Hi Stuart - do we know what percent of the fistula’s blood flow is diverted to the blood circuit?
Given, no two fistula are the same, but do we have any numbers to hazard a guess?
[SIZE=4]We know when are kidneys are at their best they are clearing 100% but as we age and have kidney disease we lose this clearance that is why we end of on dialysis, I can’t answer your question 100% because of body mass diseases etc. but i know the Best that the dialysis machine divert blood is 15% I hope this answer you question if not e-mail back
are you talking about the amount of blood that is outside the body during dialysis?[/
What I’m wondering is, talking about the blood flow through the fistula an inch up the fistula from a cannulation site, during dialysis, what percent of the blood flow is coming from the needle and what percent is the natural fistula flow?
This is coming up in regard to discussions about blood pump speed and reports that people are turning down their blood pumps in order to preserve fistula health or improve dialysis’s impact on the circulatory system. My position has changed over time, these days I don’t think blood pump speed has much of an impact on fistula/circulatory health in people with a well functioning access.
What changed my mind was hearing that the natural flow of the fistula was 800+ so pumping blood back in at 300 v 450 isn’t going to have much of an effect. Further I was thinking about my question and thinking that the relative volume of blood: the amount of blood naturally flowing through the fistula v the amount of blood entering the vein from the needle … there must be 5 times the blood flowing through the fistula as there is flowing out of the needle. Maybe more? Maybe less? Thus my question can we compare the two?
It seems to me that pumping a relatively small amount of blood into a vein flush with blood flowing at at a faster rate would result in the pumped blood having little effect.
One issue that has me unsure of all this is that the volume of blood moved in a minute isn’t really the same as the speed of the blood. I’m not really sure how long it takes a blood cell to travel 12 inches inside the fistula v how long it would take a blood cell to travel 12 inches at various blood pump speeds.
Back in the early days the blood circulated through the artificial kidney powered just by the heart - there was no blood pump. The story goes that Scribner, et al were trying to figure out how fast the blood was flowing through the blood circuit when one of their patients, and engineer, came up with the solution: introduce a bubble to the blood circuit and then time how long it takes for the bubble to traverse a measured section of the tubing. Then from the speed you could calculate volumes. Now we set the pumps based on volumes ml/min but I’m not sure how from there to get to speed.
Great question let me work on until Monday august 22 for i think (I can come up with something in this, , but a very good question. I know that higher pump speed leads to formation of aneurisms
I’d like to read the research - do you have a link? I thought that infiltrations and luck of the draw natural weak spots caused aneurisms .
Thanks Bill P for asking this, and thanks Stuart Mott for helping us out and working with it.
Is there anymore info for us here? Im thinking you took it to e mails 
I’d love to be hearing it if your willing to share.
II’m still working on this, there is a lot of info out there but I found out that the minim size of a av/f wall should be greater than 0.13 mm so that it will not infiltrate on the first cannulation, I found that in a Canada study which i will post more info on next week, and try and answer bill question
Our article : “The Application of High Frequency Ultrasound To Assess Arteriovenous Hemodialysis Fistula Vein Wall Morphology For Cannulation Readiness” will be published soon in the Journal " Radiology ".
We evaluated longitudinally the intima- media wall thickness of newly created fistula with an experimental high definition ultrasound over a period of 6 months. All fistula were cannulated when DOQI parameters were reached and with the help of bedside ultrasound for guided needle insertion to ensure placement of needle in the center of the vessel lumen and to verify that there wasn’t backwalling during insertion. We used 17g angiocaths for hemodialysis for all first cannulations. Some fistula blew inmediately after needle entry other within an hour or two of hemodialysis and without patient movement. All infiltration events showed that the cannula was in situ in the vessel lumen and that there had been a leak of blood from the vessel into the tissue around the needle enry to the vessel point.
We found that all fistula that did not blow had an Intima Media Thickness IMT measurement > than 0.13 mm , and we concluded that the evaluation of fistula wall thickness gives an added quantitative AVF vessel wall parameter that predicts cannulation readiness.
Dr. Ballyk is one of the Investigators in our group.
Hope this helps.
Take care and hope to see you soon.
Rosa M. Marticorena R.N.
Thanks Stuart - we need more studies of fistulas and how to best use them.
My specific concern is about people cutting their blood pump speeds for the sake of cutting their blood pump speeds. I did it myself incenter in 1996 (and lengthened my time) but without data and in the absence of a wide spread increase in stenosis among people using SHHD with a high Qb, I just can’t say lowering the pump speed is, in itself, a good idea.
It is hard to parse out the effects of Qb considering the large impact on the circulatory system of just having a fistula in the first place and the effect of regular cannulation. The question seems to be does high Qb increase the incidence of stenosis. This NDT article is fully available http://ndt.oxfordjournals.org/content/19/2/309.full , it discusses stenosis and puts the potential problem due to Qb in context
If it is true that 80% of stenoses occur at the anastomosis, and the remaining 20% are a mixed bag, that include stenoses resulting from the cannulation directly, I have to wonder how big a problem stenosis due to Qb could be. I haven’t heard anything that amounts to an uptick in access interventions from people using NxStage with Qb=500. The only only uptick I’ve heard about is sepsis among people using buttonholes. This has been a relatively small sepsis increase in the nominal cases but it does suggest that any increase in stenoses would be reported.
The reason I am asking about blood flows, especially blood flows in terms of actual speed rather than volume, is to try to imagine the turbulence caused by the out flow of the venous needle. If the blood coming out of the needle is going slower than the blood in the fistula that would suggest to me that there would be less turbulance than if the venous outflow was faster than the fistula.
To me it is confusing to compare the fistula with the blood circuit in terms of ml/min. ml is a volume measure but when we talk about speed we normally put it in terms of distance. The fistula is much larger so if both the fistula and the blood circuit were said to have the same flow in ml/min it would mean the fistula flow speed, call it centimeters/second, would have to be much slower. It would be like comparing a garden hose and a stream- if they were going the same speed - cm/min - the stream’s ml/min rate would be much greater than the hose’s.
So I’m not sure this is true but in general my understanding is that blood exiting the needle at Qb=500 is entering the fistula at a slower speed: cm/min, than the natural fistula flow. Whether or not that is true would say a lot about the potential for turbulence damage, it seems to me. That’s what I am hoping to clarify.
It would be nice to hear from others who read this board and have some insight on what the data shows and what data we need to develop. I’ve participated in email exchanges about this and had useful discussions … hopefully some of that can move to the forum.
I cant add any useful information, but i can add a question, or should i say a desire to know this information as well as i am one who has lowered DH’s BF just for the sake of fistula preserving. His #'s have always been good at a shorter session, and now, since he’s not yet willing to go the full ‘extended’ im wondering just how much saving of the fistula im doing by going 310 vs say 410. We, and others im sure, are willing to sit it out if need be, but if not, i wish for him a shorter time
Hi Stuart I saw the studies but they just underscore my question.
If the flow volume is described in ml/min that is describing Volume of the flow. What I am wondering is the speed of the two flows. That would have to be a distance per unit of time, rather than volume per unit of time.
If the fistula is carrying a 1,000 ml/min and the venous needle is carrying 500 ml/min that means that the venous needle flow is MUCH faster. And thus I can well imagine there is some kind of jet action stripping/damaging the vessle wall cells; “leading to progressive scarring, progressive fibrosis, progressive shrinkage, progressive stenosis”.
But what is the SPEED of the two flows?
Ok have some time to advance the subject of needle flow.In 2009 i did a study on the3/5 needle versus the 1 inch needl.there was a significant drop in versus and art pressure.when running the pump at400 the 1 inch needle pressure ran on a average pressure was280 to240.when using the 3/5the pressures drop by40 to 100.this shows that the longer the needles the more pressure is generated.Thus last damage to the vessel