Anaphylaxis in a Nutshell

anaphylaxis in a nutshell

Anaphylaxis can be broadly defined as a severe, life-threatening, generalized or systemic hypersensitivity reaction. Literature suggests that anaphylaxis is not always easily recognized in the Emergency Department (ED). One study indicates around 50% of cases being misdiagnosed and up to 80% do not receive appropriate first-line treatment.


The most commonly identified triggers of anaphylaxis include food, drugs and venom, but it is important to note that 30% of the cases can be idiopathic. Among drugs, muscle relaxants, antibiotics, NSAIDs and aspirin are the most commonly implicated.

Which patients are at an increased risk of anaphylaxis severity and mortality?

Extremes of age

Co-morbid conditions (asthma, COPD, cardiovascular disease)

Concurrent use of beta-blockers and ACE inhibitors

While the overall prognosis of anaphylaxis is good, the key to avoiding adverse outcomes is by prompt recognition and initiation of appropriate interventions. Below are key points to guide your management of anaphylaxis in the ED.

Recognizing Anaphylaxis in the ED

Anaphylaxis reactions vary significantly in duration and severity and a single set of criteria will not identify all anaphylactic reactions. The World Allergy Organization (WAO) has suggested the following criteria to help ED physicians be more consistent in their recognition of anaphylaxis.

Anaphylaxis is highly likely when any one of the following three criteria is fulfilled

1. Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (eg, generalized urticaria, itching or flushing, swollen lips-tongue-uvula) AND AT LEAST ONE OF THE FOLLOWING

  • Respiratory compromise (eg, dyspnea, wheeze-bronchospasm, stridor, reduced PEF, hypoxemia)
  • Reduced blood pressure or associated symptoms of end-organ dysfunction (eg. hypotonia [collapse], syncope, incontinence) OR

2. Two or more of the following that occur rapidly after exposure to a likely allergen for that patient (minutes to several hours)

  • Involvement of the skin-mucosal tissue (eg, generalized urticaria, itch-flush, swollen lips-tongue-uvula)
  • Respiratory compromise (eg, dyspnea, wheeze-bronchospasm, stridor, reduced PEF, hypoxemia)
  • Reduced blood pressure or associated symptoms (eg, hypotonia [collapse], syncope, incontinence)
  • Persistent gastrointestinal symptoms (eg, crampy abdominal pain, vomiting) OR

3. Reduced blood pressure after exposure to known allergen for that patient (minutes to several hours)

  • Infants and children: low systolic blood pressure (age-specific) or greater than 30% decrease in systolic blood pressure
  • Adults: systolic blood pressure of less than 90 mm Hg or greater than 30% decrease from that person’s baseline

Management Algorithm of Anaphylaxis in the ED

Anaphylaxis algorithm
Anaphyaxis algorithm 2

Key Points in Management

  • Early and prompt recognition of the anaphylaxis/severe allergic reaction is key to appropriate management. Anticipate deterioration of clinical status/airway and an early call for help.
  • Initial systematic assessment using an ABCDE approach. The most important step in the management of anaphylaxis is the early administration of epinephrine intramuscularly. Do not delay this step while securing IV access/airway. There are no absolute contradictions to the use of epinephrine in the management of anaphylaxis.
  • Be prepared for a surgical cricothyroidotomy especially in a patient who is rapidly deteriorating despite epinephrine.
  • In patients on beta-blockers, the key is to give glucagon 1mg - 3mg IV every 5 minutes and titrate for resolution of hypotension (be prepared for vomiting).
  • Remember that antihistamines and corticosteroids do NOT play a role in the management of the acute reaction.
  • Serum tryptase levels are elevated in anaphylaxis but diagnosis is clinical and laboratory tests are not helpful in acute settings.
  • Patients who respond to treatment and have complete resolution of symptoms can be discharged after an observation period of 4 – 8 hours. However, up to 20% of the patients can have a biphasic reaction, which usually occurs within 8 hours but has been reported to occur as far as 72 hours. Consider extended observation for patients who presented with protracted anaphylaxis, hypotension or airway management.
  • Patients with anaphylaxis due to insect stings or unknown/unavoidable triggers should be prescribed an epinephrine autoinjector pen on discharge and timely follow up with an allergist.

References and Further Reading

Cite this article as: Neha Hudlikar, UAE, "Anaphylaxis in a Nutshell," in International Emergency Medicine Education Project, January 31, 2020,, date accessed: August 10, 2020

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