Snake bite

First Aid on scene

• BLS
• Pressure immobilisation bandage (PIB)
  • For technique to be effective, must employ both pressured bandage and immobilisation of the bitten limb
  • Do not wash wound
  • Swab bite site and put in fridge if no signs of envenoming
  • Broad elasticized pressure bandage (if available) below bite site upwards along bitten limb
  • Leave tips of digits uncovered to test circulation
  • Do not remove pants or trousers, bandage over them
  • Mark location of bite
  • Bind a splint  to the limb after this and keep patient as still as possible

On arrival

• ABCDE
• IVC and bloods
  • Initial bloods: FBC and film, Coags (APTT, PT, Fibrinogen, D-dimer), CK, U&E, LDH, LFT
  • Serial bloods: INR, APTT, Fibrinogen, CK, FBC, U&E
• Bite swab (to keep in fridge)
• Monitoring
• Ensure adequate urine output
  • 1-2mL/kg/hr if myoglobinuria evident
• Assess (see below)

Resuscitation

• Cardiac arrest
  • Paediatric ALS + Polyvalent AV if snakebite thought to be cause
  • If resuscitation successful, return to usual snakebite + post-arrest management
• Always consider anaphylaxis to venom
  • Antivenom may be a useful adjunct in management of this as well as usual adrenaline protocol
  • If treated successfully, return to usual snakebite + post-anaphylaxis management
• Severe respiratory distress may be impending compromised airway, respiratory paralysis or severe bronchospasm from anaphylaxis

Assessment

• Circumstances
  • Witnessed bite or possible bite
  • Multiple bites?
  • Where/when/how
  • First aid
  • Past history
  • Medications esp. anticoagulants
  • Allergies
  • Past exposure to antivenom or snakebite

Assessment

• Symptoms
  • Headache
  • Nausea/vomiting
  • Abdominal pain
  • Blurred vision
  • Slurred speech
  • Muscle weakness
  • Respiratory distress
  • Bleeding from bite site, gums or elsewhere
  • Passing dark or red urine
  • Local pain or swelling at site
  • Pain in draining lymph nodes
  • Loss of consciousness and/or convulsions

Problem presentations

• Unexplained collapse
• Convulsion
• Progressive unwellness
  • Lethargic, vomiting, mild fever, abdominal pain, haematuria (= myoglobinuria), progressive paralysis and ptosis
• Renal failure without clear cause

Assessment

• Examination
  • Evidence of bite/scratch. May be multiple. Take swab.
  • Bruising around bite site (typical of Tiger snake)
  • Evidence of venom movement e.g. swollen or tender nodes
  • Neurotoxic
    • Ptosis, ophthalmoplegia, diplopia, dysarthria, limb weakness, respiratory distress
  • Myotoxic
    • Muscle tenderness, pain with movement, dark or red urine
  • Coagulopathy
    • Bleeding gums, prolonged bleeding from venepuncture site or wounds or bite site

Role of VDK

• Takes 20-30 minutes
• In inexperiened hands (most of us), have significant rates of misidentification, false positives and false negatives
• Results should never override clinical or geographic data
• Discuss use and results with clinical toxicologists
• Can use bite site swab or urine (only if sample provided after symptoms/signs of envenomation arose) for test

When can PIB be removed?

• Patient must be stable with no clinical or lab signs of envenoming
• Can then remove in resuscitation area
• Antivenom should be ready for delivery with adrenaline and resuscitation equipment at hand
• Re-apply PBI if envenoming arises after removal and deliver antivenom

Major venomous snakes

Major venoms

• Brown snake – VICC +- MAHA + Sudden collapse + presynaptic neuro (mild)
• Black snake – Rhabdo + anticoagulants
• Taipan/Tiger – Rhabdo + Neuro + VICC
• Black- and blue-bellied black snakes rarely cause systemic envenoming

Definitions

• VICC
  • Venom-induced consumptive coagulopathy
  • Fibrinogen reduced, D-dimer elevated
  • Raised INR
• Anticoagulant coagulopathy
  • APTT 1.5-2.5x normal +- minor INR elevation
  • D-dimer and fibrinogen usually normal
• MAHA
  • Microangiopathic haemolytic anaemia
  • Fragmented red cells on film, thrombocytopaenia and rising creatinine

Black snakes

• Mulga snake, Collett’s snake, Butler’s snake, Papuan black snake
  • Large painful bite with extensive local tissue swelling and local lymphadenitis
  • Systemic features rapidly, generalized myalgia and muscle weakness within 6 hours
  • Myotoxicity is frequent
  • Anticoagulant coagulopathy is frequent but bleeding is rare
  • Acute haemolysis may occur
• Red-bellied and blue-bellied black snake
  • Local pain and systemic features
  • Myotoxicity is rare
  • Anticoagulant coagulopathy may occur but is usually mild
  • Long-term anosmia, paraethesia and pain at bite site can occur

Black snakes

• Antivenom within 3 hours prevents myotoxicity
• 1 ampoule of black snake antivenom if:
  • CK >1000
  • Systemic features
  • Anticoagulant coagulopathy
• Can use black snake or tiger antivenom for blue-bellied and red-bellied black snake (tiger cheaper, more widely available and smaller volume)
• Mulga snake is referred to as a King Brown, however, it is NOT a brown snake

Brown snake

• Most common cause of severe envenoming and death from snakebite in Australia
• Presyncope or sudden collapse is typical
• VICC is common
• MAHA in 10%
• Myotoxicity does NOT occur
• Neurotoxicity is rare and mild

Brown snake

• Complete VICC vs. partial VICC
  • Complete = INR >3, undetectable fibrinogen, D-dimer >100x normal
  • Incomplete = INR <3, low but detectable fibrinogen
• Recovery from VICC takes around 20 hours
• Monitor for MAHA with LDH and free Hb/fragmented red cells
• If received antivenom, can discharge after 24 hours if INR <2, no MAHA and clinically well
• Clotting factors increase rate of recovery from VICC but not duration of hospitalization
• Antivenom may not hasten recovery from VICC

Brown snake vs. Tiger snake

• May be clinically indistinguishable initially as both can cause collapse and VICC
• Tiger have more significant neurotoxicity and myotoxicity over ensuing hours

Death adder

• Bites and envenoming are uncommon
• Not in Victoria or Tasmania
• Progressive symmetrical descending flaccid paralysis within 6 hours
• Non-specific systemic symptoms are common
• Myotoxicity is uncommon and mild
• Antivenom – 1 vial for objective paralysis
• No VICC, anticoagulant coagulopathy or MAHA
• Typically bitten at night walking barefeet. May not even notice bite
• Can be complicated by cellulitis at bite site

Tiger snake

• Mostly southern Australia (vs. taipan in northern Australia)
• The only venomous snakes in Tasmania
• Classically VICC, myotoxicity, delayed neurotoxicity (in 30%)
• MAHA can occur but is less common than with brown snakes
• Rough scaled snake is very similar
• Tiger vs. Taipan
  • Taipan has more rapid onset of neuro and myotoxicity
  • Both have VICC
  • Taipan Northern and Tiger southern Australia

Taipan snake

• Rare but frequently lethal
• Mostly northern Australia
• Often no specific history of bite
• Collapse then paralysis within 1-2 hours + VICC + myotoxicity
• MAHA occurs
• Differentiated from Brown snake by more severe neuro and myotoxicity

Sea snake

• Neurotox and myotoxicity
• No VICC/anticoagulant coagulopathy
• Unclear if tiger snake antivenom (3:1 sea snake) is still effective as previously described

When to give antivenom?

• Absolute indications
  • Any evidence of neurotoxic envenomation
    • Ptosis, ophthalmoplegia, limb weakness, respiratory distress
  • Significant coagulopathy
    • Unclottable blood, INR >1.3 or prolonged bleeding clinically
  • History of unconsciousness, collapse, convulsions or cardiac arrest
  • Evidence of acute renal damage
• Relative (discuss with clinical toxicologist before)
  • Significant systemic symptoms e.g. headache, abdo pain, vomiting
  • Abnormal INR, APTT, fibrinogen, D-dimer, FBC (leukocytosis or evidence of MAHA) or CK >1000

Timing of antivenom therapy

• It is never too late to deliver antivenom in the presence of severe envenomation
• Less effective the longer the delay
• Seek expert advice if >24 hours after the bite as benefits may be outweighed by risks

Choice of antivenom

• Always preferable to use monovalent antivenom as uses less volume and has less adverse effects (serum sickness specifically)
• If impractical to consider type (i.e. cardiac arrest), can give polyvalent, which covers 5 snake venom immunotypes predominating in land snakes in Australia and PNG
• In some regions, using two monovalent types based on geographic range is practical (seek expert advice)
  • In Tasmania and Kangaroo Island, only need Tiger snake antivenom

Monovalent antivenoms

• Brown
• Black
• Taipan
• Tiger
• Death adder
• Sea snake (not included in polyvalent)

Polyvalent antivenom

• Covers all land-based snakes in Australia 
• Product information states to use 1 vial but that more may be required depending on clinical effect
• Expert consensus states that dosing should be as per number recommended for corresponding monovalent i.e. if known brown snake but only have polyvalent, give 2 vials of polyvalent as per brown snake guidelines

Preparation for antivenom delivery

• 2x IV access
• 20mL/kg IV N/saline ready for pressure bolus if required
• IM adrenaline 0.01mg/kg of 1:1000 in case of anaphylaxis
• Dilute antivenom up to 1 in 10 normal saline (not to exceed 10mL/kg in small children)
• Start slowly and then increase rate gradually to deliver over 30 minutes

Observations during antivenom delivery

• Must remain in critical care area
• Warning signs of anaphylaxis in children
  • Rash, hypotension, bronchospasm
  • Nasal, palatal or ocular pruritis
  • Coughing
  • Sneezing
  • Profuse sweating
  • Faecal or urinary incontinence
  • Abdominal pain
  • Impending sense of doom

What if there is an adverse reaction?

• May be related to rate of infusion
• May respond to temporarily stopping, waiting to ensure it settles and then re-starting at a slower rate
• If sudden fall in BP or bronchospasm:
  • Stop infusion
  • Lie supine
  • 100% O2
  • Rapid fluid bolus 20mL/kg IV N/saline
  • Adrenailne 0.01mg/kg 1:1000 IM
  • If remains hypotensive – repeat fluid bolus and commence IV adrenaline infusion
• In most cases cautious re-introduction of antivenom is possible and necessary

Adverse reaction risk factors

• Atopic family history
• Previous exposure to equine protein
• Delayed reactions more likely with multiple doses
• Polyvalent antivenom
• Repeat doses
• IV use without dilution

Adverse reactions to antivenom

• Serious adverse reactions seen in 1% of patients
• Rash: May be mild or herald more severe reaction
• Pyrexia
• Anaphylaxis/anaphylactoid reaction
• Serum sickness
  • Up to 30% of patients
  • Flu-like syndrome with fever, myalgia, arthalgia and rash developing 4-14 days post-antivenom
  • Management
    • Oral corticosteroid short course
    • Consult with clinical immunologist

What happens after antivenom delivery?

• PIB can be removed
• Admit for observation and ongoing treatment
  • Strict fluid balance chart looking for declining urine output
  • Usually repeat blood tests at 6, 12 and 24 hours post-antivenom followed by daily testing until all within normal limits (some caveats as per discharge criteria)

Repeated antivenom dosing

• Venom-induced consumptive coagulopathy can take up to 6 hours to start improving after antivenom delivery and repeated dosing of antivenom does not provide additional benefit
  • Takes this long for depleted coagulation factors to start being replenished
  • If active bleeding (incl. ICH), need to consider repeat antivenom dosing in conjunction with FFP (>1 hour and <4 hours post-antivenom delivery) with expert advice
• Anticoagulant coagulopathy rarely requires repeated antivenom dosing

Repeated antivenom dosing

• Myolysis
  • CK level usually peaks at 24 hours then returns to baseline over several days
  • If second peak or continued rapid rise after antivenom therapy, consider repeat dose
• Neurotoxicity
  • All Australian snakes that cause paralysis, produce venoms containing both pre- and post-synaptic neurotoxins. Pre-synaptic neurotoxins are not reversible and therefore it is crucial to deliver antivenom as early as possible once neurotoxicity is recognised
  • No benefit in repeated doses of antivenom 

Is there a role for FFP/cryoprecipitate?

• Very limited
• If bleeding due to coagulopathy and antivenom already delivered in adequate dose, then there may be a place for blood constituents but need to discuss with clinical toxicologist

Discharge criteria if no antivenom

• Patient can be discharged (in daylight hours) if all results within normal limits (Initial, 1-hour post-PIB removal, 6 and 12 hours post-bite) and no signs of neurotoxicity
• Education re: serum sickness

Discharge criteria after antivenom

• As per Victoria ED management flow chart
  • Uncomplicated myotoxicity and mild neurotoxicity
    • Once clinical features resolving and blood tests normalising at least 12 hours post-antivenom
  • Venom-induced consumptive coagulopathy
    • INR, aPTT, creatinine and platelet count normalising
  • Always in daylight hours

Last Updated on October 28, 2020 by Andrew Crofton