Primary failure of the hemodialysis arteriovenous fistula

INTRODUCTION — The goal of hemodialysis arteriovenous (AV) fistula creation is to achieve a functioning access (ie, one that can be cannulated repetitively and provide adequate flow for the dialysis treatment). The best approach to reduce the risk of primary failure includes performing vascular mapping, careful surgeon selection, initiating hemodialysis vascular access early, evaluating all newly created AV fistulas at four weeks, and pursuing a program of salvage for primary failures [1]. (See "Approach to the adult patient needing vascular access for chronic hemodialysis".)

Primary AV fistula failure, which we define as an AV fistula that is never usable or fails within the first three months of its use, is a major problem. Many fistulas that fail to develop have correctable problems, and a high rate of subsequent success can be expected once these problems are addressed.

Primary failure of hemodialysis AV fistulas is reviewed. Failure of the mature AV fistula and other complications of AV fistulas, such as steal syndrome, aneurysm formation, infection, and excess flow leading to heart failure, are reviewed separately. (See "Failure of the mature hemodialysis arteriovenous fistula" and "Arteriovenous fistula creation for hemodialysis and its complications", section on 'Complications of AV fistula placement' and "Hemodialysis access-induced distal ischemia".)

FISTULA MATURATION AND EVALUATION — Once an arteriovenous (AV) fistula is created, it must develop to the point that it is adequate in size and depth, allowing repeated successful cannulation and providing adequate blood flow to support the hemodialysis prescription. Whether an AV fistula will mature without additional intervention is generally apparent at four to six weeks following creation during early fistula evaluation [1-3]. In many cases, a detailed physical examination of the access will point to the cause of the arrested maturation in nonmaturing fistulas [4-6]. (See "Early evaluation of the newly created hemodialysis arteriovenous fistula".)

If an abnormality is detected, further evaluation of the AV fistula should be accomplished as soon as possible, usually with duplex ultrasound [6], or angiography [7]. Any identified areas of stenosis can then be effectively treated with an appropriate intervention, as indicated.

PRIMARY FAILURE — We define primary failure as an arteriovenous (AV) fistula that has never been usable for dialysis or that fails within three months of use (figure 1 and table 1) [2,8]. The emphasis is generally on failure of maturation. The terms "primary failure," "early failure," and "failure to mature" are frequently heard and are essentially equivalent. We shall use the term "primary failure."

Incidence — Primary AV fistula failure has always been a problem. However, as efforts have intensified to preferentially create AV fistulas, the incidence of primary failure has only increased. When the radiocephalic AV fistula was first described in 1966 by Cimino and Brescia [9], the primary AV fistula failure rate was approximately 11 percent. Subsequent studies reported primary failure rates ranging from 10 to 25 percent [10-15]. However, in later reports, the incidence increased, ranging from 20 to 60 percent [16-23]. Why the change? Possible factors may include:

●Higher blood pump speed – The average blood pump speed of the hemodialysis machine (Qb) has increased over time from 200 to between 400 and 450 mL/minute. In early studies that reported lower primary failure rates, the lower Qb commonly prescribed placed less of a demand on the AV fistula. With changes in practice, a substantially higher Qb is used, and as a result some AV fistulas that would have been considered adequate do not provide adequate blood flow and are therefore classified as failed.

●Increases in patient age – The average age of the dialysis patient in the early period was 43 years, and almost all patients had chronic glomerulonephritis. Dialysis patients have become much older (>70), and 75 percent have five or more comorbidities; 90 percent have cardiovascular disease, and 50 percent have diabetes. It should not be surprising that creating and achieving a functional AV fistula is frequently a challenge in this population. (See "Arteriovenous fistula creation for hemodialysis and its complications".)

With the first report in 2015 , the introduction of the endovascular-created AV fistula (endoAVF) offered another option for dialysis access creation [24]. The results using two different devices, the WavelinQ EndoAVF System and the Ellipsys Vascular Access System, have been published. The simplicity of the procedures involved and the success of endoAVF creation has resulted in the increased adoption of endoAVF in clinical practice. With the increasing prevalence of the endoAVF, information concerning maturation rates has become increasingly important. Several reviews and meta-analyses have compared the data obtained using these two devices for the creation of endoAVF with surgically created AV fistulas. These have concluded that technical success and primary patency are similar for surgical AV fistulas and endoAVFs [25-27]. These comparisons lack the benefits of randomized trials comparing the two modalities. In addition, most of the reported studies are relatively small. The technical success for these procedures has been reported to range from 88 to 100 percent, and failure to mature rates have ranged from 2 to 23 percent [25]. (See "Percutaneous hemodialysis arteriovenous fistula".)

Patient risk factors — A number of patient risk factors associated with primary AV fistula failure are recognized. These are listed below and discussed in detail elsewhere. (See "Risk factors for hemodialysis arteriovenous fistula failure".)

●Obesity

●Older age

●Female sex

●Cardiovascular disease

●Diabetes

●Thrombophilia

Risk by type of AV fistula — An AV fistula can be created between essentially any artery or vein, with certain locations more conducive to fistula development and maturation. (See "Arteriovenous fistula creation for hemodialysis and its complications", section on 'Fistula creation'.)

Among the three most commonly created AV fistulas (radial-cephalic, brachial-cephalic, brachial-basilic transposition), the primary failure rate for the brachial-basilic transposed fistula has been reported to be the lowest, followed by the brachial-cephalic, and then the radial-cephalic with the highest rate [28-36].

Associated vascular lesions — Most investigators agree that nearly 100 percent of AV fistulas that present with failure to mature have an anatomic problem of some type [8,37-41]. Three important principles relate to primary failure:

●A distinct lesion or lesions can generally be identified as the cause.

●The location of lesion(s) can generally be identified by physical examination and confirmed by imaging.

●The lesion(s) can be corrected with a high expectation of success (except for certain preexisting lesions, which should have been avoided by good vascular mapping).

Multiple anatomic problems are frequently present. In one report of 100 cases of primary failure, 34 percent had more than one lesion present [8]. In another, multiple lesions were observed in 85 of 123 cases (71.4 percent) [38].

Vascular lesions causing primary failure generally can generally be classified as those that existed prior to the creation of the access and those that are acquired and the result of the surgical procedure itself. These lesions are described in the next section, and treatment is discussed below. (See 'Treatment of specific lesions' below.)

Preexisting lesions — Many potential problems associated with AV fistulas can be largely avoided by proper patient evaluation (vascular mapping) prior to access creation. There is a prevailing opinion that vascular mapping should be considered mandatory in all patients in whom a hemodialysis vascular access is planned. (See "Patient evaluation prior to placement of hemodialysis arteriovenous access" and "Risk factors for hemodialysis arteriovenous fistula failure", section on 'Hemodynamic' and "Arteriovenous fistula creation for hemodialysis and its complications", section on 'Physical evaluation'.)

Lesions and important anatomic features that should have been detected and addressed (or avoided) preoperatively are sometimes missed during preoperative vascular evaluation, in part because vascular mapping is not universally performed. The earliest report to strongly support vascular mapping demonstrated a marked increase in the percentage of arteriovenous (AV) fistulas placed (14 to 63 percent) and an equally impressive decrease in primary failure rates (38 to 8.3 percent) [34]. Not all studies have shown this degree of benefit. In some, the incidence of primary failure has not improved, and in others it has actually increased with vascular mapping [20,42]. The reasons for this are not clear. The experience of the surgeon is clearly important [43-47].

Vascular stenosis — Most cases of primary failure will have typical lesions that can be classified as inflow (arterial) or outflow (venous) problems [8]. In case series, both preexisting arterial and venous stenosis have been reported as causes of primary AV fistula failure. Varying areas of focal venous stenosis of differing lengths may be encountered. In some cases, a nonmaturing AV fistula that appears to manifest as a diffuse outflow stenosis represents a problem with inflow. The remodeling necessary for the development of a functional AV fistula depends on blood flow. If inflow is inadequate, the AV fistula will not develop. Once the inflow problem is resolved, the AV fistula may develop normally.

●Inflow artery stenosis – Finding an artery that is small or has a focal stenosis during vascular mapping generally results in the rejection of that site for the creation of the AV fistula. Nevertheless, among patients in whom an AV fistula fails to mature, small arteries or stenotic arterial lesions have been reported as a cause, with an incidence ranging from 4 to 6 percent [37,48]. In one small study, 30.5 percent of radiocephalic AV fistula access dysfunction was due to radial artery stenoses [49]. Small arteries that some may classify as diffusely stenotic may be the result of failed "arterial maturation." The artery should normally dilate in response to increasing blood flow [50]. Other inflow problems may include subclavian artery or brachial artery stenosis. Percutaneous transluminal angioplasty (PTA) has been used to dilate focal and diffuse lesions [50,51].

●Focal venous stenosis – Focal venous stenosis may also be associated with primary failure. In reported series, proximal venous stenosis occurs in 4 to 59 percent, and central venous stenosis is documented in 2.6 to 9 percent [8,37,38,48,52-54]. The wide variation in reported incidence is perhaps related to variability in the extent of preoperative evaluation (case selection). In cases with proximal venous stenosis, the problem may be recognized by an AV fistula that appears to mature too quickly or that becomes dilated very early but does not have inadequate flow.

●Diffuse venous stenosis – A marker that an AV fistula is likely to mature is dilation of the vein following completion of the anastomosis. The diameter should continue to progressively increase to a size that permits repeated cannulation for hemodialysis. The most important factor limiting the creation of an AV fistula is the availability of a suitable vein. Based upon the available evidence, a vein smaller than 2.5 mm is inadequate. In some cases, even with an appropriately sized vein, venous dilation fails to occur. In other cases, a small vessel is used due to limited availability in the hopes that the vein will nevertheless dilate to the required size [55]. In each scenario, percutaneous angioplasty has been used to achieve a usable vascular access. In these cases, sequential PTA has been used to progressively enlarge the vein and achieve a usable dialysis access. This technique has been referred to as balloon-assisted maturation (BAM).

Accessory veins — The clinical impact of accessory veins on AV fistula maturation has been controversial [56,57]. When contributory to primary AV fistula failure, obliteration of the culprit accessory vein may aid fistula maturation, although this remains to be proven [57]. Our approach to the evaluation and management of accessory veins to promote maturation of an AV fistula is discussed below. (See 'Handling accessory veins' below.)

Generally unnamed cross-communications between the various named superficial veins of the upper extremity, called accessory veins, are common and represent normal anatomy. Accessory veins occur almost exclusively in the forearm. When situated proximal to a venous stenosis, accessory veins can dilate and transform into high pressure vessels, termed collateral veins. While conceptually different, the distinction between collateral and accessory veins on clinical examination is important but is not always clear. In general, when a downstream stenosis is noted, such veins should be deemed to be collateral veins until proven otherwise. Treatment of the downstream stenosis typically resolves collateral veins. (See 'Preexisting venous stenosis' below and "Central vein obstruction associated with upper extremity hemodialysis access".)

It is important to determine to what extent an accessory vein can contribute to primary AV fistula failure since anything that interferes with blood flow can potentially adversely affect fistula maturation. However, the diameter of the accessory vein or degree of blood flow reduction needed to adversely affect AV fistula maturation is not clear. While accessory veins are commonly present adjacent to the forearm cephalic vein, most are not problematic. On occasion, an accessory vein may divert a significant quantity of blood flow away from the AV fistula, affecting its maturation; at other times, the accessory vein may remain inconsequential [58].

Because of the potential relationship between accessory veins and primary failure AV fistula failure, occlusion of accessory veins has been the subject of a series of reports [8,38,41,58-61]. Some have suggested that an accessory vein should always be occluded, and others have advocated treating only significant accessory veins [37,58,62]. However, a validated method for determining the significance of an accessory vein has been lacking. It is important to emphasize that the mere presence of an accessory vein is not an indication for its occlusion. An interventional procedure that is not medically indicated may cause the patient unnecessary discomfort and creates an unnecessary expense. In addition, accessory veins can provide a beneficial function. When a stenotic lesion develops, blood flow is frequently diverted into an accessory vein (which in this circumstance would be more appropriately referred to as a collateral), thus preventing stasis and thrombosis of the AV fistula. In the case that the AV fistula does thrombose, the collateral can limit extension of the thrombus by maintaining downstream blood flow. The AV fistula can often be salvaged by using the accessory vein. We use the criteria described below along with physical examination to help determine the significance of an accessory vein. (See 'Handling accessory veins' below.)

Acquired lesions — The most common lesion resulting in primary failure is an acquired lesion, the juxta-anastomotic stenosis [8,37,38,41,48,52-54]. Juxta-anastomotic stenosis occurs more commonly with radial-cephalic AV fistulas (64 to 77 percent) than with upper arm AV fistulas (39 to 56 percent) [63-65]. Three variations of juxta-anastomotic stenosis with common clinical manifestations include: stenosis only in the juxta-anastomotic zone of the AV fistula defined as the first 3 to 4 cm of the vessel immediately adjacent to the arterial anastomosis; anastomotic stenosis only; and a combination of the two. The luminal narrowing decreases AV fistula flow leading to problems of maturation and often early thrombosis. Regardless of the etiology, the pathologic evaluation of this lesion is always consistent with neointimal hyperplasia.

TREATMENT OF SPECIFIC LESIONS — Ultimately, accurate diagnosis and localization of lesions that led to maturation failure rely on angiography. Since many of these patients have not yet begun dialysis and virtually all have significant residual renal function, concern has been expressed regarding renal toxicity of iodinated contrast. However, the volume of iodinated contrast used for the evaluation in primary arteriovenous (AV) fistula failure is generally not enough to cause problems [66,67]. (See "Endovascular intervention for the treatment of stenosis in the arteriovenous access" and "Techniques for angioplasty of the arteriovenous hemodialysis access".)

Thrombosis of newly created AV fistula — An AV fistula that does not have a palpable pulse or thrill may represent an AV fistula with severely reduced flow or one that is thrombosed altogether (image 1). Duplex ultrasound may be necessary to differentiate between these. Although thrombosis represents a greater challenge than a dysfunctional AV fistula, some of these cases can be salvaged. In one report of 148 thrombosed immature AV fistulas, only eight cases were deemed unsalvageable with initial ultrasound evaluation [68]. Among the remaining 140 cases, 119 (85 percent) had a successful thrombectomy procedure. A variety of lesions required treatment in these cases. Following thrombectomy, additional procedures were required to attain AV fistula maturation. One hundred and eleven of the successfully treated cases were ultimately used for dialysis. Postmaturation primary patency for 108 cases (3 were lost to follow-up) at three months was 53 percent. The primary assisted patency at 12 months was 59 percent. Cumulative patency at 12 months was 90 percent.

Preexisting arterial stenosis — Focal lesions at the arterial anastomosis and within the feeding artery are amenable to percutaneous transluminal angioplasty (PTA) but represent no unique features that would distinguish them from those seen in the mature AV fistula. (See 'Preexisting lesions' above and "Endovascular intervention for the treatment of stenosis in the arteriovenous access".)

One of the primary goals of vascular mapping prior to AV fistula creation is to select an artery of the size conducive to the development of the access. However, there have been reports in which an artery that is smaller than optimal has been used. This is more likely to occur with a radial artery. The distinction between an artery that is diffusely stenotic versus being simply too small to provide sufficient flow is not clear; however, in these cases the term "stenotic" has generally been applied. There are reports of a small series in which angioplasty of either the radial or ulnar artery was used to treat these cases [50,69,70]. While success was obtained, significant complications occurred (as high as 30 percent). These were successfully treated, often by stenting. Based on these limited studies, there has not been enough experience using angioplasty for the treatment of diffuse stenosis of the radial artery to establish a recommendation related to this procedure. The reported complication rate should cause concern.

Preexisting venous stenosis

●Focal stenosis – The treatment of focal venous stenosis associated with an AV fistula requires no modification of the technique used for the treatment of focal venous stenosis associated with a mature AV fistula. (See 'Preexisting lesions' above and "Endovascular intervention for the treatment of stenosis in the arteriovenous access".)

●Balloon-assisted maturation of diffuse stenosis – Balloon-assisted maturation (BAM) is a technique that has been used to treat AV fistulas that are unusable because of diffusely small-caliber veins [55,71]. BAM involves the sequential dilatation of the usable portion of the AV fistula using a progressively larger-diameter balloons. This procedure has a long history and appears to be increasingly popular, despite few evidence-based studies and no randomized trials. In some cases, the vein is essentially converted into a collagen tube. In addition, there are reports of BAM being performed preemptively in the operating room in an attempt to create an AV fistula in a patent vessel otherwise considered suboptimal for AV fistula creation [72,73].

•In one review, 373 patients were treated using BAM two to four weeks after creation of the AV fistula [71]. The inflow and juxta-anastomotic segments were dilated to 4 mm, and the usable segment of the AV fistula was dilated to 4 to 6 mm with the initial treatment. Subsequent dilatations were performed at two- to four-week intervals, with an average of 2.7 sequential dilations required to achieve the desired goal (forearm AV fistula 8 to 10 mm; upper arm AV fistula 10 to 16 mm). Using this approach, a usable AV fistula was created in 94 percent.

•In another study, technical success using BAM was achieved in 118 of 122 patients [74]. The AV fistulas were divided into two groups. Among AV fistulas were that did not mature (2 to 5 mm), the number of procedures required to achieve maturation was 2.6 over a mean of seven weeks. Following BAM, primary patency was 39 percent at six months. Cumulative patency was 77 percent at 12 months, 61 percent at 24 months, and 32 percent at 36 months.

•A transradial approach compared with a transfistula approach has been suggested as a technically easier procedure for performing BAM. In a retrospective review of 205 cases, a transradial approach procedure was considered clinically successful if no further interventions were required for AV fistula maturation [75]. The technical success rate for this series was 100 percent, with 78 percent clinical success.

Handling accessory veins — Our sequential approach to evaluation and treatment of accessory veins that may be contributing to primary failure of an AV fistula is as follows (see 'Accessory veins' above):

●Among patients who appear to have an accessory vein adjacent to a nonmaturing fistula, we first differentiate whether the vein is an accessory or a collateral vein by evaluating for a downstream stenosis. If a stenotic lesion is present, we first treat the stenosis before performing further evaluation. (See 'Preexisting venous stenosis' above.)

●Once a stenotic lesion is ruled out or resolved, and a prominent accessory vein remains, we determine its significance using a combination of the following methods:

•Manual compression – We use duplex ultrasound to examine for changes in bruit and blood flow over the AV fistula above the level of the accessory vein, with and without manual compression of the accessory vein. If the bruit and blood flow through the AV fistula are enhanced with compression of the accessory vein, then it is likely that the accessory vein is interfering with maturation of the AV fistula.

•Accessory vein diameter or other characteristics – In an attempt to develop quantitative criteria for the management of accessory veins, a computer simulation was used to better define blood flow dynamics through a fistula in relationship to accessory vein diameter [76]. As accessory vein diameter increased relative to the diameter of the AV fistula, blood flow through the accessory vein increased by 7, 10, and 31 percent for diameters that were 33, 50, and 66 percent through the AV fistula, respectively. Based on their results, which we have adopted, a "significant" accessory vein and one that may be a candidate for occlusion included any of the following:

-An accessory vein with a diameter ≥60 percent the diameter of the AV fistula.

-An accessory vein with a diameter >50 percent the diameter of the AV fistula with at least one additional accessory vein with a diameter >40 percent the diameter of the AV fistula.

-An accessory vein with a diameter >50 percent the diameter of the AV fistula that further divided to create two of the same size.

-An accessory vein with a diameter that is >30 percent the diameter of the AV fistula, and associated with stenosis at site of origin.

-An accessory vein likely to interfere with cannulation based upon physical examination.

●Once it has been determined that an accessory vein is impeding the maturation of the AV fistula, it can be obliterated by surgical ligation (direct through the skin, or open incision) or percutaneous embolization. Regardless of the technique used, it is helpful to have a guidewire or catheter in the vein. The more common technique is percutaneous insertion of one or more embolization coils into the lumen of the accessory vein [8]. Once the coil is in position, the vein generally thromboses within a few minutes. Alternatively, if the accessory vein is easily visible or readily palpable, it can be ligated by anesthetizing the skin over the vein near the body of the AV fistula and placing a suture through the intact skin and around it [61]. The percutaneous stitch is typically left in place for approximately 10 days to ensure occlusion of the accessory vein, and then removed. Alternatively, if the accessory vein is deep, a small incision can be made overlying it, followed by isolation of the vein, which is then ligated (permanent suture) [58].

Juxta-anastomotic stenosis — The choice of treatment modality for juxta-anastomotic stenosis is controversial. The lesion is amenable to endovascular treatment (image 2) or surgery, and there have been no randomized trials comparing the two for these lesions. Among the available studies, some authors have emphasized that the two approaches should be considered equally valid [77]. Others have concluded that a reasonable approach would be to perform angioplasty first, reserving the surgical approach in the event of failure [78]. This conclusion is based upon findings that although the primary patency following surgical treatment appears superior, cumulative patency is similar, and performing angioplasty first does not exclude a later surgical correction, if required. Thus, initial angioplasty is considered the standard of practice in most centers.

●Endovascular approach – Most endovascular treatment reports involve simple percutaneous angioplasty using a plain balloon; however, the use of drug-coated balloons and stents have also been reported. Reports often mix forearm and upper arm accesses, but a few reports have specifically evaluated juxta-anastomotic stenosis [8,37,38,41,64,79-87]. In these, significant variability in results has been noted with primary patency rates ranging from 47 to 56 percent, assisted primary patency rate of 81 percent (one study), and a cumulative patency rates ranging from 64 to 96 percent [88-90]. It is difficult to make comparisons because of inconsistent reporting of relevant variables. In addition, differences in the character of the lesions (whether the anastomosis may be involved) can influence the results obtained, and the type is not always reported. In one report involving 147 endovascular interventions performed in 75 forearm radiocephalic AV fistulas, a single procedure was performed in each of 38 cases (51 percent) [90]. An additional 22 cases required two procedures, while the remaining 17 cases (23 percent) required three or more, with one case requiring nine. Primary patency was 46.6 at 12 months and 34 percent at 24 months. Assisted primary patency was 81.3 percent at 12 months and 72.4 percent at 24 months. Residual stenosis following the first endovascular procedure exerted a significant effect on assisted primary patency. For those with a ≥50 percent compared with a lesser residual stenosis, the risk of thrombosis or surgical revision was significantly increased (relative risk 2.92, 95% CI, 1.05-8.09).

Several small single-center studies have shown the feasibility of using a drug-coated balloon in treating venous stenosis lesions to improve the outcome as compared with standard balloon angioplasty. The results of the studies have been variable. One prospective, multicenter trial compared treatment with a paclitaxel-coated balloon with standard angioplasty [5]. The results obtained with the drug-coated balloon were statistically superior, but it did not report results for the juxta-anastomotic stenosis lesion separately. A prior report of 26 cases documented primary patency rates for juxta-anastomotic stenosis treated with drug-coated balloon angioplasty of 82 at 12 months and 50 percent at 24 months [65]. Cumulative patency was reported 100 and 95, respectively.

Although stent placement has not been generally considered in the management of juxta-anastomotic stenosis, two small studies have reported outcomes with the use of stents [91,92]. In these cases, the stent by necessity extended into the adjacent radial artery. In one review of 24 cases, the stent was placed following failed angioplasty [92]. Primary patency at 12 months and 24 months was 78 and 69 percent, respectively, and assisted primary patency was 92 and 82 percent, respectively. In a study of 48 cases, a stent was used as primary therapy following angioplasty [91]. Primary patency was 60 percent at 12 months, and assisted primary patency was 93 percent.

●Surgical approach – Surgical approaches include creation of a more proximal neo-anastomosis (resulting in shortening of the AV fistula) [2,8-15,17,18], vein-to-vein reanastomosis [93,94], vein patching [83,94-96], or interposition of a short segment of vein [83,94,96-98] or graft (eg, polytetrafluoroethylene [PTFE]) [47,77,78,84,85,93,95,98-100]. Four small nonrandomized cohort studies reported surgical outcomes for neo-anastomosis creation or interposition grafting [77,78,100,101]. In a meta-analysis of these, pooled primary patency at 12 and 18 months and the assisted primary patency at 24 months was significantly improved for surgery compared with angioplasty [100,101]. However, there was no significant advantage for cumulative patency in the two studies in which it was reported. Disadvantages of the surgical approach relate to the fact that although creating a neo-anastomosis is a relatively simple procedure, it does expose the patient to an increased degree of discomfort and potential complications. In addition, inserting expanded PTFE into the venous circuit imposes the increased frequency of AV graft stenosis on the fistula.

OUTCOMES FOR FISTULA SALVAGE — The results gained by the treatment of nonmaturing arteriovenous (AV) fistulas have been variable. It is very possible that the outcome differences in reported series are due to variability in the studied populations. Nevertheless, when compared with the alternative of abandonment, one is forced to conclude that the results are extraordinarily good. However, it is possible that prescreening of cases may have led to case selection favoring a successful outcome. The degree to which this was done is not clear in most reports.

Using the United States Renal Data System, one retrospective study evaluated outcomes of over 7000 older adult patients (≥67 years) who underwent assisted versus unassisted maturation of their AV fistula [102]. AV fistulas matured without prior intervention for 56 percent of the patients. Assisted AV fistula maturation with 1, 2, 3, or ≥4 prematuration interventions occurred in 23, 12, 5, and 4 percent of patients, respectively. The likelihood of functional patency loss increased with the number of prematuration interventions (odds ratio [OR] 3.46; 95% CI 1.96-6.11 among patients with four or more interventions compared with those who had unassisted maturation). The likelihood of AV fistula abandonment was no higher for patients with ≤3 prematuration interventions compared with patients with unassisted AV fistula maturation. However, it was significantly higher among those with ≥4 interventions (OR 1.44; 95% CI 1.07-1.95).

A systematic review that identified 12 studies reported success rates and complications of interventions performed for primary AV fistula failure [103]. The rate of clinical success, defined as the ability to use the AV fistula at least once for hemodialysis, was 86 percent. The average one-year primary patency rate was 51 percent (range, 28 to 68 percent). The average one-year cumulative patency rate was 76 percent (range, 72 to 95 percent). The overall complication rate was 9.3 percent, the majority of which were minor complications.

An example of a single-center study is one that collected data on 141 cases of primary AV fistula failure [104]. All cases in this cohort had significant anatomic causes for their failure of maturation. Multiple sites of stenotic lesions were found in 46.1 percent of patients. The sites of stenosis were juxta-anastomotic venous segment (65.2 percent), venous outflow (41.1 percent), AV anastomosis (30.5 percent), native artery (5.7 percent), distal outflow (9.2 percent), and central vein (3.5 percent). Technical success was achieved in 95.7 percent and clinical success in 86.5 percent. Primary patency (figure 1 and table 1) was 71.9, 60.1, and 54.5 percent at one, two, and three years, respectively. The respective cumulative patency rates were 82.8, 82.0, and 82.0 percent.

There is evidence to suggest that, compared with AV fistulas that mature without intervention, AV fistulas that require intervention have decreased cumulative survival and require more procedures to maintain their patency for hemodialysis. In a review of 173 patients requiring intervention for a nonmaturing AV fistula, 96 (56 percent) required no further intervention, 54 (31 percent) required one intervention, and 23 (13 percent) required two or more interventions to achieve suitability for dialysis [105]. For patients with ≥2, 1, or 0 interventions before maturation, cumulative AV fistula survival (access cannulation to permanent failure) was 68, 78, and 92 percent, respectively, at one year; 57, 71, and 85 percent at two years; and 42, 57, and 75 percent at three years. Using Cox regression analysis, two or more interventions before maturation was the only factor associated with cumulative AV fistula survival.

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".)

SUMMARY AND RECOMMENDATIONS

●Primary failure – A hemodialysis arteriovenous (AV) fistula that is either never usable for dialysis or fails within the first three months of use is classified as primary failure. (See 'Primary failure' above.)

●Incidence – With increased efforts to create AV fistulas in the population of patients who are starting hemodialysis, a significant percentage of patients experience primary AV fistula failure. The incidence appears comparable for surgically created compared with percutaneous AV fistulas (ie, endoAVFs). (See 'Incidence' above.)

●Fistula maturation and evaluation – A thorough evaluation of a new AV fistula four to six weeks after creation should be considered mandatory to detect problems as early as possible. Both arterial and venous stenosis have been reported to cause primary AV fistula failure. The presence of multiple lesions is very common. (See 'Fistula maturation and evaluation' above and 'Associated vascular lesions' above.)

●Fistula salvage – There is evidence to suggest that, compared with AV fistulas that mature without interventions, AV fistulas that require interventions have decreased cumulative survival and require more procedures to maintain their patency for hemodialysis. (See 'Outcomes for fistula salvage' above.)