What is dialysis?
Principles of dialysis
Dialysis removes the waste products and extra fluid from your blood by filtering them through a membrane/filter, similar to the way healthy kidneys would. During dialysis, blood is on one side of the membrane/filter and a special fluid called dialysate (containing water, electrolytes, and minerals) is on the other. Small waste products in your blood flow through the membrane/filter and into the dialysate.
The 3 principles that make dialysis work are diffusion, osmosis, and ultrafiltration.
Diffusion
During diffusion, particles in the areas of high concentration move toward the area of low concentration. Picture how a tea bag works—the leaves stay in the bag, and the tea enters the hot water. In dialysis, waste in your blood moves toward dialysate, which is a drug solution that has no (or very little) waste. How much waste is removed depends on the size of the waste, the size of the pores (holes) in the membrane, what’s in the dialysate, and—like a tea—the length of treatment.1
Osmosis
During osmosis, fluid moves from areas of high water concentration to lower water concentration across a semi-permeable membrane until equilibrium is reached. In dialysis, excess fluid moves from blood to the dialysate through a membrane until the fluid level is the same between blood and dialysate.
Ultrafiltration
Ultrafiltration is the removal of fluid volume from a patient. In dialysis, ultrafiltration removes waste and excess fluids from the blood.2