1. Process by which dissolved substances are removed from a patient’s body by diffusion from one fluid compartment to another across a semi-permeable membrane. The two types of dialysis that are in common use are hemodialysis and peritoneal dialysis. 2. Treatment that cleans the blood when the kidneys do not work. It gets rid of harmful wastes and extra salt and fluids that build up in the body. It also helps maintain blood pressure and appropriate fluid levels. Dialysis treatments help the patient feel better and live longer but are not a cure for permanent kidney failure.