Anaphylaxis is a serious, life-threatening allergic reaction. Features include airway compromise, breathing or circulation difficulties and skin changes. Skin changes alone are not a sign of anaphylaxis but are present in 80% of patients with anaphylaxis.
Signs & Symptoms
- Airway – feeling their throast closing up, stridor (inspiratory sound) & hoarse voice
- Breathing – shortness of breath, increased respiratory rate, wheeze, cyanosis
- Circulation – pale, clammy, hypotensive, tachycardic, sense of impending doom or drowsy/collapse
- Skin – erythema, urticaria, angioedema (usually affecting eyelids and lips)
Differential includes ACE inhibitor-induced angioedema, asthma, panic attack, vasovagal syncope. In the two latter differentials, the absence of skin, swelling and breathing difficulties can help differentiate.
- Stop the agent causing the reaction & call for help (ensure anaesthetic support)
- Establish airway & give high flow oxygen
- Administer IM adrenaline
- Adults – 0.5ml of 1 in 1000 adrenaline IM (500 micrograms)
- Over 12 years – dose as above
- 6-12 years – 0.3ml of 1 in 1000 adrenaline IM (300 micrograms)
- Under 6 years – 0.15ml of 1 in 1000 adrenaline IM (150 micrograms)
- Can be repeated after 5 minutes
- Fluid bolus (crystalloid only- stop colloids as they may cause anaphylaxis)
- Adults – 500ml to 1000ml crystalloid
- Children – 10mL/kg
Antihistamines are no longer recommended for the treatment of anaphylaxis as they delay emergency management. Antihistamines (e.g. cetirizine) can be effective for the cutaneous features.
Also, corticosteroids (e.g. hydrocortisone 200mg) is no longer recommended, except in refractory reactions, ongoing asthma or resistant shock.
Refractory anaphylaxis may be managed with further IV fluids and IM adrenaline every 5 minutes until an infusion of adrenaline is started.
- Ensure you document the time of onset of the anaphylaxis
- Document the preceding circumstances. Ask the patient/NOK to note down everything eaten that day, new medications or any other changes as they will forget very quickly (and it’ll be necessary to identify the trigger).
- Mast Cell Tryptase is recommended (U&Es bottle, ensure time is recorded)
- Sample 1 – as soon as feasible after resuscitation is started
- Sample 2 – within 2h (but no later than 4h) from onset of symptoms
- Sample 3 – at 24h or later following recovery for baseline
- Refer the patient (if appropriate) to allergy services
- Ensure they don’t leave until they’re comfortable taking an adrenaline pen & that they know they must call an ambulance regardless after they take it
- Provide information on avoiding triggers, signs of anaphylaxis, observing for biphasic reactions and information of follow up
- Monitor the patient for at least 12h
- Make sure to register the suspected agent as an allergy
References & Reading
Written by Dr Keryn Hall FY2
Edits by Dr Akash Doshi ST4 – updated in Nov 2021
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