Anaphylaxis

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Chapter 30 Anaphylaxis

Linda D. Arnold, MD

1 What is anaphylaxis?

Anaphylaxis is an acute, systemic allergic reaction with varied mechanisms and clinical presentations. Signs and symptoms develop rapidly as mast cells and basophils release potent biologically active mediators. The acute constellation of symptoms results from the effect of these mediators on multiple target organs, including the skin, the respiratory and gastrointestinal tracts, and the cardiovascular system. Severity can vary from mild to life-threatening or fatal; more severe reactions are characterized by respiratory insufficiency and hemodynamic compromise. “Classic” anaphylaxis refers to IgE-mediated hypersensitivity responses, though other immunopathogenic mechanisms exist.

2 How common is anaphylaxis?

Although frequency and causes vary with the population studied, most estimates of prevalence fall just below 1%. In the United States, food allergies are the most common cause of anaphylaxis, accounting for 30,000 emergency department (ED) visits, 2000 hospitalizations, and 150–200 deaths each year. Among children under age 4 years, 6–8% have documented food allergies, with the rates dropping to 2% after age 10. One percent of people in the United States are allergic to peanuts, tree nuts, or both. Hypersensitivity reactions account for one third of all adverse drug reactions. Serious systemic reactions to hymenoptera stings occur in 0.4–0.8% children and 3% of adults, resulting in approximately 50 deaths each year.

Sampson HA: Anaphylaxis and emergency treatment. Pediatrics 111:1601–1608, 2003.

Ellis AK, Day JH: Clinical reactivity to insect stings. Curr Opin Allergy Clin Immunol 5:349–354, 2005.

3 How dangerous is anaphylaxis?

Anaphylaxis often occurs outside of the hospital setting, with case fatality rates of 0.7%. The median time to respiratory or cardiac arrest in fatal cases of anaphylaxis is 5 minutes for reactions to medications or contrast material, 15 minutes for reactions to insect venom, and 30 minutes for reactions to food. Fatal reactions are frequently the first reactions for most sting, medication, and contrast deaths. Most ingestions are inadvertent, and reactions to aerosolized fish and shellfish in restaurants have been reported. The majority of allergic reactions for children take place in school or daycare. In the rare instances when written management plans exist, they are implemented only 75% of the time.

Sicherer SH, Furlong TJ, DeSimone J, et al: The US peanut and tree nut allergy registry: Characteristics of reactions in schools and day care. J Pediatr 138:560–565, 2001.

4 What are common causes of anaphylaxis?

Food allergies are the leading cause of anaphylaxis for children presenting to EDs in the United States, accounting for a third to a half of such visits. Allergies to peanuts, tree nuts, shellfish, cow’s milk, eggs, soy, and wheat are most common. Peanuts and tree nuts alone are responsible for 90% of all food anaphylactic events, with commercial catering implicated in the majority of nut-related reactions.

Among antibiotics, cephalosporins, sulfonamides, and penicillins are most frequently implicated. Insect stings and allergen immunotherapy are also important causes of anaphylaxis. Anaphylaxis to immunizations is rare.

5 What are some of the causes of anaphylaxis related to medical treatment?

image Neuromuscular blockers (succinylcholine, vecuronium, atracurium) account for 60% of episodes of anaphylaxis related to medical treatment.

image Latex, antibiotics, induction agents (barbiturates, etomidate, propofol) and narcotics (fentanyl, meperidine, morphine) are also important causes.

image Colloids, opioids, radiocontrast media, and blood products are implicated less than 10% of the time.

The incidence of latex allergy has leveled off, probably because of increased awareness and the use of latex-free and low-powder gloves. Reactions are more common in atopic individuals, health care workers, and patients with a history of genitourinary surgeries or long-term bladder catheterizations.

Lieberman P: Anaphylactic reactions during surgical and medical procedures. J Allergy Clin Immunol 110:S64–S69, 2002.

6 Is there a way to predict who is at risk for more severe anaphylactic reactions?

Most deaths from anaphylaxis due to food occur in adolescents and young adults. Patients with poorly controlled asthma and those with a history of previous anaphylaxis are at greater risk. Reactions to peanuts, tree nuts, fish, and shellfish are the most severe, with peanuts and tree nuts responsible for 94% of deaths. The severity of previous episodes does not predict the severity of future reactions, as antigen doses may vary. Large local reactions to stings are not predictive of anaphylaxis to insect venom. Many fatal or near-fatal reactions to foods and insect venom occur in children who have not required previous urgent medical intervention.

Bock SA, Munoz-Furlong A, Sampson HA: Fatalities due to anaphylactic reactions to food. J Allergy Clin Immunol 108:861–866, 2001.

KEY POINTS: RISK FACTORS FOR SEVERE ANAPHYLAXIS

1 Adolescent or young adult

2 History of previous severe reaction

3 Peanuts, tree nuts, fish, or shellfish as inciting agent

4 Asthma, especially if poorly controlled

5 Taking β-blockers

7 What are anaphylactoid reactions? How do they differ from anaphylaxis?

Anaphylactoid reactions result from non–IgE-mediated degranulation of mast cells or basophils. They are clinically indistinguishable from anaphylaxis, and the treatment is identical. Examples include reactions to nonsteroidal anti-inflammatory drugs (NSAIDs), radiocontrast media, blood products, and exercise.

8 What are the clinical manifestations of anaphylaxis?

Anaphylaxis is characterized by the abrupt onset of symptoms minutes to hours after an ingestion or exposure (Table 30-1). The timing, sequence, and severity of symptoms vary. The shorter the interval between the exposure and the symptoms, the more likely the reaction is to be severe.

image The oral cavity and throat are affected first, with a tingling or pruritic sensation and edema of the lips or mucosa. Laryngeal and epiglottic edema may develop.

image Gastrointestinal signs follow and include nausea, vomiting, and colicky pain.

image Skin symptoms and signs, which may be absent in up to 30% of severe reactions, include flushing, pruritus, and urticaria. The urticaria may be localized or diffuse.

image Respiratory symptoms, such as stridor or wheezing, may develop in more severe reactions.

image Dizziness and altered mental status are associated with hypotension, resulting from effects on the cardiovascular system.

Table 30-1 Clinical Signs and Symptoms of Anaphylaxis

Oropharyngeal: metallic taste, pruritus, and/or edema of lips, tongue, palate or uvula
Otorhinolaryngologic: congestion, rhinorrhea, pruritus, sneezing, throat tightness, hoarseness, dysphagia
Dermatologic: erythema, pruritus, urticaria, angioedema, morbilliform rash
Gastrointestinal: nausea, colicky abdominal pain, vomiting, diarrhea
Respiratory: cough, shortness of breath, dyspnea, chest tightness, stridor, wheezing
Cardiovascular: faintness, tachycardia, syncope, chest pain, hypotension
Neurologic: headache, mental status changes
General: anxiety, sense of impending doom

9 What is the differential diagnosis of anaphylaxis?

Anaphylaxis must be ruled out first since failure to identify it can have serious consequences for the patient. The differential diagnosis includes:

image Scombroid poisoning:

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