Snakebite

Introduction

While most snakebites do not result in envenoming, the potential for life threatening injury warrants all patients to receive high priority assessment and management even if they initially appear well.

Clinical features of envenoming:

Local: pain, swelling, bruising, lymphadenopathy

Systemic: nausea, vomiting, abdominal pain, diarrhoea, diaphoresis & headache

Major toxin syndromes1:

  • Venom-induced consumptive coagulopathy
    • Complete if INR > 3.0, abnormal aPTT and very high D dimer
    • Partial if INR < 3 and low but detectable fibrinogen level ( <1.5g/L)
  • Neurotoxicity
    • Descending flaccid paralysis involving ocular muscles first, followed by bulbar, respiratory muscles and limb paralysis
  • Myotoxicity
    • CK > 1000 with Myalgia or muscle tenderness
  • Anticoagulant coagulopathy
    • aPTT is moderately abnormal
  • Thrombotic microangiopathy
    • Fragmented RBC on film with MAHA, thrombocytopenia and elevated creatinine

Assessment

Important features on history

History of bite

  • Time of bite
  • First aid measures applied
  • Early symptoms; eg collapse
  • Known species if snake in captivity

Relevant comorbidities; eg coagulopathies, renal impairment

Relevant medications; eg anticoagulants,

Important feature on examination

Bite site: fang marks, bruising, local necrosis

Regional lymphadenopathy

Neurological examination; ptosis, ophthalmoplegia, bulbar weakness, limb weakness, respiratory muscle weakness

Haematological examination; bleeding from bite site or cannula site, oral cavity or occult sites

Investigations

On arrival:     FBC, EUC, CK, coags including fibrinogen & D dimer. Remember to document snakebite on the request form to assist processing in the lab.

Do not request a VDK.See additional information

Bloods (CK, coags) should be repeated 1 hour post pressure bandage removal and at 6 and 12 hours post bite.

Management

First aid Measures

  • Application of a broad (15cm), elasticised pressure bandage to the entire affected limb with immobilisation is recommended for all patients with suspected snakebite. The pressure applied should be similar to that used for a sprained ankle.
  • The application of a pressure bandage after 4 hours post bite is unlikely to be effective.
  • The bandage can be removed once there is no clinical evidence of envenoming following the return of the initial blood results.

Disposition

Patients with no evidence of envenoming:

  • Follow the Clinical Pathway See Appendix
  • This group should be observed for 12 hours with repeat testing (neurological examination, coags, CK one hour following the removal of the pressure bandage and at 6 and 12 hours following the bite.
  • This group should be admitted to the Short Stay Unit under TOXE and the toxicology registrar should be notified
  • Discharge should occur in daylight hours
  • Ensure adequate tetanus prophylaxis

Patients with evidence of envenoming:

  • This group should receive an appropriate antivenom in a timely manner
  • There is no role for redosing of antivenom
  • Discuss this group with the toxicologist on call
  • This group requires admission under the toxicology unit for observation and adjunctive therapy as required
  • Full set of bloods (FBC, EUC, CK, coags, D dimer) should be repeated 6, 12, 18 and 24 hours post bite.
  • This patient group should be recruited to the Australian Snakebite Project (ASP)

Additional Information

  • Venom Detection Kits (VDK) were traditionally used to assist in snake identification, however they have been shown to be inaccurate in 17% of envenomings.4 They are no longer recommended in the assessment of snake bite at the PA hospital. Antivenom choice should be based on the clinical features of envenomation and geographical location.
  • One vial of the appropriate venom is sufficient to treat envenomed patients. There is no role for redosing of antivenom.   Antivenom needs to be given in a resuscitation area with capacity to treat anaphylaxis should it occur. Premedication is not recommended. Acute systemic hypersensitivity occurs in 23% of patients, and is severe (hypotension) in 7%2 See table below.
  • Serum sickness occurs in 29%2 See table below of patients given antivenom and is characterised by flu like symptoms and rash which develops 4 to 14 days after antivenom administration. It is treated with prednisolone 25mg for 5 days.

  • Antivenom is diluted 1:10 with saline and administered over 15-30 minutes, dilution can be 1:5 in the paediatric population for larger volumes of antivenom.3
  • The role of treating VICC with factor replacement is controversial. While studies have shown providing FFP does restore clotting function more rapidly this hasn’t resulted in meaningful outcomes for the patient. It appears reasonable to administer FFP (rather than any other factor replacement, given these patients are deficient in factors I, V and VIII) to patients with life threatening bleeding secondary to VICC.

References

  1. Isbister GK, Brown S, Page C et al. ‘Snakebite in Australia: a practical approach to diagnosis and treatment.’ MJA 2013; 199(11): 763-8
  2. Ryan N, Kearney RT, Brown S and Isbister GK. ‘Incidence of serum sickness after the administration of Australian snake antivenom (ASP-22).’ Clin Toxicol 2016; 54(1):27-33
  1. eTG Toxicology and Wilderness 2016 ed. Snakebite chapter.
  2. Johnston CI et al. “The Australian Snakebite Project, 2005-2015 (ASP-20)” MJA 2017; 207(3) 119-125

Appendix

Clinical-pathway.pdf