Anaphylaxis

Michael E. Winters

Anaphylaxis is widely recognized by emergency care providers as an acute, severe, potentially life-threatening allergic reaction.

Anaphylaxis is a potentially life-threatening allergic reaction.
Circulatory collapse and/or respiratory failure are the major concerns.
Treatment involves securing an adequate airway, ventilation and oxygenation, aggressive fluid resuscitation, and judicious use of epinephrine.
Additional medications may include antihistamines, corticosteroids, and glucagon.
Other modalities may involve intravenous epinephrine, mechanical ventilation, vasopressor medications, inotropic support, transcutaneous pacing, or intra-aortic balloon pump counterpulsation.

Introduction

Since its original description in 1902 by Richet and Portier,¹ much has been published regarding the epidemiology, pathophysiology, clinical presentation, diagnosis, and treatment of anaphylaxis. Although significant questions remain, it is imperative that emergency care providers be able to promptly recognize and appropriately treat patients with anaphylaxis. Any delay in recognition or initiation of therapy may contribute to unnecessary increases in patient morbidity and mortality. This chapter serves to educate and update the emergency care provider about the assessment and management of patients with anaphylaxis.

While upper airway obstruction and/or bronchospasm may be prominent features of anaphylaxis in many patients, emphasis here is placed on the management of patients with impending cardiovascular collapse and circulatory arrest due to anaphylaxis.

Overview

Definition and Diagnostic Criteria

Anaphylaxis may be defined as “a serious allergic reaction that is rapid in onset and may cause death.

Currently, there is no universally accepted definition of anaphylaxis.²^,³^,⁴^,⁵^,⁶ As a result, the literature is replete with varying opinions and interpretations regarding many aspects of the assessment and management of patients with anaphylaxis. In an effort to develop a universal definition, the National Institute of Allergy and Infectious Disease along with the Food Allergy and Anaphylaxis Network gathered experts and representatives from numerous professional, governmental, and lay organizations. In 2006, recommendations from the Second Symposium on the Definition and Management of Anaphylaxis were published. As a part of their recommendations, the consensus panel proposed that anaphylaxis be defined as “a serious allergic reaction that is rapid in onset and may cause death.”³

In addition to the lack of a universal definition, there is also a lack of formal diagnostic criteria that reliably and accurately identify patients with anaphylaxis. To this end, participants at the Second Symposium on the Definition and Management of Anaphylaxis also put forth a set of diagnostic criteria designed to provide an easy and rapid means of identifying patients with anaphylaxis. Participants at this symposium felt that these criteria are “likely to capture 95% of cases.”³

The proposed diagnostic criteria for anaphylaxis are listed in Table 34-1. Although these diagnostic criteria require prospective validation, they provide an important framework for the emergency care provider to successfully identify patients with this potentially deadly disorder.

Epidemiology

Each year, anaphylaxis accounts for nearly 1% of all U.S. emergency department (ED) visits and is estimated to cause approximately 1,500 fatal reactions.

A recent review of studies from North America, Europe, and Australia reported the lifetime prevalence of anaphylaxis to be approximately 0.05% to
2.0%.⁷ Despite an often frightening clinical presentation, death from anaphylaxis is uncommon. The mortality rate reported by most studies on anaphylaxis is approximately 1%.⁸^,⁹^,¹⁰^,¹¹^,¹² In the United States, it is estimated that 1.2% to 15% of the population is at risk for anaphylaxis.¹⁰ Each year, anaphylaxis accounts for nearly 1% of all U.S. ED visits¹³ and is estimated to cause approximately 1,500 fatal reactions.¹⁰

Table 34-1 • Diagnostic Criteria for Anaphylaxis

Anaphylaxis is highly likely when any ONE of the following three criteria are fulfilled:

Acute onset of an illness (minutes to hours) with involvement of the skin, mucosal tissue, or both AND AT LEAST ONE OF THE FOLLOWING:
1. Respiratory compromise
2. Reduced blood pressure or associated symptoms of end-organ dysfunction
TWO or more of the following that occur rapidly after exposure to a likely allergen for that patient (minutes to hours)
1. Skin and/or mucosal tissue involvement
2. Respiratory compromise
3. Reduced blood pressure or associated symptoms of end-organ dysfunction
4. Persistent gastrointestinal symptoms
Reduced blood pressure after exposure to a known allergen for that patient (minutes to hours)
1. Adults: systolic blood pressure <90 mm Hg or a decrease of >30% from the baseline blood pressure
2. Infants and children: age-specific low systolic blood pressure or >30% decrease from the baseline blood pressure

Source: Adapted from Sampson HA et al. Second symposium on the definition and management of anaphylaxis: summary report. Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium. J Allergy Clin Immunol 2006;117(2):391–397, with permission.

Unfortunately, anaphylaxis is not a reportable disease. As a result, current morbidity and mortality statistics are likely an underestimate of the true impact of the disease. In addition, incidence and prevalence rates from current studies are hampered by varying patient populations, varying methods of patient identification and classification, and small sample sizes.¹⁴ Although current studies provide important epidemiologic information, it should be noted that the exact incidence of anaphylaxis remains unknown.¹⁵^,¹⁶

Etiologies

Any agent or condition that results in the release of mediators from mast cells and/or basophils can cause anaphylaxis.

Foods, medications, insect stings, and immunotherapy injections account for the majority of identifiable causes.⁹^,¹⁷^,¹⁸^,¹⁹^,²⁰ In the United States, food is the leading identifiable cause of anaphylaxis.²¹ In fact, as many as 2% of the U.S. population are reported to have a food allergy.⁷^,²² In children, peanuts and tree nuts are the most common foods implicated in cases of anaphylaxis.⁷^,²³ For adults, shellfish, peanuts, and tree nuts account for the most severe reactions.⁷^,²¹ Additional foods commonly implicated in cases of food anaphylaxis include fish, eggs, milk, soy, and wheat.⁷^,²¹ Antibiotics (especially penicillin) and nonsteroidal anti-inflammatory drugs account for the majority of cases of medication-induced anaphylaxis.⁵ Anaphylaxis caused by insects is due to stings from members of the order Hymenoptera. Insects in this order include wasps, yellow jackets, hornets, honeybees, and fire ants. In the United States, yellow jackets account for the majority of cases of anaphylaxis due to insects.²⁰ Additional identifiable etiologies of anaphylaxis are listed in Table 34-2. In as many as one-third of cases, the etiology is undetermined.¹⁷ Patients with an undetermined etiology are diagnosed as having idiopathic anaphylaxis.

Clinical Manifestations

Anaphylaxis is a multisystem disorder that can have a myriad of clinical manifestations. Importantly, the symptoms of anaphylaxis occur along a continuum and are dependent upon the type, route, and quantity of antigen exposure. Symptom onset can range anywhere from several minutes to hours after exposure to an antigen.²⁴ In general, the more rapid the onset of symptoms, the more likely the reaction is to be life-threatening.²⁵^,²⁶ Cutaneous symptoms such as urticaria and angioedema are the most common manifestation of anaphylaxis, occurring in over 90% of patients.⁵^,¹⁶^,¹⁷^,¹⁸^,²⁷

Respiratory symptoms occur in 40% to 70%,⁵^,²⁷ whereas cardiovascular manifestations are seen in 30% to 35%⁵ of patients.

Up to 40% of patients present with gastrointestinal signs and symptoms.⁵^,²⁷ Neurologic manifestations, such as headache and seizures, occur in <10% of patients with anaphylaxis.⁵
Table 34-3 lists the clinical manifestations of anaphylaxis according to organ system. As a rule of thumb, children more often have respiratory involvement, whereas adults more commonly have cardiovascular and cutaneous manifestations.²⁸^,²⁹

Table 34-2• Identifiable Etiologies of Anaphylaxis

Foods
–Peanuts
–Tree nuts
–Shellfish
–Fish
–Milk
–Eggs
–Wheat
–Soy
Medications
–Antibiotics
–Nonsteroidal anti-inflammatory drugs
–Opioids
–Muscle relaxants
–Protamine
–Insulin
–Hormones
Insect venom
Immunotherapy injections
Latex
Physical factors
–Exercise
–Temperature
Radiocontrast media
Transfusion of blood products
Intravenous immunoglobulin
Animal or human proteins
Colorants
Enzymes
Polysaccharides
Psychogenic (factitious)

Sources: Adapted from Stevenson DD. Anaphylactic and anaphylactoid reactions to aspirin and other nonsteroidal antiiflammatory drugs. Immunol Allergy Clin North Am 2001;21:745–768. and Kemp SF, Lockey RF. Anaphylaxis: a review of causes and mechanisms. J Allergy Clin Immunol 2002;110(3):341–348, with permission.

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