Hemodialysis is an effective treatment that uses an artificial kidney (dialyzer) to remove excess water and waste products from your blood.

A series of tubes connect you to the dialyzer to create a circuit, which both removes and returns your blood in a continuous cycle. The tubes are connected to a dialysis machine, which uses a pump to gently withdraw and return blood from either a surgically created vein in your arm, or through a soft plastic catheter placed in a vein in your neck or upper chest.

The dialysis dose (the amount of dialysis you need) is programmed into the dialysis machine, which contains a number of monitors and alarms to ensure that your dialysis prescription is delivered safely and efficiently.

Treatment time or dialysis prescription begins with a minimum of four hours, three times per week. Some patients may require more than this, but it is unlikely that you will need less. This dialysis dose is important: remember that healthy kidneys work constantly for 24 hours per day/seven days per week. The basic treatment standard of four hours three times per week is necessary to keep you feeling well, and to prevent complications and other health problems that often occur as a result of inadequate removal of harmful substances from your blood.

Research shows that patients who do less dialysis time than this experience far more problems than patients who have an adequate dialysis dose. They are also at a much greater risk of death. It is estimated that the risk of death increases by 10% for every 15 minutes below four hours.

How does hemodialysis work?

Blood is pumped from you into the dialyzer. The dialyzer is the small cylindrical object at the side of your dialysis machine. A drug called heparin is added to the bloodlines to prevent the blood clotting in the bloodlines or the dialyzer. The dialyzer is made from hundreds of hollow fibers that are about the thickness of a human hair. The fibers are made from a semi-permeable membrane, which means that small molecules like water, waste products, and potassium can pass across freely but larger molecules such as blood cells and protein cannot. For the duration of your dialysis, blood is continuously pumped through the inside of these tiny fibers.

At the same time, a solution called dialysate is pumped into the dialyzer, flowing in the opposite direction to your blood. The dialysate is prescribed for you by your doctor or nurse and contains the correct concentrations of sodium, potassium, glucose, and bicarbonate. As your blood flows through the filter, waste products pass across the membrane into the dialysate and are removed. They do this by a process called diffusion. Diffusion happens when molecules move from a high to a low concentration. Your blood has a high concentration of waste products and the dialysate has none, so therefore the waste will diffuse across the membrane and be removed.

The dialysis machine can also exert a negative (sucking) pressure on the dialyzer to help remove fluid from your blood. This is called ultrafiltration. The rate of ultrafiltration will be adjusted depending on how much fluid you need to lose within your dialysis time. If the ultrafiltration rate is set too high, it can make your blood pressure drop and make you feel dizzy and light-headed. For this reason, if you have gained a great deal of fluid since your last treatment, your nurse may advise that you increase your dialysis time to remove the fluid more gently and with fewer side effects.