Kidney dialysis, also known as hemodialysis, is used when the kidneys are not functioning or are improperly functioning. An artificial membrane is used to regulate blood composition, particularly the removal of toxic substances. The patient’s blood flows through artificial membrane tubing, which is immersed in a solution that differs in concentration from the normal concentration of blood plasma. Critical to this process is the composition of the dialysis fluid, which permits retention of needed substances while wastes are removed. Dialysis is usually carried out three times per week.