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Snakebite ASV Protocol

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1. Initial Assessment

History

• Time of bite, snake description (color, size, hood/rattle)
• Symptoms onset: local vs. systemic

Examination — Identify Envenomation Syndrome

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2. Indications for ASV

Definite Indications:

• Haematotoxicity: 20-minute whole blood clotting test (20WBCT) positive; spontaneous bleeding (gum, IV site, hematuria); thrombocytopenia
• Neurotoxicity: Ptosis, ophthalmoplegia, dysarthria, dysphagia, respiratory distress
• Cardiovascular: Hypotension, shock, abnormal ECG
• Renal: Oliguria/anuria, rising creatinine
• Local envenomation (severe): Rapidly progressive swelling involving >50% of limb, necrosis, finger/toe bites with any swelling

Note: A dry bite (no envenomation) does NOT require ASV. Local swelling alone (without progression) is a relative indication.

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3. 20-Minute Whole Blood Clotting Test (20WBCT)

1. Place 2 mL fresh blood in a clean, dry glass tube
2. Leave undisturbed for 20 minutes at room temperature
3. Normal: Blood clots (tube can be tilted/inverted without spillage)
4. Abnormal (Venom-Induced Consumption Coagulopathy, VICC): Blood remains liquid → ASV indicated
5. Repeat every 6 hours during monitoring

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4. ASV Administration

Antivenom Type

• India: Polyvalent ASV — covers Big Four: Russell's viper, Saw-scaled viper, Common krait, Indian cobra
• Produced from horse serum (IgG/F(ab')₂ fragments)
• Monospecific ASV if offending species clearly identified (Harrison's, p. 13049)

Route

• IV only (intramuscular is NOT recommended — unreliable absorption)

Preparation

• Dilute ASV in 100–250 mL normal saline (0.9% NS)

Dosing

• Infuse slowly over 30–60 minutes (first 10–15 min at slow rate, monitoring for reactions)
• Repeat dose: Give additional 10 vials if:
  • No clinical improvement after 1–2 hours
  • 20WBCT still positive at 6 hours
  • Neurotoxic signs progress

There is no maximum total dose — give as many vials as needed to achieve clinical neutralization.

Pediatric Dosing

• Same dose as adults (venom dose is independent of patient body weight)

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5. Pre-medication (Controversial)

WHO 2010 does not routinely recommend prophylaxis due to lack of evidence; have adrenaline drawn up and ready at all times.

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6. Monitoring for Antivenom Reactions

Early Anaphylactic Reaction (within 10–180 min)

• Urticaria, pruritus, fever, hypotension, bronchospasm
• Action: Stop ASV infusion → Adrenaline 0.5 mg IM → Antihistamine + hydrocortisone IV → Resume at slower rate once stabilized

Pyrogenic Reaction (within 1–2 hours)

• Fever, chills, rigors
• Action: Paracetamol; cool with tepid sponging

Serum Sickness (5–14 days later)

• Fever, rash, arthralgia, lymphadenopathy
• Action: Oral prednisolone 5 mg every 6 hours × 5–7 days; antihistamines

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7. Adjunct Management

Neurotoxic Bites (Krait/Cobra)

• Neostigmine test: 1.5–2 mg neostigmine IM + 0.6 mg atropine IV — if improvement in ptosis within 30 min → continue neostigmine 0.5 mg every 30 min
• Monitor respiratory rate, SpO₂; early intubation if VC <15 mL/kg or SpO₂ falling
• Mechanical ventilation may be needed for days to weeks (krait bites)

Haemotoxic Bites

• Fresh frozen plasma (FFP) or fresh whole blood if bleeding uncontrolled and ASV already given
• Do NOT give FFP before ASV — it will be consumed by ongoing coagulopathy
• Platelet transfusion only if active bleeding + severe thrombocytopenia

Local Wound Care

• Clean with antiseptic; immobilize and keep below heart level
• Tetanus prophylaxis
• Antibiotics (amoxicillin-clavulanate or ciprofloxacin) only if signs of secondary infection
• Fasciotomy: Only if confirmed compartment syndrome (not just swelling); measure compartment pressure >30 mmHg

Renal Failure

• IV fluids to maintain urine output >0.5 mL/kg/hr
• Dialysis if oliguria persists despite ASV and fluids

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8. Monitoring Schedule

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9. What NOT to Do

• ❌ Tourniquet (causes ischemia, worsens necrosis)
• ❌ Incision and suction of bite site
• ❌ Ice application
• ❌ Electric shock therapy
• ❌ Pressure immobilization for cytotoxic/hemotoxic bites
• ❌ Intramuscular ASV
• ❌ ASV without confirmed envenomation

Pressure immobilization bandage is appropriate ONLY for neurotoxic bites (krait, cobra, sea snake) where local effects are minimal.

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10. Discharge Criteria

• 20WBCT normal on ≥2 consecutive tests
• No neurotoxic signs for 24 hours
• Urine output normal, creatinine trending down
• Local swelling stable/decreasing
• Minimum observation: 24 hours after last ASV dose

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Betahistine (Vertin) in Pregnancy

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Safety Classification

• Betahistine is not assigned an FDA pregnancy category (it is not approved by the US FDA; widely used in Europe, India, and other countries).
• There are no adequate, well-controlled studies in pregnant women.
• Animal studies have shown some adverse reproductive effects at high doses, but human data are very limited.

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Key Concerns

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Trimester-Specific Guidance

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Safer Alternatives for Vertigo in Pregnancy

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Bottom Line

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Organophosphorus (OP) Poisoning

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1. Mechanism

• Muscarinic receptors (parasympathetic — smooth muscle, glands, heart)
• Nicotinic receptors (neuromuscular junction, autonomic ganglia)
• CNS receptors

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2. Clinical Features — "SLUDGE" + "DUMBELS"

Muscarinic (SLUDGE / DUMBELS)

Nicotinic (Neuromuscular Junction)

CNS

• Anxiety, restlessness, seizures
• Coma
• Central respiratory depression

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3. Intermediate Syndrome

• Occurs 24–96 hours after apparent recovery
• Proximal limb weakness, neck flexor weakness, cranial nerve palsies, respiratory failure
• Not prevented by pralidoxime
• Requires ventilatory support

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4. Delayed Polyneuropathy (OPIDN)

• Develops 2–3 weeks after exposure
• Distal sensorimotor neuropathy
• Associated with specific compounds (triorthocresyl phosphate)

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5. Diagnosis

Clinical

• History of exposure + SLUDGE features + miosis = high suspicion

Investigations

Cholinesterase levels confirm diagnosis but do not determine treatment — treat clinically.

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6. Management

A. Decontamination (First Priority)

• Remove clothing (prevents ongoing dermal absorption)
• Wash skin and hair with soap and water (staff must wear gloves — secondary contamination risk)
• Eye irrigation with NS if ocular exposure
• Gastric lavage if oral ingestion within 1 hour + airway protected
• Activated charcoal: 1 g/kg if airway secure and within 1–2 hours of ingestion

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B. Airway & Breathing

• Oxygen — high flow immediately
• Early intubation if:
  • GCS <8
  • Excessive secretions uncontrolled
  • Respiratory muscle paralysis
  • SpO₂ not maintaining
• Suction secretions aggressively before intubation
• Avoid succinylcholine (hydrolyzed by pseudocholinesterase — prolonged paralysis); use rocuronium instead

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C. Atropine — Antidote (Muscarinic Block)

Dosing Protocol:

Endpoint of Atropinization (target signs):

• ✅ Secretions dry (bronchorrhea resolved)
• ✅ Chest clear (no wheeze/crackles)
• ✅ HR >80 bpm
• ✅ Systolic BP >80 mmHg

❌ Do NOT use pupil dilation or dry skin as endpoints — unreliable in OP poisoning.

Atropine Infusion (after loading):

• 10–20% of total loading dose per hour IV infusion
• Titrate up/down based on secretions

Massive doses of atropine may be needed — 100–1000 mg in severe cases over 24 hours. Do not under-dose out of fear of toxicity.

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D. Pralidoxime (2-PAM / P2AM) — Oxime (Nicotinic + Regenerates AChE)

Controversy: WHO and some guidelines question pralidoxime efficacy based on RCT data (Eddleston 2009). Despite this, it is still widely used in most national protocols — give atropine first and never delay atropine for pralidoxime.

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E. Benzodiazepines (Seizures)

• Diazepam 5–10 mg IV (adult) for seizures or agitation
• Repeat as needed; phenytoin is ineffective for OP seizures

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7. Monitoring

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8. Summary Algorithm

Exposure confirmed/suspected
        ↓
Decontaminate + O₂ + IV access
        ↓
Atropine 2–4 mg IV → repeat/double q5–10 min
        → Goal: dry chest, clear secretions
        ↓
Pralidoxime 1–2 g IV over 15–30 min (if <48h)
        ↓
Intubate if airway compromised (use rocuronium)
        ↓
Diazepam for seizures
        ↓
Atropine infusion + ICU monitoring
        ↓
Watch for Intermediate Syndrome (day 1–4)

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9. What NOT to Do

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