Combined functional and anatomical diagnostic endpoints for assessing arteriovenous fistula dysfunction

Construction and validation of a scale to assess knowledge, attitude, and practice regarding vascular protection anticipatory to the creation of an arteriovenous fistula

BACKGROUND

The possibility of creating an arteriovenous fistula (AVF) depends on the existence of an arterial-venous network that is in good condition, defined by the size and elasticity of the blood vessels. The knowledge, attitudes, and practices (KAP) toward vascular protection play a crucial role in preserving the vascular network for patients with end-stage renal disease (ESRD), it is observed that there is a significant lack of tools to measure these variables. Thus, the aim of this study is to develop and validate a scale to assess KAP regarding vascular protection anticipatory to the creation of an arteriovenous fistula (the KAP-VPAC-AVF Scale).

METHODS

Initial item development was guided by a literature review and clinical experience, after which the items were improved and perfected through the Delphi process. The content of the scale was judged by an expert panel for content validity. In a convenience sample of 551 patients with ESRD, exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were conducted to examine the instrument's factor structure.

RESULTS

The KAP-VPAC-AVF Scale encompasses 11 items distributed over three factors: knowledge, attitude, and practice, demonstrated excellent internal consistency (Cronbach's alpha = 0.917) and construct validity, as confirmed by CFA with satisfactory fit indices (χ2/df = 2.394, RMSEA = 0.075, RMR = 0.049, CFI = 0.969, GFI = 0.936, AGFI = 0.892, TLI = 0.957, IFI = 0.970).

CONCLUSION

The KAP-VPAC-AVF Scale is a scientific and effective assessment tool that can evaluate the KAP of ESRD patients regarding measures to preserve the vascular network.

Integrating vascular access surveillance with clinical monitoring for stenosis prediction

BACKGROUND

Arteriovenous fistula and arteriovenous graft are the most common types of vascular access for dialysis; stenosis and thrombosis are major complications leading to access failure and to an incresed risk of mortality. The aim of the present study was to assess the results of integrating  strict vascular access blood flow surveillance with routine clinical monitoring for predicting vascular access stenosis in chronic hemodialysis patients.

METHODS

In this retrospective study, chronic dialysis patients with arteriovenous fistula or arteriovenous graft were included from a setting in which all patients underwent quarterly blood flow surveillance in 2017. The results of blood flow surveillance were confirmed by thorough physical examination. Predictive performance of blood flow surveillance models in detecting stenosis in patients with arteriovenous fistula or arteriovenous graft was evaluated. The predictive performance of the quarterly blood flow surveillance model was described by confusion matrix. Differences in accuracy, positive predictive value (PPV), and negative predictive value (NPV) between blood flow surveillance models with distinct blood flow thresholds were evaluated.

RESULTS

Of 397 included patients, 336 had an arteriovenous fistula and 61 had an arteriovenous graft. In 2017, 106 percutaneous transluminal angioplasty procedures were performed in patients with an arteriovenous fistula, and 63 in patients with an arteriovenous graft. The results revealed similar predictive performance of surveillance models using an absolute blood flow threshold of < 500 or < 400 mL/min in predicting stenosis in patients with arteriovenous fistula. Blood flow surveillance models for patients with an arteriovenous fistula had significantly higher accuracy than those for patients with an arteriovenous graft. Furthermore, the use of a relative threshold, defined as blood flow < 1000 mL/min and a 25% decline in blood flow, did not affect the predictive performance of blood flow surveillance models.

CONCLUSION

Blood flow surveillance models using thresholds of < 400 and < 600 mL/min, followed by thorough physical examination, showed an accuracy of 91.54% and 72.15% in predicting stenosis in patients with arteriovenous fistula and arteriovenous graft, respectively. These two blood flow surveillance models may be integrated with routine clinical monitoring to improve early detection and treatment of stenosis in hemodialysis patients.

ACR Appropriateness Criteria® Dialysis Fistula Malfunction

The creation and maintenance of a dialysis access is vital for the reduction of morbidity, mortality, and cost of treatment for end stage renal disease patients. One's longevity on dialysis is directly dependent upon the quality of dialysis. This quality hinges on the integrity and reliability of the access to the patient's vascular system. All methods of dialysis access will eventually result in dialysis dysfunction and failure. Arteriovenous access dysfunction includes 3 distinct classes of events, namely thrombotic flow-related complications or dysfunction, nonthrombotic flow-related complications or dysfunction, and infectious complications. The restoration of any form of arteriovenous access dysfunction may be supported by diagnostic imaging, clinical consultation, percutaneous interventional procedures, surgical management, or a combination of these methods. This document provides a rigorous evaluation of how variants of each form of dysfunction may be appraised and approached systematically. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Multiparametric ultrasound for upper extremity dialysis access evaluation

The evolution of ultrasound (US) techniques has greatly improved the evaluation of many parameters in dialysis vascular access, which is typically achieved through an arteriovenous fistula (AVF) or graft (AVG). These techniques include grayscale B-mode, color Doppler, power Doppler, spectral Doppler, non-Doppler US flow imaging techniques, contrast-enhanced US, and elastography. In conjunction with a patient's medical history and physical examination, US provides crucial information about the native vascular bed prior to the surgical creation of an arteriovenous anastomosis. It also tracks the maturation progress of the newly created AVF or AVG and aids in diagnosing potential complications of the vascular access. These complications include thrombosis, steal syndrome, aneurysms, pseudoaneurysms, hematomas, infection, ischemic neuropathy, exacerbation of preexisting congestive heart failure, and stenosis.

Standardized Methodology for Duplex Ultrasound Examination of Arteriovenous Access for Hemodialysis: A Proposal of the French Society of Vascular Medicine and the French-Speaking Society of Vascular Access

Duplex ultrasound (DUS) is an essential tool for characterizing and monitoring arteriovenous (AV) access for hemodialysis. The aim of the work described here, requested by the French Society of Vascular Medicine in collaboration with the French-Speaking Vascular Access Society, is to propose a standardized methodology for performing and documenting DUS, taking into account the variety of AV access techniques and the problems routinely encountered. A steering committee reviewed the literature and selected the relevant references. A draft was prepared, and all items with missing or conflicting data were submitted to a Delphi consensus. The final document was discussed and approved by all participants. The principles of DUS evaluation of AV access consist of examination of the afferent artery, the anastomosis and the entire venous drainage system. DUS uses B-mode ultrasound, color flow, pulsed wave and power Doppler analysis. DUS can be used in a variety of clinical situations, which can directly influence the methodology of the examination and the interpretation of the results. Blood flow should be assessed as it correlates with the risk of thrombosis. The measurement should be adapted to the different anatomical and hemodynamic conditions encountered. Characterization of stenosis should take into account the residual diameter of the drainage vein and its hemodynamic consequences. Other complications can be assessed with a standardized DUS examination. When performed according to a rigorous methodology, DUS of the AV access allows a comprehensive assessment of its functionality and eliminates the need for further invasive diagnostic procedures.

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.

Value of duplex Doppler ultrasonography for the evaluation of dysfunctional hemodialysis access arteriovenous fistulas prior to endovascular interventions

PURPOSE

To demonstrate accuracy of duplex Doppler ultrasonography (DUS) for the evaluation of native-vein arteriovenous fistula (AVF) dysfunction in end-stage renal disease patients.

METHODS

This retrospective study included 60 patients with dysfunctioning native-vein AVF evaluated with DUS and digital subtraction angiography (DSA) whose results were compared for detection, identification, and localization of AVF lesions. We calculated sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of DUS and evaluated the agreement between DUS and DSA by the Cohen's kappa coefficient (κ).

RESULTS

DUS identified correctly 123 of 130 lesions (sensitivity 94.6%, specificity 97.5%, PPV 98.4%, NPV 92%, accuracy of 95.7%). DUS localized correctly 123 of 130 lesions (sensitivity 94.6%, specificity 98.4%, PPV 98.4%, NPV 94.6%, accuracy 96.4%). The κ value was 0.9120 for detection of all lesions (almost perfect agreement).

CONCLUSION

DUS is a reliable method for the initial evaluation of dysfunctional AVFs, with high sensitivity for detecting and correctly localizing circuit problems.

Use of a proactive duplex ultrasound protocol for hemodialysis access

OBJECTIVE

Arteriovenous fistula (AVF) creation is the preferred approach for hemodialysis access; however, the maturation of AVFs is known to be poor. We established a proactive early duplex ultrasound (DUS) surveillance protocol for evaluating AVFs before attempted access. This study determined the effect of this protocol related to improving AVF maturation.

METHODS

From 2008 to 2013, 153 patients received new upper extremity AVFs and an early DUS surveillance protocol at a single academic institution. The protocol involved an early DUS evaluation before hemodialysis cannulation of the AVF at 4 to 8 weeks after AVF creation. A positive DUS result was identified as a peak systolic velocity of >375 cm/s or a >50% stenosis on gray scale imaging, along with decreased velocity in the outflow vein. Patients with positive DUS findings underwent prophylactic endovascular or open intervention to assist with AVF maturation. Nature of secondary interventions, as well as AVF patency and maturation, were assessed. Overall clinical outcomes and fistula patency were investigated.

RESULTS

During the study period, 183 upper extremity AVFs were created in 153 patients, including 82 radiocephalic, 63 brachiocephalic, and 38 brachiobasilic AVFs. A mortality rate of 43% (n = 66) was observed in a median follow-up period of 34.5 months (interquartile range, 19.6-46.9). A total of 164 early DUS were performed at a median of 6 weeks (interquartile range, 3.4-9.6 weeks) after the initial creation. Early DUS showed nine AVFs were occluded and were excluded from further analysis. Hemodynamically significant lesions were found in 62 AVFs (40%); however, only 17 (11%) were associated with an abnormal physical examination. Positive DUS finding prompted a secondary intervention in 81% of the patients. Among those with positive early DUS findings, AVF maturation was 70% in those undergoing a secondary intervention compared with 25% in those not undergoing a prophylactic intervention (P = .011). Primary-assisted patency for AVFs with early positive and negative DUS findings were 83% and 96% at 6 months, 64% and 89% at 1 year, and 52% and 82% at 2 years, respectively (P < .001).

CONCLUSIONS

Early DUS surveillance of AVFs before initial access is reasonable to identify problematic AVFs that may not be reliably detected on clinical examination. Although DUS criteria for AVFs have yet to be universally accepted, proactive early postoperative DUS interrogation assists in the early detection of dysfunctional AVFs and improvement of fistula maturation. Despite improved patency in those with positive DUS findings who undergo prophylactic secondary intervention, overall patency remains inferior to those without an abnormality detected on early DUS imaging.