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Anaphylaxis

Last updated: August 12, 2021

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Anaphylaxis is an acute, potentially life-threatening, type 1 hypersensitivity reaction, involving the sudden IgE-mediated release of histamine mediators from mast cells and basophils in response to a trigger (e.g., food, insect stings, medication). Anaphylactoid reactions (a subtype of pseudoallergy) are IgE-independent reactions that result from direct mast-cell activation (e.g., in response to opioids); the clinical presentation and management are the same as for anaphylaxis. Typical signs and symptoms of both reactions include the acute onset of urticarial rash, angioedema, stridor, dyspnea, bronchospasm, circulatory failure (distributive shock), vomiting, and diarrhea. The diagnosis is clinical and is based on combinations of typical symptoms, plus the presence of a known or suspected trigger. Rapid recognition and treatment are key to prevent death from airway loss, respiratory failure, or cardiovascular collapse. Management consists of initial resuscitation measures that focus on administering IM epinephrine, removing triggers, securing the airway, and giving IV fluid boluses, which take precedence over adjunctive treatment like steroids and antihistamines.

  • Trigger is idiopathic in 20% of patients [1]
  • Most common triggers leading to fatal anaphylaxis [1][2][3]
    • Younger patients: food allergies; (e.g., peanut, tree nuts), insect stings (e.g., bee stings)
    • Older patients: drug reactions, radiocontrast media
    • Hospitalized patients: food, medications (e.g., antibiotics, NSAIDs), latex

Onset of symptoms [2][4]

In general, the onset of symptoms is acute (within minutes to hours of exposure to a likely antigen).

Antigen-dependent onset of anaphylaxis [2][4]
Trigger

Median time to circulatory arrest

Food 30 min
Insect 15 min
Medication 5 min

Affected organ systems [2][4]

Beware of atypical manifestations without skin/mucosal symptoms (10% of patients) to avoid misdiagnosis and treatment delay. [1]

Diagnostic criteria for anaphylaxis [1][4][6]

If any of the following criteria are fulfilled, anaphylaxis is likely. The onset of symptoms must be acute (minutes to hours).

If anaphylaxis diagnostic criteria are met, empiric treatment should be given without delay.

The most important measures in anaphylaxis are to remove the inciting allergen and administer epinephrine as soon as possible. Delay can lead to airway compromise, respiratory failure, refractory shock, and death.

Epinephrine injections for anaphylaxis should always be given intramuscularly in a concentration of 1:1,000 (as opposed to the 1:10,000 solution used in cardiac arrest). Injecting the 1:1,000 solution into a vein can lead to cardiac arrhythmia/arrest.

Anaphylaxis is a clinical diagnosis (see “Diagnostic criteria for anaphylaxis”).

Laboratory studies [2][8][9]

Imaging [2][9]

See also “Airway management” and “Mechanical ventilation” for more details.

Obtain early anesthesia or ENT consultation in patients with a rapid decline or anticipated airway compromise.

References: [2][4][7]

Refractory anaphylaxis [2][4][7]

Adjunctive therapy [2][4][7]

Antihistamines and steroids should be administered in anaphylaxis only after the initial resuscitation measures (IM epinephrine, fluids and/or vasopressors) have been given.

A lack of response to epinephrine, antihistamines, and steroids should raise suspicion of differential diagnoses such as bradykinin-mediated angioedema, which requires its own specific treatment (see “Treatment of angioedema”).

Monitoring and disposition [2][4][7]

The differential diagnoses listed here are not exhaustive.

We list the most important complications. The selection is not exhaustive.

Pretreatment for in-hospital triggers [12][13][14]

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  2. Walls R, Hockberger R, Gausche-Hill M. Rosen's Emergency Medicine. Elsevier Health Sciences ; 2018
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  4. Long B, Koyfman A, Gottlieb M. Evaluation and Management of Angioedema in the Emergency Department. Western Journal of Emergency Medicine. 2019; 20 (4): p.587-600. doi: 10.5811/westjem.2019.5.42650 . | Open in Read by QxMD
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  7. Anagnostou K, Turner PJ. Myths, facts and controversies in the diagnosis and management of anaphylaxis. Arch Dis Child. 2018; 104 (1): p.83-90. doi: 10.1136/archdischild-2018-314867 . | Open in Read by QxMD
  8. Loprinzi Brauer, et al.. Prospective Validation of the NIAID/FAAN Criteria for Emergency Department Diagnosis of Anaphylaxis. JACI: In Practice. 2016; 4 (6). doi: 10.1016/j.jaip.2016.06.003 . | Open in Read by QxMD
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  10. International Collaborative Study of Severe Anaphylaxis.. Risk of anaphylaxis in a hospital population in relation to the use of various drugs: an international study.. Pharmacoepidemiol Drug Saf. 2003; 12 (3): p.195-202. doi: 10.1002/pds.822 . | Open in Read by QxMD
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