Snakebite

History – 62 yo man 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 IndicationsRelative Indications Reported sudden collapse, seizure, arrestSystemic symptoms: headache, abdo pain Abnormal INRLeucocytosis Any evidence of paralysis - Ptosis and ophthalmoplegia earliest Abnormal APTT CK >1000 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 effectBenefit Procoagulant coagulopathyNeutralises toxin effect, factors resynthesised Delayed improvement as factors are replenished Anticoagulant coagulopathyNeutralises inhibitor or coagulation Immediate improvement in coags Presynaptic neurotoxicityWill not reverse any effects that are already present Will prevent progression Postsynaptic neurotoxicityReverses neurotoxicity RhabdomyolysisPrevents further injury Local effectsUnlikely to reverse any effects Renal damageUnlikely to have any discernible effect Generalised systemic SxRapidly reverse non-specific effects Slow onset (c.f. Taipan rapid) Death adder

Progress 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 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/ / / / INR APTT Fibrinogen< Platelets186171

Take home messages 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