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Case 9.2 – Poisoning & Envenomation

Category: Children & Young People | Discipline: Paediatrics Medicine | Setting: Emergency Department

Case

Sven Tuk, aged 3 years, presents with an inflamed, swollen and painful hand. Her mother repeats that she was playing in the garden shed with her boys and had presented crying. The pain has not responded to Panadol, and is aggravated by movement. The pain and swelling are now extending up her arm. On examination, you note Sven is sweating and dry retching.

Questions

1. List your likely diagnosis and differential diagnosis.

Most Likely Diagnosis: Red-back spider bite

Differential Diagnosis:

  • Bee sting - not usually associated with sweating or vomiting
  • Wasp sting - not usually associated with sweating or vomiting
  • Other spider bites - unlikely:
    • Funnel web spiders do not cause a local reaction
    • White tailed spider is thought to cause only a local reaction
  • Snake bite - highly unlikely as all Australian snakes do not cause a local reaction
2. Outline your approach in terms of further history, examination and investigation.

Further History

  • Known presence of red-back or other spiders, bees, wasps, or snakes at or near their home
  • Whether any were noticed by her boys
  • Obtain precise time of incident

Examination

  • Vital signs - temperature, pulse and blood pressure (measure BP in the unaffected arm)
  • Inspect the hand for evidence of a bee sting still present in the skin
  • Inspect the rest of the skin for rashes
  • Observe sweating pattern - determine if generalized or localized to the affected arm
  • Inspect for muscle fasciculation at the site
  • Palpate the axilla for local lymphadenopathy
  • Assess for generalized muscular weakness

Investigations

Note: There are no venom detection tests for spider bites.

  • Rapid venom detection test to exclude snake bite - can be performed from:
    • Swab from the bite site
    • Blood
    • Urine
3. If red back spider bite was suspected, what would make you consider administration of antivenom?

Indications for Antivenom Administration:

Antivenom should be given if the reaction has spread beyond the local bite site, with:

  • Systemic symptoms and signs, OR
  • Severe or recurrent pain
4. If Sven had been bitten by a tiger snake, and presented with headache, abdominal pain, vomiting and ascending paralysis, how would you manage her presentation?

Background on Australian Snake Envenomation

Tiger snakes and brown snakes account for most envenomations. All Australian snakes are elapids, which have relatively small fangs and whose venoms do not cause severe local effects.

Two Most Common Acute Threats to Life:

  • Neuromuscular paralysis with respiratory failure
  • Coagulopathy causing bleeding with peripheral circulatory failure (shock)

Main Components of Venoms

  • Pre- and postsynaptic neurotoxins - cause paralysis
  • Prothrombin activators - cause disseminated intravascular coagulation and haemorrhage
  • Anticoagulants - cause spontaneous haemorrhage
  • Rhabdomyolysins - may cause renal failure
  • Haemolysins

Principles of Treatment for Snake Bite

  • Prevent rapid absorption of venom from subcutaneous tissue into circulation by application of pressure-immobilization bandage
  • Neutralize the venom by administration of antivenom
  • Treat the effects of the venom - respiratory failure and bleeding

Antivenom Administration

Available Antivenoms:

  • Specific monovalent antivenoms (Commonwealth Serum Laboratories Ltd, Melbourne) manufactured against: tiger, brown, taipan, black, death adder and beaked sea snake venoms
  • Polyvalent preparation (mixture of five terrestrial antivenoms)
  • Antivenoms are highly purified equine immunoglobulins

Geographic Antivenom Selection:

  • Tasmania: Tiger snake antivenom (snakes are black tiger snakes and copperheads)
  • Victoria: Tiger snake plus brown snake antivenom (dangerous species are tiger, brown, black and copperhead snakes)
  • Elsewhere in Australia: Polyvalent preparation (additional species exist)

Premedication (Essential):

  • Subcutaneous adrenaline (NOT IV or IM) 0.005-0.01 mg/kg - to prevent life-threatening anaphylactoid reaction
  • Additional protective agents if known allergic history:
    • Steroid (hydrocortisone)
    • Antihistamine
  • Only one premedication dose of adrenaline is required

Antivenom Delivery:

  • Administer intravenously, diluted with crystalloid solution
  • Over approximately 30 minutes
  • For severe envenomation - may be delivered rapidly

Dosing:

  • Dose is never certain at beginning (amount of venom injected is unknown)
  • Each ampoule neutralizes average yield from 'milking'
  • Venom injected is highly variable; bites may be multiple
  • Children more susceptible due to larger venom-to-body-mass ratio
  • Majority of envenomations treated with 1-3 ampoules
  • Many more ampoules usually required in life-threatening envenomations

Serum Sickness Prevention:

If polyvalent antivenom or multiple doses of monovalent antivenom required: prednisolone 1-2 mg/kg/day for 5 days

Indications for Antivenom:

  • Clinical signs or symptoms of envenomation after snake bite
  • Substantial coagulopathy present
  • May withhold if venom detected in urine but no clinical evidence or very mild coagulopathy (but monitor closely)

Life Support

Respiratory Support:

  • Endotracheal intubation and mechanical ventilation may be required for bulbar and respiratory muscle paralysis
  • If antivenom therapy delayed, mechanical ventilation may be required for many days

Coagulopathy Management:

  • May cause massive haemorrhage from mucosal surfaces and peripheral circulatory failure
  • Haemorrhage may occur into vital organs, particularly the brain
  • Restore circulatory volume with blood transfusion
  • Normalize coagulation with antivenom and coagulation factors (fresh frozen plasma)
  • Important: Antivenom neutralizes venom but does not restore coagulation per se

Monitoring:

  • Repeated laboratory tests of coagulation:
    • Prothrombin time
    • Activated partial thromboplastin time
    • Serum fibrinogen
    • Fibrin degradation products
  • Bedside tests of bleeding
  • Coagulation status is the most sensitive guide to need for additional antivenom after bite by coagulopathic species

Key Dangers and Mistakes in Management:

  • Fang marks may not be visible
  • Premature removal of pressure-immobilization bandage allows sudden systemic envenomation
  • Erroneous snake identification may cause wrong antivenom to be given (if in doubt give polyvalent)
  • Delayed onset of paralysis may not be detected
  • Insufficient antivenom
  • Antivenom without premedication
  • Antivenom without clinical or laboratory evidence of envenomation
5. Summarise the principles of pressure-immobilisation first aid.

Pressure-Immobilization First Aid for Snake Bite

Background:

  • Limbs sustain 95% of all bites
  • Snake venoms gain access from subcutaneous tissue to circulation via lymphatics

Technique

Bandaging:

  • Apply a firm crepe (or crepe-like) bandage over the bite site and whole of the limb
  • This effectively occludes lymphatic channels
  • Bandage should be no tighter than a bandage for a sprained ankle
  • Can be left in place indefinitely

Splinting:

  • Application of splint that includes joints on either side of bite
  • Prevents use of surrounding muscle groups
  • Decreases lymph flow

Application Context

  • First aid measure - should be applied at scene of snake bite to prevent initial absorption of venom
  • In hospital - also used in established envenomation to prevent additional absorption of venom while preparations are being made to administer antivenom

Important Cautions

When to Remove:

  • After asymptomatic patient reaches hospital that has antivenom stock
  • After envenomated patient has been given antivenom
  • DANGER: It is dangerous to remove bandage from envenomated patient before antivenom administration - allows substantial additional venom to rapidly access circulation

Inspection of Bite Site:

  • Do NOT remove splint and bandage solely to inspect bite site
  • Remove splint temporarily
  • Cut a window in bandage to take swab for venom testing
  • Reinforce bandage and reapply splint

Note on Venom Inactivation:

  • Bandage does NOT allow substantial inactivation of venom in tissues
  • Bites are usually visible as scratches or puncture wounds
  • Their presence/appearance/absence does not prove or disprove envenomation
  • Does not allow identification of snake involved
6. Poisoning is common in children aged 1-5 years. Outline the principles of management in suspected poisoning in a 3 year old child.

Background

Poisoning occurs most frequently in this age group. Most instances are accidental, in which the young child discovers a drug or household cleaning/chemical agent. The majority of serious poisonings occur with prescribed drugs or over-the-counter drugs. Parents often underestimate the capabilities of young children who become increasingly mobile and curious, eating substances that are not palatable to adults.

Principles of Management

The immediate aim is to attend to the effects of the poison on the patient. Later, attention should be given to circumstances with the aim of preventing recurrence. The following principles may be applied universally:

1. Support Vital Functions

  • Imperative to maintain and support vital functions if depressed
  • Many poisons are excreted adequately or metabolized by the body if vital functions are maintained
  • If patient is unconscious, examine:
    • Airway adequacy
    • Depth and frequency of breathing
    • Circulation adequacy

2. Establish the Diagnosis

Important to establish:

  • What poisons are involved
  • In what quantity
  • When exposure occurred

Clinical Considerations:

  • Often diagnosis is self-evident, but not always obvious
  • When a poison identified, never assume other poisons could not be involved
  • Symptoms and signs are diverse but dangerous drugs threaten vital functions

Seriously poisoned patients commonly present with:

  • Unconsciousness
  • Cardiorespiratory failure
  • Convulsions

If any present and cause otherwise not known, poisoning should be high on differential diagnoses list.

Investigations:

  • Meticulous physical examination and history provides invaluable help
  • Laboratory investigations may be necessary to:
    • Establish diagnosis
    • Determine amount of poison in body
    • Help determine specific treatment for certain poisons

3. Prevent Absorption

Routes of Poisoning:

  • Skin/conjunctivae/mucous membranes: Copious irrigation with water
  • Inhalational (gases): Oxygen therapy and mechanical ventilation may be required
  • Ingested (most common): Options include:
    • Activated charcoal (oral or gastric)
    • Gastric lavage
    • Whole bowel irrigation
    • Induced emesis (largely abandoned - limited effectiveness and aspiration risk)

If Poison Already Absorbed (in vascular compartment):

Invasive techniques may be required:

  • Plasmafiltration
  • Haemofiltration
  • Charcoal haemoperfusion
  • Haemodialysis
  • Peritoneal dialysis
  • Exchange transfusion

Critical Safety Considerations

CONTRAINDICATIONS:

Unconscious/drowsy patients or patients who cannot protect their airway should NOT undergo:

  • Induced emesis
  • Gastric lavage
  • Activated charcoal
  • Colonic washout solutions

Reason: Consequences of aspirating gastric contents during vomiting or regurgitation in less than fully conscious state far outweigh dangers of many untreated poisons. Mortality from severe pneumonitis is approximately 50%.

Treatment Selection

Activated charcoal: Probably the most appropriate therapy in emergency/casualty department

Whole bowel irrigation: May be preferable for some agents

Gastric lavage: Reserved for:

  • Recent (within 1 hour) serious life-threatening ingestion in conscious patient, OR
  • Serious poisoning in less than fully conscious patient who has airway protection

Treatment determined by:

  • Substance involved
  • Amount
  • Interval between ingestion and presentation
  • Effect of the poison
  • Must be weighed against hazards of removal

4. Administer an Antidote

  • Only relatively few poisons have antidotes
  • Knowledge and use of these can be life-saving
  • Appropriate dose determined by amount of poison and its effects
7. List some common strategies to prevent childhood poisoning.

Background

  • Nature of poisoning varies for different age groups in children
  • Usually unintentional, but possibility of deliberate poisoning as part of child abuse should not be forgotten
  • Pharmaceutical substances involved in 70% of poisonings
  • In hospitals, errors in drug administration are frequent causes of poisoning

Prevention Strategies

Safe Storage

  • Store medicines, chemicals and household products safely out of reach and out of sight of children
  • Store up high (at least 1.5 metres) in a locked or child-resistant cupboard
  • Separate medicines from chemicals and household products
  • Do not store medicines in refrigerator unless advised by pharmacist
  • Visitors' bags may contain medicines - keep them well out of reach of children

Safe Containers

  • Do not transfer medicines, chemicals or household products from their original containers
  • Keep everything in original, labelled containers
  • Never store in cups or soft drink bottles
  • Use medicines, chemicals and household products in child-resistant packaging (blister or strip packs or special 'push and turn' lids)
  • Remember: Child-resistant packaging is not child-proof

Safe Labels

  • Ensure all medicines, chemicals and household products are properly labelled
  • Read the label carefully before use

Safe Use

  • Use medicines, chemicals and household products safely
  • Read directions for use carefully
  • Do not leave them unattended while in use
  • Children tend to imitate adults - avoid taking medicines in their presence
  • Refer to medicines by their proper names - they are not lollies
  • Use appropriate protection when painting, spraying chemicals or cleaning oven:
    • Follow directions for use
    • Protect skin and eyes
    • Ensure adequate ventilation with air circulating continuously
    • If spill occurs, remove any contaminated clothing immediately

Safe Disposal

  • Empty containers of liquid medications, chemicals and household products should be rinsed with water before disposal
  • Clean out medicine cupboard regularly
  • Take unwanted or out of date medicines to a chemist for disposal