Blood purification by adsorption

This is a simple process. You pump anticoagulated blood through a hemoperfusion cartridge. Empirically, it seems a good blood flow rate is about 300ml/min. A rising filter pressure indicates that a clot is forming in the filter.

Mechanisms of haemoperfusion

 

Adsorption is the deposition of molecules on the surface of a medium, rather than within it (which would be aBsorption).

The adsoprtion medium needs to have several favourable properies:

• High selectivity/ affinity for noxious solutes
• Rapid adsorption
• High capacity for adsorption (i.e. large surface area)
  • Modern sorbents have a surface area of around 1000m² per gram of sorbent
• Chemical and thermal stability, including low water solubility
• Good structural integrity (i.e. non-crumbly)
• Good biocompatibility (to prevent inflammatory response or anaphylaxis)

The Cartridge:

Charcoal = 300g of activated charcoal
Resin = 650 g of XAD polystyrene resin

Primed and flushed with normal saline.

Each cartridge lasts about 4 hours.

Obviously, it is not reusable.

Practical administration of haemoperfusion

Relevant features to make note of :

• A normal CRRT machine can be used
• Blood flow rate is about 250-300ml/min
• Anticoagulation requirements are similar to normal CRRT
• A session usually lasts about 4 hours
• At the end of the 4 hours the cartidge is depleted and must be discarded.

the Rebound phenomenon

Filth getting sucked back into the patient:

If something is so highly protein bound that it is not easily dialysed, then one can assume it will be distributed into the tissue proteins as well as circulating proteins.

The result is that the toxin will redistribute back into the "clean" blood which goes back into the patient, and thus multiple sessions of hemoperfusion may be required to wash out all of the tissue-bound toxin.