Presentations
Approach to anaphylaxis
The same eight steps, every presentation: threats first, then the history and exam that discriminate, one honest sentence, a mechanism-grouped differential, and the tests read in order.
Immediate threats
- Airway edema: voice change, tongue swelling, stridor
- Distributive shock with capillary leak
- The biphasic recurrence hours after apparent recovery
History that discriminates
- Exposure within minutes to two hours: food, drug, sting
- The two-system rule: skin plus respiratory, cardiovascular, or GI involvement
- Prior reactions and their severity; asthma raises the stakes
- Beta blockade on the chart predicts epinephrine resistance
Examination
- Airway first: voice, stridor, tongue and lip swelling
- Urticaria and flushing; but 10 to 20 percent have no skin signs
- Blood pressure and perfusion; wheeze
Problem representation
Minutes after a first IV antibiotic dose: flushing, urticaria, wheeze and a falling pressure. Epinephrine now, diagnosis later.
Differential, by mechanism
The mimics
- Vasovagal reaction (pale, slow, no urticaria)
- Asthma attack alone
- ACE inhibitor angioedema (no urticaria, bradykinin-driven)
- Scombroid
- Carcinoid flush
Investigations
- None before epinephrine: anaphylaxis is a clinical diagnosis
- Serum tryptase within three hours supports the diagnosis retrospectively
- Allergy referral and specific IgE testing later, never acutely
Interpretation
- Hypotension after an exposure with any second system is anaphylaxis; urticaria is not required
- ACE inhibitor angioedema is the trap: isolated deep swelling without itch responds poorly to epinephrine
Next steps
- IM epinephrine mid-thigh, repeated at five minutes if needed; everything else is adjunct
- Observation for biphasic reaction; discharge with an autoinjector, a plan, and allergy follow-up
Connected
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