Paediatric anaphylaxis

Paediatric Anaphylaxis

• Anaphylaxis: Can arise through IgE or other mechanisms. Acute skin/mucosal features with respiratory or circulatory compromise qualify; sudden bronchospasm, airway obstruction or hypotension after a known/probable allergen can qualify even without skin findings. Give IM adrenaline promptly; do not wait for every feature.

Common Triggers in Children

• Foods: Peanuts, tree nuts, cow's milk, hen's egg, soy, wheat, sesame, fish, and shellfish.
• Insect Venoms: Honeybee, paper wasp, European wasp, jumper ant (Myrmecia pilosula).
• Medications: Beta-lactam antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs).

Clinical Diagnostic Criteria (ASCIA Guidelines)

Anaphylaxis is clinically confirmed when ANY ONE of the following three criteria is met:

1. Acute onset of illness (minutes to hours) with involvement of skin/mucosal tissue (hives, pruritus, flushed lips, tongue/uvular swelling) PLUS at least one of:
   • Respiratory compromise: Dyspnoea, wheeze, stridor, hypoxaemia, persistent cough.
   • Circulatory compromise: Hypotension, syncope, pallor, limpness, capillary refill $> 3\text{ s}$.
2. Two or more of the following occurring rapidly after exposure to a likely allergen:
   • Involvement of the skin or mucosal tissue.
   • Respiratory compromise.
   • Reduced blood pressure or associated symptoms of end-organ dysfunction.
   • Persistent gastrointestinal symptoms (cramping abdominal pain, recurrent vomiting).
3. Reduced blood pressure alone following exposure to a known allergen for that patient (e.g., systolic BP $< 70\text{ mmHg} + [2 \times \text{age}]$ for children 1 to 10 years).

Acute Management Algorithm

Key Principles of Anaphylaxis Management

1. First-Line Drug is Intramuscular Adrenaline:
   • Concentration: Adrenaline 1:1000 ($1\text{ mg/mL}$).
   • Dose: $0.01\text{ mg/kg}$ ($0.01\text{ mL/kg}$ of $1:1000$ solution), up to a maximum single dose of $0.5\text{ mg}$ ($0.5\text{ mL}$).
   • Site: Deep intramuscular injection into the mid-anterolateral thigh (vastus lateralis muscle). Intramuscular injection into the thigh achieves significantly higher and faster peak plasma adrenaline concentrations than subcutaneous injection or deltoid injection.
   • Timing: Administer immediately without delay. Repeat every 5 minutes if respiratory or circulatory distress persists.
2. Patient Posture:
   • Lay the patient flat; elevate the legs if tolerated.
   • Warning: Standing, walking, or suddenly sitting upright can trigger empty ventricle syndrome (catastrophic reduction in venous return to an underfilled, hyperdynamic heart, resulting in pulseless electrical activity arrest and sudden death).
3. Circulatory Support:
   • If hypotension or shock persists despite IM adrenaline, establish large-bore intravenous access and infuse a rapid fluid bolus of $20\text{ mL/kg}$ of $0.9\%$ sodium chloride over 10 to 15 minutes. Repeat up to $40\text{ to }60\text{ mL/kg}$ if required.
   • Refractory anaphylaxis warrants continuous intravenous adrenaline infusion ($0.05\text{ to }0.5\text{ mcg/kg/min}$) titrated to blood pressure and perfusion.
4. Role of Antihistamines and Corticosteroids:
   • H1-antihistamines (cetirizine, loratadine) and systemic corticosteroids (prednisolone, hydrocortisone) are strictly secondary adjuncts.

• Anaphylaxis adjuncts: Antihistamines may relieve skin symptoms but never replace adrenaline. Corticosteroids do not reliably prevent biphasic reactions and are not routine first-line therapy. Observe for at least four hours after the last adrenaline dose, longer/overnight for significant risk factors.
  • Antihistamines and steroids must never delay or substitute for adrenaline.

1. Post-Resuscitation Care and Discharge Planning:
   • Observation Period: Minimum of 4 to 6 hours from the last dose of adrenaline to monitor for biphasic reactions (recurrence of anaphylaxis without further allergen exposure, occurring in up to 5% to 15% of children). Prolonged observation (12 to 24 hours) is indicated for severe reactions requiring multiple doses of adrenaline, baseline severe asthma, or presentations occurring late at night.
   • Discharge Prescription: Prescribe an adrenaline autoinjector:
     • EpiPen Jr ($150\text{ mcg}$) for children weighing $7.5\text{ to }20\text{ kg}$.

• Community adrenaline devices: EpiPen Jr delivers 150 micrograms and EpiPen 300 micrograms. There is no EpiPen 500. Anapen 500 distribution ceased in 2025 and it is currently unavailable; review the current ASCIA device advice rather than assuming a 500-microgram injector can be prescribed. Weight-based IM dosing in hospital is a separate issue.
  • Provide an individualised ASCIA Action Plan for Anaphylaxis (Red Plan for autoinjector holders), demonstrate injection technique using a trainer device, and arrange referral to an accredited paediatric clinical immunology/allergy specialist.

Clinical comparison: Differential Diagnosis and Management of Paediatric Acute Airway Compromise

• Bronchiolitis: Typical Age: Infant with coryza, work of breathing and crackles/wheeze; Pathogen / Trigger: Oxygen for persistent saturation below 90% if otherwise healthy and at least six weeks, below 92% if younger or comorbid; Hallmark Clinical Features: Hydration/support; routine ward medicines avoided, with severe ICU exceptions specialist-led
• Anaphylaxis: Typical Age: Any age; Pathogen / Trigger: Foods, venoms, medications; Hallmark Clinical Features: Multisystem: hives, angioedema, stridor, wheeze, vomiting, hypotension; First-Line Emergency Therapy: Intramuscular adrenaline $1:1000$ ($0.01\text{ mg/kg}$) into anterolateral thigh; Critical Hazards & Pitfalls: Never stand patient up (empty ventricle arrest); do not rely on antihistamines
• Acute Epiglottitis: Typical Age: 2 – 7 yr (unimmunised); Pathogen / Trigger: H. influenzae type b, S. pyogenes; Hallmark Clinical Features: High fever, toxic, drooling, dysphagia, no cough, tripod sitting posture; First-Line Emergency Therapy: Gaseous induction and tracheal intubation in theatre; IV ceftriaxone; Critical Hazards & Pitfalls: Never use tongue depressor; do not distress child; causes immediate arrest

Primary references (checked 7 October 2026): RCH croup; 2025 Australasian bronchiolitis guideline; ASCIA device availability.