Snakebite

Description

Diagnostic criteria

General and supportive measures

Medicine treatment

Referral

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ICD-10 code: 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.
• Rinkhals has both cytotoxic and neurotoxic features.
• Venom causes severe local damage to tissues and vascular endothelium.
• Severe swelling and local necrosis occurs.

Neurotoxic venom

• Mamba, non-spitting cobra, e.g. Cape cobra, berg adder.
• Rinkhals has both cytotoxic and neurotoxic features.
• 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.

The bite site can be rather unremarkable, except for the berg adder, which also has some swelling.

Haemotoxic venom

• Boomslang, vine snake.
• Venom may cause: spontaneous bleeding, headache, dizziness, fainting.

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

Analgesia:

• Paracetamol, oral, 15 mg/kg/dose, 6 hourly as required.

Avoid NSAIDS and aspirin due to concerns of coagulopathy.

Opioids can be used for severe pain, but should be used cautiously in neurotoxic snakebite.

All patients not immunized within the past 5 years:

• Tetanus toxoid, IM, 0.5 mL.

In 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.

Antibiotics are seldom needed, except for secondary infection.

Antivenom therapy

Two types of snake antivenom are available:

• Polyvalent antivenom: active against puff adder, gaboon adder, rinkhals, green mamba, black mamba, Jameson’s mamba, Cape cobra, forest cobra, snouted cobra, Mozambique spitting cobra.
• Monovalent antivenom: for boomslang bites only.
• Obtainable from South African Vaccine Producers (Tel.: +2711 386 6063/2/78 or afterhours 071 680 9897 or 082 884 2971). See full details in the package insert.

Indications:

• Consider antivenom in children who are persistently and severely affected even after the first day.
• Polyvalent antivenom:
  • Positively identified snake included in polyvalent antivenom AND evidence of severe cytotoxic envenomation.
  • Unidentified snake and evidence of progressive severe cytotoxic envenomation:
    • Painful swelling of whole hand/foot within 1 hour.
    • Swelling to the elbow/knee in less than 6 hours.
    • Swelling of the whole limb in less than 12 hours.
    • Swelling progression > 2.5 cm per hour.
    • A threatened airway due to swelling.
    • Evidence of complication, e.g. compartment syndrome.
    • Systemic evidence of severe cytotoxicity.
      • Shock.
      • Haematological abnormalities: INR > 1.5 IU, Hb < 8 g/dL, thrombocytopaenia (< 100 x 10⁹ /L) or leukocytosis (> 10 x 10⁹ /L).
      • Arrhythmias (rare).
    • Any signs of neurotoxicity, i.e. weakness or paralysis.
• Monovalent antivenom:
  • Positively identified boomslang AND clinical or laboratory features of coagulopathy.
  • Unidentified snakebite with evidence of coagulopathy AND no swelling at the bite site.

Administration and antivenom dose:

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

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• In most cases patients do not need and should not be given antivenom.
• Adverse reactions to antivenom are common and may be severe.
• Pre-medication with adrenaline (epinephrine) may reduce the risk of severe adverse reactions to polyvalent snake antivenom.
  • Adrenaline (epinephrine) 1:1000, SC, 0.01 mL/kg, to a maximum of 0.25 mL.
• The dose of antivenom is the same for adults and children.
• Monitor for any deterioration in respiratory function as patients may need ventilation whether or not polyvalent antivenom has been given.
• Antivenom should be given as soon as possible, however, administration may be considered even as late as 48–72 hours after the bite, if there is continued clinical deterioration indicating ongoing venom activity.
• Polyvalent snake antivenom, IV.
  • 1 ampoule contains 10 mL antivenom.
    • Cytotoxic snakebite: give 50 mL.
    • Neurotoxic snakebite: give 80–100 mL (and up to 200 mL in black mamba bites).
  • Dilute in sodium chloride 0.9%, 50–100mL.
  • Administer IV, over 30 minutes.

LoE III⁹

• Boomslang monovalent antivenom:
  • Slow IV, 10 mL administered over 3–5 minutes.
    OR
  • IV infusion, 10–20 mL diluted in sodium chloride 0.9% or dextrose 5%, 50–100 mL administered over 5–10 minutes.

Spontaneous systemic bleeding should stop within 15–30 minutes and blood coagulability be restored within 6 hours.

• After administration of antivenom, observe patient for 24 hours.
• Contact the Poisons Information Helpline for further advice.
• Correct anaemia and bleeding tendency.

REFERRAL

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

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Standard Treatment Guidelines and Essential Medicines List for South Africa, Hospital Level, Paediatrics, 2023 Edition

Chapter 18: Poisoning, 18.2 Envenomation,  18.2.3 Snakebite