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. 

Want more???  Check out Michelle Lin’s Paucis Verbis card


  1. This is important:

    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).

    I used to blow right past this when I was a resident because I thought… when am I ever going to start IV epi on a patient? Well, when you need to do it you can’t be looking this stuff up. This is a critical action in a case if it were oral boards and generally just a good idea to be familiar with it!

    • Eric Deutsch on June 7, 2014 at 12:45 pm
    • Reply

    There are also some case studies showing utility of Glucagon in patients taking beta blockers and refractory to epi. It exerts ionotropic and chorion tropic effects independent of adrenergic system. Dosing 1-2mg IV then possibly 1-5mg/hr drip, watch out for vomiting.

    • Ben Lefkove on June 8, 2014 at 7:12 am
    • Reply

    I’ve found the anaphylaxis criteria useful in making the dx, and especially so in differentiating btw allergic reaction and anaphylaxis []

    Criterion 1
    Acute onset of an illness involving the skin, mucosal tissue, or both AND at least one of the following:
    Respiratory Compromise
    Reduced blood pressure or associated symptoms (Syncope, Dizziness)

    Criterion 2 (10-20% of pts)
    TWO OR MORE of the following that that occur rapidly after exposure to a LIKELY allergen for that patient
    Involvement of the skin-mucosal tissue (hives, swollen lips-tongue-uvula)
    Respiratory compromise
    Hypotension or associated symptoms
    Persistent gastrointestinal symptoms: (vomiting, diarrhea, crampy abdominal pain)

    Criterion 3
    Hypotension after exposure to a KNOWN allergy for that patient (minutes to hours):
    Adults: systolic blood pressure (SBP) 30% reduction from baseline
    1 month – 1 year: SBP <70 mmHg
    1 year – 10 years: SBP <(70 mmHg + [2 x age])
    11 years – 17 years: SBP <90 mmHg

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