Dialysis: Wikis

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A hemodialysis machine

In medicine, dialysis (from Greek "dialusis", meaning dissolution, "dia", meaning through, and "lysis", meaning loosening) is primarily used to provide an artificial replacement for lost kidney function in people with renal failure. Dialysis may be used for those with an acute disturbance in kidney function (acute kidney injury, previously acute renal failure) or for those with progressive but chronically worsening kidney function–a state known as chronic kidney disease stage 5 (previously chronic renal failure or end-stage kidney disease). The latter form may develop over months or years, but in contrast to acute kidney injury is not usually reversible, and dialysis is regarded as a "holding measure" until a renal transplant can be performed, or sometimes as the only supportive measure in those for whom a transplant would be inappropriate.[1]

The kidneys have important roles in maintaining health. When healthy, the kidneys maintain the body's internal equilibrium of water and minerals (sodium, potassium, chloride, calcium, phosphorus, magnesium, sulfate). Those acidic metabolism end products that the body cannot get rid of via respiration are also excreted through the kidneys. The kidneys also function as a part of the endocrine system producing erythropoietin and 1,25-dihydroxycholecalciferol (calcitriol). Erythropoietin is involved in the production of red blood cells and calcitriol plays a role in bone formation.[2] Dialysis is an imperfect treatment to replace kidney function because it does not correct the endocrine functions of the kidney. Dialysis treatments replace some of these functions through diffusion (waste removal) and ultrafiltration (fluid removal).[3]

Contents

Principle

Dialysis works on the principles of the diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane. Diffusion describes a property of substances in water. Substances in water tend to move from an area where they are in a high concentration to an area of low concentration.[4] Blood flows by one side of a semi-permeable membrane, and a dialysate, or special dialysis fluid, flows by the opposite side. A semipermeable membrane is a thin layer of material that contains various sized holes, or pores. Smaller solutes and fluid pass through the membrane, but the membrane blocks the passage of larger substances (for example, red blood cells, large proteins).[4]

The two main types of dialysis, Hemodialysis (HD) and Peritoneal dialysis (PD), remove wastes and excess water from the blood in different ways.[1] Hemodialysis removes wastes and water by circulating blood outside the body through an external filter, called a dialyzer, that contains a semipermeable membrane. The blood flows in one direction and the dialysate flows in the opposite. The counter-current flow of the blood and dialysate maximizes the concentration gradient of solutes between the blood and dialysate, which helps to remove more urea and creatinine from the blood. The concentrations of solutes (for example potassium, phosphorus, and urea) are undesirably 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 act as a pH buffer to neutralize the metabolic acidosis that is often present in these patients. The levels of the components of dialysate are typically prescribed by a nephrologist according to the needs of the individual patient. In peritoneal dialysis, wastes and water are removed from the blood inside the body using the peritoneal membrane as a natural semipermeable membrane. Wastes and excess water move from the blood, across the peritoneal membrane, and into a special dialysis solution, called dialysate, in the abdominal cavity which has a composition similar to the fluid portion of blood.

Types

There are two primary types of dialysis and another two types in addition, they are namely hemodialysis , peritoneal dialysis, and thirdly investigational type and finally intestinal dialysis.

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Hemodialysis

Hemodialysis schematic

In hemodialysis, the patient's blood is pumped through the blood compartment of a dialyzer, exposing it to a partially permeable membrane. The dialyzer is composed of thousands of tiny synthetic hollow fibers. The fiber wall acts as the semipermeable membrane. Blood flows through the fibers, dialysis solution flows around the outside the fibers, and water and wastes move between these two solutions. [5] 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 the removal of several litres of excess fluid during a typical 3 to 5 hour treatment. In the US, hemodialysis treatments are typically given in a dialysis center three times per week (due in the US to Medicare reimbursement rules); however, as of 2007 over 2,500 people in the US are dialyzing at home more frequently for various treatment lengths.[6] Studies have demonstrated the clinical benefits of dialyzing 5 to 7 times a week, for 6 to 8 hours. These frequent long treatments are often done at home, while sleeping but home dialysis is a flexible modality and schedules can be changed day to day, week to week. In general, studies have shown that both increased treatment length and frequency are clinically beneficial.[7]

Peritoneal dialysis

In peritoneal dialysis, a sterile solution containing 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 peritoneal membrane or peritoneum is a layer of tissue containing blood vessels that lines and surrounds the peritoneal, or abdominal, cavity and the internal abdominal organs (stomach, spleen, liver, and intestines). [8] 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. 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.

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, "dragging" along with it many 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.

Intestinal dialysis

In intestinal dialysis, the diet is supplemented with soluble fibres such as acacia fibre, which is digested by bacteria in the colon. This bacterial growth increases the amount of nitrogen that is eliminated in fecal waste.[1] [2][3] An alternative approach utilizes the ingestion of 1 to 1.5 liters of non-absorbable solutions of polyethylene glycol or mannitol every fourth hour.[4]

Starting indications

The decision to initiate dialysis or hemofiltration in patients with renal failure depends on several factors. These can be divided into acute or chronic indications.

  • Indications for dialysis in the patient with acute kidney injury are:[9]
    1. Metabolic acidosis in situations where correction with sodium bicarbonate is impractical or may result in fluid overload.
    2. Electrolyte abnormality, such as severe hyperkalemia, especially when combined with AKI.
    3. Intoxication, that is, acute poisoning with a dialysable drug, such as lithium, or aspirin.
    4. Fluid overload not expected to respond to treatment with diuretics.
    5. Complications of uremia, such as pericarditis, encephalopathy, or gastrointestinal bleeding.
  • 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). In diabetics dialysis is started earlier.
    3. Difficulty in medically controlling fluid overload, serum potassium, and/or serum phosphorus when the GFR is very low

See also

Materials and methods

Medical applications

References

  1. ^ a b Pendse S, Singh A, Zawada E. Initiation of Dialysis. In: Handbook of Dialysis. 4th ed. New York, NY; 2008:14-21
  2. ^ Brundage D. Renal Disorders. St. Louis, MO: Mosby; 1992
  3. ^ http://www.kidneyatlas.org/book5/adk5-01.ccc.QXD.pdf Atlas of Diseases of the Kidney, Volume 5, Principles of Dialysis: Diffusion, Convection, and Dialysis Machines
  4. ^ a b Mosby’s Dictionary of Medicine, Nursing, & Health Professions. 7th ed. St. Louis, MO; Mosby: 2006
  5. ^ Ahmad S, Misra M, Hoenich N, Daugirdas J. Hemodialysis Apparatus. In: Handbook of Dialysis. 4th ed. New York, NY; 2008:59-78.
  6. ^ http://www.usrds.org/2007/pdf/04_modalities_07.pdf USRDS TREATMENT MODALITIES
  7. ^ http://www.homedialysis.org/learn/types/ Daily therapy study results compared
  8. ^ Blake P, Daugirdas J. Physiology of Peritoneal Dialysis. In: Handbook of Dialysis. 4th ed. New York, NY; 2008:323-338
  9. ^ Irwin, Richard S.; James M. Rippe (2008). Irwin and Rippe's intensive care medicine. Lippincott Williams & Wilkins. pp. 988–999. ISBN 0781791537, 9780781791533. 

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

DIALYSIS (from the Gr. Sat, through, X15av, to loosen), in chemistry, a process invented by Thomas Graham for separating colloidal and crystalline substances. He found that solutions could be divided into two classes according to their action upon a porous diaphragm such as parchment. If a solution, say of salt, be placed in a drum provided with a parchment bottom, termed a "dialyser," and the drum and its contents placed in a larger vessel of water, the salt will pass through the membrane. If the salt solution be replaced by one of glue, gelatin or gum, it will be found that the membrane is impermeable to these solutes. To the first class Graham gave the name "crystalloids," and to the second "colloids." This method is particularly effective in the preparation of silicic acid. By adding hydrochloric acid to a dilute solution of an alkaline silicate, no precipitate will fall and the solution will contain hydrochloric acid, an alkaline chloride, and silicic acid. If the solution be transferred to a dialyser, the hydrochloric acid and alkaline chloride will pass through the parchment, while the silicic acid will be retained.


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Simple English

[[File:|thumb|A dialysis machine]] Dialysis is where a machine is used to replace a kidney after kidney failure. The word dialysis comes from the Greek word dialusis, dia meaning through, and lusis meaning loosening.

Dialysis can be used for people who have become sick and have lost the use of their kidneys for a short time, or for people who no longer have working kidneys. The purpose of the kidney is to keep a balance of water and minerals in the body. These minerals include sodium, potassium, chloride, calcium, phosphorous, magnesium and sulfate. The kidneys also take out hydrogen ions from the blood. Dialysis is able to remove these wastes from the body and help keep the minerals in balance.[1]

However the kidneys are also part of the endocrine system and make erythropoietin ans calcitriol. Dialysis machines are not able to replace this part of the kidney's function.

How dialysis works

Dialyis machines work by using diffusion and ultrafiltration. A very fine material, called a membrane, allows blood and fluid to flow through it. In the machine, the blood flows in one direction, and on the other side of the membrane, a special fluid, dialysate flows in the opposite direction. Dialysate is a fluid that has different chemicals in it, such as potassium and calcium. A doctor would decide what mixture of chemicals would be needed for each patient. The dialysate has bicarbonate in it to lower the higher acid levels that these patients often have. The blood and dialysate mix together. The waste products are removed from the blood and caught up in the fine membrane.

References

  1. http://www.kidneyatlas.org/book5/adk5-01.ccc.QXD.pdf Atlas of Diseases of the Kidney, Volume 5, Principles of Dialysis: Diffusion, Convection, and Dialysis Machines


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