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What is dialysis?
Dialysis is the process whereby waste products and excess water is removed from the body by circulating blood through an artificial filter and returned to the body.
What is the physiological basis for Hemodialysis?
Dialysis is the process whereby the solute composition of a solution A for instance is altered by exposing it to second solution B through a semi permeable membrane.
Water molecules and small molecular weight solutes in the two solution can pass through the membrane course and intermingle, but large molecules like proteins cannot pass through the semi permeable barrier. Diffusion and ultra filtration are the two mechanism by which dialysis occurs. Diffusion is the process of movement of solutes from a higher to a lower concentration across a semi–permeable membrane.
The rate of diffusion depends on:
- Concentration gradient.
- Size of the molecule.
- Membrane properties such as thickness and pore size.
Ultra filtration is the second mechanism of solute transport. The water molecule are extremely small and can pass through all semi permeable membrane. Ultra filtration occurs when water is driven by hydrostatic or osmotic force is across the membrane. Along with water, solutes are dragged across and process is called solvent drag.
Describe the dialysis filter.
Hemodialysis apparatus consists of the dialyser. It consists of a tube with four parts The tube contains the membrane in the form of hollow fibers through which blood passes.
The fibers can be of different types:
Made from processed cotton like cellulose or cellulose acetate.
Polyacrylnitrile, polysulfone, polymethylmethacrylate etc.
Which membranes are better for Hemodialysis?
Synthetic membranes have been designed to achieve more efficient dialysis and also have lesser incidence of adverse reaction.
Can dialysis membranes be reused?
Yes. But only in the same patient. Reuse is a safe and effective practice that is used worldwide. The average number of times the dialyser is reused varies although many dialysis units average about anywhere between 5 to 10 reuses per dialyser. After use the dialyser should be chemically disinfected.
What agents are used to clean the dialyser?
The dialyser is cleaned either with bleach (sodium hydrochloride) or hydrogen peroxide. Once cleaned the dialyser must undergo a physical or chemical process that renders all living organism inactive. Germicides which are used are formaldehyde, gluteraldehyde, mixture of per acetic acid and hydrochloric acid acetic acid (Renalin).