DIALYSER

The main element in a dialyser is a semipermeable membrane through which small molecules can pass by diffusion. Dialysers are encountered in medical work in renal dialysis where unwanted small molecules (e.g. urea) and water can be removed from the body. Dialysers may also be encountered in the clinical chemistry laboratory for purifying or modifying samples of fluid being analysed.

Haemodialysers (sometimes called artificial kidneys) take blood from the body and pass it along one side of the dialysing membrane so that unwanted small molecules may diffuse into a special dialysing fluid passing along the other side. Small molecules which need not be removed are included in the dialysate so that there is equal diffusion of these molecules in each direction.

Haemodialysers are constructed either as membranes wound into coils (not used now), membranes held between flat plates, or made into hollow fibres along the length of a special vessel.

The peritoneum is a double membrane enveloping most of the organs in the abdomen, and renal dialysis may be achieved by pumping a special dialysing fluid into the cavity between the two membranes and allowing time for the diffusion to occur before withdrawing it. This technique is called peritoneal dialysis which may be a hospital procedure operated by sets of pumps, valves and timers, or may be used at the patient's home without special apparatus but using a collapsible bag from which the fluid is delivered and then returned after the process is complete. Both dialysis systems have their advantages.

Content and Design Copyright 2000 Dr. Malcolm C Brown.  See Title Page for more details