Anaphylaxis

Anaphylaxis: Excerpt from The 5-Minute Pediatric Consult

Mathew Fogg, MD

Anaphylaxis - BASICS

Anaphylaxis - description

• Anaphylaxis is an explosive antigen-specific IgE-mediated response resulting in the release of potent biologically active mediators from mast cells and other inflammatory cells. However, non–IgE-mediated direct mast cell degranulation can result in a similar response.
• In fatal anaphylaxis, death may occur from airway obstruction and/or shock. When treating a patient with anaphylaxis, respiratory symptoms and hypotension should be taken very seriously.
• System(s) affected: Heart; lungs; skin; GI tract; upper respiratory tract:
  • Any or all of these target organs may be affected.

Anaphylaxis - incidence

• 0.4 cases per million individuals annually
• Increased hospital incidence of 0.6 cases per 1,000 patients
• 400–800 deaths annually in the US

Anaphylaxis - risk factors

Anaphylaxis - genetics

Atopy can be familial, and atopics are at more risk for anaphylaxis.

Anaphylaxis - pathophysiology

• Inducing agents stimulate mast cells to release inflammatory mediators via either an antigen-specific or an antigen-nonspecific manner. These mediators may then act either locally or systemically. Mediator release results are in the table Pathophysiology of Anaphylaxis.

Pathophysiology of Anaphylaxis

Anaphylaxis - etiology

• IgE mediated:
  • Antibiotics (penicillin and others)
  • Foreign protein agents (insect venom, latex antigens, fire ant venom, blood products, and others)
  • Therapeutic agents (allergen extracts, vaccines, and others)
  • Foods (peanuts, nuts, shellfish, and others)
• Non–IgE-mediated “anaphylactoid” reactions (activates histamine release from mast cells without protein binding to IgE):
  • Radiocontrast media
  • Opiates
  • Dextran
  • Vancomycin
  • Polymyxin B
  • Quaternary ammonium muscle relaxants (i.e., methyl scopolamine bromide, homatropine methylbromide, methantheline bromide, and Pro Banthine bromide)

Anaphylaxis - DIAGNOSIS

Decide quickly whether the symptoms the patient is experiencing are consistent with anaphylaxis.

• Phase 1: Initiate therapy for anaphylaxis. This generally includes epinephrine 1:1,000 administered SQ, H1 antihistamines, H2 antihistamines, and rapid volume expansion if necessary.
• Phase 2: Attempt to identify the agent that induced the anaphylactic reaction.

Anaphylaxis - signs & symptoms

• Consistent with anaphylaxis:
  • Profuse rhinorrhea
  • Urticaria
  • Wheezing
  • Throat tightness
  • Tachycardia
  • Hypotension
• Any combination of the following symptoms:
  • Cutaneous: Urticaria/angioedema
  • Respiratory: Bronchospasm/laryngeal edema
  • Cardiovascular: Hypotension, arrhythmias, myocardial ischemia
  • GI: Nausea, vomiting, pain, diarrhea
• Patients commonly describe a sense of impending doom:
  • May be the 1st sign of an impending anaphylactic reaction

Anaphylaxis - history

• Reaction time to offending allergen:
  • Anaphylactic reactions usually begin within seconds to minutes after contact with offending antigen. This can help the physician identify the antigen responsible.
• History of anaphylaxis:
  • If so, the patient likely knows the allergen responsible.
  • Efforts should be directed toward allergen avoidance.
• Does the patient have autoinjectable epinephrine?
  • Most deaths from anaphylaxis are associated with delayed administration of epinephrine. Most patients with a history of anaphylaxis should have autoinjectable epinephrine.
• Insect sting:
  • Insect or fire ant venom allergy can result in anaphylaxis. It is important to identify the insect if possible (remember that honey bees leave their stinger at the sting site). Immunotherapy is indicated and effective for anaphylaxis in venom-allergic patients.
• Food allergies:
  • Any food can cause anaphylaxis.
  • Dramatic increase in childhood food allergy in past 15 years
  • Cow’s milk, egg, soy, peanut, wheat, tree nuts, and shellfish are the most common.
• Medications:
  • Beta-blockers make treatment of anaphylaxis more difficult.
  • Alternative medications (glucagon) should be sought in patients with a history of anaphylaxis.

Anaphylaxis - physical exam

• Angioedema:
  • May be noted anywhere during a systemic allergic reaction
  • Much more significant if it involves the lips, tongue, mouth, or larynx (can result in airway obstruction)
• Urticaria:
  • Cutaneous manifestation of a systemic allergic reaction
• Profuse rhinorrhea:
  • May signal upper respiratory tract involvement in a systemic allergic reaction
• Wheezing:
  • Signals lower respiratory tract involvement in a systemic allergic reaction
• Tachycardia and hypotension:
  • Signals cardiovascular involvement in a systemic allergic reaction
  • Tachycardia usually represents a compensatory mechanism in order to maintain the patient’s BP from fluid extravasation.

Anaphylaxis - tests

• Treatment of anaphylaxis should never be withheld while awaiting laboratory confirmation.
• Electrocardiogram:
  • Anaphylaxis may show rhythm abnormalities, ischemic changes, or infarction on an ECG.

Anaphylaxis - lab

• Plasma histamine:
  • Plasma histamine is elevated during anaphylaxis, but is difficult to measure because of its extremely short half-life.
  • Useful only in research setting
• Serum tryptase level:
  • Preferred test if available
  • Serum tryptase is elevated during anaphylaxis.
  • β-Tryptase is elevated for several hours after the onset of anaphylaxis.
• CBC:
  • Hemoconcentration (as judged by an increased hematocrit or hemoglobin) is common as fluid exits the intravascular space during an anaphylactic reaction.
• Cardiac enzymes:
  • Myocardial ischemia during anaphylaxis may result in a myocardial infarction, and elevated cardiac enzymes.

Note: Skin tests are significantly better than RAST tests for diagnosis of venom and food allergy.

Anaphylaxis - imaging

Chest radiograph:

• Bronchospasm associated with anaphylaxis may result in air trapping and hyperinflated lung fields on chest film.

Anaphylaxis - differencial diagnosis

• Genetic/metabolic:
  • Hereditary angioedema
  • Systemic mastocytosis
  • Pheochromocytoma
  • Carcinoid
• Allergic/immunologic:
  • Idiopathic
  • Foods
  • Insect stings
  • Drugs
  • Latex
• Nonimmunologic mast cell degranulation
• Exercise-induced (may occur only after ingestion of a specific food)
• Serum sickness
• Miscellaneous:
  • Vasovagal collapse

Anaphylaxis - TREATMENT

Anaphylaxis - general measures

• Maintain airway.
• A tourniquet may be applied (above the injection or sting site) to decrease venous blood return from the site of antigen entry.
• Supplement with oxygen, place in recumbent position, and elevate legs. Patients have increased oxygen consumption during anaphylaxis.
• Maintain BP with volume expanders or pressors. Hypotension is a serious manifestation of anaphylaxis.

Anaphylaxis - medication

• SQ epinephrine 1:1,000 concentration:
  • Infants to adults: 0.01 mg/kg, maximum of 0.5 mg of 1:1,000 solution, repeated q3–5min
  • Early administration of epinephrine is essential.
• Diphenhydramine IV:
  • Children: 5 mg/kg in 3 or 4 divided doses; maximum 300 mg/d
  • H1 blockade is very important in the control of an anaphylactic reaction.
• Ranitidine IV:
  • 2 to 4 mg/kg in 2 divided doses
  • H1 blockade may be helpful in refractory anaphylaxis.
• Hydrocortisone or another systemic steroid should be started:
  • 1 to 5 mg/kg/d in 2–4 divided doses
  • Most helpful to prevent a late-phase reaction
  • Of little help during an immediate anaphylactic reaction

Anaphylaxis - FOLLOW UP

Patients not admitted to the hospital should be observed for several hours, because late “biphasic” reactions can begin as late as 24 hours after the initial anaphylaxis.

• These patients are at risk for a 2nd episode of anaphylaxis.
• Patients with anaphylaxis should be treated with steroids during the acute treatment, and they should be given a short course of oral corticosteroids to finish at home.
• Must be discharged with autoinjectable epinephrine (this will provide temporary relief so the patient will have time to seek medical assistance).
• Patients must know to seek immediate medical help if symptoms return.

Anaphylaxis - disposition

• All patients who have had anaphylaxis should be discharged with epinephrine in an autoinjecting apparatus.

note: All patients with anaphylaxis would benefit from consultation with an allergist.

• Factors that may help alert you to make a referral include the following:
  • History of idiopathic anaphylaxis:
    • An allergist can help by testing likely triggers.
  • History of anaphylaxis to insect stings or fire ants:
    • Anaphylaxis to insects or fire ants is an indication for venom desensitization.
  • History of food anaphylaxis:
    • The allergist can assist with an appropriate avoidance diet and support resources.
  • History of latex anaphylaxis:
    • The allergist can assist with strict latex-avoidance precautions, and latex testing if the history is unclear.

Anaphylaxis - prognosis

Excellent, provided the trigger can be avoided.

Anaphylaxis - complications

• Pulmonary edema, pulmonary hemorrhage, and pneumothorax
• Laryngeal edema with or without airway obstruction
• Myocardial ischemia and infarction
• Death may result from asphyxiation from upper airway obstruction or profound shock or both.

Anaphylaxis - patient monitoring

All patients should follow up with an allergist.

Anaphylaxis - bibliography

1. Cahaly RJ, Slater JE. Latex hypersensitivity in children. Curr Opin Pediatr. 1995;7:671–675.
2. Greenberger PA, Rotskoff BD, Lifschultz B. Fatal anaphylaxis: Postmortem findings and associated comorbid diseases. Ann Allergy Asthma Immunol. 2007;98(3):252–257.
3. Lane RD, Bolte RG. Pediatric anaphylaxis. Pediatr Emerg Care. 2007;23(1):49–56.
4. Self-injectable epinephrine for first-aid management of anaphylaxis. Pediatrics. 2007;119(3):638–646.

Anaphylaxis - CODES

Anaphylaxis - icd9

• 995.0 Anaphylactic shock
• 995.60 Food
• 995.61 Peanuts
• 995.62 Crustaceans
• 995.63 Fruits
• 995.63 Vegetables
• 995.64 Nuts (tree)
• 995.64 Seeds
• 995.64 Tree nuts
• 995.65 Fish
• 995.66 Additives
• 995.67 Milk products
• 995.68 Eggs
• 995.69 Specified NEC

Anaphylaxis - FAQ

• Q: Can a patient have an anaphylactic reaction on 1st exposure to an allergen?
• A: A patient must have had a previous exposure to the offending allergen for sensitization to occur. Therefore, anaphylactic reactions should not occur on 1st exposure. Remember: Infants can be sensitized through breast milk; therefore, a baby may react upon “1st” exposure to a food.
• Q: When should the autoinjectable epinephrine be used?
• A: It is intended for severe allergic reactions as manifested by any of the following: bronchospasm, angioedema of the lips or tongue, or hypotension (dizziness). The patient must seek immediate medical help if the autoinjectable epinephrine is required.
• Q: Do patients outgrow this condition?
• A: No. Subsequent reactions tend to have a more rapid onset, and tend to be more severe. Children often outgrow food-induced anaphylaxis.
• Q: Who should be referred to an allergist?
• A: All patients who have experienced anaphylaxis would benefit from consultation with an allergist. Patients with anaphylaxis from insect stings, fire ants, and certain antibiotics can be desensitized. In addition, the allergist can be helpful in identifying obscure triggers of anaphylaxis.

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

More About Anaphylaxis

• Back to disease: Anaphylaxis: Introduction
• Next Book Extract About Anaphylaxis: Surveys relating to Anaphylaxis
• More Book Extracts: All Online Books for Anaphylaxis

More Medical Textbooks Online about Anaphylaxis

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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

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