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Anaphylaxis is a systemic immediate hypersensitivity reaction to an allergen, which may be ingested, inhaled or injected (including bites/stings as well as medical treatment). Symptoms typically occur within 30 minutes of exposure (usually within 5 minutes). Onset can be fulminant and life threatening. Classic anaphylaxis results from IgE mediated mast cell degranulation releasing histamine and other mediators. Anaphylaxis has also been described following exercise or sudden cold exposure, and some cases are idiopathic. Non IgE mediated reactions (previously referred to as "anaphylactoid") can be clinically identical and result from direct mast cell stimulation.
Anaphylaxis is a multisystem allergic reaction with respiratory and / or cardiovascular involvement. Other organ systems are often involved such as skin (itch, rash, flushing, angioedema) and the GI tract (vomiting, diarrhoea, tummy pain - although these are a sign of anaphylaxis if occur due to bee or wasp sting). Signs and symptoms that an allergic reaction is anaphylaxis include:
- Difficulty/noisy breathing
- Swelling of tongue
- Swelling/tightness in throat
- Difficulty talking and/or hoarse voice
- Wheeze or persistent cough
- Loss of consciousness
- Pallor and floppiness (in young children)
Anaphylaxis is sometimes confused with vasovagal syncope. Syncope produces pallor and bradycardia in contrast to the flushing and tachycardia of anaphylaxis. Hyperventilation may occasionally be confused with anaphylaxis.
Anaphylaxis may evolve to being life threatening even if severe symptoms are not initially present. Other causes of hypovolaemic shock and airway obstruction should be considered in severe cases.
Other drug doses
Nebulised adrenaline: Use 5ml of 1:1000 adrenaline via nebuliser
Adrenaline infusion: see Resuscitation Drug Calculator
- Adrenaline should be given IM not subcutaneously
- Antihistamines and steroids are second line therapies in anaphylaxis.
- Adrenaline is not indicated for simple generalised urticaria with no other system involved.
Disposition from Emergency Department
Children requiring treatment with adrenaline should be observed for at least 4-6 hours as life-threatening manifestations can appear after apparent remission. All children who require more than a single dose of adrenaline should be admitted because of the possibility of recurrent symptoms.
Children with less severe disease, good family supervision, transport and telephone can be discharged after 4-6 hours observation with oral antihistamine. They should be instructed to return immediately if there are any recurrent symptoms.
For those patients who have had anaphylaxis:
Follow up should be arranged with the Paediatric Allergy/Immunology Service. Provide the family with an emergency action plan (see below) and Adrenaline auotinjector ordering information before leaving the emergency department
Ensure that the family obtains and is instructed in the use of an autoinjector. Currently only EpiPen®s are available in NZ.
The autoinjector teaching kit is in a box in the right hand side cupboard under the fax machine in the doctor's work station. Follow the check list on the lid of the box. Autoinjectors are not funded.
Be mindful that autoinjectors come in different doses.
Suggestions below from ASCIA (Australasian Society for Clinical Immunology & Allergy):
- EpiPen® Adult for children >20kg (package insert says over 30kg)
- Epipen® Jnr for children 10-20kg (package insert says 15-30kg)
- Recommendation of an EpiPen® to a child weighing <10kg should be discussed with senior medical staff
An EpiPen® is appropriate for those:
- with anaphylaxis to non-avoidable triggers eg. Beestings and most food
- with less severe allergic reaction (i.e. not anaphylaxis) but with other risk factors for anaphylaxis eg. asthma, living in remote locations, peanut allergy. This decision can generally be made at Outpatient Clinic.
Please complete an ACC form, this may assist the family with ambulance and autoinjector costs.
Patients with urticaria without an identifiable trigger do not necessarily need referral (see Urticaria guideline).
You can print an action plan form from the ASCIA website http://www.allergy.org.au/health-professionals/anaphylaxis-resources/ascia-action-plan-for-anaphylaxis. There is a non-adrenaline version for children who have had a less severe reaction.
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- Date last published: 18 October 2017
- Document type: Clinical Guideline
- Services responsible: Paediatric Immunology
- Author(s): Jan Sinclair
- Editor: Greg Williams
- Review frequency: 2 years
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