- Calcium (factor IV) is an essential substrate for all 3 clotting pathways
- Citrate is added to blood prior to the filter in the form of trisodium citrate:
- Chelates calcium forming a complex
- Prevents the involvement of calcium in the clotting cascade
- Regional anticoagulation of the filter only is ensured through several mechanisms:
- Citrate-calcium complexes are small molecules and freely pass through the filter (via diffusion or convection)
- Residual citrate in the blood is delivered to the patient and metabolised by the liver to bicarbonate
- Calcium ions are infused post-filter to replace that lost in effluent, normalising levels and clotting function
