key: cord-0050949-ubihrvpr
authors: Anvari, Evamaria; Vachharajani, Tushar J.
title: The hemodialysis access surveillance controversy continues
date: 2020-10-02
journal: Kidney Int Rep
DOI: 10.1016/j.ekir.2020.09.037
sha: 6dafcbcce0aed9aa38c2eb5f2e752e5fb37519c2
doc_id: 50949
cord_uid: ubihrvpr

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A vascular access is essential to provide life-sustaining hemodialysis treatment to patients with end-stage kidney disease (ESKD). The preferred vascular access remains to be arteriovenous fistula (AVF); however, it is often complicated by failure to mature in the early stages and in the long-term by development of stenosis, thrombosis and aneurysm/pseudoaneurysm formation. The pathophysiology for stenosis involves neo-intimal hyperplasia and poor outward remodeling of the vessel wall (1). The luminal narrowing over time causes reduction in blood flow, which at a critical juncture results in access thrombosis. Early detection of a failing vascular access can trigger a timely referral for appropriate intervention and possibly prevention of a thrombotic event. The dialysis access complications account for 12-25% of hospital admissions. More importantly, a dysfunctional vascular access remains a leading cause for morbidity requiring multiple interventions that consumes a significant portion of the healthcare budget. In 2013, the Centers for Medicare and Medicaid Services paid $2.8 billion for dialysis access related services (2) .

The basic principle of performing vascular access monitoring and surveillance is to identify a dysfunctional access for appropriate intervention and ultimately to minimize disruption of dialysis therapy. The terms monitoring and surveillance were introduced and defined by Kidney Disease Outcomes Quality Initiatives Clinical Practice Guidelines (KDOQI-CPG) (3) . Monitoring refers to utilizing physical examination along with clinical and biochemical abnormalities to detect vascular access dysfunction. Surveillance involves using special equipment to evaluate and identify access dysfunction. The objective for surveillance tests is to measure dialysis access blood flow, dynamic or static access venous pressure or evaluate anatomical abnormalities using ultrasound dilution method, pressure monitoring tools or Doppler ultrasonography, respectively. The KDOQI-CPG recommends monitoring the vascular access during the maturation phase and before each dialysis treatment, including empowering the patient to participate in their care. The role of vascular access surveillance to predict stenosis has remained controversial and has been debated now for almost two decades.

In this issue, Salman et al (4) have reported a multicenter, prospective randomized clinical trial using a complementary surveillance plus monitoring technique to assess vascular access in the surveillance group (n=229) compared with standard of care alone in the control group (n=207). The surveillance group underwent monthly access blood flow measurement using ultrasound dilution technique. The standard of care monitoring involved at least once a month detailed physical examination of the AVF by a trained dialysis provider and a monthly survey to assess the clinical indicators as outlined by KDOQI-CPG. A randomized group of 436 prevalent hemodialysis patients with either AVF/AVG were included in the study and followed for a 2-year period. The rigorous exclusion criteria included a history of a single episode of thrombosis, age more than 80-years or less than 18-years, active malignancy and life-expectancy of less than 6months. The study was completed by less than 50% of the enrolled patient (90/207; 43% in the control group and 58/229; 25% in the surveillance group). The number of thrombotic events encountered during the study period were 27 and 37 in the surveillance group versus control group, respectively. There was a statistical difference in the number of thrombotic events per patient (0.122 vs. 0.227; p=0.012) as well as per visit (0.0085 vs. 0.014; p=0.037) between the surveillance group and control group, respectively. The secondary outcomes of the number of endovascular interventions (0.991 vs. 0.981; p=0.95), and central vein catheter placements (0.039 vs. 0.053; p=0.65) were not statistically different between the surveillance group and control group, respectively.

The controversy over the utility of dialysis access surveillance in predicting the risk for a thrombotic event has remained unresolved. The surveillance method ideally should consistently detect a stenotic lesion with reasonable accuracy. Of the various methods available for access surveillance, measuring blood flow and access pressure are the most widely used parameters in clinical practice. However, other factors such as cannulation technique, variation in hemodynamics during hemodialysis, number of stenotic segments within an access circuit can all influence both flow and pressure within an access circuit (5, 6).

The access surveillance controversy began when early small cohort observational studies with historical control group reported a significant reduction in thrombotic events. These studies were questioned with equally small randomized controlled trials (RCT) reporting contradictory outcomes. The major limitations to draw any definitive conclusion from these studies were attributed to single center trials, which were non-randomized and often had a mix of AVF and arteriovenous graft accesses (7).

In the past decade, there have been several RCT with AVF alone. The studies supporting the benefits of using access surveillance to predict the risk of thrombosis continue to be small with variable access blood flow (750-900 ml/min) cut off points for intervention. The studies were further difficult to analyze as some of them used surveillance alone and others used surveillance method with a clinical indicator to intervene. The definitions used for access dysfunction were not standardized either. A systematic review of four studies with AVF (n=310) found lower risk of access loss (RR 0.5; 95% CI 0.29 -0.86) and thrombosis (RR 0.5; 95% CI 0.35 -0.71) between active surveillance group and clinical monitoring group, respectively (8). However, 3 of the 4 studies included in the analysis were performed at the same center. The indication to intervene was based on change in access flow from baseline, which was variable (>20% ->25%) in these studies making it impossible to draw any consistent conclusion. Aragoncillo et al. in their RCT (n=199) compared clinical monitoring group (control) with clinical monitoring plus ultrasound dilution flow surveillance test performed every 3 months (surveillance) with a 1-year follow up period (9) . The thrombosis events were higher in the control group compared to surveillance group (0.099 thrombosis/patient vs. 0.022 thrombosis/patient, respectively, p=0.03). However, the overall circuit patency was no different at a cost of increased therapeutic interventions (8) .

Salman et al, in their study have improved on some of the drawbacks of the past studies. They have standardized the control group and compared it with a surveillance protocol that is an add-on to the routine clinical monitoring protocol. But yet again, the surveillance protocol is different from previous studies. The ultrasound dilution blood flow test is performed at monthly intervals unlike the 3-monthly intervals in the previous RCT. The study also highlights, the challenges of recruiting less than 50% of patients and hence was not powered to answer the elusive question -Is ultrasound dilution access blood flow assessment better than clinical monitoring alone to predict a thrombotic event? The study at best demonstrates the complementary role played by the surveillance method of access blood flow measurement to clinical monitoring in real life situation.

The 2019 KDOQI Vascular Access Update redefines "access flow dysfunction" as clinically significant abnormalities in AVF flow or patency secondary to underlying stenosis or thrombosis. The 2006 guidelines included all pathologies of AVF abnormality including aneurysm/pseudoaneurysm and "steal" syndrome in the definition. The 2019 Guidelines emphasize the complementary role of surveillance to routine clinical monitoring and do not recommend pre-emptive endovascular intervention in the absence of any clinical indicators. Further, in presence of clinical indicators of dysfunction, timely and confirmatory imaging with possible intervention within 2-week is considered acceptable. The importance of careful individualized approach is stressed keeping the overall ESKD goals of care (ESKD Life-Plan) (10).

In the Covid-19 era, the dialysis vascular access evaluation becomes even more complicated as maintaining a "safe distance" and remote working protocols makes frequent clinical examination of a vascular access difficult to accomplish. Should we be looking at methods to performing surveillance tests using remote technology? The surveillance controversy continues as we are nowhere closer to finding a superior alternative to bedside monitoring of dialysis vascular access.

"No great advance has ever been made in science, politics, or religion, without controversy". Lyman Beecher

The native arteriovenous fistula in 2007 surveillance and monitoring

Medicare Costs Associated with arteriovenous fistulas among US Hemodialysis Patients

Work Group. Clinical Practice Guidelines for vascular access

Salman Loay -HASE study current study

Diagnostic accuracy of ultrasound dilution access blood flow measurement in detecting stenosis and predicting thrombosis in native forearm fistulae for hemodialysis

Intradialytic blood volume monitoring in ambulatory hemodialysis patients: a randomized trial

Vascular access surveillance: an ongoing controversy

Presumptive correction of arteriovenous access stenosis: a systematic reviewand meta-analysis of randomized controlled trials

The impact of access blood flow surveillance on reduction of thrombosis in native arteriovenous fistula:a randomized control trial

Vascular Access Guideline Work Group. KDOQI Clinical practice guideline for vascular access 2019 update