Accuracy of physical examination and intra-access pressure in the detection of stenosis in hemodialysis arteriovenous fistula

Comparison of clinical examination, doppler and fistulogram for arterio-venous fistula surveillance in detecting secondary failure

BACKGROUND

Arteriovenous Fistula (AVF) surveillance is required to detect early dysfunction (thrombosis, stenosis) and its timely correction prolongs access-patency. Clinical examination (CE) and doppler have been used as screening/surveillance of AVF, for early detection of AVF dysfunction. Since there was inadequate evidence for KDOQI to make recommendations on AVF surveillance and on secondary failure rate. We compared CE, doppler and fistulogram as surveillance modalities in detecting a secondary failure in matured AVF.

METHODOLOGY

This prospective-observational, single-center study, was done between December 2019-April 2021. CKD stage 5 patients on dialysis/Not-on-dialysis with matured AVF were included at third month. CE, doppler (blood flow, vein diameter, depth), and fistulogram were done at third and sixth month. Secondary failure was assessed at sixth month classifying AVF to patent/functional and failed group. Diagnostic tests were performed by comparing three methods considering fistulogram as gold-standard. Residual urine output is also monitored to look for any contrast induced residual renal function loss.

RESULTS

Of total 407 created AVF, 98 (24%) had primary failure. Twenty-five (6%) had surgical complications including unsuccessful AVF and aneurysm/rupture, 156 lost follow-up at third month, 104 consented patients were enrolled, 16 lost to follow-up subsequently, and 88 patients' data were analyzed at the end. At the sixth month, 76(86.4%) had patent AVF, 8 (9.1%) had secondary failure (Thrombosis-4, Central Venous Stenosis-4), and 4 (4.1%) patients expired. Considering fistulogram as a diagnostic standard, CE showed 87.5% sensitivity, and 93.4% specificity (cohen's kappa value of 0.66). Doppler had sensitivity and specificity of 87% and 96% respectively (cohen's kappa value of 0.75), Combination of clinical examination with doppler showed sensitivity and specificity of 100% and 89% respectively.

CONCLUSION

Although the secondary AVF failure rate is less than the primary, CE is an important and valuable tool in the diagnosis and surveillance of AVF in detecting its dysfunction. Moreover, CE with doppler can be used as a surveillance protocol that can detect early AVF dysfunction at par with Fistulogram.

A review of the current recommendations and practices for hemodialysis access monitoring and maintenance procedures

The growing number of prevalent arteriovenous (AV) accesses has been associated with an increase in the incidence of procedures being performed to maintain patency. To reduce the rate of unnecessary procedures, the 2019 Kidney Disease Outcome Quality Initiative guidelines addended the AV access surveillance recommendations, which includes clinical monitoring and assessment of dialysis adequacy alone. Abnormal clinical findings would necessitate follow-up angiography with or without confirmatory duplex ultrasound. Due to poor patency, increased surveillance schedules have been proposed to identify stenosis early and potentially prevent acute thrombotic events and AV access failure. In this review, we outlined current AV access monitoring and maintenance procedure recommendations, as described by the Centers for Medicare and Medicaid Services and 2019 Kidney Disease Outcome Quality Initiative guidelines. In addition, we highlight the findings of recently published randomized controlled trials that have examined increased surveillance schedules.

Evaluation of arteriovenous fistula for hemodialysis with a new generation digital stethoscope: a pilot study

BACKGROUND AND AIMS

The management of complications of arteriovenous fistula (AVF) for hemodialysis, principally stenosis, remains a major challenge for clinicians with a substantial impact on health resources. Stenosis not infrequently preludes to thrombotic events with the loss of AVF functionality. A functioning AVF, when listened by a stethoscope, has a continuous systolic-diastolic low-frequency murmur, while with stenosis, the frequency of the murmur increases and the duration of diastolic component decreases, disappearing in severe stenosis. These evidences are strictly subjective and dependent from operator skill and experience. New generation digital stethoscopes are able to record sound and subsequently dedicated software allows to extract quantitative variables that characterize the sound in an absolutely objective and repeatable way. The aim of our study was to analyze with an appropriate software sounds from AVFs taken by a commercial digital stethoscope and to investigate the potentiality to develop an objective way to detect stenosis.

METHODS

Between September 2022 and January 2023, 64 chronic hemodialysis (HD) patients were screened by two blinded experienced examiners for recognized criteria for stenosis by Doppler ultrasound (DUS) and, consequently, the sound coming from the AVFs using a 3 M™ Littmann® CORE Digital Stethoscope 8570 in standardized sites was recorded. The sound waves were transformed into quantitative variables (amplitude and frequency) using a sound analysis software. The practical usefulness of the core digital stethoscope for a quick identification of an AVF stenosis was further evaluated through a pragmatic trial. Eight young nephrologist trainees underwent a simple auscultatory training consisting of two sessions of sound auscultation focusing two times on a "normal" AVF sound by placing the digital stethoscope on a convenience site of a functional AVF.

RESULTS

In 48 patients eligible, all sound components displayed, alone, a remarkable diagnostic capacity. More in detail, the AUC of the average power was 0.872 [95% CI 0.729-0.951], while that of the mean normalized frequency was 0.822 [95% 0.656-0.930]. From a total of 32 auscultations (eight different block sequences, each one comprising four auscultations), the young clinicians were able to identify the correct sound (stenosis/normal AVF) in 25 cases, corresponding to an overall accuracy of 78.12% (95% CI 60.03-90.72%).

CONCLUSIONS

The analysis of sound waves by a digital stethoscope permitted us to distinguish between stenotic and no stenotic AVFs. The standardization of this technique and the introducing of data in a deep learning algorithm could allow an objective and fast method for a frequent monitoring of AVF.

Association of risk stratification score with dialysis vascular access stenosis

BACKGROUNDS

Clinical monitoring is the recommended standard for identifying dialysis access dysfunction; however, clinical monitoring requires skill and training, which is challenging for understaffed clinics and overburdened healthcare personnel. A vascular access risk stratification score was recently proposed to assist in detecting dialysis access dysfunction.

PURPOSE

Our objective was to evaluate the utility of using vascular access risk scores to assess venous stenosis in hemodialysis vascular accesses.

METHODS

We prospectively enrolled adult patients who were receiving hemodialysis through an arteriovenous access and who had a risk score ⩽3 (low-risk) or ⩾8 (high-risk). We compared the occurrence of access stenosis (>50% on ultrasonography or angiography) between low-risk and high-risk groups and assessed clinical monitoring results for each group.

RESULTS

Of the 38 patients analyzed (18 low-risk; 20 high-risk), 16 (42%) had significant stenosis. Clinical monitoring results were positive in 39% of the low-risk and 60% of the high-risk group (p = 0.19). The high-risk group had significantly higher occurrence of stenosis than the low-risk group (65% vs 17%; p = 0.003). Sensitivity and specificity of a high score for identifying stenosis were 81% and 68%, respectively. The positive predictive value of a high-risk score was 65%, and the negative predictive value was 80%. Only 11 (58%) of 19 subjects with positive clinical monitoring had significant stenosis. In a multivariable model, the high-risk group had seven-fold higher odds of stenosis than the low-risk group (aOR = 7.38; 95% CI, 1.44-37.82; p = 0.02). Positive clinical monitoring results and previous stenotic history were not associated with stenosis. Every unit increase in the score was associated with 34% higher odds of stenosis (aOR = 1.34; 95% CI, 1.05-1.70; p = 0.02).

CONCLUSIONS

A calculated risk score may help predict the development of hemodialysis vascular access stenosis and may provide a simple and reliable objective measure for risk stratification.

Guidelines on vascular access for hemodialysis from the Brazilian Society of Angiology and Vascular Surgery

Chronic kidney disease is a worldwide public health problem, and end-stage renal disease requires dialysis. Most patients requiring renal replacement therapy have to undergo hemodialysis. Therefore, vascular access is extremely important for the dialysis population, directly affecting the quality of life and the morbidity and mortality of this patient population. Since making, managing and salvaging of vascular accesses falls within the purview of the vascular surgeon, developing guideline to help specialists better manage vascular accesses for hemodialysis if of great importance. Thus, the objective of this guideline is to present a set of recommendations to guide decisions involved in the referral, evaluation, choice, surveillance and management of complications of vascular accesses for hemodialysis.

Deep learning analysis of blood flow sounds to detect arteriovenous fistula stenosis

For hemodialysis patients, arteriovenous fistula (AVF) patency determines whether adequate hemofiltration can be achieved, and directly influences clinical outcomes. Here, we report the development and performance of a deep learning model for automated AVF stenosis screening based on the sound of AVF blood flow using supervised learning with data validated by ultrasound. We demonstrate the importance of contextualizing the sound with location metadata as the characteristics of the blood flow sound varies significantly along the AVF. We found the best model to be a vision transformer trained on spectrogram images. Our model can screen for stenosis at a performance level comparable to that of a nephrologist performing a physical exam, but with the advantage of being automated and scalable. In a high-volume, resource-limited clinical setting, automated AVF stenosis screening can help ensure patient safety via early detection of at-risk vascular access, streamline the dialysis workflow, and serve as a patient-facing tool to allow for at-home, self-screening.

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.

Arteriovenous Hemodialysis Access Stenosis Diagnosed by Duplex Doppler Ultrasonography: A Review

Arteriovenous fistula (AVF) is currently the hemodialysis access with the longest life expectations for the patients. However, even the AVF is at risk for many complications, especially the development of stenosis. The latter can not only lead to inadequate hemodialysis but also lead to AVF thrombosis. Duplex Doppler ultrasonography is a very precise method, in the hands of experienced professionals, for the diagnosis of AVF complications. In this review, we summarize the ultrasound diagnostic criteria of significant stenoses and their indication for procedural therapy.

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.

A Korean perspective on the 2019 Kidney Disease Outcomes Quality Initiative guidelines for vascular access: what has changed and what should be changed in practice?

The Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines are developed by the National Kidney Foundation in the United States; however, the guidelines have an impact on most international societies, including those in Korea. The KDOQI recently released the updated 2019 guidelines for vascular access based on numerous papers and controversies concerning vascular access since 2006, when the first guidelines were published. The new KDOQI guidelines have undergone significant changes compared to previous guidelines, including a change in the philosophy regarding a patient-centered approach using an end-stage kidney disease “Life-Plan.” In addition, there are newly developed or revised definitions and some key differences from previous guidelines. The process of adapting guidelines needs to be individualized to hemodialysis practice in each country, while agreeing with general principles and philosophy; therefore, we summarize changes in the updated guidelines and discuss the application and implementation of the new principles and concepts of the guidelines for vascular access care in Korea.

Vascular sound visualization system is useful for monitoring and surveillance of vascular access

BACKGROUNDS

Vascular access (VA) is a lifeline for maintenance hemodialysis patients. Monitoring and surveillance of VA, therefore, play an important role for maintaining VA patency. Surveillance needs special apparatus to estimate the VA function, while, monitoring including physical examination does not usually need such devices but highly skill-dependent and qualitative.

PURPOSE

We report the clinical utility in monitoring and surveillance of VA using a newly developed electronic stethoscope and vascular sound visualization application.

METHODS

One hundred eight patients participated in the study. The vascular sounds were collected using the electronic stethoscope, converted into digital data, sent wirelessly to a personal computer, and then calculated. The units for the calculated intensity of the vascular sound were decibel [dB]. The intensity, however, was normalized as INDEX values ranging from 0 to 99 for practical use. Correlation between INDEX and the mean flow volume (mFV) and resistance index (RI) of brachial artery measured by Doppler ultrasound sonography were examined for VA surveillance. INDEX was continually measured at each dialysis session in ten patients who underwent the angioplasty for VA monitoring.

RESULTS

INDEX significantly correlated with the mFV (coefficient of correlation value = 0.68, p < 0.001) and RI (coefficient of correlation value = -0.51, p < 0.001) of brachial artery. Using the calculated cut-off values, the accuracy of INDEX for the diagnosis of AVF dysfunction ranged from 66% to 82%. INDEX attained the peak just after the angioplasty of culprit lesions and gradually decreased from one patient to another.

CONCLUSION

These results suggest that vascular sound visualization system can be useful in VA monitoring and surveillance for detecting and predicting the access stenosis.

Utility of Blood Flow/Resistance Index Ratio (Qx) as a Marker of Stenosis and Future Thrombotic Events in Native Arteriovenous Fistulas

Objective: The resistance index (RI) and the blood flow volume (Q_a) are the most used Doppler ultrasound (DUS) parameters to identify the presence of stenosis in arteriovenous fistula (AVF). However, the reliability of these indexes is now matter of concern, particularly in predicting subsequent thrombosis. In this study, we aimed at testing the diagnostic capacity of the Q_a/RI ratio (Q_x) for the early identification of AVF stenosis and for thrombosis risk stratification.

Methods: From a multicentre source population of 336 HD patients, we identified 119 patients presenting at least one “alarm sign” for clinical suspicious of stenosis. Patients were therefore categorized by DUS as stenotic (n = 60) or not-stenotic (n = 59) and prospectively followed. Q_a, RI, and Q_X, together with various clinical and laboratory parameters, were recorded.

Results: Q_a and Q_x were significantly higher while RI was significantly lower in non-stenotic vs. stenotic patients (p < 0.001 for each comparison). At ROC analyses, Q_x had the best discriminatory power in identifying the presence of stenosis as compared to Q_a and RI (AUCs 0.976 vs. 0.953 and 0.804; p = 0.037 and p < 0.0001, respectively). During follow-up, we registered 30 thrombotic events with an incidence rate of 12.65 (95% CI 8.54–18.06) per 100 patients/year. In Cox-regression proportional hazard models, Q_x showed a better capacity to predict thrombosis occurrence as compared to Q_a (difference between c-indexes: 0.012; 95% CI 0.004–0.01).

Conclusions: In chronic haemodialysis patients, Q_x might represent a more reliable and valid indicator for the early identification of stenotic AVFs and for predicting the risk of following thrombosis.

Construction and validation of a scale for assessing arteriovenous fistulas

Aim:

This methodological study was conducted to develop a reliable instrument for the assessment of the arteriovenous fistula in patients under hemodialysis therapy. The purpose of the scale is to evaluate risk of developing arteriovenous fistula complications in patients receiving hemodialysis treatment.

Methods:

An item pool was created in accordance with data obtained from our literature review and expert opinions. Validity of the scale was evaluated using construct and content validity analyses. Cronbach’s alpha coefficient, test–retest, and split-half reliability were used to assess reliability.

Results:

The final 3-point Likert-type Arteriovenous Fistula Assessment Scale developed in this study consists of 18 items in three subdimensions: arteriovenous fistula flow, stenosis and ischemia, and needle entry site. The scale-level Content Validity Ratio was 0.90. Explanatory factor analysis revealed a three-factor structure with factor loadings of 0.622–0.800, 0.361–0.891, and 0.431–0.954, respectively, explaining 55.51% of the total variance. The Cronbach’s alpha values for the subdimensions were 0.72, 0.71, and 0.83, respectively, and 0.82 for the scale overall.

Conclusion:

The Arteriovenous Fistula Assessment Scale is a valid and reliable instrument that can be used to monitor arteriovenous fistulas in hemodialysis patients.

KDOQI Clinical Practice Guideline for Vascular Access: 2019 Update

The National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) has provided evidence-based guidelines for hemodialysis vascular access since 1996. Since the last update in 2006, there has been a great accumulation of new evidence and sophistication in the guidelines process. The 2019 update to the KDOQI Clinical Practice Guideline for Vascular Access is a comprehensive document intended to assist multidisciplinary practitioners care for chronic kidney disease patients and their vascular access. New topics include the end-stage kidney disease "Life-Plan" and related concepts, guidance on vascular access choice, new targets for arteriovenous access (fistulas and grafts) and central venous catheters, management of specific complications, and renewed approaches to some older topics. Appraisal of the quality of the evidence was independently conducted by using a Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach, and interpretation and application followed the GRADE Evidence to Decision frameworks. As applicable, each guideline statement is accompanied by rationale/background information, a detailed justification, monitoring and evaluation guidance, implementation considerations, special discussions, and recommendations for future research.

Con: Vascular access surveillance in mature fistulas: is it worthwhile?

The risks and benefits of hemodialysis arteriovenous (AV) access surveillance have been debated since the introduction of AV access surveillance techniques. The debate is fuelled by the lack of robust, high-quality evidence with consistent and comparable patient-important outcomes. Additionally, there is a lack of clarity regarding the diagnostic cut points for AV access stenosis using the various surveillance techniques, questions about the appropriateness of the ‘knee-jerk’ response to intervention on a stenosis >50% regardless of the presence of clinical indicators and whether the intervention results in desired patient-important outcomes. The physiology of the AV access is complex considering the different hemodynamics within an AV fistula, which vary by time of dialysis, location, size of vessels and location of the stenosis. The current evidence suggests that the use of AV access surveillance in an AV fistula does detect more stenosis compared with clinical monitoring alone and leads to an increased number of procedures. It remains uncertain if that leads to improved patient-important outcomes such as prolonged AV fistula patency. Vascular access is an essential component of hemodialysis and further study is needed to clarify this long-standing debate. There needs to be better distinction between the strategies of vascular access surveillance, clinical monitoring with clinical indictors and preemptive intervention and their respective impacts on patient-important outcomes. Randomized controlled studies must be conducted with defined indications for intervention, reproducible methods of intervention and clinically important AV fistula and patient outcomes. The current guidelines need to be challenged and revised to permit these necessary studies to be done.

Spanish Clinical Guidelines on Vascular Access for Haemodialysis

Vascular access for haemodialysis is key in renal patients both due to its associated morbidity and mortality and due to its impact on quality of life. The process, from the creation and maintenance of vascular access to the treatment of its complications, represents a challenge when it comes to decision-making, due to the complexity of the existing disease and the diversity of the specialities involved. With a view to finding a common approach, the Spanish Multidisciplinary Group on Vascular Access (GEMAV), which includes experts from the five scientific societies involved (nephrology [S.E.N.], vascular surgery [SEACV], vascular and interventional radiology [SERAM-SERVEI], infectious diseases [SEIMC] and nephrology nursing [SEDEN]), along with the methodological support of the Cochrane Center, has updated the Guidelines on Vascular Access for Haemodialysis, published in 2005. These guidelines maintain a similar structure, in that they review the evidence without compromising the educational aspects. However, on one hand, they provide an update to methodology development following the guidelines of the GRADE system in order to translate this systematic review of evidence into recommendations that facilitate decision-making in routine clinical practice, and, on the other hand, the guidelines establish quality indicators which make it possible to monitor the quality of healthcare.

Physical examination of the hemodialysis arteriovenous fistula to detect early dysfunction

The maintenance of vascular access patency for end-stage renal disease patients on hemodialysis is necessary for survival. Many nephrologists, nurse practitioners, and nurses have limited experience with the physical examination of the arteriovenous fistula. In this review, we define key terms used in the assessment of an arteriovenous fistula. We discuss the arteriovenous fistula physical exam, including details of inspection, palpation, and auscultation. Using these concepts, we review the abnormal findings that can assist practitioners in determining the location of a stenosis. We review the existing literature that validates physical exam findings with gold standard tests such as ultrasound and angiography. Finally, we review data supporting the value of training physicians and nurses in arteriovenous fistula physical examination.

Structured physical assessment of arteriovenous fistulae in haemodialysis access surveillance: A missed opportunity?

Introduction:

Arteriovenous fistulae remain the gold standard of vascular access in haemodialysis. There is currently no consensus on standardised methods of monitoring arteriovenous fistulae. Assessment techniques and practice remain widely variable. The purpose of this study is to determine whether existing evidence supports physical assessment as an effective tool and a good predictor of arteriovenous fistulae dysfunction to allow for timely intervention and improve outcomes.

Methods:

A literature search was performed using CINAHL, PubMed, Medline and BNI databases and relevant search terms. Studies included were peer-reviewed, published after 2008, in English and related to arteriovenous fistulae only. Six key papers were identified and critically analysed for validity and relevance, in relation to outcomes, assessor experience, training duration and nurses’ ability to perform physical assessment.

Results:

Physical assessment has been shown to be effective in detecting arteriovenous fistulae dysfunction and comparable to technology-based surveillance. Physical assessment techniques generally adopt a ‘look, listen and feel’ approach to identify arteriovenous fistulae dysfunction that includes stenosis, thrombosis, ischaemia and infections. Physical assessment is a skill that can be taught with studies showing that skill-specific training is more effective than experience alone. Cost-effectiveness analysis is lacking.

Conclusion:

The analysis of evidence demonstrates that physical assessment of arteriovenous fistulae is an effective method of detecting arteriovenous fistulae dysfunction and is a skill that can be taught. A structured physical assessment and its implementation may be significant in routine care, but research into the most effective physical assessment techniques and its impact on clinical practice in haemodialysis is required.

Fistulography of a Patent Hemodialysis Access: When Not to Treat and Implications for Establishing a Nontreatment Rate

PURPOSE

To establish a rate of nonintervention in patients referred for hemodialysis access fistulography and to report clinical and fistulographic variables associated with nonintervention.

MATERIALS AND METHODS

Encounters for fistulography were reviewed from 2001 to 2016 to determine annual rates of nontreatment over 15 years. Next, an access database was used to retrospectively identify patients undergoing fistulography from 2010 to 2016. Patients who underwent fistulography without intervention (angioplasty or stent placement) served as the nontreatment group (NTG; n = 76). Patients who underwent fistulography with intervention served as the control group (CG; n = 77). Patients with thrombosed accesses were excluded. Clinical indications for intervention and physical examination findings were correlated with fistulography. Need for subsequent percutaneous intervention was recorded.

RESULTS

Annual nontreatment rates ranged from 3% to 14% (median, 10%). Preprocedure thrill was encountered in 45 patients in the NTG (59%) vs 6 in the CG (7.8%; P < .01). Aneurysm as indication for fistulography was more common in the NTG than the CG (19 [25%] vs 4 [5%]; P < .01). The NTG had a higher proportion of aneurysms noted on fistulography as well (38 [50%] vs 19 [25%]; P < .01). The CG had a higher proportion of patients needing subsequent percutaneous intervention vs the NTG (73 [96%] vs 38 [50%]; P < .001).

CONCLUSIONS

A suggested nonintervention rate for hemodialysis access fistulography is 10%. Patients in the NTG were more likely to have a thrill on physical examination or to present with aneurysms as the clinical indicator. NTG patients were less likely to require subsequent percutaneous intervention.

Performance of physical examination versus ultrasonography to detect stenosis in haemodialysis arteriovenous fistula

Purpose

The overall purpose of this study is to compare the accuracy of physical examination (PE) versus ultrasonography (US) in people with arteriovenous fistula (AVF).

Methods

This is a cross-sectional study with a total of 99 patients attended by the vascular radiology unit for AVF evaluation during January - March 2015. PE and ultrasonography were blinded performed by different radiologists. For complete and individual signs of PE, sensitivity, specificity, predictive positive (PPV) and negative (PNV) value, likelihood ratios (LR) and Cohen's κ value were measured.

Results

According to ultrasonography, the presence of stenosis was identified in 57 (58%) patients, and 61 (62%) by PE. The accuracy of PE for the diagnosis of AVF was sensitivity 82%, specificity 67%, PPV 77%, NPV 74%, LR 2.74 and 0.26. There was a moderate agreement beyond chance between PE and ultrasonography (κ = 0.5).

Conclusions

PE has shown a moderate accuracy to detect stenosis. With non-ultrasonography availability Haemodialysis Units can get benefit to optimize VA survival and professionals should improve its basic skills.

Estimation of arterio-venous access blood flow in hemodialysis patients using video image processing technique

Assessment of arterio-venous fistula (AVF) blood flow (ABF) is vital in hemodialysis (HD) patients. Currently, no non-invasive and contact-free technique is available to accurately measure ABF in routine clinical practice. In this study, we developed a novel approach using video image processing (VIP) to measure the change in optic flow in the skin. We the tested the hypothesis that the change in optical flow, expressed as the change in pixels between consecutive frames, is related to ABF. We recorded AVF videos in 40 HD patients using a digital camera and processed them by VIP technique. We then compared the actual ABF as measured by routine online clearance (ABFOLC) and the amplitude (AMP) of optical flow. Technical and procedural errors rendered VIP invalid in 13 patients. In the remaining 27 patients the optical flow AMP was significantly lower in patients with low (<;900 ml/min) ABFOLC compared to patients with normal (≥900 ml/min) ABFOLC (AMP 3.4±1*10³ vs 5.2±1.4 *10³ [pixels], p<;0.01). In these 27 patients AMP correlated with ABFOLC (R²=0.71, p<;0.0001). While more extensive research is necessary, these preliminary results indicate the potential usefulness of the VIP technique to identify low ABF.

Combined functional and anatomical diagnostic endpoints for assessing arteriovenous fistula dysfunction

Failure of arteriovenous fistulas (AVF) to mature and thrombosis in matured fistulas have been the major causes of morbidity and mortality in hemodialysis patients. Stenosis, which occurs due to adverse remodeling in AVFs, is one of the major underlying factors under both scenarios. Early diagnosis of a stenosis in an AVF can provide an opportunity to intervene in a timely manner for either assisting the maturation process or avoiding the thrombosis. The goal of surveillance strategies was to supplement the clinical evaluation (i.e., physical examination) of the AVF for better and earlier diagnosis of a developing stenosis. Surveillance strategies were mainly based on measurement of functional hemodynamic endpoints, including blood flow (Q_a) to the vascular access and venous access pressure (VAP). As the changes in arterial pressure (MAP) affects the level of VAP, the ratio of VAP to MAP (VAPR = VAP/MAP) was used for diagnosis. A Q_a < 400-500 mL/min or a VAPR > 0.55 is considered sign of significant stenosis, which requires immediate intervention. However, due to the complex nature of AVFs, the surveillance strategies have failed to consistently detect stenosis under different scenarios. VAPR has been primarily developed to detect outflow stenosis in arteriovenous grafts, and it hasn’t been successful in accurate diagnosis of outflow lesions in AVFs. Similarly, AVFs can maintain relatively high blood flow despite the presence of a significant outflow stenosis and thus, Q_a has been found to be a better predictor of only inflow lesions. Similar shortcomings have been reported in the detection of functional severity of coronary stenosis using diagnostic endpoints that were based on either flow or pressure. This limitation has been associated with the fact that both pressure and flow change in the presence of a stenosis and thus, hemodynamic diagnostic endpoints that employ only one of these parameters are inherently prone to inaccuracies. Recent attempts have resulted in development of new diagnostic endpoints that can combine the effects of pressure and flow. These new hemodynamic diagnostic endpoints have shown to be better predictors of functional severity of lesions as compared to either flow or pressure based counterparts. In this review article, we discussed the advantages and limitations of current functional and anatomical diagnostic endpoints in AVFs.

Monitoring and Surveillance of Hemodialysis Vascular Access Using StenTec and Physical Exam

Hemodialysis vascular access surveillance for hemodynamically significant stenosis can be a challenge because no universal gold standard exists. The StenTec Gauge measures static intra-access peak pressure and graphically displays the ratio of this pressure to systemic systolic (peak) arterial pressure (PIA ratio). In combination with careful physical exam (PE), the StenTec Gauge is an acceptable and cost-effective way of detecting hemodynamically significant stenosis in arteriovenous fistulas (AVF) or grafts (AVG). In a selected population of 21 hemodialysis patients with mature arteriovenous access, a StenTec reading and physical examination was measured on a weekly basis. Interventional procedures for suspected access dysfunction were performed if there was a greater than 25% increase of the PIA ratio from baseline in two consecutive readings, along with correlating clinical suspicion from physical examination findings. StenTec independently had a sensitivity of 56% and a specificity of 99% in detecting clinically significant stenosis. PE alone had a sensitivity of 89% and a specificity of 100%. StenTec combined with PE had a sensitivity of 100% and a specificity of 99% for predicting hemodynamically significant stenosis. StenTec detected 4 of 10 patients who had a PIA ratio value of ≥0.5, which correlates with current National Kidney Foundation Disease Outcomes Quality Initiative (KDOQI) criteria for mean intra-access pressure ratios indicating a clinically significant outflow stenosis. PE predicted 9 of 10 patients with stenosis, and the combination of StenTec and PE predicted all 10 patients with clinically significant stenosis using the KDOQI criteria for PIA ratio. Hemodynamically significant access stenosis can be detected with excellent accuracy using both StenTec and PE measurements combined for monitoring and surveillance methods.

The rise and fall of access blood flow surveillance in arteriovenous fistulas

Vascular access blood flow (Qa) surveillance has been described as a typical false paradigm, an example of how new tests are sometimes adopted even without good-quality evidence of their benefits. This may be true for grafts, but not necessarily for arteriovenous fistulas. We reviewed the literature on Qa surveillance in fistulas to see whether it complies with the World Health Organization's criteria for screening tests. Measuring Qa has a fairly good reproducibility. Qa shows an excellent-to-good accuracy for stenosis being the only bedside screening test that achieves a very high sensitivity while retaining a fair-to-good positive predictive value for Qa thresholds of 600 ml/minute or higher associated with a >25% drop in Qa, or findings suggesting stenosis on physical examination. The accuracy of Qa in predicting thrombosis is hard to establish because of the heterogeneity of published studies, though a Qa of 300 ml/minute seems the most reliable cutoff. Qa surveillance affords a significant 2- to 3-fold reduction in the risk of thrombosis by comparison with clinical monitoring alone when Qa criteria highly sensitive to stenosis are considered, regardless of the study design (randomized controlled trials, cohort studies with concurrent or historic controls). Using highly sensitive Qa screening criteria also halves the risk of access loss, although this effect is not statistically significant. Our analysis strongly suggests that Qa surveillance is an effective method for screening mature fistulas, though further, appropriately designed studies are needed to fully elucidate its benefits and cost effectiveness.

Monitoring Dialysis Arteriovenous Fistulae: It's in our Hands

Vascular access problems are a daily occurrence in hemodialysis units. Loss of patency of the vascular access limits hemodialysis delivery and may result in underdialysis that leads to increased morbidity and mortality. Despite the known superiority of autogenous fistulae over grafts, autogenous fistulae also suffer from frequent development of stenosis and subsequent thrombosis. International guidelines recommend programmes for detection of stenosis and consequent correction in an attempt to reduce the rate of thrombosis. Physical examination of autogenous fistulae has recently been revisited as an important element in the assessment of stenotic lesions. Prospective observational studies have consistently demonstrated that physical examination performed by trained physicians is an accurate method for the diagnosis of fistula stenosis and, therefore, should be part of all surveillance protocols of the vascular access. However, to optimize hemodialysis access surveillance, hemodialysis practitioners may need to improve their skills in performing physical examination. The purpose of this article is to review the basics and drawbacks of physical examination for dialysis arteriovenous fistulae and to provide the reader with its diagnostic accuracy in the detection of arteriovenous fistula dysfunction, based on current published literature.

Diagnosis of arteriovenous fistula dysfunction

Arteriovenous fistula (AVF) dysfunction remains a major contributor to the morbidity and mortality of hemodialysis patients. The failure of a newly created AVF to mature and development of stenosis in an established AVF are two common clinical predicaments. The goal is to identify a dysfunctional AVF early enough to intervene in a timely manner to either assist with the maturation process or to prevent thrombosis. The currently available tools in our armamentarium include clinical evaluation, physical examination of the AVF, and surveillance tests. Physical examination has been recognized as a simple and cost-effective tool, but is often not implemented either because of lack of training or time constraints. Surveillance tests include measurement of access flow or pressure as a surrogate marker of AVF dysfunction. Surveillance tests often require expensive equipment, additional personnel, and are controversial. Currently, there are guidelines and recommendations to include all of these measures while evaluating an AVF. Implementing judicious use of these tools in clinical practice can facilitate early diagnosis for timely intervention in the appropriate population. Furthermore, this strategy may avoid unnecessary interventions and assist with healthcare cost containment.

Surveillance and monitoring of dialysis access

Vascular access is the lifeline of a hemodialysis patient. Currently arteriovenous fistula and graft are considered the permanent options for vascular access. Monitoring and surveillance of vascular access are an integral part of the care of hemodialysis patient. Although different techniques and methods are available for identifying access dysfunction, the scientific evidence for the optimal methodology is lacking. A small number of randomized controlled trials have been performed evaluating different surveillance techniques. We performed a study of the recent literature published in the PUBMED, to review the scientific evidence on different methodologies currently being used for surveillance and monitoring and their impact on the care of the dialysis access. The limited randomized studies especially involving fistulae and small sample size of the published studies with conflicting results highlight the need for a larger multicentered randomized study with hard clinical end points to evaluate the optimal surveillance strategy for both fistula and graft.

Vascular access surveillance: an ongoing controversy

Hemodialysis vascular access surveillance continues to be widely recommended despite ongoing controversy as to its benefit in prolonging access patency compared with clinical monitoring alone. The most common screening tests are access blood flow and dialysis venous pressure measurements. When surveillance test results cross a predetermined threshold, accesses are referred for intervention with correction of stenosis to reduce future thrombosis and prolong access survival. Current surveillance strategies have four components: (1) underlying condition; (2) screening test; (3) intervention; and (4) outcomes. However, limitations exist within each component that may prevent achieving the desired outcomes. This review discusses these limitations and their consequences. To date, randomized controlled trials have not consistently shown that surveillance improves outcomes in grafts, and there is limited evidence that surveillance reduces thrombosis without prolonging the life of native fistulae. In conclusion, current evidence does not support the concept that all accesses should undergo routine surveillance with intervention.

In search of an optimal bedside screening program for arteriovenous fistula stenosis

BACKGROUND AND OBJECTIVES

Guidelines recommend systematically screening for stenosis using various methods, but no studies so far have compared all of the options. A prospective blinded study was performed to compare the performance of several bedside tests performed during dialysis in diagnosing angiographically proven >50% fistula stenosis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In an unselected population of 119 hemodialysis patients with mature fistulas, physical examination (PE) was conducted; dynamic and derived static venous pressure (VAPR), blood pump flow/arterial pressure (Qb/AP) ratio, recirculation (R), and access blood flow (Qa) were measured; and angiography was performed.

RESULTS

Angiography identified 59 stenotic fistulas: 43 stenoses were located upstream from the venous needle (inflow stenosis), 12 were located downstream (outflow stenosis), and 4 were located at both sites. The optimal tests for identifying an inflow stenosis were Qa < 650 ml/min and the combination of a positive PE "or" Qa < 650 ml/min (accuracy 80% and 81%, respectively), the latter being preferable because it was more sensitive (85% versus 65%, respectively) for a comparable specificity (79% versus 89%, respectively). The best tests for identifying outflow stenosis were PE and VAPR, with no difference between the two (accuracy 91% and 85%, sensitivity 75% and 81%, specificity 93% and 86%, respectively), the former being preferable because it was more reproducible, easier to perform, and applicable to all fistulas.

CONCLUSIONS

This study showed that fistula stenosis can be detected and located during dialysis with a moderate-to-excellent accuracy using PE and Qa measurement as screening procedures.

Automated intravascular access pressure surveillance reduces thrombosis rates

Although monitoring of vascular accesses by physical examination is nearly as sensitive as surveillance measurements by vascular access pressure when performed by examiners, the frequency of examinations is limited by time. We developed intravascular access pressure surveillance as a surrogate to physical examination. Using real-time data from hemodialysis machines, we derived intravascular access pressure ratios for each dialytic procedure. An automated, noninvasive surveillance algorithm that generated a "warning" list of patients at risk for thrombosis was formulated. We hypothesized that this algorithm would reduce access thrombosis frequency. We designed a study comparing thrombosis rates during a baseline 6-month interval to three subsequent 6-month periods of active surveillance. Referrals for interventions during this 18-month period were based on persistently abnormal elevated vascular access pressure ratio tests (VAPRT) >0.55. Thrombosis rates declined progressively for arteriovenous grafts (AVG) during the intervention period compared with the baseline period. Arteriovenous fistula (AVF) thrombosis rates decreased during postintervention months 13-18 during employment of the VAPRT. We conclude that use of VAPRT can reduce thrombosis rates in vascular accesses, and the magnitude of the effect is larger and more consistent in arteriovenous grafts (AVGs) than autologous AVFs.

Access Flow Reduction and Recurrent Symptomatic Cephalic Arch Stenosis in Brachiocephalic Hemodialysis Arteriovenous Fistulas

Background

Recurrent cephalic arch stenosis (CAS) has been linked to high flow and has a high rate of recurrence following angioplasty. This study investigates the effectiveness of access flow reduction in decreasing rapidly recurrent symptomatic CAS.

Methods

A retrospective study of patient records from February 2005 to April 2009 was conducted. Patients with brachiocephalic fistulas who had undergone two or more instances of cephalic arch angioplasty within 3 months, and thereafter underwent flow reduction via banding of the access inflow (n=33) were included. A before-and-after analysis was conducted: the rates of cephalic arch angioplasty were calculated for each patient before and after the banding procedure, and compared via a paired t-test.

Results

At 3, 6, and 12 months, the cephalic arch primary lesion patency was 91%, 76%, and 57%. The cephalic arch intervention rate was reduced from 3.34 to 0.9 per access-year (t=7.74, p<.001). The average follow-up time was 14.5 months (range, 4.8–32).

Conclusion

Flow reduction of a brachiocephalic arteriovenous hemodialysis fistula may effectively diminish the incidence of symptomatic CAS.