dialysis

(redirected from CAPD)
Also found in: Dictionary, Thesaurus, Medical, Acronyms, Wikipedia.

dialysis

(dīăl`ĭsĭs), in chemistry, transfer of solute (dissolved solids) across a semipermeable membrane. Strictly speaking, dialysis refers only to the transfer of the solute; transfer of the solvent is called osmosisosmosis
, transfer of a liquid solvent through a semipermeable membrane that does not allow dissolved solids (solutes) to pass. Osmosis refers only to transfer of solvent; transfer of solute is called dialysis.
..... Click the link for more information.
. Dialysis is frequently used to separate different components of a solution. For example, a solution of starch and sodium chloride in water can be separated by placing the mixture in a vessel on one side of a semipermeable membrane and placing pure water on the other side. The smaller particles of sodium chloride (which dissolve in water to form sodium and chloride ions) will diffuse across the membrane; diffusion of the much larger starch particles (which are not truly in solution but are in colloidal suspension) is hindered and may be completely prevented. By continuously or periodically replacing the solvent with fresh solvent, almost all of the sodium chloride can be removed. The method was originated by Thomas Graham, who termed the substance that remained within the membrane a colloid and the substance that diffused a crystalloid.

An extension of the method makes possible the separation of mixed colloids by the use of a semipermeable membrane (usually synthetic) of known selectivity, i.e., one that will permit the diffusion of one colloid and hinder the diffusion of others. Mixed macromolecules, such as proteins, may be similarly separated. By the use of graded semipermeable membranes chosen to allow successively smaller molecules to pass, mixtures can be separated into components of graded ranges of molecular weight.

Hemodialysis

Artificial kidney machines have been developed that make use of dialysis to purify the blood of persons whose kidneys have ceased to function. Known as hemodialysis, this procedure has saved the lives of many persons suffering from renal failure. In such machines, blood is circulated on one side of a semipermeable membrane (often cellophane) while a special dialysis fluid is circulated on the other side. The dialysis fluid must be a solution that closely matches the chemical composition of the blood. Metabolic waste products such as urea and creatinine diffuse through the membrane into the dialysis fluid and are discarded, while loss by diffusion of substances necessary to the body (such as sodium chloride) is prevented by their presence in the dialysis fluid.

In peritoneal hemodialysis, the dialysis fluid is introduced into the abdominal cavity. Waste products leach from the blood vessels into the fluid, which is later drained from the patient. Home peritoneal dialysis machines that release patients from dependence on hospital dialysis (usually three 4-hr visits weekly) have been available since the 1980s. See diffusiondiffusion,
in chemistry, the spontaneous migration of substances from regions where their concentration is high to regions where their concentration is low. Diffusion is important in many life processes.
..... Click the link for more information.
.

Dialysis

 

the removal of impurities of low-molecular-weight substances from colloidal systems and solutions of macromolecular compounds by means of semipermeable membranes, or partitions, which pass small molecules and ions but hold back colloidal particles and macromolecules.

The simplest device for dialysis, a dialyzer, is a pouch or sleeve made of semipermeable material that is filled with the liquid to be purified and immersed in a solvent (a dispersion medium). Cylindrical vessels with a semipermeable membrane instead of a bottom are often used in place of a pouch. The membranes are made of collodion, cellophane, animal and plant membranes, and synthetic materials. Diffusion processes are the basis of dialysis; therefore, it proceeds very slowly. Dialysis may be accelerated by increasing the ratio of the membrane area to the volume of the liquid to be dialyzed, by increasing the temperature, by agitation, by creating a pressure difference across the membrane, and by frequent or continuous replacement of the solvent into which the ions or molecules of the low-molecular-weight substance pass (diffuse) through the membrane.

Dialysis in an electric field (electrodialysis) accelerates the removal of electrolytes from dialyzed systems by dozens of times. A simple electrodialyzer consists of three chambers separated by membranes. The liquid to be purified is poured into the central chamber, and electrodes immersed in solvent are located in the side flow chambers. The ions in the stationary electrical field move directly to the corresponding electrodes, penetrating the membrane from the central chamber into the side chambers. Electrodialysis is particularly efficient when ionite membranes made of ion-exchange materials are used. Depending on the sign of the electrical charge on their surface, the membranes pass either cations or anions. Multichamber electrodialyzers with ionite membranes are used in hydrometallurgy, in the atomic industry (to treat effluents, concentrate saline solutions, and separate elements close in properties), and in the desalinization of seawater.

Dialysis and electrodialysis are used in many industrial processes, in physicochemical and biological research, and in medicine. The dialysis method, which was called vivi-diffusion, was used in 1913 by the American scientist D. Abel to study the components of the blood of a living organism. The animal’s blood passed from an artery into a vein through colloidal tubes placed in a glass cylinder filled with physiologic solution. Abel’s unit was the basis for the design of the artificial kidney, which is used for hemodialysis.

REFERENCES

Voiutskii, S. S. Kurs kolloidnoi khimii. Moscow, 1964.
Elektrokineticheskie svoistva kapilliarnykh sistem. Moscow-Leningrad, 1956.
Perry, J. H. Spravochnik inzhenera-khimika, vol. 1. Leningrad, 1969. Page 624. (Translated from English.)
Demineralizatsiia metodom elektrodializa (ionitovye membrany). Moscow, 1963. (Translated from English.)

dialysis

[dī′al·ə·səs]
(physical chemistry)
A process of selective diffusion through a membrane; usually used to separate low-molecular-weight solutes which diffuse through the membrane from the colloidal and high-molecular-weight solutes which do not.

dialysis

1. the separation of small molecules from large molecules and colloids in a solution by the selective diffusion of the small molecules through a semipermeable membrane
References in periodicals archive ?
We had the challenge of finding nursing home placement for her at a time when nursing homes didn't expect to accommodate people in their 30's, let alone have their staff doing procedures like CAPD.
This method of extended dialysate dwell times meant that patients could have their dialysis continuously at home; no hospital bed was needed and the number of patients requiring CAPD treatment would not be limited by the availability of hospital resources.
The patient was promptly switched back to CAPD after four months and it is worthwhile to note that the patient has no recurrence of the pleural effusion even after 8 years of follow up.
A Randomized, Multicentre, Open label Trial to Determine peritonitis Rate, Product Defect, and Technique Survival Between ANDY-disc[R] and UltraBag[R] in Patients on CAPD.
Although the incidence of CAPD is not well known, demographic data accumulated by researchers, suggests that the incidence of CAPD is similar for boys and girls but the referral rate for boys is approximately three times higher.
Additionally, CAPD three times per day, as opposed to our usual four, might eventually allow Holly to return to her day program, which she valued greatly.
We don't yet know whether CAPD is an early sign of memory impairment, or whether both CAPD and memory loss result from an underlying cause," says Dr.
The patients were undergoing conservative therapy (predialysis; n = 10 and with a creatinine clearance <30 mg/L), daily hemodialysis (DHD; n = 30), standard HD (5-HD; n = 29), or CAPD (n = 54).
CAPD does not require a machine; the process uses gravity to fill and empty the abdomen.