Acute systemic anaphylaxis

Principles to understand

• actions of mast cell mediators on respiratory, GI, circulatory systems

• timing of these responses

Mast cell activation

• low-dose subcutaneous entry of allergen, as in a bug bite

  • local release of histamine

  • this leads to a localized wheal-and-flare reaction

• high-dose intravenous entry of allergen

  • general release of histamine

  • wheal-and-flare everywhere, which is systemic anaphylaxis

• low-dose inhalation of allergen

  • increased mucus production

  • sweaty

  • wet eyes

  • “everything you get with good Mexican food”

• ingestion

  • contraction of intestinal SM; vomiting, diarrhea, or both

  • this is protective because it helps the body clear the antigen

  • if the antigen persists, it diffuses into blood and is disseminated. it is important to know that if a patient presents with hives due to food allergy, then they have absorbed the antigen into circulation

IgE-mediated allergic reactions

• the same thing that we’ve seen before

• keep in mind route of entry and the kind of reaction you expect to see

• and you can absorb large amounts of stuff from gut into bloodstream and get systemic anaphylaxis

MAP and epinephrine

• mean arterial pressure drops because blood vessels dilate

• don’t worry a lot about this
  

• emphasize this point: remember the two-phase reaction: first histamine, then leukotrienes

• this means that you can’t let someone out of the ER right after they have recovered after the first phase of an allergic attack

Category: Pathology Notes