Snake Bites

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The effect of snakebites may be, neurotoxic, haemotoxic and /or cytotoxic. The overall effect is determined by the predominant toxin in the snake venom

Clinically relevant venomous snakes in Sierra Leone and Africa as a whole include:

  • Elapidae:-g Cobra, Olive whip, Mambas (contain neurotoxic venom)
  • Viperidae:-g Vipers, Adders (contain haemotoxic venom)
  • Colubridae:- eg Tree snake or Boomslang (contain myotoxic venom)

Signs and symptoms

  • Puncture wounds, pain, swelling, discoloration, bleeding

If neurotoxic venom (e.g. green and black mamba)

  • Weakness and paralysis of skeletal and respiratory muscles (drooping eyelids, difficulty in swallowing, double vision, slurred speech, difficulty in breathing) – starting 15-30 minutes after the bite
  • Excessive sweating and salivation

If haemotoxic venom

  • Extensive local damage with swelling, pain, regional lymphadenopathy – starting 10-30 minutes after the bite
  • Bleeding oozing from the site, bloody blisters
  • Haematuria, haematemesis – even after some days

If myotoxic venom

  • Damage to striated muscles (may be associated with myoglobinuria)

Complications

  • Cellulitis
  • Hypotension
  • Acute renal failure
  • Convulsions
  • Myocardial infarction- due to vasospasm or coronary artery thrombosis
  • Pulmonary oedema

Evaluation

Measure limb circumference above and below the bite, mark border of oedema /erythema and reassess every 30 minutes.

  • Check compartment pressures if compartment syndrome suspected.
  • Full blood count
  • Kidney function tests
  • Clotting time tests

Treatment objectives

  • Neutralize envenomation
  • Limit systemic effects
  • Ensure local wound care
  • Prevent complications

Non-pharmacological treatment

  • Reassure patient
  • Assess skin for fang penetration
  • Immobilize limb with a splint
  • Apply firm (not tight) crepe bandage to entire limb to ensure constant pressure (do not occlude blood vessels)

Pharmacological treatment

Patients not immunized against tetanus within the past 5 years give

Tetanus toxoid IM

0.5ml

Tetanus immunoglobulin, IM

<5 years: 75 units

5-10 years: 125 units

>10 years: 250 units

 

To relieve pain

Paracetamol oral

Adult:               

1 g 3-4 times a day or when necessary every 6-8 hours

Child: 

125-500 mg 3-4 times a day or when necessary every 6-8 hours

 

For cobras, mambas, rinkhals, puff adders, gaboon vipers and boom slang bites

 

Antivenom

If there are systemic or severe local signs (swelling of more than half the limb or severe necrosis, bleeding), give antivenom, if available

Monovalent antivenom if the species of snake is known.

Polyvalent antivenom (PASV) if the species is not known.

Follow the directions given on preparation of the antivenom.

The dose for children is the same as that for adults.

Note:

Give a test dose of 0.5 mL (intradermal)

Procedure:

  • 2 vials(20mL) of PASV into 100 mL of 5% dextrose in 0.9% saline for one hour
  • Re-assess patient's haematological and neurological parameters.
  • If no improvement, continue one vial (10 mL) of PASV into 100 mL of 5% dextrose in saline every hour until parameters normalize
  • Then a further one vial of PASV in 500 mL of 5% dextrose in saline for next 24 hours
  • Monitor closely for anaphylaxis or other serious adverse reactions
  • If itching or an urticarial rash, restlessness, fever, cough or difficult breathing develop, stop antivenom and give adrenaline at 0.5 mL of 1:1000 IM
  • Possible additional treatment includes bronchodilators, antihistamines (chlorphenamine at 0.25 mg/kg) and hydrocorticone 100 mg IV.
  • When the patient is stable, re-start antivenom infusion slowly

If local necrosis develops

  • Remove blisters, clean and dress daily, debride after lesions stabilize (minimum 15 days)
Venom in eyes

Clinical presentation

  • Periocular swelling
  • Mild conjunctival inflammation
  • Corneal inflammation
  • Frank corneal ulceration
  • Perforation with eventual blindness

Management

  • Irrigate eyes with plenty of water or 0.9% sodium chloride
  • Cover with eye pads
  • Immediately refer to ophthalmologist

Criteria for referral for administration of antivenom

  • Signs of systemic poisoning (paralysis, respiratory difficulty, bleeding)
  • Spreading local damage:
    • Swelling of hand or foot (site of most bites) within 1 hour of bite
    • Swelling of elbow or knee within 3 hours of bite
    • Swelling of groin or chest at any time
    • Significant swelling of head or neck

Antibiotics

  • Indicated only if wound is infected

Referral

  • Snakebite with neurotoxic or haemotoxic manifestations may need intensive care.