Hemodialysis and Peritoneal Dialysis

Kidney dialysis is a treatment that compensates for kidney failure. According to the National Kidney Foundation, dialysis is used when a person has lost 85 to 90 percent of their kidney function. The kidneys are important for filtering out wastes and maintaining blood pressure. Two types of processes are used: hemodialysis, which cycles the blood through an artificial kidney outside the body, and peritoneal dialysis, which uses a solution in the abdomen to filter the blood inside the peritoneal cavity of the body.


In hemodialysis, doctors create access points to major blood vessels in the neck, arm or leg to create an external circulatory system that is joined to the body’s circulatory system. The access point is called a vascular access. For long-term dialysis, a fistula is created between an artery and vein to allow the vein to grow larger and offer more blood when dialysis is performed. If smaller veins are used then an arteriovenous graft is done surgically to create an artificial fistula. For temporary dialysis, a venous catheter in the neck or heart is used.

Blood flows from the vein through tubing to an artificial kidney, called the dialyzer or dialysis machine. Wastes are filtered from the blood by passing across small fibers that pull the wastes into a dialysis solution, called the dialysate. The cleaned blood is then returned via tubes to the fistula or vein it was taken from, easing the body’s reliance on the kidneys to filter the blood. Because of the vascular access and machine, hemodialysis is generally performed at dedicated facilities such as hospitals and dialysis clinics. Some offer high-flux hemodialysis, which is an express version of the process utilizing higher quantities of blood and larger pore filters.

Peritoneal dialysis

In peritoneal dialysis, the dialysate is placed in the abdomen, or peritoneal cavity, and the wastes dialyzed from the blood vessels of the peritoneum. A surgical operation places a flexible catheter in the abdomen for the addition and removal of the solution.

The two major types of peritoneal dialysis according to the National Kidney Foundation are continuous ambulatory peritoneal dialysis and continuous cycling peritoneal dialysis. Continuous ambulatory peritoneal dialysis requires no machines and is done at home. The dialysis occurs in a process called an exchange. For ambulatory dialysis, one exchange occurs. The patient has a bag of the dialysate that they drain into the peritoneal cavity via the access. After several hours they drain the fluid back into the bag and dispose of it. Continuous cycling peritoneal dialysis, also known as automated or cycler-assisted peritoneal dialysis, is also often done at home, but requires a special machine that performs more than one exchange. Sometimes this form of dialysis is performed as the patient sleeps.

Both mimic natural kidney function

Both forms of dialysis are important methods for maintaining the integrity of the body as the kidneys heal or a patient awaits transplantation. Which one the doctors choose depends on the extent of kidney damage, whether the dialysis is temporary or permanent, and the facilities available. To read more about the natural dialysis system inside the human body the Chemistry Dept at Washington University in St Louis provides graphic explanations on their website.