Just wanted to point out that KTV values are measured differently between shortdaily and 3x week dialysis…
For 3x Week
1.2 or higher
For ShortDaily
target .45-.5 or higher
According to who?
I do not think much of kt/v as a measure of adequate or optimal dialysis but it is what we have so it continues to be measured. Translating a flawed three times a week measure into a 5-7 times a week measure is sure to have some short comings.
Here are some comments from a 2000 panel discussion from Zbylut J. Twardowski who’s at (or at least was at the time) the University of Missouri - link.
It is not known what weekly Kt/V is needed to provide adequate dialysis with daily hemodialysis. It may be lower than with thrice weekly dialysis, because peak concentrations are lower at the same aggregate Kt/V with more frequent dialysis sessions. Gotch introduced the concept of standard Kt/V (stdKt/V), which compares equivalent Kt/V at various hemodialysis frequencies [27]. For instance, according to this model, an equilibrated Kt/V of 1.4 per each dialysis with three times weekly sessions (weekly aggregate of 4.2) provides a weekly stdKt/V of 2.4. If six dialyses per week are performed, the same weekly std Kt/V is achieved with a per session equilibrated Kt/V of only 0.5, not 0.7 (weekly aggregate of 3.0 instead of 4.2). Results equivalent to those with thrice weekly hemodialysis may be achieved with much lower Kt/V (lower total dialysis time). On the other hand, with the efficiency potential of daily home hemodialysis, optimal (not merely adequate) dialysis may be achieved.
Here is an interesting conversation from 2004 where prominent NHHD experts discuss what they’ve learned about daily nocturnal. This was published in Nephrology Incite. The article is available on ikidney.com
here - link
Incite: How much more dialysis is delivered via NHHD compared to thrice-weekly in-center HD?
Agar: In effect, [dialyzing for] eight hours 3.5 nights/week delivers more than 200% and eight hours for six nights/week 400% more dialysis when using simple membrane contact time as the yardstick. Though formal measures of “adequacy” have not yet been developed for extended hour or frequency dialysis, we have loosely used a weekly percent reduction urea (PRU) to calculate the difference. A “simplified” weekly PRU (a midweek, single pool PRU x the number of dialyses/week) shows the dialysis delivery by PRU in three small sample groups-one conventional hemodialysis (CHD) group, one short hour daily hemodialysis (SHDHD) group for two hours six days/week, and an NHHD group for eight hours six nights/week-to be 197%, 274%, and 430% between CHD, SHDHD, and NHHD, respectively. Though the true weekly PRU for each group is clearly underestimated by this simple mathematical approach as it uses a mid-week PRU as its base, it gives some dimensional insight into the differences between the three modalities.
Blagg: The dose is significantly more than what is received in-center.
Lindsay: [We achieve a] standard weekly Kt/V of 4.7 +/- 0.3 [on NHHD] versus a Kt/V of 2.4 +/- 0.1 [for conventional HD].
Lockridge: We feel that we deliver a standard Kt/V of 2.5-3.0 times that of in-center dialysis. If you look at a normal creatinine clearance of 10 cc when you start on dialysis, we are delivering a creatinine clearance somewhere between 30 cc and 50 cc a minute.
Pierratos: The Kt/V for urea… on NHD is about two per treatment (x6 per week) vs. 1.4 on conventional HD (x3 per week). Recently, the use of standard Kt/V for urea has been popularized as a measure of dialysis dose. The standard Kt/V per week on conventional HD is two, while, with NHD, it is five. As mentioned above, the dialysis dose for large molecules is four times as high with NHD compared to conventional HD.
When looking for research on daily dialysis remember to try the term “quotidian” in place of “daily”. A search for “quotidian dialysis kt/v” gets better results than “daily dialysis kt/v“
Someone asked me about the Kt/V I get on daily nocturnal, a couple of times. I don’t even know what my Kt/V is. I was told it wasn’t really relevant anyway, in the sense that nobody really knows what Kt/V means in the context of daily nocturnal hemo. This is a measure that was designed with conventional hemo in mind. There’s just no way that you’re not going to get better than adequate dialysis dialyzing 7-8 hours 6 days per week. Nevertheless, I’ve just done quarterly pre/post bloodwork, so I’ll try to get the Kt/V just for comparison.
Pierre
KT/V is derived from the pre/post BUN…
Those numbers I posted above are guidelines being used now, these guidlines are almost mentioned everywhere on the net…for example, take a look at these and notice that most say 1.20 is the baseline for 3x a week while others say 1.40 or higher is the goal…
http://www.ikidney.com/iKidney/Lifestyles/LifestyleTips/Hemodialysis/ExplainingAdequateDialisis_URR_BUN_andKTV.htm
http://www.ndt-educational.org/images/Hemodialysis%201%20Section%20II.pdf
The numbers for shortdaily, not nocturnal…is measured differently and one the reasons which I was told is because dialysis in short-daily is managed more gentle while keeping the BUN levels at marginal without huge drops or increases like 3x a week does. However, am still investigating this as there’s something that just doesn’t make sense…
What’s questionable are the number of hours we do on short-daily versus the number of hours we do 3x a week…also what’s questionable are dialysate flow rates…
On the other hand, I also was told that dialysis dose has to do with other factors like vitals and wellbeing of the patient and not just KTV values…for example, the patient might be doing very well with excellent vitals and feeling great and energetic but the KTV value may not rreflect that, so if the patient is doing well, then the KTV is ignored…
Pierre@ Hey cool, let us know your KTV values, would be interesting to know…would help alot in comparing between other patients treatments… for short-daily, my recent value wa .59
P.S. For fun tryout this online KTV calculator
KTV CALCULATOR
http://www.chip.org/~asher/ktv/dialysuite.html
Hi Gus
In terms of hours, the home hemo program here simply expects the total number of hours on short daily to be the same as the total number of hours on conventional 3 x week hemo, so, 12 hours (3 x 4 hours, or 6 x 2 hours). This where the 2 hour treatment idea comes in. Dialysate flow and blood flow are the same (500/400). When you’re on nocturnal, you have the flexibility of choosing to do a short daily instead, now and then.
Pierre
Let’s see, lemme put it this way…
In-Center Average time
3hours x 3= 9hours per week x 4 = 36 hours per month
Daily-Short 2 hours average
2hours x 6= 12hours per week x 4 = 48 hours per month
However, why the heck do they meaure short-daily differently than in-center?
Why not the same as in-center? How the heck will the extra hours gonna reflect that we’re having better dialysis than in-center? We’re not using
equal values!!
So if we’re dialyzing more then the KTV should reflect that, like say more than 1.2 or at least 2.0 …
:roll:
I think some of it is that there isn’t as drastic a difference in numbers so it is impossible for some of us to get high kt/v. For example many times my pre dialysis BUN is only in the 30’s to 40’s, and it drops to 10 or so which is a heck of a lot less than if it were 100 and dropped to 20 or so. At least that is how it was explained to me.
The whole idea behind “short daily” hemo is that except for fluid removal, most of the dialysis happens during the first 2 hours of a treatment. This is why the 12 hours per week on short daily is better than the 12 hours per week of conventional thrice weekly dialysis.
They just use a 4 hour conventional treatment as a standard. It doesn’t matter that some people on conventional hemo might do 3 hours, and some might do 4-1/2 hours. When they train them for short daily, they use 2 hour treatments, and if necessary, they make any adjustments they might need based on the bloodwork. For example, my in-centre treatments have always been 3-1/2 hours, but when I started short daily, I did 2 hour treatments. That proved to be plenty. They don’t advise anyone to do less than 2 hours per day. I guess things might be done differently elsewhere in the U.S., I don’t know.
I do know that if I was still doing short daily and I was forced to do more than 2 hours, the whole thing would lose much of it’s attraction for me. It would simply be too long. Nocturnal is much longer, but it doesn’t seem like it, since I sleep through it. Of course, if for any reason I could not continue with nocturnal, I would gladly do short daily 2 hour treatments.
Pierre
Hmm, that doesn’t answer the question…
Why the heck they measure daily-short KTV differently than the standard 3x a week therapies?..
They don’t measure it differently. They measure it exactly the same. It just doesn’t have the same significance, although in my experience, they do use it for short daily.
Pierre
Could someone please explain to me the details that go into calculating your Kt/V? Ever since I first started dialysis as a PD patient a couple of years ago, the nurses and techs always seem to be throwing the word “clearance” around like it was something that everyone was brought up to know. Like “2 x 2 = 4”. I know that everyone looks at your “clearance” to determine how well you are doing on dialysis, and sometimes my prescription is adjusted because of the value. But what does it really mean? What goes into calculating the value?
I found a great website explanation of Kt/V that might help people (math challenged beware) understand what makes up the calculation. Whether you want to sit down and plug in your numbers is something else. It discusses HD and PD, but doesn’t address how it is calculated for longer or more frequent treatments. It ends with some criticisms of Kt/V and provides a number of references and internal links that you might want to visit.
One of the external links to standardized Kt/V does address nocturnal home hemodialysis, but again, there are criticisms…one being the complexity of the formula and another being that even doctors don’t understand it–so don’t feel bad.
Beth’s reference is perhaps the best I’ve ever seen on kT/V. I have been convinced for some time that the Hemodialysis Product (HDP) is both superior and much easier to understand as a measure than kT/V.
HDP = (Hours/dialysis session) x (sessions/week)squared
The minimum HDP which can be considered adequate is probably 72. It is described in Scribner BH, Oreopoulos DG, The Hemodialysis Product (HDP): A Better Index of Dialysis Adequacy than Kt/V, Dialysis & Transplantation, 2002 Jan;31(1):13-15 and a full text copy is available via footnote 7 in Beth’s reference. The shortcoming of kT/V is that it addresses concentration only which makes it essentially a measure of urea removal and ignores removal of molecules governed by transport considerations – middle molecules, phosphorus, etc. HDP is empirical – it’s a simple equation that fits the patient response data from studies around the world.
Interestingly, the Home Dialysis Central home page feature article last week by Amy, et al compared 3x/week - 4 hr with 6x/week - 2 hour and essentially confirmed the HDP “square law” importance of frequency vs. session length.
Mel
I think only the sessions per week are squared and then the result is multiplied by the hours/session. Interesting that 72 is thought to be the magic number for adequacy. This is exactly what you get with daily done 6 times a week for 2 hours. If done 5 times a week, you’d have to do 2.88 hours per session to get a hemodialysis product of 72.
Conventional: 4 hours/session x (3 sessions/week) squared or 4 x 9 = 36
Daily: 2 hours/session x (6 sessions/week) squared or 2 x 36 = 72
NHHD: 7 hours/session x (5 sessions/week) squared or 7 x 25 = 175
NHHD: 7 hours/session x (4 sessions/week) squared or 7 x 16 = 112
Increase the time per session or the number of sessions and you increase the hemodialysis product.
If I’m calculating this correctly:
- The hemodialysis product of daily dialysis is twice that of conventional.
- The hemodialysis product of nocturnal done 5 nights a week is 4.86 times that of conventional and done 4 nights a week is 3.11 times that of conventional.
- The hemodialysis product of nocturnal done 5 nights a week is 2.43 times that of daily and done 4 nights a week is 1.56 times that of daily.
To get as much from in-center dialysis 3 times a week as from daily dialysis, someone would have to dialyze 8 hours which is what people used to do in the “old days” when 3 times a week dialysis became the norm on which everything is based today. It’s not surprising that we don’t have the outcomes that we would like to have if people on in-center dialysis are getting half the dialysis they need!
Beth’s calculation is correct – you square the sessions per week and multiply the result by hours per session to get HDP. If you read Scribner’s paper you’ll note that he reaches the same conclusion as Beth – that with thrice weekly you need eight hour sessions to achieve an adequate result. It’s important to emphasize that he bases HDP not on theoretical considerations, but empirically on reported clinical results by various investigators. As I noted I find this to be a much more useful approach than kT/V or URR.
Mel
Correct me if I’m wrong, but in practice, it’s all irrelevant anyway, because you can clearly see from your bloodwork whether you are receiving good dialysis from either short daily or daily nocturnal. Kt/V is only of use when you are using a dialysis method which is already known to be marginal anyway, and where small adjustments in treatment makes a big difference. In the conventional thrice-weekly hemo, it’s so marginal in adequacy that some people might need a half hour or an hour or so more treatment. Small differences matter in that case. It’s marginal because conventional hemo only provides somewhere around 10-15% equivalent GFR - just enough to maintain life. In the case of daily hemo, it’s so much better that you are virtually assured of better than adequate dialysis no matter what you do. Creatinine and urea just don’t have enough time to rise much, and everything else just follows. Daily dialysis, both short and nocturnal, is so much better than adequate that you have to ensure you eat normally in a big way rather than following a restricted dialysis diet. In that context, Kt/V is meaningless, no matter how you calculate it. At best, even in the context of conventional hemo, it’s only an estimate anyway.
Pierre
I agree with you. The problem is that in the U.S., there are still many – especially payers – who need to be convinced that more dialysis is better. Very few people seem to understand that the best conventional 3x/week dialysis replaces only about 15% of normal kidney function – where Medicare says your kidneys have failed and you need dialysis to survive. As you say, this is barely enough dialysis to keep someone alive. Unfortunately, in the U.S. Kt/V or URR has become the be all, end all for knowing how good someone’s adequacy is. In fact, adequacy is one of the three publicly reported outcomes on Dialysis Facility Compare – the other two being anemia management and survival (see www.medicare.gov/Dialysis/home.asp).
If someone is doing daily dialysis and his/her BUN never gets very high, it seems to me that it would be difficult to show how good his/her dialysis really is. I knew a patient who dialyzed 4.5 - 5 hours every other day. His BUN never got very high so the URR was less than 60%. Someone who didn’t think about how more frequent dialysis might affect those numbers might believe that this person was getting inadequate dialysis. I’m sure his URR messed up the clinic’s outcomes for adequacy. Of course, he was able to work full-time and live a very full life in spite of his lab measure of “inadequate dialysis.”
Estonb,
Kt/V is a mathmatical formula that means “Clearance of the dialyzer (K), multiplied by the time on dialysis (t), and then divided by the volume of fluid in the body (V)”
The term Clearance (K) means the amount of blood from which a specific chemical is removed from the dialyzer in one minute. The clearance is always stated at a specific blood flow rate and dialysate flow rate.
For example, if the dialyzer Model IP4U has a clearance of 350 ml/minute at a flow rate of 400 ml/minute. That means that during every minute of dialysis, 350 ml of blood has all of the urea removed, or “cleared”.
You therefore get better clearances from higher blood flow rates- you can’t clear 350 ml of blood per minute if your blood flow rate is 200 ml/min, right?
Let’s use this example in the Kt/V formula. We know what the K is, so that makes the formula (350 x t) / V.
You always have to compare apples to apples- our clearance is in milliliters per minute, so we have to write our t in minutes. If we have a 3 hour (180 minute) treatment the formula becomes (350 x 180)/V
or: 63,000/V
The V best accuratly calculated by formal methods, but can be roughly estimated to be about 60% of your body weight. So if someone weighed 80 kilos, their volume would be 48 kilos, or 48 liters (1 liter = 1 kg). Since our clearance is in ml/min, we have to convert this into ml’s too, 48 liters = 48,000 milliliters.
Our formula is now 63,000/48,000. The answer is 1.3
Formal kinetic modeling is more complicated, and provides more information, but this is the basics of the Kt/V formula.