Anaphylaxis: Recognition and First Line Management
Updated: Oct 14
Anaphylaxis is a severe, potentially life threatening allergic reaction that can progress from mild symptoms to airway obstruction or cardiovascular collapse within minutes. It is one of the few emergencies where a single early treatment, intramuscular adrenaline, can completely change the outcome. For students, the challenge is rarely knowing what to give. It is recognising anaphylaxis early enough and not being distracted by treatments that feel helpful but don't address the real danger.
What happens in anaphylaxis
In anaphylaxis, exposure to a trigger causes mast cells and basophils to release large amounts of histamine and other mediators throughout the body. These cause blood vessels to dilate and leak, smooth muscle in the airways to constrict and tissues to swell. The result can be airway swelling, bronchospasm, a sudden drop in blood pressure and shock.
Common triggers include foods such as peanuts, tree nuts, seafood, egg and milk, insect stings and bites, and medications such as antibiotics and anti inflammatories. In Australia, tick bites are also a recognised trigger. Sometimes no trigger is found.
Recognising anaphylaxis
Anaphylaxis should be suspected when a person develops a sudden illness after possible exposure to an allergen, with involvement of the respiratory system, the cardiovascular system, or both. Signs that suggest a severe reaction include:
Difficult or noisy breathing, wheeze or a persistent cough.
Swelling of the tongue, or swelling or tightness in the throat.
Difficulty talking or a hoarse voice.
Persistent dizziness, collapse, pale and floppy appearance in young children, or low blood pressure.
Abdominal pain and vomiting after an insect sting or bite, which can also indicate a severe reaction.
Hives, flushing and facial swelling are common, but they are not essential. Skin signs can be absent or appear late, particularly when the reaction is severe and blood pressure falls quickly. A patient with sudden breathing difficulty or collapse after a likely trigger should be treated as anaphylaxis even without a rash.
If in doubt, give adrenaline. Antihistamines do not treat airway swelling or shock.
Adrenaline comes first
Intramuscular adrenaline is the first line treatment for anaphylaxis in every major guideline, including the Australasian Society of Clinical Immunology and Allergy guidelines. It is given into the outer middle thigh, either with an adrenaline autoinjector or as a drawn up intramuscular dose, according to the dose in your clinical practice guidelines. Adrenaline reverses vasodilation, reduces swelling and relaxes the airways. Delay in giving it is associated with worse outcomes.
If there is no improvement, further doses can be given at intervals set out in your guidelines, commonly every five minutes. Adrenaline should not be withheld because the patient has already used their own autoinjector, because the symptoms seem to be settling, or because of uncertainty about the diagnosis.
Positioning matters
Do not let a patient with anaphylaxis stand up or walk, even if they feel better. Sudden standing can cause a catastrophic drop in blood pressure. Lay the patient flat, or let them sit with their legs outstretched if lying flat makes breathing harder. Small children can be held in a horizontal position rather than upright.
Other treatments
Once adrenaline has been given, supportive treatments include high flow oxygen, airway support, intravenous fluids for hypotension and bronchodilators for persistent wheeze, depending on your scope. Antihistamines can help itch and hives, but they do not treat airway swelling, bronchospasm or shock, and they should never delay adrenaline.
After the reaction
Every patient with anaphylaxis needs medical review and a period of observation, because symptoms can return hours later after an initial improvement. This is known as a biphasic reaction. Patients should leave with an action plan, an adrenaline autoinjector prescription where appropriate and a referral for allergy follow up.
Remove the trigger if it is still present, such as a tick or a stinger.
Give intramuscular adrenaline early, into the outer thigh.
Keep the patient lying flat or sitting, never standing.
Call for help and repeat adrenaline if there is no improvement.
Monitor closely and arrange medical review and observation.
Conclusion
Anaphylaxis is frightening but very treatable when it is recognised early. Think about it in any sudden illness after a possible allergen, don't wait for a rash, keep the patient lying down, and give intramuscular adrenaline without delay. Everything else is secondary.
References
Australasian Society of Clinical Immunology and Allergy (ASCIA). ASCIA Guidelines: Acute Management of Anaphylaxis. Sydney: ASCIA.
Australian and New Zealand Committee on Resuscitation (ANZCOR). Guideline 9.2.7: First Aid Management of Anaphylaxis. Australian Resuscitation Council.
Cardona V, Ansotegui IJ, Ebisawa M, et al. World Allergy Organization anaphylaxis guidance 2020. World Allergy Organ J. 2020;13(10):100472.
Brown SGA. Clinical features and severity grading of anaphylaxis. J Allergy Clin Immunol. 2004;114(2):371.
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Disclaimer: This article is general education for students. It is not medical advice, and it does not replace your service's clinical practice guidelines, your educators or your local protocols.
