Peritoneal dialysis uses the lining of your abdomen as a natural filter to clean your blood. A special fluid flows into your belly through a small tube, sits there for several hours while it draws out waste and excess water from the tiny blood vessels in that lining, and then drains back out. The whole process happens inside your body, usually at home, without a dialysis machine pumping your blood through an external filter.
Your Peritoneum as a Filter
The peritoneum is a thin membrane that lines your abdominal cavity and covers your organs. It contains thousands of tiny blood vessels, and its surface area is roughly the size of your skin. What makes it useful for dialysis is that it acts as a semipermeable membrane: it lets small molecules like waste products and water pass through while keeping larger ones (like blood cells) in place.
Two basic physics principles do the heavy lifting. The first is diffusion: waste products like urea and creatinine are more concentrated in your blood than in the clean dialysis fluid, so they naturally move from your blood across the membrane into the fluid. Small molecules cross faster than larger ones. After four hours, roughly 90% of urea has moved into the fluid, while only about 60% of creatinine (a slightly larger molecule) has crossed over in the same time.
The second principle is osmosis. The dialysis fluid contains glucose (a sugar), which makes it more concentrated than your blood. This concentration difference pulls excess water out of your bloodstream and into the fluid. Higher glucose concentrations pull more water. Solutions typically come in three strengths (1.36%, 2.27%, and 3.86% glucose), and your care team selects the right one based on how much fluid needs to be removed.
What Happens During an Exchange
Each treatment cycle is called an exchange, and it has three phases: fill, dwell, and drain. During the fill, fresh dialysis solution flows from a bag through a catheter into your abdominal cavity. Once the bag is empty, you disconnect it and cap the catheter. You’re free to walk around, work, or sleep while the solution sits in your belly. This sitting period is the dwell time, and it’s when the actual filtering happens. After the dwell, you connect a new empty bag, drain the used fluid out (it now contains waste and extra water), and discard it. Then you fill again with a fresh bag.
The fill and drain together take about 30 to 40 minutes. The dwell time varies depending on which type of peritoneal dialysis you’re on, ranging from as short as an hour to as long as overnight.
CAPD vs. Automated Peritoneal Dialysis
There are two main approaches. Continuous ambulatory peritoneal dialysis (CAPD) is done entirely by hand. You perform three to five exchanges throughout the day, with each dwell lasting four to six hours. You typically sleep with solution in your belly overnight for a longer dwell. No machine is involved, and you can do exchanges at home, at work, or wherever you happen to be.
Automated peritoneal dialysis (APD) uses a small bedside machine called a cycler. You connect to it at night, and it performs multiple shorter exchanges while you sleep, usually over eight to ten hours. This frees up your daytime almost entirely. APD is particularly useful for people who work or go to school, and for those whose peritoneal membrane transports solutes quickly. Fast transporters, as they’re called, do better with shorter, more frequent dwells because the glucose in the solution gets absorbed quickly, reducing its ability to pull water over long dwell times. Lying down during APD also lowers pressure inside the abdomen compared to sitting or standing during CAPD exchanges, which can be more comfortable.
The Catheter
Before you can start peritoneal dialysis, a surgeon places a soft, flexible catheter into your abdominal cavity. The tube is about the width of a pencil. One end sits inside your abdomen near the pelvis, and the other exits through a small incision, usually near your belly button or off to one side. The external portion stays capped between exchanges.
The catheter has one or two small fabric cuffs along its length that sit within the layers of your abdominal wall. Over a few weeks, your tissue grows into these cuffs, anchoring the catheter in place and creating a barrier against bacteria. Most centers prefer to wait two to four weeks after placement before starting dialysis, giving the site time to heal and reducing the risk of leaks.
How Your Body Responds Over Time
Not everyone’s peritoneum filters at the same rate. A test called a peritoneal equilibration test measures how quickly solutes cross your membrane. Results sort people into four categories, from slow transporters to fast transporters. This classification shapes your entire prescription: slow transporters benefit from longer dwell times to give waste products more time to cross, while fast transporters need shorter, more frequent exchanges. In practice, many centers assign slow transporters to CAPD and fast transporters to APD.
Your care team monitors whether the dialysis is removing enough waste by measuring a value called Kt/V, which reflects how thoroughly small waste molecules are being cleared relative to your body size. The current minimum weekly target is 1.7 when your kidneys still produce some urine. If clearance drops below target, adjustments might include more exchanges per day, higher glucose concentrations, or switching from CAPD to APD.
Infection Risk
The biggest concern with peritoneal dialysis is peritonitis, an infection of the peritoneal lining. Bacteria can enter through the catheter connection point during exchanges if technique isn’t sterile. Rates have improved significantly: from about 58 episodes per 100 patient-years in 2009 down to roughly 31 per 100 patient-years by 2018. That translates to an average of one infection roughly every three years for a given patient. Symptoms include cloudy drain fluid, abdominal pain, and fever. Most episodes respond to treatment, but repeated infections can scar the peritoneum and eventually make it less effective as a filter.
Diet on Peritoneal Dialysis
Your dietary needs on peritoneal dialysis differ from hemodialysis in a few important ways. Because the dialysis fluid absorbs protein from your body during each exchange, you need to eat more protein to compensate. Guidelines recommend at least 1.2 grams of protein per kilogram of body weight daily, compared to the 0.6 to 0.8 grams recommended for people with kidney disease who aren’t on dialysis.
Potassium rules can also be more relaxed. Because peritoneal dialysis runs continuously (or nearly so), it tends to remove potassium more steadily than hemodialysis, which only runs a few times a week. Some guidelines actually encourage increasing potassium intake, though others recommend keeping it below 2,500 mg per day if blood levels run high. Sodium, phosphorus, and fluid intake generally still need to be limited. The glucose in the dialysis solution adds calories you might not think about, which can contribute to weight gain over time.
What Daily Life Looks Like
Most people on peritoneal dialysis do their treatment at home without assistance. CAPD exchanges fit around a normal schedule: one in the morning, one at lunch, one in the late afternoon, and one at bedtime. Each interruption is about 30 to 40 minutes. With APD, you set up the cycler before bed, sleep through the treatment, and disconnect in the morning. You’ll need storage space at home for boxes of dialysis solution, which arrive in regular shipments.
Travel is possible with either type. You can arrange to have supplies shipped to a destination, and CAPD requires no electricity at all. Swimming and bathing require precautions to keep the catheter exit site dry and clean, and contact sports carry a risk of dislodging or damaging the catheter. Otherwise, most physical activities are fine once the insertion site has fully healed.