Are you receiving adequate dialysis? How's your Kt/V?

[angieskidney]

I don't know what URR is... what is that?? 

[BigSky]

URR is urea reduction ratio which is usually given in percentage.  Used to measure if one is getting enough dialysis like Kt/v.

It takes your pre dialysis urea measurement  and then subtracts your after dialysis urea measurment.  That number is then divided by the pre dialysis measurment and that give you the URR in a percentage.

The reduction in urea as a result of dialysis, or the URR, is one measure of how effectively a dialysis treatment removed waste products from the body. URR stands for urea reduction ratio, but it is commonly expressed as a percentage.

Predialysis urea 75, post dialysis urea 25.

75-25=50

50/75= 66.7%



One should have a URR of greater than 65%.

[AlasdairUK]

I mean if I have more than 85 litres of blood pumped through the kidney. I'm not sure of the medical term for it.

[Zach]

I mean if I have more than 85 litres of blood pumped through the kidney. I'm not sure of the medical term for it.

Now I know what you mean.  Thanks.

[Dr. Evil]

....I wish some of ya'll where my patients....someone actually posted that they want MORE time on the machine.  Clearly not one of my patients!

This is an interesting topic.  The kt/V has many flaws as a measure of dialysis dose.  However, like most of clinical medicine, it is based on the B.A.D. principal.....meaning Best Available Data.

I may have my numbers off a bit, but I think the only study that look at outcomes with different targets was the HEMO study, which overall was a negative study.... I think kt/v of 1.1 was equal to 1.3....or something like this.

The problem(s) start with realizing that kt/V is for UREA clearance.  However, urea is not really the "uremic toxin" that makes people ill with kidney failure.  The nice thing about urea is that it is cheap to measure, and it is very small.  We use it as a marker of the other stuff that builds up with kidney failure that actually would make someone ill.  Urea is very rapidly cleared with today's high-flux membranes (F-160, 180, etc...), since it is very small.  Most of the clearance of urea takes place in the first hour or two (..."zero order kinetics, for the chemists out there).  This is a CONCENTRATION dependent clearance (the higher the concentration, the faster the clearance...thus the first hour is where most of the urea is removed, because your urea is actually higher at the start of the treatment.)

However, we think that many of the toxins in renal failure are bigger than urea....this is the "middle molecule" theory.  These bigger molecules (...those into the data might have heard of beta2-macroglobulins as a marker of this size stuff), are not so eaisly cleared.  These larger compounds are removed in a more linear (or "first order" kinetics) fashion.  In other words, this is more TIME dependent.  The amount of these middle molecules removed is THE SAME for each hour of dialysis...the first hr is the same as the last hr.  The problem is that we don't measure these things.

So, just by solely focusing on urea modeling (kt/V for urea), we can miss a whole bunch of stuff....so just because your Kt/V is above goal, maybe cutting your time is not a good idea, because you will have less clearance of larger molecules (but we don't measure this).  Over time, perhaps this is why ESRD pts have other medical problems faster than other people (vascular disease, etc...).

But, this is hard to study, so a lot of what we do is based on a "belief system"...(like a religion...not proven), rather than on good clinical trials.  That is OK, but we just need to remember what our science is based on and what it is not....as to not get too dogmatic over these Kt/V number.

Of course, the government gets involved, and makes these targets that we have to meet to get paid....etc, etc..and weird things start happening that may or may not be based on the "truth", where ever that lies.

Hope I didn't confuse the hell out of everyone.  I could go on, but,...as you can guess, they have books written about this stuff (...go figure?..), and there are knock-down, drag out fights during national meetings about this stuff.

[AlasdairUK]

Thanks Dr Evil,

It is good to know some of the finner points of dialysis.

[angieskidney]

The problem(s) start with realizing that kt/V is for UREA clearance.  However, urea is not really the "uremic toxin" that makes people ill with kidney failure.  The nice thing about urea is that it is cheap to measure, and is very small.  We use it as a marker of the other stuff that builds up with kidney failure that actually would make someone ill.  Urea is very rapidly cleared with todays high-flux membranes (F-160, 180, etc...), since it is very small.  Most of the clearance of urea takes place in the first hour or two (..."zero order kinetics, for the chemists out there).  This is a CONCENTRATION dependent clearance (the higher the concentration, the faster the clearance...thus the first hour is where most of the urea is removed, because your urea is actually higher at the start of the treatment.)

However, we think that many of the toxins in renal failure are bigger than urea....this is the "middle molecule" theory.  These bigger molecules (...those into the data might have heard of beta2-macroglobulins as a marker of this size stuff), are not so eaisly cleared.  These larger compounds are removed in a more linear (or "first order" kinetics) fashion.  In other words, this is more TIME dependent.  The amount of these middle molecules removed is THE SAME for each hour of dialysis...the first hr is the same as the last hr.  The problem is that we don't measure theses things.

So, just by solely focusing on urea modeling (kt/V for urea), we can miss a whole bunch of stuff....so just because your Kt/V is above goal, maybe cutting your time is not a good idea, because you will have less clearance of larger molecules (but we don't measure this).  Over time, perhaps this is why ESRD pts have other medical problems faster than other people (vascular disease, etc...).

Very good post! Thank you for that! 
I hope you post more! 

[Dr. Evil]

If anyone is interested about the next big thing in dialysis, I think it may be Hemodiafiltration (hemodialysis + hemofiltration).

It is used in some countries in Europe.  Some data is starting to come out, and it seems promising.

If anyone is interested, post a reply and i will dive into it.

[nkviking75]

....I wish some of ya'll where my patients....someone actually posted that they want MORE time on the machine.  Clearly not one of my patients!

I think you may be referring to me.  What I meant was I found it easier to endure four days of 4 hour sessions than 3 days of 5 hour sessions.  I find 4 hours nearly intolerable some days, but 5 hours would be unbearable.  There's another advantage.  I don't have to battle the "three day weekend" of fluid control.  It's never more than 2 days between sessions for me.  I have enough trouble with fluid control without the three day business.

[Dr. Evil]

Yes- more total dialysis sessions will give you better Kt/V (for urea) than longer sessions less often.  This goes back to the concentration-dependent nature of urea clearance... the first hour is the most efficient, so the more "first hours" you have, the better.   If it was actually logistically possible, 2 hr treatments 7 days a week would probably work great.  The only problem (s) are:  Set up time for each treatment; access sticks with fistula; logistical nightmare to try to do this in-center.

If you are home with a catheter and doing home hemo, this can work, but it does take a lot of time.

And, unless you are in some kind of pilot program, there are reimbursement issues...as medicare only pays for a max of 4 treatments a week.

later

[kitkatz]

I would like to know more about hemodialysis and hemofiltration, Dr. Evil.

[Zach]

However, we think that many of the toxins in renal failure are bigger than urea....this is the "middle molecule" theory.  These bigger molecules (...those into the data might have heard of beta2-macroglobulins as a marker of this size stuff), are not so eaisly cleared.  These larger compounds are removed in a more linear (or "first order" kinetics) fashion.  In other words, this is more TIME dependent.  The amount of these middle molecules removed is THE SAME for each hour of dialysis...the first hr is the same as the last hr.  The problem is that we don't measure these things.

So, just by solely focusing on urea modeling (kt/V for urea), we can miss a whole bunch of stuff....so just because your Kt/V is above goal, maybe cutting your time is not a good idea, because you will have less clearance of larger molecules (but we don't measure this).  Over time, perhaps this is why ESRD pts have other medical problems faster than other people (vascular disease, etc...).

Is this why 8 hour treatments (nocturnal), six days a week is thought of as one of the better forms of hemodialysis? ... Because it also removes the "middle molecules?"

[Epoman]

If anyone is interested about the next big thing in dialysis, I think it may be Hemodiafiltration (hemodialysis + hemofiltration).

It is used in some countries in Europe.  Some data is starting to come out, and it seems promising.

If anyone is interested, post a reply and i will dive into it.

Yes please do but please create a NEW thread. 

[Dr. Evil]

Is this why 8 hour treatments (nocturnal), six days a week is thought of as one of the better forms of hemodialysis? ... Because it also removes the "middle molecules?"

Yes- you get the benefits of long treatment times (middle molecules) and the frequency of treatments (better urea clearance...ie. Kt/V of urea).

I will start a new thread later on dialysis vs. hemofiltration vs. hemodiafiltration.




EDITED:  Fixed quote tag - Goofynina/Moderator

[Zach]

So, just by solely focusing on urea modeling (kt/V for urea), we can miss a whole bunch of stuff....so just because your Kt/V is above goal, maybe cutting your time is not a good idea, because you will have less clearance of larger molecules (but we don't measure this).  Over time, perhaps this is why ESRD pts have other medical problems faster than other people (vascular disease, etc...).

Since Kt/V is, in part, a function of time, what would you suppose is the minimum (Kt/V) per treatment to remove some of those middle molecules?  In other words, does it take at least 3 hours of a single treatment to remove a significant amount of the larger molecules?

And of course, it also depends on the type of filter that is used.     

[Fighter]

I had never heard of Kt/V and URR, but I just calculated them for myself and they are 2,2 and 72% respectively.

pump speed: 360 mL/min
time: 4 hrs (3x a week)
weight (total): 65 kilos

urea before (last monday): 233 mg/dl
urea after: 66 mg/dL

[angieskidney]

I just had blood work again the first wed of the month and got my results on Friday. My kt/V this time is 1.75 while last month it was 1.78

while on the Fresenius 2008K machine it shows the "projected kt/V". It is important to realize that over time you reach the optimum kt/V for the duration you dialyze.

[Dr. Evil]

So, just by solely focusing on urea modeling (kt/V for urea), we can miss a whole bunch of stuff....so just because your Kt/V is above goal, maybe cutting your time is not a good idea, because you will have less clearance of larger molecules (but we don't measure this).  Over time, perhaps this is why ESRD pts have other medical problems faster than other people (vascular disease, etc...).

Since Kt/V is, in part, a function of time, what would you suppose is the minimum (Kt/V) per treatment to remove some of those middle molecules?  In other words, does it take at least 3 hours of a single treatment to remove a significant amount of the larger molecules?

And of course, it also depends on the type of filter that is used.     

Zach-  remember, the Kt/V you are talking about is for Urea.  You can pick any marker you want and calculate a Kt/V for it as well.  If you get the package insert from the dialyzer (ask your head nurse or Doc), they will have a reference chart for the kidney.  Look at the b12 clearance (i think this is about the size of a 'middle molecule').  Anyway, we just don't routinely measure these other molecules in routine care of dialysis patients. 
In response to your actual question,.....I don't know how long or how much of the middle molecules are removed in 3 hrs.  However, I can say it will be about 25% less than if you were on for 4 hrs (since this is first order clearance, and every hr is the same).  The amount of urea you remove that last hr is far less (since the concentration has fallen quite a bit since the first hr).  And nobody knows how much is too much or just enough.

This is all about how diffusive clearance works (...or dialysis..... countercurrent osmosis...).  If you do hemofiltration rather than dialysis, then you use conventive clearance.  This is for the next topic on HD vs hemodiafiltration.....I will get that to that soon.   




EDITED:  Fixed quote tags - Goofynina/Moderator

[AlasdairUK]

As far as I know I'm on Hemodiafiltration. I look forward to you new thread.

Thanks Alasdair

[Dr. Evil]

New thread started on Hemodialysis vs. Hemodiafiltration. (Under general discussion)

[Zach]

Just to reiterate:

From K/DOQI GUIDELINE 4

Minimum Delivered Dose of Hemodialysis (Adults Evidence, Children Opinion)

The dialysis care team should deliver a Kt/V of at least 1.2 (single-pool, variable volume) for both adult and pediatric hemdialysis patients. For those using the URR, the delivered dose should be equivalent to a Kt/V of 1.2, ie, an average URR of 65%. However, URR can vary substantially as a function of fluid removal.

[angieskidney]

does kt/V vary by the size of the patient for what the goal should be?? (Sorry if this is a dumb question. I am still learning)

[nkviking75]

does kt/V vary by the size of the patient for what the goal should be?? (Sorry if this is a dumb question. I am still learning)

I don't know the full answer to your question, but they tell me one thing holding my Kt/V down is my excessive weight.

[Zach]

The V in Kt/V is volume of the patient, so the larger the patient, the longer treatment time is necessary (or better filter) to reach the 1.2 Kt/V.

[angieskidney]

The V in Kt/V is volume of the patient, so the larger the patient, the longer treatment time is necessary (or better filter) to reach the 1.2 Kt/V.

So my being able to reach on average 1.7kt/V is because I am an average sized girl? (I am 165cm / 5'5" @ 63kg / 138lbs)