Snake Bite: Complete Clinical Overview

Epidemiology

Major Venomous Snakes by Region

• 22nd Edition Pye's Surgical Handicraft, p.428

Venom Composition and Mechanisms

1. Neurotoxic venoms (Elapidae - cobras, kraits, mambas; sea snakes):
   • Phospholipase A2 neurotoxins block neuromuscular transmission
   • Pre-synaptic: prevent acetylcholine release from nerve terminals
   • Post-synaptic: block acetylcholine receptors
   • Cause: ptosis, diplopia, dysphagia, respiratory paralysis
2. Cytolytic/Haemotoxic venoms (Viperidae - vipers, rattlesnakes):
   • Rich in proteases and procoagulant enzymes
   • Cause: tissue destruction, haemolysis, endothelial damage, coagulopathy
   • Local swelling, necrosis, haemorrhage, DIC

Note: Some elapid venoms also have procoagulant activity; some Viperidae contain neurotoxic phospholipase A2 - overlap exists.

• 22nd Edition Pye's Surgical Handicraft, p.430

Clinical Features

Important fact: 1/3 to 1/2 of bites by venomous snakes show no envenoming (dry bites). Many presenting symptoms are from anxiety or harmful first-aid.

Local Features

• Viperidae / cytolytic bites: Immediate pain, increasing throbbing, local swelling (within minutes to 2 hours), skin necrosis, blistering, tender lymphadenopathy
• Elapidae / neurotoxic bites (kraits, sea snakes, coral snakes): Virtually painless bite, minimal or no local swelling

Systemic Features

Early Clues to Severe Envenoming

• Snake identified as a very dangerous species
• Rapid early extension of local swelling
• Early tender lymph node enlargement
• Early systemic symptoms: collapse, nausea, vomiting, drowsiness, ptosis
• Early spontaneous systemic bleeding
• Passage of dark brown/black urine (haemoglobinuria/myoglobinuria)
• Park's Textbook of Preventive and Social Medicine, p.465-466

Diagnosis

• 20-minute Whole Blood Clotting Test (20WBCT): Place a few mL of venous blood in a clean dry glass tube and wait 20 minutes. Failure to clot = defibrination syndrome (viper envenomation)
• Urine examination: Presence of blood/myoglobin = severe systemic envenomation
• CBC, coagulation screen (PT, aPTT, fibrinogen, D-dimers)
• Renal function tests (urea, creatinine)
• Identify snake if safely possible (photograph)

Management

First Aid (Community Level - India's National Snake Bite Protocol 2007)

1. Reassure the patient - 70% of bites are from non-venomous species; only 50% of bites by venomous species actually envenomate
2. Immobilize the bitten limb like a fractured limb (splint + loose bandage)
3. Remove constrictive items (rings, watches, tight clothing) from the bitten limb
4. Transport urgently to a medical facility

• Apply tight tourniquets or constricting bands (dangerous - do not work for most bites)
• Incise, excise, cauterize, or apply ice to the bite site
• Give alcohol or stimulants (vasodilators speed venom absorption)
• Apply herbal remedies, electric shocks, or chemicals
• Apply suction

Exception for neurotoxic elapid/sea snake bites only: Where respiratory paralysis risk is high before reaching hospital, a pressure immobilization bandage (or arterial tourniquet) may be used - released 1 min every 30 min, max 2 hours total - solely to buy time until ventilation is available.

Hospital Management

• Paracetamol (adults 500mg-1g up to 4g/day; children 10-15 mg/kg)
• Codeine phosphate if needed
• Avoid aspirin and NSAIDs (increase bleeding risk)

Antivenom - The Definitive Treatment

• Evidence of systemic envenomation: coagulopathy, bleeding, neurotoxicity, shock, haemoglobinuria
• Severe local envenomation: rapidly extending swelling beyond the wrist/ankle

• Given IV (preferred) or IM
• Specific polyvalent or monospecific antivenom depending on region/species
• Observe for anaphylaxis - have adrenaline (epinephrine) ready IM
• Repeat doses if features persist or progress
• Early antivenom is more effective; late antivenom can still reverse coagulopathy

• Reverse established local necrosis
• Reliably reverse neurotoxicity (especially pre-synaptic)

Neurotoxic Envenomation

• Neostigmine + atropine can reverse post-synaptic neuromuscular blockade (cobra bites) - try neostigmine 0.02 mg/kg SC/IM with atropine 0.5 mg IV
• Mechanical ventilation may be required for respiratory paralysis

Haemotoxic Envenomation

• Cautious IV fluids for hypotension (250-500 mL 0.9% saline)
• Fresh frozen plasma/whole blood for coagulopathy if antivenom is unavailable or fails

Renal Failure

• Maintain urine output, avoid nephrotoxic drugs
• Dialysis if oliguric acute kidney injury develops

Complications

• 22nd Edition Pye's Surgical Handicraft, p.433-434

Prevention

• Wear protective footwear in fields/forests
• Avoid walking barefoot at night
• Use torches at night in endemic areas
• Sleep above ground on raised beds
• Clear vegetation and debris around homes
• Community education on first aid (especially what NOT to do)
• Ensure antivenom availability in rural health facilities

Recent Evidence (2025-2026)

• A systematic review (PMID 40691949, Toxicon, 2025) on outcomes in high-incidence Asian countries highlights that antivenom availability and timely access remain the primary determinant of survival.
• A 2026 pediatric review in Sub-Saharan Africa (PMID 41712625) identified that children face higher mortality per bite and significant care gaps.
• NSW Health GL2024_007 (2024) emphasizes early consultation with a clinical toxicologist and early antivenom for any signs of envenomation.