Dialysis

From Greek διάλυσις, dialusis (dissolution), from διά, dia (through) + λυσις, lusis (loosening). In medicine, dialysis is primarily used to provide an artificial replacement for lost kidney function (renal replacement therapy) due to renal failure. Dialysis may be used for very sick patients who have suddenly but temporarily, lost their kidney function (acute renal failure) or for quite stable patients who have permanently lost their kidney function (stage 5 chronic kidney disease). When healthy, the kidneys maintain the body's internal equilibrium of water and minerals (sodium, potassium, chloride, calcium, phosphorus, magnesium, sulfate) and the kidneys remove from the blood the daily metabolic load of fixed hydrogen ions. The kidneys also function as a part of the endocrine system producing erythropoietin and 1,25-dihydroxycholecalciferol (calcitriol). Dialysis treatments imperfectly replace some of these functions through the diffusion (waste removal) and convection (fluid removal). Dialysis is an imperfect treatment to replace kidney function because it does not correct the endocrine functions of the kidney.^[1]

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History

Many have played a role in developing dialysis as a practical treatment for renal failure, starting with Thomas Graham of Glasgow, who first presented the principles of solute transport across a semipermeable membrane in 1854.^[2] The artificial kidney was first developed by Abel, Rountree and Turner in 1913,^[3] the first Peritoneal Dialysis was by Georg Ganter (1923),^[4]the first hemodialysis in a human being was by Hass (February 28, 1924)^[5] and the artificial kidney was developed into a clinically useful apparatus by Kolff in 1943 - 1945.^[6] This research showed that life could be prolonged in patients dying of renal failure. Yet, the technical problems associated with blood access or access to the peritoneum made dialysis limited to patients with acute renal failure until 1960 (though a chronic renal failure patient was treated in 1956 with peritoneal dialysis^[7]). In 1960 work on subcutaneous arteriovenous shunt (a plastic tube connected to an artery and a vein) by Scribner and Quinton made hemodialysis available as a treatment for people with chronic renal failure.^[8].

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.

Types

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

Hemodialysis

Main article: hemodialysis

Main article: Home hemodialysis

In hemodialysis, the patient's blood is pumped through the blood compartment of a dialyzer, exposing it to a 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 fluid during a typical 3 to 5 hour treatment. 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 2,000 people in the US are dialyzing at home more frequently for various treatment lengths.^[9] 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.^[10]

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.

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.

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 edema)
  • 4) Uremic pericarditis, a potentially life threatening complication of renal failure
  • 5) And in patients without renal failure, acute poisoning with a dialysable drug, such as lithium, or aspirin.
• 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) Difficulty in medically controlling serum phosphorus or anaemia when the GFR is very low

See also

• Apheresis, also known as Plasmapharesis, is another extracorporeal technique that selectively removes specific constituents from blood.
• Acute renal failure
• Chronic kidney disease
• Hemodialysis
• Hepatorenal syndrome
• Nephrology
• Renal failure
• Dialysis tubing

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
2. ^ http://links.jstor.org/sici?sici=0261-0523(1854)144%3C177%3ATBLOOF%3E2.0.CO%3B2-E Graham T. The Bakerian lecture: on osmotic force. Philosophical Transactions of the Royal Society in London. 1854;144:177–228.
3. ^ http://books.google.com/books?id=KMcCAAAAYAAJ&dq=&pg=PA51&ots=UM7CVprPEW&sig=Xpnf-kEJTYO7iFSxhdSoC2Ujh3Y&prev Abel, J. J., Rountree, L. G., and Turner, B. B. The removal of diffusible substances from the circulating blood by means of dialysis. Tn. Assoc. Am. Phys., 28:51, 1913.
4. ^ http://www.ispd.org/history/genesis.php3 Ganter, G. About the elimination of poisonous substances from the blood by dialysis. Munch Med Wchnschr v 70:1478-1480, 1923
5. ^ http://www.uniklinikum-giessen.de/med3/history/haas/2001-Dial-Transpl.pdf Georg Haas (1886–1971): The Forgotten Hemodialysis Pioneer
6. ^ http://jasn.asnjournals.org/cgi/reprint/8/12/1959 Kolff, W. J., and Berk, H. T. J. Artificial kidney, dialyzer with great area. Geneesk. gids., 21:1944.
7. ^ http://www.multi-med.com/pdigifs/Volume5/vol5-1/27pioneer05no1.pdf Pioneers in peritoneal dialysis McBride, Patrich
8. ^ http://kidney.niddk.nih.gov/about/Research_Updates/win00-01/contrib.htm NIDDK Contributions to Dialysis
9. ^ http://www.usrds.org/2007/pdf/04_modalities_07.pdf USRDS TREATMENT MODALITIES
10. ^ http://www.homedialysis.org/learn/types/ Daily therapy study results compared