What is a normal finding when assessing an AV fistula?

Last week we looked at the basics and useful terminology employed for examining a vascular access. Now we will focus on specifics of the physical exam.

Physical Examination

Inspection (Look)

Visual inspection can provide important clues regarding the cause of AV access dysfunction. Inspect the AVF or AVG to determine its configuration and length, while also assessing for abnormalities such as aneurysms/pseudoaneurysms, collateral veins, signs of hand ischemia (cyanotic fingers, hand pallor), or signs of infection (erythema, purulent drainage). It is important to compare the AV access extremity with the contralateral extremity for asymmetry or collateral veins. Similarly, the head, neck, chest and face should be inspected for swelling or collateral veins.

Finding	What It Suggests
Head: Facial edema	Superior vena cava stenosis
Neck: Scars (prior central venous catheters)	Increased risk of central venous stenosis
Chest: EdemaBreast swellingCollateral veins Implantable devices	Central vein stenosisCentral vein stenosisCentral vein stenosis Increased risk of central vein stenosis
Arm: EdemaCollateral vein(s)Aneurysms and pseudoaneurysms Visible pulsation	Central vein stenosisStenosis near the vein(s)Outflow stenosis Outflow stenosis
Hand: Cyanosis,pallor, skin necrosis, or dystrophic nails	Vascular steal syndrome

Figures 5 & 6. Aneurysmal fistulas with a shiny central erosion. From Atlas of Dialysis Vascular Access.

Figure 7. Pseudoaneurysmal AV graft. From Atlas of Dialysis Vascular Access.

Clinical Pearl: True aneurysms are dilations involving the entire vessel wall, whereas pseudoaneurysms are dilations secondary to hematomas that occur at sites of repetitive cannulation. Unlike true aneurysms, pseudoaneurysms are not covered by the vessel wall. Glassy, thin skin or presence of ulceration over an aneurysm or pseudoaneurysm requires urgent surgical evaluation, due to high risk of AV access rupture .

Figure 8. Cyanotic fingertips, consistent with vascular steal syndrome. From Atlas of Dialysis Vascular Access.

Figure 9. Marked right arm swelling due to ipsilateral central vein stenosis. From Atlas of Dialysis Vascular Access.

The arm elevation test is a simple method to diagnose outflow vein stenosis. Under normal circumstances, when the fistula arm is raised above the level of the heart, the fistula will collapse. If an outflow stenosis is present, the area of the fistula distal to the stenosis will remain distended. Note: this test works best with forearm AVFs and is not valid for AVGs. Patients can be taught to perform the arm elevation test as a way to self-monitor their AV accesses. (Click here for a video demonstration of the arm elevation test.)

Palpation (Feel)

A normal thrill has two components: a gentle, continuous (systolic and diastolic) vibration over the length of the AV access and a soft pulsation. The thrill is best felt with the palm of the hand. Stenotic lesions intensify the thrill over the area of stenosis and lead to loss of the diastolic component. An extremely strong (“water-hammer”) pulse over an AV access is concerning for venous outflow stenosis. Weak pulsation suggests a problem with the inflow. In an AV graft, it is normal to feel a strong thrill at the arterial anastomosis that diminishes slightly as you move closer to the venous outflow

Figure 10. Palpation of an AV access is best done using the whole hand. In the absence of a stenotic lesion, the thrill is continuous (A). The thrill becomes stronger and loses its diastolic component if a stenosis is present (B). From Salman and Beathard, CJASN, 2013.

The pulse augmentation test is used to evaluate the inflow. The AV access is completely occluded several centimeters above the arterial anastomosis with one hand, while the other hand is used to assess the quality of the pulse. Increased pulse intensity (augmentation) with occlusion of the outflow vein is a normal finding. Failure of the pulse to augment when the outflow vein is occluded suggests the presence of inflow stenosis.

The pulse augmentation test may also be used to assess the direction of blood flow in an AVG. When the center of the AVG is occluded, the side with an intensified pulse is the portion of the AVG that is connected to the artery, while the side without pulsation is the portion of the AVG connected to the vein.

Figure 11. The augmentation test. The left hand (A) is used to occlude access outflow while the right (B) is used to assess the intensity of the pulse. From Salman and Beathard, CJASN, 2013.

The sequential occlusion test is used to determine the presence of collateral veins. Similar to the pulse augmentation test, one hand is used to occlude the AV access outflow while the other hand is used to palpate the thrill. The AV access is occluded progressively further down the venous outflow tract. If no collateral vein is present, no thrill will be felt. However, if a thrill is palpable despite occlusion of the AV, that indicates the presence of a collateral vein below the point of occlusion.

Figure 12. The sequential occlusion test. The left hand (occluding hand) gradually moves farther from the right hand (palpating hand), assessing the pulse each time the access is occluded. If the access is occluded distal to a collateral vein, the thrill will stop and the pulse will intensify (A). If the access is occluded proximal to the collateral vein, the thrill will continue and no pulsation will be felt (B). From Salman and Beathard, CJASN, 2013

Clinical Pearl: An absent bruit and/or thrill is concerning for AV access thrombosis. Patients should be referred to an interventionalist or surgeon for urgent thrombectomy (“declot”) as soon as thrombosis is suspected. Consider cardiac evaluation, as low LVEF may be a cause for recurrent thrombosis.

Auscultation (Listen)

A stethoscope should be used to listen along the entire length of the AV access. A normal bruit should sound like a continuous (systolic and diastolic) hum. The normally low-pitched bruit will become squeaky and high-pitched if hemodynamically significant stenosis is present. As with the thrill, a stenotic lesion will cause the bruit to lose its diastolic component.

Figure 13. Auscultation of an AV access. From Salman and Beathard, CJASN, 2013.

SummaryPhysical examination of hemodialysis vascular access is an important skill for all nephrologists to have. Any abnormal findings should prompt referral to an interventionalist for further evaluation. Learning how to conduct an AV access examination can have significant impact on patient care

Your Turn!

Practice your vascular access diagnostic skills with the following cases from NephSim:

Case 9

Case 11

Case 16

Post by: Crystal Farrington, ASDIN Fellow

An arteriovenous (AV) fistula is a type of access used for hemodialysis. It can be used whether dialysis is performed at a dialysis center or you perform home hemodialysis (HHD). An AV fistula is a connection between an artery and a vein creating a ready source with a rapid flow of blood. The fistula is located under the skin and is used during dialysis to access the bloodstream.

Fistulas are the preferred type of access because it utilizes the patient’s own vessels and does not require permanent placement of foreign materials such as those needed to create an AV graft or catheter. The AV fistula, formed by the patient's own vessels, is less infection-prone than a catheter, is less likely than a graft to have problems with clotting and provides good blood flow that can last for decades.

While a fistula is easier to work with than other access types, that doesn’t mean it’s completely care-free. So here are some tips to take care of a fistula to maintain optimal blood flow for dialysis treatments.

Exercising for your fistula after surgery

An AV fistula must mature for several weeks or months before it can be used for hemodialysis, so after it is surgically created, your doctor will ask you to work on strengthening it. The more access arm exercises you do to help strengthen it, the sooner you’ll be able to use your fistula. Your doctor may recommend certain arm and finger exercises that will strengthen the fistula. The exercises your doctor recommends will depend on where your fistula is located. Fistulas are usually located in the forearm or upper arm. Before you start any exercise, it’s important to consult your doctor.

Keeping your fistula clean

Once your AV fistula is strong enough to be used for hemodialysis, it is crucial that you keep it clean. Although a fistula is less prone to infection than other dialysis types, proper hygiene is still important:

Look for redness or swelling around the fistula area.
If you experience any pain in the fistula area, tell your doctor immediately.
If you get a fever, this can be a sign of infection.
Wash and pat dry your fistula arm thoroughly right before each treatment. Your dialysis facility will provide you with supplies.

Proper blood flow through the fistula

Blood needs to flow smoothly through your AV fistula. To reduce the risk of blood clots, be careful not to put extra pressure on the area. This may require some changes in your daily habits:

Do not wear tight-fitting shirts.
Do not wear jewelry (such as bracelets) that may restrict blood flow on your access arm.
When carrying things (groceries, bags, luggage), make sure the straps or handles don’t tighten around your fistula.
When having your blood pressure taken or blood drawn, use your non-fistula arm.
When sitting or sleeping, make certain that your head, pillow or cushion doesn’t rest on your fistula.

Checking your fistula blood flow

Check the blood flow through your AV fistula daily. This is done by touch and sound. When you place your fingers over your fistula, you should be able to feel the motion of the blood flowing through it. This sensation is the “thrill.” Let your doctor know if the thrill ever feels different. To listen for your blood flow, use a stethoscope and place the bell flat on your fistula. The sound you hear is called the “bruit” (pronounced broo-ee). Any change in the pitch may indicate a clot (thrombolysis) or a narrowing (stenosis) of the fistula. This sound may change from a whooshing noise to a whistle-like sound.

Summary

More than half of all dialysis patients are now using AV fistulas because it’s healthier, easier to maintain and produce better results than other access methods. Taking care of your fistula through strengthening exercises, cleanliness and checking daily for proper blood flow can make your dialysis treatments more manageable and effective.