Question 29

Created on Sat, 05/16/2015 - 03:46
Last updated on Wed, 07/19/2017 - 04:45
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A 25-year-old man presents to the Emergency Department following suspected snake bite. He has an effective pressure-immobilisation bandage in situ.

  • List appropriate initial investigations specific to this presentation that should be performed in conjunction with clinical assessment
  • List indications for the use of polyvalent antivenom in snake envenomation.
  • Briefly discuss the role of pharmacological pretreatment prior to the administration of snake antivenom?
  • List 3 parameters that would help you determine that adequate monovalent antivenom has been administered to a patient with snake bite envenomation.

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College Answer

Indications for the use of polyvalent antivenom in snake envenomation:

  • Unable to identify snake … could be due to no AVDK, or equivocal result.
  • Severe envenomation and can’t wait for SVDK result AND would need several monovalent snake antivenoms to cover the possible local snakes.
  • Unavailability of appropriate antivenom.
    • Rapid evolution of life-threatening clinical state (no time to wait for VDK)
    • Unavailability of appropriate monovalent antivenom
    • Equivocal VDK result
    • In setting that antivenom administration is justified
  • Initial Investigations:
    • •   CK
    • •   Coagulation
    • •   Venom detection (bite site if possible), if any clinical or investigation abnormalities are present
    • • ELFTs … renal failure are a complication of rhabdomyolysis and a direct effect of brown snake bite.
    • •   Full blood count … measure platelets

c) Role of pharmacological pretreatment prior to the administration of snake antivenom:

  • Allergic phenomena are common with snake antivenoms and preparation for anaphylaxis is mandated when administering antivenom
  • No evidence for any pretreatment
    • Steroid, antihistamine, adrenaline- all no good evidence
  • Common practice in many centres though

d) Parameters:
Several possibilities here and many controversies:

  • Empiric dose administered – concordant with guidelines / CSL recommendations (that there is variability in these can be acknowledged, as can dose for children = dose for adults). Observation and assessment then required
  • Rise in fibrinogen/ resolution of coagulopathy. Takes time, role of FFP controversial
  • Resolution of neurotoxicity (if presynaptic effect)- if postsynaptic changes are established this will be unreliable
  • Resolution of nonspecific symptoms could also be mentioned, as could halt in CK rise

Discussion

Investigations for a snake bite victim:

  • CK (rhabdmyolysis)
  • Coags (DIC, or "venom-induced consumption coagulpathy)
  • FBC (DIC, looking for thrombocytopenia and red cell fragmentation)
  • Fibrinogen (DIC)
  • EUC (renal failure)
  • LFTs (hepatic injury)
  • Snake Venom Detection Kit

Indications for polyvalent antidote:

  • Unsure which snake species was involved
  • SVDK not available
  • monovalent antivenom not available
  • the patient has been bitten by multiple different species of unidentified snakes.

Evidence for premedication for antivenom administration:

  • This is no longer recommended in Australia
  • polyvalent antidote tends to have a higher rate of anaphylaxis

How do you know your monovalent antivenom is working?

  • The short answer is, you dont.
  • It takes tme for some of the irreversible features to resolve (eg. it takes time to synthesis the coagulation factors which have been depleted)
  • Giving more antivenom will not improve the situation.

References

Isbister, Geoffrey K., et al. "Snakebite in Australia: A practical approach to diagnosis and treatment." Medical journal of Australia 199.11 (2013): 763-768.