Anaphylaxis occurs on a spectrum. Although anaphylactic shock is a well defined form of distributive shock, your patient does not have to have “shock” to have “anaphylaxis”.

Why would you care to split hairs about the definition? Because the treatment of anaphylaxis differs from the treatment of simple allergic reactions.

How do we treat hives or other simple allergic reactions? Antihistamines and maybe steroids

How do we treat anaphylaxis? Epinephrine

How do define anaphylaxis? Admittedly it is somewhat vague, but the definition is: “a serious allergic reaction that is rapid in onset and may cause death(1).”

How do we diagnose anaphylaxis?

Anaphylaxis is highly likely when any one of the following three criteria is fulfilled(1):

1. Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both
   • And at least one the following
     • Respiratory compromise (eg, dyspnea, wheeze/bronchospasm, stridor, hypoxemia)
     • Reduced Blood pressure or symptoms of end-organ damage (syncope, hypotonia, etc)
2. Two or more of the following that occur rapidly after exposure to a likely allergen for that patient
   • Involvement of the skin or mucosal tissue
   • respiratory compromise
   • reduced blood pressure or associated symptoms
   • persistent gastrointestinal symptoms (eg, crampy abdominal pain, vomiting, diarrhea)
3. Reduced blood pressure after exposure to a known allergen for that patient

By criteria 1, your patient with hives and wheezing qualifies and anaphylaxis. By criteria 2, your patient with edema of the lower lip and diarrhea after exposure to peanuts qualifies. Both of these patients would be good candidates for intramuscular epinephrine. Would they die if you just gave them antihistamines and steroids? Probably not, but anaphylaxis is much more difficult to treat once it has progressed to anaphylactic shock.

Could we treat simple urticaria with epinephrine? You bet, and it would work. For a short time, then they would come back. That’s why it is unnecessary. There is no need to ‘temporarily cure’ and non-lifethreating condition. Use the longer acting treatments (antihistamines and steroids).

Reference:

Sampson HA, et al. Second symposium on the definition and management of anaphylaxis: summary report–Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium. J Allergy Clin Immunol. 2006 Feb;117(2):391-7. doi: 10.1016/j.jaci.2005.12.1303. PMID: 16461139.