I apologize for some of the complexity that will be present in today’s blog. But, I have been using these terms for decades, and they are critical to understand the principles. I will try to explain them so you can see the issues.

Back when I first became involved in dialysis, every treatment was an ordeal. (Yes, that may still feel it to those who undergo the treatmnet, but it’s WAY different today.) Treatment regimes were 12 hours at a clip, thrice weekly. Oh, and each treatment required the building of a 39 inch long, polypropylene block with six membranes (that soaked for an hour or so), along with gaskets, and plastic widgets. Oh, and dialysate- the salt water solution that served as the “sink” for the body’s toxins- needed to be prepared, too. So, each treatment took an hour or two of professional time before the 12 hours of treatment.

The body’s toxins (urea, creatinine, and a bunch of others that we called “middle molecules” – the black box of dialysis issues) crossed the membranes, became dissolved in the dialysate (saline solution), and were carted away to the drain. We used a crude term, Kt/V (a “dimensionless” ratio), to determine if we were providing adequate dialysis. Our goal was to insure that the patient treatment, according to that formula,  was around 1.4 (over the course of a week).

The V in the equation was basically the patient’s body water volume, which is where the urea was dissolved in the body.. The t was the time the patient underwent dialysis. And, the K– that was the “clearance”, the rate at which the dialyzer was able to remove urea from the body.

As dialyzers and the membranes within them became more advanced, that K value increased a lot. So, we no longer had to make patients undergo that 12 hour, thrice weekly regimen- dropping it to 4 hours, thrice weekly. (Although some clinicians believe that more frequent and shorter dialysis is better. This, more frequent modality, certainly reduces the sawtooth toxin concentration in the patients’ bodies, as you see in the chart above.)

But, now there’s a move afoot to drop the concept. Some clinicians claim that Kt/V is way too simple to address the uremic patient and his/her treatment. The reasons? As I mentioned above, the more frequent, shorter dialysis regimens, better membranes that afford better transport of middle molecules (we still don’t know what are those critical compounds), and convective transport processes in the artificial kidney.

I have been- and still am- on the fence. Mostly because I haven’t seen a monitoring parameter that can replace it. And, I am not alone. Dr. John Daugirdas, who was at the Chicago VA when I met him (decades ago) and is now at University of Illinois (Chicago), has responded to this call to change our philosophy in the current issue of Kidney International . His premise is that more frequent dialysis does not improve uremic toxin treatment; instead, it is primarily responsible for better water volume control. (You DO remember that our kidneys not only remove toxins from our body, but excess water. When they fail, it’s up to dialysis to provide these controls.) (Note: More frequent dialysis does improve the sawtooth effect on body chemistry, as I mentioned above, too.)

The one change Daugirdas feels we should consider is that we should use body surface area and not the total body water to temper the dialysis dosage. This change, according to Daugirdas, will help choose the proper dialysis regime more accurately for women [body water is fully adequate for men], undergoing dialysis.

Of course, I would much prefer we remove the stigma against stem cell research so true kidney replacements could be provided those whose kidneys have failed.  Then, we wouldn’t need any dimensionless parameters!

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