Redback Spider Envenomation (Latrodectism)

Quick Answer

Critical Alert:

Redback Spider Envenomation

---

ACEM Exam Focus

Primary Written Exam Expectations

Basic Sciences:

• Toxin structure: Alpha-latrotoxin is a high-molecular-weight protein (130 kDa)
• Mechanism: Binds neurexin 1α and latrophilin-1 receptors → pore formation → uncontrolled Ca²⁺/Na⁺ influx → massive neurotransmitter release (acetylcholine, norepinephrine, GABA)
• Pharmacology: Equine-derived IgG antivenom, dose-dependent adverse reactions, route considerations (IM vs IV bioavailability)
• Epidemiology: Australia-wide distribution, 2,000-10,000 bites annually, rare mortality since 1956 antivenom

Common Question Themes:

1. Compare redback vs funnel-web envenomation management (PIB contraindication for redback)
2. Mechanism of alpha-latrotoxin action at presynaptic nerve terminal
3. Clinical features distinguishing latrodectism from other bites
4. Antivenom controversy: RAVE trial findings vs historical practice

Primary Viva Exam Expectations

Viva 1: Pharmacology of Antivenom

• Discuss redback spider antivenom composition (equine IgG fraction)
• Explain IM vs IV administration and bioavailability differences
• Describe acute vs delayed hypersensitivity reactions
• Discuss evidence from RAVE trial (2014) and its impact on practice

Viva 2: Pathophysiology of Latrodectism

• Explain alpha-latrotoxin mechanism at cellular level
• Describe progression from local to systemic features
• Discuss why PIB increases pain in redback bites vs funnel-web
• Explain regional diaphoresis pathophysiology

Fellowship Written Exam Expectations

SAQ Patterns:

1. Management algorithm: Patient presents with redback bite - outline initial management
2. Clinical decision: When to use antivenom vs analgesia alone (benefits vs risks)
3. Differential diagnosis: Redback bite vs other causes of abdominal pain, hypertension, diaphoresis
4. Special populations: Management in pregnancy, children, or elderly

OSCE Station Relevance:

• History: Elicit bite circumstances, identify spider, symptom progression
• Examination: Local site assessment, regional diaphoresis, vital signs, neurological exam
• Procedure: Antivenom administration (IV dilution, IM technique)
• Communication: Explain limited antivenom efficacy to distressed patient/family

---

Key Points

1. PIB NOT recommended for redback bites - use cold packs only (ANZCOR 9.4.8)
2. Alpha-latrotoxin causes massive presynaptic neurotransmitter release via pore formation and Ca²⁺ influx
3. Clinical hallmark: Progressive local pain + regional diaphoresis (sweating only in affected limb)
4. First-line treatment: Aggressive analgesia (NSAIDs, paracetamol, parenteral opioids)
5. RAVE trial (2014): IV antivenom no more effective than placebo for pain relief at 2 or 24 hours
6. Antivenom indication: Pain refractory to parenteral opioids or severe systemic toxicity
7. Adverse effects: Anaphylaxis (below 1-2%), serum sickness (1-5%), weigh benefits vs risks
8. Distribution: Australia-wide, prefers dry sheltered areas (sheds, under eaves, woodpiles, outdoor toilets)
9. Special populations: Children and pregnant women may warrant earlier antivenom consideration

---

Epidemiology

Distribution in Australia

Redback Spider Distribution

Seasonal and Temporal Patterns

Risk Factors for Envenomation

---

Pathophysiology

Alpha-Latrotoxin Mechanism of Action

Critical Alert:

Core Mechanism

Step 1: Receptor Binding

• Neurexin 1α: Primary presynaptic membrane receptor
• Latrophilin-1 (CIRL): G-protein coupled receptor, enhances toxin binding
• High-affinity binding specific to vertebrate nerve terminals

Step 2: Pore Formation

• Alpha-latrotoxin inserts into presynaptic lipid bilayer
• Forms cation-selective tetrameric channels
• Channels allow uncontrolled influx of Ca²⁺ and Na⁺ ions
• Pore size estimated 50-100 Å

Step 3: Neurotransmitter Release

• Elevated intracellular Ca²⁺ triggers massive exocytosis of synaptic vesicles
• Achetylcholine: Causes muscle fasciculation then paralysis
• Norepinephrine: Causes hypertension, tachycardia, diaphoresis
• GABA: Contributing to autonomic instability

Step 4: Nerve Terminal Exhaustion

• Sustained neurotransmitter depletion
• Presynaptic paralysis
• Clinical: Initial overstimulation → subsequent fatigue

Key Features of Envenomation:

Why PIB Is Not Recommended

Venom Pharmacokinetics:

• Redback venom: Large protein (130 kDa), slow lymphatic spread
• Systemic absorption occurs over hours, not minutes
• Local action predominates (pain, diaphoresis)

PIB Disadvantages:

• Pressure on envenomated tissue increases local pain significantly
• No evidence PIB reduces systemic envenomation for redback bites
• PIB is uncomfortable and may delay appropriate analgesia administration
• Delayed seeking medical help due to perception that PIB "treats" the bite

Comparison with Funnel-Web Bites:

---

Clinical Features

Presentation of Latrodectism

Critical Alert:

Clinical Stages

Local Features (Present in greater than 95% of Cases)

Systemic Features (Present in 20-30% of Cases)

Autonomic Overactivity:

• Hypertension: SBP often 140-180 mmHg, can exceed 200 mmHg in severe cases
• Tachycardia: HR 100-140 bpm, sometimes higher
• Generalized diaphoresis: Profuse sweating beyond affected limb
• Facial flushing: Common with systemic envenomation
• Mydriasis: Dilated pupils due to sympathetic stimulation

Gastrointestinal:

• Nausea: Very common (40-60% of systemic cases)
• Vomiting: May be persistent
• Abdominal pain: Can mimic appendicitis, colic, or peritonitis
• Diarrhoea: Less common

Neurological/Psychiatric:

• Headache: Frontal or diffuse, moderate to severe
• Agitation and anxiety: Due to pain and catecholamine surge
• Restlessness: Patient unable to find comfortable position
• Tremor: Fine tremor of hands, can be generalized
• Paraesthesias: Tingling sensations in affected limb

Musculoskeletal:

• Muscle cramps: Particularly in affected limb
• Fasciculations: Localised muscle twitching
• Weakness: Generally mild, can be localised
• Joint pains: Arthralgia in some patients

Clinical Grading

Mild Latrodectism:

• Local pain only
• Local erythema and oedema
• Regional diaphoresis present
• No systemic features

Moderate Latrodectism:

• Moderate-severe local pain
• Regional diaphoresis prominent
• Systemic autonomic features present (mild hypertension, tachycardia)
• Nausea/vomiting may occur
• Pain responds to NSAIDs/paracetamol

Severe Latrodectism:

• Severe pain (refractory to oral analgesics)
• Marked autonomic instability (SBP greater than 180, HR greater than 120)
• Profuse sweating, agitation
• Persistent vomiting, significant abdominal pain
• May require parenteral opioids or antivenom

Differential Diagnosis

---

Clinical Approach

ED Assessment Algorithm

Critical Alert:

Systematic Assessment

Initial Assessment

Airway & Breathing:

• Airway protection rarely compromised unless severe agitation causing distress
• Monitor for respiratory depression if high-dose opioids administered

Circulation:

• Blood pressure: Check both arms if hypertensive
• Heart rate: Tachycardia common with sympathetic overdrive
• ECG: Not routinely required but consider if chest pain, hypertension greater than 180, or cardiovascular disease

Disability:

• GCS: Assess if altered mental status (consider alternative diagnoses)
• Pain score: Use standard scoring (0-10 VAS), track response to analgesia
• Pupils: Mydriasis suggests sympathetic overactivity

Exposure (Focused Local Examination):

• Bite site: Location, number of fang marks (usually 2), local findings
• Regional diaphoresis: Compare affected limb to contralateral side
• Regional lymph nodes: Check for lymphadenopathy (common but not diagnostic)
• Distal neurovascular status: Ensure no compartment syndrome (rare in redback bites)

Essential History

Bite Circumstances:

• Time of bite (onset of symptoms typically within 30-60 min)
• Location of bite (outdoor toilet, shed, garden)
• Spider description (red stripe on black abdomen is pathognomonic)
• Any retained spider (capture if possible, handle safely)

Symptom Progression:

• Pain intensity trajectory (worsening over first hour is typical)
• Timing of regional diaphoresis onset
• Systemic symptom onset (nausea, vomiting, headache)
• Any improvement with initial analgesia

Medical History:

• Cardiovascular disease (coronary artery disease, hypertension, arrhythmias)
• Pregnancy (current possibility, LMP)
• Previous redback bites and response to treatment
• Allergies (particularly horse products - relevant to antivenom)
• Medications (antihypertensives, beta-blockers may blunt tachycardia)

Red Flags Requiring Antivenom Consideration

Critical Alert:

Antivenom Consideration Triggers

---

Investigations

Routine Investigations

Most redback spider bites require minimal investigations.

When to Consider Additional Investigations

Suspected Alternative Diagnosis:

• Full blood count: If suspected infection (cellulitis) - leukocytosis in infection, normal in envenomation
• CRP/ESR: If unclear cellulitis vs envenomation - elevated in infection
• Creatine kinase: If compartment syndrome suspected (rare in redback bites)
• Coagulation profile: If coagulopathic envenomation considered (snake, funnel-web) - normal in redback

Severe Systemic Features:

• Troponin: If chest pain, significant hypertension, cardiovascular risk factors
• Chest X-ray: If suspected pulmonary oedema (rare, more funnel-web)
• CT head: If altered mental status, severe headache (consider alternative diagnoses)

Special Populations:

• Pregnancy: Obstetric ultrasound if maternal instability, fetal monitoring
• Children: Consider metabolic causes if altered behaviour (not pure envenomation)

Diagnostic Criteria

Definite Redback Envenomation:

1. Witnessed spider bite with spider description consistent with Latrodectus hasselti
2. Progressive local pain at bite site
3. Regional diaphoresis (pathognomonic)
4. Exclusion of alternative diagnoses

Probable Redback Envenomation:

1. Suspected spider bite (not witnessed)
2. Progressive local pain
3. Regional diaphoresis
4. Systemic autonomic features

Unsuspected Envenomation:

• Presenting with abdominal pain, hypertension, diaphoresis
• Consider redback bite in differential, especially if regional diaphoresis noted

---

Management

First Aid (Pre-Hospital)

CRITICAL: DO NOT Apply Pressure Immobilization Bandage

Critical Alert:

ANZCOR Guideline 9.4.8 - Redback Spider First Aid

Correct First Aid Steps:

1. Keep patient calm and at rest

   • Minimise movement to reduce pain and anxiety
   • Sit or lie in comfortable position

2. Apply cold pack

   • Ice wrapped in cloth, applied directly to bite site
   • Apply for 15-20 minutes, then remove for 15-20 minutes
   • Repeat cycle as needed for pain relief
   • Avoid direct ice contact to skin (risk of cold injury)

3. DO NOT apply pressure bandage

   • PIB is for snakes and funnel-web spiders
   • PIB increases pain significantly in redback bites
   • PIB provides no benefit as venom spreads slowly

4. DO NOT apply tourniquet

   • No evidence of benefit
   • Increases tissue damage and pain

5. Transport to medical facility

   • Urgent if systemic features present
   • Non-urgent if local pain only responding to simple analgesia
   • Bring spider if safely captured (sealed container)

ED Management

Analgesia (First-Line)

Special Population Considerations

Children

Critical Alert:

Paediatric Considerations

Dose Adjustments:

• Paracetamol: 15 mg/kg PO/PR q4-6h (max 90mg/kg/24h)
• Ibuprofen: 10 mg/kg PO q6-8h (max 40mg/kg/24h)
• Morphine: 0.05-0.1 mg/kg IV q10-15min PRN
• Antivenom: 500 units (full adult dose) for all children

Specific Considerations:

• Higher index of suspicion for envenomation in children with unexplained irritability, crying
• Parental reassurance important (pain can be distressing)
• Admit young children with significant systemic features

Pregnancy

Critical Alert:

Pregnancy Considerations

Management:

• Paracetamol and NSAIDs (ibuprofen) safe in pregnancy
• Opioids (morphine, oxycodone) can be used, monitor for respiratory depression
• Antivenom 500 units safe in pregnancy (equine IgG, category B)
• Obstetric consultation recommended for systemic envenomation
• Cardiotocography (CTG) if gestational age greater than 20 weeks and systemic features present

Considerations:

• Theoretical risk of uterine stimulation from catecholamine surge
• Maternal hypertension can compromise uteroplacental perfusion
• Antivenom benefits in severe cases outweigh risks

Elderly

Specific Considerations:

• Higher cardiovascular risk from hypertension and tachycardia
• Polypharmacy interactions (opioids with sedatives, antihypertensives)
• Lower threshold for admission and monitoring
• Consider delirium risk with opioids in patients with dementia

---

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Health

Critical Alert:

Indigenous Health Context

Environmental Exposure Factors:

• Housing quality: Inadequate flyscreens, gaps around doors/windows increase spider entry
• Outdoor facilities: Higher reliance on outdoor toilets in remote communities
• Traditional dwellings: Some community housing has more open spaces and sheltered areas
• Geographic distribution: Remote and rural areas have higher spider populations

Access to Care Barriers:

• Distance: Remote communities may be hours from nearest hospital stocked with antivenom
• Transport: Limited availability of emergency transport, especially at night
• Cultural factors: Distrust of mainstream healthcare, preference for traditional healing first
• Cost: Financial barriers to accessing care (though public ED is free)
• Communication: Language barriers for some Aboriginal languages

Health Disparities:

• Higher baseline cardiovascular disease → increased risk from hypertension
• Diabetes complications may be exacerbated by autonomic stress
• Higher rates of chronic pain → potential under-recognition of redback bite pain
• Later presentation to medical facilities (average delay 4-12 hours vs 1-3 hours urban)

Culturally Safe Management:

1. Communication

   • Use plain English, avoid medical jargon
   • Use Aboriginal Health Workers if available
   • Ask about traditional medicine use (avoid dismissal of cultural practices)
   • Explain management clearly, involve family in decision-making

2. Antivenom Decision-Making

   • Discuss risks/benefits thoroughly with patient and family
   • Acknowledge cultural concerns about horse-derived product
   • Respect autonomy if antivenom declined after informed discussion
   • Ensure adequate analgesia provided regardless of antivenom decision

3. Follow-up Care

   • Consider remote area implications of serum sickness (may not have easy access)
   • Arrange telehealth follow-up if returning to remote community
   • Coordinate with Aboriginal Medical Service if available
   • Provide clear written instructions in plain English

4. Environmental Prevention

   • Advise on spider-proofing homes (flyscreens, sealing gaps)
   • Discuss safe outdoor toilet construction and maintenance
   • Encourage regular cleaning and decluttering around homes
   • Work with local council or health service on community-wide spider control

Māori Health Considerations (New Zealand)

Context:

• Redback spiders introduced to New Zealand
• Established populations in Auckland, Waikato, Bay of Plenty
• Māori communities in rural/semi-rural areas at higher risk

Cultural Considerations:

• Whānau involvement: Include family in decision-making about antivenom
• Kaitiakitanga (guardianship): Connection to land/environment, consider environmental prevention
• Rongoā Māori (traditional medicine): Ask about traditional remedies used
• Cultural protocols: Allow time for karakia (prayers) if requested

Management Adaptations:

• Involve Kaumātua (elder) if complex medical decisions needed
• Use Māori Health Workers if available
• Provide explanations that acknowledge cultural worldview
• Consider whānau support systems for post-discharge care

---

Remote and Rural Emergency Medicine

Retrieval and Transport Considerations

Critical Alert:

Remote Area Management

Antivenom Availability:

• Major hospitals: Usually stock redback antivenom
• Rural hospitals: May have limited stock or require retrieval from regional centre
• Remote clinics: Often do not stock antivenom
• Royal Flying Doctor Service (RFDS): Stock antivenom on retrieval aircraft, can transport to remote facilities

Management in Rural Facilities:

Step 1: Assess and Stabilize

• ABCDE assessment (same as urban)
• Aggressive analgesia (may be limited by drug stock)
• Cold packs first aid
• Contact regional toxicology service (13 11 26 - Poisons Information Centre)

Step 2: Determine Need for Retrieval Retrieval indicated if:

• Pain refractory to available analgesia
• Severe systemic features (hypertension greater than 180, agitation)
• Pregnancy with systemic envenomation
• Children below 5 years with systemic features
• Cardiovascular disease with sympathetic overdrive

Step 3: Coordinate Retrieval

• Contact RFDS or state retrieval service
• Provide: Age, weight, vital signs, analgesia given, time of bite, symptoms
• Confirm receiving hospital has antivenom stock
• Consider pre-retrieval antivenom if available and patient deteriorating

Step 4: Transport Considerations

• Road transport: For distances below 2 hours, ambulance transport appropriate
• Aeromedical: For distances greater than 2 hours, severe envenomation, or pregnancy
• Escort: Consider escorting medical officer if available (particularly for RFDS missions)

Telemedicine Support:

• Use telehealth for real-time specialist consultation
• Video assessment can assist with clinical decision-making
• Remote monitoring of vital signs during transport
• Specialist advice on analgesia titration in limited resource settings

Resource Limitations:

Documentation for Retrieval:

• Time of bite
• Time of ED presentation
• Analgesia given (dose, time, response)
• Vital signs trend
• Red flags identified
• Patient comorbidities
• Reason for retrieval request

Antivenom Administration in Remote Settings:

• If antivenom available and indicated (pain refractory to opioids):
  • IM administration preferred if IV access difficult (e.g., difficult veins in children, obese patients)
  • Monitor for 30-60 minutes for acute reactions
  • If retrieval en route, continue monitoring and document response

Post-Discharge Considerations in Remote Communities:

• Ensure adequate supply of analgesia (may be limited by local pharmacy)
• Clear red flag education for return (may be long distance to medical care)
• Consider follow-up telehealth consultation if pain persists
• Arrange community health nurse check-in if available
• Provide written discharge instructions for local clinic

---

Pitfalls and Pearls

Common Mistakes

Critical Alert:

Critical Pitfalls

1. Applying pressure immobilization bandage

   • PIB increases pain significantly in redback bites
   • Provides no benefit as venom spreads slowly
   • Can delay appropriate analgesia administration
   • Correct action: Apply cold packs only

2. Routine antivenom administration

   • RAVE trial (2014) showed no significant benefit vs placebo
   • Antivenom has risk of anaphylaxis (below 1-2%) and serum sickness (1-5%)
   • Correct action: Reserve for pain refractory to parenteral opioids or severe systemic features

3. Underestimating pain severity

   • Redback bite pain is often severe and progressive
   • Patients may be agitated, appear anxious
   • Correct action: Treat pain aggressively, use opioids early if moderate-severe pain

4. Missing systemic features

   • Hypertension and tachycardia can be attributed to pain/anxiety
   • Abdominal pain can mimic acute abdomen
   • Correct action: Assess for red flags: check BP, HR, abdominal examination, mental status

5. Inadequate analgesia before antivenom decision

   • Antivenom not trialed before opioids adequately titrated
   • Correct action: Ensure adequate parenteral opioid trial before considering antivenom

6. Discharging too early

   • Pain may peak at 2-6 hours post-bite
   • Patients discharged at 1 hour may return with worsening pain
   • Correct action: Observe 2-4 hours if systemic features, 1-2 hours if local only

7. Not offering antivenom when indicated

   • Withholding antivenom in refractory cases due to RAVE trial interpretation
   • Correct action: Antivenom still has role in severe, refractory envenomation - discuss with patient

Clinical Pearls

Critical Alert:

Expert Tips

1. Regional diaphoresis is pathognomonic

   • Sweating only in affected limb (not generalized) strongly suggests redback
   • Can be subtle - compare limb to contralateral side
   • Often more prominent than patient reports

2. Pain trajectory is diagnostic

   • Redback pain worsens over first hour (not typical for cellulitis)
   • Cellulitis pain tends to be steady or progressive over hours
   • Use pain history to differentiate from infection

3. Antivenom debate: clinical nuance

   • RAVE trial limitations: IV administration only, heterogeneous population
   • Some patients still benefit from antivenom (refractory pain)
   • Shared decision-making essential - discuss limited efficacy with patient

4. Red flag recognition

   • Hypertension greater than 180 mmHg can be significant even if asymptomatic
   • Children with irritability and tachycardia: consider envenomation
   • Pregnant women: maternal stabilization priority, antivenom safe

5. Analgesia: be generous

   • Opioids often required for severe pain (not just "weak opioids")
   • Morphine 0.1mg/kg IV, repeat if needed
   • Add benzodiazepine for muscle spasm and anxiety (diazepam 5-10mg IV)

6. Outdoor toilets: historical but still relevant

   • Ask about bite location (outdoor toilet is classic redback setting)
   • May explain delayed presentation (patient unable to seek immediate help)

7. Spider identification: patient descriptions helpful

   • Red stripe on black abdomen = pathognomonic
   • Size (10-12mm) and body shape helpful
   • Redbacks are common, funnel-webs are rare - redback more likely in urban areas

8. Follow-up: warn about pain duration

   • Pain can persist 24-72 hours even with treatment
   • Patients often return next day concerned pain hasn't resolved
   • Set expectations at discharge: "pain may take several days to fully resolve"

9. Indigenous and remote communities

   • Consider antivenom earlier if delayed presentation to medical care
   • Ensure adequate analgesia supply for remote patients
   • Telehealth follow-up useful for remote communities

10. Antivenom adverse reactions

    • Anaphylaxis rare but can be life-threatening
    • Have adrenaline immediately available during administration
    • Serum sickness delayed (5-14 days) - warn patient to return if occurs

---

Viva Practice

Viva Scenario 1: Basic Sciences (Primary Viva)

Examiner: A 45-year-old man presents with a redback spider bite. He is experiencing severe pain and sweating only in his affected arm. He is asking about how the spider venom causes these symptoms.

Q1: What is the primary toxin in redback spider venom, and what is its mechanism of action?

Model Answer: The primary toxin is alpha-latrotoxin (α-LTX), a 130 kDa protein neurotoxin. Its mechanism involves:

1. Receptor binding: Binds to neurexin 1α and latrophilin-1 (CIRL) receptors on presynaptic nerve terminals
2. Pore formation: Inserts into presynaptic membrane, forming cation-selective tetrameric channels
3. Calcium influx: Allows uncontrolled influx of Ca²⁺ and Na⁺ ions
4. Neurotransmitter release: Elevated intracellular Ca²⁺ triggers massive exocytosis of synaptic vesicles, releasing acetylcholine, norepinephrine, and GABA
5. Nerve terminal exhaustion: Sustained release leads to neurotransmitter depletion and presynaptic paralysis

Clinical manifestations result from:

• Acetylcholine excess: Muscle fasciculation then weakness
• Norepinephrine excess: Hypertension, tachycardia, diaphoresis
• Autonomic effects: Nausea, vomiting, abdominal pain

Q2: Why is regional diaphoresis considered a pathognomonic feature of redback spider envenomation?

Model Answer: Regional diaphoresis (sweating only in the affected limb) is pathognomonic for latrodectism because:

1. Localized neurotransmitter release: Alpha-latrotoxin affects presynaptic terminals near the bite site initially
2. Norepinephrine-mediated sweating: Sympathetic overactivity in the envenomated region causes sweating limited to that limb
3. Distinct from generalized sweating: Unlike systemic envenomation or heat exhaustion, sweating is confined to the affected area
4. Diagnostic value: Regional diaphoresis combined with progressive pain strongly supports redback envenomation diagnosis
5. Comparison to limb: Comparing affected limb to contralateral limb highlights the asymmetry

Q3: How does redback spider venom pharmacokinetics differ from funnel-web spider venom, and why does this affect first aid?

Model Answer:

Pharmacokinetic rationale for different first aid:

• Redback: Slow lymphatic spread means PIB provides no benefit but increases pain significantly
• Funnel-web: Rapid systemic absorption means PIB is critical to delay potentially fatal envenomation

Q4: What is the evidence for redback spider antivenom efficacy, and how has this changed clinical practice?

Model Answer: The evidence for redback antivenom is controversial:

Key studies:

1. RAVE Trial (Isbister et al., 2014): Multicenter RCT comparing IV antivenom vs placebo

   • Found no significant difference in pain relief at 2 or 24 hours
   • No significant difference in systemic symptom resolution
   • Led to shift away from routine antivenom use

2. IM vs IV comparison (Isbister et al., 2008):

   • Showed poor absorption of IM antivenom
   • IV route has better bioavailability but questionable efficacy

Current clinical practice:

• First-line: Aggressive analgesia (NSAIDs, paracetamol, parenteral opioids)
• Antivenom indication: Pain refractory to parenteral opioids or severe systemic features
• Shared decision-making: Discuss limited efficacy and risks (anaphylaxis 1-2%, serum sickness 1-5%)

---

Viva Scenario 2: Clinical Management (Fellowship Viva)

Examiner: A 32-year-old woman presents 2 hours after a suspected redback spider bite while gardening. She reports progressive pain in her left forearm, sweating only in that arm, nausea, and headache. BP 165/95, HR 105, RR 18, SpO2 99%, temp 37.2°C.

Q1: What are your immediate priorities in managing this patient?

Model Answer: Immediate priorities follow ABCDE framework with focus on pain assessment:

1. Airway/Breathing: Not compromised (patient stable, RR 18, SpO2 99%)

2. Circulation:

   • BP elevated (165/95) - likely sympathetic overdrive, no organ damage signs
   • HR tachycardic (105) - consistent with sympathetic stimulation
   • Assess for chest pain, palpitations (consider demand ischaemia if history)

3. Disability:

   • Assess pain score (likely severe given description)
   • GCS normal (no encephalopathy)
   • Pupils - check for mydriasis (sympathetic overactivity)

4. Exposure:

   • Examine bite site: look for fang marks, erythema, oedema
   • Confirm regional diaphoresis (compare to right arm)
   • Assess distal neurovascular status
   • Check for other spider bites

5. Immediate interventions:

   • DO NOT apply pressure immobilization bandage
   • Apply cold pack to bite site
   • Start analgesia: paracetamol 1g + ibuprofen 400mg PO immediately
   • Establish IV access (for opioids if needed)
   • Monitor vitals q30-60min

Q2: This patient has moderate systemic features (hypertension, tachycardia, nausea, headache). When would you consider redback spider antivenom?

Model Answer: Indications for antivenom in this patient:

I would not give antivenom initially because:

1. Pain not yet assessed with adequate analgesia
2. Systemic features (HTN 165/95, HR 105) are moderate, not severe
3. No pain refractory to parenteral opioids yet
4. RAVE trial evidence suggests limited benefit

Antivenom consideration criteria:

• Pain refractory to parenteral opioids (primary indication)
• Severe hypertension (SBP greater than 180 or symptomatic)
• Severe agitation/restlessness
• Pregnancy (not applicable here)
• Child below 5 years (not applicable here)

Stepwise approach:

1. Give simple analgesia first (paracetamol + ibuprofen)
2. Reassess pain at 30-60 minutes
3. If VAS greater than 7 despite oral analgesia: give IV morphine 0.1mg/kg
4. Reassess pain after adequate opioid titration
5. If pain remains severe despite parenteral opioids: discuss antivenom with patient

Shared decision-making:

• Explain RAVE trial results: antivenom not more effective than placebo for most patients
• Discuss benefits (may help with refractory pain)
• Discuss risks: anaphylaxis (below 1-2%), serum sickness (1-5%)
• Respect patient preference after informed discussion

Q3: If you decide to administer antivenom, what dose and route would you use, and how would you monitor for adverse effects?

Model Answer: Antivenom administration:

Dose: 500 units (1 vial) - same dose for adults and children Route: Intravenous preferred (better bioavailability than IM)

Preparation:

• Dilute 500 units in 100mL normal saline
• Infuse over 15-30 minutes
• Have adrenaline, diphenhydramine, hydrocortisone available

Monitoring:

Management of acute reactions:

• Stop infusion immediately
• Adrenaline (epinephrine) 0.5mg (0.5mL 1:1000) IM for anaphylaxis
• Airway: 100% oxygen, prepare for intubation if needed
• Diphenhydramine 50mg IV for urticaria/angioedema
• Hydrocortisone 200mg IV for moderate-severe reactions
• Fluid: 500-1000mL normal saline IV for hypotension

Patient education about delayed reactions:

• Serum sickness: 5-14 days post-dose (fever, rash, joint pain)
• Return if delayed symptoms develop

Q4: This patient is a 32-year-old woman. What pregnancy considerations would be relevant if she were pregnant?

Model Answer: Pregnancy considerations for redback envenomation:

Risks to fetus:

• Theoretical risk of uterine stimulation from catecholamine surge
• Maternal hypertension can compromise uteroplacental perfusion
• Tachycardia may cause fetal distress
• Documented fetal loss is extremely rare

Antivenom safety in pregnancy:

• Redback antivenom is considered safe in pregnancy
• Equine-derived IgG, no evidence of teratogenicity
• Benefits of maternal stabilization generally outweigh theoretical risks
• Obstetric consultation recommended for systemic envenomation

Management modifications:

• Paracetamol and NSAIDs safe in pregnancy
• Opioids can be used (morphine, oxycodone) - monitor for respiratory depression
• Antivenom 500 units safe (no dose adjustment needed)
• Cardiotocography (CTG) if gestational age greater than 20 weeks and systemic features present
• Admission for monitoring if significant systemic envenomation

Counselling:

• Explain limited fetal risk
• Emphasize importance of maternal stabilization
• Discuss antivenom safety profile
• Involve obstetrics early if systemic features

---

Viva Scenario 3: Differential Diagnosis and Decision Making

Examiner: A 28-year-old man presents with severe abdominal pain, hypertension (170/100), tachycardia (110), and sweating. He mentions finding a spider in his bathroom earlier but didn't see it bite him.

Q1: What is your differential diagnosis, and what features would help distinguish redback spider envenomation from other causes?

Model Answer: Differential diagnosis for abdominal pain + hypertension + sweating:

Redback Spider Envenomation:

• Key distinguishing feature: Regional diaphoresis (sweating only in one limb or area)
• Progressive pain worsening over hours
• Possible bite site with local findings
• History of spider in environment

Acute Abdomen (appendicitis, cholecystitis, perforation):

• Focal tenderness, peritonitis signs
• Fever, leukocytosis on blood tests
• No regional diaphoresis
• CT/US would show pathology

Pheochromocytoma:

• Paroxysmal hypertension, headache, sweating, palpitations
• No bite history, no regional diaphoresis
• Often recurrent episodes
• 24-hour urine metanephrines elevated

Serotonin Syndrome:

• Medication history (SSRIs, MAOIs)
• Clonus, hyperreflexia, fever
• No regional diaphoresis
• Autonomic instability

Heat Exhaustion:

• Environmental exposure history
• Generalized sweating (not regional)
• Usually resolves with cooling
• No bite site

Sepsis:

• Fever, tachycardia, hypotension (not hypertension)
• Generalized symptoms
• Focus of infection on examination/imaging
• Elevated inflammatory markers

Distinguishing examination for redback envenomation:

1. Carefully examine skin for bite marks or local erythema
2. Compare limbs for asymmetrical sweating (pathognomonic)
3. Look for regional diaphoresis pattern
4. Ask about pain trajectory (worsening vs onset)

Q2: You suspect redback spider envenomation but the patient cannot confirm the bite. How would you manage the uncertainty?

Model Answer: Management with diagnostic uncertainty:

Diagnostic approach:

1. Detailed history:

   • Spider sighting (description, red stripe on black abdomen?)
   • Timing relative to symptom onset
   • Pain progression (worsening over hours suggests envenomation)
   • Any environmental exposure (outdoor toilet, gardening, shed)

2. Focused examination:

   • Full skin inspection for possible bite sites (check back, arms, legs)
   • Compare sweating pattern between limbs (regional diaphoresis?)
   • Abdominal examination (rebound, guarding, localisation?)
   • Neurological examination (fasciculations, weakness)

3. Basic investigations:

   • ECG: Hypertension workup
   • Venous lactate: Rule out sepsis/ischaemia
   • FBC: Check leukocytosis (elevated in infection, normal in envenomation)
   • CRP: Elevated in infection, normal in envenomation

Management approach:

• Treat as suspected redback envenomation if:

  • Progressive pain trajectory
  • Regional diaphoresis present
  • Possible spider exposure
  • No alternative diagnosis on initial workup

• Initial treatment:

  • Analgesia (paracetamol + ibuprofen)
  • IV access
  • Vital sign monitoring
  • Apply cold packs if any localised pain or tenderness identified

• Reassess at 30-60 minutes:

  • Response to analgesia (redback pain may partially improve)
  • Progression of symptoms
  • Vitals trend

• If uncertainty persists:

  • Obtain senior emergency physician review
  • Consider CT abdomen if acute abdomen features present
  • Observe 2-4 hours for symptom evolution
  • Early toxicology consultation (13 11 26)

Q3: The patient's pain is partially controlled with morphine but remains severe (VAS 7/10). Hypertension persists at 175/105. Discuss the decision to give antivenom in this uncertain diagnosis scenario.

Model Answer: Antivenom decision with diagnostic uncertainty:

Benefits of antivenom:

• May provide pain relief if redback envenomation (though evidence limited)
• May reduce sympathetic overactivity (hypertension, tachycardia)
• Low cost relative to potential benefit if diagnosis correct

Risks of antivenom:

• Anaphylaxis (below 1-2%) - life-threatening if occurs
• Serum sickness (1-5%) - causes additional morbidity
• Giving unnecessary treatment if diagnosis incorrect

Shared decision-making framework:

1. Explain diagnostic uncertainty: "We suspect redback spider bite but cannot confirm"
2. Explain evidence: "Antivenom helps some patients but not most; RAVE trial showed limited benefit"
3. Explain risks: "Small risk of severe allergic reaction and delayed serum sickness"
4. Present options:
   • Option A: Continue analgesia, observe, avoid antivenom risks
   • Option B: Give antivenom, possible benefit but small risk of severe reaction
5. Respect patient preference after informed discussion

Factors favouring antivenom:

• High clinical suspicion (regional diaphoresis present)
• Refractory pain despite opioids
• Persistent hypertension (symptomatic or greater than 180)
• Patient preference after informed discussion

Factors against antivenom:

• Diagnostic uncertainty (no clear bite, no regional diaphoresis)
• Patient declining after risk-benefit discussion
• Consider alternative diagnoses (acute abdomen, pheochromocytoma)

Q4: If antivenom is given, how would you monitor for improvement vs alternative diagnoses?

Model Answer: Monitoring after antivenom administration:

Expected response to antivenom (if redback envenomation):

• Pain reduction: Should see improvement within 30-60 minutes (though not guaranteed)
• Hypertension: BP may decrease over 1-2 hours
• Tachycardia: HR may normalize
• Systemic features: Nausea, headache, agitation may improve

Monitoring timeline:

Lack of response to antivenom: If no improvement in pain or vitals after 1-2 hours:

• Reconsider diagnosis (may not be redback envenomation)
• Consider alternative diagnoses:
  • CT abdomen (acute abdomen)
  • Workup for pheochromocytoma (urine metanephrines)
  • Evaluate for sepsis (blood cultures, CXR if indicated)
• Senior review and possibly surgical consultation if abdominal features persist

Admission criteria if diagnosis uncertain:

• No improvement with antivenom and analgesia
• Worsening abdominal pain or peritonitis signs
• Persistent hypertension greater than 180 or symptomatic
• Diagnostic workup incomplete (awaiting CT, labs)

---

Viva Scenario 4: Complex Clinical Scenario

Examiner: A 6-year-old Aboriginal girl presents to a remote clinic 4 hours after a spider bite. Her grandmother found a redback spider in the outdoor toilet. The child is crying inconsolably, has a mark on her left ankle, and her left leg is sweating profusely while the right leg is dry. HR 125, BP 115/70, RR 22, SpO2 98%, temp 37.5°C. The clinic has limited medications: paracetamol syrup and no opioid analgesia. No antivenom stock. The nearest hospital with antivenom is 3 hours by road.

Q1: How would you assess and manage this child, considering the remote context?

Model Answer: Assessment and management in remote clinic:

Immediate assessment (ABCDE):

1. Airway/Breathing: Crying inconsolably, airway patent, RR 22 (normal for age), SpO2 98%
2. Circulation: HR 125 (tachycardic for age), BP 115/70 (normal for 6-year-old)
   • HR likely due to pain and sympathetic stimulation
   • No signs of shock
3. Disability:
   • Pain assessment: Use FLACC or Wong-Baker scale (child cannot use VAS)
   • Likely severe pain given inconsolable crying
   • GCS: Assess despite crying (should be normal)
   • Pupils: Check for mydriasis
4. Exposure:
   • Inspect bite site on left ankle (fang marks, erythema, oedema)
   • Confirm regional diaphoresis (left leg sweating vs right leg dry) - pathognomonic

Diagnosis: Severe redback spider envenomation in a child

Initial management in remote clinic:

1. DO NOT apply pressure immobilization bandage
2. Apply cold pack to bite site
3. Analgesia:
   • Paracetamol 15mg/kg PO/PR (approximately 300-400mg)
   • Ibuprofen 10mg/kg PO if available (approximately 200mg)
   • May need to combine for better effect
4. Comfort measures: Calm child, grandmother present for comfort
5. Monitoring: Vitals q30min, pain assessment using age-appropriate scale

Decision for retrieval: RFDS retrieval INDICATED because:

• Child below 5 years (higher risk of systemic features)
• Severe pain (inconsolable crying, limited response to oral analgesia)
• No parenteral analgesia available in remote clinic
• No antivenom stock in clinic
• Systemic features (tachycardia, regional diaphoresis)
• Distance to hospital (3 hours - too long for road transport with severe pain)

Retrieval coordination:

1. Contact RFDS immediately (phone number prominently displayed)
2. Provide information:
   • Age: 6 years
   • Weight: Estimate if not known
   • Time of bite: 4 hours ago
   • Symptoms: Severe pain, inconsolable crying, regional diaphoresis, HR 125
   • Management given: Paracetamol dose, cold packs
   • No antivenom available
3. Confirm receiving hospital has antivenom stock
4. Consider if retrieval doctor can administer antivenom in-flight

Q2: Discuss the management of this child during the 1-2 hour wait for RFDS arrival.

Model Answer: Management during retrieval wait:

Analgesia optimization:

1. Reassess paracetamol response at 30-60 minutes
2. If pain continues severe (crying, distress):
   • Repeat paracetamol 15mg/kg PRN (max 90mg/kg/24h)
   • If clinic has IM morphine (unlikely in remote clinic): 0.05-0.1mg/kg IM
   • Most remote clinics do not have opioids - this is why retrieval needed

Comfort measures:

• Keep grandmother with child (familiar presence reduces distress)
• Use non-pharmacological comfort: distraction, calming techniques
• Allow child to adopt comfortable position
• Continue cold packs to bite site

Monitoring:

• Vitals q30min: HR, RR, BP, SpO2, temp
• Pain assessment: Use FLACC scale (Face, Legs, Activity, Cry, Consolability)
• Document response to analgesia
• Watch for progression: Worsening systemic features, vomiting, agitation

Communication:

• Continue communication with RFDS during flight
• Update on any deterioration
• Confirm estimated arrival time
• Provide directions to clinic for RFDS crew

Antivenom considerations during retrieval:

• If retrieval doctor can administer antivenom:
  • Discuss with receiving hospital
  • "Dose: 500 units IV or IM (IM may be easier in aircraft)"
  • Monitor for reactions
• If antivenom to be given at receiving hospital:
  • Continue analgesia en route
  • Manage pain as best as possible with available medications

Cultural considerations:

• Use Aboriginal Health Worker if available at clinic
• Respect grandmother's role in decision-making
• Explain management in plain English
• Acknowledge cultural connection to country and environment

Q3: The retrieval doctor arrives and administers antivenom. What dose and route would be appropriate for this child, and what monitoring is needed during the 2-hour flight to hospital?

Model Answer: Antivenom administration for child:

Dose and route:

• Dose: 500 units (1 vial) - same dose for all children and adults
• Route options:

Recommended approach:

• Attempt IV access first (preferable route)
• If IV access unsuccessful, administer IM (anterolateral thigh)
• Retrieval doctor has experience with difficult IV access in children

Administration details:

• IV route: Dilute 500 units in 100mL normal saline, infuse over 15-30 minutes
• IM route: 500 units undiluted, IM injection to anterolateral thigh
• Have adrenaline, diphenhydramine, hydrocortisone immediately available

Monitoring during flight:

Anaphylaxis management in flight:

• Stop infusion immediately
• Adrenaline 0.15mg (0.15mL 1:1000) IM (weight-based dose for 6 yo: 0.15mg)
• Airway: 100% oxygen, have airway equipment available
• Diphenhydramine 25mg IV
• Hydrocortisone 100mg IV
• Consider urgent diversion if reaction severe

Post-antivenom monitoring:

• Document response to antivenom (pain reduction? HR reduction?)
• Continue analgesia as needed (may still require opioids)
• Observe for serum sickness education (5-14 days post-dose)

Q4: Discuss the importance of cultural safety and follow-up planning for this Aboriginal child returning to her remote community.

Model Answer: Cultural safety and follow-up considerations:

Cultural safety principles:

1. Respect and partnership:

   • Involve grandmother in all discussions and decisions
   • Acknowledge family's knowledge and expertise about the child
   • Work with, not for, the family

2. Communication:

   • Use plain English, avoid medical jargon
   • Have Aboriginal Health Worker or cultural liaison involved if available
   • Confirm understanding (teach-back method)
   • Allow time for questions and family discussion

3. Decision-making:

   • Explain antivenom decision clearly
   • Discuss risks and benefits in culturally appropriate manner
   • Respect family's preferences and autonomy
   • Acknowledge concerns about horse-derived product if raised

Follow-up planning for remote community:

Immediate discharge considerations:

• Do NOT discharge immediately if antivenom just given (observe minimum 4-6 hours)
• If discharged: Ensure adequate analgesia supply for remote location

Analgesia supply planning:

• Provide sufficient paracetamol syrup for 3-5 days
• If opioids needed (uncommon for outpatient), ensure adequate supply
• Clear dosing instructions in plain English
• Consider blister packs for clarity

Education for grandmother and family:

• Pain may persist 24-72 hours (expected)
• Use cold packs at home
• Red flags requiring return:
  • Vomiting, dehydration
  • Chest pain, difficulty breathing
  • Worsening pain despite analgesia
  • Fever or rash in 5-14 days (serum sickness)

Serum sickness education:

• Explain: "May get fever, rash, joint pain 5-14 days after antivenom"
• Advise: Return to clinic if these symptoms develop
• Provide written instructions with local clinic contact

Coordination with local community:

• Provide discharge summary to local clinic
• Alert community health nurse if available
• Consider telehealth follow-up in 2-3 days
• Ensure remote clinic aware of antivenom administration

Environmental prevention education:

• Spider-proof outdoor toilet (flyscreens, sealed gaps)
• Regular cleaning of outdoor areas
• Safe spider removal methods (call council or pest control)
• Education about redback spiders and first aid

Long-term considerations:

• Document episode in child's medical record
• Consider if recurrence risk is high (housing conditions)
• Advocate for housing improvements if appropriate (flyscreens, maintenance)
• Link with Aboriginal Medical Service for ongoing care

---

OSCE Practice

OSCE Station 1: History Taking

Setting: Emergency Department cubicle

Scenario: A 38-year-old woman presents with severe left arm pain and sweating in that arm only. She mentions finding a spider in her garden shed but didn't see it bite her.

Task: Take a focused history to determine the likely diagnosis and severity of envenomation.

Time: 8 minutes

---

Marking Criteria:

Pass Mark: 18/26

---

OSCE Station 2: Clinical Examination

Setting: Emergency Department examination area

Scenario: A 42-year-old man presents 3 hours after a redback spider bite to his right forearm. He reports progressive pain and sweating only in that arm. BP 160/95, HR 105.

Task: Examine the patient with focus on the envenomation and identify any red flags.

Time: 8 minutes

---

Marking Criteria:

Pass Mark: 23/33

---

OSCE Station 3: Management and Procedure

Setting: Emergency Department resuscitation bay

Scenario: A 29-year-old woman presents with severe redback spider envenomation. Pain is refractory to morphine 10mg IV. BP 175/100, HR 115. You have decided to administer redback spider antivenom.

Task: Demonstrate the preparation and administration of redback spider antivenom, including safety measures and monitoring.

Equipment provided:

• Redback spider antivenom (500 units vial)
• Normal saline 100mL bag
• IV giving set
• Adrenaline 1:1000 (1mg)
• Diphenhydramine 50mg
• Hydrocortisone 100mg
• Suction, oxygen, airway equipment

Time: 11 minutes

---

Marking Criteria:

Pass Mark: 22/32

---

SAQ Practice

SAQ 1: Initial Management

Question:

A 35-year-old man presents to the Emergency Department 1 hour after a redback spider bite to his left forearm. He reports progressive pain and notes that his left arm is sweating profusely while his right arm is dry. He feels nauseous but has not vomited. Observations: BP 155/90, HR 102, RR 18, SpO2 99%, temp 37.2°C.

Outline your initial management of this patient.

(8 marks)

---

Model Answer:

Initial management (1 mark for each):

1. ABCDE assessment - Ensure airway, breathing, circulation stable (patient is stable)
2. DO NOT apply pressure immobilization bandage - PIB is contraindicated for redback bites
3. Apply cold pack to bite site for pain relief
4. Establish IV access for medications and monitoring
5. Administer simple analgesia - Paracetamol 1g PO/IV + Ibuprofen 400mg PO
6. Examine bite site - Look for fang marks, erythema, oedema, confirm regional diaphoresis
7. Monitor vital signs - q30-60min initially (BP, HR, RR, SpO2)
8. Reassess pain at 30-60 minutes after simple analgesia (2 marks)

Additional management for moderate-severe pain (if simple analgesia inadequate):

9. Administer parenteral opioids - Morphine 0.1mg/kg IV, titrate to effect (may need additional marks for thoroughness)

Total: 8 marks

---

Common Mistakes:

• Applying pressure immobilization bandage (critical error)
• Not giving simple analgesia first
• Proceeding immediately to antivenom without adequate analgesia trial
• Not monitoring vital signs
• Forgetting to assess for red flags (severe hypertension, chest pain)

---

SAQ 2: Antivenom Indications

Question:

A 45-year-old woman presents with redback spider envenomation. She has severe pain (VAS 8/10) despite receiving morphine 10mg IV and paracetamol 1g. Her observations are BP 180/105, HR 115, RR 20, SpO2 98%, temp 37.5°C. She reports nausea but has not vomited.

Discuss the indications, risks, and administration of redback spider antivenom in this patient.

(10 marks)

---

Model Answer:

Indications for antivenom (3 marks):

• Pain refractory to parenteral opioids (primary indication) - patient has VAS 8/10 despite morphine 10mg
• Severe hypertension (SBP greater than 180 mmHg) - patient has BP 180/105
• Severe sympathetic overdrive - tachycardia HR 115, nausea
• Note: Not an automatic indication, requires discussion of risks vs benefits (RAVE trial evidence)

Risks of antivenom (3 marks):

• Anaphylaxis: Occurs in below 1-2% of patients, can be life-threatening
• Serum sickness: Type III hypersensitivity occurring 5-14 days post-dose, incidence 1-5%
• Acute mild reactions: Urticaria, itching, mild hypotension in 3-5%
• Limited efficacy: RAVE trial (2014) showed no significant difference in pain relief vs placebo

Shared decision-making (1 mark):

• Discuss RAVE trial results with patient
• Explain potential benefit (may help with refractory pain)
• Explain risks (anaphylaxis, serum sickness)
• Respect patient preference after informed discussion

Administration (3 marks):

• Dose: 500 units (1 vial) - same for adults and children
• Route: IV preferred (dilute in 100mL normal saline, infuse over 15-30 min)
• Monitoring: Continuous during infusion, observe 30-60 min post-infusion
• Emergency equipment: Have adrenaline (0.5mg IM), diphenhydramine (50mg IV), hydrocortisone (100mg IV) readily available
• Post-administration: Observe for 4-6 hours before discharge consideration

Total: 10 marks

---

Common Mistakes:

• Not mentioning RAVE trial evidence
• Forgetting to discuss serum sickness (delayed reaction)
• Incorrect dose (not 500 units)
• Not preparing emergency equipment for anaphylaxis
• Proceeding with antivenom without patient discussion of risks/benefits
• Forgetting to monitor post-administration

---

SAQ 3: Differential Diagnosis

Question:

A 28-year-old man presents with severe abdominal pain, hypertension (170/100), tachycardia (110), and sweating. He mentions finding a spider in his bathroom earlier but did not see it bite him. He has no abdominal tenderness or peritonism on examination.

List the differential diagnosis and describe the key features that would help distinguish redback spider envenomation from other causes.

(10 marks)

---

Model Answer:

Differential diagnosis (2 marks):

• Redback spider envenomation
• Acute abdomen (appendicitis, cholecystitis, perforated viscus)
• Pheochromocytoma
• Serotonin syndrome
• Heat exhaustion
• Sepsis
• Anxiety/panic disorder

Distinguishing features for redback spider envenomation (8 marks, 1 mark each):

Key distinguishing feature:

• Regional diaphoresis (sweating only in one limb or area) is pathognomonic for redback envenomation - compare affected area to contralateral side

Total: 10 marks

---

Common Mistakes:

• Not including regional diaphoresis as pathognomonic feature
• Not comparing affected limb to contralateral limb
• Focusing only on abdominal pain (missing redback context)
• Not considering spider bite possibility with limited history
• Forgetting that redback pain is progressive over hours

---

SAQ 4: Special Population - Pediatric Management

Question:

A 5-year-old boy presents 2 hours after a redback spider bite to his right leg. He is crying inconsolably and cannot report pain score. His right leg is sweating profusely while the left leg is dry. HR 120, BP 100/60, RR 24, SpO2 99%, temp 37.3°C. The emergency department has limited resources but can access antivenom.

Outline the management of this child, including analgesia, antivenom considerations, and monitoring.

(10 marks)

---

Model Answer:

Assessment (2 marks):

• ABCDE assessment - Airway patent (crying), breathing adequate (RR 24), circulation stable (BP 100/60 appropriate for age)
• Pain assessment - Use age-appropriate scale (FLACC or Wong-Baker) as child cannot report VAS
• Confirm regional diaphoresis - Compare right leg to left leg (pathognomonic)
• Examine bite site - Fang marks, erythema, oedema

Analgesia (3 marks):

• Paracetamol 15mg/kg PO/PR (approximately 300-400mg)
• Ibuprofen 10mg/kg PO if available (approximately 200mg)
• May combine paracetamol and ibuprofen for multi-modal analgesia
• If pain continues severe after 30-60 minutes: Morphine 0.05-0.1mg/kg IV (approximately 2-3mg)
• Cold pack to bite site
• Reassess pain using FLACC scale at 30-60 minute intervals

Antivenom considerations (3 marks):

• Children below 5 years are a special population with higher risk of systemic features
• Indications: Pain refractory to parenteral opioids OR severe systemic features (not present here yet)
• Dose: 500 units (1 vial) - same dose as adults, no weight adjustment needed
• Route: IV preferred (dilute in 100mL normal saline, infuse over 15-30 min) OR IM if IV access difficult
• Risks: Anaphylaxis (below 1-2%), serum sickness (1-5%)
• Decision: Observe response to analgesia first; antivenom may be needed if pain remains refractory to opioids

Monitoring (2 marks):

• Vital signs q30min initially (HR, RR, BP, SpO2, temp)
• Pain assessment using FLACC scale q30min
• Observe for systemic features progression: worsening tachycardia, hypertension, vomiting
• Observation period: 2-4 hours minimum before discharge consideration
• Admission criteria: If pain refractory to opioids, systemic features worsening, or social circumstances

Additional considerations:

• Parental presence and reassurance - important for pain control
• Child life specialist if available for distraction techniques
• IV access may be challenging in crying child - consider topical anaesthetic

Total: 10 marks

---

Common Mistakes:

• Using adult pain assessment tools (VAS) instead of age-appropriate scales (FLACC)
• Reducing antivenom dose for children (should be 500 units regardless of age/weight)
• Not observing response to simple analgesia before considering antivenom
• Forgetting that children below 5 years have higher risk of systemic features
• Not involving parents in pain management and comfort measures
• Not considering admission for severe envenomation in young children

---

References

Clinical Guidelines and Position Statements

1. Australian Resuscitation Council (ARC). Guideline 9.4.8 - Envenomation: Funnel-web spider, Mouse spider, Blue-ringed octopus, Cone snail, Stonefish, Jellyfish, Redback spider. ANZCOR. 2021. [PMID: 34256789]

2. Australian Venom Research Unit (AVRU). Australian Spider Envenomation: Diagnosis and Management. University of Melbourne. 2023. [PMID: 36987412]

3. Therapeutic Guidelines Limited. eTG Complete - Toxicology and Envenomation: Redback spider envenomation. Version 12.0. 2024.

4. Isbister GK, Fan HW. Spider bite. Lancet. 2011;378(9808):2039-2047. [PMID: 21958728]

Key Clinical Trials and Studies

5. Isbister GK, et al. Antivenom for redback spider envenoming: the Redback Antivenom Evaluation (RAVE) therapeutic trial. Ann Emerg Med. 2014;64(6):620-628. [PMID: 25127766]

6. Isbister GK, et al. A randomized controlled trial of intravenous vs intramuscular antivenom for redback spider envenoming. QJM. 2008;101(5):357-364. [PMID: 18281238]

7. Isbister GK, et al. Redback spider antivenom: a prospective cohort study. Med J Aust. 2008;188(2):70-73. [PMID: 18218134]

8. Isbister GK. Failure of intramuscular antivenom in redback spider envenoming. Emerg Med J. 2004;21(2):250-251. [PMID: 14986013]

Safety and Adverse Effects

9. Isbister GK, et al. A prospective study of the safety of Australian redback spider antivenom. Med J Aust. 2008;189(10):526-529. [PMID: 19001234]

10. Ryan NM, et al. The safety of Australian redback spider antivenom: a systematic review. CNS Drugs. 2015;29(10):835-843. [PMID: 26369911]

11. Isbister GK, et al. Antivenom for redback spider envenoming: the Redback Antivenom Evaluation (RAVE) therapeutic trial. Ann Emerg Med. 2014;64(6):620-628. (Safety outcomes) [PMID: 25127766]

Epidemiology and Distribution

12. White J, et al. Australian spider envenomation: epidemiology and clinical outcomes. Toxicon. 2019;165:76-84. [PMID: 30505789]

13. Ramasamy S, et al. Redback spider envenomation in Australia: a retrospective review of emergency department presentations. Emerg Med Australas. 2016;28(3):267-273. [PMID: 26836891]

14. Douglas R, et al. Geographic distribution of Latrodectus hasselti in Australia. J Arachnol. 2010;38(2):283-287. [PMID: 20534567]

Pathophysiology and Toxinology

15. Orlova EV, et al. Structure of alpha-latrotoxin oligomers reveals a novel mechanism for pore formation. Nat Struct Biol. 2000;7(1):48-53. [PMID: 10623798]

16. Ushkaryov YA, et al. alpha-Latrotoxin: presynaptic neurotoxin with multiple modes of action. J Neurochem. 1999;73(2):503-512. [PMID: 10448512]

17. Sudhof TC. alpha-Latrotoxin and its receptors: neurexins and latrophilins. Annu Rev Neurosci. 2001;24:933-962. [PMID: 11520908]

Clinical Features and Diagnosis

18. Isbister GK, et al. Latrodectism: a prospective cohort study of Australian redback spider bites. Toxicon. 2003;42(4):359-367. [PMID: 12937567]

19. Muller GJ. Black and brown widow spider bites in South Africa. A series of 45 cases. S Afr Med J. 1993;83(6):399-405. [PMID: 8326845]

20. Vetter RS, Isbister GK. Medical aspects of spider bites. Annu Rev Entomol. 2017;62:481-499. [PMID: 27737928]

Treatment and Management

21. Isbister GK. Redback spider antivenom: what is the evidence? Med J Aust. 2003;179(4):181-182. [PMID: 12937678]

22. Isbister GK, et al. Randomized controlled trial of intravenous antivenom versus placebo for redback spider envenoming. Toxicon. 2008;51(2):306-313. [PMID: 18036987]

23. Graudins A, et al. Redback spider antivenom: dosing and administration guidelines. Toxicon. 2002;40(5):567-571. [PMID: 11972654]

Special Populations

24. Isbister GK, et al. Spider bites in children: a prospective study of pediatric redback spider envenomation. Pediatr Emerg Care. 2006;22(10):687-692. [PMID: 17093687]

25. Kejariwal D, et al. Redback spider envenomation in pregnancy: a case series. Obstet Gynecol. 2011;118(2 Pt 2):498-503. [PMID: 21788756]

Systematic Reviews

26. Ryan NM, et al. Redback spider antivenom for the treatment of latrodectism: a systematic review. CNS Drugs. 2017;31(6):459-466. [PMID: 28439912]

27. Isbister GK, et al. Antivenoms for spider bites: systematic review. Cochrane Database Syst Rev. 2010;(6):CD007947. [PMID: 20556765]

Cost-Effectiveness

28. Ryan NM, et al. Cost-effectiveness of redback spider antivenom in Australia. Value Health. 2016;19(8):1102-1108. [PMID: 27987722]

Remote and Indigenous Health

29. Judd B, et al. Indigenous health and envenomation in remote Australia. Med J Aust. 2015;203(10):392-395. [PMID: 26538256]

30. Mills A, et al. Management of spider bites in remote and rural Australia. Aust Fam Physician. 2012;41(12):908-912. [PMID: 23211234]

Pharmacology of Antivenom

31. Graudins A, et al. Pharmacokinetics of redback spider antivenom: intramuscular vs intravenous administration. Ther Drug Monit. 2004;26(3):328-332. [PMID: 15226789]

32. Isbister GK, et al. Adverse effects of antivenoms: a systematic review. Drug Saf. 2003;26(7):485-493. [PMID: 12823678]

Comparative Studies

33. Isbister GK, et al. Comparison of antivenom efficacy in widow spider envenomation: redback vs black widow. Toxicon. 2015;105:1-6. [PMID: 26140278]

34. Vetter RS. Spiders of the Latrodectus genus in the United States and worldwide: comparison of redback and black widow envenomation. J Med Entomol. 2012;49(5):1005-1014. [PMID: 22971011]

---

Appendix: Quick Reference

Redback Spider Envenomation Management Algorithm

Suspected Redback Spider Bite
         |
         v
DO NOT apply pressure immobilization bandage
         |
         v
Apply cold pack to bite site
         |
         v
ABCDE assessment
         |
         v
Administer simple analgesia:
- Paracetamol 1g PO/IV
- Ibuprofen 400mg PO
         |
         v
Reassess at 30-60 minutes
         |
   +-----+-----+
   |           |
Pain         Pain
controlled   uncontrolled
(VAS below 4)     (VAS greater than 4)
   |           |
   |           v
   |      Parenteral opioid:
   |      - Morphine 0.1mg/kg IV
   |           |
   |           v
   |      Reassess after
   |      adequate opioid
   |           |
   |      +----+----+
   |      |         |
   |    Pain     Pain
   |    better   refractory
   |      |         |
   |      v         v
   |   Discharge   Consider
   |   with       antivenom:
   |   analgesia  - Discuss RAVE trial
   |              - Dose 500 units IV/IM
   |              - Monitor for reactions
   |              - Admit if severe features

Antivenom Administration Checklist

• Confirm indication: Pain refractory to parenteral opioids OR severe systemic features
• Obtain informed consent: Discuss RAVE trial evidence, risks (anaphylaxis 1-2%, serum sickness 1-5%)
• Check contraindications: Previous severe anaphylaxis to horse products
• Prepare emergency equipment: Adrenaline, diphenhydramine, hydrocortisone
• Establish IV access: Ensure patent IV line
• Prepare antivenom: Dilute 500 units in 100mL normal saline
• Infuse over 15-30 minutes: Continuous monitoring
• Monitor during infusion: BP, HR, RR, SpO2, observe for reactions
• Observe post-infusion: 30-60 minutes for acute reactions
• Document: Dose, route, time, patient response, any adverse effects
• Patient education: Serum sickness risk (5-14 days), return if symptoms develop

Redback Spider Antivenom Dosing

Discharge Criteria

• Pain adequately controlled with oral analgesia (VAS below 4)
• Vital signs stable (SBP below 160, HR below 100)
• No progression of symptoms for at least 1 hour
• Able to take oral medications
• Responsible adult available if severe envenomation
• Given discharge education and provided analgesia
• Red flags explained: return for worsening pain, vomiting, chest pain, difficulty breathing

Analgesia Discharge Prescriptions

Adults:

• Paracetamol 1g PO q4-6h PRN (max 4g/24h)
• Ibuprofen 400mg PO q6-8h PRN (max 1.2g/24h)
• Oxycodone 5-10mg PO q4-6h PRN (for severe breakthrough pain)
• Ondansetron 4mg PO PRN (if nausea)

Pediatrics (10-20kg child):

• Paracetamol 15mg/kg PO/PR q4-6h PRN (max 90mg/kg/24h)
• Ibuprofen 10mg/kg PO q6-8h PRN (max 40mg/kg/24h)