ICU Management of Snakebite Poisoning

Introduction

Classification of Medically Important Snakes

Pathophysiology of Venom

Neurotoxins

• Post-synaptic (alpha-bungarotoxin type): Competitive antagonism at nicotinic ACh receptors (cobra, sea snake) — potentially reversible with antivenom + neostigmine
• Pre-synaptic (beta-bungarotoxin type): Destroy nerve terminal vesicles, block ACh release (krait, taipan) — poor response to antivenom or neostigmine; effects may persist >48 h

Haemotoxins / Coagulotoxins

• Procoagulant enzymes (e.g., thrombin-like enzymes) → Venom-Induced Consumption Coagulopathy (VICC) or DIC
• Fibrinogenolysis, thrombocytopenia, platelet dysfunction
• Russell's viper activates Factor X and prothrombin → consumptive coagulopathy + spontaneous haemorrhage

Cytotoxins / Myotoxins

• Phospholipase A₂ destroys cell membranes → local and systemic rhabdomyolysis
• Hyaluronidase spreads venom through tissues
• Proteases cause local necrosis, compartment syndrome

Cardiotoxins

• Direct myocardial depression (Naja spp.)
• Autonomic dysregulation: hypotension, bradycardia, arrhythmias

ICU Admission Criteria

1. Evidence of neurotoxicity (ptosis, respiratory compromise)
2. Systemic envenomation: coagulopathy, haematuria, haemoglobinuria, spontaneous bleeding
3. Haemodynamic instability (hypotension, shock)
4. Signs of rhabdomyolysis / myoglobinuria
5. Renal impairment or oliguria
6. Cardiac arrhythmias or ECG changes
7. Local envenomation with rapid progression, bullae, or compartment syndrome signs
8. Need for antivenom infusion (mandatory ICU/ED monitoring)

Initial Assessment and Monitoring

History

• Time of bite, snake description (photograph if safe)
• First aid measures applied (tourniquets, incision, suction — discourage harmful practices)
• Pre-existing conditions, medications (anticoagulants)

Physical Examination — Systematic

• Fang marks: number, site, depth, local swelling measurement (circumference q1-2h)
• Neurotoxicity screen: ptosis test (sustained upgaze for 30 sec), pupillary reflexes, gag reflex, grip strength, forced vital capacity (FVC) — if FVC <15 mL/kg → intubate
• Coagulopathy screen: spontaneous bleeding from gums, venepuncture sites, haematuria
• 20-minute whole blood clotting test (20WBCT): place 2 mL fresh blood in clean glass tube, leave undisturbed at room temperature for 20 min. If blood is unclotted → systemic envenomation confirmed

ICU Monitoring

• Continuous ECG, SpO₂, ETCO₂ (if ventilated)
• Arterial line for IBP and serial ABG
• Central venous access for antivenom infusion + CVP monitoring
• Urinary catheter: hourly urine output, colour (haemoglobinuria, myoglobinuria)
• Serial limb circumference measurements (q1-2h for viper bites)
• Compartment pressure monitoring if indicated

Laboratory Investigations

Antivenom Therapy — The Cornerstone of Treatment

Types

• Monovalent antivenom: species-specific (higher efficacy, less cross-reactivity)
• Polyvalent antivenom (VINS, Bharat Serum): covers multiple species; standard in India and Africa

Indications

1. Neurotoxicity (ptosis, respiratory weakness)
2. Haemodynamic instability
3. Spontaneous systemic bleeding
4. Coagulopathy (prolonged PT/aPTT, positive 20WBCT, fibrinogen <1 g/L)
5. Thrombocytopenia (<100,000/μL)
6. Haemoglobinuria / myoglobinuria
7. AKI with oliguria
8. ECG/cardiac abnormality
9. Local swelling crossing >2 joints, crossing half the bitten limb within 48h

Note: Pregnancy is NOT a contraindication to antivenom therapy.

Contraindications

• No absolute contraindications when life-threatening envenomation is present
• Relative: known horse protein allergy, prior antivenom reaction → premedicate

Pre-treatment

• Epinephrine (adrenaline) 1:1000, 0.5 mL SC drawn up and ready at bedside
• Optional premedication: IV promethazine 25 mg + SC adrenaline (controversial but common in India)
• Hydrocortisone 200 mg IV (debated benefit for anaphylaxis prevention)

Dosing and Administration

• Initial dose: 10 vials (India, polyvalent) or per manufacturer protocol
• Reconstitution: dilute each vial in 250–500 mL normal saline
• Infusion: start slowly at 1–2 mL/min for first 10 minutes; if no reaction, increase to 2–4 mL/min; complete infusion over 1 hour
• Children receive the same dose as adults (venom load is the same; dilute in smaller volume)
• Route: IV only — never IM; never inject directly into digit

Monitoring During Infusion

• Observe for anaphylaxis: urticaria, bronchospasm, hypotension, angioedema
• If reaction: stop infusion immediately → adrenaline IV/IM → antihistamines → steroids → restart at slower rate after stabilisation

Endpoint/Reassessment

• Haemotoxic: fibrinogen should begin recovering within 6h; repeat 20WBCT at 6h
• Neurotoxic: FVC, ptosis, gag reflex; neostigmine challenge (see below)
• Additional antivenom doses: if signs of envenomation persist/recur at 6h → repeat initial dose
• Monitor for "late recurrence" of coagulopathy (redistribution of venom from tissues) — reassess at 3, 6, 12, 24h

Airway and Ventilatory Management

Indications for Intubation (act early, do not delay)

• FVC <15 mL/kg or <1 litre
• SpO₂ <95% on room air
• Accessory muscle use, paradoxical breathing
• Inability to swallow secretions / absent gag reflex
• PaO₂ <60 mmHg or PaCO₂ >50 mmHg on ABG
• Clinically progressing ptosis → presumptive early intubation in krait bite

RSI Considerations

• Succinylcholine: AVOID in established rhabdomyolysis (risk of hyperkalaemic arrest); use rocuronium 1.2 mg/kg + sugammadex reversal available
• Pre-oxygenation is critical as patients may desaturate rapidly
• Awake fibreoptic intubation if oropharyngeal oedema (cobra bite to face/neck)
• Have cricothyroidotomy kit ready for angioedema cases

Ventilation Strategy

• Protective lung ventilation: Vt 6–8 mL/kg IBW, PEEP 5–8 cmH₂O
• Target SpO₂ >94%, PaO₂ 60–80 mmHg
• Weaning: begin once ptosis resolves, FVC >15 mL/kg, NIF > -25 cmH₂O
• Krait envenomation: ventilation often required for >72 hours; NEVER rush extubation

Neostigmine Challenge (Post-synaptic neurotoxicity — cobra)

• Neostigmine 0.04 mg/kg IV + atropine 0.02 mg/kg IV
• Improvement in ptosis/ventilation within 20–30 min → continue neostigmine infusion (0.04–0.08 mg/kg/h)
• No response → pre-synaptic toxin (krait) → continue ventilatory support only

Haemodynamic Management

Mechanism of Hypotension

1. Hypovolaemia: increased vascular permeability, third-spacing, bleeding
2. Direct vasodilation (viper venoms)
3. Anaphylaxis (venom or antivenom)
4. Cardiac toxicity (direct myocardial depression)

Management

• Fluid resuscitation: crystalloids (normal saline or balanced crystalloid) — target MAP >65 mmHg, UO >0.5 mL/kg/h
• Vasopressors: noradrenaline first-line if fluid-refractory shock (target MAP 65–70 mmHg)
• If anaphylactic shock: adrenaline 0.3–0.5 mg IM (anterolateral thigh) + IV fluids + antihistamines
• Inotropes: dobutamine if myocardial depression with cardiogenic component
• Avoid excessive fluids in context of acute kidney injury or DIC

Coagulopathy Management

Approach to VICC/DIC

1. Antivenom first — the primary treatment; do not wait for coagulopathy to worsen
2. Fresh Frozen Plasma (FFP): 10–15 mL/kg; restores clotting factors; but venom continues to consume factors if antivenom not given
3. Cryoprecipitate: fibrinogen <1 g/L → 10 units cryoprecipitate (raises fibrinogen by ~1 g/L)
4. Platelet transfusion: only for active bleeding + platelets <50,000/μL
5. Packed RBCs: if Hb <7 g/dL or haemodynamic instability
6. Vitamin K: if hepatotoxicity-associated coagulopathy
7. Avoid heparin: worsens bleeding risk; no role in VICC

Key principle: FFP and blood products are a temporising measure — antivenom is the definitive therapy. Fibrinogen recovery post-antivenom lags behind clotting factor recovery (may take 24–48h).

Renal Management (Acute Kidney Injury)

Mechanisms

• Direct nephrotoxicity of venom (tubular necrosis)
• Haemoglobinuria (intravascular haemolysis)
• Myoglobinuria (rhabdomyolysis)
• Hypotension → ischaemic ATN
• DIC → renal microthrombosis
• Bilateral cortical necrosis (Russell's viper — irreversible)

Prevention and Management

• Maintain euvolaemia: hourly urine output target >1 mL/kg/h (higher if myoglobinuria)
• Urine alkalinisation: NaHCO₃ infusion to maintain urine pH >6.5 (reduces myoglobin cast formation)
• Avoid nephrotoxins: NSAIDs, aminoglycosides, contrast
• Renal replacement therapy (RRT):
  • Haemodialysis or CVVHDF for oliguria/anuria unresponsive to fluids, hyperkalaemia, acidosis, volume overload
  • Early RRT in Russell's viper bite with established AKI
  • Some patients require chronic dialysis if cortical necrosis occurs

Wound and Local Complication Management

Grading of Local Envenomation

• Grade 0 (Dry bite): No envenomation, pain only
• Grade 1 (Minimal): Local swelling/ecchymosis, no systemic effects
• Grade 2 (Moderate): Swelling >2 joints, mild systemic effects
• Grade 3 (Severe): Systemic involvement, compartment syndrome risk

Wound Care

• Keep limb elevated at heart level (do NOT elevate above heart in severe cases → decreases perfusion)
• Immobilise with splint; remove constricting jewellery/clothing
• Mark swelling margins with pen + time every 1–2 hours
• Tetanus toxoid if not vaccinated
• Antibiotics: only if signs of secondary infection; prophylactic antibiotics NOT recommended routinely

Compartment Syndrome

1. Measure intracompartmental pressure (normal <10 mmHg; fasciotomy threshold >30 mmHg OR >20 mmHg persistent with symptoms)
2. If elevated: elevate limb + mannitol 1–2 g/kg IV over 30 min + additional antivenom simultaneously
3. Reassess after 60 minutes
4. Fasciotomy ONLY if compartment pressure remains elevated despite antivenom + mannitol; snakebite fasciotomy has high complication rate — reserve for true refractory cases
5. Debridement of necrotic tissue: defer to >72–96h when demarcation is clear

Systemic Complications and Management Summary

Measures NOT Recommended (Harmful)

• Tourniquet — causes ischaemic necrosis, worsens local toxicity
• Incision and suction — increases infection risk, minimal venom removal
• Electric shock therapy — no benefit
• Ice application / cryotherapy — worsens local ischaemia
• Oral potassium permanganate — harmful
• Arterial tourniquet for >30 minutes — limb-threatening
• Pressure immobilisation bandage — ONLY for elapid bites (neurotoxic); contraindicated for vipers as it worsens local tissue necrosis

Specific Antidote: Neostigmine Protocol (Cobra Bites — Post-synaptic Neurotoxin)

Disposition and Duration of ICU Stay

• Off mechanical ventilation (if was intubated)
• No spontaneous bleeding; coagulation normalised
• Stable renal function with adequate urine output
• No active infection
• Able to swallow and protect airway

Summary Flow — ICU Management Algorithm

SNAKEBITE → SECURE IV ACCESS + OXYGEN
         ↓
IDENTIFY SNAKE / SYNDROME
(Neurotoxic vs. Haemotoxic vs. Cytotoxic)
         ↓
BASELINE LABS + 20WBCT + FVC
         ↓
ANTIVENOM: Indicated? → YES → Premedicate → Infuse under observation
                      → NO → Watch 8-24h (dry bite possible)
         ↓
AIRWAY: FVC <15 mL/kg → RSI (avoid succinylcholine if myolysis) → Ventilate
         ↓
HAEMODYNAMICS: Crystalloids → Vasopressors → Inotropes
         ↓
COAGULOPATHY: FFP + Cryoprecipitate + Platelets (AFTER antivenom)
         ↓
RENAL: Hydration + Alkalinisation + RRT if oliguric AKI
         ↓
WOUND: Elevation + Splint + Compartment pressure monitoring
         ↓
SERIAL REASSESSMENT q6h: Repeat antivenom if envenomation recurs

Key Points for MD Anaesthesia Exam

1. Antivenom is the only specific treatment — all supportive care is adjunctive
2. 20WBCT is the most practical bedside test for coagulopathy in resource-limited settings
3. FVC <15 mL/kg is the threshold for intubation in neurotoxic bites — do not wait for cyanosis
4. Succinylcholine is relatively contraindicated in established rhabdomyolysis — use rocuronium
5. Neostigmine is useful only for post-synaptic neurotoxins (cobra); krait bites (pre-synaptic) do NOT respond
6. Pressure immobilisation bandage — ONLY for elapids; harmful in viper bites
7. Fasciotomy is a last resort in compartment syndrome — antivenom + mannitol first
8. Russell's viper is the most common cause of renal failure and DIC from snakebite in India
9. Antivenom dose in children = adults (same dose, smaller volume diluent)
10. Late recurrence of coagulopathy can occur 24–48h after apparent correction — continue monitoring