A quick refresher on how to treat anaphylaxis

Anaphylaxis is most commonly triggered by foods, drugs, insect bites and stings. Less commonly, it can be caused by latex, cold temperature or in 20% of cases, there may be no clear trigger at all. Symptoms usually commence within one to two hours of exposure. Biphasic reactions (delayed recurrence of symptoms) occur in 3-20% of cases of anaphylaxis and 90% of these occur within four hours of the initial reaction).

Clinical features

ASCIA defines anaphylaxis as:

Any acute onset of hypotension, bronchospasm or upper airway obstruction where anaphylaxis is considered possible, even in the absence of skin features OR

Any acute onset illness with typical skin features (urticaria, flushing or angioedema) PLUS symptoms from the respiratory (dyspnoea, wheeze, stridor), cardiovascular (chest pain, presyncope, diaphoresis) or gastro-intestinal systems (nausea, vomiting, abdominal pain).

Management

1. Call for help from staff and 000
2. Remove precipitant if known
3. Lay the patient flat – do not allow them to stand or walk

• If unconscious or pregnant, lay them in the lateral position
• If the patient has breathing difficulty, they may prefer to sit on the floor with legs out
• Children should lay flat and this may be in the parent’s arms

4. Give INTRAMUSCULAR ADRENALINE without delay into outer mid thigh

Supportive management

• Monitor pulse, blood pressure, respiratory rate and pulse oximetry if able
• Give oxygen to maintain saturations >92% and airway support if needed
• Intramuscular adrenaline can be repeated every 5 to 15 minutes if symptoms are not resolving
• If a patient is nauseated, shaky, vomiting, or tachycardic but has a normal or elevated systolic blood pressure, this may be adrenaline toxicity rather than worsening anaphylaxis

Additional measures to consider AFTER IM adrenaline

Bronchospasm/wheeze

• Give Salbutamol via nebulizer (5mg) or spacer (8-12 puffs) immediately after adrenaline
• Give repeat doses of IM adrenaline if ongoing wheeze

Note that bronchodilators don’t prevent or improve upper airway obstruction, hypotension or shock, and therefore should never be used first line treatment.

Upper airway obstruction (stridor)

• Give Adrenaline 5mL (1:1000) via nebulizer

Hypotension

• Obtain IV access and give IV normal saline 20mL/kg bolus
• If persistent hypotension, give IV normal saline up to 50mL/kg in first 30 minutes
• If ongoing hypotension and shock despite 2 doses of IM adrenaline, contact 000 or the local Emergency Department for advice on initiating an IV adrenaline infusion
• If cardiogenic shock, especially in patients on beta-blockers, consider giving Glucagon
• Adult 1-2mg IV bolus
• Children 20-30mcg/kg up to 1mg IV bolus

Steroids

• The role of corticosteroids is unclear, but may be given in moderate (multiple systems) to severe (hypotension/shock) cases of anaphylaxis after adrenaline treatment
• Hydrocortisone IV 5mg/kg up to 200mg OR
• Prednisone PO 1mg/kg up to 50mg

Antihistamines

• Antihistamines have no role in treating respiratory or cardiovascular symptoms of anaphylaxis
• Giving antihistamines delays treatment with IM adrenaline
• Oral non-sedating antihistamines treat itch and urticaria
• DO NOT use injectable antihistamines in anaphylaxis due to risk of worsening hypotension

Severe anaphylaxis and cardiac arrest

• Initiate cardiac arrest protocol including doses of IV adrenaline
• Consider prolonged CPR because the patient arrested rapidly with previously normal tissue oxygenation and has a potentially reversible cause

Aftercare

• Clinical observation for at least 4hours from last dose of adrenaline—or longer if severe reaction
• Revisit history to determine possible trigger
• Provide adrenaline injector prescription, ASCIA action plan for anaphylaxis and education to patient and family
• Refer patient to an allergy specialist for follow-up

Pitfalls

• Failing to consider anaphylaxis as a cause of symptoms due to:
• first episode with no known history of allergy
• the absence of skin symptoms
• the presence of non-specific symptoms, especially in infants and young children
• the lack of a clear trigger
• Failing to give early IM adrenaline
• Failing to provide an auto-injector/education/follow up

For more information
ASCIA Guidelines for Acute Management of Anaphylaxis
This content was reviewed by ASCIA in October 2023.

References
R., Dunn. et al. (2006) “Anaphylaxis,” in The emergency medicine manual. Tennyson, South Australia: Venom Publishing, pp. 401–404.
Acute management of anaphylaxis – allergy.org.au. (n.d.). Retrieved March 1, 2023, from https://allergy.org.au/images/ASCIA_HP_Guidelines_Acute_Management_Anaphylaxis_2023.pdf
Anaphylaxis: Emergency management for health professionals. (2018, April 01). Retrieved March 1, 2023, from https://www.nps.org.au/australian-prescriber/articles/anaphylaxis-emergency-management-for-health-professionals