KTV

[Sugarlump]

I  am looking for someone who can explain to me how this is calculated and what factors affect it? 
Like after a really good dialysis session, clearing 77 litres, can produce a KTV of only O.8 ?

[billybags]

Sugarlump, I dont understand it either. My husband does the overnight cycler and a manual tea time bag. The nurse did the test last week. she took fluid from all bags and his KTV came up at 2.1 UK terms. She said he is a high transporter and she is quite happy with this. I am still no wiser.

[jeannea]

It's a complicated calculation. Be sure to dig out your calculus. If you want to google it and read about it type in kt/v. It has to do with the amount of toxins that are being removed from your body during your dialysis time. If you sit there for all those hours your blood keeps flowing through the machine. But if it doesn't remove the toxins it was a waste of your time. They measure kt/v to see if the dialysis is actually helping. If your number is too low, the doctor needs to adjust your prescription. Different dialyzer, time, bath, whatever. If it's really high maybe you can do less time. For PD, if you can't get a decent kt/v you may have to switch to hemo.

[Weggy]

I don't know the formulas for KTV. I think my nurse just inputs the data into a computer to get the number as it requires some derivatives and lots of calculation. However, the key things for calculating it are:

1. BUN levels
2. Dialyzing time
3. Body mass

I think in-center takes BUN pre and post dialysis to calculate KTV. PD also uses the amount of urea in a 24 hour urine collection and in the dialysate as well.

KT/V is clearance, time and volume (body mass). The formula is different, but to improve your KTV there are really only two things you can do:

1. Increase your dialysis-The more the better.
2. Lower body mass-The body is 60% water. More mass means more water which means you have to clean more fluid. Really only applicable to overweight people.

At least I think that is how it works. 

[Sugarlump]

I've read the Wikipedia entry but can't say I really understand how they calculate it other than the ratip of urea in the blood.
So if your blood was reasonably clean to start you wouldn't get a high ktv?
(I am wondering if my blood transfusion affected the results???)

I assume the BUN level is the nitrate/nitrogen level in the blood pre and post dialysis?
I did 4 hours
with a pump speed of 320
Clearing 77 litres
and change in body weight from 88.5kgs to 85.5kg

Can anybody work out my correct ktv?

[Henry P Snicklesnorter]

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[Henry P Snicklesnorter]

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[Sugarlump]

Thanks Henry, I will have to pick up the urea figures on Monday and then see if the answer makes any sense. Our nurses don't have a clue but tell you off if you don't reach 1.2 !!!

[Weggy]

I don't know the formulas for KTV. I think my nurse just inputs the data into a computer to get the number as it requires some derivatives and lots of calculation. However, the key things for calculating it are:

1. BUN levels
2. Dialyzing time
3. Body mass

I think in-center takes BUN pre and post dialysis to calculate KTV. PD also uses the amount of urea in a 24 hour urine collection and in the dialysate as well.

KT/V is clearance, time and volume (body mass). The formula is different, but to improve your KTV there are really only two things you can do:

1. Increase your dialysis-The more the better.
2. Lower body mass-The body is 60% water. More mass means more water which means you have to clean more fluid. Really only applicable to overweight people.

At least I think that is how it works. 

Weggy, the V in Kt/V is the volume of water in your body, - not body mass


Henry P   

I know. I just interchanged the terms since the formula uses a percentage of your body weight (the water part).  Since water has a density of 1, you can interchange volume and mass since 1mL=1g.

[Sugarlump]

Maths was never my best subject at school and my I can feel my palms sweat if i have to make any kind of difficult calculation...

What is the difference between KTV and URR and which is the the most accurate representation of your dialysis.?

[obsidianom]

URR is urea reduction ratio. It is a measure of BUN before and after dialysis. BUN changes quickly with dialysis and is easy to measure,.  The URR is the pre BUN MINUS the post  dialysis BUN , then take the differance between the two and that number is divided by the pre BUN and expressed as a percentage. 65 % or higher is good.
example:    pre BUN 60 , post BUN 20 .    Take 60 minus 20 and get 40. You have cleared 40 parts of the original 60 . Then 40 is divided by 60 which gives 66.7 % which is very good.
BUN is Blood Urea Nitrate which is a good marker for urea in blood., and is representitive of the toxins . It is only one toxin so they have to look at potassium and phisphorus and other electroytes too. It is easier to work with then KT/V  and a good represention of the effect od dialysis on your blood. I believe it is not perfect and KT/V is more accurate but I am not an expert on the math. At least this is easy to work with .

[PatDowns]

If running conventional incenter treatment times of 4 hours or less x 3 weekly, neither kt/v or URR are good indicators of quality dialysis.  Urea is a small, easy clearable solute from the blood stream and therefore easily quantified.   While urea is an indicator of impaired kidney function, larger solutes like potassium, phosphorous and b2-microglobulin have a more profound effect on physical well-being and patient morbidity/mortality rates.  Because of the molecular size of these solutes, it takes longer to get cleared from the blood, especially with mandatory run times of less than 4 hours found in most dialysis centers. 

Dr. Peter Lundin, a nephrologist/patient advocate who went through medical school in the mid-1960s while on dialysis, actually put it very simply: "Those who are well dialyzed should have the appetite to eat well enough to return toward their pre-illness real weight. Also, they should be able to do many or the things they planned to do before becoming sick."

A better gauge of adequate dialysis in the Hemodialysis Product (HDP).  As explained by Bill Peckham: "The underlying premise for the HDP is Babb's Middle Molecule theory of dialysis which is not accounted for by the Kt/V concept of adequacy.  Scribner and Oreopoulos argued that the Kt/V measurement is inadequate in that it only deals with the fast diffusing urea, arguably a nontoxic molecule, and it fails to take into account time dependent molecules such as B-2 microglobulin and phosphorus which acts like a middle molecule. 

Removal of these time dependent middle molecules depends on the duration of exposure to the dialysis membrane. Removal is independent of blood flow rates, ultrafiltration rates and even, to an extent, the clearance rates of the artificial kidney. Time is the key variable and this is what allows for the elegant simplicity of the HDP.

HDP = (hours of dialysis per session) x (sessions per week)2"

Here is a more easily understandable explanation:  http://www.therenalnetwork.org/qi/resources/HDP.pdf

Also, please read about the GOOD DIALYSIS INDEX. - http://www.nocturnaldialysis.org/good_dialysis_index.htm

I guess all this begs the question, "why are kt/v and URR still used as the benchmarks of dialysis adequacy?"  Again, to quote Bill Peckham,"The only interests served by measuring urea are business interests. Urea is easy and inexpensive to measure. Urea is easy and inexpensive to remove."  In other words, profit over good patient care.

[obsidianom]

Using the above equation, as I have mentioned before, home dialysis is the way to go. By dialyzing at least 5 times per week you square that number times the hours . In effect the number of times per week is the real key. That makes sense as the kidneys function every day normally, not 3 days per week.
3 hours of dialysis times 5 times per week squared equals, 75 .     4 hours times 3 times per week squared is only 36.  so by adding 2 days and actualy shortening dialysis , you are more than DOUBLING the effective treatment.    So the real key is going home and doing it 5 or 6 times per week.  Nxstage is perfect for that.
That is why I chose Nxstage for my wife.

[PatDowns]

Using the above equation, as I have mentioned before, home dialysis is the way to go. By dialyzing at least 5 times per week you square that number times the hours . In effect the number of times per week is the real key. That makes sense as the kidneys function every day normally, not 3 days per week.
3 hours of dialysis times 5 times per week squared equals, 75 .     4 hours times 3 times per week squared is only 36.  so by adding 2 days and actualy shortening dialysis , you are more than DOUBLING the effective treatment.    So the real key is going home and doing it 5 or 6 times per week.  Nxstage is perfect for that.
That is why I chose Nxstage for my wife.

Some patients are unable to do daily home dialysis because of having a graft instead of an AV fistula.  Grafts do not allow for buttonhole cannulation and everyday usage would weaken the artificial material in a shorter period of time.  Other patients may not have a care partner, a large enough home to set up and store equipemt/supplies, or other reason for not wanting to bring treatment inside their homes.   So for them, going to 5 hours x 3 per week in center would show a significant increase in HDP.  Also, many centers are now providing overnight extended hours treatment options, running patients from 6-8 hours.   

[Sugarlump]

I do three sessions of 4 hours a week on an HDF machine but I have noticed the better my pre-dialysis figures (of urea/creatinine/potassium) the lower my KTV and URR figures are??? I can't be getting less effective dialysis but it must be the way it's calculated. 

[obsidianom]

If your pre dialysis figures are better , then not as much will occur during dialysis so the numbers will look lower. For example if you start at a BUN of 80 (which is quite high) and go down to 20 after dialysis your URR will be 75%. That is good . If you start at 40 and go to 20 the URR will only be 50% which looks bad, but in reality you still ended at 20 which is a decent BUN . As posted above by others, the most important thing IS HOW YOU FEEL.  Numbers in medicine are just guides but should never be used as the absolute indicater of treatment results in many areas.  Nephrology is one specialty where that is very true.
I have seen patients not start dialysis even though they feel awful all the time but their creatinine is "only " 3.2 and BUN around 40.   The nephrologists often hold off based on these numbers while the patient is getting sicker and is miserable. I saw this in my wife and in many patients in my office over the years. Some patients can feel ok with a creatinine of over 4 or even 5 , while others can be very uncomfortable at creatinine of 2.8.   
Bottom line is HOW DO YOU FEEL???

[Tío Riñon]

If running conventional incenter treatment times of 4 hours or less x 3 weekly, neither kt/v or URR are good indicators of quality dialysis.  Urea is a small, easy clearable solute from the blood stream and therefore easily quantified.   While urea is an indicator of impaired kidney function, larger solutes like potassium, phosphorous and b2-microglobulin have a more profound effect on physical well-being and patient morbidity/mortality rates.  Because of the molecular size of these solutes, it takes longer to get cleared from the blood, especially with mandatory run times of less than 4 hours found in most dialysis centers. 

Dr. Peter Lundin, a nephrologist/patient advocate who went through medical school in the mid-1960s while on dialysis, actually put it very simply: "Those who are well dialyzed should have the appetite to eat well enough to return toward their pre-illness real weight. Also, they should be able to do many or the things they planned to do before becoming sick."

A better gauge of adequate dialysis in the Hemodialysis Product (HDP).  As explained by Bill Peckham: "The underlying premise for the HDP is Babb's Middle Molecule theory of dialysis which is not accounted for by the Kt/V concept of adequacy.  Scribner and Oreopoulos argued that the Kt/V measurement is inadequate in that it only deals with the fast diffusing urea, arguably a nontoxic molecule, and it fails to take into account time dependent molecules such as B-2 microglobulin and phosphorus which acts like a middle molecule. 

Removal of these time dependent middle molecules depends on the duration of exposure to the dialysis membrane. Removal is independent of blood flow rates, ultrafiltration rates and even, to an extent, the clearance rates of the artificial kidney. Time is the key variable and this is what allows for the elegant simplicity of the HDP.

HDP = (hours of dialysis per session) x (sessions per week)2"

Here is a more easily understandable explanation:  http://www.therenalnetwork.org/qi/resources/HDP.pdf

Also, please read about the GOOD DIALYSIS INDEX. - http://www.nocturnaldialysis.org/good_dialysis_index.htm

I guess all this begs the question, "why are kt/v and URR still used as the benchmarks of dialysis adequacy?"  Again, to quote Bill Peckham,"The only interests served by measuring urea are business interests. Urea is easy and inexpensive to measure. Urea is easy and inexpensive to remove."  In other words, profit over good patient care.

I agree with your assertion that kt/v isn't a good benchmark for adequacy.  Unfortunately, I know that my clinic--and I suspect others--are required by their corporate heads to use this value to determine whether patients are meeting their goals.  My own kt/v has decreased since I got a nephrectomy and I keep being told that if it doesn't improve, they may need to look at switching to another modality.  Yet, when I'm doing everything perfectly, I feel just fine although my results don't reflect it. 

The articles you've listed appear to discuss better options for patients on HD.  Do you have anything that speaks to the situation for PD patients?