How Does a Renal Dialysis Machine Work?


The dialysis machine was engineered by Dr. Willem Kolff in 1943. While the first machines were huge, bulky devices whose use was controversial, improvements made them smaller and more effective. Dialysis machines can even be used in the home, which frees patients with failing kidneys from visiting their local dialysis center several times a week to have their blood cleaned.

Vascular Access

The dialysis machine is coupled to the patient’s blood supply using a catheter connected to a fistula or graft in the patient’s arm. The fistula or graft is surgically created before the first dialysis session so the patient can be treated as needed. This opening provides vascular access to the patient’s blood.

For dialysis performed in an emergency, the machine is coupled to the patient via a catheter connected to arteries in his neck.


After the blood is removed for cleansing, it enters the dialysis machine and passes through various pressure monitors and pumps that control the speed of dialysis. If the patient becomes nauseated, the technician can slow the rate of dialysis.

In addition to the pressure monitors and pumps, dialysis machines include a heparin pump that prevents blood from clotting while it is being cleaned.


The blood enters a special filter called a dialyzer, nicknamed an artificial kidney. The National Institute of Diabetes, Digestive and Kidney Disease describes the dialyzer as “a large canister containing thousands of small fibers.” A special dialysis solution flows through the dialyzer. This solution pulls wastes products from the blood. The formula for this solution can be adjusted for each individual.

Upon leaving the dialyzer, the blood is clean and the impurities have been removed.

Checking for Air

Upon exiting the dialyzer, the blood passes though another pressure monitor before it enters an air trap and air monitor. The air monitor checks for any air that may have accidentally entered the line. The air trap removes any air that has entered the line.

Returning Blood

Just as the blood exited the patient via a first needle in the fistula or graft, the clean blood is returned to the patient via a second needle in her fistula or graft.

The use of multiple needles troubles some dialysis patients. Since patients have a better feel for their own bodies, they can take on the job of needling themselves if they wish. Patients who perform hemodialysis in their homes must be able to needle themselves without supervision so they can hook themselves up to their dialysis machine.

About this Author

Shelly Morgan has been writing and editing for over 25 years for various medical and scientific publications. Although she began her professional career in pharmacological research, Morgan turned to patent law when she specialized in prosecuting patents for various medical devices. She recently began writing about renal disease for various non-profits.