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.
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.