Last Updated on by frcemuser

Signs and Symptoms

Airway: lip and tongue swelling/angioedema, hoarseness, stridor
Breathing: rapid breathing(tachypnoea), wheeze/ bronchospasm, fatigue, cyanosis, SpO2 < 92%, confusion due to hypoxia, cyanosis, respiratory arrest
Circulation: pale, clammy, hypotension, tachycardia, faintness, drowsy/coma, arrhythmia, myocardial ischemia, cardiac arrest, signs of shock
Skin: Urticaria and/or angioedema


There are a sensitization phase and an effector phase that give rise to the symptoms:

Sensitization phase

  • Immune system encounters allergen and makes immunoglobulin E (IgE) against it
  • No clinical features occur

Effector phase

  • Allergen cross-links IgE on the surface of mast cells ( Type 1 hypersensitivity )
  • Causes widespread degranulation and release of histamine which mediates inflammatory bronchospasm, vasodilatation, increased capillary permeability, and tissue edema

Common agents to cause anaphylaxis

  • Medication: Antibiotics (Penicillin) , Aspirin, NSAIDs, Angiotensin Converting Enzyme Inhibitors, Anaesthetic agents, contrast media.
  • Food Food, e.g. peanuts, egg and seafood.
  • Insect stings

Lab test

Mast cell tryptase: Take three samples taken- as soon as possible, after 1-2 hours (not later than 4 hours) and after 24 hours. Useful in making a retrospective diagnosis but the absence of rising does not exclude anaphylaxis

Differential diagnosis

  • C1 esterase inhibitor deficiency –  autosomal dominant. Hereditary angio-oedema is not usually accompanied by urticaria and is treated with C1 esterase inhibitor/or fresh frozen plasma.
  • Idiopathic (non-allergic) urticaria or angioedema
  • Systemic mast cell disorders
  • Septic shock presents with hypotension with a petechial/purpuric rash.
  • Asthma can present with similar symptoms and signs to anaphylaxis, particularly in children.
allergic Angioedema Non-Allergic Angioedema Anaphylaxis
Anatomically localised attack Anatomically localised attack Systemic symptoms
Urticaria Gradual onset Rapid onset and progression
Pruritis No Pruritis Respiratory failure (wheeze, fatigue, cyanosis, hypoxia, tachypnoea)
Normotension Previous identical episodes Cardiovascular Collapse (Diaphoretic, hypotensive, tachycardia, drowsiness)
Abdominal pain

Emergency Treatment

  • Call for help, lie the patient flat and raise the patient’s legs
  • Establish an airway if necessary and apply high flow oxygen
  • Give IM Adrenaline- -Can be repeated after 5 min if no better
    • In adults and children over 12 years, give 0.5ml(500 micrograms) of 1:1000 adrenaline
    • In children aged 6-12 years, give 0.3ml (300 micrograms) of 1:1000 adrenaline intramuscularly.
    • In children aged under 6 years, give 0.15ml (150 micrograms) of 1:1000 adrenaline intramuscularly.
    • IV dose: Adults 50 micrograms; Children 1 microgram/kg (1:10,000 )(Risk of Cerebrovascular hemorrhage, Cardiac arrhythmias or infarction)
    • Give only 50 % of the usual dose of adrenaline to patients taking tricyclic antidepressants, MAOIs, or B –blockers.
    • Glucagon can be helpful in patients with anaphylaxis who are taking beta-blockers. 1–2mg IM/IV every 5min
  • Give a crystalloid fluid bolus (A crystalloid may be safer than a colloid)
    • Adults: 500-1000ml intravenously (4-8 L of crystalloid may be required peri-arrest)
    • Children: 20ml/kg intravenously
  • Antihistamines
  • Corticosteroids

Further management of anaphylaxis

  • Observe for at least six hours
  • Beware biphasic reactions
  • Advise patient to return immediately if symptoms reoccur
  • Admit under 16 years of age
  • Provide three-day prescription of oral steroid and anti-histamine
  • Consider an adrenaline auto-injecter (EpiPen)- 300mcg dose
  • Referral to allergy specialist

What are relative contraindications while using adrenaline

Adrenaline may be administered in life-threatening anaphylactic reactions, even when the following relative contraindications are present:

  • Coronary artery disease
  • Uncontrolled hypertension
  • Serious ventricular arrhythmias
  • The second stage of labour

How does Adrenaline work?

  • Adrenalines alpha-adrenoceptor actions reverse the peripheral vasodilatation and reduce oedema.
  • It also has a beta-receptor action that causes airway dilation, increases the force of myocardial contraction and suppresses the histamine and leukotriene release

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