Anaphylaxis

last authored: July 2010, Caleb Zelenietz
last reviewed:

 

 

 

Introduction

Anaphylaxis is a potentially fatal, systemic allergic reaction with an acute onset. Prompt recognition and treatment greatly reduces its mortality. As a clinician, anaphylaxis provides an excellent opportunity for life saving interventions.

 

 

 

The Case of Alex R

A 12 year old boy presents to the emergency department with urticarial hives, mucous membrane swelling, stridor and diarrhea. The symptoms onset 30 minutes ago after ingestion of a peanut containing snack. The child has no previous history of allergic reactions.

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Causes and Risk Factors

There are many potential causes of anaphylaxis. Any allergen can evoke and anaphylactic response in a previously sensitized individual. Food allergens are the most common cause in children, while medication (especially penicillin) and insect stings (ie Hymenoptera) predominate in adults (Sampson et al, 1992). Fire ants, in the southern US and Central/South America, can cause anaphylaxis. Spider bites do NOT cause anaphylaxis.

Size of previous reaction does not relate to increased risk.

 

A major risk factor for anaphylaxis is a previous anaphylactic episode. Risk factors that increase the chance of death include asthma and cardiovascular disease. Other respiratory conditions such as chronic obstructive pulmonary disease also increase the risk of death.

 

Smelling food, kissing, etc does not cause anaphylaxis. The only rule is no sharing food.

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Pathophysiology

Anaphylaxis is typically an immediate hypersensitivity reaction causing the release of immunoglobulin E (IgE). Autoimmune and non immune mechanisms can also be involved, although to a much lesser extent. The pathophysiology of the anaphylactic reaction does not alter management.

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Signs and Symptoms

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Investigations

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Differential Diagnosis

The differential diagnosis of anaphylaxis includes many conditions, both benign and life threatening. The benign causes include:

• vasovagal reaction
• alcohol consumption
• anxiety
• generalized urticaria
• menopause

Potentially fatal conditions include:

• other forms of shock
• myocardial infarction
• stroke
• angioedema
• asthma exacerbation
• vocal cord dysfunction
• other causes of respiratory distress (Lieberman et al, 2009).

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Treatments

The treatment for anaphylaxis is to:

• remove the suspected antigen
• call for help
• maintain the airway
• administer supplemental oxygen
• administer intramuscular or intravenous epinephrine
• place the patient in a supine position
• volume resuscitate as needed (normal saline preferred)

 

Epinephrine is the pharmacological intervention of choice. The preferred intramuscular dosing is 0.01 mg/kg (with a maximum dose of 0.5 mg) of a 1:1000 aqueous dilution of epinephrine should be given every 5 to 15 minutes as needed. The dosage range used is typically 0.3 mg to 0.5 mg in adults as well as children. The injection should be given in the mid-anterolateral thigh, the location of the vastus lateralis muscle.

 

In patients with severe hypotension or cardiac arrest intravenous infusion of epinephrine may be necessary. There is variability in the recommended dosing. In adults the dose is 2 - 10 micrograms per minute of a 1:10000 solution. In children 0.1 - 1 microgram per kilogram per minute of a 1:10000 solution is the preferred dose. In severe cases of cardiovascular collapse boluses as large as 0.1 - 0.5 mg have been suggested in the literature.

 

Patients who are on beta-blocker therapy may be resistant to epinephrine treatment and have refractory bradycardia and hypotension. In these patients glucagon must be administered as an adjuvant to epinephrine. In adults 1 - 2 mg intravenous bolus over 5 minutes is preferred. In children 20 - 30 micrograms per kilogram with a max dose of 1 mg is recommended. This initial bolus may be repeated as needed or an infusion of 5 - 15 micrograms per minute started.

 

There are no absolute contraindications to the use of epinephrine in the treatment of anaphylaxis. Patients with cardiac disease are at increased risk with the use of epinephrine, however the risks of delaying treatment outweigh the benefits.

 

Other medications to consider include:

• antihistamines (diphenydramine, cetirizine, others) for symptomatic treatment of hives and itch
• bronchodilators
• glucocorticoids (take 1 h to work)

If patients have a rapid response, they may be discharged after 8-10 hours. If, however, their symptoms are moderate or severe, they should be admitted.

Patients should be provided with an written anaphylaxis emergency plan and an Epi-pen on discharge. If etiology is unclear, allergy testing may be warranted. An allergy bracelet may be worn to advise others of the allergy.

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Consequences and Course

Anaphylaxis can rapdily be fatal:

• iatrogenic: 5 min
• stings: 15 min
• food: 30 min

 

If promptly recognized and treated anaphylaxis has no long term sequela. A delay in the recognition and treatment can result in death. For this reason clinicians should begin treatment with epinephrine as soon as anaphylaxis is suspected. Patients who have had an anaphylactic reaction are at increased risk of having another episode if exposed to the same antigen.

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Resources and References

Sampson HA, Mendelson LM, Rosen JP. Fatal and near-fatal anaphylactic reactions to food in children and adolescents. N Engl J Med. 1992;327:380-384.

 

Sheikh A, Shehata YA, Brown SGA, Simons FER. Adrenaline (epinephrine) for the treatment of anaphylaxis with and without shock. Cochrane Database of Systematic Reviews 2008, Issue 4. Art. No.: CD006312. DOI: 10.1002/14651858.CD006312.pub2.

 

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. Sampson HA, Muñoz-Furlong A, Campbell RL, Adkinson NF Jr, Bock SA, Branum A, Brown SG, Camargo CA Jr, Cydulka R, Galli SJ, Gidudu J, Gruchalla RS, Harlor AD Jr, Hepner DL, Lewis LM, Lieberman PL, Metcalfe DD, O'Connor R, Muraro A, Rudman A, Schmitt C, Scherrer D, Simons FE, Thomas S, Wood JP, Decker WW. Ann Emerg Med. 2006 Apr;47(4):373-80.

 

Lieberman, PL. Anaphylaxis. In: Middleton's Allergy Principles & Practice, Adkinson, NF Jr, Bochner, BS, Busse, WW, et al (Eds), 7th ed, St Louis 2009. p.1027.

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