Anaphylaxis: 5 Clinically Relevant Questions:
1) Whats the difference between anaphylaxis and anaphylactoid?
Anaphylaxis: IgE mediated
Anaphylactoid: Direct degranulation of mast cells
2) What are the main causes?
Main classes: Food, insects, medications.
–PCN Cross Reactivity with Cephalosporin? True incidence <0.1% true anaphylactic cross reactivity
–Radiocontrast material(RCM): Shellfish and iodine allergies are not relevant! That being said,
some people are truly allergic to RCM and require pre-treatment (prednisone, H2blocker)
3) How do truly anaphylactic patients present?
–Hx: exposure to a known allergen
–PE: skin (hives), respiratory (bronchoconstriction), and
hypotension. But don’t forget GI findings (diarrhea, cramping, abdominal pain).
4) What is the treatment? This is a distributive shock, the vessels are dilated and the volume is out in the tissues. So treatment should center on constricting the vessels and filling the tank. Start 2 L NS!
–Anaphylaxis: IM Epi: 0.3ml of 1:1000 (which is 1mg/1ml) so you are giving 0.3mg INTRAMUSCULAR!
–Refractory Hypotension: IV Epi: Take 1mg of 1:10,000 Epi in 1L NS. This is [1mcg/mL]. A wide open 18g will run at 20-30 ml/min (20-30mcg/min).
–Upper airway involvement: Take (3-5) 1mg ampules of 1:1000 Epi and nebulize the solution
–Steroids and antihistamines are important additional treatments, however, Epi is the mainstay
of true anaphylaxis!
5) What about rebound reactions? “Rebound” biphasic reactions occur 1-24 hours after initial event and does not correlate with severity of initial presentation.
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