ARTIFICIAL KIDNEY

Typical Number in Hospital: 10

Cost Bands: 1,4

References: 3,4

This is the dialyser as used in haemodialysis. It basically consists of a semipermeable membrane having pores about 500 nm in diameter. Molecules with molecular weight of less than 5000 can diffuse fairly easily through these pores; molecules of 500 to 40 000 molecular weight will pass more slowly, whereas larger molecules are restrained. Blood is passed along one side of the membrane while a special dialysate solution is passed along the other. The dialysate solution contains molecules which are not required to be withdrawn from the blood so that only unwanted molecules will diffuse from the blood into the dialysate. Also the dialysate may contain molecules to be passed to the blood and the concentration or pressure may be such as to withdraw water from the body.

There are three main types of artificial kidney: the coil dialyser in which the membranes are wound round in a spiral (this type is no longer used), the plate or parallel flow dialyser in which the blood and the dialysate flow on either side of large flat membranes (e.g. the Kiil dialyser), or there may be several parallel plates, and the hollow fibre dialyser, in which the membrane is made as many parallel small tubes. The Kiil dialyser is reusable except for the membranes and must be assembled and sterilized before each use. Other types are normally disposable or may be reused a few times following a regeneration and sterilization programme.

The term 'artificial kidney' is often applied to the whole system including the pumps and control circuitry for the dialysate mixing and delivery, and for the blood preparation and monitoring, pumping, de-aerating and return to the body.