Dialysis (from the Greek dia : through, and luein : dissolve) is also called extrarenal purification and is most often practiced with an artificial kidney. This temporary or permanent therapeutic process eliminates toxins (urea, uric acid) and water contained in too large quantities in the blood when the kidneys no longer maintain a balance of water, sodium, potassium and calcium. In general, the number of dialysis patients and the time spent depend on the degree of renal failure. This number is usually three sessions per week, lasting about 4 hours each. Kidney dialysis is not always established once and for all, it may be necessary on a temporary basis, for example after an infection.