by toxinologist » Sun Jun 26, 2011 9:11 am
Under normal conditions, the coagulation cascade is tightly controlled by a range of proteins and other factors which regulate one another to ensure that only enough thrombin is produced to generate a clot at the site of a specific injury - a cut finger for example, likewise only enough fibrinogen is then converted to produce sufficient fibrin to support this clot, etc ... the system works in a balance and the small quantities used up are readily replenished through normal blood protein and blood cell synthesis involving bone marrow and the liver. Normal synthesis in the liver of blood factors takes 6-9 hours in a healthy individual. If liver function is compromised it takes longer.
In snakebite however the activation of clotting proteins is system-wide - massive quantities are artificially activated and artificially consumed. Much too fast for the body to replenish them quickly enough to prevent bleeding from taking place. If blood or plasma is transfused, and venomis still present in the system, then any factors added by transfusion will also be quickly activated and used up, and there is a strong argument for avoiding transfusion of blood or plasma until AFTER antivenom is administered and the toxins have been neutralised, since the heightened risk of a catastrophic bleed, such as an intracranial haemorrhage needs to be avoided.
Does that help?
Cheers
David
Australian Venom Research Unit
University of Melbourne
Parkville Vic 3010 AUSTRALIA
http://www.avru.org