Flow Fraction and When To Change

[PrimeTimer]

Is the Flow Fraction part of your dialysis prescription and/or can it be changed without doctor permission? While I somewhat understand that the Flow Fraction has nothing to do with "how good of dialysis" you are getting, it does play a part when setting the Dialysate/UF rates on the cycler. I also wonder how a doctor decides on what FF the patient should use. Before we bring it up with the Neph or NxStage and cause an uproar or confusion, I just want to know if any of you have changed the FF on your own and if you received any backlash from your Neph or nurse for doing that. Thanks. 

[obsidianom]

Is the Flow Fraction part of your dialysis prescription and/or can it be changed without doctor permission? While I somewhat understand that the Flow Fraction has nothing to do with "how good of dialysis" you are getting, it does play a part when setting the Dialysate/UF rates on the cycler. I also wonder how a doctor decides on what FF the patient should use. Before we bring it up with the Neph or NxStage and cause an uproar or confusion, I just want to know if any of you have changed the FF on your own and if you received any backlash from your Neph or nurse for doing that. Thanks.

I have posted on this numerous times . THE FLOW FRACTION IS A MEANINGLESS NUMBER CONCOCTED BY NXSTAGE. Even they admitted to me it is basically irrelevant. No other system uses it.  We just set ours on the background settings at a maximum of 100 so we can ignore it when running. I don't even know what ours runs.
All that really matters is the speed of the dialysate which effects the time on machine and the total volume of dialysate . Then of course keep the blood speed down to under 350 to be safe.   So go change your background settings with the machine off to 100 on the flow fraction (setting 1 , Max. flow fraction) . Then forget it. You will be happier and it is one less thing to worry about.

[caregivertech1]

FF is simply the dialysate flow rate divided by the blood flow rate. Yes I have changed it on my own kinda following the dosing calculator and information from other posters on this board.. My Neph once asked me what it was so as long as you can "quote" the dosing calculator recommendations you'll probably be good to go. Definitely change it if will help. We were trained at 35% at Qb of 500 which is 175ml/min. We now run at 45% with a Qb of 350. Our dialysate volume increased from 20L to 30L. Bottom line we're doing a longer session with a dramatic drop in venous and arterial pressures and a big jump in Kt/V. Good Luck.

[PrimeTimer]

Thank you, obsidianom and caregivertech1. I have found that altho we entered an initial "setting" for the Flow Fraction, it changes during treatment if you have to make any changes to rates, such as speeding up/slowing down the UF removal rate due to high/low blood pressure and in turn, we have to adjust the dialysate rate...which then affects and can change the FF rate that appears in the far left screen on the cycler during treatment. Because of that, we can't always run at the initial FF setting and end up going below it at a lower FF. I note any adjustments/changes on his treatment logs to reflect initial settings and then any changes made during treatment and so far, the Neph and nurse haven't said anything but still, I wondered about it. Thanks again for your input.

[chuckdims]

I don't even know what the significance of the FF is.  I asked my nurse during my training, and he rattled off some stuff, but I could tell he was BS-ing me, trying not to say that he had no idea.

[Hemodoc]

I wouldn't say that Flow Fraction is meaningless,  it is quite well defined although widely misunderstood. It s simply the ratio between dialysate flow rate and blood flow rate.

For those who use NxStage, it determines TIME on the machine when Volume is pre-set which it is in all treatments. If you run at a stead blood flow rate, the FF will determine the length of treatment. There is NO TIMER on the NxStage machine. The timer is a relative one with the FF determining TIME with a set Volume and blood flow.

NxStage uses FF as a means to keep the dialysate flow rate low which was the philosophy of NxStage at the beginning. They are designed to keep dialysate flow rates less than 200 ml/min. Remember their marketing ploy, one liter of dialysis is one liter of clearance. Well that is a meaningless statement since no system is 100% efficient, none. In addition, clearance likewise has no dimensions, rendering that marketing ploy doubly meaningless.

The strategy that works best in my opinion is keeping blood flow rates a "lower" levels, increase the volume to a maximum for your situation and increase the FF to match your planned TIME also understanding that longer TIME on dialysis improves long term outcomes no matter the volume, blood flow rate or ultimately dialysate flow rate. Nevertheless, I maximize volume and TIME even though I readily understand that TIME is the most important element of dialysis.

[PrimeTimer]

I wouldn't say that Flow Fraction is meaningless,  it is quite well defined although widely misunderstood. It s simply the ratio between dialysate flow rate and blood flow rate.

For those who use NxStage, it determines TIME on the machine when Volume is pre-set which it is in all treatments. If you run at a stead blood flow rate, the FF will determine the length of treatment. There is NO TIMER on the NxStage machine. The timer is a relative one with the FF determining TIME with a set Volume and blood flow.

NxStage uses FF as a means to keep the dialysate flow rate low which was the philosophy of NxStage at the beginning. They are designed to keep dialysate flow rates less than 200 ml/min. Remember their marketing ploy, one liter of dialysis is one liter of clearance. Well that is a meaningless statement since no system is 100% efficient, none. In addition, clearance likewise has no dimensions, rendering that marketing ploy doubly meaningless.

The strategy that works best in my opinion is keeping blood flow rates a "lower" levels, increase the volume to a maximum for your situation and increase the FF to match your planned TIME also understanding that longer TIME on dialysis improves long term outcomes no matter the volume, blood flow rate or ultimately dialysate flow rate. Nevertheless, I maximize volume and TIME even though I readily understand that TIME is the most important element of dialysis.

Thank you for the input and contributing to the thread, Hemodoc. I have started a new thread re: dialysate running out before the UF goal is met..thought it may have something to do with the FF but not so sure. Any input you might have on that will also be appreciated, thanks.

[*kana*]

I've been forced in center for 5 weeks now because I decided to change my flow  fraction on my machine.  My nephrologist, Voodooshi Maru, Brighton, Mi turned into an evil person when I tried to make things better for myself.  I've switched nephrologists, but it is her partner and he believes what she is saying about me.  So..unless you want to be punished like me, don't tell them you changed your settings.

[obsidianom]

I've been forced in center for 5 weeks now because I decided to change my flow  fraction on my machine.  My nephrologist, Voodooshi Maru, Brighton, Mi turned into an evil person when I tried to make things better for myself.  I've switched nephrologists, but it is her partner and he believes what she is saying about me.  So..unless you want to be punished like me, don't tell them you changed your settings.

I would threaten their license to get their attention. You could tell the evil doctor you are writing a formal complaint to THE MEDICAL LICENSING BOARD of the state. That will scare the crap out of them. Any complaint goes on their record and they have to answer it formally. It is a mess for the doctor and should get their attention.
I wouldn't stand for that kind of abuse.   If they dont come around quickly, write the letter and send it . 

[caregivertech1]

Have your clinic run the NxStage dosing calculator for you. If any of the treatment settings are close to what you changed to show them to the Neph. He might come around.

[Simon Dog]

I've been forced in center for 5 weeks now because I decided to change my flow  fraction on my machine.  My nephrologist, Voodooshi Maru, Brighton, Mi turned into an evil person when I tried to make things better for myself.  I've switched nephrologists, but it is her partner and he believes what she is saying about me.  So..unless you want to be punished like me, don't tell them you changed your settings.

What did you change it from/to?   Your neph should be your partner in treatment, not an overlord.    Whenever I change treatment settings or deviate from the prescribed Rx, I report it to the RN and/or MD handling my case.   They have both been very understanding and respond with medical advice, not admonishment.

Is the 5 weeks permanent, or some sort of punishment period?   I was forced in-center for about 4 weeks, but it was because my HGB was down to 6.2 and the MD and RN felt it was safest to do it in-center until I was back up to at least 8.5.   This was a reasonable action, as their concern was that I could not tolerate an incident of a setups worth of blood loss (190ml) until my HGB was at a more respectable level.

I couldn't "not tell" them about changed settings, since I use the iPad Nx2Me app and the machine info is uploaded directly to NxStage so the clinic staff can see it on the clinic web portal.

[Simon Dog]

I don't even know what the significance of the FF is.  I asked my nurse during my training, and he rattled off some stuff, but I could tell he was BS-ing me, trying not to say that he had no idea.

Some of the RN's have a general idea of FF, but may not be able to explain it in detail because they don't know how to run the numbers.

FF = (D+UF)/B

Where

D=Dialysate flow rate
UF=Ultrafiltration
B=Blood flow rate

Units for D,U and B must be the same.   I'll use L/hr, so 450ml/min => 450ml*1/1000ml*60min/hr => 27 L./hr

To predict the dialysate flow speed at a given FF and UF,

FF*B-UF=D

So, assuming a FF of 40% (.40), blood flow of 450 (27L/hr) and 1L/hr of UF (big numbers used for example only):

.40*27-1 = 9.8

or, 40*.27 = 10.8 after you have hit "Alarm 5" (UF complete)

Try it with your numbers - do it right, and you will find your prediction of how high you can set the dialysate flow rate on the machine matches reality.

[obsidianom]

I don't even know what the significance of the FF is.  I asked my nurse during my training, and he rattled off some stuff, but I could tell he was BS-ing me, trying not to say that he had no idea.

Some of the RN's have a general idea of FF, but may not be able to explain it in detail because they don't know how to run the numbers.

FF = (D+UF)/B

Where

D=Dialysate flow rate
UF=Ultrafiltration
B=Blood flow rate

Units for D,U and B must be the same.   I'll use L/hr, so 450ml/min => 450ml*1/1000ml*60min/hr => 27 L./hr

To predict the dialysate flow speed at a given FF and UF,

FF*B-UF=D

So, assuming a FF of 40% (.40), blood flow of 450 (27L/hr) and 1L/hr of UF (big numbers used for example only):

.40*27-1 = 9.8

or, 40*.27 = 10.8 after you have hit "Alarm 5" (UF complete)

Try it with your numbers - do it right, and you will find your prediction of how high you can set the dialysate flow rate on the machine matches reality.

Flow fraction is a bogus useless number created by Nxstage. It has no effect at all on dialysis . I ignore it. I just preset ours at 100% in background and never look at it. What matters is the volume of dialysate and UF and the rates of both. 

[Simon Dog]

Flow fraction is a bogus useless number created by Nxstage. It has no effect at all on dialysis . I ignore it. I just preset ours at 100% in background and never look at it. What matters is the volume of dialysate and UF and the rates of both.

Winner winner chicken dinner.

It is convenient for many in that is provides a mechanism to configure the NxStage machine to not allow you to run the dialysate "too fast".   It would have made more sense to simply allow the user to configure a "max dialysate speed" in their machine setup rather than inventing a new number which is the indirect product of the numbers which do have meaning.

It also allows the machine to be configured to slow down the dialysate when the blood flow is turned down, so you don't waste dialysate which would otherwise be available during the higher blood flow portions of a treatment.

But, since it's part of a typical Rx, and a setup parameter, it's relevant to understand exactly what it is.