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