Patient selection,education,and cannulation of percutaneous arteriovenous fistulae: An ASDIN White Paper

Why is a team approach needed?

Dialysis vascular access care is often fragmented with suboptimal communication between patients, families, nephrologists, dialysis units, surgeons, and interventionalists. Typically, vascular access procedures are planned and executed by one provider such that details of what was done or why may be lacking. Communication and education among all stakeholders are necessary for successful creation and maintenance of all forms of accesses, but particularly for pAVFs, given their differences and novelty.

Who are the team members?

The patient and their relevant loved ones (supporters) must understand their dialysis options and the advantages and disadvantages of a pAVF compared with an sAVF. In order to properly inform the patient, the nephrologist must understand the technology, appropriate patient selection, and whether the pAVF or sAVF will provide the prescribed dialysis dose. The dialysis unit should understand the anatomic and physical examination nuances of a pAVF and techniques for successful cannulation. A close working relationship between the interventionalist and surgeon is necessary in the event of a complication, need for secondary procedure, or conversion to an alternate access.

How can team member engagement be achieved?

Multidisciplinary meetings and shared decision-making are recommended for successful patient screening and procedural and cannulation outcomes. Timely communication with dialysis centers, and support by providing patient and staff educational materials and on-site ultrasound-guided initial cannulation (as necessary), will help achieve successful pAVF use.

Patient eligibility

Vascular eligibility

How does a pAVF differ from an sAVF?

A pAVF is created percutaneously using a needle and special device, rather than surgically, so it lacks a traditional surgical scar and may not be easily recognized by care providers. Thus, the pAVF outflow veins could inadvertently be injured with phlebotomy, blood pressure cuff inflation, or IV needle insertion. Therefore, patient and supporter education must focus on protecting the pAVF; this is best achieved during informed decision-making before creation and reinforced at the time of pAVF creation by the physician and supporting dialysis access care team. Medical alert bracelets indicating pAVF presence are also helpful for patients with communication difficulties or where English is not their first language.

How can the patient take care of their access site?

As with any access, a patient must avoid inadvertent injury to the pAVF. First, the proceduralist can provide both documentation (including a diagram indicating the vessels used and location) and proceduralist contact information. Prior to cannulation, an ultrasound and a photo of the arm with the outflow cannulation zone clearly marked can be taken. These materials can be saved on the patient’s phone and sent to the managing nephrologist, dialysis unit, and other providers. Other methods are similar to sAVF protection, including the use of patient wrist bands stating “no venipuncture, IV or BP” and so on. ³

The patient should be instructed on care of the access arm, including washing it daily with soap and warm water and before each dialysis treatment, avoiding phlebotomy or blood pressure measurements, and checking it daily to ensure it is working normally and has blood flow (One-Minute Access Check). ⁶

Can a patient with a pAVF self-cannulate?

The patient should be informed and offered the option for self-cannulation by the outpatient dialysis facility. Therefore, pre-procedure planning should include every attempt to place the pAVF in the non-dominant arm, allowing the dominant arm to perform the cannulation. There are several advantages to self-cannulation, including reduced risk of cannulation injury from multiple dialysis personnel, control over infection risk, and ensuring proper cannulation and site rotation. Patients can start with small steps in the cannulation procedure, learn at their own pace, and master as much of the procedure as they can.

How long does it take for a pAVF to mature?

Following creation of a pAVF, the typical time to physiologic maturation is 6–10 weeks. If pAVF physiologic maturation is achieved at 4 weeks, it is reasonable to attempt cannulation sooner, depending on individual dialysis unit expertise.

How is pAVF maturation defined?

Physiologic maturation is defined as a blood flow volume (Qa) in the brachial artery of >500 mL/min and a cannulatable vein diameter of >5 mm; ⁷ a diameter of >4 mm may be acceptable if the vein is palpably superficial or there is ultrasound-guided cannulation available at the dialysis facility. ²

How is pAVF maturation assessed?

Physiologic maturation is assessed with ultrasound and physical examination. An ultrasound brachial artery Qa measurement may be obtained at 1 week to assess patency of the pAVF. A second ultrasound may be obtained at 4 weeks to assess physiologic maturation—to assess brachial artery and outflow vein Qa, and superficial outflow vein diameter, as pAVFs often have a bifurcated outflow. Deep veins (brachial) should be evaluated for excessive shunting to a non-targeted outflow vein.

Physical examination is a crucial component of the maturation assessment and should be performed at each follow-up visit post-creation. It may be performed monthly if the patient is pre-ESKD or more often when dialysis initiation is indicated and should include visual examination of the outflow veins that will be used for cannulation. By palpation, the veins should feel full without a tourniquet. A tourniquet should be applied to determine which outflow veins augment to select potential cannulation sites.

What ultrasound parameters should be expected at week 1 in a pAVF?

If the brachial artery Qb is >500 mL/min 1 week following pAVF creation, physiologic maturation is likely to occur. If the Qb is <500 mL/min, a 2-week post-procedure evaluation is indicated. The proper timing for intervention with balloon angioplasty for non-maturation differs between the two devices, and the interventionalist should be aware of the appropriate recommendations.

What ultrasound parameters should be expected by week 4 in pAVFs?

At 4 weeks following pAVF creation, brachial artery Qa should be >500 mL/min; if it is <500 mL/min, a fistulogram, often from a distal arterial approach, should be performed to evaluate the arterial anastomosis and juxta-anastomotic segment with the intention to treat if a high-grade stenosis is present.

If brachial artery Qa is >500 mL/min but blood flow volume is inadequate in the outflow veins, redirecting the flow into the superficial veins should be considered. If needed, coil embolization of a competing brachial vein can be performed to redirect flow into the superficial circulation. Coiling, ligation, or banding of the median cubital vein to favor flow into the cephalic vein may be considered, but there is no evidence to date to support its impact on long-term functionality and durability of a pAVF.

What ultrasound parameters indicate that the pAVF has reached physiologic maturation?

The benchmark flows needed to support sustained dialysis in the ipsilateral brachial artery are ⩾800 and ⩾500 mL/min in the cannulation vein segment(s).^1,2 If Qa is >800 mL/min in the brachial artery and a cannulatable outflow vein diameter of >5 mm, the outflow veins should be marked with indelible ink to aid in the first few cannulations and the pAVF should be cannulated using a tourniquet. If the pAVF can sustain a dialysis blood pump speed (Qb) of 400–450 mL/min with two needles, the fistula is considered mature for typical North American dialysis prescriptions. The dialysis prescription should be assessed to accommodate the Qb setting that is achievable within safe arterial and venous pressure limits. In other areas of the world or other dialysis techniques (e.g. long nocturnal dialysis) that may only require Qb < 300, a pAVF outflow vein Qa of 350 mL/min may be acceptable.

What additional procedures may be necessary to promote pAVF use?

Balloon angioplasty or side branch ligation may be required for pAVF maturation, highlighting the need for excellent multidisciplinary communication among team members, as the creating proceduralist may be different than the one maintaining or salvaging the pAVF. As with other vascular access procedures, all pAVF procedures are done after determining that the arterial supply to the hand is adequate, and hand ischemia is not anticipated.

What should happen prior to the first pAVF cannulation?

The physician creating the pAVF should schedule patient follow-up 1–2 weeks after the procedure to evaluate the patient and assess the pAVF diameter for outflow size and flow volume to determine pAVF progress toward maturation. A goal of initial cannulation within 6–10 weeks of creation is reasonable in properly selected patients for pAVFs; if the pAVF is not progressing toward maturation, then an ultrasound (if not already done) ± fistulogram and intervention as indicated is recommended.

What role does the interventionalist have in promoting successful cannulation?

It is recommended that a “cannulation map” be made prior to cannulation, detailing cannulation zones, blood flow direction, vessel depth from the skin to determine the needle angle of entry, and cannulation zone length for successful needle placement. This can be easily created with ultrasound imaging. If a specific needle length is recommended (3/5-inch needle for shallow vessel, 1 inch for typical depth vessel, or 1¼ inch for deep vessel), it should be highlighted on the cannulation map, and the map should be updated if any interventions impact the pAVF. This map is a critical part of the patient’s medical record and should be accessible to anyone needing to cannulate the pAVF should the patient be hospitalized.

Prior to cannulation, the targeted outflow cannulation sites should be marked, ideally by ultrasound (Figure 2), and the cannulation plan should be reviewed by both the patient and relevant dialysis unit staff, for example, a head nurse and vascular access coordinator. Photographs of the pAVF marked with the cannulation zones should be found in the patient’s medical record and used by an expert cannulator assigned for the first few cannulations, as similarly recommended for all vascular access patients.

OPEN IN VIEWER

Figure 2.

Percutaneous AVF and marking by ultrasound for cannulation.

The cannulation technique of a pAVF is similar to an sAVF

It is important to ensure that the staff members are familiar with their individual dialysis unit cannulation policy, as pAVF cannulation builds on existing techniques. A tourniquet should be used, regardless of the size or appearance of vessel, as it helps to engorge, visualize, palpate, and stabilize the pAVF. The perforating vein joins the superficial veins below the elbow crease, and since there is no surgical scar here, this segment frequently offers a reliable pAVF cannulation segment.

Ultrasound availability and use for the first cannulation has proven to be valuable in select patients, particularly in obese individuals.^11–13

How is the cannulation site selected?

One must be mindful of patient comfort during a dialysis session and consider arm positioning (e.g. patient works on computer and knits) when selecting suitable cannulation sites. The most common suitable vein will be the upper arm cephalic, although significant outflow may develop into the basilic system. Sites closer to the elbow crease may be cannulated with the needle in a retrograde position to minimize needle movement with arm motion.

If cannulation of the median cubital vein is difficult or additional flow through the cephalic vein is needed for reliable cannulation, then banding, ligation, or coil occlusion of the median cubital vein may be necessary, directing all outflow into the cephalic system. These interventions, if needed, parallel the same maturation processes often required for establishing a functional sAVF. Occasionally, the patient’s cephalic vein is inadequate, and all flow is into the basilic or brachial vein. A staged elevation or transposition will typically be needed for those individuals, just as with sAVFs.

What is the recommended position for the patient and cannulator?

We recommend that the patient’s arm be extended in a comfortable position on the chairside table, resting on a pad or pillow, and that the cannulator be seated at the same level as the pAVF. The seated position stabilizes the cannulator, prevents bending over the pAVF, and allows to better control the forward pressure when puncturing the skin, tissue, and vessel with the needle tip. A new cannulator commonly applies excessive pressure to the needle wings, and thus the cutting bevel, and can easily enter the vessel and depress the vessel leading to a backwall puncture and infiltration. It is recommended that the cannulator remains seated until the needles are fully stabilized with tape as per facility policy and procedure.

What needle size and pump speed should be used initially?

We suggest that the initial dialysis cannulation protocol for sAVFs should be followed for pAVFs, including using a single, smaller (17 Ga) needle for the arterial limb and returning through the catheter (if present) and progressing to higher pump speeds and dual-needle cannulation as tolerated.

Providers and patients using a catheter should be educated in advance of a possible decline in dialysis adequacy with pAVF use, since a lower pump speed may be required (~350 mL/min) until optimal pAVF flow rates are achieved (similar to sAVFs). Of note, if two well-developed outflow veins develop, for example, median cubital/basilic and cephalic, cannulation of these may result in improved dialysis adequacy, given the lack of recirculation in this setting.

Which cannulation technique is recommended for pAVFs?

Rope ladder cannulation will be appropriate for most patients, with buttonhole cannulation used in selected patients, per the Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines. Expert cannulators note that a pAVF feels softer as the needle tip enters the vessel and that blood flashback is often less vigorous than an upper arm sAVF, and thus, wet needle cannulation may be helpful.

With tourniquet in place, cannulation should proceed with light pressure to avoid vessel collapse and backwall injury. Vessel depth is used to determine the needle angle, and typically, a 20–35° angle is used for pAVF cannulation. The cannulation zone length must also be clearly identified. The standard metal fistula needles come in 1-inch or 1¼-inch lengths, while a shorter, 3/5-inch metal fistula needle may be beneficial. The needle direction for the venous needle should always point toward the venous return to the central system. The arterial needle can be pointed toward the inflow (retrograde) or toward the venous return (antegrade), depending on the cannulation zone length and unit-specific policy/procedure for cannulation. Outside the United States, plastic cannulae are commonly used to cannulate pAVFs, especially if the cannulation zone crosses the elbow crease, where there is increased risk of infiltration related to arm movement.^13–15

What parameters are important to monitor during dialysis?

The arterial and venous pressures should be monitored in these moderate flow pAVFs, with particular attention to the arterial pressure, as it may become too negative to support a standard blood pump speed.

How should a pAVF be monitored?

Access monitoring utilizing the standard physical examination or the One-Minute Check is recommended per facility policy and procedure for all pAVFs. ⁶ The augmentation test may vary if the pAVF outflow has significant side branches or several outflow segments. Further, in the setting of multiple egress vessels, the arm elevation maneuver with resultant AVF collapses to ascertain draining vein stenosis does not exclude a downstream stenosis in one segment. This is may be problematic when the main draining vein is being cannulated, as typical signs of an outflow vein stenosis are absent, although there might be a failure to deliver adequate dialysis (i.e. high recirculation).

When an abnormality, such as high pressure, low flows, recirculation, and/or difficult cannulation, is detected, a prompt referral should occur for evaluation by the treating physician, ensuring that communication occur between all members of the multidisciplinary team.

What is the best way to conduct flow surveillance of a pAVF?

The presence of a pAVF must be clearly delineated in the patient’s medical record for accuracy in reporting and tracking. Ultrasound measurement of Qa using brachial artery flow is a reliable and reproducible surrogate for AVF flow and has become a common adjunct for evaluation and treatment decisions, but this is not readily available in the dialysis unit.

Both the Transonic Ultrasound Dilution and the Fresenius Online Clearance methods require reversal of the bloodlines to the needle connection point to create reversed flow within the AV access. If the pAVF has branch flow and both needles are not in the same vessel, the Qa measurement cannot be properly determined and will not be accurate. The Vasc-Alert’s Vascular Access Pressure Ratio and other Transonic measurements including delivered flow, recirculation, or cardiac output are not impacted by the branch flow needle placement.