Normal functioning kidneys filter the blood and remove waste and excess salt and water.. Kidney failure is also known as end-stage kidney disease, where the kidney function has declined to the point that it is no longer working. Without renal replacement therapy, kidney failure can lead to death. Renal replacement therapy" is another term for the different treatments for kidney failure, including dialysis and kidney transplantation. Kidney transplantation will be discussed separately.
Dialysis refers to an artificial means of removal of the waste substances from the body using a specialised membrane. There are two types of dialysis: Haemodialysis and peritoneal dialysis.
Haemodialysis
Hemodialysis is a procedure in which a dialysis machine takes over the job of the kidneys. In haemodialysis, a mechanised blood pump is needed to draw blood from the patient. The blood is circulated into the machine and passes along a specialised membrane (a dialyser), which essentially functions as an artificial kidney. Waste substances from the blood move across the membrane into a "solution" called dialysate by a physical process called diffusion. The cleaned blood exits the dialyser and is returned back to the patient.
In haemodialysis, the patient needs to have a surgically created vein that is large enough and with a high enough blood flow to allow efficient and adequate dialysis. The surgeon will create this specialised vein called an arterio-venous fistula (aka vascular access) by connecting 2 blood vessels together. Usually, the operation is done initially at the wrist, but other sites along the arm can also be chosen. Sometimes patients' veins are too small for such surgery. Under these circumstances, the surgeon may create vascular access by placing a graft that essentially functions as an artificial blood vessel connecting two adjacent blood vessels. This artificial graft is left permanently under the skin of the patient and is repeatedly cannulated for dialysis.
Peritoneal Dialysis
Peritoneal dialysis is a procedure that people do at home every day. A permanent tube (called a tenchkoff catheter) is placed under sterile conditions into the abdominal cavity in peritoneal dialysis. A specialised fluid called dialysate is filled into the abdomen using this tube. Peritoneal membrane is the membrane lining the abdomen that can function like a dialyser membrane. Waste substances present in the blood flowing through the blood vessels of the abdomen itself move across the peritoneal membrane into the dialysate. The used dialysate with waste products is then drained out of the abdomen via the tenchkoff catheter and discarded. Fresh dialysate is filled back into the abdomen to continue dialysis.
