Arteriovenous Fistula Ultrasound: How, What, Where?

As we know, anything is possible in vascular surgery and vascular surgeons like to get creative at times. Also, 90% of the time patients will not be able to tell you what kind of fistula was created. Hence, as the sonographer you have the fun task to figure out what kind of fistula was created and if there's anything wrong with it.

Besides, venous insufficiency exams, AVF cases are another of my favorites, due to the simple fact that you never know what you're getting yourself into, and I LOVE that thrill lol.

Speaking about thrills, prior to starting your scan ALWAYS palpate the area of access for that thrill. This will give you so much information even before you start scanning.

By simply doing that, you will know two important things:

1. Where the inflow anastomosis is located and

2. If the AVF is working adequately

If the fistula is patent you should be able to feel a strong and steady thrill. If you aren't able to feel it then the fistula is likely thrombosed or failing.

In this blog, we will start by reviewing the type of fistulas that could be created, protocol, technique, and criteria.

*Note: this protocol/criteria may vary from facility to facility, below is what I personally do. However, this can serve as a baseline for those of you that currently do not have a protocol in place.

Types of Arteriovenous Fistulas and Grafts

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Types of Arteriovenous Fistulae

1. Side of artery to side of vein

2. Side of artery to end of vein (Brescia-Cimino AVF) (Most Common)

3. End of artery to side of vein

4. End of artery to end of vein

Types of A-V Grafts

1. Straight graft

2. Loop graft

Possible Connections

Forearm AVF

1. Radial artery to cephalic vein

2. Radial artery to basilic vein

3. Radial artery to other suitable vein (transposition)

Upper arm AVF

1. Brachial artery to cephalic vein

2. Brachial artery to basilic vein

3. Brachial artery to other suitable vein (transposition)

Forearm graft

1. Brachial artery and antecubital vein (loop graft)

Upper arm graft

1. Brachial artery and high brachial or basilic vein

Thigh graft

1. CFA to CFV

Protocol

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Before starting to document your images, find out what type of fistula your patient has. If the patient does not know, then, simply sweep through to find out, once you're sure of what you're dealing with, start your protocol. The reason for this is that you don't want to start scanning with your labels saying AVF when in reality is an AVG or say it's a brachio-cephalic when in reality it's a brachio-basilic. This will save you some time, and you will feel more confident throughout your scan.

Arteriovenous Fistula (If located in the Upper Arm)

Arterial Inflow

1. Velocity (cm/s)

Inflow Anastomosis

1. Velocity (cm/s)

Upper Arm Fistula Inferior

1. Velocity (cm/s)

2. Depth (mm)

3. Diameter (mm)

Upper Arm Fistula Mid

1. Velocity (cm/s)

2. Depth (mm)

3. Diameter (mm)

4. Volume Flow (mL)

Upper Arm Fistula Superior

1. Velocity (cm/s)

2. Depth (mm)

3. Diameter (mm)

Axillary Vein

1. Velocity (cm/s)

Subclavian Vein

1. Velocity (cm/s)

*If the fistula is located in the forearm, it is the same concept, simply change "upper arm" to "forearm" in your protocol.

*Obtain velocities were "X's" are located.

Arteriovenous Graft (if located in the Upper Arm)

Arterial Inflow

1. Velocity (cm/s)

Inflow Anastomosis

1. Velocity (cm/s)

Upper Arm Graft Inferior

1. Velocity (cm/s)

2. Depth (mm)

3. Diameter (mm)

Upper Arm Graft Mid

1. Velocity (cm/s)

2. Depth (mm)

3. Diameter (mm)

4. Volume Flow (mL)

Upper Arm Graft Superior

1. Velocity (cm/s)

2. Depth (mm)

3. Diameter (mm)

Outflow Anastomosis

1. Velocity (cm/s)

Axillary Vein

1. Velocity (cm/s)

Subclavian Vein

1. Velocity (cm/s)

*If the graft is located in the forearm, simply change "upper arm" to "forearm". If it is a loop graft in the thigh, then change it from "upper arm" to "thigh". Also, always document whether it is a straight graft or looped graft.

*Obtain velocities were "X's" are located.

Technique

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How to Measure the Volume Flow:

*Keep physics in mind in order to make sense of this calculation. Take a look at the formula ->

1. Make sample gate as big as the vessel

2. Angle parallel to the vessel (≤ 60° angle correct )

3. Measure AP diameter perpendicular to angle,

inner to inner (will kind of look like a plus sign + )

How to measure the depth: distance from skin to anterior wall of draining vein

How to measure the diameter: inner wall to inner wall of draining vein

Additional tips: Document aneurysmal dilatations, abscesses, hematomas, seromas, and stenosis. If stenosis present measure original lumen and residual lumen within the area of stenosis, as imaged below.

Criteria

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6-8 weeks after surgery should meet the 3 following criteria

1. AP diameter of draining vein - at least 4 mm

2. Distance from the skin to the anterior wall of the draining vein - less than 5mm

3. Flow volume - at least 500 mL/min

Normal Findings:

• Increased monophasic flow in feeding artery

• Perivascular tissue vibration (thrill) in area of anastomosis

• Increased monophasic, pulsatile flow within vein (arterialized vein)

• Volume flow >500mL/min

Volume Flow Criteria

Normal value

• Forearm fistula: 600 - 800

• Upper arm fistula: 900 - 1200

Mature fistula: ≥500

High risk of occlusion:

• AVF: <300

• Graft: <650

High-output cardiac failure

• Adult: >3.000

• Children: >700

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I hope you all enjoyed this blog,

Daryan Garcia, B.S, RDMS, RVT

P.S. Feel free to share your thoughts, your feedback is truly valuable.

References

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Robbin, M.L., et al. (2002). Hemodialysis arteriovenous fistula maturity: US evaluation. Radiology. 225(1):59-64. DOI: 10.1148/radiol.2251011367.

Singh, P., et al. (2008). Clinically immature arteriovenous hemodialysis fistulas: effect of US on salvage. Radiology. 246(1):299-305. DOI: 10.1148/radiol.2463061942.

Schäberle, W. (2011). Ultrasonography in Vascular Diagnosis. Springer-Verlag Berling Heidelber.

Pellerito J., Polak, J. (2012). Introduction to Vascular Ultrasonography. Saunders.