–1039.0) | 937.5 (424.5–1566.5) | <0.001 |
| Anastomosis flow (mL/min) | 651.0 (300.0–1287.0) | 474.0 (246.0–829.0) | 827.0 (357.0–1547.5) | <0.001 |
| Flow at 5 cm from anastomosis (mL/min) | 498.0 (204.0–1104.0) | 388.0 (189.0–681.0) | 660.0 (217.5–1432.0) | <0.001 |
| Flow at 10 cm from anastomosis (mL/min) | 394.0 (140.0–918.0) | 290.0 (130.0–546.0) | 555.5 (153.0–1181.5) | <0.001 |
| Qmin (mL/min) | 354.0 (129.0–817.0) | 268.0 (122.0–493.0) | 502.5 (137.5–1024.5) | <0.001 |
| Qmean (mL/min) | 605.3 (272.8–1182.3) | 469.5 (247.3–782.3) | 779.5 (294.9–1420.3) | <0.001 |
Table 3 shows the results of both univariable and multivariable logistic regression analyses examining the associations between Doppler ultrasound-derived blood flow parameters and significant AVF stenosis. After adjustment for sex, age, AVF side, AVF location, outflow vein, and inflow artery, higher blood flow values were consistently associated with lower odds of significant stenosis across all measured sites. For every 500 mL/min increase in brachial artery flow, the adjusted odds of significant stenosis decreased by 27% (adjusted OR 0.73, 95% CI 0.67–0.79, p < 0.001). Similar inverse associations were observed for anastomosis flow (adjusted OR 0.76, 95% CI 0.71–0.83, p < 0.001), flow measured 5 cm from the anastomosis (adjusted OR 0.83, 95% CI 0.78–0.89, p < 0.001), flow measured 10 cm from the anastomosis (adjusted OR 0.81, 95% CI 0.75–0.87, p < 0.001), Qmin (adjusted OR 0.63, 95% CI 0.56–0.71, p < 0.001), and Qmean (adjusted OR 0.76, 95% CI 0.70–0.82, p < 0.001) (Table 3).
Table 3.
Univariable and Multivariable Analysis of Arterial and AVF Characteristics Associated with Stenosis Among Hemodialysis Patients (n = 1541)
| Crude | Adjustedb | |||
|---|---|---|---|---|
| OR (95% CI)a | p | OR (95% CI)a | p | |
| Brachial artery flow (mL/min) | 0.71 (0.66–0.77) | <0.001 | 0.73 (0.67–0.79) | <0.001 |
| Anastomosis flow (mL/min) | 0.74 (0.69–0.80) | <0.001 | 0.76 (0.71–0.83) | <0.001 |
| Flow at 5 cm from anastomosis (mL/min) | 0.81 (0.76–0.86) | <0.001 | 0.83 (0.78–0.89) | <0.001 |
| Flow at 10 cm from anastomosis (mL/min) | 0.78 (0.73–0.84) | <0.001 | 0.81 (0.75–0.87) | <0.001 |
| Qmin (mL/min) | 0.61 (0.55–0.68) | <0.001 | 0.63 (0.56–0.71) | <0.001 |
| Qmean (mL/min) | 0.74 (0.69–0.80) | <0.001 | 0.76 (0.70–0.82) | <0.001 |
Notes: aFor every increase in 500 mL/minute in flow; bAdjusted for sex, age, AVF side, AVF location, outflow vein and inflow artery.
Figure 1 presents the adjusted estimated probability of significant AVF stenosis derived from the multivariable logistic regression models. Even at relatively high flow levels, there remained a certain probability of significant stenosis. In addition, the probability of stenosis varied continuously according to the magnitude of each flow parameter across different Doppler flow ranges.
Figure 1.
Adjusted estimated probabilities of Doppler-defined AVF stenosis according to Doppler-derived blood flow parameters among hemodialysis patients. (A) The association between brachial artery flow and AVF stenosis. (B) The association between anastomosis flow and AVF stenosis. (C) The association between flow at 5 cm from anastomosis and AVF stenosis. (D) The association between flow at 10 cm from anastomosis and AVF stenosis. (E) The association between minimum flow and AVF stenosis. (F) The association between mean flow and AVF stenosis. AVF stenosis probability was adjusted for sex, age, AVF side, AVF location, outflow vein and inflow artery.
Discussion
The present study evaluated Doppler ultrasound-derived blood flow parameters measured at different AVF locations in a large cohort of Vietnamese hemodialysis patients. This study demonstrated a high prevalence of significant AVF stenosis among maintenance hemodialysis patients, with approximately 38% of patients showing clinically significant narrowing on Doppler ultrasound evaluation. Moreover, lower Doppler ultrasound-derived blood flow parameters were consistently associated with significant stenosis across all evaluated measurement sites, and these associations remained statistically significant after adjustment for relevant demographic and AVF characteristics.
The high prevalence of AVF stenosis observed in this study underscores the substantial burden of vascular access dysfunction among hemodialysis patients. Previous studies have consistently reported AVF stenosis as one of the leading causes of vascular access failure, thrombosis, repeated interventions, and inadequate dialysis delivery.11,19 The prevalence of significant AVF stenosis observed in our cohort was comparable to or higher than rates reported in previous Doppler ultrasound studies of hemodialysis access dysfunction.6,12 This relatively high prevalence may partly reflect the inclusion of patients undergoing Doppler ultrasound due to suspected AVF dysfunction during routine clinical practice, alongside the progressive accumulation of vascular injury in long-term hemodialysis patients.20,21 Furthermore, Doppler ultrasound-based anatomical criteria for defining significant stenosis likely enabled detection of clinically important lesions that might remain under-recognized by routine physical examination alone.6,22 These findings support the potential role of Doppler-derived flow assessment as one component of comprehensive vascular access evaluationin maintenance hemodialysis populations.
Our findings also demonstrated that lower blood flow measurements at the brachial artery, anastomosis, and venous outflow segments were all independently associated with significant stenosis. These findings are consistent with previous studies reporting reduced access flow among stenotic AVFs while further suggesting that Doppler-derived flow measurements at locations beyond conventional brachial artery assessment may provide additional clinically relevant information.6,12 Because stenoses at different anatomical locations influence local hemodynamics differently, flow measurements at various sites may reflect distinct aspects of vascular access dysfunction.22 Among the evaluated parameters, Qmin showed the largest magnitude of inverse association with significant stenosis, with an adjusted odds ratio of 0.63 per 500 mL/min increase. Because Qmin represents the lowest flow value recorded across the four predefined measurement sites, this finding suggests that relying exclusively on brachial artery flow may not fully characterize the local hemodynamic effects associated with stenotic lesions. Nevertheless, the observed differences in odds ratios should not be interpreted as evidence that Qmin is a superior diagnostic or predictive tool, because no formal comparison of diagnostic performance, ROC analysis, or model validation was performed. Importantly, even at relatively high flow levels, a certain probability of significant stenosis remained. This suggests that preserved blood flow alone may not fully exclude clinically significant anatomical narrowing, likely owing to compensatory hemodynamic adaptations, collateral circulation, or localized stenotic lesions without immediate marked global flow reduction.23 Therefore, Doppler-derived flow parameters should be interpreted within the broader context of vascular access assessment rather than as isolated indicators.
These findings have important implications for vascular access surveillance in Vietnam. The persistently high prevalence of AVF stenosis, even at a major tertiary referral center, suggests that vascular access dysfunction may remain under-recognized or insufficiently monitored across different healthcare levels.24 Furthermore, significant stenosis persisting despite relatively preserved flow measurements highlights the necessity of comprehensive vascular access evaluation rather than sole reliance on a single Doppler flow threshold.6,22 These observations underscore the potential value of standardized surveillance strategies and national guidelines for Doppler ultrasound assessment of AVFs in Vietnamese hemodialysis patients.11 Together with our previous findings regarding the role of bedside clinical assessment for early AVF stenosis detection,16 the current results further support the incorporation of Doppler ultrasound-derived hemodynamic evaluation into comprehensive vascular access surveillance programs.
Several limitations should be acknowledged. First, this was a retrospective, single-center study conducted at a tertiary referral hospital, which may limit the generalizability of the findings to other hemodialysis populations and healthcare settings. Second, the study cohort included patients who underwent Doppler ultrasound either during routine clinical care or because of suspected AVF dysfunction. However, the retrospective records did not consistently document whether each Doppler examination was performed as part of routine assessment or was prompted by suspected AVF dysfunction. Therefore, the numbers of patients in these two categories could not be reliably quantified. Patients with clinical evidence of access dysfunction may therefore have been more likely to undergo ultrasound evaluation, introducing potential referral and diagnostic bias. Consequently, the observed 38% prevalence of Doppler-defined stenosis may be higher than that in an unselected hemodialysis population and should not be interpreted as a population-based prevalence estimate.
Third, although all Doppler ultrasound examinations were performed by a single experienced physician using the same standardized protocol, formal intraobserver reproducibility was not assessed. Measurement variability therefore cannot be completely excluded, and the use of a single operator may limit the reproducibility of the findings across different ultrasonographers and clinical settings. Moreover, in our study, stenosis was defined by Doppler ultrasound, while the main study variables were also Doppler-derived flow parameters. Since there was no independent reference standard such as fistulography, angiography, intervention findings, thrombosis, or access failure, the results should be interpreted cautiously. Finally, the study primarily evaluated associations between Doppler ultrasound-derived blood flow parameters and stenosis and did not assess long-term clinical outcomes such as thrombosis, access failure, the need for intervention, or repeated interventions. Therefore, the clinical and prognostic value of these flow parameters requires further evaluation in prospective, multicenter studies with longitudinal follow-up.
Conclusions
Doppler-defined significant AVF stenosis remained common among long-term hemodialysis patients and was independently associated with lower Doppler ultrasound-derived blood flow parameters at different AVF locations. However, significant stenosis could still be present despite relatively preserved blood flow, indicating that these measurements should be interpreted as part of a comprehensive vascular access assessment rather than as stand-alone diagnostic or predictive tools. Further prospective studies using independent reference standards and clinically relevant outcomes, including thrombosis, access loss, and the need for intervention, are required to determine their diagnostic and prognostic value.
Acknowledgment
The authors would like to thank the patients who participated in this study.
Funding Statement
The authors declared that financial support was not received for this work and/or its publication.
Data Sharing Statement
Collected and analyzed data during the study are available from the corresponding author upon reasonable request.
Disclosure
The authors declare that they have no conflicts of interest.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Collected and analyzed data during the study are available from the corresponding author upon reasonable request.