Dialysis is the medical term for removing the waste and extra fluid from your blood that your kidneys can no longer remove themselves. When the waste is gone, you may feel better.
Dialysis removes the waste products and extra fluid from your blood by filtering them through a membrane/filter, similar to the way healthy kidneys would. During dialysis, blood is on one side of the membrane/filter and a special fluid called dialysate (containing water, electrolytes, and minerals) is on the other. Small waste products in your blood flow through the membrane/filter and into the dialysate.
Larger particles, like red blood cells, remain in your blood. In this way, your blood is cleaned.
The three principles that make dialysis work are osmosis, diffusion, and ultrafiltration.
DiffusionDuring diffusion, particles in the areas of high concentration move towards the area of low concentration. Picture how a tea bag works – the leaves stay in the bag and the tea enters the hot water. In dialysis, waste in your blood moves towards dialysate, which is a drug solution that has none (or very little waste). How much waste is removed depends on the size of the waste, the size of the pores (holes) in the membrane, what’s in the dialysate and like a tea, the length of treatment.1
OsmosisDuring osmosis, fluid moves from areas of high water concentration to lower water concentration across a semi-permeable membrane until equilibrium. In dialysis, excess fluid moves from blood to the dialysate through a membrane until the fluid level is the same between blood and dialysate
UltrafiltrationUltrafiltration is the convective flow of water and dissolved solute down a pressure gradient caused by hydrostatic forces or osmotic forces. In dialysis, ultrafiltration removes molecules of waste and excess fluids from blood.
- Schatell, Dori MS, and Agar, John MD. Help, I Need Dialysis! How to have a good future with kidney disease. Madison, WI: Medical Education Institute, Inc.; 2012. P. 34–38.
Peritoneal Dialysis (PD) uses a special solution (dialysate) and your own peritoneal membrane – the lining of your abdomen – as the filter to clean the blood and remove excess fluids. This method is like your regular kidney where fluid removal is continuous inside your body.
A PD catheter is placed in the abdomen in an operation and is used to access the peritoneal membrane to allow for dialysis.
A special solution (dialysate, or dialysis solution) is placed in the abdomen through the PD catheter and is in contact with the peritoneal membrane. Waste in the blood and bodily fluids then pass through the peritoneal membrane (the filter) into the solution.
Waste products and extra water in the blood are pulled into the solution by means of diffusion and osmosis. The used dialysis solution is then drained out through the PD catheter into a collection bag. This process is then repeated with fresh dialysis solution.
The small particles of waste float out of the blood, through the tiny holes in the peritoneum, and into the dialysis solution. The waste particles float from the blood side where it is more crowded to the solution side that is less crowded.
The dialysis solutions that are used help your body remove extra fluid, help with nutrition, replace some of the lost protein, and balance the blood acid levels. The dialysis prescription (number of exchanges and dialysis solution) is determined by your doctor.
Peritoneal dialysis is done at home so that you have more flexibility to arrange your daily activities and schedule. You can even perform PD at work, in an RV or in a hotel. This may give you more time to enjoy your favorite things like travelling, school, work, hobbies, sports, visiting with friends and a full family life. PD is performed by yourself or with the support of your family member or caregiver. Your healthcare team will train you and/or your family member on the steps of the dialysis until you are comfortable with the steps to do it at home.
The word “hemo” refers to blood. Hemodialysis (HD) filters your blood outside your body using a machine and a manufactured filter, called a dialyzer. This dialyzer acts as an artificial kidney. The machine makes the dialysis solution, which is needed to remove excess water and waste from your blood.
During HD, your blood is removed from your body by the machine through a needle or a central venous catheter, and then is pumped through the dialyzer to clean your blood. After this, the clean blood is returned to your body through a second needle or a second branch of catheter.
Hemodialysis is usually performed during a scheduled time at the hospital or in a dialysis clinic, and is referred to as in-centre hemodialysis (ICHD). Most people require hemodialysis 3 times a week, with each treatment session lasting about 4 hours, depending on the dialysis prescription recommended by the doctor.
Instead of spending your time in a clinic during treatments, you may be able to dialyze in your own home – a process called home hemodialysis (HHD). That means you don’t have to schedule your day around travelling to a clinic or hospital for dialysis treatment. You may not need to dialyze during business hours, so you may be able to maintain work schedules. HHD is performed by yourself or with the support of your family member or caregiver. Your healthcare team will train you and your family member on the steps of the dialysis until you are comfortable with the steps to do it at home.
Please click here if you would like to read more detailed information about different types of dialysis and different ways of doing dialysis.
It’s important to note that each person is different, so not every type of dialysis is suitable for you. There are different ways of doing peritoneal dialysis and hemodialysis.
Different types of dialysis may have different risks; please speak with your doctors about which therapy may be right for you.