Australian Spider Envenomation

1. Quick Answer

Australian spider envenomation encompasses two clinically significant syndromes: funnel-web spider envenomation (Atrax/Hadronyche species) causing potentially lethal neurotoxicity with autonomic storm, and redback spider envenomation (Latrodectus hasselti) causing latrodectism with severe pain and systemic features.

Key Clinical Features:

• Funnel-web: Autonomic storm (SLUDGE - salivation, lacrimation, urination, defecation, GI upset, emesis), fasciculations, pulmonary oedema, hypertension, arrhythmias
• Redback: Severe local pain, regional diaphoresis, hypertension, generalised pain, nausea, vomiting

Emergency Management:

1. Funnel-web: Pressure Immobilisation Bandaging (PIB) immediately, CSL Funnel-Web Spider Antivenom, ICU admission
2. Redback: Analgesia first-line, antivenom controversial (RAVE trial), NO pressure immobilisation (worsens pain, ineffective)
3. Supportive care: Airway protection, manage pulmonary oedema, control arrhythmias

ICU Mortality: Funnel-web 0% since antivenom introduction (1981); Redback <1%

Must-Know Facts:

• No deaths from funnel-web spider envenomation since antivenom introduction in 1981
• Pressure immobilisation bandaging is ESSENTIAL for funnel-web but CONTRAINDICATED for redback
• Redback antivenom efficacy is controversial (RAVE trial showed no benefit over placebo)
• White-tailed spider necrosis is a MYTH - debunked by Australian studies

---

2. CICM Exam Focus

What Examiners Expect

Second Part Written (SAQ):

Common SAQ stems:

• "A 35-year-old male presents to a rural ED 2 hours after spider bite with salivation, diaphoresis, and muscle fasciculations. HR 140, BP 200/120, RR 35. Describe the likely diagnosis and management."
• "A 6-year-old child from Sydney presents with witnessed funnel-web spider bite. Outline the initial assessment and ICU management."
• "Compare and contrast the management of funnel-web and redback spider envenomation including the role of antivenom."
• "Discuss the pathophysiology of funnel-web spider venom and its effects on the autonomic nervous system."

Expected depth:

• Systematic approach to envenomation assessment
• Detailed knowledge of venom toxicology (delta-atracotoxin, alpha-latrotoxin)
• Evidence-based antivenom use including RAVE trial
• First aid differences between funnel-web and redback
• Complications: pulmonary oedema, arrhythmias, rhabdomyolysis
• Australian-specific geography and spider identification

Second Part Hot Case:

Typical presentations:

• Intubated patient post-funnel-web bite with pulmonary oedema on Day 1 ICU
• Patient with severe latrodectism receiving antivenom with ongoing pain

Examiners assess:

• Recognition of envenomation syndrome
• Evidence of antivenom administration
• Management of pulmonary oedema without diuretics initially
• Autonomic storm control
• Serum sickness recognition post-antivenom
• Indigenous health considerations for remote presentations

Second Part Viva:

Expected discussion areas:

• Delta-atracotoxin mechanism: voltage-gated sodium channel effects
• Alpha-latrotoxin mechanism: massive neurotransmitter release
• Pressure immobilisation bandaging rationale and technique
• Antivenom dosing, redosing criteria, and adverse reactions
• RAVE trial and its implications for redback antivenom
• Remote and Indigenous community considerations

Examiner expectations:

• Safe, consultant-level toxicology management
• Knowledge of Australian Poisons Information Centre resources
• Understanding of antivenom availability and CSL products
• Cultural competence for Indigenous communities

Common Mistakes

• Applying pressure immobilisation for redback spider bites (contraindicated)
• Giving diuretics for funnel-web pulmonary oedema (not cardiogenic)
• Not recognising serum sickness post-antivenom
• Attributing necrotic wounds to white-tailed spider without evidence
• Underestimating severity in children (more severe envenomation)
• Not consulting Poisons Information Centre early (13 11 26)

---

3. Key Points

Must-Know Facts

1. No funnel-web deaths since 1981: No fatalities since antivenom introduction; prior mortality was 13 deaths from 1927-1980 (PMID: 7029180)

2. Delta-atracotoxin mechanism: Delays inactivation of voltage-gated sodium channels in autonomic and motor neurons, causing repetitive firing and massive neurotransmitter release (PMID: 12351150)

3. Alpha-latrotoxin mechanism: Binds neurexin and latrophilin receptors, triggering massive vesicular neurotransmitter release (ACh, noradrenaline, glutamate) causing severe pain and autonomic dysfunction (PMID: 11113304)

4. Pressure immobilisation differentiation: ESSENTIAL for funnel-web (slows venom spread), CONTRAINDICATED for redback (worsens pain, ineffective for slow-acting venom)

5. RAVE trial implications: Randomised placebo-controlled trial showed IV redback antivenom NOT superior to placebo for pain relief; current recommendation is supportive care and analgesia first-line (PMID: 24251411)

6. Envenomation grading for funnel-web: Minor (local effects) → Moderate (systemic features) → Severe (pulmonary oedema, hypotension, unconsciousness)

7. White-tailed spider necrosis myth: Australian studies demonstrate no association between white-tailed spider bites and necrotic ulcers; likely caused by bacterial infection or misidentification (PMID: 12710724)

8. Funnel-web antivenom dosing: Initial 2 vials (250 units each), repeat every 15-20 minutes as needed until symptoms resolve; no maximum dose

9. Geographic distribution: Sydney funnel-web (Atrax robustus) - Sydney basin 100km radius; Northern tree-dwelling funnel-web (Hadronyche formidabilis) - northern NSW/southern Queensland; Redback (Latrodectus hasselti) - Australia-wide

10. ICU priorities: Airway protection, manage pulmonary oedema with positive pressure ventilation (NOT diuretics), control hypertension, treat arrhythmias, antivenom, supportive care

Memory Aids

Mnemonic FUNNEL for Funnel-Web Envenomation:

• F: Fasciculations and muscle twitching
• U: Unconsciousness in severe cases
• N: Nausea, vomiting, salivation (autonomic)
• N: Neurological effects (lacrimation, diaphoresis)
• E: Elevated BP and HR (autonomic storm)
• L: Lungs fill with fluid (pulmonary oedema)

Mnemonic REDBACK for Latrodectism:

• R: Regional diaphoresis at bite site
• E: Escalating pain (local → generalised)
• D: Diaphoresis and nausea
• B: Blood pressure elevated
• A: Antivenom controversial (RAVE trial)
• C: Cramps and muscle spasms
• K: Keep comfortable with analgesia

---

4. Definition & Epidemiology

Definition

Spider envenomation occurs when venom is injected through spider fangs (chelicerae) during a defensive bite. In Australia, two spider genera cause clinically significant envenomation requiring potential ICU admission:

1. Funnel-web spiders (Atrax and Hadronyche species): Produce potentially lethal neurotoxic envenomation
2. Redback spiders (Latrodectus hasselti): Cause latrodectism with severe pain and systemic effects

Diagnostic Criteria for Significant Envenomation:

Funnel-web:

• Witnessed bite or spider identification + systemic features OR
• Characteristic clinical syndrome: autonomic features, fasciculations, pulmonary oedema

Redback:

• Characteristic local pain with regional diaphoresis OR
• Generalised latrodectism features in endemic area

Severity Classification - Funnel-Web Envenomation:

Epidemiology

International Context:

• Spider envenomation predominantly Australian clinical entity for severe cases
• Latrodectus species worldwide (Black Widow Americas, Katipo New Zealand)
• Atrax/Hadronyche unique to eastern Australia

Australian Data (ANZICS APD, Australian Venom Research Unit):

• Approximately 2,000 spider bites present to Australian EDs annually (PMID: 16825067)
• Funnel-web envenomation: ~30-40 significant cases annually (PMID: 18296830)
• Redback envenomation: ~2,000 cases annually, ~300 receive antivenom (PMID: 18476757)
• No deaths from funnel-web since antivenom (1981)
• Rare redback deaths (last confirmed death 2016)

Geographic Distribution:

Funnel-web spiders:

• Sydney funnel-web (Atrax robustus): Sydney basin, 100km radius, male more dangerous
• Northern tree-dwelling (Hadronyche formidabilis): SE Queensland, Northern NSW
• Victorian (H. modesta): Eastern Victoria highlands
• Toowoomba funnel-web (H. infensa): Southern Queensland
• Approximately 40 Atrax/Hadronyche species; most are potentially dangerous

Redback spider:

• Australia-wide distribution
• Urban and rural environments
• Under logs, rocks, garden furniture, toilet seats, sheds
• Female only causes significant envenomation (larger fangs)

Risk Factors:

• Non-modifiable: Male funnel-web bites more dangerous (venom more potent); children more susceptible (smaller body mass)
• Modifiable: Gardening without gloves, outdoor work, barefoot walking
• Occupational: Landscapers, pool cleaners, outdoor workers

High-Risk Populations:

• Children: More severe envenomation due to lower body mass; higher surface area to body weight ratio
• Aboriginal and Torres Strait Islander peoples: Remote community access to antivenom, delayed presentation
• Māori in New Zealand: Katipo spider (related to redback)
• Rural/remote populations: Delayed access to antivenom, need for retrieval

Outcomes:

• ICU mortality funnel-web: 0% since 1981 (with antivenom)
• Hospital mortality redback: <1%
• Morbidity: Serum sickness post-antivenom (5-10%), prolonged pain syndromes

---

5. Applied Basic Sciences

This section bridges First Part basic sciences with Second Part clinical practice

Toxinology

Funnel-Web Spider Venom - Delta-Atracotoxin (δ-ACTX):

Delta-atracotoxin is a 42 amino acid peptide that is the principal lethal component of funnel-web spider venom (PMID: 12351150, PMID: 10651933).

Molecular Mechanism:

1. Binds to site 3 of voltage-gated sodium channels (Nav1.1-1.9)
2. Delays or prevents channel inactivation
3. Causes repetitive, uncontrolled action potential firing
4. Preferentially affects autonomic and motor neurons
5. Results in massive release of acetylcholine, catecholamines, and other neurotransmitters

Target Selectivity:

• Highly selective for mammalian and primate sodium channels
• Does NOT affect insect, reptile, or amphibian sodium channels (explains why funnel-webs prey on insects but venom is lethal to humans)
• This selectivity is due to specific amino acid differences in channel subunit structure

Physiological Effects:

• Autonomic nervous system: Simultaneous parasympathetic AND sympathetic activation
  • "Parasympathetic: Salivation, lacrimation, urination, defecation, miosis"
  • "Sympathetic: Hypertension, tachycardia, diaphoresis, mydriasis (may see mid-position pupils)"
• Motor neurons: Fasciculations, muscle twitching, progressing to weakness
• Cardiovascular: Massive catecholamine release → severe hypertension, tachycardia, arrhythmias
• Respiratory: Bronchospasm, bronchorrhoea, pulmonary oedema (neurogenic and increased permeability)

Redback Spider Venom - Alpha-Latrotoxin (α-LTX):

Alpha-latrotoxin is a 130 kDa protein that is the principal toxin causing latrodectism (PMID: 11113304, PMID: 15652976).

Molecular Mechanism:

1. Binds to three receptor types on presynaptic nerve terminals:
   • Neurexin 1α (Ca2+-dependent binding)
   • Latrophilin/CIRL (G-protein coupled receptor, Ca2+-independent)
   • Protein tyrosine phosphatase σ (PTPσ)
2. Forms large pores (conductance ~200 pS) in presynaptic membrane
3. Allows Ca2+ influx into nerve terminal
4. Triggers massive vesicular fusion and neurotransmitter release
5. Depletes synaptic vesicles → eventual transmission failure

Target Selectivity:

• Affects all vertebrate peripheral synapses
• Both cholinergic and adrenergic terminals affected
• Neuromuscular junction: Muscle spasms, then weakness
• Autonomic: Pain, sweating, hypertension

Comparison of Venom Mechanisms:

Anatomy

Spider Anatomy - Venom Apparatus:

• Chelicerae: Paired jaws containing fangs
• Funnel-web: Large fangs (5-6mm), capable of penetrating fingernails
• Redback: Small fangs (~1mm), require soft tissue for penetration
• Venom glands: Located in cephalothorax, drain through fangs

Relevant Human Anatomy for Envenomation:

• Autonomic ganglia: Primary target for systemic effects
• Neuromuscular junction: Site of fasciculations
• Pulmonary vasculature: Target for neurogenic pulmonary oedema
• Lymphatic system: Route of venom dissemination (slowed by PIB)

Physiology

Autonomic Nervous System Response:

Funnel-web (Mixed Autonomic Storm):

Neurogenic Pulmonary Oedema Mechanism:

1. Massive sympathetic discharge (catecholamine surge)
2. Pulmonary venoconstriction → increased hydrostatic pressure
3. Increased pulmonary capillary permeability (direct venom effect?)
4. Left ventricular dysfunction (transient cardiomyopathy)
5. Result: Protein-rich pulmonary oedema fluid

Clinical Differentiation:

• NOT cardiogenic (PCWP usually normal or low)
• Do NOT give diuretics as first-line
• Requires positive pressure ventilation (CPAP, BiPAP, or intubation)

Pharmacology

Key ICU Drugs:

1. CSL Funnel-Web Spider Antivenom:

• Class: F(ab')2 antibody fragments (equine-derived)
• Mechanism: Binds and neutralises circulating delta-atracotoxin
• ICU Indication: All cases of suspected or confirmed funnel-web envenomation with systemic features
• Dosing:
  • "Initial: 2 vials (250 units each = 500 units total)"
  • "Repeat: 2 vials every 15-20 minutes until clinical improvement"
  • No maximum dose (up to 12 vials reported in severe cases)
• Monitoring: Vital signs, ECG, respiratory status, resolution of autonomic features
• Adverse Effects:
  • "Immediate: Anaphylaxis (1-5%), urticaria, bronchospasm"
  • "Delayed: Serum sickness (5-10%), occurs 4-14 days post-administration"
• PBS/TGA: Available nationally via CSL; stocked in hospitals throughout endemic areas
• Administration: IV preferred; premedication with adrenaline controversial (not routine)

2. CSL Redback Spider Antivenom:

• Class: F(ab')2 antibody fragments (equine-derived)
• Mechanism: Binds and neutralises circulating alpha-latrotoxin
• ICU Indication: Historically for systemic latrodectism; NOW CONTROVERSIAL after RAVE trial
• Dosing:
  • 1-2 vials IM (traditional) or IV (if severe)
  • Can repeat after 2 hours if no improvement
• RAVE Trial Evidence (PMID: 24251411):
  • "RCT: IV antivenom vs placebo for latrodectism"
  • No significant difference in pain at 2 hours
  • No significant difference in need for analgesia
  • "Conclusion: Antivenom NOT routinely recommended"
• Current Recommendation: Supportive care, analgesia first-line; antivenom reserved for severe/refractory cases
• Adverse Effects: Anaphylaxis, serum sickness

3. Atropine:

• Class: Muscarinic antagonist
• Mechanism: Competitive antagonist at muscarinic ACh receptors
• ICU Indication: For severe cholinergic features (bradycardia, bronchorrhoea) if antivenom not immediately available
• Dosing: 0.6-1.2 mg IV, repeat as needed (large doses may be required)
• Monitoring: Heart rate, pupil size, secretions
• Note: Treats symptoms, does NOT neutralise venom; antivenom is definitive treatment

4. Analgesia for Latrodectism:

• Opioids: Morphine 2.5-5 mg IV titrated to pain (first-line)
• Paracetamol: 1g IV/PO (adjunct)
• NSAIDs: Ibuprofen 400-800 mg PO (adjunct)
• Benzodiazepines: Diazepam 5-10 mg IV for muscle spasms
• Local anaesthesia: Ice packs, local infiltration (limited efficacy)

5. Adrenaline (for Anaphylaxis to Antivenom):

• Indication: Anaphylaxis to antivenom
• Dosing: 0.5 mg IM (adult), 0.01 mg/kg IM (child), IV if refractory
• Premedication: NOT routinely recommended before antivenom

Pharmacokinetics in Critical Illness:

• Antivenom distribution: Large molecules (F(ab')2 ~100 kDa), initially intravascular
• Half-life: ~12-24 hours (shorter than whole IgG antivenoms)
• Volume of distribution: Increased in critical illness (capillary leak)
• Elimination: Reticuloendothelial system

Pathology

Histopathology of Envenomation:

Funnel-web:

• Local: Minimal tissue damage
• Pulmonary: Alveolar oedema, protein-rich fluid, minimal inflammatory infiltrate
• Myocardium: Catecholamine-induced injury (contraction band necrosis) in severe cases

Redback:

• Local: Erythema, minimal tissue damage (NO necrosis)
• Nerve terminals: Vesicle depletion, synaptic swelling

Laboratory Pathology:

Funnel-web:

• Elevated troponin (catecholamine-induced myocardial injury)
• Elevated CK (fasciculations, rhabdomyolysis in severe cases)
• Metabolic acidosis (hypoperfusion, seizures)
• Hyperglycaemia (catecholamine surge)
• Leucocytosis (stress response)

Redback:

• Usually normal laboratory findings
• Occasional mild CK elevation
• Occasional mild leucocytosis

---

6. Clinical Presentation

ICU Admission Scenarios

Scenario 1: Severe Funnel-Web Envenomation (Most Common ICU Presentation)

• History: 8-year-old boy bitten on foot while playing in Sydney backyard; spider captured (identified as male Atrax robustus); onset of symptoms within 20 minutes
• Examination:
  • HR 160, BP 180/110, RR 40, SpO2 88% on room air
  • Profuse salivation, lacrimation, diaphoresis
  • Fasciculations visible in face, limbs
  • Bilateral crackles on auscultation
  • Agitated, confused (GCS 12)
• Severity: Severe envenomation - pulmonary oedema, autonomic storm

Scenario 2: Severe Latrodectism (Less Common ICU Presentation)

• History: 45-year-old woman bitten on hand while gardening in Adelaide; identified redback spider on glove; progressive severe pain over 6 hours
• Examination:
  • HR 110, BP 175/100, RR 22, SpO2 98%
  • Severe pain in bitten hand spreading to arm, chest, abdomen
  • Regional sweating around bite site and arm
  • No fasciculations, no pulmonary oedema
  • Distressed but alert
• Severity: Moderate-severe latrodectism

Symptoms & Signs

Funnel-Web Envenomation:

Time Course:

• Onset: 10-30 minutes post-bite (rapid)
• Peak: 1-2 hours
• Without antivenom: Death from pulmonary oedema/arrhythmias within hours
• With antivenom: Clinical improvement within 1-2 hours

Local Effects:

• Immediate severe pain at bite site
• Fang marks may be visible (5-6mm apart)
• Local erythema and swelling
• Paraesthesia around bite site

Systemic Effects (Graded):

SLUDGE Features (Cholinergic):

• Salivation
• Lacrimation
• Urination
• Defecation
• GI upset (nausea, vomiting)
• Emesis

Redback Envenomation (Latrodectism):

Time Course:

• Onset: 30 minutes to 2 hours post-bite (slower than funnel-web)
• Peak: 4-12 hours
• Duration: 24-72 hours without treatment, may persist for weeks
• Rare fatalities (last Australian death 2016)

Local Effects:

• Initial: Mild stinging sensation (often unnoticed)
• 30-60 minutes: Increasing local pain
• Erythema at bite site (may not be visible)
• Regional lymphadenopathy
• Pathognomonic: Localised diaphoresis at/around bite site

Systemic Effects:

• Pain: Spreading from bite site to limb, trunk, generalised
• Diaphoresis: Regional then generalised
• Nausea and vomiting: Common
• Hypertension: Moderate (150-180 systolic typical)
• Tachycardia: Mild (100-120 bpm)
• Muscle cramps: Abdominal, limb
• Headache: Common
• Facial oedema: Occasionally seen (facies latrodectismica)

Comparison Table - Clinical Features:

Severity Scoring

Funnel-Web Envenomation Grading (Modified from Sutherland):

Latrodectism Grading:

Differential Diagnosis

Key Differentials for Autonomic Storm:

1. Organophosphate/Carbamate poisoning: SLUDGE features similar, but usually history of pesticide exposure; responds to atropine and pralidoxime
2. Nerve agent exposure: Similar autonomic features; mass casualty setting
3. Cholinergic crisis (myasthenic): Usually in known myasthenia patient on anticholinesterases
4. Sympathomimetic toxidrome: Amphetamines, cocaine - HTN, tachycardia but NO cholinergic features
5. Scorpion envenomation: Autonomic features similar; no scorpions with lethal envenomation in Australia
6. Snake envenomation: Different syndrome (coagulopathy, paralysis); venom detection kit positive

Key Differentials for Severe Local Pain:

1. Cellulitis: Bacterial infection, may follow minor bite; fever, spreading erythema
2. Snake bite: Coagulopathy, paralysis features; venom detection kit
3. Bee/wasp sting: Allergic reaction, localised swelling; usually obvious history
4. Trauma: Direct injury history

---

7. Investigations

Laboratory Investigations

Bedside Tests:

Arterial Blood Gas:

• Funnel-web severe envenomation typical findings:

  • pH: 7.20-7.35 (metabolic acidosis)
  • "PaCO2: 30-40 mmHg (may be low initially from hyperventilation)"
  • "PaO2: 40-70 mmHg (hypoxaemia from pulmonary oedema)"
  • "HCO3: 16-22 mmol/L (metabolic acidosis)"
  • "Lactate: 3-8 mmol/L (tissue hypoperfusion)"
  • "Interpretation: Mixed metabolic acidosis with hypoxaemic respiratory failure"

• Redback envenomation: Usually normal ABG

Blood Glucose:

• Funnel-web: Hyperglycaemia common (catecholamine surge) - may see 12-20 mmol/L
• Redback: Usually normal

Blood Tests:

Full Blood Count:

• Funnel-web: Leucocytosis (stress response), 15-25 x 10^9/L typical
• Redback: Usually normal or mild leucocytosis

Urea, Electrolytes, Creatinine:

• Funnel-web: May show hypokalaemia (catecholamine shift), elevated creatinine (hypoperfusion)
• Redback: Usually normal

Creatine Kinase:

• Funnel-web: Elevated in moderate-severe cases (fasciculations, rhabdomyolysis)
  • CK 1,000-10,000+ U/L may be seen
• Redback: Usually normal or mildly elevated

Troponin:

• Funnel-web: May be elevated (catecholamine-induced myocardial injury)
  • Indicates severity but does not change management
• Redback: Usually normal

Coagulation:

• Both: Usually normal (unlike snake envenomation)
• No venom-induced consumptive coagulopathy

Liver Function Tests:

• Usually normal
• May show minor transaminitis in severe cases (hypoperfusion)

Specific Tests:

Venom Detection:

• No commercial venom detection kit available for spider envenomation in Australia
• Clinical diagnosis based on spider identification and clinical syndrome
• Snake venom detection kit: Useful to EXCLUDE snake envenomation if uncertain

Spider Identification:

• Ideal: Bring spider specimen for expert identification
• If killed, preserve in alcohol or photograph
• Australian Museum identification services available
• Key identifying features:
  • "Funnel-web: Large, black, robust, aggressive, fangs visible"
  • "Redback: Distinctive red/orange dorsal stripe on black abdomen"

Imaging

Chest X-Ray:

• Funnel-web with pulmonary oedema:
  • Bilateral alveolar infiltrates (bat-wing pattern)
  • Normal heart size (unlike cardiogenic)
  • May show upper lobe redistribution
  • Serial CXRs to monitor response to treatment
• Redback: Usually normal

CT Scan:

• Not routinely indicated
• Consider CT brain if persistent altered consciousness after antivenom (rule out other pathology)

Echocardiography:

• Funnel-web: May show transient LV dysfunction (stress cardiomyopathy)
  • LVEF may be reduced during acute phase
  • Usually recovers within days
• Useful to differentiate neurogenic vs cardiogenic pulmonary oedema

Physiological Monitoring

Non-Invasive Monitoring:

• Continuous ECG: Arrhythmia detection (VT, VF, SVT, AF in funnel-web)
• SpO2: Target >94%
• NIBP: Frequent monitoring during autonomic storm
• Temperature: Fever uncommon; hypothermia if prolonged exposure
• Respiratory rate: Tachypnoea indicates severity
• Capnography: If intubated

Invasive Monitoring:

• Arterial line: Indicated for severe envenomation with haemodynamic instability
• Central venous catheter: For vasopressor/inotrope administration if needed
• Urinary catheter: For fluid balance monitoring

Organ-Specific Monitoring:

• Urine output: Target >0.5 mL/kg/hr
• Serial CK if rhabdomyolysis suspected
• Cardiac monitoring for 24-48 hours post-severe envenomation

---

8. ICU Management

This is the core clinical section - most detailed

Initial Resuscitation (First Hour)

First Aid (Pre-Hospital - Funnel-Web ONLY):

Pressure Immobilisation Bandaging (PIB):

• Indication: Funnel-web spider bite ONLY
• Contraindicated: Redback spider bite (worsens pain, ineffective)

Technique:

1. Keep patient still and calm
2. Apply broad elastic bandage (10-15 cm) over bite site
3. Bandage upward to include entire limb (from toes/fingers to groin/axilla)
4. Pressure: Firm but not arterially occlusive (can slip finger underneath)
5. Splint limb to prevent movement
6. Mark bite site on bandage
7. Do NOT remove bandage until in hospital with antivenom available

Rationale:

• Venom travels via lymphatic system
• PIB compresses lymphatics, slowing venom dissemination
• Buys time for antivenom administration
• DOES NOT work for redback (venom acts locally, slow absorption)

A - Airway:

Assessment:

• Airway patency: Secretions, tongue swelling
• Voice: Hoarse voice suggests laryngeal oedema
• Drooling: Indicates excessive salivation and possible inability to swallow

Intervention:

• Suction for secretions (SLUDGE features)
• Position: Sit up if possible (aids secretion drainage)
• Consider early intubation if:
  • GCS <8
  • Severe respiratory distress
  • Copious secretions unmanageable
  • Rapid deterioration

RSI Drug Choices:

• Induction: Ketamine 1-2 mg/kg (maintains BP) OR Propofol 1-2 mg/kg (if stable)
• Paralysis: Rocuronium 1.2 mg/kg (standard)
• Caution: Suxamethonium may exacerbate hyperkalaemia if rhabdomyolysis present; avoid if CK significantly elevated

Post-Intubation:

• Ventilator: PEEP 10-15 cmH2O initially for pulmonary oedema
• Ongoing sedation: Propofol/fentanyl or midazolam/fentanyl

B - Breathing:

Oxygen Therapy:

• High-flow oxygen for all significant envenomation
• Target SpO2 >94%

Ventilatory Support:

• NIV (CPAP/BiPAP): First-line for mild-moderate pulmonary oedema if patient cooperative
  • CPAP 8-12 cmH2O
  • "BiPAP: IPAP 12-16, EPAP 8-10"
• Invasive ventilation: For severe pulmonary oedema, altered consciousness, failure of NIV
  • "Mode: VC-CMV or PC-CMV"
  • "Vt: 6-8 mL/kg PBW"
  • "PEEP: 10-15 cmH2O (higher if severe oedema)"
  • "FiO2: Titrate to SpO2 >94%"

Key Point: Pulmonary oedema is NEUROGENIC, not cardiogenic

• Do NOT give diuretics as first-line
• Positive pressure ventilation is primary treatment
• Antivenom reverses underlying cause

C - Circulation:

Fluid Resuscitation:

• Initial: Crystalloid 10-20 mL/kg bolus if hypotensive
• Caution: Avoid fluid overload in pulmonary oedema
• Endpoints: MAP >65 mmHg, improving lactate

Blood Pressure Management:

• Hypertensive phase (early funnel-web): Observe unless severe (>200/120)
  • Usually resolves with antivenom
  • "Short-acting agents if needed: Glyceryl trinitrate, esmolol"
• Hypotensive phase (late/severe): Indicates severe envenomation
  • Fluid resuscitation first
  • "Vasopressors: Noradrenaline if refractory"
  • Prioritise antivenom administration

Arrhythmia Management:

• VT/VF: Standard ACLS algorithms
• Atrial arrhythmias: Usually resolve with antivenom
• Bradycardia: Atropine 0.6-1.2 mg IV

D - Disability:

GCS Monitoring:

• Frequent assessment in severe envenomation
• Altered consciousness indicates severity

Sedation:

• Target RASS 0 to -2 if intubated
• Avoid over-sedation (masks clinical improvement)

Seizure Management:

• Seizures may occur in severe funnel-web envenomation
• First-line: Benzodiazepines (midazolam 0.1 mg/kg IV)
• Second-line: Levetiracetam, phenytoin

Glucose Control:

• Hyperglycaemia common (catecholamine surge)
• Target 6-10 mmol/L
• Insulin infusion if persistent hyperglycaemia

E - Everything Else:

Temperature:

• Normothermia target
• Hyperthermia possible (autonomic storm)

Remove PIB:

• ONLY after antivenom available and IV access secured
• Removal may cause transient clinical deterioration (venom release)
• Have resuscitation equipment ready

Definitive Management (Antivenom)

CSL Funnel-Web Spider Antivenom:

Indications:

• All patients with systemic envenomation features
• Consider for asymptomatic patients with definite funnel-web bite and spider identification

Dosing Protocol:

1. Initial dose: 2 vials (500 units) IV
2. Administration: Dilute in 100 mL normal saline, infuse over 15-30 minutes
3. Reassess: Every 15-20 minutes after infusion
4. Repeat: If no clinical improvement or ongoing deterioration, give additional 2 vials
5. Repeat again: Continue 2 vials every 15-20 minutes until clinical improvement
6. No maximum dose: Up to 12+ vials documented in severe cases

Expected Response:

• Improvement usually within 30-60 minutes of adequate antivenom
• Autonomic features resolve first
• Pulmonary oedema clears over hours
• Fasciculations and weakness may persist briefly

Monitoring During Antivenom:

• Vital signs every 5 minutes during infusion
• Watch for anaphylaxis (urticaria, bronchospasm, hypotension)
• If anaphylaxis: Stop infusion, treat with adrenaline, resume with premedication

Premedication:

• NOT routinely recommended (delays treatment)
• Consider if prior antivenom reactions

CSL Redback Spider Antivenom:

Current Evidence (RAVE Trial - PMID: 24251411):

• Randomised, double-blind, placebo-controlled trial
• 224 patients with latrodectism
• IV antivenom vs IV placebo
• Primary outcome: No significant difference in pain at 2 hours (VAS reduction -6 vs -6)
• Secondary outcomes: No difference in need for analgesia, admission rates
• Conclusion: IV antivenom NOT superior to placebo

Current Recommendation:

1. First-line: Analgesia and supportive care
   • Opioids (morphine, oxycodone)
   • Paracetamol
   • NSAIDs if not contraindicated
   • Ice packs (limited efficacy)
2. Antivenom: Reserved for refractory severe latrodectism
   • Dose: 1-2 vials IM or IV
   • May repeat after 2 hours
   • Consider if severe pain unresponsive to adequate analgesia

Antivenom Adverse Reactions:

Organ Support Strategies

Respiratory Support:

Pulmonary Oedema Management:

• Position: Sit up 45-60 degrees if conscious
• Oxygen: High-flow to maintain SpO2 >94%
• Positive pressure: CPAP/BiPAP or mechanical ventilation
• Diuretics: NOT first-line (not cardiogenic); may use late if fluid overloaded
• Antivenom: Definitive treatment

Ventilator Management if Intubated:

• Lung-protective ventilation principles
• Higher PEEP (10-15 cmH2O)
• Titrate FiO2 to SpO2 >94%
• Monitor for improvement; consider weaning as pulmonary oedema resolves

Cardiovascular Support:

Arrhythmia Management:

• VT: Amiodarone 150 mg IV, cardioversion if unstable
• VF: Standard ACLS
• Bradycardia: Atropine 0.6-1.2 mg IV
• SVT: Usually resolves with antivenom; consider adenosine if refractory

Haemodynamic Targets:

• MAP >65 mmHg
• Avoid excessive fluid (pulmonary oedema)
• Vasopressors if hypotension refractory to fluids and antivenom

Renal Support:

Rhabdomyolysis Prevention/Management:

• Monitor CK every 6-12 hours in moderate-severe envenomation
• Aggressive IV fluids if CK rising (target UO >1 mL/kg/hr)
• Avoid nephrotoxins
• RRT if AKI with indications (AEIOU)

Ongoing ICU Care

Daily Management:

• Neurological assessment: GCS, resolution of agitation
• Respiratory: Wean ventilatory support as pulmonary oedema resolves
• Cardiovascular: Wean monitoring as stable
• Renal: Monitor UO, creatinine, CK
• Nutrition: Early enteral feeding once stable

Complications Prevention:

• VTE prophylaxis (LMWH once stable)
• Stress ulcer prophylaxis (PPI if ventilated)
• Glycaemic control (6-10 mmol/L)
• Pressure injury prevention

ICU Liberation:

• Extubation: When pulmonary oedema resolved, patient awake, airway protected
• Usually achievable within 24-48 hours for funnel-web with adequate antivenom
• Redback: Rarely requires ventilation

Australian-Specific Protocols

Poisons Information Centre:

• Phone: 13 11 26 (24/7)
• Consult for all significant envenomation
• Expert advice on antivenom dosing, species identification, ongoing management
• Telemedicine support for remote areas

Antivenom Availability:

• CSL Funnel-Web Spider Antivenom: Stocked at major hospitals in NSW, Victoria, Queensland
• CSL Redback Spider Antivenom: Widely available nationally
• Regional hospitals: Check stock availability; may need retrieval transfer if unavailable

Retrieval Medicine Considerations:

• RFDS (Royal Flying Doctor Service): Remote envenomation retrieval
• State retrieval services: NSW CareFlight, NETS (paediatric), VicECMO
• Aeromedical transfer: Stable patients; consider if ICU care needed and not available locally
• Telemedicine: Poisons Information Centre, specialist toxicology advice

Indigenous Health Considerations:

• Remote communities may have limited antivenom stocks
• Cultural considerations: Involve Aboriginal Health Workers (AHWs), Aboriginal Liaison Officers (ALOs)
• Extended family involvement in decision-making
• Language: Use interpreter services if needed
• "Sorry business": Be aware of cultural protocols that may affect family presence
• Education: Community spider awareness programs

---

9. Monitoring & Complications

ICU-Specific Monitoring

Daily Parameters:

• Vital signs: Hourly during acute phase, then 2-4 hourly
• Fluid balance: Input/output charting, daily weights
• Laboratory: ABG, CK, creatinine, electrolytes every 6-12 hours initially
• ECG: Continuous monitoring during acute phase

Trend Monitoring:

• Lactate clearance: Indicates tissue perfusion improvement
• CK trend: Rising CK suggests ongoing rhabdomyolysis
• Pulmonary oedema resolution: Serial CXR, SpO2/FiO2 ratio

Safety Monitoring:

• Antivenom reaction: Observe for serum sickness days 4-14
• Line position: CXR post-insertion
• Endotracheal tube: Cuff pressure, position

Complications

Early Complications (First 24-48 hours):

Complication 1: Pulmonary Oedema (Funnel-Web)

• Incidence: 20-40% of moderate-severe funnel-web envenomation
• Risk factors: Delayed antivenom, large venom dose, young children
• Presentation: Hypoxia, pink frothy sputum, bilateral crackles
• Prevention: Early antivenom, supportive care
• Management: Positive pressure ventilation, antivenom, NOT diuretics initially

Complication 2: Arrhythmias (Funnel-Web)

• Incidence: 10-20% of severe envenomation
• Risk factors: Severe envenomation, pre-existing cardiac disease
• Presentation: VT, VF, AF, SVT, bradycardia
• Prevention: Early antivenom
• Management: ACLS algorithms, antivenom

Complication 3: Rhabdomyolysis

• Incidence: 5-10% of moderate-severe funnel-web
• Risk factors: Prolonged fasciculations, immobility
• Presentation: Elevated CK, myoglobinuria, AKI
• Prevention: Early antivenom (stops fasciculations)
• Management: Aggressive IV fluids, monitor renal function, RRT if needed

Complication 4: Aspiration Pneumonia

• Incidence: 5-10% if altered consciousness with excessive secretions
• Risk factors: GCS <8, profuse salivation, vomiting
• Prevention: Early airway protection, suction
• Management: Antimicrobials (cover oral flora), supportive care

Late Complications (Beyond 48 hours):

Complication 5: Serum Sickness

• Incidence: 5-10% post-antivenom (higher with repeated doses)
• Timing: 4-14 days post-antivenom
• Presentation: Fever, arthralgia, myalgia, urticarial rash, lymphadenopathy
• Prevention: Minimise antivenom doses (while ensuring adequate treatment)
• Management: Prednisolone 0.5-1 mg/kg/day for 5-7 days, antihistamines

Complication 6: Persistent Pain (Redback)

• Incidence: 10-20% of latrodectism cases
• Duration: May persist for weeks to months
• Presentation: Ongoing limb or regional pain
• Management: Multimodal analgesia, physiotherapy, pain clinic referral

ICU-Acquired Complications:

• Standard ICU complications: VAP, CRBSI, ICU-acquired weakness, delirium
• Prevention: ABCDEF bundle, early mobilisation (when safe)

---

10. Prognosis & Outcome Measures

Mortality

Funnel-Web Spider Envenomation:

• Pre-antivenom era (1927-1980): 13 deaths reported (case fatality ~10-15%)
• Post-antivenom era (1981-present): 0 deaths (PMID: 18296830)
• ICU mortality: 0% with appropriate antivenom treatment
• Hospital mortality: 0%

Redback Spider Envenomation:

• ICU mortality: <1% (rare ICU admissions)
• Hospital mortality: <1%
• Last confirmed Australian death: 2016

Morbidity

Functional Recovery:

• Funnel-web: Full recovery expected within 24-72 hours with antivenom
• Redback: Pain may persist for weeks; most recover fully

ICU Survivorship:

• Short ICU stay (usually 24-48 hours for funnel-web)
• PICS uncommon for spider envenomation
• Serum sickness may cause delayed morbidity

Prognostic Factors

Good Prognostic Factors:

• Early presentation and antivenom administration
• Mild envenomation grade
• Adult patients (larger body mass)
• No pre-existing cardiopulmonary disease

Poor Prognostic Factors (Historical - Pre-Antivenom):

• Children (higher envenomation severity)
• Delayed presentation or antivenom
• Severe autonomic features at presentation
• Pulmonary oedema at presentation
• Hypotension at presentation

Current Era:

• With antivenom availability: All prognostic factors improved to excellent outcomes

Scoring Systems

Funnel-Web Envenomation Grading:

• Grade 0-3 as described above
• Higher grade = more aggressive antivenom dosing required
• All grades: 0% mortality with antivenom

APACHE II/SOFA:

• May be elevated during acute phase
• Not validated specifically for spider envenomation
• Expect rapid improvement with antivenom

Australian/NZ Outcome Data

ANZICS/Australian Venom Research Unit Data:

• 0 funnel-web deaths since 1981 (40+ years)
• Approximately 30-40 significant funnel-web envenomations annually
• Antivenom highly effective
• Regional variations in presentation (coastal NSW/Queensland)

Indigenous Health Outcomes:

• Limited specific data
• Concerns regarding remote access to antivenom
• May present later due to geographic isolation
• Culturally appropriate education programs important

---

11. Progressive Difficulty Assessments

Basic Level (Foundation Knowledge)

Question 1: Spider Identification

Q: Name the two spider genera that cause clinically significant envenomation requiring ICU admission in Australia.

A:

1. Funnel-web spiders (Atrax and Hadronyche species) - cause potentially lethal neurotoxic envenomation
2. Redback spiders (Latrodectus hasselti) - cause latrodectism with severe pain and systemic features

---

Question 2: First Aid Differences

Q: Compare the first aid for funnel-web versus redback spider bites.

A:

---

Question 3: Funnel-Web Venom

Q: What is the principal lethal toxin in funnel-web spider venom and what is its mechanism of action?

A:

• Toxin: Delta-atracotoxin (δ-ACTX)
• Mechanism:
  • Binds to voltage-gated sodium channels (site 3)
  • Delays or prevents channel inactivation
  • Causes repetitive, uncontrolled action potential firing
  • Results in massive release of acetylcholine and catecholamines
  • Produces autonomic storm with both parasympathetic and sympathetic features

---

Question 4: Antivenom Dosing

Q: What is the initial dose of CSL Funnel-Web Spider Antivenom?

A:

• Initial dose: 2 vials (500 units total)
• Administration: IV infusion over 15-30 minutes
• Repeat: Every 15-20 minutes until clinical improvement
• No maximum dose: Up to 12+ vials documented in severe cases

---

Intermediate Level (Applied Knowledge)

Question 1: Case-Based Scenario

Stem: A 7-year-old boy is brought to a regional NSW ED 45 minutes after a witnessed spider bite to his foot. His mother captured the spider (identified as a male Sydney funnel-web). A pressure immobilisation bandage was applied at the scene.

Observations: HR 150, BP 160/110, RR 35, SpO2 92% on room air, T 37.8°C, GCS 13 (E4V4M5)

Examination reveals profuse salivation, lacrimation, generalised fasciculations, and bilateral crackles on auscultation.

Q1: What severity grade is this envenomation? (2 marks)

A1:

• Grade 3 (Severe) envenomation (1 mark)
• Features indicating severity:
  • Pulmonary involvement (crackles, hypoxia)
  • Altered consciousness (GCS 13)
  • Multiple systemic features (1 mark)

Q2: What are your immediate management priorities? (5 marks)

A2:

1. Airway/Breathing: High-flow oxygen, consider CPAP/intubation for pulmonary oedema (1 mark)
2. IV access and bloods: Two large bore cannulae, ABG, FBC, UEC, CK, glucose (1 mark)
3. Do NOT remove PIB yet: Keep in place until antivenom ready (1 mark)
4. Antivenom: CSL Funnel-Web Spider Antivenom 2 vials IV immediately (1 mark)
5. Remove PIB after antivenom started: Have resuscitation equipment ready (1 mark)
6. ICU admission: For monitoring and ongoing care
7. Contact Poisons Information Centre: 13 11 26

Q3: The patient develops hypotension (BP 70/40) and VT on cardiac monitor. What is your management? (4 marks)

A3:

1. Call for help: Cardiac arrest team if pulseless VT (1 mark)
2. If pulseless VT: Start CPR, defibrillation, ACLS algorithm (1 mark)
3. If VT with pulse: Synchronised cardioversion, amiodarone 150 mg IV (1 mark)
4. Continue antivenom: Additional 2 vials IV immediately (1 mark)
5. Fluid resuscitation: Crystalloid bolus for hypotension
6. Vasopressors: Noradrenaline if refractory

---

Question 2: RAVE Trial

Q: Describe the RAVE trial and its implications for redback spider envenomation management.

A:

RAVE Trial (PMID: 24251411):

• Design: Randomised, double-blind, placebo-controlled trial
• Population: 224 patients with latrodectism
• Intervention: IV redback antivenom vs IV placebo
• Primary outcome: Pain at 2 hours (VAS reduction)
• Result: No significant difference (VAS reduction -6 vs -6)
• Secondary outcomes: No difference in analgesia requirements, admission rates
• Adverse events: Serum sickness higher in antivenom group

Implications:

• IV redback antivenom is NOT superior to placebo for pain relief
• First-line management is supportive care and analgesia
• Antivenom reserved for severe/refractory cases
• Reduces antivenom-related adverse events (anaphylaxis, serum sickness)

---

Question 3: Pulmonary Oedema Management

Q: A patient with funnel-web envenomation develops pulmonary oedema. Why should diuretics NOT be used as first-line treatment?

A:

Pathophysiology:

• Pulmonary oedema in funnel-web envenomation is NEUROGENIC, not cardiogenic
• Caused by:
  • Massive sympathetic discharge → pulmonary venoconstriction
  • Increased pulmonary capillary permeability (direct venom effect)
  • Transient cardiomyopathy (catecholamine surge)

Why diuretics are ineffective:

• Intravascular volume is often normal or depleted
• Diuresis may worsen hypotension
• Does not address underlying mechanism (neurogenic, permeability)

Appropriate management:

• Positive pressure ventilation (CPAP/BiPAP/intubation)
• Antivenom (definitive treatment - reverses underlying cause)
• Supportive care
• Diuretics may be considered LATE if fluid overloaded

---

Exam Level (CICM Second Part Standard)

See SAQ Practice section below.

---

12. SAQ Practice

SAQ 1: Funnel-Web Spider Envenomation in a Child

Time Allocation: 10 minutes
Total Marks: 20

Stem: A 6-year-old girl is brought to the Emergency Department of a major Sydney children's hospital. She was bitten on the hand by a large black spider while playing in the garden 40 minutes ago. Her father captured the spider and it has been identified as a male Sydney funnel-web spider (Atrax robustus).

A pressure immobilisation bandage was applied at home by her father.

Observations on arrival:

• HR: 160 bpm
• BP: 175/105 mmHg
• RR: 42 breaths/min
• SpO2: 89% on room air
• Temperature: 37.5°C
• GCS: 11 (E3V3M5)

Examination:

• Profuse salivation requiring suctioning
• Lacrimation, rhinorrhoea
• Generalised diaphoresis
• Visible fasciculations in face and limbs
• Bilateral coarse crackles to mid-zones

---

Question 1.1 (8 marks)

Outline your immediate management priorities for this child in the first 30 minutes.

Question 1.2 (6 marks)

The child receives 2 vials of CSL Funnel-Web Spider Antivenom but there is no clinical improvement after 30 minutes. Her SpO2 has dropped to 82% despite high-flow oxygen, and she is now unconscious (GCS 6).

Describe your ongoing management.

Question 1.3 (6 marks)

Explain the pathophysiology of pulmonary oedema in funnel-web spider envenomation and why diuretics are not first-line treatment.

---

Model Answer

Question 1.1 (8 marks total)

Immediate Assessment and Resuscitation (4 marks):

• Call for help: Activate resuscitation team, ICU notification (0.5 marks)
• Airway: Suction secretions, position upright, assess for need for intubation (0.5 marks)
• Breathing: High-flow oxygen, prepare for CPAP or intubation (1 mark)
• Circulation: 2 IV cannulae (weight-appropriate), bloods (ABG, FBC, UEC, CK, glucose, group and hold) (1 mark)
• Monitoring: Continuous ECG, SpO2, NIBP; attach defibrillator pads (0.5 marks)
• Keep PIB in place: Do not remove until antivenom available and ready (0.5 marks)

Antivenom Administration (2 marks):

• CSL Funnel-Web Spider Antivenom: 2 vials (500 units) IV (1 mark)
• Dilute in normal saline, infuse over 15-30 minutes (0.5 marks)
• Have adrenaline and resuscitation equipment at bedside (0.5 marks)

Post-Antivenom (2 marks):

• Remove pressure immobilisation bandage after antivenom infusion started (1 mark)
• Reassess every 15 minutes; repeat antivenom 2 vials if no improvement (1 mark)
• Contact Poisons Information Centre (13 11 26)
• Arrange ICU admission

---

Question 1.2 (6 marks total)

Airway Management (2 marks):

• Immediate intubation for GCS 6 and severe respiratory failure (1 mark)
• RSI: Ketamine 1-2 mg/kg + Rocuronium 1.2 mg/kg (0.5 marks)
• Post-intubation: Confirm ETT position, initiate mechanical ventilation (0.5 marks)

Ventilatory Support (2 marks):

• Mode: Pressure control or volume control ventilation (0.5 marks)
• Settings: Vt 6-8 mL/kg, PEEP 12-15 cmH2O, FiO2 1.0 initially (0.5 marks)
• Target: SpO2 >94%, permissive hypercapnia acceptable (0.5 marks)
• Monitor for improvement with antivenom (0.5 marks)

Further Antivenom and ICU Care (2 marks):

• Repeat antivenom: Additional 2 vials (4 vials total now) (1 mark)
• Continue to repeat every 15-20 minutes until improvement
• No maximum dose
• ICU: Ongoing monitoring, invasive arterial line, consider central access (0.5 marks)
• Manage complications: Arrhythmias (ACLS), hypotension (fluids, vasopressors if needed) (0.5 marks)

---

Question 1.3 (6 marks total)

Pathophysiology (4 marks):

• Delta-atracotoxin causes massive autonomic nervous system activation (1 mark)
• Catecholamine surge leads to:
  • Pulmonary venoconstriction → increased hydrostatic pressure (1 mark)
  • Increased pulmonary capillary permeability → protein-rich oedema fluid (1 mark)
• Transient cardiomyopathy (stress/takotsubo-like) may contribute (0.5 marks)
• Negative intrathoracic pressure from inspiratory effort against airway obstruction (0.5 marks)

Why Diuretics Are Not First-Line (2 marks):

• Pulmonary oedema is neurogenic/permeability-based, NOT cardiogenic (1 mark)
• Intravascular volume may be normal or depleted
• Diuresis does not address underlying mechanism
• May worsen hypotension (0.5 marks)
• First-line: Positive pressure ventilation (CPAP/intubation) + antivenom (0.5 marks)

---

Common Mistakes:

• Removing PIB before antivenom available
• Delaying intubation in deteriorating child
• Using diuretics for pulmonary oedema
• Not repeating antivenom when no improvement
• Forgetting to contact Poisons Information Centre

---

SAQ 2: Redback Spider Antivenom Decision

Time Allocation: 10 minutes
Total Marks: 20

Stem: A 52-year-old woman presents to a rural Queensland ED with a suspected redback spider bite to her left hand 4 hours ago. She was gardening and felt a sharp sting. She did not see the spider but noticed a small black spider with a red stripe on her gardening glove.

Past Medical History: Hypertension, type 2 diabetes Medications: Amlodipine 10 mg daily, metformin 1g BD

Observations:

• HR: 105 bpm
• BP: 185/100 mmHg (baseline 140/85)
• RR: 20 breaths/min
• SpO2: 98% on room air
• Temperature: 37.2°C

Examination:

• Severe pain in left hand, spreading to forearm and shoulder
• Regional diaphoresis on left arm and axilla
• Erythema at bite site on dorsum of hand
• No fasciculations, no pulmonary oedema
• GCS 15, distressed due to pain

---

Question 2.1 (8 marks)

Outline your initial assessment and management of this patient.

Question 2.2 (6 marks)

The patient asks whether she should receive antivenom. Discuss the evidence for and against redback spider antivenom and explain your recommendation.

Question 2.3 (6 marks)

Twelve days after receiving redback antivenom (which she ultimately received), she returns with fever, joint pains, and a rash. What is the likely diagnosis and how would you manage it?

---

Model Answer

Question 2.1 (8 marks total)

Clinical Assessment (3 marks):

• Confirm diagnosis: History consistent with redback bite, systemic latrodectism features present (1 mark)
• Exclude differential diagnoses: No fasciculations (not funnel-web), no necrosis (not cellulitis/necrotising fasciitis) (0.5 marks)
• Assess severity: Moderate-severe latrodectism (spreading pain, regional diaphoresis, hypertension) (0.5 marks)
• Risk assessment: Diabetes and hypertension are not contraindications to treatment (0.5 marks)
• Document: Photograph bite site, describe spider if available (0.5 marks)

Immediate Management (3 marks):

• Analgesia first-line:
  • Paracetamol 1g IV/PO (0.5 marks)
  • Morphine 2.5-5 mg IV titrated to pain (1 mark)
  • Consider NSAIDs (ibuprofen 400 mg) if not contraindicated by diabetes/renal function (0.5 marks)
• Ice packs to bite site (limited efficacy)
• IV fluids: Maintenance fluids (0.5 marks)
• Blood pressure monitoring: Treat if severe (>200 systolic) (0.5 marks)

Do NOT Apply Pressure Immobilisation (1 mark):

• Contraindicated in redback bite
• Worsens pain, does not prevent venom spread

Observation (1 mark):

• Monitor for 6-12 hours minimum
• Serial pain assessments
• Reassess need for antivenom if analgesia inadequate (1 mark)

---

Question 2.2 (6 marks total)

Evidence FOR Antivenom (Historical) (1 mark):

• Prior observational studies suggested benefit for pain relief
• Mechanism: Neutralises circulating alpha-latrotoxin
• May shorten duration of symptoms

Evidence AGAINST Antivenom - RAVE Trial (3 marks):

• Design: Randomised, double-blind, placebo-controlled trial (PMID: 24251411) (0.5 marks)
• Population: 224 patients with latrodectism (0.5 marks)
• Intervention: IV redback antivenom vs placebo (0.5 marks)
• Primary outcome: No significant difference in pain at 2 hours (VAS -6 vs -6) (0.5 marks)
• Secondary outcomes: No difference in analgesia requirements (0.5 marks)
• Adverse effects: Serum sickness higher in antivenom group (0.5 marks)

Recommendation (2 marks):

• First-line: Supportive care and adequate analgesia (opioids, paracetamol, NSAIDs) (1 mark)
• Antivenom: Reserved for severe/refractory latrodectism where pain is uncontrolled despite adequate analgesia (0.5 marks)
• Informed discussion: Explain RAVE trial findings, risk of serum sickness, patient choice (0.5 marks)

---

Question 2.3 (6 marks total)

Diagnosis: Serum Sickness (2 marks):

• Type III hypersensitivity reaction to equine-derived antivenom (1 mark)
• Timing: 4-14 days post-antivenom (consistent with 12 days) (0.5 marks)
• Features: Fever, arthralgia, urticarial rash, lymphadenopathy (0.5 marks)

Differential Diagnoses (1 mark):

• Viral illness
• Drug reaction (other medications)
• Arthropathy (diabetes-related, coincidental)

Management (3 marks):

• Confirm diagnosis: Exclude infection (FBC, CRP, blood cultures if febrile) (0.5 marks)
• First-line treatment:
  • Prednisolone 0.5-1 mg/kg/day PO for 5-7 days (1 mark)
  • "Antihistamines: Cetirizine 10 mg daily or promethazine 25 mg BD (0.5 marks)"
• Supportive: Paracetamol for fever/pain, rest (0.5 marks)
• Follow-up: Review in 5-7 days, symptoms usually resolve within 1-2 weeks (0.5 marks)
• Documentation: Note serum sickness reaction for future reference (avoid antivenom if possible in future)

---

Common Mistakes:

• Applying PIB for redback bite
• Recommending antivenom as first-line despite RAVE trial
• Not recognising serum sickness (delayed presentation)
• Using antibiotics for serum sickness

---

13. Hot Case Scenarios

Hot Case 1: Child with Funnel-Web Envenomation - Day 1 ICU

Setting: Paediatric ICU Bed 4
Duration: 20 minutes (10 min assessment + 10 min discussion)
Equipment: Ventilator, monitors, IV pumps, charts available

---

Actor/Simulator Briefing (Not given to candidate):

Patient Details:

• Age: 8 years
• Gender: Male
• Weight: 28 kg
• Admission diagnosis: Severe funnel-web spider envenomation
• Day of ICU stay: Day 1 (12 hours post-bite)

History:

• Bitten on right foot in Sydney backyard yesterday afternoon
• Spider captured and identified as male Sydney funnel-web
• PIB applied by paramedics
• Received 4 vials of CSL Funnel-Web Spider Antivenom in ED
• Intubated for GCS 8 and pulmonary oedema
• Received further 2 vials of antivenom overnight (6 vials total)

Examination Findings:

• General: Intubated, sedated, appears stable
• Airway: ETT 5.5 cuffed, 14 cm at lips
• Breathing: Ventilated on SIMV, crackles now only at bases (improving)
• Circulation: HR 110, BP 120/70, well perfused
• Disability: RASS -3, no fasciculations visible
• Exposure: Right foot bite site with small puncture marks

Charts/Data Available:

• ABG (now): pH 7.38, PaCO2 42, PaO2 120 (FiO2 0.4), HCO3 24, Lactate 1.5
• CK: 2,500 U/L (down from 5,800)
• Creatinine: 45 μmol/L (normal)
• CXR: Improving pulmonary oedema

Current Management:

• Ventilator: SIMV, Vt 280 mL (10 mL/kg), RR 16, PEEP 8, FiO2 0.4
• Infusions: Propofol 2 mg/kg/hr, Fentanyl 1 mcg/kg/hr
• Fluids: 0.9% NaCl at 80 mL/hr
• Antivenom: Last dose 6 hours ago (total 6 vials)

---

Candidate Task:

"You are the ICU registrar. This 8-year-old boy was admitted yesterday with severe funnel-web spider envenomation. He is now 12 hours post-envenomation. Please assess the patient and present your findings to the consultant. You have 10 minutes to examine the patient and review the charts, then 10 minutes for discussion."

---

Expected Performance

Assessment Phase (10 minutes) - 15 marks:

One-Minute Summary:

"This is an 8-year-old, 28 kg boy admitted 12 hours ago with severe funnel-web spider envenomation following a bite to his right foot. He received 6 vials of CSL antivenom and was intubated for decreased consciousness and pulmonary oedema. He is currently stable on SIMV with improving oxygenation and resolving pulmonary oedema. His CK is trending down. The plan is to assess readiness for extubation today."

---

Discussion Phase (10 minutes) - 15 marks

Opening Question: "What are your management priorities for the next 12-24 hours?"

Expected Answer (3 marks):

1. Wean ventilation and aim for extubation when awake and protecting airway
2. Continue monitoring for delayed complications (rhabdomyolysis, serum sickness)
3. Liaise with Poisons Information Centre regarding further antivenom need (unlikely if improving)
4. Family communication: Update parents on progress and expected outcomes
5. Plan for step-down to ward when extubated

Q2: "What would make you give further antivenom?" (3 marks)

Expected Answer:

• Clinical deterioration (recurrence of autonomic features, worsening pulmonary oedema)
• Rising CK suggesting ongoing envenomation
• Would consult Poisons Information Centre
• Currently improving → antivenom not indicated

Q3: "The parents are Aboriginal and from a remote community. How would you approach discharge planning and follow-up?" (3 marks)

Expected Answer:

• Involve Aboriginal Health Worker (AHW) and Aboriginal Liaison Officer (ALO) early
• Assess transport needs back to community
• Ensure local health service aware of serum sickness risk (days 4-14)
• Provide culturally appropriate education to family
• Written information about serum sickness symptoms
• Follow-up phone call or telehealth if returning to remote community
• Ensure antivenom availability known for local health service

---

Hot Case 2: Adult with Severe Latrodectism

Setting: ICU Bed 12
Duration: 20 minutes (10 min assessment + 10 min discussion)
Equipment: Monitors, IV pumps, charts available

---

Actor/Simulator Briefing:

Patient Details:

• Age: 58 years
• Gender: Female
• Admission diagnosis: Severe latrodectism, refractory pain
• Day of ICU stay: Day 1 (8 hours post-bite)

History:

• Bitten on left thigh while using outdoor toilet at rural property
• Identified redback spider
• Presented to local hospital with severe generalised pain
• Received morphine 20 mg IV over 4 hours with inadequate relief
• Transferred to tertiary centre for ongoing management
• Received 2 vials of redback antivenom IM 2 hours ago

Examination Findings:

• General: Distressed, awake, not intubated
• Cardiovascular: HR 115, BP 175/95
• Respiratory: RR 22, SpO2 99% on room air
• Pain: Severe generalised pain (VAS 8/10 despite opioids)
• Diaphoresis: Generalised
• No fasciculations, no pulmonary oedema

Current Management:

• Morphine PCA: 1 mg/5 min lockout
• Paracetamol 1g IV Q6H
• IV fluids: 0.9% NaCl at 100 mL/hr
• Redback antivenom: 2 vials IM given

---

Candidate Task:

"You are the ICU registrar. This 58-year-old woman was transferred with severe latrodectism refractory to analgesia. She received redback antivenom 2 hours ago. Please assess the patient and present your findings to the consultant."

---

Discussion Points:

1. Role of antivenom in latrodectism (RAVE trial)
2. Multimodal analgesia strategies
3. When to consider further antivenom
4. Expected duration of symptoms
5. Serum sickness monitoring plan

---

14. Viva Questions

Viva Question 1: Child with Funnel-Web Envenomation

Stem: "A 6-year-old boy is brought to your regional ED following a spider bite. The spider has been identified as a Sydney funnel-web. He has profuse salivation and visible fasciculations. His mother is extremely anxious."

Duration: 12 minutes (2 min reading + 10 min discussion)

---

Opening Question:

"What are your immediate concerns about this child?"

Expected Answer (2-3 minutes):

• Potential severe/lethal envenomation - funnel-web spider
• Airway compromise from secretions
• Risk of pulmonary oedema
• Risk of arrhythmias and cardiovascular collapse
• Need for immediate antivenom
• Child at higher risk due to smaller body mass

---

Follow-up Question 1:

"Walk me through your management in the first 30 minutes."

Expected Answer:

• Call for help, resuscitation team
• High-flow oxygen, suction secretions
• Maintain PIB until antivenom ready (if in place)
• Large bore IV access, bloods (ABG, CK, glucose)
• Continuous monitoring including ECG
• Antivenom: 2 vials CSL Funnel-Web Spider Antivenom IV
• Remove PIB after antivenom started
• Reassess every 15 minutes, repeat antivenom if no improvement
• Consider early intubation if deteriorating (GCS <8, severe pulmonary oedema)
• Contact Poisons Information Centre (13 11 26)

---

Follow-up Question 2:

"Explain the mechanism of delta-atracotoxin."

Expected Answer:

• 42 amino acid peptide
• Binds to site 3 of voltage-gated sodium channels
• Delays or prevents channel inactivation
• Causes repetitive, uncontrolled action potential firing
• Preferentially affects autonomic and motor neurons
• Results in massive neurotransmitter release (ACh, catecholamines)
• Produces mixed autonomic storm (SLUDGE + sympathetic features)
• Selective for mammalian sodium channels (why it's lethal to humans but not insects)

---

Follow-up Question 3:

"The child develops pulmonary oedema. How do you manage this?"

Expected Answer:

• Positive pressure ventilation: CPAP initially, intubate if deteriorating
• High PEEP (10-15 cmH2O)
• Continue antivenom - definitive treatment
• NOT diuretics initially (neurogenic, not cardiogenic)
• Monitor for arrhythmias
• May need repeated antivenom doses
• ICU admission

---

Viva Question 2: Redback Antivenom Controversy

Stem: "A 45-year-old woman presents with a redback spider bite and severe pain radiating up her arm. She asks you about antivenom."

Duration: 12 minutes

---

Opening Question:

"What do you tell her about antivenom?"

Expected Answer:

• Acknowledge her pain and distress
• Explain that redback antivenom was traditionally used
• Discuss the RAVE trial (2014):
  • Randomised, placebo-controlled
  • No difference in pain relief between antivenom and placebo
  • Risk of serum sickness with antivenom
• Current recommendation: First-line treatment is analgesia (opioids, paracetamol)
• Antivenom reserved for severe/refractory cases
• Shared decision-making: Explain risks and benefits

---

Follow-up Question 1:

"What first aid would you advise for future bites?"

Expected Answer:

• Do NOT apply pressure immobilisation bandage
• Ice pack may help for pain
• Clean wound
• Seek medical attention if symptoms develop
• Do NOT apply tourniquet
• Rationale: PIB worsens pain and is ineffective for slow-acting redback venom

---

Follow-up Question 2:

"Compare the mechanisms of funnel-web and redback venom."

Expected Answer:

---

Viva Question 3: Indigenous Health and Remote Presentation

Stem: "A Poisons Information Centre call comes in from a remote Aboriginal community health centre. A 12-year-old Aboriginal girl was bitten by a suspected funnel-web spider (Northern tree-dwelling species) 2 hours ago. She has salivation and fasciculations. The nearest hospital with antivenom is 3 hours away by road. RFDS is available."

---

Opening Question:

"How do you approach this situation?"

Expected Answer:

• Telephone assessment of severity
• Confirm PIB in place
• Assess available resources (IV access, oxygen, monitoring)
• Determine antivenom availability (may need to be flown in)
• Activate RFDS retrieval immediately
• Provide remote guidance for supportive care
• Consider telehealth video consultation if available
• Involve Aboriginal Health Worker for cultural liaison

---

Follow-up Question:

"What are the challenges of managing envenomation in remote Indigenous communities?"

Expected Answer:

• Geographic isolation: Long transport times
• Limited resources: May not have antivenom stocked locally
• Infrastructure: Variable road access, weather-dependent RFDS
• Health literacy: Need culturally appropriate communication
• Family/community involvement: Extended family decision-making important
• Language barriers: May need interpreter
• Cultural protocols: "Sorry business" may affect family availability
• Trust: Historical factors may affect health-seeking behaviour
• Follow-up: Serum sickness monitoring at distance

---

15. Interactive Elements

[INTERACTIVE: Antivenom Decision Tool]

Clinical Scenario Input:

Spider Identification:

• Confirmed funnel-web (Atrax/Hadronyche)
• Confirmed redback (Latrodectus hasselti)
• Unidentified spider
• Spider not available

Clinical Features:

• Local pain only
• Salivation/lacrimation
• Fasciculations
• Diaphoresis (localised)
• Diaphoresis (generalised)
• Pulmonary oedema
• Hypertension
• Altered consciousness

Decision Output:

Based on inputs, tool provides:

• Likely diagnosis
• Severity grading
• Antivenom recommendation
• First aid advice
• Monitoring requirements

---

[INTERACTIVE: Severity Grading Flowchart]

Funnel-Web Envenomation Grading:

Witnessed bite or suspected funnel-web?
          |
          v
    Local effects only?
    /           \
   YES          NO
    |            |
 Grade 0      Systemic features?
 (Observe)    /            \
            YES            NO (observe)
             |
    Pulmonary oedema/hypotension/arrhythmias?
    /                      \
   NO                      YES
    |                        |
 Grade 2 (Moderate)      Grade 3 (Severe)
 2 vials antivenom       4+ vials, ICU, intubation