Anaphylaxis is an acute, potentially fatal, multiorgan system reaction caused by the release of chemical mediators from mast cells and basophils.[1, 2] 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.[3] 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 [2] .
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.
Background
Portier and Richet first coined the term anaphylaxis in 1902 when a second vaccinating dose of sea anemone toxin caused a dog’s death. The term is derived from the Greek words ana - (“up, back, again”) and phylaxis (“guarding, protection, immunity”).
Anaphylaxis is an acute, potentially fatal, multiorgan system reaction caused by the release of chemical mediators from mast cells and basophils.[1, 2] The classic form involves prior sensitization to an allergen with later re-exposure, producing symptoms via an immunologic mechanism. (See Pathophysiology and Etiology.)
The most common organ systems involved include the cutaneous, respiratory, cardiovascular, and gastrointestinal systems. The full-blown syndrome includes urticaria (hives) and/or angioedema with hypotension and bronchospasm. (See Clinical Presentation.)
Anaphylaxis has no universally accepted clinical definition. It is a clinical diagnosis based on typical systemic manifestations, often with a history of acute exposure to a causative agent. (See Diagnosis.)
Because anaphylaxis is primarily a clinical diagnosis, 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, some limited laboratory studies are indicated. Skin testing and in vitro IgE tests may be helpful. (See Workup.)
Anaphylaxis is a medical emergency that requires immediate recognition and intervention. Disposition of patients with anaphylaxis depends on the severity of the initial reaction and the response to treatment.
Go to Pediatric Anaphylaxis and Pediatric Exercise-Induced Anaphylaxis for complete information on these topics.
Pathophysiology
The traditional nomenclature for anaphylaxis reserves the term anaphylactic for reactions mediated by immunoglobulin E (IgE) and the term anaphylactoid for non-IgE-mediated reactions, which can be clinically indistinguishable. The World Allergy Organization has recommended replacing this terminology with immunologic (IgE-mediated and non–IgE-mediated [eg, IgG and immune complex complement–mediated]) and nonimmunologic anaphylaxis (events resulting in sudden mast cell and basophil degranulation in the absence of immunoglobulins).[4]
The physiologic responses to the release of anaphylaxis mediators include smooth muscle spasm in the respiratory and gastrointestinal (GI) tracts, vasodilation, increased vascular permeability, and stimulation of sensory nerve endings. Increased mucous secretion and increased bronchial smooth muscle tone, as well as airway edema, contribute to the respiratory symptoms observed in anaphylaxis.
Cardiovascular effects result from decreased vascular tone and capillary leakage. Hypotension, cardiac arrhythmias, syncope, and shock can result from intravascular volume loss, vasodilation, and myocardial dysfunction. Increased vascular permeability can produce a shift of 35% of vascular volume to the extravascular space within 10 minutes.
These physiologic events lead to some or all of the classic symptoms of anaphylaxis: flushing; urticaria/angioedema; pruritus; bronchospasm; laryngeal edema; abdominal cramping with nausea, vomiting, and diarrhea; and feeling of impending doom. Concomitant signs and symptoms can include rhinorrhea, dysphonia, metallic taste, uterine cramps, light-headedness, and headache.
Additional mediators activate other pathways of inflammation: the neutral proteases, tryptase and chymase; proteoglycans such as heparin and chondroitin sulfate; and chemokines and cytokines. These mediators can activate the kallikrein-kinin contact system, the complement cascade, and coagulation pathways. The development and severity of anaphylaxis also depend on the responsiveness of cells targeted by these mediators.
Interleukin (IL)–4 and IL-13 are cytokines important in the initial generation of antibody and inflammatory cell responses to anaphylaxis. No comparable studies have been conducted in humans, but anaphylactic effects in mice depend on IL-4Rα-dependent IL-4/IL-13 activation of the transcription factor, STAT-6 (signal transducer and activator of transcription 6).[5] Eosinophils may be inflammatory (release cytotoxic granule-associated proteins, for example) or anti-inflammatory (metabolize vasoactive mediators, for example).
Additional mediators include newly generated lipid-derived mediators such as prostaglandin D2, leukotriene B4, and platelet-activating factor (PAF), as well as the cysteinyl leukotrienes, such as LTC4, LTD4, and LTE4. These mediators further contribute to the proinflammatory cascade seen in anaphylaxis.
Under rigid experimental conditions, histamine infusion alone is sufficient