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How does a dialysis machine work?

Submitted by Joe S., DaVita Bio-medical Technician

Dialysis patients are all too familiar with the routine of their treatments:  Go to the clinic, get weighed, have their temperature and blood pressure taken, get stuck with needles (unless the patient has a catheter access), have tubes connected from their access to the dialyzer and then sit in the chair until it is time to go home. While waiting, have you ever wondered how a dialysis machine works? 

As “the machine man,” I would like to take this opportunity to explain how your dialysis machine works by answering some of the most frequently asked questions.

What does my dialysis machine do?

The dialysis machine mixes and monitors the dialysate. Dialysate is the fluid that helps remove the unwanted waste products from your blood. It also helps get your electrolytes and minerals to their proper levels in your body. The machine also monitors the flow of your blood while it is outside of your body. You may hear an alarm go off from time to time. This is how the machine lets us know that something needs to be checked.

What are those plastic jugs sitting in front of my machine? 

The plastic jugs hold the liquids used to mix the dialysate. The machine mixes the dialysate, which is made up of an acidified solution, bicarbonate and purified water. The acidified solution contains electrolytes and minerals. You may hear it referred to as “acid.” The other solution is bicarbonate or bicarb, which is like baking soda. Both are mixed inside the machine with purified water. While you are dialyzing, dialysate and your blood flow through the dialyzer (but they never touch). Fresh dialysate from the machine enters your dialyzer throughout your treatment. Impurities are filtered out of your blood into the dialysate. Dialysate containing unwanted waste products and excess electrolytes leave the dialyzer and are washed down the drain.

How does my blood get in and out of my body? 

Blood tubing carries your blood from your access to the dialyzer. The blood tubing is threaded through the blood pump. You’ll see the blood pump turning in a circular motion. The pumping action of the blood pump pushes your blood through the dialyzer and back into your body.

What’s in the syringe that’s attached to my machine?

Blood tends to clot when it moves through the blood tubing. To prevent this the nurse will give you a drug called “heparin.” Your doctor orders the amount of heparin you get at each treatment. That amount of heparin is drawn up into a syringe then placed on the machine into the “heparin pump.” The heparin pump is programmed to release the right amount of heparin into your blood tubing during your treatment. The heparin prevents your blood from clotting.

How does the machine keep me safe?  

One problem that may occur during dialysis is that air gets into the blood tubing. To prevent this from happening, blood tubings have two air traps built into them. One trap is before the dialyzer and the other is after it. These traps catch any air that may get into the system. If air does get past these traps an internal machine air sensor shuts down the blood pump and an alarm will sound. All blood flow is stopped until the air is removed.

Why are there so many alarms? 

The machine continuously monitors the pressures created by your blood inside the blood tubing and dialyzer. It also monitors the blood flow, temperature and proper mixture of the dialysate. If any of these go out of range, the machine lets us know by sounding an alarm, blinking lights and shutting down blood or dialysate flow. It also lets us know if your blood pressure is too low or high. Oh yes, it also alarms when it’s time to go home.

Want to know more?

I realize that this may not answer all of your questions. That’s why I invite you to ask the bio-medical technician (machine person) at your dialysis center any questions you have. Your bio-medical technician will be happy to share any information with you. The more you know, the more comfortable you will be with your treatments.


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