Why do you need an arterio venous fistula to do haemodialysis?

[scilearner]

Hello everyone,

Why do you need to create an arterio venous fistula for haemodialysis? I don't understand how it makes a good access site for dialysis. Also when not performing dialysis, wouldn't this AV fistula be bad for the body. The deoxygenated and venous blood with all its wastes mixing with arterial blood due to fistula (I'm assuming due to higher pressure in arteries, arterial blood flows to veins not vise versa but still isn't it bad for arterial blood to get mixed with venous). Also in dialysis why should the blood be pumped back into the person, isn't their a way to filter it right at the start, pumping blood back would make the person more prone to infection. Thanks :smile:

[Tzurain]

10 Months Later...

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This reply is pretty late, but I'll try to answer it now, since it's best to do it now then never.

An AV fistula is a connection, made by a vascular surgeon, of an artery to a vein.

The purpose is to cause extra pressure and extra blood to flow into the vein, making it grow large and strong. The larger vein provides easy, reliable access to blood vessels. Without this kind of access, regular hemodialysis sessions would extremely hard to conduct. Untreated veins (usually) cannot withstand repeated needle insertions. They would collapse the way a straw collapses under strong suction.

I hope I helped ^^

 

Also in dialysis why should the blood be pumped back into the person, isn't their a way to filter it right at the start, pumping blood back would make the person more prone to infection.

 

A dialysis is like a filter, it removes waste from the blood, and puts the 'clean' blood back into the body.

If we don't pump the blood back, then the person would die of lack of blood. I guess. :|

Edited October 2, 2014 by Tzurain

[Marat]

Actually a fistula access for dialysis is not necessary, since a central-line catheter will do just as well. While needling via a fistula is extremely painful, and patients report that local anesthetic does not help much, a central-line catheter is completely painless. Fistulas tend to break down over time, so painful 'mapping' procedures are necessary to assess their patency and blood flow rates. They often have to be reconstructed, which is also a painful surgical process. Sometimes they fail to work from the outset, and so have to be constructed again. The patient has to do demanding exercises to get the fistulas to work, and the access requires about six weeks to mature before it is ready. In contrast, a central catheter is ready to use right after it is inserted.

 

The reason why fistulas are preferred is that catheters are slightly more prone to infection, and the patients have to be careful not to get them wet. However, with some care in avoiding infection, they can last much longer and work much better than fistulas. Still, because nephrologists tend not to be able to appreciate how much pain and inconvenience patients go through with fistulas, most refuse even to permit the option of central line catheters. I have witnessed patients even refuse to continue dialysis from the pain of fistula needling, so you could even say that fistulas indirectly cause a certain percentage of patients to die.

 

You would think that the reasons for preferring catheters would be clear, but in the highly resigned, depressive, defeatist atmosphere of renal dialysis, lots of practices prevail which would not be conceivable in more sane environments. For those considering nephrology, I would recommend internal medicine as a specialization instead, since at least some cases there are successful.

[Harold Squared]

A third alternative not mentioned so far is known as a shunt, a loop of synthetic material implanted subcutaneously which serves as a "scaffold" for natural vascular tissue to grow over which will remain patent after being punctured repeatedly- in theory. I have seen patients with such devices in all four limbs as they work better in theory than in practice for various reasons.

 

 

The usual practice is to not stick the fistula too close to the last access point in order to avoid provoking an aneurysm or weak point, but one method is to never let such points completely heal by accessing the same spot repeatedly by carefully picking off the scab and then using a special blunt needle. If I were a patient I would prefer such a system, and a fistula as it involves no foreign body introduction.

 

In conclusion the two access points, withdrawal and return, must be far enough apart to prevent ineffective filtration through the system, and using the blunt needle method would help prevent this error as well.