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Anaphylaxis

Definition
Anaphylaxis is a severe, potentially life-threatening allergic reaction that can occur rapidly after exposure to an allergen.
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Pathophysiology
The pathophysiology of anaphylaxis involves the release of inflammatory mediators, primarily through the activation of IgE antibodies. This leads to systemic inflammation and can affect multiple organ systems.
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Epidemiology
The incidence of anaphylaxis in the US is estimated at 49.8 per 100,000 person-years.
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Disease course
Clinical manifestations of anaphylaxis are diverse and can include skin reactions (such as hives and itching), respiratory distress, cardiovascular complications (such as hypotension and tachycardia), gastrointestinal symptoms (such as vomiting and diarrhea), and psychological symptoms like anxiety.
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Prognosis and risk of recurrence
The prognosis of anaphylaxis can be severe, with the potential for rapid deterioration and fatal outcomes if not promptly treated. The severity of anaphylaxis can range from mild to severe.
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Key sources
The following summarized guidelines for the evaluation and management of anaphylaxis are prepared by our editorial team based on guidelines from the American Academy of Allergy, Asthma & Immunology (AAAAI 2023), the European Academy of Allergy and Clinical Immunology (EAACI 2022; 2014), the Wilderness Medical Society (WMS 2022), the American Academy of Allergy, Asthma & Immunology (AAAAI/ACAAI 2020; 2014), and the American Heart Association (AHA 2020).
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Guidelines

1.Screening and diagnosis

Diagnostic criteria: as per AAAAI 2023 guidelines, avoid using the clinical decision to administer epinephrine or the clinical response to epinephrine as a surrogate marker to establish a diagnosis of anaphylaxis.
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2.Diagnostic investigations

Serum tryptase: as per AAAAI 2023 guidelines, obtain baseline serum tryptase measurement in patients presenting with a history of recurrent, idiopathic, or severe anaphylaxis, particularly with hypotension.
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  • Evaluation for mastocytosis

  • Evaluation for alpha-gal syndrome

3.Respiratory support

Supplemental oxygen: administer high-flow oxygen by face mask in all patients with anaphylaxis.
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4.Medical management

General principles: as per AAAAI 2023 guidelines, avoid requiring meeting diagnostic criteria for anaphylaxis before administering epinephrine.
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  • Epinephrine (clinician-delivered)

  • Epinephrine (patient-delivered)

  • Corticosteroids and antihistamines

  • Intravenous fluids

  • Inhaled beta-2 agonists

  • Glucagon

  • Management of beta-blockers and ACEIs

5.Nonpharmacologic interventions

Removal of allergen: as per WMS 2022 guidelines, separate the patient from the inciting allergen, if possible, but do not induce vomiting to eliminate a food-based allergen.
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  • Patient positioning

  • Evacuation

6.Specific circumstances

Pediatric patients: consider using the current NIAID/FAAN or WAO anaphylaxis criteria to assist in the diagnosis of anaphylaxis in infants/toddlers, as there are no criteria specific to this age group.
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  • Patients with food-dependent exercise-induced anaphylaxis

  • Patients with perioperative anaphylaxis

  • Patients in cardiac arrest

  • Austere or disaster conditions

7.Patient education

Patient education: as per AAAAI 2023 guidelines, counsel patients at high risk of anaphylaxis to always carry self-injectable epinephrine and teach patients proper indications and use.
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8.Preventative measures

Premedication
Insufficient evidence to recommend for or against the use of premedication with antihistamines to prevent anaphylaxis.
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Consider administering premedication with SC epinephrine to prevent anaphylaxis when snake bite anti-venom is given to a patient.
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  • Allergen immunotherapy

  • Desensitization

9.Follow-up and surveillance

Clinical observation: as per WMS 2022 guidelines, obtain clinical observation after treatment of anaphylaxis with a length of observation depending on the severity of the initial reaction and risk factors for a biphasic reaction.
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  • Discharge from hospital

  • Indications for allergist referral

10.Quality improvement

Medical alert bracelet: consider advising patients at risk of anaphylaxis to wear or carry medical identification (such as jewelry or wallet card). Ensure that the wording on medical alert jewelry or wallet cards is verified for accuracy by a healthcare professional.
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  • Health professional training

  • School policies