Snakebite

T63.0

DESCRIPTION

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

In the majority of cases, the species of snake is unknown. The patients can be divided into:

  • no evidence of bite, no envenomation,
  • evidence of bite, minor envenomation, i.e. fang marks, minimal pain, minimal swelling and no systemic signs,
  • evidence of serious envenomation.

DIAGNOSTIC CRITERIA

Cytotoxic venom

  • Puff adder, spitting cobra, gaboon adder.
  • Venom causes severe local damage to tissues and vascular endothelium.
  • Severe swelling and local necrosis occurs.

Neurotoxic venom

  • Mamba, non- spitting cobra, rinkhals, berg adder.
  • Venom causes a paresis and paralysis of skeletal muscles.
  • Paralysis of respiratory muscles with respiratory failure may occur.
  • Preceded by severe pain and paraesthesias.
  • Ophthalmoplegia occurs when ocular muscles become paralysed.
  • Speech and swallowing may be affected.
  • Signs and symptoms start within 15–30 minutes.

Haemotoxic venom

  • Boomslang, vine snake.
  • Venom may cause:
    • haemolysis of red blood cells,
    • ecchymosis,
    • anaemia,
    • epistaxis,
    • consumptive coagulopathy,
    • haemoptysis
    • bruises,
    • haematuria.

GENERAL AND SUPPORTIVE MEASURES

  • Patients with no evidence of bite and patients with evidence of bite but only minor envenomation should be admitted for observation. No anti-venom is indicated.
  • Do not suck or cut the wound.
  • Do not apply tourniquet.
  • Where serious envenomation is suspected, immediate treatment includes:
    • minimising movement of affected limb,
    • emergency treatment by bandaging affected limb with crepe bandage without compromising blood supply,
    • rapid transportation to a facility with antivenom available is the most important principle of pre-hospital care,
    • optimal therapy consisting of placing the patient at rest with the affected body part raised to the level of the heart,
    • stabilising circulation and blood pressure.
  • For cytotoxic envenomation, surgical intervention, i.e. decompression surgery for established compartment syndrome and debridement of necrotic tissue should only be done when absolutely necessary and as conservatively as possible.
  • For neurotoxic envenomation, ventilatory and cardiovascular support may be needed in an ICU.

MEDICINE TREATMENT

All patients not immunized within the past 5 years:

  • Tetanus toxoid, IM, 0.5 mL.

If children with penetrating wound and who are not completely immunised:

  • Tetanus immunoglobulin, IM.
    • If < 5 years of age: 75 IU.
    • If 5–10 years of age: 125 IU.
    • If > 10 years of age: 250 IU.

Clean wound:

  • Chlorhexidine 0.05% solution in water.

Antivenom therapy

Indications:

  • Consider antivenom in children who are persistently and severely affected even after the first day.
  • Painful swelling of the whole hand/foot within 1 hour, spreading to elbow/knee in 3–6 hours.
  • Swelling of head, neck or chest.
  • Significant envenomation e.g. overt neurological signs or bite in close proximity to airway structures.
  • Platelet count less than 100 x 10⁹/L.
  • Fibrinogen less than 100 mg/dL.

The dose of antivenom is the same for adults and children.

CAUTION
Never administer antivenom without being fully prepared to manage acute anaphylaxis.

Give pre-treatment with adrenaline (ephinephrine):

  • Adrenaline (ephinephrine) 1:1000, SC, 0.01 mL/kg, to a maximum of 0.25 ml

CAUTION
Polyvalent antivenom is only effective for the following common snake bites:

  • Cape cobra
  • Mamba
  • Puff adder
  • Gaboon adder
  • Rinkhals
  • Spitting cobras

Boomslang requires specific antivenom.

Antivenoms are available from the South African Vaccine Producers (SAVP).
SAVP emergency number: 011 386 6000.

Snakebite antivenoms may be available from specific hospitals in each province.

For cobras, mambas, rinkhals, puff adders and Gaboon viper:

  • Polyvalent snake antivenom, IV.
    • 60–120 mL antivenom diluted in 50 - 100 mL sodium chloride 0.9%, administered slowly over 30 minutes.

For boomslang bites:

  • Boomslang antivenom, slow IV, 10 mL administered over 3–5 minutes.

OR

  • Boomslang antivenom, IV infusion, 10–20 mL diluted in sodium chloride 0.9% or dextrose 5%, 50–100 mL administered over 5–10 minutes.
    • After administration, observe patient. Correct anaemia and bleeding tendency.

REFERRAL

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