Tuesday, September 24, 2013

Know your dialysis: Blood flow rate and dialysate flow rate

As we saw in the last article of this series, the dialyzer has two compartments - the blood compartment and the dialyzer compartment. The blood flows through the blood compartment and a special fluid called the dialysate flows through the dialysate compartment. The dialysate is prepared by the dialysis machine by mixing three liquids - the acid solution, the bicarbonate solution and pure water in a certain proportion.

The most important part of our dialysis happens in this dialyzer. This is the artificial kidney which is performing the most important task the kidney performs - that of cleaning the blood of the excess toxins and water.

Since the cleaning happens in the dialyzer, it is important that more and more blood passes through the dialyzer from the body. There is a pump that pumps blood out of the body through the arterial needle. The faster the pump rotates, the greater the quantity of blood that is pumped through the dialyzer and the better the blood is cleaned.

Similarly, since the dialysate is the fluid that is surrounding the blood compartment, the volume of dialysate also impacts the amount of cleaning that happens. More dialysate means more toxins can be removed from the blood. The dialysate flow rate can also be controlled by the machine based on a setting.

If you are getting four hours of dialysis, thrice a week (and that is the bare minimum anyone with CKD on Maintenance hemodialysis must get!), the number of hours you are spending on the machine is limited to twelve per week. So, it is important for you to ensure that you get the best dialysis possible during those twelve hours. The blood flow rate and dialysate flow rate are by far the most important parameters that affect the cleaning of your blood of toxins. Ultrafiltration rate is not affected by these parameters at all. But the clearing of toxins is almost entirely dependent on these two parameters.

Generally, our extremely knowledgeable technicians and nurses who are totally committed to our well-being and would go to any extent to help us feel better, would be aware of all these finer nuances of dialysis. :-)

However, for those unlucky few patients who go to centers where they have clueless staff who will do everything possible to reduce their work and headaches, there could be a chance that your blood flow rate and dialysate flow rate is set to unreasonably low numbers. This is because low blood and dialysate flow rates means less chance of anything going wrong. Never mind if the clearance achieved is low. Never mind if this could spoil your quality of life and not allow you to feel your best. Never mind if this could actually reduce your lifespan!

One thing to be careful about is to make sure you don't go overboard with these changes since too high a blood flow rate could have some negative consequences as well. Make sure you discuss with your nephrologist before making any changes. The human body is very individualistic. Each one has its own quirks. What I have explained here are only general guidelines.

One thing is for sure though - the higher your blood and dialysate flow rate - the better your clearance!


Shravan Vasishth said...

These are very useful articles. One thing that happened to me last Saturday, when I dialysed for 6 hours, was that I felt a whole lot better during and after the dialysis. It's probably due to the lower pump speed (250 instead of 330), but could it maybe also be due to the lower flow rate (300 instead of 500?).

My doctor told me to reduce the flow rate to 300 for the long dialysis session. He said the reduction in effectivity is not linear (well, I think that's what he meant).

Kamal Shah said...

For the long dialysis sessions, they do generally advise a lower dialysate flow rate. And it is true, that longer, more gentler dialysis makes you feel better. The issue is - people do four hours and still run at a low blood flow rate. That does not give good dialysis.

Anonymous said...

can dialysate flow rate affect our blood pressure??

Talker said...

I like your information as posted here.
There is a statement that I would much appreciate your saying more about.
You said 'Ultrafiltration rate is not affected by these parameters at all. But the clearing of toxins is almost entirely dependent on these two parameters.'
Is Ultrafiltration not a better way, or more efficient way to be doing?
If NOT doing Ultrafiltration what is that process called?
Be Well

Kamal Shah said...

What I meant is that the rate of ultrafiltration is not affected by the blood and dialysate flow rate. Typically most people would be doing ultrafiltration and clearing of toxins both.

Talker said...

Thank you for the response.
I am still a bit confused here though.
Is Ultrafiltration alone a separate machine setting ?
Is clearing of toxins a separate machine setting?
What should one ask for to achieve the better dialysis session?
My two questions were not addressed for some reason.
They were:
Is Ultrafiltration not a better way, or more efficient way to be doing?
If NOT doing Ultrafiltration what is that process called?
Would so much appreciate your thoughts here.
Be Well

Kamal Shah said...

Yes, ultrafitration is a separate machine setting. You set the amount of fluid to be removed during your dialysis session. clearing of toxins is not a separate setting but it happens when the dialysate flows in the opposite direction as the blood within the dialyzer. This can be indirectly controlled when you set the blood flow rate and the dialysate flow rate. The higher these both are, the more toxin removal there is.

To achieve better dialysis, you need to set a high blood and dialysate flow rate. However, these are also limited by the quality of the access and your heart and general body condition. Also, if you're doing long duration, more frequent dialysis, these can be low as well.

Ultrafiltration is a part of dialysis. So, the first question is not valid as fluid almost always needs to be removed. If you are not doing ultrafiltration (probably because you might have a normal urine output), then you're only removing toxins. I am not aware of any special name for this.

would be happy to clarify any further questions you might have.

Talker said...

Thank you for the rapid and clarity of your response.
Much appreciated
Be Well

Melody McDaniel said...

Why is my DFR measured maxed out as 6.9 ?
While on here you all refer to 300 and 400

Melody McDaniel said...

Why is MY dfr maxed out listed as 6.9 .while on here you all have 300 and 400?