Version May 2024
INTRODUCTION — Arteriovenous (AV) fistulas are capable of providing rapid extracorporeal blood flow that is necessary for hemodialysis; however, vascular stenosis is common and can lead to inadequate hemodialysis or AV fistula thrombosis if not identified and treated in a timely fashion.
Issues surrounding monitoring and surveillance of hemodialysis AV fistulas are reviewed here. Similar issues for hemodialysis AV grafts are discussed separately. (See "Clinical monitoring and surveillance of hemodialysis arteriovenous grafts to prevent thrombosis".)
RATIONALE FOR MONITORING AND SURVEILLANCE OF AV FISTULAS — Nearly all thrombosed mature AV fistulas have an underlying stenotic lesion. This was shown in a series of 93 consecutive clotted AV fistulas in which 100 percent had an underlying stenosis [1]. (See "Failure of the mature hemodialysis arteriovenous fistula".)
Although angiography is the most sensitive and specific imaging modality to identify and characterize stenotic vascular lesions, it is expensive and invasive [2-6]. For screening, noninvasive assessment is preferred to first identify AV fistulas with a high likelihood of stenosis. AV fistulas with sufficiently abnormal screening tests would then undergo diagnostic angiography and, if indicated, treatment. Clinical monitoring and surveillance are currently used to screen for vascular stenotic lesions.
●Clinical monitoring (see 'Clinical monitoring' below)
•Routine examination of the AV fistula
•Monitoring for problems with dialysis
•Monitoring Kt/V
●Surveillance (see 'Surveillance' below)
•Measuring intra-access flow
•Using duplex ultrasound to evaluate access flow
•Measuring static dialysis venous pressure
CLINICAL MONITORING — Clinical monitoring refers to assessments that can be performed by physical examination of the access or by using readily available information that is collected in the course of treating dialysis patients [7]. Clinical monitoring may include routine examination of the AV fistula, monitoring for problems with dialysis sessions, and monitoring Kt/V. The effectiveness of these methods is discussed below. (See 'Effectiveness' below.)
Routine examination — The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (KDOQI) Clinical Practice Guideline for Vascular Access: 2019 Update recommends that routine physical examination be performed on all mature AV fistulas on a weekly basis [8]. Such monitoring is also recommended by the 2008 Society for Vascular Surgery [9]. Abnormalities of physical examination, such as extremity edema, alterations in the pulse, thrill, or bruit, may signal a problem with the AV fistula. Some experts suggest that failure of the AV fistula to collapse when the arm is elevated and lack of pulse augmentation are particularly suggestive of underlying stenosis; however, it is unclear whether the accuracy of these tests in detecting stenosis is reproducible at all dialysis centers [10]. Pulse augmentation may be more useful in relatively new AV fistulas compared with mature AV fistulas that are relatively more rigid. (See "Physical examination of the mature hemodialysis arteriovenous fistula".)
Problems with dialysis — Problems noted during the dialysis session may signal a problem, such as difficulty with cannulation, aspiration of clots, inability to achieve the target dialysis blood flow, or prolonged bleeding from the needle puncture sites.
Decreased Kt/V — An unexplained (>0.2 units) decrease in the delivered dialysis dose (Kt/V) on a constant dialysis prescription requires further evaluation. Kt/V is the preferred method for measuring the dialysis dose. (See "Prescribing and assessing adequate hemodialysis".)
SURVEILLANCE — Surveillance methods include measuring intra-access blood flow, duplex ultrasound access flow, and static dialysis venous pressure [7]. Unlike clinical monitoring, each of the AV fistula surveillance methods requires specialized equipment or specially trained staff. Each relies upon the observation that progressive stenosis increases intra-fistula pressure (normalized for systemic blood pressure) and/or decreases access blood flow rate. Thus, the theoretical advantage of access surveillance over clinical monitoring is that it is more likely to be consistent and reproducible. However, implementing an access surveillance program requires additional cost, which is not currently reimbursed in the United States. To justify the added expense, surveillance methods must prove that their use is associated with improved patency. The effectiveness of surveillance methods is reviewed below. (See 'Effectiveness' below.)
Intra-access flow rate — Flow monitoring is the optimal surveillance method for AV fistula stenosis due, most likely, to the AV fistula being a low pressure system. Methods to monitor flow rate are described separately. (See "Clinical monitoring and surveillance of hemodialysis arteriovenous grafts to prevent thrombosis", section on 'Intra-access blood flow monitoring'.)
In one randomized trial, the positive predictive value of flow monitoring for AV fistula stenosis was twice as good as that obtained with clinical monitoring [11]. However, in another trial, monthly flow measurement for AV access surveillance (AV fistulas or AV grafts) reduced the per-patient thrombotic event rate (0.12/patient versus 0.23/patient), but did not significantly affect the rate of and time to first thrombotic event, total number of catheters used, or total number of angiographic procedures [12].
The optimal threshold of access flow for detecting stenosis appears to be lower (approximately 450 to 500 mL/min) for AV fistulas compared with AV grafts [13-15]. As an example, in one study, an access flow of 465 mL/min was associated with a sensitivity and false-positive rate of 0.89 and 0.32, respectively, for predicting AV fistula stenosis [13]. We consider an access flow rate less than 500 mL/min as suggestive of underlying stenosis.
Duplex ultrasound — There are only very limited data concerning the use of duplex ultrasonography for AV fistulas. Most of the studies have primarily evaluated patients with AV grafts, but data also suggest that duplex flow measurements may be useful for patients with native AV fistulas [16,17]. In a systematic review, four randomized trials evaluated access flow-based monitoring in native AV fistulas [17]. Although access blood flow screening with Doppler ultrasound, in conjunction with preemptive angioplasty of hemodynamically significant stenosis, prevented access thrombosis in AV fistulas (relative risk 0.45, 95% CI 0.28-0.77), it did not reduce the risk of access loss or extent of resource use.
Static dialysis venous pressure — Static dialysis venous pressures have a lower positive predictive value for stenosis in AV fistulas as compared with AV grafts [18]. We do not consider static dialysis venous pressures to be useful for AV fistulas.
EFFECTIVENESS — There is a paucity of evidence concerning the effectiveness of clinical monitoring and surveillance for AV fistulas. Because thrombosis is much less common in AV fistulas compared with AV grafts, it is more difficult to demonstrate a reduction in the rate of thrombosis or show a definitive improvement in patency rates.
In general, clinical monitoring, most commonly by dialysis nurses, is less accurate for AV fistulas compared with AV grafts to detect stenoses, although the evidence is conflicting. This may be due in part to the lower frequency of stenosis in AV fistulas compared with AV grafts. Thus, negative fistulograms are not uncommon among patients referred for the study based upon abnormal clinical monitoring.
●One study evaluated 543 angiograms in 358 AV grafts and 185 AV fistulas, which were prompted by abnormalities of clinical monitoring detected by dialysis nurses [19]. The positive predictive value for greater than 50 percent access stenosis was only 39 percent for AV fistulas compared with 69 percent for AV grafts.
●The findings of a preprocedure physical examination were compared with results via angiography in a prospective trial of 142 consecutive patients with AV fistula dysfunction [10]. The sensitivity and specificity of physical examination for outflow stenosis were 92 and 86 percent, respectively, and, for inflow stenosis, 85 and 71 percent, respectively [10]. The examinations were performed by a nephrologist who was highly experienced in clinical access assessment, and it is unclear whether comparable results can be obtained by less experienced clinicians or dialysis nurses.
Observational and nonrandomized studies are conflicting concerning any benefits for surveillance methods such as blood flow rate monitoring on AV fistula thrombosis [20-22]. The only randomized trial reported a significantly lower AV fistula failure rate in patients undergoing flow monitoring with preemptive angioplasty than in patients without surveillance [23]. In this trial, 79 patients with AV fistulas with a proven stenosis were randomly assigned to preemptive angioplasty, surgical revision, or a control group in which intervention was deferred until there was a decrease in Kt/V or the AV fistula clotted. Cumulative AV fistula survival was significantly higher in the intervention group. However, the generalizability of these findings may be limited for two reasons: it was a single-center study, and the type of intervention may be important as the same group reported better patency with surgical revision than with angioplasty. Further study may be required to better understand the role of flow monitoring in patients with AV fistulas.
INDICATIONS FOR ANGIOGRAPHY REFERRAL — In the absence of high-quality evidence to guide clinical practice, our approach is consistent with the Kidney Disease Outcomes Quality Initiative (KDOQI) Clinical Practice Guideline for Vascular Access: 2019 Update [8]. We suggest diagnostic angiography for patients with the abnormalities listed below [24]:
●Physical findings suggestive of stenosis including persistent arm swelling, prolonged bleeding after needle withdrawal, collateral veins, and altered features of the pulse or thrill.
●Unexplained, persistent, decreased Kt/V (>0.2 units) on a fixed dialysis prescription.
●Directly measured access flow rate less than 400 to 500 mL/min.
●Noninvasive evidence of AV fistula abnormality.
With each of the monitoring and surveillance methods, the clinician should rely on persistent findings with prospective trend analysis consistent with stenosis rather than a single, isolated value.
Angiography should examine the arterial inflow, the anastomosis, and the outflow veins [3,25,26]. Multiple lesions can be detected in at least one-third of cases. In addition to defining the anatomy of the AV fistula, immediate percutaneous transluminal angioplasty with or without stenting can be performed, if indicated, or the angiogram can serve as a guide for surgical revision.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Dialysis" and "Society guideline links: Hemodialysis vascular access".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Preparing for hemodialysis (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Hemodialysis arteriovenous (AV) fistulas should be routinely monitored to detect potentially treatable causes of failure. Monitoring of hemodialysis AV fistulas may involve routine clinical assessment or more elaborate surveillance programs.
•Clinical monitoring falls into the following three broad categories: abnormalities of physical examination, problems noted during the dialysis session, or an unexplained decrease in the delivered dialysis dose (Kt/V) on a constant hemodialysis prescription. Although not clearly reproducible, some experts suggest that failure of the AV fistula to collapse when the arm is elevated and the lack of pulse augmentation when the outflow vein is occluded transiently are particularly suggestive of underlying stenosis. (See 'Clinical monitoring' above.)
•The three major types of access surveillance are intra-access blood flow monitoring, static dialysis venous pressure, and duplex ultrasound. Access flow monitoring is the optimal surveillance method for AV fistula stenosis due most likely to the AV fistula being a low pressure system. (See 'Surveillance' above.)
●There is insufficient evidence to support complex surveillance programs, and there is general agreement that simple clinical monitoring of AV fistula performance by dialysis center personnel is preferred. Given the lack of evidence suggesting efficacy with surveillance, the dialysis staff at our center performs physical examination of the AV fistula weekly and notes any abnormalities during the dialysis session. Routine clinical assessment should be supplemented with noninvasive testing prior to angiography. (See 'Effectiveness' above.)
●Angiography should be reserved for patients with physical findings or other noninvasive evidence of probable AV fistula abnormalities. Similarly, an unexplained (>0.2 units) or persistent decrease in Kt/V should prompt angiography. (See 'Indications for angiography referral' above.)
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