← Chapter 9
Medical-Surgical Nursing II · Chapter 9

The First Sixty Seconds: Hypersensitivity and Anaphylaxis

The mechanism of a hypersensitivity reaction predicts both its timing and its treatment, and only one of the four types kills in minutes. Sort ten real reactions into their type, then build the first five moves of an anaphylaxis response — the tool will tell you exactly what your ordering would have done to the patient — and finish by calculating the epinephrine dose, route and site.
The reaction in front of you
Which hypersensitivity type?
0 of 10 typed

The four mechanisms, and what each one means at the bedside

TypeMechanismOnsetExamples
I — ImmediateIgE on mast cells, degranulationSeconds to 30 minutesAnaphylaxis, food and sting allergy, allergic rhinitis, atopic asthma
II — CytotoxicIgG or IgM against a cell-surface antigen, complement lysisMinutes to hoursABO haemolytic transfusion reaction, immune thrombocytopenia, heparin-induced thrombocytopenia, Goodpasture
III — Immune complexAntigen–antibody complexes deposit in tissue, complement consumedHours to weeksSerum sickness, post-streptococcal glomerulonephritis, lupus nephritis and vasculitis
IV — DelayedSensitised T cells and macrophages, no antibody24 to 72 hours or longerTuberculin skin test, contact dermatitis, graft rejection, Stevens–Johnson syndrome
Why the timing matters. A Type IV reaction will never be caught in a thirty-minute post-dose observation. Patients started on a new sulfonamide, allopurinol, lamotrigine or antiepileptic must be taught to report a spreading rash, mucosal blistering or fever days into therapy.