American Society of Diagnostic and Interventional Nephrology Section Editor: Stephen Ash: Stenosis Surveillance of Hemodialysis Grafts by Duplex Ultrasound Reduces Hospitalizations and Cost of Care

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.

Screening and surveillance of venous stenosis in AVG: Is it time to rethink our assumptions?

Guidelines make no firm recommendations about surveillance of arteriovenous grafts as several randomised trials (RCT) have not shown a clear benefit in patency. However a more thorough review of these RCT based on epidemiological principles reveals significant limitations. In particular a key weakness of these older studies is the interventions performed for venous stenosis detected that was largely angioplasty. However, the observational data of modern stent-grafts shows a clear benefit over angioplasty, and thus seems to suggest that a modern well considered RCT is now mandated.

Value of Doppler evaluation of physically abnormal fistula: hemodynamic guidelines and access outcomes

BACKGROUND/AIMS

The strategy of access care at out center involves the use of ultrasound (USG) in case of physical examination (PE) abnormality. USG determines the need of angiography. This study investigated the possible association between the need for percutaneous transluminal angioplasty (PTA) and hemodynamic parameters of USG. The study also assessed the effects of this monitoring strategy on outcomes in comparison with a historical control.

METHODS

A retrospective study of the medical records of 127 patients (65 PTA, 62 non-PTA) was conducted. Data were analyzed using logistic regression analysis and receiver operating characteristic curve. Fistula outcomes and intervention rates were calculated and compared with 100 historic controls.

RESULTS

Logistic regression analysis showed that brachial artery flow volume (FV) < 612.9 mL/min or brachial artery resistance index (RI) > 0.63 was independently associated with the need for PTA. This monitoring strategy showed an a reduction in thromboses (0.02 ± 0.11 events/arteriovenous fistula [AVF]-year vs. 0.07 ± 0.23 events/AVF-year, p = 0.046), reduction in central venous catheter placement (0.01 ± 0.05 events/AVF-year vs. 0.06 ± 0.22 events/AVF-year, p = 0.010), reduction in access loss (0.02 ± 0.13 events/AVF-year vs. 0.19 ± 0.34 events/AVF-year, p = 0.015), and increase in access selective repair (0.49 ± 0.66 events/AVF-year vs. 0.21 ± 0.69 events/AVF-year, p = 0.003), compared to historic control.

CONCLUSION

There was significant stenosis if brachial artery FV was < 612.9 mL/min or RI was > 0.63 for PE abnormality. These parameters should be used as markers for assessing PTA risk in hemodialysis patients. Addition of USG to determine the need of angiography after detection of PE abnormality leads to decreases in access thrombosis, catheter placement, and access loss despite increasing access intervention rates compared to clinical monitoring.

Simulation for competency assessment in vascular and cardiac ultrasound

Healthcare providers who use peripheral vascular and cardiac ultrasound require specialized training to develop the technical and interpretive skills necessary to perform accurate diagnostic tests. Assessment of competence is a critical component of training that documents a learner's progress and is a requirement for competency-based medical education (CBME) as well as specialty certification or credentialing. The use of simulation for CBME in diagnostic ultrasound is particularly appealing since it incorporates both the psychomotor and cognitive domains while eliminating dependency on the availability of live patients with a range of pathology. However, successful application of simulation in this setting requires realistic, full-featured simulators and appropriate standardized metrics for competency testing. The principal diagnostic parameter in peripheral vascular ultrasound is measurement of peak systolic velocity (PSV) on Doppler spectral waveforms, and simulation of Doppler flow detection presents unique challenges. The computer-based duplex ultrasound simulator developed at the University of Washington uses computational fluid dynamics modeling and presents real-time color-flow Doppler images and Doppler spectral waveforms along with the corresponding B-mode images. This simulator provides a realistic scanning experience that includes measuring PSV in various arterial segments and applying actual diagnostic criteria. Simulators for echocardiography have been available since the 1990s and are currently more advanced than those for peripheral vascular ultrasound. Echocardiography simulators are now offered for both transesophageal echo and transthoracic echo. These computer-based simulators have 3D graphic displays that provide feedback to the learner and metrics for assessment of technical skill that are based on transducer tracking data. Such metrics provide a motion-based or kinematic analysis of skill in performing cardiac ultrasound. The use of simulation in peripheral vascular and cardiac ultrasound can provide a standardized and readily available method for training and competency assessment.

Ultrasound-guided angioplasty for treatment of peripheral stenosis of arteriovenous fistula - a single-center experience

PURPOSE

In patients with end-stage renal disease, arteriovenous fistulas (AVFs) are the access of choice for hemodialysis but are often complicated by stenosis. We present single-center experience of 78 ultrasound-guided angioplasty procedures for treating peripheral stenoses of AVFs.

METHODS

Between January 2013 and November 2015, 78 angioplasties were performed under ultrasound guidance in 53 patients with end-stage renal disease who were referred from dialysis centers with low flow rate, difficult cannulation, increased cannulation site bleeding, immature or thrombosed AVF. Angioplasties were carried out in the presence of a structural lesion in the AVF resulting in at least 50% reduction in vein diameter with a blood flow of &lt;250 mL/min or a peak systolic velocity &gt;300 cm/s. Clinical success, anatomical success and post-intervention primary and secondary patency rates at 6, 12, 18 and 24 months were studied.

RESULTS

In 49/53 patients (92.4%), 74 angioplasty procedures were successfully performed, whereas 4/53 patients (7.6%) had primary failure. A total of 35/49 patients (71.4%) underwent single angioplasty procedure whereas 14/49 patients (28.6%) underwent multiple angioplasty procedures. Post-intervention primary patency rates at 6, 12, 18 and 24 months were 78.6%, 60.2%, 53.8% and 48.9%, respectively. Post-intervention secondary patency rates at 6, 12, 18 and 24 months were 100%, 100%, 95.4% and 89%, respectively. Clinical success and anatomical success was 94.8% and 89.7%, respectively.

CONCLUSIONS

Ultrasound-guided angioplasty is an effective method with good long-term outcomes in selected dialysis patients with peripheral stenosis of AVF.

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.

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.

Outcomes of endovascular intervention for salvage of failing hemodialysis access

OBJECTIVE

To investigate the effectiveness of endovascular balloon angioplasty to preserve the patency of failing hemodialysis arteriovenous fistulas (AVF) and prosthetic arteriovenous grafts (AVG).

METHODS

Patients on hemodialysis who received endovascular intervention for access problems were retrospectively analyzed. Fistulography was performed on patients who were suspected to have access stenosis and balloon angioplasty performed in the same setting if a stenosis of ≥50% is detected. Patients were followed up for post-operative complications and access restenosis or failure.

RESULTS

42 hemodialysis patients with 44 access sites (29 AVFs, 15 AVGs) required endovascular balloon angioplasty. There were no perioperative complications. Technical success rate was 100%. Median time from initial access creation to first balloon angioplasty was 13 months (2-146 months) for AVFs and 8 months (2-71 months) for AVGs. 19 of 44 patients subsequently developed restenosis. Median time for restenosis or access failure was 11 months (1-18 months) for AVFs and 5 months (1-10 months) for AVGs. Kaplan-Meier analysis for access patency after endovascular intervention showed 72% patency at 6 months and 32% at 12 months.

CONCLUSIONS

Endovascular balloon angioplasty is effective in restoring patency of failing hemodialysis accesses. Recurrence is common, and repeat interventions are required.

Maintenance of hemodialysis arteriovenous fistulas by an interventional strategy: clinical and duplex ultrasonographic surveillance followed by transluminal angioplasty

OBJECTIVE

A native arteriovenous fistula (NAF) is a widely used access location for hemodialysis (HD). Monitoring of the NAF followed by percutaneous transluminal angioplasty (PTA) as needed may reduce the incidence of NAF failure according to nonrandomized studies. The aim of this randomized study was to determine whether an interventional strategy consisting of clinical and duplex ultrasonographic (DUS) surveillance of NAFs followed by PTA reduces the rate of the need of central venous dialysis catheters (CVCs) and NAF thrombosis in patients undergoing HD.

METHODS

A total of 108 patients with 111 functioning NAFs in an HD program were randomized to control and interventional strategy groups. The control group received standard care: clinical and hemodynamic NAF assessment followed by vascular surgeon consultation in cases of dysfunction. In the interventional group, the patients underwent clinical monitoring and systematic DUS surveillance every 3 months. Cases with access dysfunction underwent angiography followed by PTA for stenosis of 50% or greater. Primary outcomes were the need of temporary CVCs and fistula thrombosis.

RESULTS

Fifty-eight NAFs were randomized to the control group, and 53 were randomized to the interventional group. Groups had similar baseline characteristics. The interventional strategy showed a significant reduction in the CVC need (25.9% versus 7.5% for control and interventional groups, respectively; P = .021). No significant difference was observed for thrombosis rates (24.1% versus 17.0%; P = .487). The composite end point of NAF thrombosis or CVC need was reduced by the interventional strategy (44.8% versus 20.8%; P = .033).

CONCLUSIONS

This randomized study indicates the benefit of a surveillance program for maintenance of NAFs based on clinical and DUS surveillance followed by PTA of major stenosis.

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.

Effect of online haemodialysis vascular access flow evaluation and pre-emptive intervention on the frequency of access thrombosis

Introduction. Guidelines advocate surveillance of vascular access to reduce incidences of thrombosis. However, the value of online vascular access flow monitoring is still under debate.

Methods. Through a systematic literature search, the effect of online access flow surveillance combined with pre-emptive intervention on thrombosis frequency is reviewed.

Results. Due to methodological differences, adequate comparison of the individual study results is not possible. Moreover, the methodological quality of most of the included studies is not suitable for an adequate statistical analysis of the results.

Conclusion. Until now, there is no conclusive evidence that online access flow evaluation has a significant effect on the rate of thrombosis. Future large-scale studies with adequate study design, adequate surveillance and intervention protocols and, possibly, better pre-emptive intervention alternative(s) are necessary.

Mathematical model demonstrates influence of luminal diameters on venous pressure surveillance

BACKGROUND

The reliability of dialysis venous pressure (VP) in detecting stenosis is controversial. A mathematical model may help to resolve the controversy by providing insight into the factors that influence static VP.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

This study used inflow artery and outflow vein luminal diameters from duplex ultrasound studies of 94 patients. These diameters were applied to a mathematical model, and how they affect the relation among VP, mean arterial pressure (MAP), blood flow, and stenosis was determined. Whether VP/MAP is a valid adjustment for the influence of MAP on VP, and whether the standard VP/MAP referral threshold of 0.50 is valid, were also determined.

RESULTS

It was found that there is an approximate one-to-one relation between MAP and VP, so VP/MAP is a valid adjustment. Also, the 0.50 threshold successfully identifies most grafts with stenosis of 65% or more. However, the ratio of artery/vein diameters varied widely between patients, and the ratio independently influences VP/MAP. When the inflow artery is relatively narrow, the VP/MAP increase is delayed followed by a more rapid increase as critical stenosis is reached.

CONCLUSIONS

VP/MAP is a valid adjustment for the influence of MAP on VP, and the standard VP/MAP threshold of 0.50 warns of the transition to critical stenosis. However, relatively narrow arteries cause a delay followed by a rapid increase in VP/MAP that may not be detected before thrombosis unless measurements are very frequent. Clinical trials that emphasize trend analysis with frequent measurements are needed to evaluate the efficacy of VP surveillance.