Dialysis
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This article is about renal dialysis; for the laboratory technique, see dialysis (biochemistry); for the treatment for liver failure, see liver dialysis.
In medicine, dialysis is a type of renal replacement therapy which is used to provide an artificial replacement for lost kidney function due to renal failure. It is a life support treatment and does not treat any kidney diseases. Dialysis may be used for very sick patients who have suddenly lost their kidney function (acute renal failure) or for quite stable patients who have permanently lost their kidney function (end stage renal failure). When healthy, the kidneys remove waste products (for example potassium, acid and urea) from the blood and also remove excess fluid in the form of urine. Dialysis treatments have to duplicate both of these functions as dialysis (waste removal) and ultrafiltration (fluid removal).
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[edit] Principle
Dialysis works on the principle of the diffusion of solutes along a concentration gradient across a semipermeable membrane. In all types of dialysis, blood passes on one side of a semipermeable membrane, and a dialysis fluid is passed on the other side. By altering the composition of the dialysis fluid, the concentrations of undesired solutes (chiefly potassium and urea) in the fluid are low, but the desired solutes (for example sodium) are at their natural concentration found in healthy blood, or in the case of bicarbonate, greater, to neutralise the acidosis that is often present.
[edit] Types
There are two main types of dialysis, hemodialysis and peritoneal dialysis. Hemofiltration is not strictly speaking a dialysis treatment, but is extremely similar.
[edit] Hemodialysis
In hemodialysis, the patient's blood is passed through a system of tubing (a dialysis circuit) via a machine to a semipermeable membrane, (dialyzer) which has dialysis fluid running on the other side. The cleansed blood is then returned via the circuit back to the body. Ultrafiltration occurs by increasing the hydrostatic pressure of the blood in the dialysis circuit to cause water to cross the membrane down a pressure gradient. The dialysis process is very efficient, allowing the treatment to be undertaken intermittently, usually three times a week, but often fairly large volumes of fluid must be removed in a session which can sometimes be demanding on the patient and their family.
[edit] Peritoneal dialysis
In peritoneal dialysis, a special sterile solution is run through a tube into the peritoneal cavity, the abdominal body cavity around the intestine, where the peritoneal membrane acts as a semipermeable membrane. The fluid is left there for a period of time to absorb waste products, and then is removed via a sterile procedure through the tube. This is usually repeated a number of times during the day. Ultrafiltration occurs via osmosis in this case, as the dialysis solution is supplied in varying osmotic strengths to allow for some control over the amount of fluid to be removed. The dialysis process in this case is less efficient than hemodialysis, but the ultrafiltration process is slower and gentler and is carried out at home by the patient. This gives them more control over their lives than a hospital/clinic based dialysis option.
[edit] Hemofiltration
Hemofiltration is a similar treatment to hemodialysis, but in this case, the membrane is far more porous and allows the passage of a much larger quantity of water and solutes to pass across it. The fluid which passes across the membrane (the filtrate) is discarded and the remaining blood in the circuit has its desired solutes and fluid volume replaced by the addition of a special hemofiltration fluid. It is a slow continuous therapy with sessions typically lasting 12-24 hours, usually daily. This, and the fact that ultrafiltration is very slow and thus gentle, makes it ideal for patients in intensive care units, where acute renal failure is common. A combination of hemofiltration and hemodialysis, called hemodiafiltration (incorporating a hemofilter to a standard hemodialysis circuit), is being used in some centres for chronic maintenance therapy.
[edit] Starting indications
The decision to initiate dialysis or hemofiltration in patients with renal failure can depend on several factors, which can be divided into acute or chronic indications.
- Acute Indications for Dialysis/Hemofiltration:
- 1) Hyperkalemia
- 2) Metabolic Acidosis
- 3) Fluid overload (which usually manifests as pulmonary oedema)
- 4) Uremic pericarditis, a potentially life threatening complication of renal failure
- 5) And in patients without renal failure, acute poisoning with dialysable toxins, such as lithium
- Chronic Indications for Dialysis:
- 1) Symptomatic renal failure
- 2) Low glomerular filtration rate (GFR) (RRT often recommended to commence at a GFR of less than 10-15 mls/min/1.73m2)
- 3) Other biochemical markers of inadequate renal function in the context of a GFR (slightly)greater than 15 mls/min/1.73m2. This would usually be hyperphosphatemia which is resistant to medical treatment or EPO resistant anemia in the context of a GFR not much greater than 15 mls/min/1.73m2.
[edit] See also
- Apheresis is another extracorporeal technique that selectively removes specific constituents from blood.
[edit] External links
- http://vam.anest.ufl.edu/dialysis A free transparent reality simulation of a Continuous Veno-Veno Hemodialysis (CVVH) machine
- Dialysis Tips - Resource for dialysis personnel and general background with good understanding of the basic problems of dialysis therapy.
- Global Dialysis - Resource and community for dialysis patients and professionals
- Virtual Dialysis Museum - History and pictures of dialysis machines through time
- The Renal Unit - News and resources for those undergoing dialysis
- [1] - Kidney disease and dialysis clinics.
