Graft surveillance: venous pressure, access flow, or the combination?

FLOW: Flow dysfunction of hemodialysis vascular access: A randomized controlled trial on the effectiveness of surveillance of arteriovenous fistulas and grafts

INTRODUCTION

It is assumed that identification and correction of asymptomatic stenoses in the vascular access circuit will prevent thrombosis that would require urgent intervention to continue hemodialysis treatment. However, the evidence base for this assumption is limited. Recent international clinical practice guidelines reach different conclusions on the use of surveillance for vascular access flow dysfunction and recommend further research to inform clinical practice.

METHODS

The FLOW trial is a double-blind, multicenter, randomized controlled trial with a 1:1 individual participant treatment allocation ratio over two study arms. In the intervention group, only symptomatic vascular access stenoses detected by clinical monitoring are treated, whereas in the comparison group asymptomatic stenoses detected by surveillance using monthly dilution flow measurements are treated as well. Hemodialysis patients with a functional arteriovenous vascular access are enrolled. The primary outcome is the access-related intervention rate that will be analyzed using a general linear model with Poisson distribution. Secondary outcomes include patient satisfaction, access-related serious adverse events, and quality of the surveillance process. A cost effectiveness analysis and budget impact analysis will also be conducted. The study requires 828 patient-years of follow-up in 417 participants to detect a difference of 0.25 access-related interventions per year between study groups.

DISCUSSION

As one of the largest randomized controlled trials assessing the clinical impact of vascular access surveillance using a strong double-blinded study design, we believe the FLOW trial will provide much-needed evidence to improve vascular access care for hemodialysis patients.

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.

Brief overview of surgical aspect of autologous arterio-venous fistula for dialysis access

Patients with the end-stage renal disease require renal replacement therapy in renal transplant, peritoneal dialysis, and intermittent hemodialysis. Hemodialysis remains the primary modality for renal replacement therapy. Excellent vascular access is a mainstay for performing hemodialysis. Here we present a brief review of the various surgical aspects of AV fistula creation. Preoperative physical examination and judicious use of the imaging modalities to define the artery and venous mapping provide a good outcome of the fistula formation. Surgical creation of RC-AVF is preferred for the end-stage renal disease patient. The end-to-side anastomosis between the radial artery and cephalic vein has shown very good results.

Effects of hemodialysis access surveillance on reducing risk of hemodialysis access thrombosis: A meta-analysis of randomized studies

INTRODUCTION

Vascular access thrombosis remains the Achilles Heel for many a hemodialysis patient. We performed a systematic review and meta-analysis to assess the impact of monitoring vascular access blood flow on prediction and prevention of vascular access thrombosis. We hypothesized that monitoring vascular access blood flow has a pivotal role in lowering the risk of thrombosis and subsequent access failure.

METHODOLOGY

We conducted a systematic review in PubMed and EMBASE databases to identify randomized studies that have assessed the effect of hemodialysis access surveillance on the risk of thrombosis. A random-effects model was used for the meta-analysis. Subgroup analysis was performed among patients with arterio-venous fistula (AV-fistulas) and those with arterio-venous graft (AV-grafts).

RESULTS

Ten randomized studies were included in the meta-analysis. The total number of patients included in the analysis was 1430. On performing the random-effects model among the included studies, hemodialysis access surveillance was associated with better outcomes (risk ratio = 0.73, 95% confidence interval ranges from 0.55 to 0.98). The analysis of the AV-fistula group showed an estimated overall risk ratio of 0.55 (95% confidence interval ranges from 0.33 to 0.89) favoring access surveillance. However, in the AV-grafts group, the estimated overall risk ratio was 0.92 (95% confidence interval ranges from 0.65 to 1.29) showing no additional benefit for access surveillance.

CONCLUSION

Hemodialysis access surveillance using access blood flow monitoring can reduce the risk of access thrombosis for patients with AV-fistulas, but this is not the case with AV-grafts.

A systematic follow-up protocol achieving a low hemodialysis graft thrombosis rate

INTRODUCTION

Graft is an alternative to native arteriovenous fistula to ensure permanent vascular access in hemodialysis patients. The most common complication is significant stenosis, which frequently causes thrombosis and graft loss. Periodic monitoring and surveillance with elective correction of stenotic lesions can prolong graft survival.

OBJECTIVE

To describe the effect of early diagnosis of significant stenosis on the rate of thrombosis and graft patency.

METHODS

Retrospective, observational study of a cohort of 86 prevalent patients undergoing hemodialysis with a graft as their vascular access. We applied a systematic follow-up protocol of 115 grafts based on various screening methods of monitoring (clinical monitoring, pre-pump arterial pressure, dynamic venous pressure, percentage of recirculation, and dose of dialysis) in conjunction with surveillance (normalized intra-access venous pressure and access flow). The annual rates of thrombosis, and primary, primary-assisted, and secondary patency were assessed.

RESULTS

The incidence of significant stenosis and thrombosis was 57.4% (65/115) and 39.0% (45/115), respectively. Of all screening procedures, normalized intra-access venous pressure was the best predictor of significant stenosis (hazards ratio, 7.71; 95% confidence interval, 3.06-19.46). The annual rate of thrombosis fluctuated from 0 to 0.26 thromboses/patient/year, with an average rate of 0.14 thromboses/patient/year. Primary, primary-assisted, and secondary patency were 74%/79%/82%, 50%/60%/66%, and 23%/35%/37% at 1, 2, and 5 years, respectively.

CONCLUSION

The implementation of a systematic graft follow-up protocol combined with monitoring and surveillance enabled early diagnosis and elective correction of significant stenosis, prolonged graft patency, and a low thrombosis rate.

Prediction of vascular access stenosis: Blood temperature monitoring with the Twister versus static intra-access pressure ratio

Background

The Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines recommend intra-access flow (Qa) measurement as the preferred vascular access surveillance method over static intra-access pressure ratio (SIAPR). Recently, it has become possible to perform Qa measurement during hemodialysis using thermodilution method called blood temperature monitoring (BTM) with the Twister device. The aim of this study was to investigate the correlation between Qa by BTM and SIAPR and to compare the performance of two tests in prediction of vascular access stenosis.

Methods

The study was performed from January 2016 to November 2017 and included 97 patients with arteriovenous fistulas (AVF). Qa by BTM and SIAPR were simultaneously measured every 1~3 months with a total of 449 measurements during study period.

Results

In our study population, mean age was 59.9±10.0 years and 61.9% were diabetes. The mean Qa obtained by BTM was 1186±588 mL/min. There was no correlation between Qa by BTM and venous SIAPR (r = 0.061, P = 0.196). Angiography identified 36 stenotic AVFs (37.1%) among the study subjects. They included 13 cases with only inflow stenosis, 6 with only outflow stenosis, and 17 with stenosis on both sides. Receiver-operating characteristic (ROC) curve analysis showed that Qa by BTM had higher discriminative ability to diagnose vascular access stenosis compared to SIAPR (P <0.001). The Qa less than 583 mL/min showed the highest diagnostic accuracy in vascular stenosis prediction.

Conclusion

Intradialytic measurement of Qa by BTM showed better diagnostic power over venous SIAPR in prediction of vascular access stenosis.

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.

Comparison of ultrasound scan blood flow measurement versus other forms of surveillance in the thrombosis rate of hemodialysis access: A systemic review and meta-analysis

BACKGROUND

The benefit of access flow surveillance in preventing vascular access thrombosis and failure remains controversial, as many randomized clinical trials (RCTs) have failed to demonstrate consistent results. The aim of this study was to perform a meta-analysis including newly published RCTs with a subgroup analysis for arteriovenous fistulas (AVFs) and arteriovenous grafts (AVGs).

METHODS

A systematic review of the available literature was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. An electronic search was conducted using the MEDLINE, EMBASE, and Cochrane Library databases of RCTs conducted from 1970 to 2017 that involved access flow surveillance. As a result, 9 RCTs met our criteria. The control group was defined by indirect and various surveillance methods such as dynamic venous pressure measurement and physical examination. Conversely, the interventional group was defined as a noninvasive duplex ultrasound scan (USS) or ultrasound dilution that directly measured the flow of vascular access.

RESULTS

The studies included 990 patients comprising 658 native AVFs and 332 AVGs. The prevalence of diabetes was 29.3%and 30.5% in the interventional and control groups, respectively. The estimated overall pooled risk ratio (RR) of thrombosis was 0.782 [95% confidence interval (95% CI), 0.553-1.107; P = .17], favoring interventional group, although this was not statistically significant. In the subgroup analysis, the pooled RR of thrombosis was .562 (95% CI, 0.346-0.915; P = .02) for AVFs, which significantly favored the interventional group. Conversely, the pooled RR for AVGs was 1.104 (95% CI, 0.672-1.816; P = .70).

CONCLUSION

The surveillance method to measure access flow through USS showed a significant benefit for reducing thrombosis in AVFs. The result encourages adherence to the current guidelines for AVFs. However, no benefit was found regarding AVGs. Recent guidelines with a "one-size-fits-all" approach may be revised to a "tailored-to-risk" approach.

Methods for the evaluation of biomarkers in patients with kidney and liver diseases: multicentre research programme including ELUCIDATE RCT

Background

Protein biomarkers with associations with the activity and outcomes of diseases are being identified by modern proteomic technologies. They may be simple, accessible, cheap and safe tests that can inform diagnosis, prognosis, treatment selection, monitoring of disease activity and therapy and may substitute for complex, invasive and expensive tests. However, their potential is not yet being realised.

Design and methods

The study consisted of three workstreams to create a framework for research: workstream 1, methodology – to define current practice and explore methodology innovations for biomarkers for monitoring disease; workstream 2, clinical translation – to create a framework of research practice, high-quality samples and related clinical data to evaluate the validity and clinical utility of protein biomarkers; and workstream 3, the ELF to Uncover Cirrhosis as an Indication for Diagnosis and Action for Treatable Event (ELUCIDATE) randomised controlled trial (RCT) – an exemplar RCT of an established test, the ADVIA Centaur® Enhanced Liver Fibrosis (ELF) test (Siemens Healthcare Diagnostics Ltd, Camberley, UK) [consisting of a panel of three markers – (1) serum hyaluronic acid, (2) amino-terminal propeptide of type III procollagen and (3) tissue inhibitor of metalloproteinase 1], for liver cirrhosis to determine its impact on diagnostic timing and the management of cirrhosis and the process of care and improving outcomes.

Results

The methodology workstream evaluated the quality of recommendations for using prostate-specific antigen to monitor patients, systematically reviewed RCTs of monitoring strategies and reviewed the monitoring biomarker literature and how monitoring can have an impact on outcomes. Simulation studies were conducted to evaluate monitoring and improve the merits of health care. The monitoring biomarker literature is modest and robust conclusions are infrequent. We recommend improvements in research practice. Patients strongly endorsed the need for robust and conclusive research in this area. The clinical translation workstream focused on analytical and clinical validity. Cohorts were established for renal cell carcinoma (RCC) and renal transplantation (RT), with samples and patient data from multiple centres, as a rapid-access resource to evaluate the validity of biomarkers. Candidate biomarkers for RCC and RT were identified from the literature and their quality was evaluated and selected biomarkers were prioritised. The duration of follow-up was a limitation but biomarkers were identified that may be taken forward for clinical utility. In the third workstream, the ELUCIDATE trial registered 1303 patients and randomised 878 patients out of a target of 1000. The trial started late and recruited slowly initially but ultimately recruited with good statistical power to answer the key questions. ELF monitoring altered the patient process of care and may show benefits from the early introduction of interventions with further follow-up. The ELUCIDATE trial was an ‘exemplar’ trial that has demonstrated the challenges of evaluating biomarker strategies in ‘end-to-end’ RCTs and will inform future study designs.

Conclusions

The limitations in the programme were principally that, during the collection and curation of the cohorts of patients with RCC and RT, the pace of discovery of new biomarkers in commercial and non-commercial research was slower than anticipated and so conclusive evaluations using the cohorts are few; however, access to the cohorts will be sustained for future new biomarkers. The ELUCIDATE trial was slow to start and recruit to, with a late surge of recruitment, and so final conclusions about the impact of the ELF test on long-term outcomes await further follow-up. The findings from the three workstreams were used to synthesise a strategy and framework for future biomarker evaluations incorporating innovations in study design, health economics and health informatics.

Trial registration

Current Controlled Trials ISRCTN74815110, UKCRN ID 9954 and UKCRN ID 11930.

Funding

This project was funded by the NIHR Programme Grants for Applied Research programme and will be published in full inProgramme Grants for Applied Research; Vol. 6, No. 3. See the NIHR Journals Library website for further project information.

The formulation and characterization of 3D printed grafts as vascular access for potential use in hemodialysis

Arteriovenous graft (AVG) failure continues to be a life-threatening problem in haemodialysis. Graft failure can occur if the implanted graft is not well-matched to the vasculature of the patient. Likewise, stenosis often develops at the vein-graft anastomosis, contributing to thrombosis and early graft failure. To address this clinical need, a novel ink formulation comprised of ACMO/TMPTA/TMETA for 3D printing a AVG was developed (ACMO-AVG), in which the printed AVG was biocompatible and did not induce cytotoxicity. The ease of customizing the ACMO-AVG according to different requirements was demonstrated. Furthermore, the AVG displayed similar mechanical properties to the commercially available arteriovenous ePTFE graft (ePTFE-AVG). Unlike ePTFE-AVG, the ACMO-AVG displayed excellent anti-fouling characteristics because no plasma protein adsorption and platelet adhesion were detected on the luminal surfaces after 2 h of incubation. Similarly, exposure to human endothelial cells and human vascular smooth muscle cells did not result in any cell detection on the surfaces of the ACMO-AVG. Thus, the present study demonstrates a newly developed 3D printing ink formulation that can be successfully 3D printed into a clinically applicable vascular access used for haemodialysis.

The Role of Doppler Ultrassonography in Significant and Borderline Stenosis Definition

Background: The definition of significant stenosis (SS) remains controversial. Methods: We retrospectively reviewed 1,040 consultations. SS was defined in the presence of clinical and echo-Doppler (DDU) criteria: Qa <500 mL/min or Qa decrease >25%; RI >0.7 in the feeding artery or absolute minimal luminal stenosis diameter <2.0 mm. Stenosis without any additional criteria were considered borderline stenosis (BS). Results: Two hundred twenty-one arteriovenous fistulas (AVFs) were included: 58.8% had SS, 18.6% had BS, and 22.6% had no dysfunctional access (ND). SS had a significantly higher thrombotic events than BS and ND (13.1 vs. 4.4%, p = 0.018). The annual thrombosis rate was 0.007, 0.037, and 0.004 in the ND, SS, and BS, respectively. AVF cumulative survival at 5 years was significantly lower in SS (89.5%) compared to BS (100%) and ND (97.4%; p = 0.03). BS had an HR for AVF failure of 1.1, p = 0.955, while the SS presented an HR of 5.9, p = 0.09. Conclusion: AVF clinical monitoring with additional DDU criteria appear to be appropriate for therapeutic referral.

Color Doppler Ultrasonography Percutaneous Transluminal Angioplasty of Vascular Access Grafts

Percutaneous transluminal angioplasty (PTA) is a possible treatment for stenosis. This study aimed to verify the impact of a vascular access (VA) surveillance protocol, based on the detection of functional changes and their correction by a new PTA method for VA performed under color Doppler ultrasonography (CDU) guidance. We divided the patients into two groups: group A, before May 1999 (retrospective study) without the surveillance protocol, and group B, from 1 May 1999 to January 2001 (prospective study) with the surveillance protocol. Access blood flow (Qa) was assessed every 4 weeks by ultrasound velocity dilution. In cases of a reduction of ≥35% from the baseline value, VA was examined using CDU: if a stenosis >50% was detected, angioplasty was performed. In cases of Qa reduction <35% we continued monitoring. By Cox's multivariate analyses, only the use of PTA with or without stenting reduced the relative risk of thrombosis by 64% during the follow-up (p=0.017 confidence intervals 88%-15%) in group B patients. Secondary patency was 80% for VA in which we performed PTA with or without stenting at 18 months, and 58% at 18 months in which we did not perform PTA. Our data show how PTA under CDU is useful to maintain and to improve graft patency. This PTA under CDU guidance allows patients to avoid surgical intervention, hospitalization, and adverse reactions to contrast media and exposure to ionizing radiation, with reduced cost and with better graft survival.

Comparison of urea recirculation and thermodilution for monitoring of vascular access in patients undergoing hemodialysis

Introduction

It is important to monitor vascular access in patients with stage 5 chronic kidney disease receiving hemodialysis. Access recirculation can help to detect a need for intervention.

Objectives:

To compare urea recirculation with recirculation by thermodilution using blood temperature monitoring to predict a need for intervention of vascular access over a 6-month period.

Methods:

We analyzed urea recirculation and blood temperature monitoring simultaneously in 61 patients undergoing hemodialysis. During the 6-month follow-up, we recorded all cases of angioplasty or surgery (thrombectomy or reanastomosis). In line with previous studies, we considered a value to be positive when urea recirculation was >10% and blood temperature monitoring >15%. Receiver operating characteristic curves were constructed.

Results:

Mean urea recirculation was 9.5% ± 6.6% and mean blood temperature monitoring 12.9% ± 4.3% (p = 0.001). Urea recirculation >10% had a sensitivity of 80% and specificity of 78%. Blood temperature monitoring >15% had a sensitivity of 33% and specificity of 85%. During follow-up, 25% of patients developed need for intervention of vascular access. We found an association between vascular access dysfunction and urea recirculation. The Kaplan–Meier analysis confirmed an association between urea recirculation and risk of vascular access dysfunction (log rank = 17.2; p = 0.001). We were unable to confirm this association with blood temperature monitoring (log rank = 0.879; p = 0.656).

Conclusion:

Urea recirculation is better predictor of vascular access dysfunction than thermodilution.

Functional vascular access evaluation after elective intervention for stenosis

Purpose

To evaluate the functional effects of preventive vascular access (VA) intervention through periodic blood flow (QA) measurements during hemodialysis (HD) by the delta-H method.

Methods

We prospectively monitored the blood flow rate (QA) of 100 VA (arteriovenous fistula (AVF) 81% or AV graft (AVG) 19%; mean VA duration 24.6 ± 42.3 months) during HD in 89 end-stage renal disease patients (mean age 62.7 ± 13.6 yrs; mean time on HD 30.9 ± 43.9 months; 18% with diabetes) over a 3-yr period. QA was measured at least every 4 months by the delta-H method (Yarar (6)) using the Crit Line III Monitor (overall mean QA 1247.6 ± 519.7 ml/min). The mean arterial pressure (MAP) and Kt/V index were measured simultaneously with QA. Thirty-eight VA (38%) met the positive evaluation criteria (absolute QA <700 ml/min 50%, QA decreased >20% from baseline 50%). Most cases with positive evaluation underwent angiography (36/38, 95%) and had stenosis ≥50% (34/36, 94%). Of VA with significant stenosis, 17 (17/34, 50%) VA (AVF 76.5%, AVG 23.5%; mean VA duration 12.5 ± 22.4 months, mean percentage of VA stenosis 75.8%) in 15 patients (mean age 68.4 ± 9.8 yrs; mean time on HD 14.2 ± 18.2 months; 33.3% with diabetes) underwent corrective intervention by angioplasty, 35.3% (6/17), and revision surgery, 64.7% (11/17).

Results

Short-term results: Elective intervention was successful in 88% of treated VA (15/17). Mean QA increased from 563.8 ± 115.4 ml/min just before intervention (QA pre) to 975.7 ± 351.8 ml/min just after intervention (QA post) (mean ΔQA = 411.8 ± 290.1 ml/min) (p < 0.001). We found a significant difference between the overall mean QA before (689.6 ± 227.0 ml/min) vs after intervention (965.9 ± 396.8 ml/min) (p = 0.011). No difference was found when the highest recorded mean QA before intervention (877.7 ± 415.4 ml/min) and mean QA post were compared (p = 0.25). Mean MAP did not change after intervention (91.5 ± 12.5 vs 92.7 ± 14.2 mmHg, p = 0.46). Mean Kt/V index improved from 1.44 ± 0.24 just before intervention to 1.49 ± 0.23 just after intervention without any change in dialyzer type or HD duration (p = 0.025). Mean ΔQA was similar for diabetic patients vs non-diabetic patients (p = 0.34), for younger patients (age < 65 yrs) vs older patients (age ≥65 yrs) (p = 0.64) and for AVF vs AVG (p = 0.39). We found a positive correlation between mean ΔQA and mean QA post (r = 0.95, p < 0.001) or between mean ΔQA and overall mean QA after intervention (r = 0.77, p < 0.001).

Long-term results

Prevalence of VA thrombosis during the follow-up period (354.4 ± 293.1 days): 17.6% (3/17). Five (29.4%) treated VA showed restenosis and two of them (40%) underwent reintervention by surgery. Mean restenosis period and mean decrease in QA were 232.6 ± 74.1 days and 2.8 ± 0.6 ml/min/day, respectively. No significant correlation was found between mean ΔQA or QA pre and mean restenosis period or decrease in QA (p = ns).

Conclusions

1) Monitoring QA by the delta-H method is useful in assessing the hemodynamic response to elective VA intervention. 2) Mean QA post was similar to the highest recorded mean QA before intervention. 3) Mean ΔQA was related to mean QA post and overall mean QA after intervention. 4) The HD effectiveness (Kt/V index) improved after intervention.

Surgery versus Interventional Radiology in the Management of Thrombosed Vascular Access for Hemodialysis

Thrombosis is the most frequent complication occurring in vascular access (VA). The two widely used treatment strategies for thrombosed VA are surgical and endovascular. Which is the best and whether different approaches should be used on proximal versus distal VA, is still debated. This is a retrospective study. Over a three years period, we studied among a population of 475 dialysis patients, 54 VA thromboses in 46 patients. Surgical procedure was successful in 14/17 (82%) distal artero-venous fistulas (AVF) while, in 9 proximal AVF, it led to initial success in 6 patients (66%), with a six months primary patency respectively of 93% and 84%. Radiological procedure resolved 6/10 distal AVF (initial success 60%) with primary patency of 66%, and was successful in 16/18 proximal AVF (initial success 89%) with primary patency of 81%. Taking our data all together, no differences are found between two thrombolitic (surgical and endovascular) procedures. But results were different in thrombosed proximal VA (where endovascular treatment should be preferred) versus distal ones (where surgery seems better).

Comparison of access blood flow and venous pressure measurements as predictors of arteriovenous graft thrombosis

Purpose

The purpose of the present study was to prospectively compare the predictive accuracy of static venous pressure (SVP); dynamic venous pressure (DVP) and access blood flow (ABF) in determining subsequent graft thrombosis and/or failure.

Methods

This study included 43 patients with functional arteriovenous grafts (AVG's) who underwent monthly serial measurements of SVP, DVP and ABF for 3 consecutive months. Patients were then followed for an additional 6 months. The primary end point was graft thrombosis.

Results

Six patients were excluded from the final analysis. Of the 37 patients completing the study, 7 episodes of graft thrombosis occurred within 6 months of follow up. Neither SVP nor DVP exhibited satisfactory sensitivity or specificity for graft thrombosis. Ten patients either began with or developed an ABF < 600 during the 3 months of measurements, but only 5 clotted. Δ ABF of >20% provided the best combination of sensitivity (86%) and specificity (90%) for graft thrombosis. In AVG's that have an ABF<600, it is those grafts with falling ABF that appear most likely to clot in the short term.

Conclusion

The study supports the concept that it is a falling level of access flow rather than the absolute level that is the most potent predictor of graft thrombosis.

Pre-emptive correction for haemodialysis arteriovenous access stenosis

BACKGROUND

Guidelines recommend routine arteriovenous (AV) graft and fistula surveillance (technology-based screening) in addition to clinical monitoring (physical examination) for early identification and pre-emptive correction of a stenosis before the access becomes dysfunctional. However, consequences on patient-relevant outcomes of pre-emptive correction of a stenosis in a functioning access as opposed to deferred correction, i.e. correction postponed to when the access becomes dysfunctional, are uncertain.

OBJECTIVES

We aimed to evaluate 1) whether pre-emptive correction of an AV access stenosis improves clinically relevant outcomes; 2) whether the effects of pre-emptive correction of an AV access stenosis differ by access type (fistula versus graft), aim (primary and secondary prophylaxis), and surveillance method for primary prophylaxis (Doppler ultrasound for the screening of functional and anatomical changes versus measurement of the flow in the access); and 3) whether other factors (dialysis duration, access location, configuration or materials, algorithm for referral for intervention, intervention strategies (surgical versus radiological or other), or study design) explain the heterogeneity that might exist in the effect estimates.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Specialised Register to 30 November 2015 using search terms relevant to this review.

SELECTION CRITERIA

We included all studies of any access surveillance method for early identification and pre-emptive treatment of an AV access stenosis.

DATA COLLECTION AND ANALYSIS

We extracted data on potentially remediable and irremediable failure of the access (i.e. thrombosis and access loss respectively); infection and mortality; and resource use (hospitalisation, diagnostic and intervention procedures). Analysis was by a random effects model and results expressed as risk ratio (RR), hazard ratio (HR) or incidence rate ratio (IRR) with 95% confidence intervals (CI).

MAIN RESULTS

We identified 14 studies (1390 participants), nine enrolled adults without a known access stenosis (primary prophylaxis; three studies including people using fistulas) and five enrolled adults with a documented stenosis in a non-dysfunctional access (secondary prophylaxis; three studies in people using fistulas). Study follow-up ranged from 6 to 38 months, and study size ranged from 58 to 189 participants. In low- to moderate-quality evidence (based on GRADE criteria) in adults treated with haemodialysis, relative to no surveillance and deferred correction, surveillance with pre-emptive correction of an AV stenosis reduced the risk of thrombosis (RR 0.79, 95% CI 0.65 to 0.97; I² = 30%; 18 study comparisons, 1212 participants), but had imprecise effect on the risk of access loss (RR 0.81, 95% CI 0.65 to 1.02; I² = 0%; 11 study comparisons, 972 participants). In analyses subgrouped by access type, pre-emptive stenosis correction did not reduce the risk of thrombosis (RR 0.95, 95% CI 0.8 to 1.12; I² = 0%; 11 study comparisons, 697 participants) or access loss in grafts (RR 0.9, 95% CI 0.71 to 1.15; I² = 0%; 7 study comparisons; 662 participants), but did reduce the risk of thrombosis (RR 0.5, 95% CI 0.35 to 0.71; I² = 0%; 7 study comparisons, 515 participants) and the risk of access loss in fistulas (RR 0.5, 95% CI 0.29 to 0.86; I² = 0%; 4 studies; 310 participants). Three of the four studies reporting access loss data in fistulas (199 participants) were conducted in the same centre. Insufficient data were available to assess whether benefits vary by prophylaxis aim in fistulas (i.e. primary and secondary prophylaxis). Although the magnitude of the effects of pre-emptive stenosis correction was considerable for patient-centred outcomes, results were either heterogeneous or imprecise. While pre-emptive stenosis correction may reduce the rates of hospitalisation (IRR 0.54, 95% CI 0.31 to 0.93; I² = 67%; 4 study comparisons, 219 participants) and use of catheters (IRR 0.58, 95% CI 0.35 to 0.98; I² = 53%; 6 study comparisons, 394 participants), it may also increase the rates of diagnostic procedures (IRR 1.78, 95% CI 1.18 to 2.67; I² = 62%; 7 study comparisons, 539 participants), infection (IRR 1.74, 95% CI 0.78 to 3.91; I² = 0%; 3 studies, 248 participants) and mortality (RR 1.38, 95% CI 0.91 to 2.11; I² = 0%; 5 studies, 386 participants).In general, risk of bias was high or unclear in most studies for many domains we assessed. Four studies were published after 2005 and only one had evidence of registration within a trial registry. No study reported information on authorship and/or involvement of the study sponsor in data collection, analysis, and interpretation.

AUTHORS' CONCLUSIONS

Pre-emptive correction of a newly identified or known stenosis in a functional AV access does not improve access longevity. Although pre-emptive stenosis correction may be promising in fistulas existing evidence is insufficient to guide clinical practice and health policy. While pre-emptive stenosis correction may reduce the risk of hospitalisation, this benefit is uncertain whereas there may be a substantial increase (i.e. 80%) in the use of access-related procedures and procedure-related adverse events (e.g. infection, mortality). The net effects of pre-emptive correction on harms and resource use are thus unclear.

The Impact of Access Blood Flow Surveillance on Reduction of Thrombosis in Native Arteriovenous Fistula: A Randomized Clinical Trial

Purpose

The usefulness of access blood flow (QA) measurement is an ongoing controversy. Although all vascular access (VA) clinical guidelines recommend monitoring and surveillance protocols to prevent VA thrombosis, randomized clinical trials (RCTs) have failed to consistently show the benefits of QA-based surveillance protocols. We present a 3-year follow-up multicenter, prospective, open-label, controlled RCT, to evaluate the usefulness of QA measurement using Doppler ultrasound (DU) and ultrasound dilution method (UDM), in a prevalent hemodialysis population with native arteriovenous fistula (AVF).

Methods

Classical monitoring and surveillance methods are applied in all patients, the control group (n = 98) and the QA group (n = 98). Besides this, DU and UDM are performed in the QA group every three months. When QA is under 500 ml/min or there is a >25% decrease in QA the patient goes for fistulography, surgery or close clinical/surveillance observation. Thrombosis rate, assisted primary patency rate, primary patency rate and secondary patency rate are measured.

Results

After one-year follow-up we found a significant reduction in thrombosis rate (0.022 thrombosis/patient/year at risk in the QA group compared to 0.099 thrombosis/patient/year at risk in the control group [p = 0.030]). Assisted primary patency rate was significantly higher in the QA group than in control AVF (hazard ratio [HR] 0.23, 95% confidence interval [CI] 0.05-0.99; p = 0.030). In the QA group, the numbers unddergoing angioplasty and surgery were higher but with no significant difference in non-assisted primary patency rate (HR 1.41, 95% CI 0.72-2.84; p = 0.293). There was a non-significant improvement in secondary patency rate in the QA group (HR 0.510, 95% CI 0.17-1.50; p = 0.207).

Conclusions

The measurement of QA combining DU and UDM shows a reduction in thrombosis rate and an increased assisted primary patency rate in AVF after one-year follow-up.

Trial registration

ClinicalTrials.gov Identifier: NCT02111655.

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.

A meta-analysis of randomized clinical trials assessing hemodialysis access thrombosis based on access flow monitoring: where do we stand?

The National Kidney Foundation Kidney Disease Outcomes Quality Initiative recommends the routine use of hemodialysis arteriovenous (AV) access surveillance to detect hemodynamically significant stenoses and appropriately correct them to reduce the incidence of thrombosis and to improve accesses patency rates. Access blood flow monitoring is considered as one of the preferred surveillance method for both AV fistulas (AVF) and AV grafts (AVG); however, published studies have reported conflicting results of its utility that led healthcare professionals to doubt the benefits of this surveillance method. We performed a meta-analysis of the published randomized controlled trials (RCTs) of AV access surveillance using access blood flow monitoring. Our hypothesis was that access blood flow monitoring lowers the risk of AV access thrombosis and that the outcome differs between AVF and AVG. The estimated overall pooled risk ratio (RR) of thrombosis was 0.87 (95% confidence interval [CI], 0.67-1.13) favoring access blood flow monitoring. The pooled RR of thrombosis were 0.64 (95% CI, 0.41-1.01) and 1.06 (95% CI, 0.77-1.46) in the subgroups of only AVF and only AVG, respectively. Our results added to the uncertainty of access blood flow monitoring as a surveillance method of hemodialysis accesses.

Color Doppler ultrasound and arteriovenous fistulas for hemodialysis

Native arteriovenous fistula (AVF) is the vascular access of choice for hemodialysis patients. Compared with grafts and central venous catheters, AVFs last longer and are associated with fewer complications. The widespread use of the Doppler ultrasound (DUS) has increased the number of patients who are eligible for AVF by facilitating the identification of vessels that are suitable for fistula construction (preoperative vascular mapping). DUS can also extend native AVF survival by improving the early detection of complications (post-operative surveillance). It is the only imaging modality that furnishes both morphological and functional data on the native vascular access, and it is also the only imaging tool that can be used directly by the surgeon, an indisputable advantage. This review examines the numerous roles played by DUS in the construction and postoperative follow-up of AVFs, including preoperative vascular mapping, AVF maturation, and surveillance.

Thermodilution versus Saline Dilution Method for Vascular Access Blood Flow Measurement in High-Flux and On-Line Hemodiafiltration

Purpose

Access blood flow (Qa) measurements are one of the most important components in vascular access monitoring programs, even though these indirect methods have only been validated with high-flux hemodialysis (HF; pump flow [Qb] 300 mL/min). This study was to assess the utility from thermodilution (BTM) with respect to the saline dilution method (SDM) in HF and on-line hemodiafiltration (OL-HDF) with routinely prescribed parameters in comparison with validation conditions.

Methods

Three consecutive sessions were assessed in 31 hemodialysis patients (27AVF). The Bland-Altman method and Lin's concordance coefficient (ρc) were used to study accuracy and precision. We used the student t test for the analysis of Qa-value in the different subgroups.

Results

In HF-hemodialysis 1 (Qb 300 mL/min), Qa was 1109 ± 541 mL/min SDMa and 1213 ± 639 mL/min BTM (P=.993a; bias 103.7 mL/min and ρc 0.78). In HF-hemodialysis 2 (Qb 420 mL/min) Qa 1071 ± 578 mL/min SDM (P=1.0a; -38.2 mL/min and 0.96) and 1216 ± 667 mL/min BTM (P=.992a; 127.3 mL/min and 0.70). In OL-HDF hemodialysis 3 (Qb 420 mL/min) Qa 1071 ± 510 mL/min SDM (P=1.0a; -48.4 mL/min and 0.96) and 1219 ± 580 mL/min BTM (P=.977a; 99.2 mL/min and 0.75). Statistically significant differences were only obtained in patients aged ≥ 65 years old (P=.016) and peripheral vascular disease (P=.007).

Conclusions

Our results demonstrate how the saline dilution method was more accurate than thermodilution in the HF and OL-HDF modalities with routinely prescribed parameters. Finally, in this study, advanced age (>65 years old) and peripheral vascular disease were associated with a significantly lower Qa-value.

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.

Surveillance of hemodialysis vascular access

A mature, functional arteriovenous (AV) access is the lifeline for a hemodialysis (HD) patient as it provides sufficient enough blood flow for adequate dialysis. As the chronic kidney disease (CKD) and end-stage renal disease (ESRD) population is expanding, and because of the well-recognized hazardous complications of dialysis catheters, the projected placement and use of AV accesses for HD is on the rise. Although a superior access than catheters, AV accesses are not without complications. The primary complication that causes AV accesses to fail is stenosis with subsequent thrombosis. Surveying for stenosis can be performed in a variety of ways. Clinical monitoring, measuring flow, determining pressure, and measuring recirculation are all methods that show promise. In addition, stenosis can be directly visualized, through noninvasive techniques such as color duplex imaging, or through minimally invasive venography. Each method of screening has its advantages and disadvantages, and several studies exist which attempt to answer the question of which test is the most useful. Ultimately, to maintain the functionality of the access for the HD patient, a team approach becomes imperative. The collaboration and cooperation of the patient, nephrologist, dialysis nurse and technician, vascular access coordinator, interventionalist, and vascular surgeon is necessary to preserve this lifeline.

Optimizing function and treatment of hemodialysis grafts and fistulae

We are entering a new era for the management of hemodialysis grafts and fistulae. The hallmark of this new era will be the use of quantitative, hemodynamic parameters to optimize vascular access function and improve the results of our endovascular interventions. The implementation of vascular access surveillance programs has not only decreased the incidence of vascular access thrombosis, but also has provided new insights into the hemodynamic performance of grafts and fistulae. The measurement and analysis of intra-access blood flow has proven useful for the early detection of developing stenosis, and also provides a quantitative method to assess the results of our endovascular interventions. In the future, the use of quantitative hemodynamic measurements will play an increasingly important role in our evaluation and treatment of hemodialysis grafts and fistulae.

Vascular Access Monitoring Improves Outcomes

Vascular access monitoring can identify patients at increased risk of future access thrombosis. When coupled with a program of elective stenosis correction, access thrombosis rates decline approximately 50-75%. This results in arteriovenous (AV) fistula thrombosis rates of 0.1-0.2/patient year (vs. 0.2-0.4 at baseline) and AV graft thrombosis rates <0.5/patient year (vs. 0.8-1.2 thromboses/patient year at baseline). Evaluating the long-term impact on access survival remains problematic. There are no large-scale randomized trials and existing studies exhibit marked differences in target populations, clinical protocols and outcome definitions. Differences in payment systems also significantly influence the efficacy of monitoring and intervention programs. Despite these challenges, the current data support the K/DOQI recommendations that all patients undergo a program of regular access monitoring preferably by access flow measurement coupled with prompt imaging and elective stenosis correction for low flow accesses.

Ultrahigh-Pressure Angioplasty versus the Peripheral Cutting Balloon™ for Treatment of Stenoses in Autogenous Fistulas: Comparison of Immediate Results

Purpose

To compare the immediate results of ultrahigh-pressure (UHP) balloons vs. peripheral cutting balloons (PCB) for the treatment of stenoses associated with autogenous fistulas using intra-access blood flow measurements.

Materials and Methods

This prospective randomized study consisted of 22 hemodialysis (HD) patients with autogenous fistulas who had decreased intra-access blood flow (<500 mL/min). All patients underwent a fistulogram and intraprocedural blood flow measurements. Patients were randomized once into two groups; one group undergoing UHP angioplasty and the second group undergoing PCB angioplasty. Randomization occurred once after the diagnostic fistulogram and each patient in each arm only underwent percutaneous transluminal angioplasty with either UHP or PCB. The study cohort consisted of 12 patients in the UHP group and 10 patients in the PCB group. Data collected included fistula anatomy, degree of stenosis, length of stenosis, balloon specifications and residual stenosis.

Results

The 22 study patients underwent 35 angioplasty procedures; 23 in the UHP group (12 patients) and 12 in the PCB group (10 patients). The technical success rate was 91%. The pre-intervention mean blood flow was 288 mL/min in the UHP group and 391 mL/min in the PCB group. The post-intervention mean blood flow was 613 mL/min in the UHP group and 606 mL/min in the PCB group. The mean increase in blood flow was 325.8 mL/min in the UHP group and 213 mL/min in the PCB group. This represents a relative mean increase in blood flow of 253% in the UHP group and 85% in the PCB group. An unpaired t-test showed there was no significant difference between the groups with respect to pre-flow, post-flow, and mean and relative mean increase in flow. There were two failures; one in the UHP group and one in the PCB group. There was one minor complication (2.8%) but no major complications.

Conclusions

In this small group of HD patients with autogenous fistulas our comparison of UHP to the PCB demonstrated that the immediate results, as determined by measurement of intra-access blood flow, were equivalent. Further long-term follow-up will be required to determine the longevity of these results

Hemodialysis vascular access monitoring: current concepts

Most arteriovenous grafts fail due to irreversible thrombosis, and most clotted grafts have an underlying stenotic lesion. These observations raise the plausible hypothesis that early detection of graft stenosis with preemptive angioplasty will reduce the likelihood of graft thrombosis. A number of noninvasive methods can be used to detect hemodynamically significant graft stenosis with a high positive predictive value. These tests include clinical monitoring, as well as surveillance by static dialysis venous pressures, flow monitoring, or duplex ultrasound. However, these surveillance tests have a much lower positive predictive value for graft thrombosis in the absence of preemptive angioplasty. In other words, none of the currently available surveillance tests can reliably distinguish between stenosed grafts destined to clot, and those that will remain patent without intervention. As a consequence, any program of graft surveillance necessarily results in a substantial proportion of unnecessary angioplasties. Moreover, a substantial proportion of grafts thrombose despite a normal antecedent surveillance test. Numerous observational studies have found an impressive reduction of graft thrombosis after implementation of a stenosis surveillance program. In contrast, 5 of 6 randomized clinical trials failed to show a reduction of graft thrombosis in patients undergoing graft surveillance, as compared with those receiving only clinical monitoring. The lack of benefit of surveillance is largely attributable to the rapid recurrence of stenosis after angioplasty. Thus, routine surveillance for graft stenosis, with preemptive angioplasty, cannot be recommended for reduction of graft thrombosis. Future research should be directed at pharmacologic interventions to prevent graft stenosis.

Clinical surveillance and monitoring of arteriovenous access for hemodialysis

Clinical surveillance and monitoring of arteriovenous access for hemodialysis can best ensure long term access function. The failing access can be identified and referred for intervention prior to complete access failure. This article reviews the basic science of access function and the various techniques for detecting the failing access. These techniques are utilized by the dialysis unit staff and by the physician, often the interventionalist, who takes primary care of the access. A combination of various techniques to detect dysfunction and trend analysis of various parameters is most likely to identify in a timely manner, those patients who need intervention.

Surveillance of arteriovenous hemodialysis access: a systematic review and meta-analysis

OBJECTIVES

Hemodialysis centers regularly survey arteriovenous (AV) accesses for signs of dysfunction. In this review, we synthesize the available evidence to determine to what extent proactive vascular access monitoring affects the incidence of AV access thrombosis and abandonment compared with clinical monitoring.

METHODS

We searched electronic databases (MEDLINE, EMBASE, Cochrane CENTRAL, Web of Science, and SCOPUS) and sought references from experts, bibliographies of included trials, and articles that cited included studies. Two reviewers independently assessed trial quality and extracted data. We used random effects meta-analysis to estimate the pooled relative risk (RR) and 95% confidence interval (CI) across studies and conducted subgroup analyses to explain heterogeneity. The I(2) statistic was used to assess heterogeneity of treatment effect among trials.

RESULTS

Nine studies (1363 patients) compared a strategy of surveillance vs clinical monitoring. A vascular intervention to maintain or restore patency was provided to both groups if needed. Surveillance followed by intervention led to a nonsignificant reduction of the risk of access thrombosis (RR, 0.82; 95% CI, 0.58-1.16; I(2) = 37%) and access abandonment (RR, 0.80; 95% CI, 0.51-1.25; I(2) = 60%). Three studies (207 patients) compared the effect of vascular interventions vs observation in patients with abnormal surveillance result. Vascular interventions after an abnormal AV access surveillance led to a significant reduction of the risk of access thrombosis (RR, 0.53; 95% CI, 0.36-0.76) and a nonsignificant reduction of the risk of access abandonment (RR, 0.76; 95% CI, 0.43-1.37).

CONCLUSION

Very low quality evidence yielding imprecise results suggests a potentially beneficial effect of AV access surveillance followed by interventions to restore patency. This inference, however, is weak and will require randomized trials of AV access surveillance vs clinical monitoring for rejection or confirmation.

Arterial line pressure control enhanced extracorporeal blood flow prescription in hemodialysis patients

Background

In hemodialysis, extracorporeal blood flow (Qb) recommendation is 300–500 mL/min. To achieve the best Qb, we based our prescription on dynamic arterial line pressure (DALP).

Methods

This prospective study included 72 patients with catheter Group 1 (G1), 1877 treatments and 35 arterio-venous (AV) fistulae Group 2 (G2), 1868 treatments. The dialysis staff was trained to prescribe Qb sufficient to obtain DALP between -200 to -250 mmHg. We measured ionic clearance (IK: mL/min), access recirculation, DALP (mmHg) and Qb (mL/min). Six prescription zones were identified: from an optimal A zone (Qb > 400, DALP -200 to -250) to zones with lower Qb E (Qb < 300, DALP -200 to -250) and F (Qb < 300, DALP > -199).

Results

Treatments distribution in A was 695 (37%) in G1 vs. 704 (37.7%) in G2 (P = 0.7). In B 150 (8%) in G1 vs. 458 (24.5%) in G2 (P < 0.0001). Recirculation in A was 10.0% (Inter quartile rank, IQR 6.5, 14.2) in G1 vs. 9.8% (IQR 7.5, 14.1) in G2 (P = 0.62). IK in A was 214 ± 34 (G1) vs. 213 ± 35 (G2) (P = 0.65). IK Anova between G2 zones was: A vs. C and D (P < 0.000001). Staff prescription adherence was 81.3% (G1) vs. 84.1% (G2) (P = 0.02).

Conclusion

In conclusion, an optimal Qb can de prescribed with DALP of -200 mmHg. Staff adherence to DLAP treatment prescription could be reached up to 81.3% in catheters and 84.1% in AV fistulae.

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

Both physical examination (PE) and intra-access pressure (IAP) measurements have been used in the identification of stenosis in an arteriovenous access. The aim of this study was to evaluate the accuracy of PE and IAP in the diagnosis of arteriovenous fistula (AVF) stenosis. A total of 84 patients were enrolled in the study (54% men, mean age of 50.7 +/- 12.7 years and mean AVF patency of 24.9 +/- 7.8 months, 52% radiocephalic). Abnormalities of pulse and thrill were used as the diagnostic tools for the detection of stenosis using the physical examination. For IAP, stenosis was suspected when the ratio between IAP at the arterial puncture site and the mean blood pressure was <0.13 or >0.43. The diagnosis of stenosis was confirmed by Doppler ultrasound (DU). Sensitivity (S), specificity (SP), positive predictive value (PPV), negative predictive value (PNV), and accuracy were calculated for the two early detection tests. According to DU, 50 (59%) AVF were considered positive for the presence of stenosis. Fifty-six (66%) AVF were considered positive for the presence of stenosis by PE and 34 (40%) by IAP. S, SP, PPV, and NPV for PE and IAP were 96%, 76%, 86%, and 93% and 60%, 88%, 88%, and 60%, respectively. The accuracy for PE and IAP was 88% and 71%, respectively. PE proved to be an accurate method for the diagnosis of stenosis and should be part of all surveillance protocols of stenosis detection in AVF.

Surgical versus percutaneous care of arteriovenous access

Current clinical practice patterns have led to the performance of many percutaneous vascular procedures outside the traditional operating room and led to significant changes in management strategies for treatment of complications of arteriovenous access. In an effort to identify optimal treatment for failed or failing arteriovenous fistulas and grafts, percutaneous and surgical techniques are analyzed. Assessment of the functioning or failing access by physical examination is critical in determining proper treatment and in assessing outcomes of interventions. Percutaneous and surgical techniques are available for the treatment of AV access thrombosis and venous stenosis. Techniques for percutaneous thrombectomy and stent placement for venous stenosis and AV graft pseudoaneurysms are reviewed. Management of arterial inflow disease, steal syndrome and nonmaturing AV fistulas is also addressed. Overall, percutaneous techniques are assuming an increasingly important role in the treatment of failed or failing AV fistulas and grafts. Ongoing analysis of outcomes of both percutaneous and surgical interventions is necessary to continue to identify optimum treatment algorithms.

Noninvasive Methods to Identify Early Vascular Access Dysfunction

A functional vascular access is of critical importance to the hemodialysis patient, the patient's healthcare providers, and the hemodialysis treatment center. A poorly functioning or thrombosed vascular access can lead to increased morbidity, hospitalization, length of stay, and cost. This article reviews the increasing evidence supporting surveillance of arteriovenous (AV) hemodialysis access and the various strategies and techniques available for detection of a failing access.

Ultrahigh-pressure versus High-pressure Angioplasty for Treatment of Venous Anastomotic Stenosis in Hemodialysis Grafts: Is There a Difference in Patency?

PURPOSE

Ultrahigh-pressure (UHP) balloon catheters were compared with high-pressure (HP) balloon catheters to determine if there was a difference in patency after percutaneous transluminal angioplasty (PTA) of venous anastomotic stenoses.

MATERIALS AND METHODS

A retrospective study was conducted from January 2001 to September 2005 that included 22 patients with synthetic hemodialysis grafts who underwent 110 PTA procedures for venous anastomotic stenoses. Data collected included graft configuration and location, percent stenosis, balloon type used, residual stenosis, and total access blood flow before and after intervention. Patency from time of initial PTA to the next intervention was estimated with the Kaplan-Meier technique, with initial failures included in the analysis.

RESULTS

A total of 55 PTAs were performed in each group. Technical success rate was 96% (n = 106) and clinical success rate was 100%. Median survival times were 4.6 months for the UHP cohort and 5.4 months for the HP group. When each event was considered independent, the difference was significant (P = .014). However, when each PTA event was considered dependent on earlier PTA events, no significant difference in patency was observed (P = .64). The mean increases in access blood flow rate by ultrasound dilution (available for 71 events) after PTA were 264 mL/min with UHP and 524 mL/min with HP (P = .14, Student t test). One minor complication (0.9%) of focal extravasation after PTA occurred and resolved with prolonged balloon inflation.

CONCLUSION

Routine use of UHP for PTA of venous anastomotic stenoses in synthetic hemodialysis grafts was not associated with any significant change in patency compared with routine HP balloon angioplasty.

Results of aggressive graft surveillance and endovascular treatment on secondary patency rates of Vectra Vascular Access Grafts

OBJECTIVE

The aim of the present study was to determine the effect of an aggressive graft surveillance and endovascular treatment protocol on secondary patency rates of a polyetherurethaneurea vascular access graft, specially designed to provide early access and rapid hemostasis.

METHODS

One hundred and ninety Vectra Vascular Access Grafts (C. R. Bard, Inc, Murray Hill, NJ) were placed in 176 patients (78 females and 98 males, mean age 61.7 years). There were 41 forearm grafts, 145 upper arm grafts and four thigh grafts. Graft surveillance was performed by using clinical and hemodialysis parameters to detect a failing/failed graft and followed by endovascular treatment, rheolytic thrombectomy (AngioJet, Possis Medical Inc, Minneapolis, Minn) and/or angioplasty +/- stenting of the anatomical lesion (arterial anastomosis, graft, venous outflow, draining or central veins).

RESULTS

Hemodialysis started after a median of 15.5 days, as soon as from the day of the operation in some cases. Bleeding complications occurred in six patients (3.2%), venous hypertension in seven (3.7%), steal syndrome in two (1.1%), neurological complications in two (1.1%), while late infection (range 2.7-14.6 months) was seen in six patients (3.2%). Thrombectomy and angioplasty (median number of sessions 1, interquartile range 1-2) was performed in 43 grafts. Isolated angioplasty, not associated with thrombosis (median number of sessions 1, interquartile range 1-2), was performed in 50 grafts. These interventions increased primary assisted patency from 69% and 63% at 12 and 18 months, respectively to a secondary patency rate of 86%. Taking into account grafts removed for late infection, functional secondary patency rate dropped to 83% and 81%, at 12 and 18 months, respectively. Arterial anastomosis angioplasty was performed more frequently in thrombosed grafts (28.6%) than failing grafts (6.7%), P < .001 and had a significant negative predictive value on secondary patency rates at 12 and 18 months, which were 60.5% compared with 89% for grafts that had no interventions performed (P = .007) and 90.9% for grafts that had any intra-graft, venous outflow, or draining or central vein stenosis treated with angioplasty at any stage (P = .002). Multivariate analysis identified the presence of arterial anastomosis stenosis as the single predictor of secondary patency (relative risk 0.247, P = .002).

CONCLUSIONS

Aggressive graft surveillance and endovascular treatment increases significantly secondary patency rates of Vectra Vascular Access Grafts. Longer follow-up will determine the effectiveness of this policy. The role of inflow stenosis on graft longevity and alternative treatment options warrant further investigation.

Routine Surveillance in Vascular Access for Hemodialysis

There is increasing evidence that surveillance of AV access for haemodialysis prevents access thrombosis and improves the quality of care. This article reviews the evidence for surveillance and the various strategies and techniques available for detection of the failing access.

Access flow after angioplasty predicts subsequent arteriovenous graft survival

PURPOSE

The effectiveness of angioplasty can be assessed by access blood flow (ABF) measurements after the procedure; however, ABF after angioplasty is highly variable. The purpose of this study was to determine if the level of ABF achieved after angioplasty of arteriovenous (AV) grafts was predictive of subsequent graft outcomes.

MATERIALS AND METHODS

Retrospective review was performed of 51 shunt images in 31 patients who were receiving dialysis via functioning AV grafts. Patients were referred for shunt imaging because of low ABF rates, increased venous pressure, or clinical indications. Only those patients with ABF measurements performed less than 1 month after angioplasty were included. Patients were then followed for at least 12 months after the initial angioplasty and access-related events were recorded (eg, thrombosis, repeat angioplasty, infection, loss of access).

RESULTS

Average ABF rates increased from 655 mL/min+/-45 before angioplasty to 946 mL/min+/-50 after angioplasty. The median ABF rate after the procedure was 1,040 mL/min. Grafts with an ABF rate after angioplasty of less than 1,000 mL/min were more likely to require repeat intervention and to exhibit thrombosis within the first 6 months compared with those with ABF rates greater than 1,000 mL/min. They also had a lower 1-year assisted patency rate (ie, graft survival). The most important determinant of flow after angioplasty was the ABF before angioplasty.

CONCLUSION

Grafts with an ABF rate greater than 1,000 mL/min after prophylactic angioplasty required fewer repeat interventions and had longer assisted patency after prophylactic angioplasty than those with ABF rates less than 1,000 mL/min.

Analysis of the optical concentration curve to detect access recirculation

The optical blood volume curve sometimes presents either a positive or a negative rapid and reversible variation (spike) during the step of the dialysate conductivity, automatically set by the monitor for the ionic dialysance (ID) measurement. We studied whether this feature was in relation with access recirculation. Firstly, we studied if the manoeuvre of reversed position of the blood lines created the same feature in the blood volume curve. Secondly, two medical teams systematically checked for the presence of spikes and measured the access recirculation by way of an ultrasound dilution technique. The manoeuvre of reversed position of the blood lines invariably reproduced the same feature on the curve of the optical blood volume measurement in case of a recirculation greater than 20%. In the normal position of the blood lines, the 16 patients with an access recirculation greater than 20% had spikes. Spikes during ID measurement were not constant for an access recirculation between 10 and 20% and did not occur for an access recirculation of less than 10% or an undetectable one. The special spike of the optical blood volume curve occurring during the ID measurement clearly detects access recirculation. The specificity is of 100% when this modification is present all along the dialysis session for all the ID measurements and the sensitivity is 100% when the access recirculation is greater than 20%.

Access Monitoring Is Worthwhile and Valuable

During the past several years, a limited number of small clinical trials have questioned the role of surveillance in the management of vascular accesses, since the prolongation of access longevity until replacement was not altered. Although prolongation of access life span is an important endpoint, it is not the only one. Reduction in thrombotic events reduces the risks to the patient resulting from loss of access patency. The body of evidence suggests that the detection of stenosis and prevention of thrombosis are valuable. When a test indicates the likely presence of a stenosis, venography or fistulography should be used to definitely establish the presence and the degree of the stenosis. In most cases, angioplasty should be performed if the stenosis is greater than 50% by diameter. The value of routine use of any surveillance technique for detecting anatomic stenosis alone without concomitant functional assessment by measurement of access flow, venous pressure, recirculation, or other physiologic parameter has not been established. Stenotic lesions should not be repaired merely because they are present. If such correction is performed, then intra-procedural studies of access flow or intra-access pressure prior to and following percutaneous transluminal angioplasty should be conducted to demonstrate a functional improvement with a 'successful' percutaneous transluminal angioplasty.