Dialysers

Dialysers

Dialysers are small plastic cylinders. These have an inlet for blood entry and outlet for blood exit.

It also has an entry opening for dialysate and exit for the fluid.

Its main body has hundreds of small tubes all connected to a common plate at the top and bottom portion of the dialyser. Blood enters at the entry point and flows through these tubes. These tubes are again joined at the exit and then blood goes out through a common tube back to the patient.

These tubes are nowadays made of synthetic material of different types. Some common types are polysulfone, polymethamethyl acrylate, poly acrylonitrile and polyamide. Earlier cellular or semisynthetic membranes were also in use (hemophane, cuprophane, cellulose etc. ) These membranes are now gradually being replaced by synthetic membranes. Synthetic membranes are comparatively inert and produce fewer reactions. These are easy to clean and sterilise.

The large no of tubes (called capillariesin medical parlance) increase the surface area to about .5 to 1.8 sq meters. Thus larger amount of blood can interchange impurities across the membranes.

Dialysate fluid flows outside the capillaries and the exchange of water, ions and waste material occurs through the membrane. Membranes have small micropores to facilitate this exchange.

Dialysis reuse : its benefits and harms.

Dialysers are reused in many centers across the world. This has the advantage of reducing dialysis costs. The protein loss (due to protein stuck on membranes) is less when dialysers are reused.

Some patients react when their blood comes in contact with dialysis membrane. This is called a first use effect. In reuse cases this is not seen.

The dialysers are checked prior to reuse to see that capillaries are intact. A large no of capillaries are functional (measured by total volume of capillaries.), and harmful chemicals used in cleaning dialysers are cleared.

Dialyser reuse is done semi-automatically by machines which also check for its safety before reuse is permitted. Manual washing and checking only by visual estimates is not useful and hence discarded by good centers. After cleaning of blood products dialysers are sterilised and kept separately for each patient in a clean container.

 

Hemo – Dialyser

 

Dialysis Water

Dialysis water

During hemo-dialysis about 500 ml (range 50-800 ml) of dialysate flows through the dialyer (The plastic casing that contains dialysis membrane and which partitions blood on one side and dialysate on the other).

Water treatment is an essential requisite for safe dialysis.

In a 4 to 5 hrs session about 120 to 150 liters of water thus comes into contact with blood.

A very small impurity in this water thus can get magnified and produce serious consequences in the renal failure patient.

If dialysis water is unfit, it results in recurrent fever, poor health and nutrition of patient, electrolyte abnormalities etc. High aluminium levels can produce brain disorder called dementia and aluminium related bone disease. High chlorine levels can cause severe reactions.

Water treatment is done for ensuring safe dialysis water.

If ground or municipal supply provides hard water it is softened by machine.

Particulate matter is removed by filters consisting of pebbles, sand and other materials first so that large particles are removed, small particles than are removed by microfilters which can remove 5-micron size particles.

Chlorine is removed by adsorption on to carbon particles. It should be present in water before it is treated but removed during water treatment.

Excessive salts are measured as TDS (total dissolved solids) expressed as parts per million or ppm in short.Both cations and anions measured and TDS is equal to about 100 X total ions expressed as milliequivalents. It is usually 0.5 to 1 times the conductivity value.

Bacteria and their products produce harmful substances. These need to be removed and water prevented from letting them grow again by regular maintenance of the pipes and drainage system.

To produce water of sufficiently good quality, various criteria have been laid by different countries. AAMI dialysis criteria is one such criteria. In these acceptable levels of various chemicals and other impurities are mentioned.

Good quality dialysis water reduces morbidity, mortality, and complications in dialysis. It results in better overall health and quality of life for the patient.