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Anaphylaxis

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⚡ Anaphylaxis is a severe, life-threatening, generalised or systemic hypersensitivity reaction. 💉 Adrenaline 0.5 mg IM (0.5 mL of 1:1000) into the lateral thigh is first-line and potentially life-saving. 👉 Give promptly, through clothes if needed. Delay in adrenaline = poorer outcomes.

🚨 Acute Anaphylaxis
🔑 First steps Recognise sudden onset Airway/Breathing/Circulation compromise ± skin changes (urticaria, flushing, angioedema). 📞 Call for HELP – Resus/MET team in hospital, 🚑 999 in community. 🩺 Initial Management Summary (Resus UK) Remove trigger if possible – stop infusion, remove stinger, cease food ingestion. Position: Lie flat + elevate legs. If pregnant (>20 weeks), place on left side. Sitting may help breathing but avoid standing suddenly. Give IM Adrenaline (1:1000) lateral thigh: 👨 Adult & Child >12 y: 0.5 mg (0.5 mL) 👧 Child 6–12 y: 0.3 mg (0.3 mL) 👶 Child 6 mo–6 y: 0.15 mg (0.15 mL) 👼 Infant <6 mo: 100–150 µg (0.1–0.15 mL) 💨 High-flow O₂ 15 L/min via non-rebreather mask. Secure airway early if threatened. ⏱ Repeat adrenaline IM every 5 min if no response. 💧 IV fluids: Adult 500–1000 mL 0.9% NaCl bolus (repeat as required). Child 20 mL/kg. 🌬 If wheeze: Nebulised salbutamol 5 mg. Add ipratropium if severe. 🧪 Send Mast cell tryptase (within 1h + 24h) for confirmation. ⚠️ Antihistamines and steroids are no longer first-line – used for cutaneous/late-phase only. If refractory ➝ progress to Adrenaline infusion (see below). 🔥 Refractory Anaphylaxis 🚰 Rapid IV fluid bolus (0.9% NaCl or balanced crystalloid). May need 3–5 L in adults. 💉 Adrenaline infusion (1 mg in 100 mL NaCl). Start 0.5–1 mL/kg/hr. Use dedicated line. Titrate to effect. Monitor continuously. Airway: Nebulised adrenaline if stridor. Call anaesthetics for obstruction. Breathing: Prioritise O₂ delivery over intubation if hypoxaemia is severe. Bronchospasm: Nebulised salbutamol/ipratropium, IV salbutamol or aminophylline if refractory. Circulation: If unresponsive to adrenaline, add second vasopressor (noradrenaline, vasopressin, metaraminol). 📌 If on beta-blockers → consider IV glucagon. 💔 Cardiac arrest: follow ALS algorithm, early chest compressions, IV/IO adrenaline boluses, consider ECMO/E-CPR.

🚨 Acute Anaphylaxis

🔑 First steps

Recognise sudden onset Airway/Breathing/Circulation compromise ± skin changes (urticaria, flushing, angioedema).
📞 Call for HELP – Resus/MET team in hospital, 🚑 999 in community.

🩺 Initial Management Summary (Resus UK)

Remove trigger if possible – stop infusion, remove stinger, cease food ingestion.
Position: Lie flat + elevate legs. If pregnant (>20 weeks), place on left side. Sitting may help breathing but avoid standing suddenly.
Give IM Adrenaline (1:1000) lateral thigh:
- 👨 Adult & Child >12 y: 0.5 mg (0.5 mL)
- 👧 Child 6–12 y: 0.3 mg (0.3 mL)
- 👶 Child 6 mo–6 y: 0.15 mg (0.15 mL)
- 👼 Infant <6 mo: 100–150 µg (0.1–0.15 mL)
💨 High-flow O₂ 15 L/min via non-rebreather mask. Secure airway early if threatened.
⏱ Repeat adrenaline IM every 5 min if no response.
💧 IV fluids: Adult 500–1000 mL 0.9% NaCl bolus (repeat as required). Child 20 mL/kg.
🌬 If wheeze: Nebulised salbutamol 5 mg. Add ipratropium if severe.
🧪 Send Mast cell tryptase (within 1h + 24h) for confirmation.
⚠️ Antihistamines and steroids are no longer first-line – used for cutaneous/late-phase only.
If refractory ➝ progress to Adrenaline infusion (see below).

🔥 Refractory Anaphylaxis

🚰 Rapid IV fluid bolus (0.9% NaCl or balanced crystalloid). May need 3–5 L in adults.
💉 Adrenaline infusion (1 mg in 100 mL NaCl). Start 0.5–1 mL/kg/hr. Use dedicated line. Titrate to effect. Monitor continuously.
Airway: Nebulised adrenaline if stridor. Call anaesthetics for obstruction. Breathing: Prioritise O₂ delivery over intubation if hypoxaemia is severe. Bronchospasm: Nebulised salbutamol/ipratropium, IV salbutamol or aminophylline if refractory.
Circulation: If unresponsive to adrenaline, add second vasopressor (noradrenaline, vasopressin, metaraminol). 📌 If on beta-blockers → consider IV glucagon.
💔 Cardiac arrest: follow ALS algorithm, early chest compressions, IV/IO adrenaline boluses, consider ECMO/E-CPR.

⚠️ Treat immediately if there are any life-threatening ABC signs: Hoarse voice, stridor, wheeze, ↑ work of breathing, SpO₂ <94%, hypotension, shock, confusion, collapse. 👉 Rash alone is not sufficient, but beware evolving reactions.

🔬 Pathophysiology

IgE-mediated mast cell/basophil degranulation after allergen cross-linking.
Massive histamine release → H1: bronchospasm, vasodilation, urticaria. H2: gastric acid, tachycardia. H3/4 modulate CNS & immune cells.
Increased vascular permeability → angioedema, hypotension.
Cytokine cascade → further tissue injury + biphasic reactions.

🦠 Common Triggers

Drugs: penicillin, contrast media, NSAIDs, chemotherapy.
Foods: peanuts, tree nuts, shellfish, eggs, milk, fish.
Insect stings (bee, wasp, hornet).
Blood products in IgA deficiency.
Latex.

🩺 Differentials

Septic shock (warm peripheries, infection signs).
Asthma exacerbation (but no hypotension/urticaria).
Vasovagal syncope.
Panic attack.
Scombroid (histamine fish poisoning).
Hereditary angioedema (no urticaria, C1 esterase deficiency).

🧪 Investigations

FBC, U&E, LFTs, ABG, lactate (if shocked).
Mast cell tryptase within 1h & at 24h. More reliable in drug/sting than food allergy.
Allergy clinic follow-up: Skin prick test, specific IgE (RAST/ImmunoCAP).

🛡️ Prevention & Education

Avoid identified allergen (strict dietary, drug alerts, hospital wristbands).
⚠️ Always prescribe & teach use of adrenaline auto-injector (EpiPen, Jext, Emerade).
Educate patient/family on early recognition & action plan.
MedicAlert bracelet and referral to immunology specialist.

📌 Clinical Pearls

💉 Adrenaline IM is safe and life-saving. Do not delay for IV access.
🏥 Monitor 6–12h: biphasic reactions occur in up to 20% of cases.
📊 Risk factors for fatal anaphylaxis: delayed adrenaline, asthma, beta-blocker use, adolescents/young adults.
⚡ IV adrenaline is cardiac arrest only. Outside that, infusion only with senior help.

📚 References

🧑‍⚕️ Case Examples — Acute Anaphylaxis

Case 1 (Food allergy — Peanut): 🥜 A 17-year-old boy develops sudden breathlessness, throat tightness, urticaria, and hypotension 5 minutes after eating a peanut bar. Diagnosis: Severe food-induced anaphylaxis. Teaching point: Immediate IM adrenaline 500 micrograms into the anterolateral thigh; repeat every 5 minutes if no improvement. Call 999, lie patient flat, give high-flow O2 and IV fluids if shocked.
Case 2 (Drug reaction — Antibiotic): 💉 A 62-year-old woman in hospital develops hypotension, widespread rash, and wheeze within minutes of IV co-amoxiclav. Diagnosis: Drug-induced anaphylaxis. Teaching point: Stop the trigger, give IM adrenaline immediately, start ABC resuscitation. NICE: Monitor patient for ≥6–12 h due to risk of biphasic reaction.
Case 3 (Insect sting): 🐝 A 45-year-old beekeeper stung on the arm develops rapid onset angioedema, stridor, and dizziness. Diagnosis: Anaphylaxis secondary to bee sting. Teaching point: Adrenaline is first-line. Arrange referral to allergy clinic post-stabilisation (venom immunotherapy may be considered).
Case 4 (Perioperative): 🛏️ A 55-year-old man under anaesthesia develops sudden hypotension and bronchospasm shortly after muscle relaxant administration. Diagnosis: Perioperative anaphylaxis. Teaching point: Immediate adrenaline + IV fluids; involve anaesthetics and allergy team for investigation. NICE: All perioperative suspected anaphylaxis should be referred for specialist testing.
Case 5 (Late-phase biphasic reaction): ⏱️ A 30-year-old woman treated for nut-induced anaphylaxis with IM adrenaline improves initially, but 8 hours later develops recurrent wheeze and urticaria. Diagnosis: Biphasic anaphylaxis. Teaching point: NICE recommends observation for at least 6–12 h after resolution, and to provide adrenaline auto-injector + written emergency plan at discharge.

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PLEASE NOTE LEGAL ADVICE: The contents are under continuing development and improvements and may contain errors of omission or fact. Feedback vital and always welcome at drokane at gmail.com. This is not to be used for the assessment, diagnosis or management of patients. It should not be regarded as medical advice. It is only for educational purposes. Please adhere to your local protocols. If you are unwell please seek healthcare advice from your doctor. This does not replace senior or specialist advice. If you do not accept this then please do not use the website. If you need medical advice, please consult a doctor or other appropriate medical professional. If you are a medical professional and you need advice then speak to your senior or colleagues.

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