From the Guidelines
Anaphylaxis is defined as an acute, life-threatening systemic allergic reaction that may have a wide range of clinical manifestations, and anaphylactic shock is the most severe manifestation of anaphylaxis, characterized by a dramatic drop in blood pressure leading to inadequate blood flow to vital organs. According to the 2020 practice parameter update, systematic review, and grading of recommendations, assessment, development and evaluation (GRADE) analysis published in the Journal of Allergy and Clinical Immunology 1, anaphylaxis is an acute, life-threatening systemic allergic reaction that may have a wide range of clinical manifestations. The clinical criteria proposed in 2006 by National Institute of Allergy and Infectious Diseases (NIAID) continue to provide a helpful framework in approaching patients with acute allergic symptoms.
Key Characteristics of Anaphylaxis
- Anaphylaxis involves multiple body systems and is characterized by symptoms such as hives, swelling, difficulty breathing, wheezing, rapid heartbeat, dizziness, and gastrointestinal issues like vomiting or diarrhea
- Risk factors for severe anaphylaxis include cardiovascular disease, asthma, older age, and additional coexisting, comorbid conditions
- Medications and stinging insects are the leading triggers in adults, with foods and stinging insects the most frequently implicated triggers in children and adolescents
Treatment of Anaphylaxis
- Epinephrine administered intramuscularly (in a dose of 0.01 mg/kg of a 1:1000 [1 mg/mL] solution to a maximum of 0.5 mg in adults and 0.3 mg in children) into the anterolateral thigh is the first-line treatment for anaphylaxis 1
- Additional treatments may include antihistamines, corticosteroids, and bronchodilators, though these are secondary to epinephrine
- People with known severe allergies should carry an epinephrine auto-injector (like EpiPen) at all times and seek emergency medical care immediately after use, even if symptoms appear to improve
Underlying Mechanism
- The underlying mechanism involves the release of inflammatory mediators from mast cells and basophils triggered by an allergen, causing widespread vasodilation, increased vascular permeability, and bronchial constriction 1
- IgE binding and cross-linking of the high affinity IgE receptor (FcεRI) on the surface of mast cells and basophils is an important mechanism in many cases of anaphylaxis 1
From the FDA Drug Label
Emergency treatment of allergic reactions (Type I), including anaphylaxis, which may result from allergic reactions to insect stings, biting insects, foods, drugs, sera, diagnostic testing substances and other allergens, as well as idiopathic anaphylaxis or exercise-induced anaphylaxis. The signs and symptoms associated with anaphylaxis include flushing, apprehension, syncope, tachycardia, thready or unobtainable pulse associated with hypotension, convulsions, vomiting, diarrhea and abdominal cramps, involuntary voiding, airway swelling, laryngospasm, bronchospasm, pruritus, urticaria or angioedema, swelling of the eyelids, lips, and tongue.
- Anaphylaxis is defined as a severe, life-threatening allergic reaction (Type I) that may result from various allergens, including insect stings, foods, drugs, and others.
- The signs and symptoms of anaphylaxis include:
- Cardiovascular: flushing, tachycardia, thready or unobtainable pulse, hypotension
- Respiratory: airway swelling, laryngospasm, bronchospasm
- Gastrointestinal: vomiting, diarrhea, abdominal cramps
- Dermatological: pruritus, urticaria, angioedema, swelling of the eyelids, lips, and tongue
- Neurological: apprehension, syncope, convulsions
- Anaphylactic (hypersensitivity) shock is implied by the presence of hypotension, thready or unobtainable pulse, and other severe symptoms associated with anaphylaxis 2
From the Research
Definition of Anaphylaxis
- Anaphylaxis is defined as a severe life-threatening generalized or systemic hypersensitivity reaction characterized by rapidly developing airway and/or circulation problems 3
- It is a severe systemic allergic reaction that can involve multiple systems of the body, often unpredictable, and can have life-threatening consequences 4
- Anaphylaxis is most commonly defined as an acute, severe, potentially life-threatening systemic hypersensitivity reaction 5
- It is a rapid, systemic, often unanticipated, and potentially life-threatening immune reaction occurring after exposure to certain foreign substances 6
Definition of Anaphylactic (Hypersensitivity) Shock
- Anaphylactic shock is a severe and potentially life-threatening condition that can occur as a result of anaphylaxis, characterized by a rapid onset of symptoms, including airway obstruction, hypotension, and shock 3, 6
- It is a serious reaction that is rapid in onset and can be fatal, and is a severe, potentially life-threatening systemic hypersensitivity reaction 5
- Anaphylactic shock can lead to death by airway obstruction or vascular collapse 7
Key Characteristics
- Anaphylaxis can present with very different combinations of symptoms and apparently mild signs, and can progress to fatal anaphylactic shock unpredictably 3
- The diagnosis of anaphylaxis is typically made when symptoms occur within one hour of exposure to a specific antigen 7
- Anaphylaxis often involves multiple systems of the body, including dermatologic, respiratory, cardiovascular, gastrointestinal, and neurologic symptoms 4, 7