History Taking in a Case of Snake Bite

1. Presenting Complaint

• Snake bite / swelling at bite site / pain / neurological symptoms

2. History of Presenting Illness (HPI)

A. Circumstances of the Bite

• When did the bite occur? (Time of bite - crucial for antivenom timing)
• Where did it happen? (Field, home, jungle, water - helps identify likely snake species)
• How did it happen? (Accidental, while sleeping, while working, provoked bite)
• Body part bitten? (Lower limb, hand - assess risk of deep envenomation)
• Was the patient barefoot or wearing protective footwear?
• Any previous snake bites?

B. Snake Identification

• Did the patient see the snake? Can they describe it?
  • Color, size, markings, hood, rattle, shape of head
• Was the snake killed/brought to the hospital? (Do NOT encourage bringing live snakes)
• Was a photo taken safely?
• Single or multiple bites?

C. First Aid Given Before Arrival

• Was a tourniquet applied? (Where, how tight, how long - risk of ischemia)
• Was the bite site incised or sucked?
• Any traditional remedies applied? (Herbs, tourniquets, cuts - can cause misleading signs)
• Any medications given en route?
• Time elapsed since bite to hospital arrival

3. Symptom Enquiry - Local Features (at bite site)

• Pain at bite site: onset, severity, progression
• Swelling: when did it start, how rapidly is it spreading?
• Blistering or skin changes at the site
• Bleeding from the wound

4. Symptom Enquiry - Systemic Features

Haematotoxic Envenomation (Vipers - Russell's viper, Saw-scaled viper)

• Bleeding from gums (gingival bleeding - earliest sign)
• Bleeding from nose, skin (petechiae/ecchymoses)
• Blood in urine (haematuria)
• Haemoptysis, haematemesis
• Passing dark/red stools

Neurotoxic Envenomation (Elapids - Cobra, Krait, Sea snake)

• Ptosis (drooping of eyelids - earliest sign of paralysis)
• Diplopia, blurred vision
• Difficulty swallowing (dysphagia)
• Difficulty speaking (dysphonia, dysarthria)
• Breathlessness - respiratory muscle weakness
• Numbness or tingling around mouth

General Systemic Symptoms

• Nausea and vomiting (common early in many envenomations)
• Dizziness or fainting (syncope - especially after viper bite)
• Abdominal pain / colic / diarrhoea
• Headache
• Altered sensorium / loss of consciousness
• Muscle pain/stiffness (suggests rhabdomyolysis - sea snake, Russell's viper)
• Dark urine (myoglobinuria or haemoglobinuria)
• Oliguria/anuria (acute kidney injury - Russell's viper)

Eyes

• Spit in eyes? (spitting cobras - causes severe eye pain, chemosis)

5. Past History

• Previous snake bite? (Risk of anaphylaxis to antivenom if previously treated)
• Bleeding disorders, liver disease, anticoagulant use (worsens coagulopathy)
• Known allergies (especially to horse serum - antivenom reaction risk)
• Tetanus immunization status

6. Drug History

• Anticoagulants (warfarin, aspirin - worsen bleeding)
• Any drugs given at local/primary centre before arrival

7. Personal and Social History

• Occupation (farmer, rubber tapper, hunter - determines exposure risk)
• Alcohol intake (may mask neurological symptoms)
• Socioeconomic status and access to care (delay in presentation)

Key Points to Remember in Short Case Presentation

"The history must establish the time and circumstances of the bite, identification of the snake, and the progression of symptoms."

• 22nd Edition Pye's Surgical Handicraft

"Key points of the history include time, place, and circumstances of the bite; whether bitten once or multiple times; description of the offending animal; type and timing of first aid; type and time of onset of symptoms; relevant past medical history; and any medications used."

• Goldman-Cecil Medicine, International Edition

Quick Mnemonic for Symptom Enquiry

• S - Site and swelling (local features)
• N - Neurotoxic symptoms (ptosis, diplopia, dysphagia, dyspnoea)
• A - Anti-haemostatic features (bleeding gums, haematuria, skin bleeds)
• P - Prior first aid and past history

Summary Table: Symptoms by Snake Type

Viva Questions - Snake Bite

Q1. What are the "Big Four" venomous snakes of India?

1. Russell's viper (Daboia russelii) - haemotoxic + neurotoxic
2. Indian cobra (Naja naja) - neurotoxic + cytotoxic
3. Indian krait (Bungarus caeruleus) - neurotoxic
4. Saw-scaled viper (Echis carinatus) - haemotoxic

Q2. Classify snake venoms. What are their effects?

Q3. What is the earliest sign of neurotoxic envenomation?

• Ask the patient to look upward - failure of full lid retraction = ptosis
• Progresses to: diplopia → dysphagia → dysarthria → respiratory paralysis

Q4. What is the earliest sign of haemotoxic envenomation?

• Also look for: epistaxis, petechiae, ecchymosis, haematuria, haemoptysis

Q5. What is the 20-minute Whole Blood Clotting Test (20WBCT)? What is its significance?

• Place 2-3 ml of fresh venous blood in a clean, dry glass tube
• Leave undisturbed at room temperature for 20 minutes
• Normal: blood clots within 20 minutes
• Abnormal (positive test): blood remains unclotted = defibrination = systemic haemotoxic envenomation
• Indicates: antivenom is needed
• Repeat every 6 hours to monitor response to antivenom
• Simple bedside test - no lab equipment needed

Q6. What are the indications for antivenom?

• Hypotension / shock / cardiovascular toxicity
• Neurotoxicity (ptosis, paralysis)
• Rhabdomyolysis
• Impaired consciousness
• Spontaneous systemic bleeding
• Non-clotting blood (positive 20WBCT)
• Acidosis, WBC >20,000/µL, elevated enzymes

• Known necrotic venom species
• Swelling involving more than half the bitten limb
• Rapid progression of swelling
• Bites on digits or tight fascial compartments

Remember: Antivenom is NOT indicated for dry bites or mild local reaction alone.

Q7. What is the dose and route of antivenom? Do children need less?

• Route: Slow intravenous injection or infusion (NOT intramuscular)
• Initial dose: minimum 5 vials × 10 ml = 50 ml (varies by manufacturer)
• Children need the SAME dose as adults (because the amount of venom injected is the same regardless of body weight)
• Repeat within 1 hour if life-threatening signs persist
• For procoagulant venoms: repeat every 6 hours until coagulability restored

Q8. What are the types of antivenom reactions and how are they managed?

Skin/conjunctival sensitivity tests are of no predictive value - do NOT perform them.

Q9. What first aid measures are recommended and what should be AVOIDED?

1. Reassure the patient
2. Immobilize the bitten limb with splint/sling (reduces venom spread)
3. Transfer to hospital quickly and passively

• Incisions, excisions, cauterizations, amputations
• Application of ice packs
• Electric shocks
• Herbal/traditional remedies
• Tight tourniquets (EXCEPT for identified dangerously neurotoxic elapid - to delay respiratory paralysis during transport)

Q10. What is "dry bite"?

Q11. How does krait bite present differently from cobra bite?

Krait venom acts presynaptically (b-bungarotoxin) - harder to reverse with antivenom. Cobra venom acts postsynaptically (a-neurotoxin) - more responsive to antivenom.

Q12. What complications can Russell's viper cause?

• Coagulopathy / DIC - defibrination, bleeding
• Acute Kidney Injury (AKI) - most common cause of AKI from snakebite
• Neurotoxicity - bilateral ptosis, ophthalmoplegia
• Rhabdomyolysis - myalgia, myoglobinuria
• Pituitary infarction (Sheehan-like syndrome) - rare, delayed
• Hypotension/Shock

Q13. What is the mechanism of renal failure in snake bite?

• Haemoglobinuria (haemolysis) and myoglobinuria (rhabdomyolysis) → tubular obstruction and toxicity
• Defibrination/DIC → glomerular fibrin deposition
• Direct nephrotoxicity of venom
• Hypotension → renal ischaemia
• Most common with Russell's viper and sea snakes

Q14. What monitoring is done for a snake bite patient?

• Frequent assessment of new symptoms and signs
• Level of consciousness
• Ptosis (for neurotoxic progression)
• Pulse rate and rhythm, blood pressure
• Respiratory rate and ventilatory capacity (peak expiratory flow / vital capacity)
• Progression of local swelling (mark with pen)
• Urine output and colour
• 20WBCT every 6 hours
• Observation for at least 24 hours

Q15. What is polyvalent vs monovalent antivenom?

• Polyvalent (polyspecific): covers multiple venomous species of a geographical region - used when species is unknown
• Monovalent (monospecific): effective against one specific snake species - used when species is positively identified
• Children require the same dose as adults
• Effective only against venoms listed on the ampoule