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 scientiﬁc process involves separating crystalloid 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, so far as the crystalloid substances are concerned, 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.
Haemodialysis Blood is removed from the circulation either through an artiﬁcial arteriovenous ﬁstula (junction) or a temporary or permanent internal catheter in the jugular vein (see CATHETERS). It then passes through an artiﬁcial kidney (‘dialyser’) to remove toxins (e.g. 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.
Peritoneal dialysis uses the peritoneal lining (see PERITONEUM) as a semi-permeable membrane. Approximately 2 litres of sterile ﬂuid is run into the peritoneum through the permanent indwelling catheter; the ﬂuid is left for 3–4 hours; and 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.
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 endogenous renal 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 carry a relatively high morbidity and the ideal treatment for patients with end-stage renal failure is successful renal TRANSPLANTATION.