Know your dialysis: Blood flow rate and dialysate flow rate
Posted Sep 23 2013 9:20pm
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!