Haemodialyser Design and performance

Design requirements

Efficiency in removal of waste solutes

small internal blood volume

Minimal blood retention

Moderate resistance to blood flow

Compatibility of blood contacting surfaces

Safety, ease of use, sterility and cheapness

Small internal blood volune

40-140ml (depends on device)

Minimal blood retention after use

2-7ml (device and washback technique dependant)

Synthetic EPO important for maintaining RBC levels

Moderate resistance to blood flow

Ultrafiltration most effective at low resistances

The 2 main geometries used

Parallel Plate (rarely used, <10%)

Hollow tibe (>90% of dialysers)

Parallel Plate design mechanism

Blood passes through 2 sheets of membrane, dialysate flow is in opposite direction to bloodflow, high membrane area is required by stacking multiple plates.

Hollow fibre design

5-20,000 fine bore (200 micrometres) membrane tubes.

End of fibres are embedded in potting resin

Fibre bundle is encased in a plastic shell

Entry and exit points allow dialysate fluid to be pumped around outside surface of the hollow fibres

Mass transfer rate of solute crossing membrane

m=QbiCbi-QboCbo

Solute clearece (subbing in m)

Cl= (QbiCbi-QboCbo)/Cbi

Cl

Solute clearence (can be thought of as blood flow rate)

m

Mass transfer rate