Anaphylaxis involves a severe, systemic hypersensitivity reaction involving rapid-onset symptoms, with airway, breathing and/or circulation compromise. It is a life-threatening medical emergency.
Immunoglobulin E (IgE) stimulates mast cells to rapidly release histamine and other pro-inflammatory cytokines, called mast cell degranulation.
Presentation
Patients will present with a history of exposure to an allergen (although it can be idiopathic). There will be a rapid onset of allergic symptoms:
- Skin symptoms (e.g., itching, urticaria and angioedema)
- Respiratory symptoms (e.g., cough, wheeze, breathlessness, hoarse voice and stridor)
- Gastrointestinal symptoms (e.g., nausea, vomiting and diarrhoea)
- Systemic symptoms (e.g., tachycardia, hypotension, collapse and confusion)
The key features that distinguish anaphylaxis from other allergic reactions are airway, breathing or circulatory problems (e.g., stridor, wheeze and hypotension). Skin changes alone do not indicate anaphylaxis.
Principles of Management
Anaphylaxis requires immediate medical attention and management. Experienced clinicians should be involved early. Refer to the resuscitation guidelines and local policies before managing patients.
Initial assessment of an acutely unwell child is with an ABCDE approach, assessing and treating:
- A – Airway: Assess for signs of airway compromise (with early senior/anaesthetic support if suspected)
- B – Breathing: Give oxygen if required and consider salbutamol for wheezing
- C – Circulation: Get IV access and give an IV fluid bolus if hypotensive
- D – Disability: Assess for confusion, agitation or impaired consciousness
- E – Exposure: Assess for flushing, urticaria and angioedema
Intramuscular adrenaline is the key treatment for anaphylaxis. A second dose may be given after 5 minutes if required.
| Age | Adrenaline Dose For Anaphylaxis (1mg in 1ml, 1:1000) |
| Over 12 years | 500 mcg (0.5ml) |
| 6 – 12 years | 300 mcg (0.3ml) |
| 6 months – 6 years | 150 mcg (0.15ml) |
| Under 6 months | 100-150 mcg (0.1-0.15ml) |
Antihistamines and hydrocortisone are not recommended in the routine anaphylaxis algorithm.
After the Event
Patients have a period of assessment and observation after an anaphylactic reaction, as biphasic reactions can occur. A biphasic reaction is a second anaphylactic reaction that occurs after successful treatment of the first. This occurs in around 5-10% of cases.
Serum mast cell tryptase should ideally be measured as soon as possible and again at 1-2 hours (no later than 4 hours) after the onset of symptoms to support the diagnosis. Tryptase is released during mast cell degranulation. It peaks at around 1-2 hours and gradually declines thereafter, often returning to baseline by 6-8 hours.
Patients and families require education on how to avoid allergens and spot the signs of anaphylaxis. Parents should have basic life support training. Patients with suspected anaphylaxis should be referred to an allergy specialist.
Adrenaline Auto-Injectors
Adrenaline auto-injectors (e.g., EpiPen and Jext) are given to children and adolescents after an episode of anaphylaxis. They may also be considered in children with generalised allergic reactions (without anaphylaxis) based on an individual risk assessment, taking into account:
- Asthma (particularly if poorly controlled)
- Reduced access to urgent medical treatment (e.g., rural locations)
- Adolescents (higher risk)
- Nut or insect sting allergies (higher risk)
- Significant co-morbidities (e.g., cardiovascular disease)
Two devices are provided. They may require a second dose if there is an inadequate response after 5 minutes of the first.
Adrenaline Auto-Injector Instructions
Prepare the device by removing the safety cap on the non-needle end.
Grip the device in a fist with the needle end pointing downwards. Avoid placing a thumb over the other end. If the device is upside down, there is a risk of injecting the thumb with adrenaline.
Administer the injection by firmly jabbing the device into the outer portion of the mid thigh until the device clicks. It is held in place for several seconds before removal (the duration varies between devices).
Remove the device and gently massage the area for 10 seconds.
Call emergency services when administering adrenaline for suspected anaphylaxis.
A second dose may be given (with a second device) after 5 minutes if required.
TOM TIP: You may be asked to show a parent or child how to use an adrenaline auto-injector, either in exams or in clinical practice. Drug companies provide dummy devices that are usually somewhere on the paediatric wards. They can help you get familiar with the device and practise your explanations.
Last updated April 2026
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