Artificial kidneys: Hemodialysis therapy

  • If the kidneys fail, toxic substances build up in the body until cells and organs begin to deteriorate and eventually die.
  • Many tens of thousands of people around the world suffer from kidney failure, but a large number of them are leading relatively normal lives because of the successful use of the artificial kidney or hemodialysis therapy.

Working mechanism:

  • The principle of diffusion is basic to the working mechanism of the artificial kidney.
  • Very simply, the artificial kidney is a machine that pumps 5 to 6 liters of blood from the body through a hollow fiber dialyzer.
  • The blood is rinsed by a briny solution, and sodium, potassium, and waste products such as urea, uric acid, excess water, and creatinine diffuse through the dialyzer by osmotic pressure.
  • The cleansed blood is then routed back into the body.


  • One tube is permanently implanted into an artery (usually in the arm), and another is implanted into a nearby vein.
  • During dialysis, the tubes are hooked up to the machine.
  • Blood is pumped from the artery through an oxygenated salt solution similar in ionic concentration to body plasma.
  • Because the concentration of wastes is higher than the normal concentration of the plasma-like fluid, the wastes automatically diffuse through the semipermeable membrane of the tubes into this rinsing fluid.
  • The membrane is porous to all blood substances except proteins and red blood cells.
  • The wastes are eliminated from the body, and the purified blood is free to flow back into the body.
  • Dialysis is sometimes also used to add nutrients to the blood. For instance, large amounts of glucose may be added to the salt-solution so that the glucose may be diffused into blood at the same time that wastes are being removed.
  • It takes about 6 hours and 20 passes through the bathing fluid to complete a full cycle of dialysis, and most patients receive treatment two or three ties a week.
  • Unfortunately, even this highly successful machine, which can remove wastes from the blood 3o times faster than the natural kidney does, provides only partial relief for kidney-failure victims. All patients remain uremic (urine in the blood) to some degree.

Alternative method:

  • Another method is peritoneal dialysis, which uses the patient’s peritoneal membrane instead of an artificial membrane for diffusion.
  • The ‘clean’ fluid (dialysis fluid) is injected into the peritoneal cavity each day for 3 to 4 days. Three daytime exchanges remain in the body for 5 hours each before they are removed, and the fourth overnight exchange remains in the body for 8 to 10 hours.

Artificial kidneys: Hemodialysis therapy