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Anaphylactic shock

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Anaphylactic shock is a medical emergency; it is a life- threatening type I hypersensitivity reaction.

  • Anaphylaxis is characterised by:
    • Sudden onset and rapid progression of symptoms.
    • Airway and/or Breathing and/or Circulation problems.
    • Usually, skin and/or mucosal changes (flushing, urticaria, angioedema)
    • diagnosis is supported if a patient has been exposed to an allergen known to affect them. However, in up to 30% of cases there may be no obvious trigger
    • note that (1)
      • Skin or mucosal changes alone are not a sign of anaphylaxis.
      • Skin and mucosal changes can be subtle or absent in 10–20% of reactions
        (e.g. some patients present initially with only bronchospasm or hypotension).
    • Gastrointestinal symptoms (e.g. nausea, abdominal pain, vomiting) in the absence of Airway and/or Breathing and/or Circulation problems do not usually indicate anaphylaxis. Abdominal pain and vomiting can be symptoms of anaphylaxis due to an insect sting or bite.
  • the main characteristics are rapidly developing life-threatening circulatory collapse and airway impairment in response to an allergen to which the patient has previously been sensitized.Usually skin and mucosal changes are associated.

In the UK it is estimated that 500,000 people have had a venom-induced anaphylactic reaction and 220,000 people up to the age of 44 have had a nut-induced anaphylactic reaction (2)

  • available UK estimates suggest that approximately 1 in 1333 of the population of England has experienced anaphylaxis at some point in their lives
  • there are approximately 20 deaths from anaphylaxis reported each year in the UK, with around half the deaths being iatrogenic, although this may be an underestimate

Key recommendations for clinical practice (1):

  • Anaphylaxis is a potentially life-threatening allergic reaction.
  • Recognise anaphylaxis based on:
    • sudden onset and rapid progression of symptoms
    • Airway and/or Breathing and/or Circulation problems
    • skin and/or mucosal changes (flushing, urticaria, angioedema) – but these may be absent in up to 20% of cases

The diagnosis is supported if a patient has been exposed to an allergen known to affect them

Treat life-threatening features, using the Airway, Breathing, Circulation, Disability, Exposure (ABCDE) approach:

  • Adrenaline is the first-line treatment for anaphylaxis. Give intramuscular (IM) adrenaline early (in the anterolateral thigh) for Airway/Breathing/Circulation problems.
  • A single dose of IM adrenaline is well-tolerated and poses minimal risk to an individual having an allergic reaction. If in doubt, give IM adrenaline.
  • Repeat IM adrenaline after 5 minutes if Airway/Breathing/Circulation problems persist.
    • Intravenous (IV) adrenaline must be used only in certain specialist settings, and only by those skilled and experienced in its use.
    • IV adrenaline infusions form the basis of treatment for refractory anaphylaxis: seek expert help early in patients whose respiratory and/or cardiovascular problems persist despite 2 doses of IM adrenaline
  • All patients should be referred to a specialist clinic for allergy assessment.
  • Offer patients (or, if appropriate, their parent and/or carer) an appropriate adrenaline injector as an interim measure before the specialist allergy assessment (unless the reaction was drug-induced).
  • Patients prescribed adrenaline auto-injectors (and/or their parents/carers) must receive training in their use, and have an emergency management or action plan


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