A procedure used to filter off waste products from the blood and remove surplus fluid from the body in someone who has kidney failure (see KIDNEYS, DISEASES OF). The process involves separating crystalloid (mostly minerals, electrolytes, etc.) and COLLOID substances from a solution by interposing a semi-permeable membrane between the solution and pure water. The crystalloid substances pass through the membrane into the water until a state of equilibrium is established between the two sides of the membrane. The colloid substances do not pass through the membrane.
Dialysis is available as either haemodialysis or peritoneal dialysis. Disadvantages of haemodialysis include cardiovascular instability, HYPERTENSION, bone disease, ANAEMIA and development of periarticular AMYLOIDOSIS. Disadvantages of peritoneal dialysis include peritonitis, poor drainage of fluid, and gradual loss of overall efficiency as kidney function declines. Haemodialysis is usually done in outpatient dialysis clinics by skilled nurses, but some patients can carry out the procedure at home. Both haemodialysis and peritoneal dialysis can be exhausting, demoralising and carry some potentially unpleasant ill-effects, so the ideal treatment for patients with end-stage renal failure is successful renal TRANSPLANTATION.
Blood is removed from the circulation either by making an artificial link between an artery and a vein (arterio-venous fistula) or through a temporary or permanent internal catheter in the jugular vein (see CATHETERS). It then passes through an artificial kidney (‘dialyser’) to remove unwanted material such as excess potassium and urea by diffusion and excess salt and water by ultrafiltration from the blood into dialysis fluid prepared in a ‘proportionator’ (often referred to as a ‘kidney machine’). Dialysers vary in design and performance but all work on the principle of a semi-permeable membrane separating blood from dialysis fluid. Haemodialysis is undertaken two to three times a week for 4–6 hours a session.
uses the peritoneal lining (see PERITONEUM) as a semi-permeable membrane. Approximately 2 litres of sterile fluid is run into the peritoneum through a permanent indwelling catheter; the fluid is left for 3–4 hours and then run out; the cycle is repeated 3–4 times per day. Most patients undertake continuous ambulatory peritoneal dialysis (CAPD), although a few use a machine overnight (continuous cycling peritoneal dialysis, CCPD) which allows greater clearance of toxins.