The Purple Book

Anaphylaxis

• Allergy and hypersensitivity are the same - an immune response to an allergen
• Intolerance is NOT the same - refers to the body's inability to respond normally due to eg enzyme deficiency (eg. lactose intolerance)

• most common
• IgE mediated
• eg. allergies to food, pollen, drugs, stings
• causes: urticaria, asthma, angio-oedema, anaphylaxis
• testing: eosinophilia, se tryptase elevated ≤2/24 of anaphylaxis, fluoroenzyme tests for allergen specific IgE, skin tests.

• general: often restless and anxious. May have a sense of impending doom.
• skin: urticaria, erythema
• CVS: Tachycardia, hypotension
• Respiratory: nasal congestion, cough, angioedema of tongue/lips, tachypnoea, stridor, hoarse voice, wheeze
• Gastro-intestinal: dysphagia, N&V, cramps
• CNS: agitation, irritable, coma

• remove patient from any further exposure if possible
• assess and ensure patent airway
• oxygen support

• establish IV access for fluid resuscitation and give bolus if hypotensive - 500-1000ml
• antihistamines are NOT 1st line but may be beneficial for cutaneous symptoms
• bronchodilators - salbutamol neb
• steroids - NOT 1st line - hydrocortisone, prednisolone may be useful following success with Adrenaline to assists stabilisation
• inotropes and vasopressors - glucagon, dopamine etc may be required for refractory anaphylaxis

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Type II Hypersensitivity:

• auto-immune reactions involving IgM and IgG
• eg. bullous pemphigoid, pemphigus vulgaris

Type III Hypersensitivity:

• IgG mediated - bind to antigens
• eg. Rheumatoid, small vessel vasculitis, Henoch-Schonlein, Lupus

Type IV Hypersensitivity:

• delayed hypersenstivity - generally 48-72/24 post exposure
• NOT mediated by Ig - instead by eosinophils, monocytes, lymphocytes
• eg. contact dermatitis, morbilliform drug reactions, erythema multiforme