MODEL RELEASED. Dialysis unit. Nurse checking on a patient in a dialysis treatment unit. Kidney dialysis, or haemodialysis, is required when the kidneys are no longer able to filter waste products from the blood properly. A patient's blood flows out of their body through a tube into a dialysis machine (blue), or dialyser, which acts as an artificial kidney, removing waste products and excess fluid from the blood. The cleaned blood is then returned to the patient through a second tube. The procedure takes several hours and needs to be repeated several times a week.