How does a dialysis machine clean the blood?

A hemodialysis machine draws blood from a patient and passes it through a dialyzer, often called an artificial kidney. Inside the dialyzer, blood flows on one side of a semipermeable membrane while a cleansing fluid called dialysate flows on the other. Waste products such as urea and excess electrolytes move across the membrane, while blood cells and most proteins stay in the bloodstream. The process can also remove extra fluid to help control blood pressure and swelling. Many patients receive hemodialysis several times a week, typically for about 3 to 4 hours per session.