US Volume Flow Assessment to Optimize Angioplasty of Dysfunctional Dialysis Access: The VOLA-II Multicenter Study

Background Digital subtraction angiography and thrill palpation demonstrate limitations when used to assess the outcomes of angioplasty in autologous arteriovenous fistulas (AVFs). Purpose To investigate a new functional quantifiable index of successful angioplasty for failing AVFs using intraprocedural percutaneous US volume flow (VF) measurements. Materials and Methods This prospective, multicenter, single-arm, cohort clinical trial included consecutive patients with indications for fluoroscopically guided balloon angioplasty due to AVF dysfunction between June 2020 and May 2022. Intraprocedural VF measurements were obtained before the procedure and after balloon dilation using transcutaneous duplex US. The primary end points were the quantification of VF-guided angioplasty outcomes and assessment of the association between postprocedural VF and freedom from target lesion reintervention (TLR) due to recurrence of access failure. Cox multivariate regression analysis was performed to identify predictors of TLR-free survival, which was estimated using Kaplan-Meier methods. Receiver operating characteristic curve analysis was used to determine the optimal cutoff VF value. Results In total, 100 participants (mean age, 67 years ± 12 [SD]; 84 male) were evaluated. The rate of freedom from TLR was 73% at 6 months. The mean pre- and postintervention VF values were 353 mL/min ± 199 and 1045 mL/min ± 413, respectively. Higher VF at completion of angioplasty (hazard ratio, 0.89 per 100 mL/min [95% CI: 0.82, 0.98]; P = .01) and forearm versus upper arm AVF (hazard ratio, 0.51 [95% CI: 0.27, 0.95]; P = .03) were independent predictors of increased freedom from TLR. A postprocedural VF of 720 mL/min (P < .001) was identified as the optimal cutoff point for predicting increased fistula freedom from reintervention and freedom of restenosis for radiocephalic AVFs, compared with an optimal cutoff point of 1120 mL/min (P = .03) for upper arm AVFs. Conclusion Intraprocedural VF measurement is a quantifiable functional index and postprocedural predictor of outcomes following angioplasty for failing dialysis AVFs. ClinicalTrials.gov identifier: NCT04694287 © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Prince et al this issue.

Dialysis nurses' knowledge, attitude, practice and self-efficacy regarding vascular access: A cross-sectional study in Singapore

INTRODUCTION

Dialysis nurses play a paramount role in vascular access (VA) management. The aim of this study is to evaluate dialysis nurses' knowledge, attitude, practice and self-efficacy (KACP-SE) pertaining to VA cannulation and evaluation.

METHOD

An anonymous self-administered survey was administered to dialysis nurses from two tertiary hospitals (four dialysis units) and two community dialysis centres from April to May 2022. The 37-items survey consists of four dimensions of questions relating to VA cannulation and management: knowledge, attitude, practice and self-efficacy. The content validity and face validity of the survey was reviewed by three experienced VA professionals and five dialysis nurses respectively. The internal consistency and construct validity of the survey have been assessed with psychometric tests.

RESULTS

There were 23 and 47 nurses, working in the participated community and tertiary hospital dialysis centres respectively, responded to the survey. The internal consistency coefficients indicated acceptable reliability of the instrument (KR-20 coefficient was 0.55 and 0.76 for knowledge and practice domains; Cronbach's α was 0.85 and 0.64 for self-efficacy and attitude domains). In the exploratory factor analysis for attitude and self-efficacy, the instrument could account for 64.0% and 53.0% of the total variance respectively. In the knowledge domain, five out of eight single-select multiple-choice questions were correctly answered by >70% of the participants. Overall, the mean (±SD) of participants' total self-efficacy score was 24.3 (±3.1) over total score of 30. The majority of the participants (82.4%) either agreed or strongly agreed that ultrasound guidance is useful for cannulation.

CONCLUSION

This KAP-SE instrument can be used to evaluate knowledge, attitude, practice and self-efficacy of dialysis nurses toward VA management. The participants demonstrated acceptable knowledge level, but with some knowledge gaps identified. It also revealed nurses' good self-efficacy level and welcoming attitude towards adopting ultrasound in VA cannulation among the participants.

Doppler ultrasound surveillance of recently formed haemodialysis arteriovenous fistula: the SONAR observational cohort study

Background

Arteriovenous fistulas are considered the best option for haemodialysis provision, but as many as 30% fail to mature or suffer early failure.

Objective

To assess the feasibility of performing a randomised controlled trial that examines whether, by informing early and effective salvage intervention of fistulas that would otherwise fail, Doppler ultrasound surveillance of developing arteriovenous fistulas improves longer-term arteriovenous fistula patency.

Design

A prospective multicentre observational cohort study (the 'SONAR' study).

Setting

Seventeen haemodialysis centres in the UK.

Participants

Consenting adults with end-stage renal disease who were scheduled to have an arteriovenous fistula created.

Intervention

Participants underwent Doppler ultrasound surveillance of their arteriovenous fistulas at 2, 4, 6 and 10 weeks after creation, with clinical teams blinded to the ultrasound surveillance findings.

Main outcome measures

Fistula maturation at week 10 defined according to ultrasound surveillance parameters of representative venous diameter and blood flow (wrist arteriovenous fistulas: ≥ 4 mm and > 400 ml/minute; elbow arteriovenous fistulas: ≥ 5 mm and > 500 ml/minute). Mixed multivariable logistic regression modelling of the early ultrasound scan data was used to predict arteriovenous fistula non-maturation by 10 weeks and fistula failure at 6 months.

Results

A total of 333 arteriovenous fistulas were created during the study window (47.7% wrist, 52.3% elbow). By 2 weeks, 37 (11.1%) arteriovenous fistulas had failed (thrombosed), but by 10 weeks, 219 of 333 (65.8%) of created arteriovenous fistulas had reached maturity (60.4% wrist, 67.2% elbow). Persistently lower flow rates and venous diameters were observed in those fistulas that did not mature. Models for arteriovenous fistulas' non-maturation could be optimally constructed using the week 4 scan data, with fistula venous diameter and flow rate the most significant variables in explaining wrist fistula maturity failure (positive predictive value 60.6%, 95% confidence interval 43.9% to 77.3%), whereas resistance index and flow rate were most significant for elbow arteriovenous fistulas (positive predictive value 66.7%, 95% confidence interval 48.9% to 84.4%). In contrast to non-maturation, both models predicted fistula maturation much more reliably [negative predictive values of 95.4% (95% confidence interval 91.0% to 99.8%) and 95.6% (95% confidence interval 91.8% to 99.4%) for wrist and elbow, respectively]. Additional follow-up and modelling on a subset (n = 192) of the original SONAR cohort (the SONAR-12M study) revealed the rates of primary, assisted primary and secondary patency arteriovenous fistulas at 6 months were 76.5, 80.7 and 83.3, respectively. Fistula vein size, flow rate and resistance index could identify primary patency failure at 6 months, with similar predictive power as for 10-week arteriovenous fistula maturity failure, but with wide confidence intervals for wrist (positive predictive value 72.7%, 95% confidence interval 46.4% to 99.0%) and elbow (positive predictive value 57.1%, 95% confidence interval 20.5% to 93.8%). These models, moreover, performed poorly at identifying assisted primary and secondary patency failure, likely because a subset of those arteriovenous fistulas identified on ultrasound surveillance as at risk underwent subsequent successful salvage intervention without recourse to early ultrasound data.

Conclusions

Although early ultrasound can predict fistula maturation and longer-term patency very effectively, it was only moderately good at identifying those fistulas likely to remain immature or to fail within 6 months. Allied to the better- than-expected fistula patency rates achieved (that are further improved by successful salvage), we estimate that a randomised controlled trial comparing early ultrasound-guided intervention against standard care would require at least 1300 fistulas and would achieve only minimal patient benefit.

Trial Registration

This trial is registered as ISRCTN36033877 and ISRCTN17399438.

Funding

This award was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme (NIHR award ref: NIHR135572) and is published in full in Health Technology Assessment; Vol. 28, No. 24. See the NIHR Funding and Awards website for further award information.

Hemodialysis nurses' knowledge, attitude, and practices in managing vascular access: A cross-sectional study in Saudi Arabia

Hemodialysis continues to be the primary approach for renal replacement therapy. Vascular access (VA), particularly arteriovenous fistula or arteriovenous graft, is the preferred technique for establishing hemodialysis access due to its lower risk of infection and central venous stenosis compared to catheters. The aim of this cross-sectional investigation was to examine hemodialysis nurses' knowledge, confidence, and practices in managing VA in Saudi Arabia. This is an online cross-sectional survey study that was conducted in Saudi Arabia between June and August 2023. This study utilized a previously validated questionnaire. Examined dialysis nurses' knowledge, attitude, practice, and self-efficacy pertaining to VA cannulation and evaluation. Binary logistic regression analysis was used to identify predictors of better knowledge of dialysis VA. A total of 197 participants were involved in this study. Around one-third of the study participants (37.0%) reported that they have received specialized training in managing VA. Participants agreement (answered agree or strongly agree) on statements that examined attitudes toward dialysis VA cannulation and management was high and ranged between 75.0% and 93.0%. The majority of participants (97.5%) reported that they perform this assessment. Most nurses (65%) preferred the rope-ladder technique. Participants agreement on statements that examined self-efficacy on dialysis VA cannulation and management was high and ranged between 72.1% and 98.0%. The most commonly agreed upon statement was that "they have confident in performing hemodialysis access (arteriovenous fistula and arteriovenous graft) assessment before cannulation." With 98.0% (answered agree and strongly agree). The mean knowledge score for our study sample was 6.4 (SD: 2.0) out of 12 (53.3%); which reflects marginal-level of knowledge on dialysis VA. Binary logistic regression analysis identified that nurses who have undergraduate degree are 92% more likely to be knowledgeable on dialysis VA compared to others (P < .05). Concerning VA, the level of knowledge among hemodialysis nurses working in Saudi Arabia was inadequate. Nurses who hold an undergraduate degree are presumed to have a more extensive understanding of dialysis VA. Further education programs are necessary for HD nurses to enhance their knowledge of VA, thereby optimizing their professional practices and enhancing the outcomes for their patients.

Hemodynamics in AVF over time: A protective role of vascular remodeling toward flow stabilization

The mechanisms underlying vascular stenosis formation in the arteriovenous fistula (AVF) for hemodialysis (HD) remain mostly unknown. Several computational fluid dynamics (CFD) studies have suggested a potential role for unsteady flow in inducing intimal hyperplasia and AVF stenosis, but the majority of these observations have been limited to a single time point after surgical creation. The aim of the present study was to investigate the relation between hemodynamic conditions and AVF vascular remodeling through a CFD longitudinal study. Non contrast-enhanced MR images and Doppler Ultrasound (US) examinations were acquired at 3 days, 40 days, 6 months, 1 year, and 1.5 years after surgery in a 72-year male referred for native radio-cephalic AVF. Three-dimensional AVF models were generated and high fidelity CFD simulations were performed using pimpleFoam, setting patient-specific boundary conditions derived from US. Morphological and hemodynamic changes over time were then analyzed. Analysis of vessel morphology and hemodynamics during follow-up showed that the AVF had a successful maturation process, characterized by a massive arterial and venous dilatation within the 6 months after surgery, a corresponding increase in blood flow volume and important flow instabilities. Between 6 months and 1 year, a stenosis developed in the juxta-anastomotic vein and caused AVF failure at 1.5 years. The development of stenosis was paralleled by the regularization of blood flow velocity pattern and consequent decrease in the near-wall disturbed flow metrics. These results suggest that development of intimal hyperplasia and vessel stenosis, triggered by unsteady flow, could be the result of vascular inward remodeling toward regularization of turbulent-like flow.

Reassessing the utility of access recirculation and Kt/V for the prediction of arteriovenous fistula failure using online clearance monitoring: the SHUNT STUDY

BACKGROUND

The arteriovenous fistula (AVF) is prone to thrombosis which can be avoided by use of monitoring and surveillance programmes. Although surveillance imaging techniques have been shown to be more sensitive and specific than clinical monitoring during dialysis, monitoring may have significant advantages in terms of cost and time saving. In this study we evaluate the yield of two monitoring techniques [blood temperature monitoring (BTM) access recirculation (AR) and Kt/V via online-clearance-monitoring (OCM)].

METHODS

In this single-centre prospective observational study, 101 patients were followed-up for one year. The primary outcome measure was a composite of AVF failure. OCM-Kt/V and BTM-AR were recorded at every dialysis session.

RESULTS

Of all baseline characteristics only a prior history of percutaneous transluminal angioplasty (PTA) to the AVF conferred a significant change in AVF survival (failure events/100 pt years with prior PTA vs. without = 64.0 vs. 17.3, log-rank p = 0.0014; unadjusted hazard ratio (HR) 3.74 (95% CI 1.56-8.94) p = 0.003). Participants with baseline AR < 10% vs. > 15% had poorer AVF survival (p = 0.0002) and HR for baseline AR 10-15% group vs. AR > 15% group = 4.5 (95% CI 1.55-13.05). There was no combination of change in (Δ) AR, ΔKt/V or its presence over any number of dialysis sessions that provided an acceptable combination of sensitivity and specificity or discrimination for AVF failure.

CONCLUSIONS

BTM-AR and OCM-Kt/V are specific but insufficiently sensitive tools for the prediction of AVF failure. BTM-AR and OCM-Kt/V use at every dialysis session appears to add little to the traditional, infrequent use of these evaluations.

Development and Validation of a Machine Learning Model Predicting Arteriovenous Fistula Failure in a Large Network of Dialysis Clinics

Background: Vascular access surveillance of dialysis patients is a challenging task for clinicians. We derived and validated an arteriovenous fistula failure model (AVF-FM) based on machine learning. Methods: The AVF-FM is an XG-Boost algorithm aimed at predicting AVF failure within three months among in-centre dialysis patients. The model was trained in the derivation set (70% of initial cohort) by exploiting the information routinely collected in the Nephrocare European Clinical Database (EuCliD^®). Model performance was tested by concordance statistic and calibration charts in the remaining 30% of records. Features importance was computed using the SHAP method. Results: We included 13,369 patients, overall. The Area Under the ROC Curve (AUC-ROC) of AVF-FM was 0.80 (95% CI 0.79–0.81). Model calibration showed excellent representation of observed failure risk. Variables associated with the greatest impact on risk estimates were previous history of AVF complications, followed by access recirculation and other functional parameters including metrics describing temporal pattern of dialysis dose, blood flow, dynamic venous and arterial pressures. Conclusions: The AVF-FM achieved good discrimination and calibration properties by combining routinely collected clinical and sensor data that require no additional effort by healthcare staff. Therefore, it can potentially enable risk-based personalization of AVF surveillance strategies.

Results of the implementation of a triage system of vascular access performance in haemodialysis patients: experience of a single dialysis centre

BACKGROUND

Routine systems for monitoring vascular access (VA) performance are lacking. We developed a vascular access triage system to evaluate the monthly performance of the access, developed a specific score and assessed the association between score improvement and clinical outcomes.

METHODS

Vascular access was triaged (Green, Yellow or Red) according to a score generated by dialytic and clinical parameters in all patients who, from 1/1/2014 to 31/03/2014, had been receiving haemodialysis treatment for at least 3 consecutive months in our Unit and who were then followed up for 4 years.

RESULTS

We enrolled 130 patients, 78 with arteriovenous fistula (AVF) and 52 with tunnelled central venous catheter (CVC). During a median of 29 ± 11 months of follow up (range 3-46 months), 28 deaths and 303 hospitalizations (lasting 16 ± 30 days) were recorded. Vascular access triage scores improved over time (2014 vs 2015 vs 2016 vs 2017) in the population with an AVF (Green from 25% to 58% to 77% to 79%, Yellow from 65% to 39% to 18% to 20% and Red from 10% to 3% to 5% to 1%, respectively; χ² p < 0.01) but not in the CVC group (Green 58% to 57% to 80% to 92%; Yellow 37% to 36% to 20% to 8%; Red 5% to 7% to 0%; χ² = n.s). Blood pressure and dialysis efficiency improved in the population as a whole and in the two subgroups (AVF and CVC) separately. AVF and CVC populations, stratified separately according to median VA score, had different event-free follow-up, which was higher (p = 0.0085) in patients with lower scores in the AVF population only.

CONCLUSION

The vascular access monitoring system improved the vascular access score as well as some clinical and dialytic parameters. Green triage in AVF patients identify those with better outcomes, in agreement with the commonly recognized clinical value of a well-functioning vascular access.

The role of Doppler ultrasonography in vascular access surveillance-controversies continue

Chronic hemodialysis therapy required regular entry into the patient’s blood stream with adequate flow. The use of arteriovenous fistulas and grafts is linked with lower morbidity and mortality than the use of catheters. However, these types of accesses are frequently affected by stenoses, which decrease the flow and lead to both inadequate dialysis and access thrombosis. The idea of duplex Doppler ultrasound surveillance is based on the presumption that in-time diagnosis of an asymptomatic significant stenosis and its treatment prolongs access patency. Details of performed trials are conflicting, and current guidelines do not support ultrasound surveillance. This review article summarizes the trials performed and focuses on the reasons of conflicting results. We stress the need of precise standardized criteria of significant access stenosis and the weakness of the metaanalyses performed.

Analysis of access flow using duplex ultrasonography and the ultrasound dilutional method

BACKGROUND

This study aimed to evaluate the correlation between duplex ultrasonography (DUS) and ultrasound dilution (UD) measurement's results and determine the factors affecting the correlation of the measured values among other clinical factors in patients.

METHODS

This cross-sectional study was conducted from April 2020 to May 2020 and included 60 patients who visited our dialysis centre. The flow of the fistula was measured in the proximal brachial artery using DUS. While dialysis was performed on the same day, the access flow was measured using the UD method. The correlation and agreement between the access flows acquired by each measurement method were analysed. Similarly, the correlation was analysed by classifying the groups based on the predisposing factor, and statistically significant factors were observed through comparison.

RESULTS

Both measurements showed a moderate positive correlation (r = 0.60, p < 0.01). The bias (mean of UD-DUS) between the two measurements was about 230 mL/min. When the measurement site of DUS was near the inflow artery and in the same anatomical section, a strong correlation with the measurement value of UD was observed (brachial based fistula: r = 0.85, radial based fistula: r = 0.87). Similarly, for patients without diabetes and those who regularly underwent access surveillance for the dialysis route, strong correlations were observed between the two measurements (r = 0.79 and r = 0.88).

CONCLUSIONS

Several factors can influence the correlation between UD and DUS. The findings showed a high correlation for DUS measurement sites within the same anatomical section as the inflow artery, patients without diabetes, and patients undergoing periodic surveillance.

A Multicenter Randomized Clinical Trial of Hemodialysis Access Blood Flow Surveillance Compared to Standard of Care: The Hemodialysis Access Surveillance Evaluation (HASE) Study

Introduction

Arteriovenous (AV) access thrombosis remains 1 of the most troubling AV access–related complications affecting hemodialysis patients. It necessitates an urgent and occasionally complicated thrombectomy procedure and increases the risk of AV access loss. AV access stenosis is found in the majority of thrombosed AV accesses. The routine use of AV access surveillance for the early detection and management of stenosis to reduce the thrombosis rate remains controversial.

Methods

We have conducted a multicenter, prospective, randomized clinical trial comparing the standard of care coupled with ultrasound dilution technique (UDT) flow measurement monthly surveillance with the standard of care alone.

Results

We prospectively randomized 436 patients with end-stage renal disease on hemodialysis with arteriovenous fistula (AVF) or arteriovenous graft (AVG) using cluster (shift) randomization to surveillance and control groups. There were no significant differences in the baseline demographic data between the 2 groups, except for ethnicity (P = 0.017). Patients were followed on average for 15.2 months. There were significantly less per-patient thrombotic events (Poisson rate) in the surveillance group (0.12/patient) compared with the control group (0.23/patient) (P = 0.012). There was no statistically significant difference in the total number of procedures between the 2 groups, irrespective of whether thrombectomy procedures were included or excluded, and no statistically significant differences in the rate of or time to the first thrombotic event or the number of catheters placed due to thrombosis.

Conclusion

The use of UDT flow measurement monthly AV access surveillance in this multicenter randomized controlled trial reduced the per-patient thrombotic events without significantly increasing the total number of angiographic procedures. Even though there is a trend, surveillance did not reduce the first thrombotic event rate.

Predicting arterio-venous fistula failure by urea-method derived access blood flow in chronic hemodialysis patients

BACKGROUND

Dialysis access is an essential part of hemodialysis. Determining the access blood flow (Qa) can help predict arterio-venous fistula thrombosis. Qa determination by the urea method, which was previously described in the past is simple and is available in most of the dialysis units but was not be able to predict arterio-venous fistula thrombosis.

AIM

To compare the efficacy of Qa determination by the urea method and by ultrasound dilution methods in predicting arterio-venous fistula failure.

METHODS

Qa was measured by urea method and by ultrasound dilution simultaneously, every 3 months for a period of 1 year, in stable chronic hemodialysis patients with arterio-venous fistula. Arterio-venous fistula failure determined by clinical parameters and confirmed by Doppler ultrasound before sending the patient for interventional angioplasty.

RESULTS

This study enrolled a total of 16 patients, with 63% being male, 75% with lower-arm arterio-venous fistula and around 43% with previously done angioplasty. 59-Qa measurements were done, and 6 patients underwent angioplasty (one patient for severe upper limb edema, one for access thrombosis, and four for access dysfunction). Qa determination by the urea method had non-significantly lower Qa, (745 mL/min (interquartile range: 509-1143) and 779 mL/min (interquartile range: 530-1160), (p = 0.58)) and high correlation (r = 0.83, p < 0.001) to Qa by ultrasound dilution. The cut-off criteria with its sensitivity and specificity in predicting the access failure were 440 mL/min, 66.67%, and 96.15% for Qa determination by the urea and 400 mL/min, 66.67% and 90.38% for Qa by ultrasound dilution, respectively, with no difference in the area under the receiver operating characteristic curve.

CONCLUSION

Measurement of Qa determination by the urea method is well correlated with Qa by ultrasound dilution and can be used to predict vascular access failure.

Flexible, Skin Coupled Microphone Array for Point of Care Vascular Access Monitoring

Point-of-care screening for hemodialysis vascular access dysfunction requires tools that are objective and efficient. Listening for bruits during physical exam is a subjective examination which can detect stenosis (vascular narrowing) when properly performed. Phonoangiograms (PAGs)-mathematical analysis of bruits-increases the objectivity and sensitivity and permits quantification of stenosis location and degree of stenosis (DOS). This work describes a flexible and body-conformal multi-channel sensor and associated signal processing methods for automated DOS characterization of vascular access. The sensor used an array of thin-film PVDF microphones integrated on polyimide to record bruits at multiple sites along a vascular access. Nonlinear signal processing was used to extract spectral features, and cardiac cycle segmentation was used to improve sensitivity. PAG signal processing algorithms to detect stenosis location and severity are also presented. Experimental results using microphone arrays on a vascular access phantom demonstrated that stenotic lesions were detected within 1 cm of the actual location and graded to three levels (mild, moderate, or severe). Additional PAG features were also used to define a simple binary classifier aimed at patients with failing vascular accesses. The classifier achieved 90% accuracy, 92% specificity, and 91% sensitivity at detecting stenosis greater than 50%. These results suggest that point-of-care screening using microphone arrays can identify at-risk patients using automated signal analysis.