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Emergency And Acute Medicine – Anaphylaxis
Clinical Overview
Anaphylaxis is an acute, life-threatening systemic hypersensitivity reaction that develops rapidly after exposure to an antigen in a sensitized individual. It represents a form of distributive shock caused by widespread mediator release, leading to vasodilation, increased vascular permeability, smooth-muscle contraction, and excessive glandular secretion. These physiologic changes result in reduced systemic vascular resistance, decreased venous return and cardiac output, and intravascular volume depletion. Anaphylaxis accounts for hundreds of deaths annually in the United States and thousands of emergency department visits each month.
Underlying Causes
IgE-mediated reactions are most commonly triggered by antibiotics (particularly penicillins), insect venoms, foods such as peanuts, shellfish, and tree nuts, latex, vaccines, and monoclonal antibody therapies. Non–IgE-mediated reactions may occur with iodine-based contrast agents, opiates, and vancomycin.
Special Considerations In Children: Food allergens—especially milk, egg, wheat, soy, and peanuts—are the most frequent triggers, and even trace exposures may provoke severe reactions.
Clinical Manifestations
Symptoms typically begin within minutes of antigen exposure. Skin and mucosal involvement is present in the vast majority of cases, with urticaria, erythema, pruritus, and angioedema being common. Patients may report an early sense of impending doom. Respiratory findings range from nasal congestion to bronchospasm and upper airway edema. Cardiovascular involvement may include hypotension, arrhythmias, or myocardial ischemia. Gastrointestinal symptoms such as nausea, vomiting, and diarrhea may occur, along with ocular irritation, neurologic symptoms including seizures, and, rarely, hematologic abnormalities such as coagulopathy.
Key Historical Features
Diagnosis is clinical. A focused history should identify prior allergic reactions, known triggers, and recent exposures to foods, medications, or environmental allergens.
Physical Examination Focus
Findings usually involve two or more organ systems, commonly the skin, respiratory tract, gastrointestinal tract, or cardiovascular system. Airway compromise or hypotension may not be present initially but can develop rapidly.
Essential Clinical Assessment
Anaphylaxis is diagnosed on clinical grounds, and early recognition is critical. Ancillary testing should not delay treatment. ECG monitoring is advised in patients with cardiac history, ischemic symptoms, or advanced age.
Diagnostic Evaluation
Laboratory studies are generally not useful in the acute setting. Serum tryptase levels may aid retrospective confirmation. Chest radiography may show hyperinflation in cases with bronchospasm.
Alternative Diagnoses To Consider
Conditions that may mimic anaphylaxis include pulmonary embolism, acute coronary syndromes, asthma, airway obstruction, vasovagal syncope, hereditary angioedema, systemic mastocytosis, hypoglycemia, carcinoid syndrome, and foreign body aspiration.
Prehospital Care Principles
Early airway assessment, oxygen supplementation, IV access, and continuous monitoring are essential. Intramuscular epinephrine should be administered promptly, even before IV access is obtained. Progressive laryngeal edema may necessitate early airway intervention.
Immediate Stabilization Measures
Airway protection and adequate ventilation take priority. Orotracheal intubation is preferred when airway compromise is anticipated. Advanced airway techniques may be required in the presence of significant edema. Epinephrine may be administered via IM, IV, or endotracheal routes, along with aggressive fluid resuscitation.
Emergency Department Management
Continuous cardiac and vital-sign monitoring is required. Persistent bronchospasm is treated with inhaled β2-agonists. Hypotension is addressed with IV fluids and vasopressors if needed. Antihistamines reduce histamine-mediated effects, corticosteroids help prevent biphasic reactions, and glucagon is indicated for epinephrine-resistant anaphylaxis in patients taking β-blockers.
Pharmacologic Therapy
First-line therapy includes intramuscular epinephrine, H1 antihistamines, corticosteroids, and inhaled bronchodilators. Second-line agents include racemic epinephrine, H2 blockers, and glucagon when indicated. Special caution is required in patients receiving β-blockers.
Disposition Planning
Patients requiring intubation or ongoing respiratory or hemodynamic support should be admitted to an intensive care setting. Those with persistent or severe reactions warrant inpatient observation due to the risk of biphasic reactions. Patients with complete symptom resolution may be discharged after a period of observation.
Post-Discharge Follow-Up
All patients should receive early outpatient follow-up, ideally with an allergist. Education regarding trigger avoidance and prescription of self-injectable epinephrine are essential. Patients should be instructed on proper auto-injector use and advised to carry it at all times.
Clinical Pearls And Pitfalls
Delayed recognition of anaphylaxis can result in rapid airway compromise and cardiovascular collapse. Early administration of epinephrine is the single most critical intervention. Patients with a prior history of anaphylaxis require education on avoidance strategies and prompt self-treatment to prevent fatal outcomes.
Clinical Overview
Anaphylaxis is an acute, life-threatening systemic hypersensitivity reaction that develops rapidly after exposure to an antigen in a sensitized individual. It represents a form of distributive shock caused by widespread mediator release, leading to vasodilation, increased vascular permeability, smooth-muscle contraction, and excessive glandular secretion. These physiologic changes result in reduced systemic vascular resistance, decreased venous return and cardiac output, and intravascular volume depletion. Anaphylaxis accounts for hundreds of deaths annually in the United States and thousands of emergency department visits each month.
Underlying Causes
IgE-mediated reactions are most commonly triggered by antibiotics (particularly penicillins), insect venoms, foods such as peanuts, shellfish, and tree nuts, latex, vaccines, and monoclonal antibody therapies. Non–IgE-mediated reactions may occur with iodine-based contrast agents, opiates, and vancomycin.
Special Considerations In Children: Food allergens—especially milk, egg, wheat, soy, and peanuts—are the most frequent triggers, and even trace exposures may provoke severe reactions.
Clinical Manifestations
Symptoms typically begin within minutes of antigen exposure. Skin and mucosal involvement is present in the vast majority of cases, with urticaria, erythema, pruritus, and angioedema being common. Patients may report an early sense of impending doom. Respiratory findings range from nasal congestion to bronchospasm and upper airway edema. Cardiovascular involvement may include hypotension, arrhythmias, or myocardial ischemia. Gastrointestinal symptoms such as nausea, vomiting, and diarrhea may occur, along with ocular irritation, neurologic symptoms including seizures, and, rarely, hematologic abnormalities such as coagulopathy.
Key Historical Features
Diagnosis is clinical. A focused history should identify prior allergic reactions, known triggers, and recent exposures to foods, medications, or environmental allergens.
Physical Examination Focus
Findings usually involve two or more organ systems, commonly the skin, respiratory tract, gastrointestinal tract, or cardiovascular system. Airway compromise or hypotension may not be present initially but can develop rapidly.
Essential Clinical Assessment
Anaphylaxis is diagnosed on clinical grounds, and early recognition is critical. Ancillary testing should not delay treatment. ECG monitoring is advised in patients with cardiac history, ischemic symptoms, or advanced age.
Diagnostic Evaluation
Laboratory studies are generally not useful in the acute setting. Serum tryptase levels may aid retrospective confirmation. Chest radiography may show hyperinflation in cases with bronchospasm.
Alternative Diagnoses To Consider
Conditions that may mimic anaphylaxis include pulmonary embolism, acute coronary syndromes, asthma, airway obstruction, vasovagal syncope, hereditary angioedema, systemic mastocytosis, hypoglycemia, carcinoid syndrome, and foreign body aspiration.
Prehospital Care Principles
Early airway assessment, oxygen supplementation, IV access, and continuous monitoring are essential. Intramuscular epinephrine should be administered promptly, even before IV access is obtained. Progressive laryngeal edema may necessitate early airway intervention.
Immediate Stabilization Measures
Airway protection and adequate ventilation take priority. Orotracheal intubation is preferred when airway compromise is anticipated. Advanced airway techniques may be required in the presence of significant edema. Epinephrine may be administered via IM, IV, or endotracheal routes, along with aggressive fluid resuscitation.
Emergency Department Management
Continuous cardiac and vital-sign monitoring is required. Persistent bronchospasm is treated with inhaled β2-agonists. Hypotension is addressed with IV fluids and vasopressors if needed. Antihistamines reduce histamine-mediated effects, corticosteroids help prevent biphasic reactions, and glucagon is indicated for epinephrine-resistant anaphylaxis in patients taking β-blockers.
Pharmacologic Therapy
First-line therapy includes intramuscular epinephrine, H1 antihistamines, corticosteroids, and inhaled bronchodilators. Second-line agents include racemic epinephrine, H2 blockers, and glucagon when indicated. Special caution is required in patients receiving β-blockers.
Disposition Planning
Patients requiring intubation or ongoing respiratory or hemodynamic support should be admitted to an intensive care setting. Those with persistent or severe reactions warrant inpatient observation due to the risk of biphasic reactions. Patients with complete symptom resolution may be discharged after a period of observation.
Post-Discharge Follow-Up
All patients should receive early outpatient follow-up, ideally with an allergist. Education regarding trigger avoidance and prescription of self-injectable epinephrine are essential. Patients should be instructed on proper auto-injector use and advised to carry it at all times.
Clinical Pearls And Pitfalls
Delayed recognition of anaphylaxis can result in rapid airway compromise and cardiovascular collapse. Early administration of epinephrine is the single most critical intervention. Patients with a prior history of anaphylaxis require education on avoidance strategies and prompt self-treatment to prevent fatal outcomes.
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