How Is Fistula Flow Measured?

[PrimeTimer]

If a person does in-center HD and the clinic wants to measure their fistula flow, how is that performed? For instance, in addition to feeling the fistula for the buzz and listening with a stethoscope, they measure the "flow" during a treatment. And apparently this has to be approved by the head nurse. But how do they measure the flow? Is it some sort of device attached to the dialysis machine?

[cassandra]

Mine gets measured with an ultra sound in hosp.

[PrimeTimer]

Thanks for answering so quickly, Cas! And you ought to know about fistula's...your experience is invaluable! Thank you! A tech (with several years experience) said she could hear a whistle in hubby's fistula -right in the same spot where he usually has to be ballooned. Usually they just send him over to the vascular clinic if they suspect anything only this time, he was told they would have to "measure the flow" first. That was last week. His fistula seems to be working fine and the machine hasn't been alarming. We have no idea how they go about "measuring the flow" or why they want to do this before sending him to the vascular clinic.

BTW Cas, hope you are feeling better! Please keep us updated on your upcoming fistula surgery. Pray it goes well for you.



self-edited to correct grammar/spelling

[Michael Murphy]

At the center I go to the test is called a access flow and a small device is added to the tubing and the rare of blood flow is measured.  Most patients don't notice when it's done.

[Simon Dog]

There is a technique commonly used in-center with a twister dialysis line set.   This line set allows the arterial/venous lines to be swapped by rotating a connection 180 degrees.  They run the machine with the  lines  reversed for a period of time and compare measurement of something that is a proxy for clearance (I think Na) and compare between flipped an unflipped.   The amount of fistula impedance can determine how much recirculation you get with the lines reversed, and allows the  flow rate of the fistula to be inferred.  They deduce a flow rate from the difference, and generally  are happy with anything over 500.   The local FMC clinic does this monthly for in-center patients.   I don't think this directly measures the rate of blood flow, as that is controlled by the perstaltic pump on the machine.

I suspect this was what was meant by the clinic measuring the flow.    I don't think any extra hardware is needed, but I have read this is a separately sold software feature  for the 2008 series Fresenius machines.

I am a home hemo/NxStage patient.   There are occasions when I book in-center (wife traveling, etc.) and if it's been a long time, I ask my MD to order this test.   I also had one done recently  since I had  low URR at a monthly lab and wanted to confirm it was a fluke, and not indicative of fistula problems.

[PrimeTimer]

Thanks a bunch, Michael and Simon Dog. He's going to inquire about this at his next treatment. Another sign that he needs an angioplasty has been an increase in AVF pressures. He asked a tech the other day what his pressures were. She looked kind of befuddled by his question and asked how he would know anything about that. He said "home hemo". Apparently she wasn't there the day he was introduced to the clinic. A tech had announced to the others that he was coming from home hemo and so "he is aware". Yeah, he's aware alright. Anyways, he didn't find out what his current pressures are but will next go around. Thanks again for coming thru for us (again) and answering.

[Riki]

My unit has a machine that the nurses call a "transonic" and it has sensors that are connected to the blood lines.. I'm not sure how it works, but it can read the flow speed and recirculation.. they run this test every 3 months or so..

[Charlie B53]

As a lifelong mechanic I can see this from a whole different perspective.  Measuring flow through a vessel within the body can be very difficult.  The Ultrasound Doppler must be the best method currently known.

Measuring any flow during a Hemo treatment may be far from exact as blood flow through the lines/machine is dependent on the pump speed.  However it may be possible to use that pump speed to make an observation and get very close too an approximate flow.

Everyone is familiar with the 'thrill', feeling the heartbeat/blood flow through their access.  Imagine how much that 'thrill' is reduced during dialysis as blood is pulled out and returned such that that area of the vein between the needles there is a much lesser 'thrill' than with the needles diverting flow out and back in.  Increasing pump speed it is conceivable that you could reduce flow until almost a negligible amount.

Just a thought.

Now, how many of you are going to check your 'thrill' during your next session to see how much it is reduced??

[Riki]

I can feel my thrill during treatment.  I have a large, well developed fistula, with 4 or 5 needle sites, so that could be why

[Simon Dog]

He asked a tech the other day what his pressures were.

Ask the tech to turn the machine so he can see it during treatment.

[PrimeTimer]

I keep telling him to have the monitor turned so he can see his numbers but...he still hasn't asked them. I don't know why he doesn't. He must think it would put them out in some way but I've been telling him and...well... But he did ask what his pressures were and they are fine. You guys were right, they checked his access flow thru the line setup last week. He didn't even know it. Today they told him that his flow numbers were "within perimeters". Right about then his neph happened to come into the clinic. She told them to run another Kt/V at next treatment and if it is off again (was a slight decrease), she will sign the orders for him to go to the vascular clinic. Hopefully this was all just a blip.   

[Simon Dog]

She told them to run another Kt/V at next treatment

Kt/V or flow rate measurement?

Kt/V is measured every 30 minutes or so on a routine basis (it how the machine decides if you get a green orange light).  But, the measure is dependent on the estimated blood volume (or some similar parameter) that is keyed into the machine, so it can be hooey if this number is inaccurate.

Ask that the flow rate is.   Above 500 is considered OK, though above 2000 is cause for concern.   I did 1065 at my last test.

[PrimeTimer]

She told them to run another Kt/V at next treatment

Kt/V or flow rate measurement?

Kt/V is measured every 30 minutes or so on a routine basis (it how the machine decides if you get a green orange light).  But, the measure is dependent on the estimated blood volume (or some similar parameter) that is keyed into the machine, so it can be hooey if this number is inaccurate.

Ask that the flow rate is.   Above 500 is considered OK, though above 2000 is cause for concern.   I did 1065 at my last test.

His monthly Kt/V was slightly lower last month. They are going to run or recalculate it next treatment. While they talk about that, I am concerned about the "whistling" the tech heard thru her stethoscope in the area of his fistula where he usually gets stenosis. But the good news is that his pressures are good and the machine has not alarmed. 

[GA_DAWG]

Our techs do something they call twisty lines in order to measure the flow.

[PrimeTimer]

They recalculated his kt/V and it looked alright but now his arterial pressure is a bit high. That's usually a sign of needing another angioplasty. Neph wants him to go to the vascular doc this week or next. Ah well...it's these balloons that keep his fistula open and alive so he's not complaining. He's usually in and out of there in a couple of hours and back at work the same day.

[Simon Dog]

Our techs do something they call twisty lines in order to measure the flow.

"Twisty lines" are a special line set that can reverse arterial and venouos.   Some characteristic of the blood is measured (not sure what) to get an idea the amount of reflow, and by inference, the quality of the fistula flow.

[PrimeTimer]

Our techs do something they call twisty lines in order to measure the flow.

"Twisty lines" are a special line set that can reverse arterial and venouos.   Some characteristic of the blood is measured (not sure what) to get an idea the amount of reflow, and by inference, the quality of the fistula flow.

I wonder why they always want to "recalculate" the kt/V while there are so many other signs of a fistula not working right. I guess I understand that a lower kt/V could signal a problem but they recently recalculated my husband's kt/V and said it was fine. Fast forward to the next week...arterial pressure up a bit, neph made him an appt to see the vascular doc. Hubby always knows that when his pressures go up, it's time for another angioplasty. They dismissed that until the neph came in and saw his pressures for herself. She doesn't mess around when it comes to his fistula but the staff? Well...that's another story.

[cassandra]

Good to hear your hubby has a neph who seems to have a dare I say: brain?

Good luck, Cas

[PrimeTimer]

Hubby had a fistulagram and all is well. In fact, things looked SOO good that the vascular surgeon said he doesn't need to come back for a year! WOO-HOO! That's a big deal for him because during these first 4 years of dialysis he has needed an angioplasty every few to six months. As for the arterial pressure being high, it was not a good stick (and the sticker is a newbie). The neph's nurse finally caught on to this fact to relay to the neph. A few adjustments and pillowing and his pressures are fine. So that is that. A relief! 

[Charlie B53]

I have an appt 6/21 for the doppler ultrasound to check flow in my new fistula.  It is growing slowly.  They will tell me how it is and when/if we get to 'stick' it.

Needle-phobia tells me that I can wait.

[PrimeTimer]

I have an appt 6/21 for the doppler ultrasound to check flow in my new fistula.  It is growing slowly.  They will tell me how it is and when/if we get to 'stick' it.

Needle-phobia tells me that I can wait.

New fistula's can take a couple months or so to mature. I'd hate having a fistula but glad my husband has one. And he's glad that he made the choice to stay in the game and do dialysis. You will do fine. We'll all be here for when the time comes, Charlie. Might not even be as bad as removing an ingrown toe nail (I read your other post). Keep up the nail filing and good work!

[Simon Dog]

My fistula was growing slowly, so I had a fistulagram done.  The surgeon tied of a tributory vessel so the fistula could build up more pressure, it matured nicely, and has been working without incident for 4 years and counting.