18th March 2024

Pathophysiology of anaphylaxis

Symptoms of anaphylaxis are mediated by extensive release of histamine from mast cells and basophils. Degranulation of these cells is triggered by cross-linking of antigen-specific IgE binding to high affinity receptors expressed on the surface of the mast cells and basophils. Histamine released causes systemic symptoms, including vasodilation, tissue oedema and bronchoconstriction, resulting in hypotension, intravascular volume depletion and airway constriction. The cumulation of these features causes hypoxia, hypotension and shock with loss of organ perfusion.

It is important to note that a significant proportion of reactions result from mast cell and basophil activation independent from IgE; these reactions are termed anaphylactoid. Common causes include non-steroidal anti-inflammatories and contrast media. Vancomycin is a well-known cause of anaphylactoid reaction and is sometimes termed “Red Man Syndrome”. Presentation of anaphylactoid reactions and, therefore, their management is identical to that of anaphylaxis.