Anaphylaxis is a severe, potentially life-threatening syndrome due to a hypersensitivity reaction involving two or more organ systems. It often occurs within minutes after exposure to an offending allergen; however, it can present up to many hours after. Manifestations can include a pruritic rash, urticaria, or angioedema; nausea, vomiting, or abdominal pain; respiratory compromise associated with airway edema and bronchospasm; and cardiovascular compromise that can result in distributive shock.

The estimated rate of anaphylaxis in the pediatric population in the United States ranges from 0.18% to 0.54%; however, this likely is an underestimate of the true severity of the problem due to underdiagnosis, underreporting, and miscoding.^1,2 Food allergy is the most common cause of anaphylaxis (up to 85% of pediatric cases), and is increasing in frequency with over 170 known food allergens.^3–5 Anaphylaxis from food allergy leads to approximately 150 fatalities in the United States each year, and the more rapid the onset of symptoms, the more likely the reaction will be life-threatening.^6,7 In up to 50% of all anaphylaxis cases, adults and children, no precipitating cause is initially identified; therefore the emergency physician must have a high level of suspicion for the disorder to recognize the symptoms and initiate proper treatment.⁸ Asthma and atopy are known to have a strong association with anaphylaxis, which may aid in a more rapid diagnosis.^5,9,10

Anaphylaxis is a syndrome that can be caused by multiple immunologic pathways.³ Anaphylactic reactions are primarily mediated by IgE. An initial exposure to an allergen results in the development of a specific IgE antibody to the antigen which resides on the cell membrane of basophils and mast cells. When a subsequent exposure to the allergen occurs, the allergen binds to the IgE on the basophil and mast cells, and stimulates the release of multiple mediators, including histamine, tryptase, leukotrienes, and prostaglandins.³ These mediators lead to increased production and release of respiratory secretions, increased bronchial smooth muscle tone, decreased vascular smooth muscle tone, and increased capillary permeability.

Non-IgE–mediated pathways for anaphylaxis include direct release of immunomodulators from both mast cells and basophils. Inciting substances for the non-IgE–mediated pathway include latex and antibiotics and do not need prior exposure to trigger the response.³

Anaphylactoid reactions can also result in anaphylaxis; however, this is due to direct activation of the complement pathway or the bradykinin cascade.³ Intravenous (IV) contrast allergy is an example of an anaphylactoid reaction.

FOOD

Food is the number one cause of anaphylaxis. More than 90% of food-related anaphylaxis is caused by exposure to nuts and shellfish.^11,12 In infants, cow’s milk and eggs are the most common causes of anaphylaxis.¹³ Adolescent and young adults are more likely to suffer from fatal food-related anaphylaxis, thought to be related to risk-taking behaviors.¹⁴

Once the food that caused the anaphylaxis is identified, thorough education of the parents and child is necessary to avoid re-exposure. Although there has been an increase in hospital admissions due to food-related anaphylaxis, fatalities have remained stable.^5,9

ENVENOMATION

Hymenoptera venom, from bee and wasp stings, is a common cause of a localized allergic reaction and can also cause anaphylaxis. According to the CDC there are 90 to 100 deaths per year in the United States from insect stings.¹⁵

DRUG

Drug-related allergies are quite common. The most common medications causing anaphylaxis are NSAIDs and β-lactam antibiotics. IV administration of medication has a higher incidence of anaphylaxis and a more rapid onset of the anaphylactic symptoms. Rates of death due to drug allergies have increased 300% over the last decade.⁹

Latex allergy is becoming an increasingly common cause of allergic reaction in children. It can occur following exposure to gloves, tourniquets, or a urinary catheter. Chiu found that in pediatric patients, risk factors for developing a latex allergy included spina bifida, surgery in the first year of life, multiple surgeries, urogenital malformations, and atopy.⁶ Atopy is the genetic predisposition to produce IgE to common proteins, and can lead to hay fever; allergies to dust, grass, and pollen; and asthma.

OTHER

Parents often worry about the risk of childhood immunizations causing an allergic reaction or anaphylaxis: Lajeunesse recently published that the risk of anaphylaxis after vaccination continues to be rare, without any fatalities.¹⁶

Cold-induced urticaria is often associated with aquatic activities, and the only predictor for cold-induced anaphylaxis is previous systemic symptoms after cold exposure.¹⁷ The mean age for cold-induced urticaria is 7 years old, and most have a strong family history of atopy.¹⁸

The organ systems involved in anaphylaxis usually include the dermatologic, gastrointestinal, respiratory, and cardiovascular systems, though rarely the central nervous system may also be involved.¹⁹ In general, allergic reactions are categorized as mild, moderate, and severe, anaphylaxis being the most severe. Anaphylaxis itself has varying degrees of presentation, from mild to severe.²⁰ Allergic reactions may evolve into anaphylaxis quickly, so early recognition is key.

Mild anaphylaxis symptoms include cutaneous and mucosal manifestations (redness, flushing, urticaria, and itching), lip swelling, congestion, nausea, mild abdominal pain, mild wheezing without respiratory distress, or tachycardia. Moderate symptoms are typically defined by crampy abdominal pain, recurrent emesis, and more significant respiratory symptoms including barky cough, stridor, hoarseness of voice, and difficulty swallowing. Loss of bowel control, severe respiratory distress including saturation less than 92%, and cardiovascular manifestations that range from mild hypotension and tachycardia to fulminant shock are classified as severe anaphylaxis.