Snakebite
History – 62 yo man
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Usually well, recently started antihypertensive
Bite occurred 2 hours prior to arrival in ED
Bitten saw large tiger snake bite his left hand
Carried on doing jobs
Started to feel clammy and unwell
In ambulance feeling numb around lips/mouth
On arrival to ED c/o unable to swallow
Nauseated, headache behind his eyes
Examination
• Looks like crap
• BP 210/110
• What are you looking for on examination?
– Signs of neurotoxicity: ptosis, diplopia
– Signs of VICC (oozing from cannula sites)
– Signs of local damage
– Draining lymph nodes may be tender
Risk assessment
• Potentially life-threatening
• What are the early life threats?
– VICC with uncontrolled haemorrhage
– Paralysis with respiratory failure
– Hypotension
– Collapse/cardiac arrest (rare)
Initial Ix
• Insert 2 large bore IV lines
• Which bloods do you send?
– FBC
– UEC, LFT
– CK
– Coags, D-dimer, fibrinogen (NOT bedside INR/DD)
– BGH
• Do you use VDK?
Management: antivenom
• Should he be given antivenom?
• Now or wait for blood results?
• Indications for antivenom
– Clinical or laboratory evidence of envenoming
– VICC, neurotoxicity, rhabdo, renal impairment
– Collapse or cardiac arrest
– Non-specific symptoms may not be an indication
• No absolute contraindications
Isbister et al 2013
Absolute Indications
Relative Indications
Reported sudden collapse, seizure, arrest
Systemic symptoms: headache, abdo pain
Abnormal INR
Leucocytosis
Any evidence of paralysis
- Ptosis and ophthalmoplegia earliest
Abnormal APTT
CK >1000
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No high level evidence
Balance risks (anaphylaxis and serum sickness) against benefits
Use of antivenom for mild non-specific symptoms or mild coagulopathy unclear
Suggest consulting with toxicologist if indication is unclear
Effects of antivenom
Clinical effect
Benefit
Procoagulant coagulopathy
Neutralises toxin effect, factors resynthesised
Delayed improvement as factors are replenished
Anticoagulant coagulopathy
Neutralises inhibitor or coagulation
Immediate improvement in coags
Presynaptic neurotoxicity
Will not reverse any effects that are already present
Will prevent progression Slow onset (c.f. Taipan rapid)
Postsynaptic neurotoxicity
Reverses neurotoxicity
Rhabdomyolysis
Prevents further injury
Local effects
Unlikely to reverse any effects
Renal damage
Unlikely to have any discernible effect
Generalised systemic Sx
Rapidly reverse non-specific effects
Death adder
Progress
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Has antivenom per protocol
Bandage removed
Still looks crap
C/O headache behind eyes, not resolving
BP 220/120
Lab phones to say blood not clotting at all
What is the risk?
Snake bloke
• Spoke to Geoff Isbister about risk of ICH
– ?manage hypertension and observe
– ?role of FFP
• His opinion:
– Pre-existing HTN (even if Rx) highest risk ICH
– CT head (headache not resolving after antivenom)
– Control BP
– Discussed FFP…
FFP and VICC
• Small RCT of 65 patients (Isbister et al, 2013)
• FFP vs. no FFP
• FFP administration after antivenom results in
more rapid restoration of clotting function
• No decrease in time to discharge
• Early FFP (<6-8h) LESS likely to be effective
The coagulation cascade bit…
• Snake toxins include thrombin-like enzymes, prothrombin
activators and Factor X activators
• Coagulation pathway is activated
• Results in consumptive coagulopathy
• Some patients develop thrombotic microangiopathy with
renal failure, thrombocytopenia MAHA
• Rapid onset and resolution (differs from DIC)
– Median time to recovery of INR <2 is 15h
– INR normalises in 24-36 h
• Clotting factors in FFP will be consumed in coagulation
cascade if given early, so less clinical benefit
• Can make things worse (more microthrombi)
So…
• If not actively bleeding: not for FFP initially
• If bleeding: probably best to give FFP (difficult)
• Give 4 units FFP after 8 hours
Admission
• Admitted ICU
• VICC resolved (FFP given)
25/10
1845
25/10
2100
INR
26/10
0100
26/10
0500
1.3
1.2
APTT
46
31
30
Fibrinogen
<0.5
0.5
0.6
Platelets
186
171
Take home messages
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Tiger snake bite potentially lethal
VICC reverses slowly after antivenom
Risk ICH, esp in hypertensive patient
Role of FFP: best to wait 8h unless bleeding
Discuss with snake person on poisons info line