Does Kt/V kill people?


#1

No silly, people kill people, plus there are some diseases. The misuse of Kt/V is a symptom of a much bigger problem.

Everyone knows that ineffective dialysis causes higher death rates and dialysis effectiveness is defined by Kt/V. It’s obvious. If Kt/V is zero the patient will die early. But like most common knowledge there are no facts to support how much is enough or what constitutes adequate dialysis dose in terms of mortality. There were a couple of faulty studies decades ago that made the link. Later studies proved no link at higher Kt/V values. Now, because of CMS policies and institutional bias we can’t do studies at lower values. So the myth persists and people die prematurely.

Kt/V only measures how fast urea is cleared. It gives a higher value for higher blood flow so clinics seek to maximize blood flow. Look at the package insert for your dialyzer cartridge. For NxStage the sieving rate is 100% and clearance for BUN, creatine and Vit B12 are 100% at any blood flow above 200 mL/min. You can’t get any better than 100%. At 200 mL/min BFR, the Kt/V will always be low but you can use smaller needles, the pressure on the blood cells will be lower, the pressure inside the fistula will be lower and the heart will function more normally. There’s less pressure washer effect in the fistula and less recirculation.

There’s also the issue of toxin gradient. At 500 mL/min it takes 10 minutes to push 5 liters of blood, all there is for most perople, through the dialyzer. At 100% clearance, in 10 minutes all that is left of BUN and most other tosins is what has rebounded from the extremities. Numerous studies have shown that it takes BUN 40 to 60 minutes, likely 50 minutes on average, post dialysis to attain a new equilibrium. In 10 minutes you are only 20% there but you’ve cleared 14% of the BUN from the body and the BUN in the extremities is still close to where it started. If Pre BUN was 100 mg/dL, BUN at th start of pass 2 will be 100 x 86% x 20% or 17.2 mg/dL. That gradient, 100 / 17.2 has to cause stress on the system. Similar to the stress caused by excessive UFR which is similar in that the gradient of fluid retention in the extremities to that in the blood is excessive and it is well established that excessive fluid gradient causes early death.

One other point on Kt/V. It does not measure anything other than how fast BUN is cleared over the course of a dialysis cycle. It doen’t tell you how well the BUN is being controlled. Nothing about how much is being added by daily activity and nothing about the residual, average amount that is left in the body. Nothing related to the real purpose of dialysis which is kidney function replacement. Kidneys function slowly and yield a low level of toxins in the body. Dialysis is supposed to yield a low level of toxins and it matters not how fast that is achieved. Kt/V also tells you nothing about any of the other toxins. They are independent. They regenerate from different processes. They rebound at different rates and many clear differently depending on shape and size and affinity to other molecules.

One size does not fit all. As an engineer I always want a way to measure success. Kt/V does not provide that for dialysis. How about this:

                                 Normal      <<< ===    on Dialysis    === >>>
                                 Kidneys     better   good      OK       Marginal     bad
BUN  mg/dL                7-25            32      40         60             85          100
Creatinine  mg/dL     <1.5                4      10         15              20           25
Phos (PO4) mg/dL     2.5-4.5           3      3.5        4.5            5.5          6.5
Potassium meq/L       3.5-5.4          4      4.0        5.5            6.5          7.5

Score                           3.0                2.0    1.5        1.2           1.0           0.8

To use: put an x on each scale where the patient’s 3 month average falls then put an x in the middle of the cluster, drop down to the score line & assign that value.

Focusing on something that doesn’t matter allows you to ignore something that does. I’ve seen a number of comments and studies lamenting that the death rate for dialysis patients in the US is higher than other similar countries, that mortality has to be related to dialysis adequacy and that death rates for dialysis patients haven’t changed in decades while mortality for regular people age 60 and up has been improving.

It’s time to make a change and CMS is where the change has to start because they set the standards. Send them a letter. Make a complaint. This needs to be fixed.

I am still seeking information. If anyone has facts to dispute any of my conclusions please pass them on. Thanks for your consideration.