The Univ. of California@San Diego site you referenced below is good one. It gives information on quite a few snakes. I have some time so I’ll take the opportunity to eat a late sandwich and expand on your posted excerpt. Hopefully, you and other interested forum readers may gain greater appreciation & respect for venomous herps and their venoms through closer consideration of what they do. It helps me, too, to review this stuff now and then. Your UCSD website excerpts are italicized:
Hematological signs and symptoms:
The blood is a fascinating organ that is made up of formed elements (blood cells, platelets) and plasma (a.k.a. serum). Blood serves to carry vital substances like oxygen and nutrients to the body’s tissues. It also carries waste products from these tissues to other organs like the liver, lungs, and kidneys for disposal. Blood is essential for fighting infection because it carries antibodies, complement, and white blood cells (essential components of the immune system) to areas where they are needed. The vascular system is made up of blood vessels and lymphatic vessels. These serve as the "roadway" along which blood and blood components travel while carrying out their duties. Blood contains the raw materials for clot formation, which is one of the essential first steps, along with platelet aggregation, in repairing vascular damage like that seen during normal wear and tear (analogous to pot holes in a road) or trauma. These clotting materials or "factors" circulate in an inactive state in blood, but activate upon encountering evidence of vascular damage or tissue damage, directing clot formation to areas where it is needed and thereby, hopefully, decreasing loss of blood from the vascular system.
We often hear that viperid venoms "attack the blood" or are "tissue destructive". Thinking about this as disruption of the processes / systems I mentioned in the above paragraph might give you some idea of the clinical potential of such venoms.
Gabbon Viper venom has a thrombin-like enzyme which quickly depletes serum fibrin levels thus rendering the blood incoagulable.
I’m not tremendously knowledgeable about the contents of Gaboon venom. But, if you have a look at the diagram below outlining the events in clot formation, you will see that thrombin (the red TH) or thrombin-like action would deplete fibrinogen (fibrin precursor) by converting it to fibrin (and therefore actually increase fibrin!). This point is of academic interest only, however, since the result is the same: fibrinogen used up = can’t make more fibrin = can’t make a clot = "blood incoagulable".
In addition the venom has hemorrhagic activity as it causes widespread damage to the microvasculature.
In other words, not only does it disrupt the ability to patch holes in the road, it also blows holes in the road. This translates into unstoppable leakage of blood into tissue, producing severe swelling and discoloration / blistering at the bite site (imagine filling a water balloon from a blood-delivering faucet). If the swelling becomes extremely severe, pressures inside a bitten extremity can become high enough to directly damage tissue as well as impede flow of blood in and out of the area, which, as you recall, is carrying tissue-sustaining oxygen (imagine the water balloon is actually a leather sac that is eventually stretched to its limit with blood – the pressure inside will eventually exceed the line pressure pushing blood out of he faucet, halting forward blood flow). This represents a "compartment syndrome", requiring fasciotomy to relieve the pressure and restore the flow of blood.
Of note, the lungs and gastrointestinal tract are extremely sensitive to this hemorrhagic activity.
This reflects the relatively large size of the vascular bed supplying these organs. You will often find that organs serving to exchange substances with the environment (lungs-oxygen and carbon dioxide / gastrointestinal – nutrients, waste / kidneys – waste) are "vasculary endowed". This makes sense since blood and blood vessels are responsible for transporting these substances to their destinations.
Finally, disseminated intravascular coagulopathy and anemia may also occur.
I prefer the words disseminated intravascular coagulation because tihs is more reflective of the underlying process. This is the entity I described in my previous post that results in depletion of clotting factors (represented by green Roman numerals in the above diagram), platelets, and fibrinogen. Again, this process involves inappropriate activation of the clotting cascade, and usually primarily occurs the smaller blood vessels. The widespread precipitation of tiny clots in these small vessels not only uses up platelets and clotting factors, but also causes damage to tissues supplied by these now blocked vessels. This can be a very bad situation resulting, at the same time (and somewhat paradoxically), in ischemic organ damage and hemorrhage. Severe DIC has at least a 50% associated mortality. As I said in my previous post, causes of DIC are varied, including things like infection, tissue damage, cancer, and yes, venom. Clues to the cause are provided by timing / onset and associated medical history.
The patient should be monitored closely and blood products including whole blood, packed RBC's platelets, cryoprecipitate, and fresh frozen plasma should be given when indicated.
It is interesting to consider each of these treatments and when / why one would be more appropriate than the next. Whole blood is rarely used nowadays. The individual components of blood store much better when separated from one another, but if WB is all you have, that’s what you have to use. "Packed" red blood cells are red blood cells minus plasma and minus most of the white blood cells. Red cells carry oxygen and carbon dioxide. Without these, blood cannot supply oxygen to or remove CO2 from tissues. PRBC’s are used to treat significant blood loss or anemia. In the context of snakebite, PRBC’s would be indicated for significant (shock-producing) internal hemorrhage. Platelets are formed elements of blood that, along with fibrin, provide the structural building blocks for clot formation. They also represent the first "finger in the dike" when a hole appears in a vessel wall. If platelet numbers are decreased significantly, clot formation is hindered. Spontaneous hemorrhage is a real risk if platelet numbers are extremely low. Giving platelets is indicated for thrombocytopenia (low platelet count) accompanied by evidence of hemorrhage like that which might occur in the setting of venomous snakebite (from direct platelet destruction, consumption through clotting activation, DIC etc.). In addition to decreasing platelet number, venoms also can affect platelet function, but this is a lengthy discussion topic in itself and one I can’t get into during my lunch break. Fresh frozen plasma and cryoprecipitate are used to replace coagulation factors and fibrinogen (cryo is better for fibrinogen) so they would be useful in countering the effects of a thrombin-like venom component or severe DIC + hemorrhage.
Thanks for providing the additional information about your bite. You are lucky to have your life and limbs! One more question, if you don’t mind - when you eventually received the right AV (one vial day 4 post bite?!), did you or your doctor note any change in your status? If so, what changed, exactly?
Well, back to work.
Cheers,
WK
as it was the middle of the rainy season...December.
