Practice Essentials
Anaphylaxis is an acute, potentially fatal, multiorgan system reaction caused by the release of chemical mediators from mast cells and basophils.
The classic form involves prior sensitization to an allergen with later reexposure, producing symptoms via an immunologic mechanism.
Signs and symptoms
Anaphylaxis most commonly affects the cutaneous, respiratory, cardiovascular, and gastrointestinal systems. The skin or mucous membranes are involved in 80-90% of cases. A majority of adult patients have some combination of urticaria, erythema, pruritus, or angioedema. However, for poorly understood reasons, children may present more commonly with respiratory symptoms followed by cutaneous symptoms.
It is also important to note that some of the most severe cases of anaphylaxis present in the absence of skin findings.
Initially, patients often experience pruritus and flushing. Other symptoms can evolve rapidly, such as the following:
Dermatologic/ocular: Flushing, urticaria, angioedema, cutaneous and/or conjunctival injection or pruritus, warmth, and swelling
Respiratory: Nasal congestion, coryza, rhinorrhea, sneezing, throat tightness, wheezing, shortness of breath, cough, hoarseness, dyspnea
Cardiovascular: Dizziness, weakness, syncope, chest pain, palpitations
Gastrointestinal: Dysphagia, nausea, vomiting, diarrhea, bloating, cramps
Neurologic: Headache, dizziness, blurred vision, and seizure (very rare and often associated with hypotension)
Other: Metallic taste, feeling of impending doom
See Clinical Presentation for more detail.
Diagnosis
Anaphylaxis is primarily a clinical diagnosis. The first priority in the physical examination should be to assess the patient’s airway, breathing, circulation, and adequacy of mentation (eg, alertness, orientation, coherence of thought).
Examination may reveal the following findings:
General appearance and vital signs: Vary according to the severity of the anaphylactic episode and the organ system(s) affected; patients are commonly restless and anxious
Respiratory findings: Severe angioedema of the tongue and lips; tachypnea; stridor or severe air hunger; loss of voice, hoarseness, and/or dysphonia; wheezing
Cardiovascular: Tachycardia, hypotension; cardiovascular collapse and shock can occur immediately, without any other findings
Neurologic: Altered mentation; depressed level of consciousness or may be agitated and/or combative
Dermatologic: Classic skin manifestation is urticaria (ie, hives) anywhere on the body; angioedema (soft-tissue swelling); generalized (whole-body) erythema (or flushing) without urticaria or angioedema
Gastrointestinal: Vomiting, diarrhea, and abdominal distention
Testing
Laboratory studies are not usually required and are rarely helpful. However, if the diagnosis is unclear, especially with a recurrent syndrome, or if other diseases need to be excluded, the following laboratory studies may be ordered in specific situations:
Serum tryptase may help confirm the diagnosis of anaphylaxis
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Urinary 24-hour histamine may help in the diagnosis of recurrent anaphylaxis
Urinary 24-hour 5-hydroxyindoleacetic acid levels: If carcinoid syndrome is a consideration
Skin testing, in vitro immunoglobulin E (IgE) tests, or both may be used to determine the stimulus causing the anaphylactic reaction. Such studies may include the following:
Testing for food allergy(ies)
Testing for medication allergy(ies)
Testing for causes of IgE-independent reactions
See Workup for more detail.
Management
Anaphylaxis is a medical emergency that requires immediate recognition and intervention. Patient management and disposition are dependent on the severity of the initial reaction and the treatment response. Measures beyond basic life support are not necessary for patients with purely local reactions. Patients with refractory or very severe anaphylaxis (with cardiovascular and/or severe respiratory symptoms) should be admitted or treated and observed for a longer period in the emergency department or an observation area.
Nonpharmacotherapy
Supportive care for patients with suspected anaphylaxis includes the following:
Airway management (eg, ventilator support with bag/valve/mask, endotracheal intubation)
High-flow oxygen
Cardiac monitoring and/or pulse oximetry
Intravenous access (large bore)
Fluid resuscitation with isotonic crystalloid solution
Supine position (or position of comfort if dyspneic or vomiting) with legs elevated
Pharmacotherapy
The primary drug treatments for acute anaphylactic reactions are epinephrine and H1 antihistamines. Medications used in patients with anaphylaxis include the following:
Adrenergic agonists (eg, epinephrine)
Antihistamines (eg, diphenhydramine, hydroxyzine)
H2 receptor antagonists (eg, cimetidine, ranitidine, famotidine)
Bronchodilators (eg, albuterol)
Corticosteroids (eg, methylprednisolone, prednisone)
Positive inotropic agents (eg, glucagon)
Vasopressors (eg, dopamine)
Surgical option
In extreme circumstances, cricothyrotomy or catheter jet ventilation may be lifesaving when orotracheal intubation or bag/valve/mask ventilation is not effective. Cricothyrotomy is easier to perform than emergency tracheostomy.
See Treatment and Medication for more detail.