The blood urea level rises abnormally (uremia) in patients suffering from renal failures. An artificial kidney is used for removing excess urea from the blood of the patient by a process called hemodialysis. Blood is taken out form an artery of the patient, cooled to 0�C, mixed with an anticoagulant, such as heparin, and then pumped into the apparatus called the artificial kidney. In this apparatus, blood flows through channels or tubes bounded by cellophane membrane. The membrane is impermeable to macromolecules, such as plasma proteins, but permeable to small solutes, such as urea, uric acid, creatinine and mineral ions. The membrane separated the blood flowing inside the channels or tubes from a dialysing fluid flowing outside the membrane. The dialysing fluid contains some small solutes and mineral ions, but does not contain nitrogenous waste product, such as urea, uric acid and creatinine. So. these wastes diffuse from the blood to the dialysing fluid across the cellophane membrane, following the concentration gradient. Thus, the blood is considerable cleared of nitrogenous waste products without losing plasma proteins. Such a process of separating small solutes from macromolecular colloids with the help of a selectively permeable membrane is called dialysis. The blood coming out of the artificial kidney is warmed to body temperature, mixed with an antiheparin to restore its normal coagulability, and returend to a vein of the patient. Hemodialysis saves and prolongs the life of many uremic patients.
If the kidney failure cannot be treated, by drug of dialysis, the patients are advised for kidney transplantation.