I have a question concerning Arteriovenous Fistula's.

[missmollie, ADN, BSN, RN]

I am a nursing student and I have a question. I've searched everywhere for the answer, but was wondering if anyone has any insight. This is not for a class (I'm in fundamentals of nursing) and just more a curiosity.

Patients on dialysis are given an arteriovenous fistula because the higher blood flow from the artery directly to the vein causes the vein to thicken (about eight weeks) thus preventing the vein collapsing during dialysis.

My question is this: If the structure of a vein allows for a low pressure, and an artery conversely allows for high pressure, why doesn't the vein break or tear when connected to the high pressure artery? I have pulled out my AP book, I've looked up sites, I have read more info about fistula's than I should, but I can't find the answer!

If anyone has any insight, I'd appreciate it so much! I know the high pressure strengthens the vein, but why doesn't the vein tear when that high pressure is first introduced?

Thanks in advance.

[Chisca, RN]

The right artery has to be matched up to the right vein and this is determined by doppler studies. The minimal arterial size is 2.0mm and the minimal vein size is 2.5 mm. The vein is tested for dilation by occluding the proximal portion and measuring the distension, an increase of 50% is considered good. Collateral circulation is mapped to ensure good flow and absence of strictures. The vein isn't as fragile as you think because a mature fistula is at least 4 mm in diameter before it is used for dialysis access. I think you could potentially have a problem of rupture at the anastomosis but that would be more related to the skill of the surgeon rather than the weakness of the vein.

[missmollie, ADN, BSN, RN]

Thank you for your reply! I didn't even consider that the size of the artery and vein would be would have to be matched up, but the way you explain it makes so much sense. Thanks again!