The Dialysis Waterfall (Forget Urea: It’s Fluid That Kills)
Far too much emphasis has been placed on an arbitrary and flawed concept—Kt/Vurea—to the detriment of all else.
Kt/Vurea was developed over 30 years ago after the publication of the NCDS study following 165 patients over 24-48 weeks of 1970's low-flux hemodialysis. None were over 60 and none were diabetic ... not quite a "normal" dialysis population.
Worse, all focus was on one small molecule, urea, thought then to best represent a marker of good clearance. While we now know that it would be hard to find a less representative "toxin" (its trans-compartmental kinetics bear little or no relationship or similarity to the behavioral kinetics of any of Vanholder's vast list of uraemic toxins), Kt/Vurea is still used in the US as the marker of "adequacy." What bunkum!
We now better understand the importance of middle molecules like β2M, homocysteine, and the hydrophilic envelope around tiny phosphate that turns it into a time dependent trans-membrane traveller. Even then, this focus implies that dialysis is all about solute clearance. Another myth. Bunkum again!
Most commonly it is fluid, not solute, that maims and kills the dialysis patient. It is fluid that stifles the breath, stretches the heart past the zenith of Starling's curve, and—when removed—is commonly removed so fast that the blood pressure and circulation collapses, coronary and myocardial perfusion falls, and the heart is stunned. That sequence is not solute-related. Tick that up to fluid!
In the dialysis setting, when fluid is discussed, it is all too often in tones of anger and confrontation. Dialysis staff regularly berate patients over excess fluid gain (the surrogate phrase for non-compliance) without considering why. After all, it is the patients' fault. More bunkum!
A daily scenario in most dialysis units:
A patient arrives for dialysis with excess fluid to remove.
This is what tends to happen:
- A (sometimes ugly) confrontation occurs with: "... you have not adhered to your fluid restriction ..."
- With lots of fluid to remove, a high ultrafiltration rate (UFR) is required and set.
- Surprise: the patient goes "flat" halfway through. Urgent "resuscitation" starts, with N saline (of course). But wait: isn't dialysis meant to be removing excess salt and water?
- After loading up with salt and water, more fluid is taken off, and fast, for time is now short. Even if more flats are avoided, cramp is not and, at the end of dialysis, the patient is as limp as a potted plant at the end of a hot day ... and is grumpy ... and feels like death warmed up.
- Before you is a patient with a maximally contracted circulating volume —to the point of circulatory collapse and hypotension. Before you is a patient with a maximally activated thirst mechanism. Thirst is an irresistible, primal, survival instinct buried deep in the brain stem. The patient is without a hope of suppressing it.
- What, then, does the patient do? He/she drinks! So would you —you would have to! Your brain stem would insist on it! And so this "noncompliant" patient complies with the primal survival drive of thirst, and drinks!
- In 2 days time (or 3, at the staff-convenient weekend), the patient returns, finally revitalized by fluid, but extra kilos "over". More angry berating ensues "You must be more compliant, you are killing yourself ..."
- No ... we are the ones doing the killing.
- Mistake #1:
- The dialysis session is too short. A longer session allows the removal of the same volume over a longer time at a lower UFR.
- Mistake # 2:
- Berating a patient for "non-compliance" is (a) cruel and (b) an abuse of a patient for our own mistake: the 'excess fluid to remove' is fluid that we forced the patient to drink by switching on a primal, irresistible instinct —an instinct we ignited—through far too rapid a contraction of blood volume abetted by further salt loading during the inevitable circulatory resuscitation.
- Mistake # 3:
- It isn't the patient who "doesn't get it." We are the ones that don't get it!
But, there is one last page to the fluid story: the plasma refill rate.
When fluid is rapidly removed, as it is during dialysis, fluid "waterfalls" into the circulation from the extravascular space. Then, in turn, the extravascular space is refilled from the intracellular fluids. A 3-way trans-compartmental fluid shift is set in motion. The contraction of one forces a refilling from the next, and back down the line. But—and here's the key—this re-filling is rate-limited!
While dependent on many factors far too complex to tease out here, the approximate plasma refill rate can be estimated. Kim (1972), Chaigon (1981) and Schneiditz (1992) each estimated the maximal plasma refill rate to lie somewhere in the range of 5-7 ml/kg/hr.
McIntyre has reported that the risk of myocardial stunning (perfusion failure of the myocardium that results from an excess UFR) becomes clinically threatening if the UFR exceeds 10 ml/kg/hr. This is a removal rate of 3-5 ml/kg/hr in excess of the plasma refill rate. In other words, and this is a difficult concept, if contraction of the intravascular volume exceeds the refill rate by just ~3-5 ml/kg/hr, watch out!
I think in 5's. I remember a plasma refill rate of 5 ml/kg/hr. Then I remember the threat-level for myocardial stunning is 5 ml/kg/hr more than the refill rate. Remember this, and you won't be too far out.
For any dialysis patient, multiply their ideal weight x 5 ml/hr for their plasma refill rate. Each ml/min of UFR above that = the approximate rate of plasma volume contraction, remembering that poor hearts poorly tolerate rapid volume contraction. Exceed a contraction rate >2 x the plasma refill rate, and any heart is threatened.
Dialysis should (must) be long enough - at the absolute minimum - to allow for the removal of all required fluid at a UFR that lies within these limits, but any rate in excess of the plasma refill rate will begin to trigger volume driven thirst. Slowing the UFR as closely as possible to the plasma refill rate will prevent thirst-driven volume overload prior to the next dialysis.
The path to compliance – and optimized cardiovascular stability – is not by forcing uncomfortable fluid restriction, but by increasing dialysis frequency to lessen the accumulation of fluid to remove, and by lengthening dialysis sessional duration to a UFR that does not exceed the plasma refill rate (the ideal), or at least to a rate that protects the heart from dialysis-induced 'stunning'.
So ... do we now have a patient who is suddenly "compliant"?
No ... we have a dialysis program that is suddenly thinking!
And, there is one more mistake we make. Subscribe to this blog to be notified when my next post on The Solute Mistake goes live.
- Kim KE, NefT M, Cohen B, Somerstein M, Chinitz J, Onesti G, Swartz C. Blood volume changes and hypotension during hemodialysis. Trans Amer Soc Artif Int Organs 16: 508, 1970
- Chaignon M, Chen WT, Tarazi RC, Bravo EL, Nakamoto S. Effect of hemodialysis on blood volume distribution and cardiac output. Hypertension. 1981;3:327-332
- McIntyre CW, Burton JO, Selby NM, Leccisotti L, Korsheed S, Baker CSR, Camicic PG. Hemodialysis-Induced Cardiac Dysfunction Is Associated with an Acute Reduction in Global and Segmental Myocardial Blood Flow. Clin J Am Soc Nephrol. 2008 January; 3(1): 19–26.
Vincent rommel narvaez
Nov 03, 2021 10:37 AM
I did an experiment , basically i did not eat anything between two sessions of dialysis. Just drank as much as i could. I still pee regularly.
I come back and i did not gain any weight at all . They still take “excess” fluids and i almost pass out .
I keep telling them its not “excess” fluids !!!
Am i wrong or what
Sep 17, 2019 5:38 PM
Sep 17, 2019 9:11 PM
I am so sorry to hear about your cousin. But, there are so many reasons why things turned out the way they did for her, so it is not only her dialysis treatment per se that may have been responsible. I sincerely wish you well as you and your family try to move on from her loss.
Nov 18, 2017 3:14 PM
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Mar 04, 2016 8:05 AM
When Carol first started on dialysis, we had planned a holiday when her Nephrologist told her she would have to have an Hickman line inserted and start dialysis. She was soooooo shocked after the first couple of sessions and ended up in tears because she expected to feel much better having no more nausea e.t.c.
She has probably never felt so bad in her life with extreme low blood pressure and cramps e.t.c. as they tried to basically dehydrate her when in the long run at the end of each session they were giving her fluid back.
When she was able, she decided to give PD a go, so she could do it at home and it would not give so much trouble after most hospital dialysis washed her out as you have related in the blog. Due to complications with the catheter and trouble draining fluid and an operation to fix this and a stint in ICU with internal bleeding, they decided PD was not viable. This resulted in HD and now HHD and we are now traveling with the machine in our van , dialysing 2 days on , 1 day off , 5 hours each session and your UF rates are basically what she aims for as it works for her. She has tried and tested times and UF rates and it works for her without any complications and she can still manage to function normally, something she was NOT capable of doing after dialysing at the hospital.
Jan 14, 2014 4:01 PM
I know Steve very well - you are being looked after the best of the best there.
If you like the book, let others here in OZ know of it for, while the bits about the US Medicare system are very US-oriented and don't apply to us here (thank goodness for small mercies) the dialysis parts are, for the main, applicable.
Of course, we do NOT embrace or encourage short daily here - why would you when we offer you much better - but the information about dialysis is otherwise pertinent and would be of great value to others here in OZ.
The messages contained in Dialysis Waterfall - Parts I and II, are good messages to understand and underline some of the themes the book supports. As such, the two are ideally absorbed together.
Jan 11, 2014 2:10 PM
Jan 10, 2014 4:41 PM
I enjoyed reading this information and I forwarded this to PCT's that I know.
Dec 24, 2013 10:57 AM
I wish this simplified/simplistic message coul be heard more widely. In my view, it is THE dialysis message that needs to be understood ... but rarely is.
Hence the crap dialysis most are given - and yet they think that's the best there is ... poor benighted souls that they are ... and scurrilous purveyors of myth that I and my colleagues are.
Dec 22, 2013 1:12 AM
As you will likely know, the data I have presented on plasma refill rates is aggregate data. While the factors that affect, alter, and modify the plasma refill rate are numerous, and the plasma refill rate also alters throughout the dialysis treatment, the data I have represented give the best rates available for the mean 'across-a-full-dialysis-treatment' rate I was able to find.
While it is an incredibly difficult physiological fact to measure and few have tried to do so, the 'concept' is crucial to understanding within-treatment fluid dynamics and the reasons that short, fast and violent dialysis is so damaging and so poorly tolerated - as common sense would have it known.
We need to better understand - in a simplistic way - the outcomes we create in our patients ... even if I will have offended some purists in by using a ' single number' for a moving feast. It is the concept I espouse ... not the 'yes, but ...' argument over the exact number and/or its variability.
While I know you understand that, I thought I should just underline here that it is that concept I want to get across, even if that means playing laisez faire with the measurements.
Dec 21, 2013 9:33 PM
One way to frame this question is to ask should (in the absence of any kidney function) people be allowed to dialyze for less than four hours/three times a week? Should payers reimburse for such a small dose?
I'm all for patient agency but isn't this more a question of medical ethics? I don't think someone facing radiation treatments could say I only want half the number of treatments the doctor says would be best to treat my cancer. I think the message would be that it is a binary choice either commit to the dose that will work or choose another approach entirely but half the necessary dose is not an option.
Is this a case of the 'dialysis system' wimping out and allowing people the false hope of half the needed dose? If three hours a treatment three treatments a week worked well that would be my choice but since it would not work (in terms of leaving me feeling well) how is it that it is even an option? Could we accept people not being dialyzed if they would only agree to 3hs/3x/week? If not why not?
Dec 21, 2013 8:14 PM
Peter A. Laird, MD
Dec 20, 2013 2:06 AM
Dec 19, 2013 11:55 PM
It is an issue that, sadly, is under-appreciated by many dialysis patients but - much more importantly - by dialysis staff. Both groups seek to shorten treatment whereas, by doing so, they are simply compounding the problems and are maximising the symptoms that make dialysis so hard for many.
The role of the dialysis professional should be three-fold: (1) to teach the benefits of longer (and preferably more frequent) dialysis; (2) to find ways of making longer, gentler dialysis more acceptable to all; (3) lobbying whomever and wherever we can to abolish the 'long weekend' such that dialysis rolls - second daily - Mon, Wed, Fri, Sun, Tue, Thu, Sat ... and on.
While I know 'more' dialysis is anathema to many, if the trade-offs of better health, well-being and off-dialysis time were better explained rather than doing as we do now - aiding and abetting short dialysis - dialysis units would be a much more pleasant place to be ... as, I hope, my own is.
Watch out for Part II = the mistakes we make in solute clearance.
Dec 19, 2013 11:09 AM
Thank you for addressing this issue in this forum.