Management of autogenous arteriovenous (AV) fistula stenosis part 1

Relevant stenosis

Stenosis  should be treated if the diameter is reduced by >50% and is accompanied with a reduction in access flow or in measured dialysis doses. Other indications for stenosis treatment are dificulties in cannulations, painful arm oedema, prolonged bleeding time after cannulation or after removal of the canullae (due to high venous pressure) and hand ischemia due to arterial inflow or distal stenosis. A stenotic lesion, due to intimal hyperplasia, is the most cause for low access flow. In radial-cephalic arteriovenous fistula, 55-75% of these stenosis are located close to the areteriovenous anastomosis and 25% in venous outflow tract.  In bracial-cephalic and/or basilic arteriovenous fistula, the typical location (55%) is at the junction of the cephalic with the subclavian vein and the basilic with the axillary vein, respectively. An arterial inflow stenosis >2cm from the anastomosis is uncommon, but may endanger the flow in the arteriovenous fistula.

Allen test part 8

Clinical significance:


The Allen Test (AT) and Modified Allen Test (MAT) tests are used to ensure collateral circulation of the hand. The test can be used as a diagnostic tool  for any numbers of disorders with a reduced vascular flow to the arm or after operations on the hand. More commonly, it is used to assess collateral flow to the hand through ulnar artery when the radial artery is going to be used for arterial punctures for drawing  blood gases,  cannulation for placement of arterial lines, catheterizations or radial artery harvest for bypass surgeries. These procedures are typically done involving the radial artery because its easily palpable nature at the bedside. One of the risks associated with the arterial punctures include ischemia distal to the puncture site which could lead compromise of the limb if there is not adequate collateral blood flow. Though ischemia is a rare complications associated with an arterial puncture, in most patients, in the clinical setting the Allen test  is not often performed. There is weak evidence supporting the accuracy of this test in assesing ulnar artery patency and ensure collateral circulation.

Allen test part 7

Complications:

There are no known complication other than those caused by not performing the procedure or performing it incorectly. Rarely, radial arterial blood sampling/cannulation, including disruption of the artery due to clot obstruction, places the hand at risk of ischemia. Individuals without dual supply are at much greater risk of ischemia.

Allen test part 6

In a patient with normal patent arteries, the color should return to the palms relatively quickly ( within 10 seconds) after the release either artery. If pallor persist within the palm after the patient unclenches his fist and one of the arteries is released, then the test is positive and indicative of an occlusion  within the artery that is being released. For example, if the radial artery is being compressed and palmar pallor persists then that is indicative of compromised blood flow of the ulnar artery. The same is true if the ulnar artery is compressed  and palmar pallor persists then the compromised blood flow is in the arterial artery.

Allen test part 5

Technique:

The modified Allen test differs mainly by examining both radial and ulnar arteries on the one hand and then repeated on the other side. Traditionally, it is performed by first having the patient arm flexed at the elbow with the fist clenched tightly or by asking the patient first to open and close their fist to help increase the draining of blood from the hands. The ulnar and radial arteries are then compressed by the provider's thumbs simultaneously. The elbow is then extended to no more than 180 degrees, avoiding overextension as that could lead to a false positive test. The fist is then unclenched, and the palm should appear white. The compression is then released from the ulnar artery while maintaining pressure  over the radial artery. Once the compression is released color should return to the palm usually within 10 seconds. The test is repeated on the same hand while releasing the radial artery first and continuing to compress the ulnar artery.

Allen test part 4

Technique:

The original Allen test  can be performed by asking the patient to elevate both their hands above their head for thirty seconds. This will help with draining  blood from the patient hands. Next, the patient is then asked to squeeze their hands into tight fists, and the radial artery is occluded simultaneously on both hands. The patient then open both  hands rapidly, and the examiner will compare the color of both palms. The initial pallor should be replaced with the normal erythematous color of the hand as the blood from the collateral flow returns. The test is the repeated while occluding ulnar arteries instead of the radial arteries. The time it takes to the normal color to return helps indicate the degree of collateral blood flow. It is referred to as a negative test when there is a return of normal color to both hands during occlucion of either artery alone.  A positive test will be when there is persistent pallor in palm indicating no collateral blood flow to the hand.

Allen test part 3

Indication:

The radial artery is easily palpable. The need for this test arises from inabiliity to palpate the ulnar artery. Because the ulnar artery cannot be palpated its patency cannot be assessed, and therefore, collateral circulation of the hand cannot be confirmed. If the radial artery needs to be canulated or catheterized and there is a risk for thrombosis, then the Allen test help to confirm that the hand will maintain adequate blood flow through the ulnar artery and collaterals in the event it becomes occluded. A positive Allen test means that the patient does not have an adequate dual blood supply to the hand which would be a negative indication for catheterization, removal of radial artery or any procedure which may result in occlusion of the vessels.