Snake envenomation — viva (Big Four, 20WBCT, ASV)

Opening stem

"A farmer is bitten on the foot while walking at dusk. How do you assess and treat?"

Q1: Syndromes and Big Four (2 min)

• India’s medically important Big Four: Russell’s viper, saw-scaled viper, Indian cobra, common krait (polyvalent ASV targets these).^[1][2]
• Elapid (cobra/krait): neuromuscular paralysis — ptosis, ophthalmoplegia, dysphagia, respiratory failure; krait often nocturnal bite with minimal local signs.
• Viper: local pain/swelling/blistering/necrosis + venom-induced consumption coagulopathy (VICC) — bleeding, incoagulable blood; Russell’s may add neurotoxicity/rhabdo/AKI/capillary leak.
• Dry bites exist — observe, do not give ASV without evidence of envenoming unless high-risk context and evolving signs.

Q2: First aid and resuscitation (2 min)

• Reassure, immobilise limb in neutral position, remove rings/tight objects, rapid transport to hospital with ASV.
• Pressure-immobilisation may be considered for elapid neurotoxic bites in some systems; not a substitute for transport. Avoid tourniquets, cutting, suction, ice, electric shock, traditional herbs.
• ABC: early elective intubation if progressive bulbar/respiratory paralysis; oxygen; IV access; analgesia (avoid IM injections if coagulopathic).
• Tetanus status; no routine empirical antibiotics unless necrosis/infection.

Q3: 20WBCT and labs (2 min)

• 20-minute whole blood clotting test: 2 mL venous blood in clean dry glass tube; leave undisturbed 20 min; tip once — if liquid/not clotted = incoagulable (positive for VICC). Pitfalls: plastic tubes, disturbance, wrong timing, recently given ASV.
• Labs: PT/INR, aPTT, fibrinogen, D-dimer, CBC, U&E/creatinine, CK, urine (myoglobin/blood), ECG.
• Serial neurological observations and peak flow/spirometry if available for evolving paralysis.

Q4: Antivenom and adjuncts (3 min)

• Indications for ASV: systemic envenoming (neurotoxicity, coagulopathy/bleeding, shock, AKI, rhabdomyolysis) or severe local envenoming (rapid swelling, bite on digits with progressive necrosis risk — follow national protocol).
• Indian polyvalent ASV: dose is based on venom load, not weight — children receive the same ASV dose as adults; give IV infusion with adrenaline ready.
• Typical starting regimens follow national guidelines (e.g. 10 vials initial for many systemic bites — state local protocol); reassess 20WBCT and clinical syndrome; repeat if progression/persistent incoagulability per protocol.
• Anaphylaxis to ASV: stop infusion, IM adrenaline 0.5 mg (adult) / 0.01 mg/kg child, airway support, fluids; restart ASV cautiously when stable if still needed.
• Neostigmine + atropine trial may help post-synaptic cobra neurotoxicity; often ineffective in presynaptic krait venom — still prepare to ventilate.
• Supportive: ventilation, blood products only if bleeding with ASV (ASV is definitive for VICC), dialysis for AKI, surgical review for compartment syndrome after ASV and measured pressures — fasciotomy rare and never first-line.

Q5: Complications and special groups (1 min)

• Early: paralysis, haemorrhage, shock, anaphylaxis to ASV.
• Late: necrosis, infection, contractures, serum sickness (5–14 days), chronic pituitary insufficiency after Russell’s viper in some regions.
• Children: more severe mg/kg venom dose; same ASV vials; careful fluids.
• Pregnancy: give ASV if indicated; monitor fetus.

Key phrases examiners want

• "Big Four; polyvalent ASV same dose in children."
• "Twenty-minute whole blood clotting test for VICC."
• "Ventilate early in progressive neurotoxicity."
• "No tourniquet, no cutting, no delay to hospital."

References2ShowHide

1. [1]Gutiérrez JM, et al. Snakebite envenoming. Nat Rev Dis Primers, 2017.PMID 28980622
2. [2]Suraweera W, et al. Trends in snakebite deaths in India 2000–2019. eLife, 2020.PMID 32633232