Dialysis machines work by using diffusion and ultrafiltration. A very fine material, called a membrane, allows blood and fluid to flow through it. In the machine, the blood flows in one direction, and on the other side of the membrane, a special fluid, dialysate flows in the opposite direction, this process is known as osmosis. Dialysate is a fluid that has different chemicals in it, such as potassium and calcium. A doctor would decide what mixture of chemicals would be needed for each patient. The dialysate has bicarbonate in it to lower the higher acid levels that these patients often have. The blood and dialysate mix together. The waste products are removed from the blood and caught up in the fine membrane.