Dialysis Defined

Ever wonder how dialysis works? Dialysis works to remove toxins and excess fluid through the process of diffusion and osmosis.

And now for the rest of us....

First the toxin removal

When you are hooked up to a dialysis machine, your dialyzer works as a filter. Inside the dialyzer are lots of cellulose (natural) or polysulphone (artificial) semi-permeable membranes. Your blood is circulated on the inside of these membranes, while dialysate is circulated on the outside of these membranes, all within the dialyzer.

Dialysate is a liquid medium made from filtered water and components that are similarly found within your blood. These components are your electrolytes such as potassium, and sodium.

Here is where the word diffusion comes into play. In science difussion occurs when molecules move from an area of higher concentration to an area of lower concentration. An evening out of sorts, for molecules. Diffuse means to spread out.

Because the dialysate contains no toxin molecules, these molecules that are in your blood pass through the membranes/filter and out into the dialysate fluid. Once the dialysate has taken in as many toxin molecules as possible, it can no longer remove any more poisons through diffusion, so this dialysate is dumped and fresh dialysate in circulated through again. This whole process continues over and over during your treatment time to remove more and more toxins.

Picture a rectangular fish tank with a screen separating the middle. Both sides have water, but into one side you toss in some fish food, (this could be your toxins). The fish food is small enough to pass through the screen and so some will end up moving across it into the other side. Now picture tossing in some popcorn. (this could be your blood cells) This popcorn is too large to pass though the screen holes and so it remains on the side in which it had originated.

Blood cells and other important cells are not lost through dialysis as they are larger than what the semi-permeable membrane will allow to pass. Because the dialysate contains the electrolytes that are found in your blood, you don't lose those either.

Now the fluid removal

The dialysate flow is moving at a faster rate than your blood flow, creating a negative pressure. Because of the pressure on the dialyzer membrane, water is forced out.

Picture a tornado that sucks out the windows in a home. The tornado is low pressure and inside the home is high pressure. This high pressure in the home is actually what causes the windows to blow out. It's trying to even out the pressure a little.