Section 5: Common Complications with AVF

Juxta-Anastomotic Stenosis is a common reason for failure to mature (FTM) with all types of AVFs, leading to early thrombosis from neo-intimal proliferation. Physical examination can detect this condition easily (Figure 37)

A juxta-anastomosis stenosis is amenable to treatment. There are two choices for therapy: percutaneous angioplasty (PTA) or surgery. There are no randomized controlled studies to determine which of these two modalities represents the better choice for therapy. Surgery consists of a new anastomosis higher up on the artery (Figure 38) or interposition of a short interposition graft segment with transposed vein or a polytetrafluoroethylene (ePTFE) graft. A short stenosis can also be patched with a harvested vein or ePTFE (Figure 39).

The choice between patch-plasty of a stenosis, re-anastomos by moving the anastomosis further up, or place and interposition graft of a vein or a PFTE is determined by local anatomy, size of vein, length of  remaining cannulation segment (Figure 38) and Figure 39). Outflow lesions that result in FTM include accessory veins or pre-existing small and stenotic veins.

Diffuse venous stenosis occurs with small pre-existing veins smaller than 2.5 mm, when small veins fail to dilate. Repeat primary balloon angioplasty (PBA has been utilized to achieve adequate outflow vein size. The sequential dilatation of the outflow veins using progressively larger sized, also known as Balloon Assisted Maturation (BAM) is done at 2-4 weeks interval following creation to salvage non-maturing access with good results reported (1)

Focal venous stenosis along the fistula vein may also be seen associated with failure of maturation. Mid-vein stenoses are commonly the results from past IV or blood drawings causing local hematomas and vein scarring from fibrosis (Figure 39).

Endovascular Technique for Creating Arteriovenous Fistulae.

Recent endovascular innovations have developed two minimally invasive techniques to create AVF fistula using one or two catheter techniques respectively. Both techniques use preoperative vascular mapping of the antecubital vessels to determine suitability for respective techniques (2-8). For details on endovascular AVFs the reader is referred to the chapter, dedicated to Minimal Invasive Dialysis Access (MIDA). The MIDA concept in addition to AVF includes the percutaneous modified Seldinger technique for peritoneal catheter placement. The percutaneous MIDA technique for PD catheters uses endovascular instruments and will decrease the unfortunate separation between Hemo and peritoneal dialysis in clinical practice caused by specialty and society policies (9-11).

The antecubital superficial veins are best understood by having an archetypal roadmap of single veins made up of five essential veins: the perforating vein, medial cubital vein (MCV), the cephalic vein, the median basilic vein (MBV), basilic vein (Figure 34).

The anastomosis is created with radiofrequency power, and electrocautery across vessels aligned by opposing magnets to create the AVF anastomosis for the single and dual catheter technique respectively. Both devices have CE mark status in Europe and recently also FDA approvals in the US (3,4).

Preliminary results report near 100 % technical success and a fistula maturation rate approaching 90%, better than usual is reported for surgically created AVFs (8-11).

Accessory veins (“side branches”) are part of normal arm anatomy and can affect AVF development and maturation. (Accessory veins must not be confused with collateral veins which are pathological and related to down-stream stenosis). The reported incidence of accessory veins varies from 4 to 78%, likely to represent differences in case selection. Preoperative assessment looking for accessory veins has been recommended, and it has been proposed that ligation of these vessels during initial AVF creation to potentially reduce non-maturation. The treatment of an accessory vein is ligation, but controversial. When side branches are observed on the angiogram of an AVF which has failed to mature, the first step is to determine if they are accessory or collateral veins.

The mere presence of an accessory vein is not an adequate indication for ligation. Small side branches are frequently encountered and are of no consequence. There should be evidence that the FTM is attributed to the accessory vein based on size, flow and changes that occur with manual occlusion. There are no reports to provide guidance in this respect. Changes that occur with manual compression of the side branch are often best evaluated using a vascular Doppler and comparing the sound and blood volume flow over the AVF above the accessory vein with and without compression of the accessory vein. This requires an experienced dialysis clinician.

Dialysis Access Steal Syndrome (DASS) is rare with AVFs created at the wrist (<1 %.) In brachial artery access DASS occurs in 5 – 10% of cases. This has prompted the use of proximal radial artery (if feasible) instead of distal brachial artery. Using proximal brachial and the axillary artery has remarkable low incidence of DASS which is the reason to the proximal artery as inflow (PAI procedure) concept in treating DASS in the upper arm.

For detailed description of hand ischemia after dialysis access the reader is referred to and the linked manuscript from J Vasc Access.  (REFERENCE 2).

Aneurysms. Pseudo aneurysms (pAVA) are rare in a native vessel (false aneurysm, associated with a defect in the vessel wall), most of the bulges that are noted in association with AVF are true aneurysms (containing all layers of the vessel wall (Figure 41) represent a pathological dilatation of the vessel rather than a rupture of its wall components. The treatment options are guided by team skills, the skin quality, the size and extent of the aneurysm to mention a few factors.

For in-depth review of dialysis access aneurysms, the reader is referred to chapter x, www.kidneyacademy.com

Limitation of cannulation sites or the ability to cannulate a fistula is its prime function. Yet, in some patients’ cannulation is performed repeatedly over a small area (“area cannulation”.  The reasons for this are multifactorial include patient preference or cannulator preference for an area of fistula that is easily palpable. This should be discouraged, and education directed to cannulate with either rope ladder or buttonhole techniques. Repeated area cannulation of a fistula results in premature failure through stenosis or aneurysm formation. In some patients superficialization may be needed but in most an expert cannulator and/or ultrasound guided cannulation will allow new sites to be identified and used.

Thinning of the skin. Repeated cannulation and dilatation of a fistula results in thinning of the overlying skin. While most fistulas with time experience scaring at needle sites arises as to what point in this progression is the appropriate time for concern. This decision is generally based on experience and subjective assessment. If the skin is shiny, tissue paper thin and if you cannot pinch the skin between your index finger and thumb, it has advanced to a dangerous degree and intervention should occur. This may include revision or creation of new access including the PD option.

Spontaneous bleeding from a fistula is a potential life-threatening situation. In aneurysmal fistulas as the skin becomes increasingly thin, the aneurysm becomes more susceptible to spontaneous bleeding. This may be related to the ill-advised cannulation of the structure or inadvertent trauma. Increased pressure in the fistula may be due to outflow stenosis. Increased bleeding of cannulation sites indicates outflow stenosis and should be correlated with dialysis parameters (high venous pressures) and physical examination.

Check the patient’s dialysis prescription. Anticoagulant medication also results in prolonged bleeding. Bleeding from a fistula should be taken seriously and often a herald bleed occurs before the main rupture. Avoiding this is best by immediate surgical treatment although temporizing the situation with a stent graft may be lifesaving.

Dr. NC LIEW from Kuala Lumpur is sharing three cases of life-threatening bleedings from Arteriovenous Fistulas with various forms of aneurysms.  You can reach Dr Liew at ncliew6629@gmail.com 

Ulceration on an AVF often precedes life-threatening bleeding and must be dealt with on an emergency basis. Ulceration generally indicates that rupture is imminent.

Failure to mature (FTM) has many definitions but in practice it is an AVF that is never usable for dialysis. It may be termed early failure or “primary failure”. As efforts have been intensified to create more AVFs, studies of 20 to 25 years ago observed early failure rate was in the range of 10 to 25 %, while recent reports are much higher, in the range of 20 to 60 % (1). This may reflect more stringent definitions and better follow up to define outcome. Published studies claim excellent success of AVF techniques but in practice when functional outcomes are assessed only about 50% of AVFs created get cannulated (primary functional patency).

Other drifts in practice are that dialysis machine blood flow requirements have increased from 200 to 400 ml/min and 75% of patients now have more than five co-morbidities, most notably hypertension, diabetes, obesity and cardiac vascular nature.   A confounding factor is the impact of the “Fistula First” movement emphasizing the placement of AVFs over other forms of access.

Failure to mature (FTM) is usually described as a purely biological phenomenon related to pathological vessel remodeling, but it has many causes. These include complications resulting in failure such as hematomas, pseudo aneurysms, infections, compression, thrombosis secondary to hypotension etc. as well as technical issues at surgery.

As efforts have been intensified to create more AVFs such as the “Fistula First” initiative, and one size fits all guidelines emphasizing the placement of AVFs over other forms of access, the failure rate of AVFs appears to have increased. While a failed fistula attempt may not be immediately life threatening it is an added burden to a patient and reduces the overall Quality of life (2). In addition, it may reduce confidence in future attempts and encourage increased CVC use.

Table 9.  Early Fistula Failure include inflow, out flow and general factors.

Inflow problems

• Pre-existing arterial anomalies
• Anatomically small artery (less than 3 mm)
• Atherosclerotic disease
• Anastomotic stenosis
• Juxta-anastomotic stenosis 

Outflow problems

• Pre-existing venous anomalies
• Diffuse venous stenosis (small veins)
• Focal venous stenosis (from veno-punctures)
• Accessory veins (side branches)
• Thrombosis
• Venesection/blood draws from target vein

General Issues (Center Effects)

• Referral pattern
• Surgeon proficiency
• Team skills
• Cannulation techniques and policies
• Fistula First, Distal First policies influence
• Ultrasound is not used for preop vascular mapping.

Inflow lesions include artery stenosis, atherosclerosis, particularly diabetes, anastomosis and juxta anastomotic stenosis.

Feeding artery. The criteria below are small, or stenotic artery should not be used site for the AVF but is found in 4-6% of FTM cases. Fistula maturation requires a rapid increase in blood flow through the vein, and this relies on arterial recruitment. A non-calcified artery dilates in parallel with increasing blood flow in the fistula.

Arterial anastomosis: It is difficult to evaluate the arterial anastomosis in absolute terms because it is an artificially created orifice. However, it has become common practice to compare the diameter of the orifice to the adjacent normal feeding artery and if it is less than 50% to consider it as stenotic. The incidence of anastomotic stenosis has been reported to range from 38 to 47% usually associated with juxta anastomotic lesions.

Diffuse venous stenosis may occur with small pre-existing veins smaller than 2.5 mm, when small veins fail to dilate. Focal venous stenosis along the fistula vein may also be seen associated with failure of maturation (Figure 37). These are commonly the results from past IV or blood drawings causing local hematomas and vein scarring from fibrosis although common sites such as the juxta-anastomotic segment may represent aggressive inward neo-intimal hyperplasia.

Accessory veins are part of normal arm anatomy but can affect development and maturation of the veins used for the construction of an AVF. The incidence of accessory veins varies from 4 to 78% likely representing differences in case selection. Preoperative assessment of looking for accessory veins has been recommended. It has been proposed that ligation of these vessels during initial AVF creation could potentially reduce non-maturation rates. Treatment of an accessory vein is ligation or endovascular coiling, but this is controversial as many maturing AVFs have similar accessory veins also. When side branches are observed on the angiogram of an AVF which has failed to mature, the first step is to determine if they are accessory or collateral veins.

The mere presence of an accessory vein is not an adequate indication for ligation. Small side branches are frequently encountered and are of no consequence. There should be evidence that the FTM is attributed to the accessory vein based on size, flow and changes that occur with manual occlusion. Manual compression of the side branch evaluated using a vascular Doppler may establish the effect of ligation on flow.

Early failure evaluation is mandatory after four to six weeks after creation to detect problems. Experienced evaluation prior to cannulation has been shown to improve successful cannulation and overall outcome (19).

Excessive AVF blood volume flow rate may cause high-output heart failure. As most reports are based on a few case reports, the incidence, causes, risk factors and definitions of AVF induced heart failure are not well known but likely affect most patients with underlying cardiac disease (3).

The Thrombosed AVF. Treatment of fistula thrombosis may use several techniques with initial success been shown to be over 50%. Aneurysmatic AVF may be troublesome because of the large thrombus volume and tortuosity. There is a risk of pulmonary embolism with all thrombectomy methods and should therefore be treated by open surgery with up to 90% successful outcome, although major revision of the fistula may be required. Evidence for modality of thrombectomy is varied with differences between the endovascular and surgery thrombectomy modalities due to different approaches. Endovascular approaches use mechanical thrombectomy devices or delivery of thrombolytic agents. In addition, endovascular approaches allow identification of outflow stenosis and visualization of the entire access circuit. In addition, causative stenosis can be treated. Surgical studies have in many cases totally revised the original access or formed new access at the time of surgical thrombectomy

Difficult Cannulation The constant site or “buttonhole” technique is more common with AVFs than with grafts and may be advantageous in situation of challenging cannulations. This method may shorten the bleeding time, decrease cannulation pain, and the tendency for aneurysms. (Figure xx). Cannulas are inserted at exactly the same spot at consecutive dialysis sessions. With these repeated cannulations into the exact same puncture site, a scar tissue tunnel tract develops. This tract allows the needle to pass through to the vessel of the fistula following the same path each time. The needle tract is developed after about 10 cannulations. Once the track is established, other cannulators can perform the procedure. Maintenance of the track through needle insertion is always at the same penetration angle.

Using plastic needles is common in some countries such as Japan, enables using smaller veins for cannulation and veins in the elbow area as these allow bending 4).

There are other advantages with plastic needles such as less risk for vascular damage, and infiltrations, improved access longevity and patient comfort. Using longer dialysis sessions with lower machine flow also helps patient comfort as practiced in Japan (4).

Why Does the U.S. Still Use Steel Needles for Hemodialysis?

Japan runs at machine blood flow rates of 250-300 ml/min in contrast to most western countries with flow rate of 450-500 ml/min. The median time to maturation in Japan is 10 days, 46 days in Europe and Australia, and 82 days in the U.S (12,13).

The choice of needles for dialysis is likely financial as dialysis treatment is dominated by two commercial companies.

The use of plastic needles does not adhere to the “rules of 6s” (Table 3).