Anaphylaxis 2021

Not all Allergies are Anaphylaxis!

Anaphylaxis is defined as:

  • Severe life-threatening systemic hypersensitivity reaction
  • Where BOTH of the following criteria are met:
    1. Sudden onset & rapid progression
    2. Life-threatening compromise of ONE or MORE of: Airway/Breathing/Circulation

Supporting Signs:

  • Skin/Mucosal changes (flushing, urticaria, angioedema) often occur but are absent/subtle in 20% of cases.
  • Gastro-intestinal symptoms (vomiting, diarrhoea, abdominal pain) can be associated anaphylaxis.

Note: Skin/mucosal or GIT signs WITHOUT Airway/Breathing/Circulatory compromise DO NOT constitute anaphylaxis

Management of anaphylaxis:



Look for precipitants and remove if possible.

Common precipitants include:

  • Food
  • Drugs
  • Stings
  • Idiopathic in up to 20%

Rapidity of onset from stimulus varies according to the stimulus type. As you would suspect injection/sting has a faster onset time compared to ingestion, however, there is significant overlap.


Mast cell Tryptase

Mast cell tryptase should be measured in all patients with suspected anaphylaxis where the diagnosis is uncertain.

The time of onset of anaphylaxis is the time when symptoms were first noticed. It is important that this time is recorded accurately

Minimum: one sample, ideally within 2 h (when peak tryptase levels generally occur) and no later than 4 h after onset of symptoms.

Ideally: take three timed samples:

  1. An initial sample as soon as feasible – but do not delay treatment to take sample.2)
  2. A second sample 1 – 2 h (but no later than 4 h) after onset of symptoms.3)
  3. A third sample at least 24 h after complete resolution. This sample is important as it provides a baseline tryptase value


Refractory anaphylaxis:

Anaphylaxis requiring ongoing treatment (due to persisting respiratory or cardiovascular symptoms) despite two appropriate doses of IM adrenaline

Nebulised adrenaline may be effective as an adjunct to treat upper airways obstruction/stridor but only after treatment with IM (or IV) adrenaline and not as an alternative.

  • 5 mL of 1 mg/mL (1:1 000) adrenaline.

Nebulised salbutamol/ipratropium for severe/persistent bronchospasm

  • Salbutamol nebulised:
    • <5 years: 250 micrograms
    • >5 years: 500 micrograms
  • Ipratropium nebulised:
    • < 2 years: 125 micrograms
    • 2 -12 years: 250 micrograms
    • >12 years: 500 micrograms

Follow-up treatment and management


Antihistamines and steroids are not recommended as part of the initial emergency treatment for anaphylaxis

Antihistamines, only the patient is stabilised, can be used to treat skin symptoms that often occur as part of allergic reactions including anaphylaxis. Cetirizine is preferred over chlorphenamine as it is non-sedating.

Steroids should be considered after initial resuscitation for refractory reactions or ongoing asthma/shock to downregulate the late-phase inflammatory response. Earlier corticosteroids maybe indicated if an acute asthma exacerbation may have contributed to the severity of the anaphylaxis reaction.



Discharge considerations:

Patient education

We need to ensure that patient is aware of the possibility of a biphasic reactions and future reactions.  We must document safety netting given.

  • Use one adrenaline auto-injector and then call 999, ask for an ambulance, and state ‘anaphylaxis’, even if symptoms are improving.
  • Lie flat with the legs raised to maintain blood flow. If the person has breathing difficulties, they should sit up to make breathing easier.
  • Use the second auto-injector if they don’t start to feel better 5 to 15 minutes after the first injection.

Reporting reaction

  • Healthcare professionals are encouraged to report all anaphylaxis events  (to register, healthcare professionals should email
  • All cases of fatal anaphylaxis must be reported to the coroner.
  • Adverse drug reactions that involve anaphylaxis should be reported to the Medicines and Healthcare products Regulatory Agency (MHRA) using the yellow card scheme

Prescribing Adrenaline Injectors:

  • Prescription of adrenaline auto-injectors is appropriate for all patients who have had anaphylaxis, except for those with a drug-induced reaction (unless it is difficult to avoid future exposure to the trigger drug)
  • a demonstration of the correct use of the adrenaline injector and when to use it
  • a prescription for 2 adrenaline injectors, with advice to always carry the injectors with them


Further Reading

Thanks to Dr. Rebecca Talbott for putting this together!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.