Adrenaline IM is first line for hypotension or bronchospasm. Stop all potential allergens (antibiotics, neuromuscular blockers, chlorhexidine, latex).
Common triggers in theatre
- Neuromuscular blockers (most often rocuronium/suxamethonium)
- Antibiotics, patent blue, chlorhexidine
- Latex, colloid, contrast (rare intraop)
Diagnosis clues
- Sudden hypotension, bronchospasm, rash, angioedema
- Rising tryptase at 1 h and 24 h (baseline too)
- Sudden ETCO2 drop with bronchospasm
Grade 1 to 2
- Skin or mucosal, or mild features
- Stop the likely trigger, observe
- Take tryptase
Grade 3 (life-threatening)
- Hypotension, bronchospasm, angioedema
- IM adrenaline 500 micrograms, repeat
- Fluids, 100% oxygen
Grade 4 (arrest)
- Cardiac arrest
- ALS, IV adrenaline infusion (senior)
- ITU, serial tryptase, allergy referral
Treatment
1
1. Stop
Cease infusion and allergen. Call for help. Adrenaline IM 500 micrograms (repeat every 5 min if needed).
Cease infusion and allergen. Call for help. Adrenaline IM 500 micrograms (repeat every 5 min if needed).
↓
2
2. Resuscitate
IV fluid boluses. IV adrenaline infusion if refractory (senior). 100% oxygen.
IV fluid boluses. IV adrenaline infusion if refractory (senior). 100% oxygen.
↓
3
3. Adjuncts
Chlorphenamine, hydrocortisone after initial resuscitation. Bronchodilators for wheeze.
Chlorphenamine, hydrocortisone after initial resuscitation. Bronchodilators for wheeze.
↓
4
4. Follow-up
ITU observation. Refer allergy clinic with tryptase and detailed anaesthetic record.
ITU observation. Refer allergy clinic with tryptase and detailed anaesthetic record.
Differential
- LAST, MH, vagal response to stimulus
- Equipment failure (disconnection)
Pitfalls
- Antihistamine before adrenaline in shock
- No tryptase sampling
- Re-exposure without allergy workup
MedPrep - www.medprep.uk - Educational revision aid only. Not clinical guidance. Doses are adult examples; check the BNF, current guidelines and local policy, and seek senior advice. Nov 2026