Allergic Reaction & Anaphylaxis 🤧⚡️
Emergency management of allergic reactions and anaphylaxis. Recognition, adrenaline administration, ABCDE protocol, and treatment for on-call doctors.
📌 Overview
- This topic covers the spectrum from mild allergic reactions to life-threatening anaphylaxis in adults.
- Allergic reactions range from localised urticaria to systemic involvement with hypotension or airway compromise.
- Management differs based on severity — assess airway, breathing, circulation and skin findings to triage appropriately.
📖 Types of Reaction
- IgE-mediated: prior sensitisation (e.g. peanuts, penicillin).
- Complement-mediated: e.g. hereditary angioedema (C1 esterase inhibitor deficiency).
- Anaphylactoid: first exposure (e.g. morphine, NAC); IgE not involved; same treatment.
🟡 Mild to Moderate Allergic Reaction
- Symptoms: localised urticaria, pruritus, mild swelling, no airway/breathing/circulation involvement.
- Oral antihistamines: Cetirizine (non-sedating) 10mg PO once daily or Chlorphenamine (sedating) 4mg PO QID.
- Steroids are generally not required.
- Monitor for progression if recent exposure to allergen.
- Patient can usually be discharged if symptoms resolve and no systemic features emerge.
⚠️ Red Flags for Anaphylaxis
- Feeling of doom, nausea, vomiting, diarrhoea.
- Airway: stridor, hoarseness, facial/airway swelling.
- Breathing: wheeze, hypoxia, tachypnoea.
- Circulation: hypotension, tachycardia, syncope.
- Skin/mucosa: urticaria, erythema, angioedema.
🔴 Anaphylaxis Management
- Call for senior help immediately.
- Remove trigger if known (e.g. stop infusion).
- IM adrenaline 500 micrograms (0.5ml of 1:1000) to anterolateral thigh.
- Use 25 mm needle for IM injection; use 38–40 mm if patient >100 kg to ensure intramuscular delivery.
- Repeat every 5 minutes up to three times as needed.
- No contraindication to IM adrenaline — give early if anaphylaxis suspected.
- High-flow O₂, IV access, ECG, and obs.
- Fluids: 500–1000ml crystalloid bolus if hypotensive. Don't sit patient up.
- For cutaneous symptoms, non-sedating antihistamines (e.g. Cetirizine 10mg PO) can be given after adrenaline.
- If patient is on beta-blockers and not responding to adrenaline, consider IV glucagon 2–3 µg/kg (max 1–2 mg).
- Role of steroids is not proven.
🩺 Monitoring
- Continuous vitals for ≥6h; ≥12h if adrenaline given.
- Watch for biphasic reaction.
- Cardiac monitoring if circulatory involvement.
🔎 Further Workup / Follow-Up
- Document allergen. Educate on avoidance.
- Prescribe adrenaline auto-injector on discharge. Note: auto-injectors are for patient/community use and are not first-line in clinical emergencies.
- Refer to GP/allergy clinic for long-term management.
🚨 Refractory Anaphylaxis / Ongoing reaction
- No response despite 2 adrenaline doses
- Hypotension despite fluid resuscitation
- Recurrent symptoms (biphasic reaction)
- Consider ICU if ongoing instability