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Sunday, October 31, 2010

How Fistula Are Created

• A native arteriovenous fistula (AVF) is made by surgically linking an artery to a vein.
• This link is the anastomosis, and the site is marked by a scar.
• It takes 1-3 months for AVF to be strong enough to use large-gauge needles, so it is best to create one long before dialysis is needed.
• As soon as the surgery is done, rapid and strong arterial blood flow sent to the vein starts to enlarge the fistula vein and make it tougher. This is called arterialization. and we say the fistula is maturing.
• The most common type of native AVF links the radial artery and cephalic vein in the distal forearm (below the wrist and the elbow). This is called a radiocephalic fistula.
• The brachiocephalic (brachial artery and cephalic vein) fistula is used, and is the most common AVF of the upper arm.
• Other vessels that can be used are:
     • Basilic vein
     • Transposed basilic vein (the deep vein is brought closer to the surface of the skin and the vein is moved to the anterior [front] surface of the upper arm for easier needle insertion)
     • Transposed one of the brachial veins ( a pair of veins closely accompanying brachial artery and draining to the axillary vein)

Other vessels that can be used are:
     • Perforated vein in the antecubital fossa anastomosed to the brachial artery (perforating veins connect superficial and deep veins)
     • Ulnar artery .
     • Proximal radial artery
• While AVF is the best type of access, not every, patient can have one.
• The chosen veins must be healthy, straight, large enough to allow for large-gauge needles, and long enough to permit a number of needle sites.

• Patients must also be able to handle a 10% more increase in cardiac output (the amount of blood passing through the heart) to have a fistula.
     • A new access strains the heart, because arterial blood quickly short-circuits through tiny capillary blood vessels.
     • The heart must work harder due to rapid blood flow.
• Reasons why a patient may not be able to have an AVF:
     • Damage to veins due to intravenous drugs
     • Previous surgeries on the arteries and/or veins
     • Atherosclerosis: plaque or waxy cholesterol that blocks the vessels
     • Poor quality arteries due to peripheral vascular disease (PVD) or advanced diabetes
     • Only one working artery to bring blood to the hand
     • Damage to blood vessels due to intravenous drugs

Radiocephalic Fistula: Source: wikipedia.org

Fistula Procedure
• Vessel mapping to find the best vessels for a fistula
• Blood vessel sites are marked on the skin.
• An incision is made in the skin over the chosen vessel
• Then the vessels are sewn together There are four ways that arteries and veins can be joined to create AVF. Each has pros and cons:
     • The side-to-side (artery-side to vein-side.) anastomosis is easiest for a surgeon to do.
     • It is also the most likely to cause venous hypertension,
     • This is the problem in which the hand fills with fluid due to high pressure in the veins,
     • Sometimes the surgeon will do a side-to-side anastomosis, then tie off one or more of the vessels leading to the hand

• The side-to-end (artery-side to vein-end) anastomosis is preferred by many surgeons, even though it is hardest to do. This method gives high blood flows with few complications.
• The end-to-side (artery-end to vein-side) anastomosis has slightly lower blood flow rates than side-to-side.
• The end-to-end (artery-end to vein-end) anastomosis permits less blood flow through the access.

Source and for more information checkout http://www.mcs.anl.gov/uploads/cels/papers/P1410.pdf

• After the incision is closed, a thrill, or purring vibration, should be present over the new fistula.
• You should be able to hear a whooshing "bruit" with a • stethoscope along the course of the. vein.
• The bruit should be continuous and low-pitched. Both the thrill and the bruit help prove that the new fistula is patent (open).

How Fistula Are Created - Related Hemodialysis Article


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