Anaphylaxis is a serious, life threatening allergic reaction. There are two type of anaphylactoid reactions:
  • Uniphasic - comes on quickly with rapidly worsening symptoms, when treated the symptoms go and do not return.
  • Biphasic - starts with a mild to severe reaction to begin with, then symptoms resolve, then reoccur.
Signs and symptoms
  • Swelling of the throat, tongue and mouth (angioedema)
  • Difficulty swallowing/ speaking
  • Urticarial rash/ hives
  • Sense of impending doom
  • Tachycardia
  • Severe asthmatic symptoms
  • Abdominal pain
  • Collapse/ unconsciousness
Emergency Management
  • Stop the agent causing the reaction & Call for help (ensure anaesthetic support) 
  • Establish airway
  • Administer IM adrenaline
    • Adults - 0.5ml of 1 in 1000 adrenaline IM (500 micrograms)
    • Children 
      • Over 12 years - dose as above
      • 6-12 years – 0.3ml of 1 in 1000 adrenaline IM (300 micrograms)
      • Under 6 years – 0.15ml of 1 in 1000 adrenaline IM (150 micrograms)
  • Fluid bolus (crystalloid only- stop colloids as they may cause anaphylaxis)
    • Adults - 500ml to 1000ml crystalloid
    • Children - 20mL/kg
  • Chlorphenamine
    • Adults – 10mg IM or slow IV
    • Children
      • Over 12 years - dose as above
      • 6-12 years – 5mg IM or slow IV
      • 6 months to 6 years – 2.5mg IM or slow IV
      • Under 6 months – 250 micrograms/ kg IM or slow IV
  • Hydrocortisone
    • Adults – 200mg IM or slow IV
    • Children
      • Over 12 years – dose as above
      • 6-12 years – 100mg IM or slow IV
      • 6 months to 6 years – 50mg IM or slow IV
      • Under 6 months – 25mg IM or slow IV
Further Management
  • Ensure you document the time of onset of the anaphylaxis
  • Document the preceding circumstances. Ask the patient/NOK to note down everything eaten that day, new medications or any other changes as they will forget very quickly (and it'll be necessary to identify the trigger).
  • Mast Cell Tryptase is recommended by NICE at presentation & 1-2h from the onset of symptoms (must be before 4h). 
  • Refer the patient (if appropriate) to allergy services (where they can review the mast cell tryptase with a fresh one >24h after the event for a baseline reading)
  • Ensure they don't leave until they're comfortable taking an adrenaline pen & that they know they must call an ambulance regardless after they take it
  • Provide information on avoiding triggers, signs of anaphylaxis, observing for biphasic reactions and information of follow up
  • Monitor the patient for at least 12h
  • Make sure to register the suspected agent as an allergy.
References & Reading
Written by Dr Keryn Hall FY2
Edits by Dr Akash Doshi CT2