A client starting continuous ambulatory peritoneal dialysis asks what it entails. Which statement is correct?

• A. Hemodialysis and peritoneal dialysis will be done together.
• B. Peritoneal dialysis is performed in an ambulatory care clinic.
• C. About a quarter of a liter of dialysate is maintained in the peritoneal cavity.
• D. Constant contact is maintained between the dialysate and the peritoneal membrane.

Answer: (D)

In continuous ambulatory peritoneal dialysis, the dialysis solution stays in the abdominal cavity long enough for substances to move across the peritoneal membrane by diffusion and for water to be drawn out by osmosis. This ongoing contact between dialysate and the peritoneal membrane is what enables waste products like urea and creatinine, as well as excess fluid, to move from the blood into the dialysate and then be drained away. The key idea is that the exchange depends on the dialysate remaining in contact with the membrane for a period of time to allow diffusion and osmosis to occur.

CAPD is usually performed by the patient at home, not in a clinic, and uses relatively large volumes of dialysate (about 1–2 liters per exchange, depending on the patient), not a small fraction of a liter. It is a standalone form of dialysis, not something done together with hemodialysis. These points help distinguish why the statement about maintaining constant contact between the dialysate and the peritoneal membrane best describes CAPD.