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

[sameeralord]

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

 

[aroc91]

http://en.wikipedia.org/wiki/Hemodialysis#AV_fistula

The complications are fewer than with other access methods. If a fistula has a very high blood flow and the vasculature that supplies the rest of the limb is poor, a steal syndrome can occur, where blood entering the limb is drawn into the fistula and returned to the general circulation without entering the limb's capillaries. This results in cold extremities of that limb, cramping pains, and, if severe, tissue damage

but still isn't it bad for arterial blood to get mixed with venous?

Why would it be? As long as it doesn't significantly affect circulation and oxygen perfusion, it shouldn't really have an effect.

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

Not sure what you mean here.

 

[TheBioGeek]

Mixing of oxygenated blood with deoxygenated blood would however cause problems such as hypoxia, cyanosis and reduced oxygen supply to all the body tissues thereby putting severe physical and metabolic restrictions on the subject. This how ever is not fatal as due to high arteriole pressure it is the arteriole blood that enters the veins and not vice versa. This however leads to swollen veins and increased venous blood pressure and requires proper administration

 

[Fervent Freyja]

pumping blood back would make the person more prone to infection. Thanks

The process of filtering blood carries a risk of infection, you will be exposing the blood to both air and contact with numerous objects. Higher pressure translates into a more effective treatment. I don't see a better alternative.

 

[TheBioGeek]

The dialysis machine so far is capable of performing only ultrafilteration. It is not capable of selective reabsorption or tubular secretion
Inspire the risk AV Fistula must be done for the following reasons:
1. Ultrafiltration takes place within our a kidneys at a much higher pressure even compared to the arteries. This is because of the different diameters if the efferent and afferent arteriole. Only drawing blood from the veins which is at a very low pressure compared to optimum won't facilitate the process in dialysis. The fistula thus supplements additional pressure to the outgoing blood so that ultrafiltration may occur.
2 The more trivial reason is that if we were to draw the blood simply out of the veins which are much thinner and carry much less blood than the arteries the overall time span required to conduct dialysis would increase drastically which would not only result in inconvenience but will also increase the cost making it less affordable and hence less beneficial for the subject.