Treatment of Snake Bite

Overview

Step 1 - Severity Assessment

• Snake identified as highly dangerous
• Rapid spread of local swelling from the bite site
• Early tender enlargement of regional lymph nodes
• Early systemic symptoms: collapse, hypotension/shock, nausea, vomiting, diarrhea, severe headache, drowsiness, ptosis/ophthalmoplegia
• Spontaneous systemic bleeding
• Dark brown/black urine (myoglobinuria)

Step 2 - First Aid (Prehospital)

1. Reassure the patient - most bites do not result in significant envenomation
2. Immobilize the bitten limb as you would a fracture - use splints with bandages, but do NOT apply pressure bandaging or tight tourniquets (they do not work and are dangerous)
3. Remove constrictive items - rings, bracelets, watches, footwear - before swelling develops
4. Do NOT incise or manipulate the bite site
5. Do NOT apply ice to the bite site
6. Do NOT give alcohol or stimulants (vasodilators that accelerate venom absorption)
7. Transport immediately to the nearest medical facility

Step 3 - Hospital Evaluation

• History (snake identification if possible, time of bite, first-aid given)
• Local assessment: swelling progression marked with pen and timed (Fig. 44.5 in Sabiston), ecchymosis, blistering, necrosis
• Systemic: BP, pulse, respiratory rate, level of consciousness, ptosis
• 20-Minute Whole Blood Clotting Test (20WBCT) - place 2 mL of fresh venous blood in a clean glass tube; if not clotted in 20 minutes, coagulopathy is present
• Urine: color (myoglobinuria/hemoglobinuria), dipstick
• ECG or continuous cardiac monitoring in severe cases
• Coagulation profile (PT, APTT, fibrinogen, D-dimer)
• FBC, renal function, electrolytes
• Tetanus toxoid - administer to all patients

Step 4 - Antivenom (Definitive Treatment)

Indications for antivenom:

• Systemic envenomation signs: coagulopathy (positive 20WBCT), spontaneous bleeding, shock, neurotoxicity (ptosis, respiratory muscle weakness)
• Rapid local progression: cranial advancement of ecchymosis >10 cm/hour
• Dark urine (myoglobinuria/hemoglobinuria)
• Any life-threatening symptom

Contraindications:

• No absolute contraindication when life-threatening envenomation is present
• Known hypersensitivity to horse/sheep products - use with caution; have epinephrine ready

Dosing principles:

• Dose is not based on body weight - it is based on the amount of venom injected (the same dose is used in children as in adults)
• In North America (Crotalid bites): 4-6 vials of CroFab (Crotalidae Polyvalent Immune Fab [Ovine]) for life-threatening symptoms initially
• In India/Asia: initial 20-100 mL of polyvalent antivenom, followed by repeated doses of 25-50 mL every 4-6 hours until systemic envenomation signs resolve
• Monitor coagulation; it is typically restored within 6 hours of an adequate dose
• Continue coagulation monitoring for at least 3 more days after apparent resolution (delayed venom absorption can cause recurrence)

Available products in North America (Sabiston):

• CroFab (Crotalidae Polyvalent Immune Fab [Ovine]) - Fab fragments, half-life ~15 hours; cost ~$3,200/vial (2023)
• ANAVIP (Crotalidae Immune F[ab']2 [Equine]) - F(ab')2 fragments, half-life 133 hours, less expensive ($1,220/vial), room temperature stable; theoretically less late coagulopathy recurrence
• Coral snake antivenom - No longer available in the United States; treatment is supportive only
• Exotic/non-native snakes - Contact the Association of Zoos and Aquariums antivenom index or the American Association of Poison Control Centers (1-800-222-1222)

Antivenom adverse reactions:

Step 5 - Supportive Care

Shock and fluid resuscitation:

• IV fluid challenge: 250-500 mL 0.9% saline for hypovolemic shock
• In severe envenomation with diffuse capillary leakage: monitor for pulmonary edema

Respiratory failure (Elapid envenomation):

• Oxygen by mask
• Atropine + neostigmine (for postsynaptic alpha-neurotoxin bites, e.g., cobra) - may reverse neuromuscular blockade
• Mechanical ventilation if respiratory muscles fail

Coagulopathy and bleeding:

• Antivenom is first-line
• If clinical bleeding occurs (hemoptysis, intracranial hemorrhage, GI bleeding): correct with fresh blood, fresh frozen plasma
• Do NOT routinely treat thrombocytopenia or coagulopathy in the absence of clinical bleeding
• Coagulopathy can recur up to 2 weeks after the bite

Renal failure:

• Management of snake bite-induced AKI is the same as AKI from any other cause
• Early antivenom is key; delayed administration greatly increases dose requirements
• Hemodialysis (HD) outcomes appear better than peritoneal dialysis (PD) in venom-induced AKI - Brenner and Rector's The Kidney

Analgesia:

• Paracetamol (acetaminophen): >2 years - 0.5 mg/kg up to 2 mg/kg/day
• Avoid aspirin and NSAIDs (promote bleeding)
• For severe pain: parenteral opioids (pethidine 50-100 mg IM adult, or morphine 5-10 mg IM adult)

Step 6 - Wound Management

• Infection prevention: Prophylactic antibiotics have NOT been shown in clinical trials to reduce infection rates; culture-proven infection should be treated specifically. If the wound was tampered with or incised with unsterile instruments, use broad-spectrum coverage (penicillin/erythromycin + gentamicin or cefuroxime)
• Blisters/bullae: Leave alone unless threatening to rupture; aspirate dry with a fine needle
• Limb elevation: Nurse in a comfortable position, often in a sling
• Avoid occlusive dressings
• Tetanus toxoid booster in all cases

Surgical indications:

• Necrosis: Surgical debridement at earliest signs; general/spinal/local anaesthesia needed (tissue damage often extends far beyond visible surface). Immediate split-skin grafting is recommended to prevent chronic ulceration and risk of malignant transformation (after 8+ years in neglected wounds)
• Compartment syndrome: Intracompartmental pressure measurement; fasciotomy if confirmed. Note: fasciotomy results can be disfiguring; adequate early antivenom is preferred to prevent compartment syndrome
• Abscesses: (Especially Bothrops bites in South America) - aspirate or incise; treat with broad-spectrum antibiotics
• Amputation: Should be a last resort; every effort must be made to preserve the limb

What NOT to Do

• Tourniquet / tight ligature (dangerous, ineffective)
• Incision and suction of the bite site (no evidence of benefit, increases infection risk)
• Ice application (worsens tissue ischemia)
• Alcohol or stimulants
• Corticosteroids (no benefit in humans for primary envenomation; only used for allergic reactions to antivenom)
• Antihistamines and heparin as primary treatment (ineffective)
• Routine prophylactic antibiotics

Indications for Transfer to Higher Level of Care

• Positive 20WBCT 6 hours after initial antivenom dose (ongoing coagulopathy)
• Progressive paralysis or respiratory difficulty
• Reduced urine output
• Anaphylaxis unresponsive to epinephrine
• Shock/hypotension unresponsive to fluids
• Severe local necrosis or compartment syndrome

Recent Evidence