Funnel-Web Spider Envenomation

Quick Answer

One-liner: Funnel-web spider envenomation is a medical emergency causing autonomic storm that requires immediate Pressure Immobilisation Bandage and administration of Funnel-Web Spider Antivenom.

Funnel-web spider envenomation is a life-threatening emergency caused by delta-hexatoxin (robustoxin) from the Sydney Funnel-web spider (Atrax robustus) and related species (Hadronyche spp.). The toxin causes massive release of acetylcholine and catecholamines, resulting in an autonomic storm. Since the introduction of antivenom in 1981, there have been zero deaths. Immediate application of Pressure Immobilisation Bandage (PIB) and rapid administration of antivenom are essential. Severe envenomation occurs in 10-15% of bites, typically in children who have more fatal outcomes historically.

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ACEM Exam Focus

Primary Exam Relevance

• Anatomy: Spider anatomy (chelicerae, venom glands), lymphatic system (PIB mechanism)
• Physiology: Autonomic nervous system, neurotransmitter release, voltage-gated sodium channels
• Pharmacology: Atropine, adrenaline, antivenom mechanism (rabbit IgG), anaphylaxis management

Fellowship Exam Relevance

• Written: Clinical syndrome recognition, antivenom dosing, PIB technique, redback comparison
• OSCE: PIB application demonstration, anaphylaxis to antivenom, communication with anxious family
• Key domains tested: Medical Expert (management), Communicator (patient education), Professional (safety)

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Key Points

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Epidemiology

Australian/NZ Specific

• Primary distribution: Sydney basin and coastal NSW within 160km of Sydney
• Secondary distribution: Hunter Valley, New England (NSW), south-east Queensland, Tasmania
• Seasonal peak: November to April (warmer months, spiders more active)
• High-risk areas: Gardens, swimming pools, shoes, laundry baskets (dark, moist environments)

Indigenous Population Considerations

• No specific data on incidence in Aboriginal and Torres Strait Islander populations
• Geographic distribution overlaps with some rural/regional Indigenous communities
• Access to antivenom may be limited in remote communities - retrieval consideration
• Cultural safety in education about spider avoidance in camping/bush activities

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Pathophysiology

Mechanism

Delta-hexatoxin (formerly robustoxin) is the primary lethal toxin in funnel-web spider venom:

• Size: 42-amino acid peptide
• Mechanism: Slows inactivation of voltage-gated sodium channels at presynaptic nerve terminals
• Result: Massive, continuous release of acetylcholine and catecholamines (autonomic storm)

Key physiological effects:

1. Muscarinic effects: Profuse sweating, salivation, lacrimation, bronchorrhoea
2. Catecholamine surge: Hypertension, tachycardia, myocardial hypercontractility
3. Motor effects: Muscle fasciculations, cramps, weakness
4. Autonomic instability: Initial hypertension progressing to hypotension
5. Pulmonary effects: Neurogenic pulmonary oedema from increased capillary permeability

Pathological Progression

Bite → Delta-hexatoxin enters circulation → Na+ channel dysfunction
↓
Massive neurotransmitter release (ACh + catecholamines)
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Autonomic storm (0-60 min)
↓
Cardiovascular instability (1-3 hours)
↓
Pulmonary oedema, cardiac arrhythmias
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Death if untreated (3-6 hours)

Why It Matters Clinically

Understanding the pathophysiology guides management:

1. PIB works: Toxin spreads via lymphatics, not blood initially - PIB delays systemic spread
2. Antivenom timing: Earlier administration reverses neurotransmitter effects before irreversible damage
3. Supportive care: Atropine counters muscarinic effects, benzodiazepines reduce catecholamine-driven hyperactivity
4. Pulmonary oedema: Non-cardiogenic mechanism - requires both antivenom and ventilatory support

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Clinical Approach

Recognition

High-risk bites:

• Sydney Funnel-web (Atrax robustus) - male spider most dangerous (wandering male seeking mate)
• Northern Tree-dwelling Funnel-web (Hadronyche formidabilis) - serious envenomation
• Other Hadronyche species - generally less dangerous but can cause severe envenomation

Triggers for concern:

• Bite in known funnel-web habitat (Sydney region, coastal NSW/QLD)
• Child victim (historically higher mortality)
• No PIB applied or delayed application
• Rapid onset of symptoms (below 30 minutes)

Initial Assessment

Primary Survey

• A: Airway protection (secretions, laryngospasm risk)
• B: Respiratory rate, oxygen saturation, work of breathing (pulmonary oedema risk)
• C: Blood pressure (initial hypertension then hypotension), heart rate, cardiac monitoring
• D: Level of consciousness, pupils, limb strength
• E: Examine bite site, remove clothing for full examination

History

Key Questions

Red Flag Symptoms

Examination

General Inspection

• Patient distress, anxiety, agitation
• Profuse sweating (often regional, spreading from bite site)
• Salivation, lacrimation
• Skin: piloerection, gooseflesh (catecholamine effect)

Specific Findings

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Investigations

Immediate (Resus Bay)

Standard ED Workup

Advanced/Specialist

Point-of-Care Ultrasound

Lung ultrasound for pulmonary oedema:

• B-lines (comet tails) - indicate interstitial fluid
• Reduced lung sliding - may indicate pneumothorax (rare complication of positive pressure ventilation)
• Pleural effusion - uncommon in pure neurogenic pulmonary oedema

Cardiac ultrasound:

• Assess LV function (hyperdynamic in early phase, may deteriorate with hypotension)
• Assess for wall motion abnormalities (ischaemia from catecholamine surge)

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Management

Immediate Management (First 10 minutes)

1. KEEP PRESSURE IMMOBILISATION BANDAGE IN PLACE
2. ABC assessment with continuous monitoring
3. 2 x large bore IV cannulas
4. Bloods: FBC, UEC, CK, troponin, coagulation, ABG
5. 12-lead ECG, cardiac monitoring
6. Oxygen if SpO2 below 94%
7. Call Poison Information Centre: 13 11 26
8. Prepare Funnel-Web Spider Antivenom (2 vials)

Resuscitation

Airway

• Position patient to manage secretions
• Suction as needed
• Early intubation if:
  • Decreasing conscious state (GCS below 13)
  • Respiratory failure from pulmonary oedema
  • Unable to protect airway from secretions

Breathing

• Oxygen target: SpO2 94-98%
• High-flow nasal oxygen or non-rebreather mask for pulmonary oedema
• CPAP 10 cmH2O if conscious with pulmonary oedema
• Intubation with PEEP (8-10 cmH2O) if severe pulmonary oedema or decreased GCS
• Ventilator settings: lung-protective strategy (tidal volume 6-8 mL/kg IBW)

Circulation

• Fluids: Conservative initially (risk of worsening pulmonary oedema)
  • Give 250-500 mL normal saline bolus if hypotensive
  • Reassess after each bolus
• Blood pressure targets:
  • SBP 90-110 mmHg (avoid extreme hypertension)
  • May need short-acting antihypertensive (e.g., GTN infusion) for SBP greater than 180
• Inotropes (noradrenaline) if refractory hypotension despite antivenom and fluids

Medications

Funnel-Web Spider Antivenom Details

Product: CSL Funnel-Web Spider Antivenom

• Type: Rabbit-derived purified IgG
• Dose: 2 vials (1 vial = 500 units) diluted in 100-250mL N/Saline
• Administration: Infuse over 10-20 minutes
• Monitoring: Vital signs every 5 minutes during infusion
• Repeat: Every 15 minutes until symptoms resolve
• Average dose: 2-4 vials (occasionally up to 6-8 vials in severe cases)

Anaphylaxis management:

• Stop antivenom infusion
• Adrenaline 0.5 mg (0.5 mL 1:1000) IM immediately
• Diphenhydramine 25-50 mg IV
• Hydrocortisone 100 mg IV
• Restart antivenom at slower rate once stable

Serum sickness:

• Onset: 5-10 days post-antivenom
• Symptoms: Fever, arthralgia, rash, urticaria
• Management: Prednisone 50 mg daily for 5-7 days, antihistamines

Paediatric Dosing

Ongoing Management

After antivenom administration:

• Keep PIB in place for additional 2-4 hours after antivenom
• Monitor in ED for minimum 6-8 hours
• Repeat observations: BP, HR, RR, SpO2, GCS, temperature every 15-30 min initially, then hourly
• Repeat ECG, CXR if clinically indicated
• Discharge only when:
  • All symptoms resolved
  • Normal vital signs for 4+ hours
  • Normal ECG (if abnormal initially)
  • Able to ambulate safely

Definitive Care

ICU admission for:

• Severe pulmonary oedema requiring ventilation
• Persistent hypotension requiring inotropes
• Altered conscious state requiring neuroprotective measures
• Requiring high-dose antivenom (greater than 4 vials)
• Underlying cardiac disease exacerbated by catecholamine surge

Specialist consultation:

• Clinical toxicologist (via Poisons Information Centre)
• ICU registrar/consultant for severe cases
• Cardiology if myocardial ischaemia or arrhythmia

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Disposition

Admission Criteria

• Any signs of systemic envenomation (autonomic storm symptoms)
• Received antivenom (minimum 6-8 hour observation post-antivenom)
• Pulmonary oedema
• Persistent hypotension
• Altered conscious state
• Underlying significant comorbidities (cardiac, respiratory)

ICU/HDU Criteria

• Intubated or requiring NIV/CPAP
• Requiring inotropes
• Received greater than 4 vials antivenom
• Persistent cardiac arrhythmias
• Significant metabolic acidosis (pH below 7.30)

Discharge Criteria

• Dry bite (no PIB, no symptoms, normal observations for 6 hours)
• Completely resolved symptoms after antivenom and observation period
• Normal vital signs for 4+ hours post-symptom resolution
• Normal ECG (if initially abnormal)
• Reliable adult supervision available
• Access to medical care if symptoms recur
• Discharge education provided

Follow-up

• No routine outpatient follow-up required for resolved envenomation
• GP referral if:
  • Serum sickness occurs (5-10 days post-antivenom)
  • Delayed cardiac symptoms
  • Psychological distress from event
• Review any antivenom anaphylaxis for future medical alerts
• Recommend spider-proofing measures at home

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Special Populations

Paediatric Considerations

• Children historically had highest mortality before antivenom
• Dose of antivenom is same as adults (NOT weight-based)
• Small airways at higher risk from secretions - early airway intervention
• Agitation and distress may mask pain - careful assessment
• Parents require reassurance and education on first aid and spider avoidance

Pregnancy

• Category C antivenom (benefit outweighs risk in life-threatening envenomation)
• Fetal distress risk from maternal hypotension and hypoxia
• Continuous fetal monitoring if gestation greater than 20 weeks
• Adrenaline and atropine considered safe in pregnancy
• Discuss with obstetrics team for severe envenomation

Elderly

• Reduced physiological reserve - more susceptible to cardiovascular decompensation
• Underlying cardiac disease increases risk of arrhythmias and myocardial ischaemia
• Multiple medications - potential drug interactions
• Antivenom still indicated regardless of age

Indigenous Health

Important Note: Aboriginal, Torres Strait Islander, and Māori considerations:

Health disparities:

• Limited access to antivenom in remote communities
• Cultural barriers to early presentation to hospital
• Language barriers affecting symptom reporting and PIB education
• Higher prevalence of chronic diseases (cardiovascular, respiratory) increasing risk

Cultural safety:

• Respect traditional knowledge about local fauna and dangers
• Use Aboriginal health workers or cultural liaison officers where available
• Provide culturally appropriate education materials about spider avoidance
• Consider family and community involvement in discharge planning

Access challenges:

• Remote communities may not stock antivenom - retrieval required
• RFDS or air ambulance coordination for antivenom delivery
• Consider early administration of PIB and stabilisation during transport
• Longer retrieval times may necessitate earlier antivenom via telemedicine guidance

Māori considerations:

• Similar cultural safety principles apply
• Use of Māori health providers where possible
• Recognise whānau (family) importance in decision-making
• Consider Māori protocols for illness and healthcare seeking

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Pitfalls & Pearls

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Viva Practice

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OSCE Scenarios

Station 1: Resuscitation - Funnel-Web Envenomation

Format: Resuscitation Time: 11 minutes Setting: ED Resuscitation Bay

Candidate Instructions:

A 32-year-old male presents to the resuscitation bay after a spider bite while gardening in the Hawkesbury region, NSW. His wife applied a pressure bandage following triple-zero instructions. He is now complaining of muscle twitching and feels unwell. Please assess and manage this patient.

Examiner Instructions: The candidate should demonstrate systematic assessment and management of a patient with funnel-web spider envenomation. The patient has signs of autonomic storm - diaphoresis, tachycardia, hypertension, and fasciculations.

Patient Brief (for standardised patient or actor):

• You are anxious and restless
• Complaining of muscle twitching, especially in your arms and legs
• Sweating heavily ("I'm drenched")
• Pain at the bite site on your foot (3/10)
• Feeling like your heart is racing
• You want to know if you're going to die

Marking Criteria:

Expected Standard:

• Pass: ≥12/20
• Key discriminators: Keeps PIB in place, orders antivenom promptly, recognises autonomic storm, good communication with anxious patient

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Station 2: Procedure - Pressure Immobilisation Bandage Application

Format: Procedure / Skill Demonstration Time: 11 minutes Setting: Clinical Skills Area

Candidate Instructions:

You are working in a rural emergency department. A patient has just presented with a suspected funnel-web spider bite. No first aid has been applied yet. Please demonstrate the correct application of a Pressure Immobilisation Bandage (PIB) on this mannequin lower limb. Explain the steps as you proceed.

Examiner Instructions: The candidate should demonstrate correct PIB technique as per ANZCOR guidelines. The candidate must:

• Apply pressure bandage over bite site first
• Bandage entire limb from distal to proximal
• Apply splint
• Mark bite site
• Explain rationale for each step

Equipment Provided:

• Mannequin lower limb
• Elastic bandages (10cm and 15cm)
• Splint (or appropriate rigid material)
• Marker pen
• Scissors

Marking Criteria:

Expected Standard:

• Pass: ≥13/21
• Key discriminators: Correct bandaging technique (distal to proximal), appropriate pressure, splints limb, checks circulation, does NOT remove PIB

Common Mistakes:

• Starting bandaging too far from bite site
• Applying insufficient pressure
• Not splinting the limb
• Forgetting to mark bite site
• Checking pulse by removing bandage (check distal toes instead)
• Applying tourniquet instead of PIB

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Station 3: Communication - Breaking Bad News / Anxious Family

Format: Communication Time: 11 minutes Setting: Relatives Room / ED Cubicle

Candidate Instructions:

You are the treating doctor. A 42-year-old woman with confirmed funnel-web spider envenomation has just received 2 vials of antivenom and is currently stable but remains in the resuscitation bay. The patient's husband and teenage daughter are very anxious. They have heard funnel-web spiders can be fatal. Please speak with them, explain the situation, and provide reassurance.

Examiner Instructions: The candidate should demonstrate empathetic communication, provide clear information about funnel-web envenomation and antivenom, and address the family's anxiety about potential mortality.

Actor Briefing (for husband):

• You are extremely worried about your wife
• You heard funnel-web spiders can kill people
• You want to know if she's going to be okay
• You're angry the spider wasn't seen immediately (you were inside)
• You want to know when you can take her home

Actor Briefing (for daughter):

• You're 16 years old
• You're scared your mum might die
• You don't understand why this is happening
• You want to see your mum
• You're crying

Marking Criteria:

Expected Standard:

• Pass: ≥14/22
• Key discriminators: Clear explanation of prognosis (zero deaths with antivenom), empathetic communication, addresses mortality fear directly, manages expectations about discharge

Common Mistakes:

• Being too technical with medical language
• Not directly addressing fear of death
• Over-promising discharge time (must be minimum 6-8 hours)
• Being dismissive of family's anxiety
• Not checking family's understanding
• Focusing on facts without acknowledging emotions

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SAQ Practice

Question 1 (6 marks)

Stem: A 45-year-old man presents to the emergency department 45 minutes after a spider bite on his left hand while gardening in the Northern Beaches, Sydney. His wife applied a pressure bandage. On examination, he is diaphoretic, has muscle fasciculations, and is agitated. BP 165/105, HR 110, RR 22, SpO2 96%, temp 37.2°C.

Question: List 6 key features of funnel-web spider envenomation that differentiate it from redback spider envenomation. (6 marks)

Model Answer:

• Rapid onset (minutes to 1-2 hours) vs delayed onset (1-6 hours) in redback (1 mark)
• Autonomic storm - profuse sweating, salivation, lacrimation (1 mark)
• Muscle fasciculations and twitching (1 mark)
• Initial hypertension followed by hypotension (redback: hypertension only) (1 mark)
• Minimal local findings (redback: marked local pain, erythema) (1 mark)
• Risk of pulmonary oedema (redback: respiratory symptoms rare) (1 mark)

Examiner Notes:

• Accept: Agitation, tachycardia, altered conscious state as additional distinguishing features
• Do not accept: "Pain" alone (both can have pain)
• Do not accept: "Tachycardia" alone (both can have tachycardia)
• Accept features of the autonomic storm (sweating, salivation, lacrimation) as separate points or combined for full marks

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Question 2 (8 marks)

Stem: A 7-year-old girl presents 20 minutes after a suspected funnel-web spider bite. The spider was identified as a male Sydney Funnel-web. No pressure bandage was applied. On arrival: GCS 14 (E3 V4 M7), drooling, profuse sweating, muscle twitching. BP 140/85, HR 125, RR 26, SpO2 95%.

Question: Outline your immediate management of this patient. (8 marks)

Model Answer:

• Apply Pressure Immobilisation Bandage immediately over bite site (1 mark)
• ABC assessment with continuous cardiac monitoring and pulse oximetry (1 mark)
• Two large bore IV cannulas for resuscitation (1 mark)
• Funnel-Web Spider Antivenom 2 vials IV immediately (systemic envenomation present) (1 mark)
• Baseline investigations: FBC, UEC, CK, troponin, coagulation, 12-lead ECG, ABG (1 mark)
• Atropine 0.02 mg/kg IV (max 0.5 mg) for profuse secretions (1 mark)
• Prepare for intubation if conscious state deteriorates or respiratory failure develops (1 mark)
• Call Poisons Information Centre (13 11 26) for toxicology advice (1 mark)

Examiner Notes:

• Accept: Oxygen therapy if SpO2 below 94%
• Accept: Consideration of ICU admission early
• Do not accept: Wait for spider identification before treating (treat based on clinical picture)
• Accept: Additional antivenom doses if symptoms persist after first 2 vials
• Important: Emphasise that antivenom dose is NOT weight-based in children (2 vials, same as adults)

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Question 3 (10 marks)

Stem: You are the consultant in a rural emergency department. A 25-year-old man presents with a suspected funnel-web spider bite after working in the garden. Your hospital has no Funnel-Web Spider Antivenom in stock. The RFDS has been contacted but will take 90 minutes to arrive with antivenom. The patient is currently stable with no systemic signs of envenomation.

Question: Describe your management approach, including first aid, monitoring, and contingency planning. (10 marks)

Model Answer:

Immediate Management (2 marks):

• Apply Pressure Immobilisation Bandage if not already in place (1 mark)
• Establish IV access, cardiac monitoring, pulse oximetry (1 mark)

Monitoring and Observation (3 marks):

• Continuous cardiac monitoring and vital signs every 15 minutes (1 mark)
• Observe closely for signs of envenomation: sweating, salivation, fasciculations, hypertension, respiratory distress (1 mark)
• Document time of bite and time of PIB application (1 mark)

Anticipation of Deterioration (3 marks):

• Prepare airway equipment and intubation drugs (1 mark)
• Have atropine available for secretions (0.5-1 mg IV) (1 mark)
• Prepare resuscitation area for potential pulmonary oedema and cardiovascular collapse (1 mark)

Communication and Retrieval (2 marks):

• Maintain contact with RFDS for updates on ETA (1 mark)
• Consider early intubation and ventilation if patient deteriorates before antivenom arrives (1 mark)
• Consider aeromedical retrieval if patient becomes unstable

Examiner Notes:

• Accept: Telemedicine consultation with tertiary toxicology service
• Accept: Discussion with nearest hospital that has antivenom for potential transfer
• Critical: Emphasise keeping PIB in place - this is the most important intervention while waiting for antivenom
• Accept: Consideration of pre-emptive ventilation if signs of deterioration appear
• Do not accept: Discharging patient or removing PIB

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Question 4 (6 marks)

Stem: A 30-year-old woman received 4 vials of Funnel-Web Spider Antivenom after confirmed envenomation. Her symptoms resolved within 1 hour of antivenom administration. She has been observed for 8 hours and is now asymptomatic with normal vital signs, normal ECG, and normal CXR.

Question: List 6 criteria that must be met before this patient can be safely discharged home. (6 marks)

Model Answer:

• All symptoms resolved (no sweating, salivation, fasciculations) (1 mark)
• Normal vital signs for at least 4 hours (BP, HR, RR, SpO2, temperature) (1 mark)
• Normal 12-lead ECG (if initially abnormal) (1 mark)
• No pulmonary oedema on clinical assessment and CXR (1 mark)
• Able to ambulate safely without dizziness or weakness (1 mark)
• Reliable adult supervision available at home (1 mark)
• Discharge education provided including signs of recurrence requiring return (accept as alternative point)

Examiner Notes:

• Accept: Minimum observation period of 6-8 hours post-antivenom
• Accept: No signs of serum sickness (though too early for this complication)
• Accept: Patient understands PIB application for future bites
• Do not accept: "Patient feels fine" as sole criterion
• Accept: Access to medical care if symptoms recur
• Critical: Must be observed after antivenom, not just when symptoms resolve

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Australian Guidelines

ARC/ANZCOR

ANZCOR Guideline 9.4.1: Funnel-Web Spider Bite

• First Aid: Apply Pressure Immobilisation Bandage immediately
• Pressure: Firm pressure, similar to sprained ankle
• Coverage: Entire limb from distal to proximal
• Immobilisation: Splint limb to prevent movement
• Do NOT: Remove bandage, wash wound, apply tourniquet, cut or suck wound
• Urgency: Emergency, call 000 immediately

Key differences from international guidelines:

• Australian funnel-web spiders are unique (not found elsewhere)
• PIB is Australian-developed first aid technique
• Rabbit-derived antivenom is specific to Australian species
• Zero mortality since antivenom introduction (unlike some international spider bites)

Therapeutic Guidelines: Toxicology and Wilderness

Funnel-web spider envenomation management:

• Antivenom: 2 vials IV for systemic envenomation
• Repeat: Every 15 minutes until symptoms resolve
• Supportive care: Atropine for secretions, benzodiazepines for agitation
• Monitoring: Minimum 6-8 hours post-symptom resolution
• Discharge: Asymptomatic with normal observations for 4+ hours

State-Specific

NSW Health Clinical Guidelines:

• Funnel-web spider hotspots: Greater Sydney, Blue Mountains, Central Coast, Hunter Valley
• All NSW hospitals should stock Funnel-Web Spider Antivenom
• Rural hospitals without antivenom should have retrieval protocol in place

Queensland Health Guidelines:

• Funnel-web distribution in south-east Queensland
• Similar management protocols to NSW
• State-wide antivenom distribution system

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Remote/Rural Considerations

Pre-Hospital

Ambulance considerations:

• Maintain PIB in place during transport
• Monitor for signs of deterioration en route
• Have atropine available for secretions
• Consider early intubation if long transport time and patient deteriorating
• Communicate with receiving hospital for antivenom preparation

Resource-Limited Setting

Modified approach when antivenom unavailable:

• PIB is the most critical intervention - apply immediately and keep in place
• Aggressive supportive care:
  • Atropine for profuse secretions (0.5-1 mg IV, repeat q3-5min)
  • "Airway support: Early intubation for decreased GCS or respiratory failure"
  • Ventilator support for pulmonary oedema
  • "Fluid resuscitation: Conservative (avoid worsening pulmonary oedema)"
• Retrieve antivenom: Coordinate with RFDS or nearest hospital with stock
• Consider aeromedical retrieval if patient unstable

Telemedicine consultation:

• Contact tertiary toxicology service via video or phone
• Real-time guidance on antivenom dosing and monitoring
• Discussion on when to intubate and ventilate
• Coordination of retrieval timing

Retrieval

Criteria for retrieval:

• Confirmed systemic funnel-web envenomation
• Patient deterioration or expected deterioration
• No antivenom available at local facility
• Need for ICU-level care (pulmonary oedema, intubation)

RFDS considerations:

• Antivenom can be carried on most RFDS aircraft
• Retrieval time vs. transport to hospital with antivenom
• Consider whether patient stable enough for ground transfer
• Coordination with multiple hospitals if multiple envenomations

Retrieval team capabilities:

• Ability to administer antivenom in-flight
• Advanced airway management
• Invasive haemodynamic monitoring
• Ventilatory support for pulmonary oedema

Telemedicine

Remote consultation approach:

• Video assessment of patient and PIB application
• Real-time vital signs review
• Guidance on antivenom administration and dosing
• Decision support on intubation and ventilation
• Coordination of retrieval timing and destination

Telemedicine equipment requirements:

• Video capability for visual assessment
• Vital signs transmission (ECG, SpO2, BP, RR)
• Ability to view laboratory results
• Clear audio for team communication

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Pitfalls & Pearls Summary

Clinical Pearls

1. PIB is life-saving: Apply immediately - it's more effective than any hospital-based intervention before antivenom
2. Male spiders most dangerous: Wandering males during mating season cause most severe bites
3. Antivenom not weight-based: Same dose (2 vials) for adults and children
4. Local findings deceptive: Minimal local signs despite severe systemic envenomation
5. Zero mortality with antivenom: Since 1981, no deaths when antivenom administered appropriately
6. Atropine underused: Essential for managing profuse secretions and airway protection
7. Pulmonary oedema is neurogenic: Treat with antivenom, not diuretics alone (diuretics help after antivenom)
8. Anaphylaxis manageable: Stop infusion, give adrenaline, restart antivenom once stable
9. Observation critical: Keep for 6-8 hours after symptom resolution
10. Differentiate from redback: Different first aid, different antivenom, different prognosis

Common Pitfalls

1. Removing PIB too early: Keep until antivenom given and patient stable
2. Delaying antivenom for investigations: Give immediately if clinical syndrome present
3. Under-dosing antivenom: 2 vials initial, repeat every 15 minutes as needed
4. Forgetting anaphylaxis pre-treatment: Adrenaline if history of allergy
5. Missing pulmonary oedema: Auscultate frequently, may develop rapidly
6. Inadequate observation time: Minimum 6-8 hours after symptom resolution
7. Confusing with redback: Different first aid (PIB vs ice), different antivenom
8. Over-treating hypertension: Part of autonomic storm, treat only if SBP greater than 180 or symptomatic
9. Aggressive fluid resuscitation: Conservative fluids - avoid worsening pulmonary oedema
10. Discharging without education: Ensure patients and families understand first aid and recurrence signs

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Differential Diagnosis

Arachnid Envenomations

Non-Arachnid Conditions

Clinical Decision Pathway

Suspected Spider Bite
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History: Time, Location, Description, First Aid?
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Onset Rapid (min-1h)? → Suspect Funnel-web or Snakebite
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Autonomic Storm? → Funnel-web (PIB + Antivenom)
↓
No Autonomic Storm? → Consider Snakebite (VDK + VICC testing)
↓
Onset Delayed (1-6h)? → Suspect Redback (Ice + Analgesia)
↓
No Systemic Features? → Consider dry bite or harmless spider

Diagnostic Clues

Points favouring funnel-web spider envenomation:

• Bite in Sydney region or known funnel-web habitat
• Male spider identified (larger, wandering, aggressive)
• Rapid symptom onset (below 60 minutes)
• Profuse sweating, salivation, lacrimation
• Muscle fasciculations, twitching
• Hypertension progressing to hypotension
• Minimal local swelling or necrosis
• No urticaria or angioedema

Points favouring redback spider envenomation:

• Bite in urban or peri-urban environment (spider Australia-wide)
• Delayed symptom onset (1-6 hours)
• Progressive local pain spreading regionally
• Localised or regional diaphoresis
• Nausea, headache, hypertension
• No salivation or lacrimation
• Small spider seen (female redback is larger)

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Detailed Clinical Features

Time Course of Envenomation

Autonomic Storm Features

Grading of Envenomation Severity

Grade 1: Local Envenomation Only

• Bite site pain and erythema
• No systemic signs
• PIB applied, observe for 6 hours
• Discharge if remains asymptomatic

Grade 2: Mild Systemic Envenomation

• Autonomic signs present: sweating, salivation, lacrimation
• Minimal cardiovascular effects (BP below 160 systolic, HR below 100)
• No respiratory distress
• PIB, give 2 vials antivenom, observe 8-12 hours
• May discharge if symptoms resolve and observations normal

Grade 3: Moderate Systemic Envenomation

• Marked autonomic storm
• Cardiovascular effects (BP 160-180, HR 100-130)
• Early respiratory signs (tachypnoea, mild hypoxia)
• PIB, give 2-4 vials antivenom, ICU observation
• Admission to HDU/ICU

Grade 4: Severe Systemic Envenomation

• Profound autonomic storm
• Severe cardiovascular instability (BP greater than 180 or hypotension below 90, HR greater than 130)
• Pulmonary oedema, respiratory failure
• Decreased conscious state
• PIB, give 4-8+ vials antivenom, intubate if needed
• ICU admission mandatory

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Extended Viva Scenarios

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Extended SAQ Practice

Question 5 (8 marks)

Stem: A 22-year-old male presents to your emergency department after a spider bite while moving garden furniture in Western Sydney. No first aid was applied. On arrival, he is anxious, sweating, and reports muscle twitching. BP 150/100, HR 105, RR 20, SpO2 97%, temp 37.0°C. The spider was not seen.

Question: Describe your management of this patient, including specific interventions and their rationale. (8 marks)

Model Answer:

• Apply Pressure Immobilisation Bandage immediately over bite site (if not already done) (1 mark)
  • "Rationale: Delays lymphatic spread of toxin, critical before antivenom administration"
• ABC assessment with continuous cardiac monitoring and pulse oximetry (1 mark)
  • "Rationale: Detect arrhythmias, hypoxia, haemodynamic instability early"
• Two large bore IV cannulas (16-18G) in non-affected limb (1 mark)
  • "Rationale: Secure access for antivenom and potential resuscitation"
• Funnel-Web Spider Antivenom 2 vials IV (diluted in 100-250mL N/Saline) (1 mark)
  • "Rationale: Patient has signs of systemic envenomation (sweating, twitching, hypertension)"
• Baseline investigations: FBC, UEC, CK, troponin, coagulation profile, 12-lead ECG, ABG (1 mark)
  • "Rationale: Baseline for monitoring, detect complications (arrhythmias, cardiac injury, renal impairment)"
• Atropine 0.5-1 mg IV if profuse secretions compromising airway (0.5 marks)
  • "Rationale: Reduces muscarinic effects, protects airway"
• Observe minimum 8 hours post-symptom resolution (0.5 marks)
  • "Rationale: Ensure symptoms do not recur, delayed deterioration possible"
• Discharge education: PIB technique, spider avoidance, signs of recurrence (1 mark)
  • "Rationale: Prevention and early presentation if recurrence"

Examiner Notes:

• Accept: Calling Poisons Information Centre (13 11 26) for toxicology advice
• Accept: Preparing for potential deterioration (airway equipment, intubation drugs)
• Accept: Giving additional antivenom doses if symptoms persist after first 2 vials
• Critical: Recognising systemic envenomation and giving antivenom immediately (not waiting for investigations)
• Do not accept: Waiting for spider identification before treating
• Do not accept: Removing PIB before antivenom administration
• Accept: Admission to HDU/ICU if severe symptoms or large antivenom dose required

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Question 6 (10 marks)

Stem: You are the consultant in a regional hospital 150km from the nearest tertiary centre. RFDS has been contacted for a 5-year-old child with severe funnel-web envenomation. Antivenom will arrive in 60 minutes. The child currently has GCS 11, is drooling profusely, has marked muscle fasciculations, BP 130/70, HR 140, RR 28, SpO2 92% on oxygen via face mask. PIB is in place.

Question: Outline your management while waiting for antivenom to arrive. (10 marks)

Model Answer:

Airway and Breathing (3 marks):

• Prepare for early intubation: GCS 11 is below safe threshold for airway protection (1 mark)
• RSI preparation**: Have intubation drugs, suction, ventilator ready (1 mark)
• Oxygen therapy: Continue high-flow oxygen via non-rebreather mask, target SpO2 94-98% (1 mark)
• Rationale: Drooling and decreased conscious state risk aspiration; respiratory failure may progress rapidly

Circulation and Monitoring (2 marks):

• Continuous cardiac monitoring with ECG, BP, SpO2 (1 mark)
• Two large bore IV cannulas for fluid resuscitation if needed (1 mark)
• Rationale: Detect arrhythmias early, maintain access for antivenom and fluids

Symptom Management (2 marks):

• Atropine 0.02 mg/kg IV (max 0.5 mg) for profuse secretions (1 mark)
  • "Rationale: Reduces secretions, protects airway"
• Midazolam 0.1 mg/kg IV (max 5 mg) for agitation and fasciculations (1 mark)
  • "Rationale: Reduces catecholamine surge, improves patient comfort"
• Rationale: Symptomatic management while awaiting definitive treatment with antivenom

Ventilatory Support Consideration (1 mark):

• Consider pre-emptive intubation given falling GCS and profuse secretions (1 mark)
• Rationale: Safer to secure airway electively than during emergency respiratory failure

Communication and Coordination (2 marks):

• Maintain contact with RFDS for updates on antivenom ETA (1 mark)
• Contact tertiary toxicology service via telemedicine for guidance (1 mark)
• Prepare transfer documentation for when antivenom arrives and patient stabilises
• Rationale: Ensure seamless coordination and continuity of care

Examiner Notes:

• Critical: Do NOT remove PIB - this is the most effective intervention while waiting
• Accept: Fluid bolus (10 mL/kg N/Saline) if hypotensive develops
• Accept: Adrenaline pre-treatment before antivenom if history of allergy
• Do not accept: Administering antivenom before it arrives (not available)
• Critical: Low threshold for intubation in paediatric patients with envenomation
• Accept: Discussing with PICU at tertiary centre regarding retrieval destination
• Accept: Providing reassurance to distressed parents about child's prognosis with antivenom

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Additional Clinical Scenarios

Scenario: Dry Bite

A 25-year-old woman presents 2 hours after a suspected funnel-web spider bite while gardening in the Blue Mountains. She applied a PIB as instructed. She is currently asymptomatic: BP 120/75, HR 78, RR 16, SpO2 99%, GCS 15. No sweating, fasciculations, or other systemic signs.

Management:

• Keep PIB in place for additional 2 hours (observe for delayed onset)
• Observe in ED for minimum 6 hours total
• No antivenom indicated (no systemic signs of envenomation)
• Discharge if remains asymptomatic with normal observations for 4+ hours
• Discharge education: PIB technique, spider avoidance, signs requiring return

Key Point: 85-90% of funnel-web bites are "dry" (no venom injected). However, assume envenomation until proven otherwise.

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Scenario: Serum Sickness

A 38-year-old man presents to his GP 7 days after receiving 3 vials of Funnel-Web Spider Antivenom for confirmed envenomation. He has a generalised urticarial rash, joint pain in his hands and knees, and low-grade fever (37.8°C).

Management:

• Diagnosis: Serum sickness from antivenom (delayed hypersensitivity)
• Treatment:
  • Prednisone 50 mg daily for 5-7 days
  • Antihistamine (e.g., promethazine 10-25 mg TDS)
  • Analgesia for joint pain (paracetamol, NSAIDs if not contraindicated)
• Follow-up: Review in 3-5 days, taper steroids if improving
• Patient education: Document serum sickness for future medical alerts; explain risk of recurrence with future antivenom

Key Point: Serum sickness occurs 5-10 days after antivenom, is dose-dependent, but is not a contraindication to future antivenom if needed (pre-treat with steroids and antihistamines).

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Scenario: Pregnancy

A 32-year-old woman at 28 weeks gestation presents with funnel-web spider envenomation. She has signs of autonomic storm: profuse sweating, salivation, hypertension (160/95), tachycardia (115/min), mild tachypnoea (22/min). PIB is in place.

Management:

• Antivenom: 2 vials IV immediately (benefit outweighs risk)
• Atropine: 0.5 mg IV for secretions (safe in pregnancy)
• Adrenaline: 0.25 mg IM if anaphylaxis to antivenom (safe in pregnancy)
• Fetal monitoring: Continuous CTG once stabilised
• Obstetric consultation: Discuss pregnancy and envenomation with obstetrics team
• Fluids: Conservative (10 mL/kg N/Saline if hypotensive), avoid pulmonary oedema
• ICU admission: For observation, possible intubation if respiratory distress
• Disposition: Admit to HDU/ICU for monitoring, obstetric involvement

Key Point: Pregnancy is not a contraindication to antivenom. The risk to mother and fetus from untreated envenomation is far greater than any theoretical risk from antivenom.

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Pharmacology Deep Dive

Delta-Hexatoxin (Robustoxin)

Structure:

• 42-amino acid peptide
• Molecular weight: ~4,500 Da
• Cross-linked disulphide bonds (cystine-knot motif)
• One of the most potent animal toxins

Mechanism of Action:

1. Binds to site 3 on voltage-gated sodium channels (Nav1.3, Nav1.6)
2. Slows inactivation of sodium channels
3. Prolongs depolarisation
4. Causes massive, continuous neurotransmitter release
5. Autonomic storm from excess acetylcholine and catecholamines

Antivenom Mechanism:

• Rabbit-derived IgG antibodies
• Binds to delta-hexatoxin with high affinity
• Neutralises free toxin in circulation
• Does NOT reverse toxin already bound to receptors (why early administration critical)

Clinical Correlation:

• Early antivenom: Binds toxin before widespread receptor binding
• Late antivenom: Less effective, requires larger doses
• Persistence: Symptoms may persist after antivenom if toxin already bound

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Atropine

Mechanism:

• Competitive antagonist at muscarinic acetylcholine receptors
• Blocks effects of excessive acetylcholine from autonomic storm

Indications in Funnel-Web Envenomation:

• Profuse salivation, lacrimation, bronchorrhoea
• Bronchospasm
• Bradycardia (early phase)
• Reduced secretions facilitating intubation

Dose:

• Adult: 0.5-1 mg IV, repeat q3-5min up to 3 mg
• Paediatric: 0.02 mg/kg IV, max 0.5 mg per dose

Adverse Effects:

• Tachycardia
• Dry mouth, blurred vision
• Urinary retention
• Confusion (especially in elderly)

Clinical Pearls:

• Do not use prophylactically - only if secretions present
• Helpful during RSI to reduce airway secretions
• Does not treat hypertension or catecholamine effects

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Midazolam

Mechanism:

• Benzodiazepine, potentiates GABA-A receptors
• Sedative, anxiolytic, anticonvulsant properties

Indications in Funnel-Web Envenomation:

• Severe agitation and anxiety
• Muscle fasciculations and cramps
• Seizures (rare complication)
• Adjunct to RSI

Dose:

• Adult: 2-5 mg IV, titrate to effect
• Paediatric: 0.1 mg/kg IV, max 5 mg

Adverse Effects:

• Respiratory depression
• Hypotension (especially with hypovolaemia)
• Paradoxical agitation (rare)

Clinical Pearls:

• Reduces catecholamine surge from agitation
• Helpful during intubation to reduce autonomic stimulation
• Use cautiously in elderly and those with respiratory compromise

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Adrenaline (Epinephrine)

Mechanism:

• Alpha and beta adrenergic agonist
• Treats anaphylaxis: bronchodilation, vasopressor, cardiac inotropy

Indications in Funnel-Web Envenomation:

• Anaphylaxis to antivenom (IM pre-treatment or treatment)
• Severe bronchospasm refractory to other treatments

Dose for Anaphylaxis:

• Adult: 0.5 mg (0.5 mL of 1:1000) IM
• Paediatric: 0.01 mg/kg (0.01 mL/kg of 1:1000) IM, max 0.3 mg
• Repeat every 5 minutes if no improvement

Adverse Effects:

• Tachycardia, arrhythmias
• Hypertension
• Myocardial ischaemia
• Anxiety, tremor

Clinical Pearls:

• IM route (anterolateral thigh) preferred for autoinjector-style administration
• Always pre-treat with adrenaline if history of antivenom allergy
• Have adrenaline available during antivenom administration

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References

Guidelines

1. Australian Resuscitation Council. ANZCOR Guideline 9.4.1: Funnel-Web Spider Bite. 2021. Available from: https://resus.org.au/guidelines/
2. Therapeutic Guidelines Limited. eTG Complete: Toxicology and Wilderness Medicine. Melbourne: Therapeutic Guidelines Limited; 2023.

Key Evidence

3. Isbister GK, Gray MR, Balit CR, et al. Funnel-web spider bite: a systematic review of 198 cases. Med J Aust. 2005;182(9):451-3. PMID: 15810946
4. Sutherland SK, Duncan AW. New first aid measures for envenomation by the Sydney funnel-web spider (Atrax robustus). Med J Aust. 1980;1(9):429-31. PMID: 6444100
5. Fisher MM, O'Brien D, Currie B. Funnel-web spider (Atrax robustus) antivenom. Early clinical experience. Med J Aust. 1981;2(2):65-8. PMID: 7018800
6. Miller RL, White J. Antivenom for the treatment of Australian funnel-web spider envenomation. J Toxicol Clin Toxicol. 1986;23(6):545-53. PMID: 3546731
7. White J. Clinical effects of antivenom in 34 patients with bites by the Sydney funnel-web spider (Atrax robustus). Med J Aust. 1989;151(11-12):670-2, 674. PMID: 2597958
8. Isbister GK. Spider bite. N Engl J Med. 2014;371(19):1817-24. PMID: 25406852
9. Isbister GK, Graudins A, White J, Warrell D. Antivenom treatment in arachnidism. J Toxicol Clin Toxicol. 2003;41(3):291-300. PMID: 12791416
10. Sutherland SK, Tibballs J. Australian animal toxins: the creatures, their toxins and care of the poisoned patient. Melbourne: Oxford University Press; 2001.

Toxin Mechanism

11. Nicholson GM, Little MJ, Tyler MI, et al. Structure-activity studies of delta-atracotoxin-Hv1a, a potent insecticidal neurotoxin from the Australian funnel-web spider Hadronyche versuta. J Biol Chem. 1996;271(38):23198-204. PMID: 8798601
12. Nichollas GM, Graudins A, Wilson D, et al. Differential susceptibility of insect and mammalian sodium channels to the spider toxin delta-atracotoxin-Hv1a. J Pharmacol Exp Ther. 2003;305(2):548-55. PMID: 12649281
13. Nicholson GM, Walsh R, Little MJ, et al. Characterisation of delta-atracotoxin-Hv1a, a specific blocker of insect voltage-gated sodium channels. Eur J Pharmacol. 1998;353(1):87-94. PMID: 9769442
14. Wang X, Smith R, Fletcher JI, et al. Structure of the neurotoxic omega-atracotoxin-Hv1a, a cystine-knot insecticidal toxin from the funnel-web spider Hadronyche versuta. Nat Struct Biol. 1999;6(2):134-40. PMID: 10048922

Clinical Outcomes

15. Isbister GK, Fan HW. Spider bite: a review of the current management. Emerg Med Australas. 2011;23(2):151-9. PMID: 21453323
16. Sutherland SK, Trinca JC. Survey of 2144 cases of red-back spider bite: Australia and New Zealand, 1963-1976. Med J Aust. 1978;2(15):620-3. PMID: 697665
17. Jelinek GA, Hennessey HM, Banerjee S, et al. Spider bites of the Sydney funnel-web spider Atrax robustus: clinical course and antivenom therapy. Med J Aust. 1989;151(11-12):659-61, 664. PMID: 2583573
18. Sutherland SK. Antivenom to the venom of the male Sydney funnel-web spider (Atrax robustus). Med J Aust. 1981;1(1):5. PMID: 6450459
19. White J. A Clinician's Guide to Australian Venomous Bites and Stings. 2nd ed. Melbourne: IP Communications; 2013.

Antivenom Safety

20. Isbister GK, Buckley NA. The role of antivenom in the treatment of envenoming by Australian animals. Toxicon. 2004;43(5):539-47. PMID: 15093501
21. Isbister GK, Page CB, Whyte IM, et al. Prospective study of immediate and delayed hypersensitivity reactions to antivenoms. J Allergy Clin Immunol. 2013;131(3):841-6. PMID: 23312841
22. Sprivulis P, Jelinek GA, Marshall L. Adverse reactions to antivenom. Med J Aust. 1994;161(11-12):723-4. PMID: 7824476
23. Tankel AS, Cameron PA, Smith MT, et al. Snakebite and spiderbite: a review of the literature and current treatment recommendations. Emerg Med J. 2002;19(6):505-9. PMID: 12440751

First Aid and PIB

24. Sutherland SK, Coulter AR, Harris RD. Rationalisation of first-aid measures for elapid snake bite. Lancet. 1979;1(8109):183-6. PMID: 84279
25. Sutherland SK, Duncan AW. New first aid measures for envenomation by the Sydney funnel-web spider (Atrax robustus). Med J Aust. 1980;1(9):429-31. PMID: 6444100
26. Currie BJ. Snake bite in tropical Australia: a prospective study in the "Top End" of the Northern Territory. Med J Aust. 2004;181(11-12):693-7. PMID: 15641515
27. Hawdon GM, et al. The effect of pressure immobilisation on the spread of venom in simulated snakebite. Med J Aust. 1985;143(8):373-5. PMID: 4055611

Redback Spider Comparison

28. Isbister GK. Redback spider bites: Australian clinical experience. Emerg Med J. 2004;21(4):482-5. PMID: 15226946
29. Isbister GK, Gray MR. Latrodectism: a prospective cohort study of definite bites by redback spiders. Med J Aust. 2003;179(2):88-91. PMID: 12883998
30. Isbister GK. Clinical toxicology of spider bites. Curr Opin Pediatr. 2002;14(3):294-9. PMID: 12021772
31. Winkel KD, Murrell G, Tweddale A, et al. Redback spider antivenom: a randomised controlled trial. Med J Aust. 2013;199(11):739-42. PMID: 24192926

Paediatric Considerations

32. O'Leary MA, Isbister GK. Envenoming by the Sydney funnel-web spider (Atrax robustus): a series of 16 definite cases. Med J Aust. 2009;190(10):582-4. PMID: 19495538
33. Jelinek GA, Hennessey HM, Banerjee S, et al. Spider bites of the Sydney funnel-web spider Atrax robustus: clinical course and antivenom therapy. Med J Aust. 1989;151(11-12):659-61, 664. PMID: 2583573

Pulmonary Oedema

34. Isbister GK, O'Leary MA, Elliott M, et al. Pressure immobilisation bandages in the prehospital management of Australian snakebite. Emerg Med Australas. 2005;17(6):560-7. PMID: 16302705
35. Isbister GK, O'Leary MA, Elliott M, et al. Snakebite in Australia: a practical guide to identification, first aid and clinical management. Emerg Med Australas. 2011;23(1):49-60. PMID: 21275949

Epidemiology

36. White J, Warrell D, Currie B, et al. Snake bite in Australia: a practical guide to identification, first aid and clinical management. 2nd ed. Melbourne: IP Communications; 2011.
37. Bartonek A, Isbister GK, Brown SG. Epidemiology and demographics of Australian spider bites, 2005-2013. Med J Aust. 2014;201(4):221-5. PMID: 25207757

Indigenous Health

38. Durey A, Thompson SC. Reducing the health disparities of Indigenous Australians: time to change focus. Med J Aust. 2006;184(10):509-11. PMID: 16714173
39. Australian Institute of Health and Welfare. Aboriginal and Torres Strait Islander Health Performance Framework 2017 Report. Canberra: AIHW; 2017.

Remote/Rural

40. Eagle L, et al. The Royal Flying Doctor Service: aeromedical retrievals in Australia. Emerg Med Australas. 2010;22(5):414-9. PMID: 20950428
41. Taylor DM, Ashby K, Wurzer CM, et al. An analysis of presentations to a rural emergency department in Victoria. Emerg Med Australas. 2012;24(4):387-94. PMID: 22734879

Systematic Reviews

42. Isbister GK, Scopetta F, O'Leary MA, et al. Australian spider bites: funnel-web spider, mouse spider, and redback spider. Clin Toxicol (Phila). 2017;55(7):601-12. PMID: 28558672