Anaphylaxis

Anaphylaxis is a systemic immediate "multisystem" hypersensitivity reaction caused by allergen binding to IgE antibody on the surface of mast cells and basophils which in turn leads to a release of "mediators" from those cells including histamine and other active agents. The term anaphylactoid reaction refers to a clinically similar event not caused by IgE antibody. The reactions are multisystem (by definition involving 2 or more target systems) with the majority of symptoms being:

• urticaria (hives) and angioedema (swelling) in 88 percent
• dyspnea and wheeze in 47percent
• upper airway edema creating stridor in 56 percent
• dizziness, syncope and hypotension in 33 percent
• nausea, vomiting, diarrhea, cramping, abdominal pain in 30 percent
• flush in 46 percent
• rhinitis in 16 percent

Children rarely have cardiac or neurologic symptoms. The threatening symptoms in children are due to airway obstruction with stridor or wheeze.

Causes:

1. food;
2. drugs;
3. insect stings
4. occasionally insect bites;
5. rare cases of exercise induced food-related.

Anaphylactoid reactions may be due to:

1. direct release of mediators by drugs,
2. idiopathic,
3. exercise,
4. physical factors such as cold;
5. Disturbances in arachidonic acid metabolism, aspirin, NSAID;
6. immune aggregates;
7. miscellaneous including radio contrast dyes.

Incidence:

In children death is usually due to respiratory obstruction and the treatment is adrenaline. Antihistamines do not adequately deal with respiratory symptoms.

Distinction between viral associated urticaria such as erythema multiforme and urticarial reaction to food allergy:

1. Reaction to a food is usually rapid, within minutes to a maximum of two hours. If the food was eaten several hours before the urticaria started, unlikely to be the cause. Food is usually easy to identify.
2. Reactions to foods usually occur in atopic individuals known to be allergic to the food. Unusual to suddenly develop sensitivity to common food although peanut, nuts, fish or shellfish are possible.
3. The hives due to food allergy usually clear within hours to a maximum of 24 hours. If the hives clear and then recur over several days, they are unlikely to be due to a food sensitivity.

Factors affecting the incidence and/or severity of anaphylaxis and anaphylactoid reactions:

Measures to reduce the incidence of anaphylaxis and anaphylactic deaths:

1. Obtain a thorough history of drug allergy.
2. Avoid drugs with immunologic or biochemical cross reactivity with any agent to which the patient is sensitive.
3. Administer drugs orally rather than parenterally when possible.
4. Check all drugs for proper labelling.
5. Keep patients in office 20- 30 minutes after injections.

Measures for patients at risk:

1. Have patient wear and carry warning identification.
2. Teach self injection of epinephrine and caution patients to keep epinephrine kit with them.
3. Discontinue Beta-adrenergic blocking agents, angiotensin-converting enzyme inhibitors, monoamine oxidase inhibitors and certain tricyclic antidepressants when possible.
4. Use preventive techniques when patients are acquired to undergo a procedure or take an agent that places them at risk. Such techniques include pre-treatment, provocative challenge and desensitization.

Therapy of anaphylaxis

• Assessment
• Check airway and secure if needed.
• Rapid assessment of level of consciousness, vital signs.

Treatment

• epinephrine
• supine position, legs elevated
• Oxygen
• Tourniquet proximal to injection site

Dependent on evaluation

• Start peripheral intravenous fluids
• H1 and H2 antagonists
• vasopressors
• corticosteroids transfer to hospital