Envenomation (Snake bites)

Introduction

Snake bite is an injury caused by a bite from a snake.
This can be life-threatening if the snake is venomou suck as bite from the black mamba, king cobra, banded krait, saw-scaled viper and rattlesnake.
In Africa, snake bites often occur among farmers who walk unshod.
It occasionally occur around homes when snakes are accidentally stepped upon.
Poisonous snakes belong to the families of:

  • Viperidae (responsible for most snake bites in Africa)
  • Subfamilies: viperinae (old world vipers),
  • Crotalinae (New world vipers, Asian pit vipers)
  • Elapidae (e. g. cobras)
  • Colubridae (e. g. boomslang)
    • A large group; only a few species are dangerously toxic to humans
  • Hydrophidae (sea snakes)

Clinical features of snake bites

These depend on the type of snake, location of bite and promptness of intervention

Local effects:

  • Pain
  • Swelling
  • Bruising
  • Tender enlargement of regional lymph nodes

Systemic effects:

  • Early anaphylactoid symptoms,
  • Transient hypotension with syncope,
  • Angioedema
  • Urticaria,
  • Abdominal colic,
  • Diarrhoea
  • Vomiting,
  • Late persistent or recurrent hypotension,
  • Electrocardiograph abnormalities,
  • Spontaneous systemic bleeding,
  • Coagulopathy,
  • Adult respiratory distress syndrome,
  • Acute renal failure

Viperidae and crotalidae

  • Local and systemic bleeding,
  • Impairment of organ function,
  • Reduction of cardiac output,
  • Inhibition of peripheral nerve impulses
  • Multisystem effects: Rhabdomyolysis,
  • Haemolysis
  • Blood vessel damage

Elapidae

  • Neurotoxic effects

Snake bite wounds may become secondarily infected with:

  • Clostridium tetani, causing tetanus
  • Clostridium welchi, causing gas gangrene

Initial assessment

Brief history: time and circumstances of
bite, progression of local and systemic
symptoms; antibiotic allergy,
immunization of patient and other
morbid condition(s).
Examination: to look for tooth marks,
local swelling, bleeding, shock,
cardiovascular and respiratory systems,
evidence of paralysis, level of consciousness,

Investigations

  • FBC and differentials
  • Test for haemostasis (20-Minute Blood Clotting Test)
  • Electrolytes and Urea
  • Blood clotting profile
  • Arterial blood gas estimations
  • Chest radiographs
  • Wound and blood cultures

Treatment for snake bites

Treatment objectives

The treatment objectives of snake bites are to:

  1. Limit systemic effects
  2. Neutralize envenomation
  3. Local wound care
  4. Prevent onset of complications
  5. First-Aid and Transport to the Hospital
  6. Move the victim to safety from area  where they may have been bitten
  7. Reassure the patient (only 50% of the bites by venous snakes cause envenoming)
  8. Remove constricting clothings, rings, shoes, bracelets, bands from the bitten limb
  9. Immobilize the whole patient, especially the bitten limb, using a splint or sling
  10. Transport the patient to the hospital as quickly and passive as possible
  11. Avoid harmful practices:
    • never attempt to suck out or aspirate the poison
    • do not make incisions
    • never attempt to catch the snake
    • a tight arterial tourniquet should never be used)

Non-drug measures

  • Assess and observe the patient for at least 24 hours.
  • Cardiopulmonary resuscitation may be necessary: clearing of the airway,  oxygen administration by face mask or nasal cannula, intravenous access to allow treatment of shock with intravenous fluids
  • Identification of the snake would help in the choice of antivenom (where specific antivenoms are available)
  • Wound debridement and fasciotomy for compartment syndrome may become necessary

Drug treatment

  • Intravenous fluid administration to
    maintain circulation: use colloids or
    cystalloids as clinically appropriate

Antivenom:

Indications for antivenom treatment:

  1.  envenomation (neurotoxicity, spontaneous systemic bleeding, incoagulable blood (20MWBCT), cardiovascular abnormality (hypotension, shock, arrhythmia, abnormal electrocardiogram)
  2. Local envenomation: extensive swelling (involving more than half of the bitten limb), rapidly progressive swelling, bites on fingers and toes

Usually polyvalent antivenoms are used, but where specific species are identified, a monospecific antivenom may be used
Adult and child:

  • No dose difference between adult and child in terms of dosage.

Contents of the antivenom

  • vial diluted in sodium chloride 0.9 intravenous infusion, and infused. intravenously over 30 minutes
  • Intradermal, subcutaneous testing with diluted venom before administration are not predictive of venom reaction and should not be done

Antivenom reactions:

  • Early reactions (3-60 minutes): cough, tachycardia, itching, urticarial, fever, nausea, vomiting, headache.
  • Treatment of anaphylaxis with antihistamines (H blockers), epinephrine (adrenaline) and corticosteroids
  • Pyrogenic reactions: due to pyrogen contamination of antivenom during manufacture begins 1-2 hours after treatment and characterized by fever and chills
  • Tepid sponging and administration of paracetamol are useful
  • Late reactions: occurs 5-24 days (average 7 days) following antivenom. There are Characterized by itching, urticaria, fever, arthralgia, periarticular swellings, proteinuria and sometimes neurological symptoms.
  • Antihistamines are used for milder
    attacks, but in severe cases, including those with neurological symptoms, a short course of prednisolone should be used.

Prophylactic antibiotics as
appropriate

Tetanus prophylaxis