Dialysis

From Wikipedia, the free encyclopedia

Jump to: navigation, search
This article is about renal dialysis; for the laboratory technique, see dialysis (biochemistry); for the treatment for liver failure, see liver dialysis.
This article does not cite any references or sources.
Please help improve this article by adding citations to reliable sources.
Unverifiable material may be challenged and removed.
A hemodialysis machine

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. First used at the Mayo Clinic in 1955, 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).

Contents

  • 1 Principle
  • 2 Types
    • 2.1 Hemodialysis
    • 2.2 Peritoneal dialysis
    • 2.3 Hemofiltration
  • 3 Starting indications
  • 4 See also
  • 5 External links

[edit] Principle

Dialysis works on the principles of the diffusion and osmosis of solutes and fluid across a semipermeable membrane. Blood flows by one side of a semipermeable membrane, and a dialysate or fluid flows by the opposite side. Smaller solutes and fluid pass through the membrane. The blood flows in one direction and the dialysate flows in the opposite. The concentrations of undesired solutes (for example potassium, calcium, and urea) are high in the blood, but low or absent in the dialysis solution and constant replacement of the dialysate ensures that the concentration of undesired solutes is kept low on this side of the membrane. The dialysis solution has levels of minerals like potassium and calcium that are similar to their natural concentration in healthy blood. For another solute, bicarbonate, dialysis solution level is set at a slightly higher level than in normal blood, to encourage diffusion of bicarbonate into the blood, to neutralise the metabolic acidosis that is often present in these patients.

[edit] Types

There are two main types of dialysis, hemodialysis and peritoneal dialysis.

[edit] Hemodialysis

Hemodialysis schematic
Main article: hemodialysis

In hemodialysis, the patient's blood is pumped through the blood compartment of a dialyzer, exposing it to a semipermeable membrane. Dialysis solution is pumped through the dialysate compartment of the dialyzer, which is configured so that the blood and dialysis solutions flow on opposite sides of the semipermeable membrane. The cleansed blood is then returned via the circuit back to the body. Ultrafiltration occurs by increasing the hydrostatic pressure across the dialyzer membrane. This usually is done by applying a negative pressure to the dialysate compartment of the dialyzer. This pressure gradient causes water and dissolved solutes to move from blood to dialysate, and allows removal of several litres of excess salt and water during a typical 3 to 4 hour treatment. Hemodialysis treatments are typically given three times per week, but more frequent sessions, which are usually 2 to 3 hours in duration given 5 or 6 times per week can be sometimes prescribed. Hemodialysis treatments can be given either as an outpatient or as home hemodialysis.

[edit] Peritoneal dialysis

Main article: peritoneal dialysis

In peritoneal dialysis, a sterile solution containing minerals and glucose 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 dialysate is left there for a period of time to absorb waste products, and then it is drained out through the tube and discarded. This cycle or "exchange" is normally repeated 4-5 times during the day, (sometimes more often overnight with an automated system). Ultrafiltration occurs via osmosis; the dialysis solution used contains a high concentration of glucose, and the resulting osmotic pressure causes fluid to move from the blood into the dialysate. As a result, more fluid is drained than was instilled. Peritoneal dialysis is less efficient than hemodialysis, but because it is carried out for a longer period of time the net effect in terms of removal of waste products and of salt and water are similar to hemodialysis. Peritoneal dialysis is carried out at home by the patient and it requires motivation. Although support is helpful, it is not essential. It does free patients from the routine of having to go to a dialysis clinic on a fixed schedule multiple times per week, and it can be done while travelling with a minimum of specialized equipment.

[edit] Hemofiltration

Main article: hemofiltration

Hemofiltration is a similar treatment to hemodialysis, but it makes use of a different principle. The blood is pumped through a dialyzer or "hemofilter" as in dialysis, but no dialysate is used. A pressure gradient is applied; as a result, water moves across the very permeable membrane rapidly, facilitating the transport of dissolved substances, importantly ones with large molecular weights, which are cleared less well by hemodialysis. Salts and water lost from the blood during this process are replaced with a "substitution fluid" that is infused into the extracorporeal circuit during the treatment. Hemodiafiltration is a term used to describe several methods of combining hemodialysis and hemofiltration in one process.

[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.