Anaphylactic Shock — Recognition and Epinephrine Use

Anaphylaxis is a severe, life-threatening allergic reaction that causes anaphylactic shock — a form of distributive shock where widespread vasodilation and fluid leak from blood vessels cause a catastrophic drop in blood pressure. Unlike hypovolaemic shock where blood is lost externally, in anaphylaxis the circulating blood volume effectively collapses within the vessels themselves.

Anaphylaxis is rapidly fatal without treatment. Epinephrine (adrenaline) is the definitive treatment and should be given immediately when anaphylaxis is suspected — not after confirming the diagnosis, and not waiting for emergency services. A delay of minutes in epinephrine administration significantly worsens outcomes.

Common Triggers

Trigger Category	Examples
Foods	Peanuts, tree nuts, shellfish, fish, milk, eggs, sesame
Medications	Penicillin and antibiotics, aspirin and NSAIDs, IV contrast dye
Insect stings	Bee, wasp, hornet
Latex	Medical gloves, balloons, certain food handling equipment
Exercise (exercise-induced anaphylaxis)	Sometimes in combination with food
Idiopathic	No identifiable trigger (~20% of cases)

Recognising Anaphylaxis

Anaphylaxis is a multi-system reaction. It is characterised by the rapid onset (usually within minutes) of multiple symptoms across organ systems:

The Classic Presentation

System	Symptoms
Skin	Urticaria (hives) — itchy red welts; flushing; swelling (angioedema) of face, lips, or tongue
Respiratory	Throat tightening or swelling; hoarse voice; stridor; wheeze; difficulty breathing
Cardiovascular	Rapid heartbeat; dizziness; faintness; collapse; loss of consciousness
Gastrointestinal	Nausea, vomiting, cramping, diarrhoea
Neurological	Anxiety, sense of impending doom; confusion

Diagnosing Anaphylaxis — Key Criteria

Anaphylaxis is likely when:

1. There is a sudden onset after exposure to a likely trigger AND
2. There is involvement of at least two body systems — typically skin plus respiratory or cardiovascular

⚠️ Anaphylaxis can occur without skin symptoms in approximately 20% of cases. Do not wait for hives or swelling if there are respiratory or cardiovascular symptoms following a known or likely trigger. Act on the combined picture.

Anaphylaxis vs. Panic Attack or Vasovagal Episode

Feature	Anaphylaxis	Panic Attack	Vasovagal (Faint)
Skin changes (hives, swelling)	Often present	Not present	Pallor only
Wheeze or stridor	May be present	Not present	Not present
Following exposure to trigger	Usually	Usually not	Usually stressful event
Epinephrine should be given	Yes	No	No

If uncertain: administer epinephrine. The risk of giving epinephrine to someone with a panic attack is minor discomfort; the risk of withholding it from someone with anaphylaxis is death.

Epinephrine Auto-Injector (EpiPen) — How to Use

In the UK, epinephrine auto-injectors are prescribed for individuals with known severe allergies. There are several brands (EpiPen, Emerade, Jext) — the procedure is similar for all:

EpiPen / Jext Procedure

1. Remove from the carrier case.
2. Remove the blue safety cap by pulling it straight off (EpiPen) or removing the needle cap (Jext).
3. Grip firmly in your dominant fist — do not place thumb over the orange/yellow tip.
4. Press firmly against the outer thigh — can be administered through clothing; the outer mid-thigh is the correct site.
5. Hold firmly in place for 10 seconds — the needle deploys and the medication is injected.
6. Remove and massage the area for a few seconds.
7. Note the time of administration.
8. Call 999 immediately if not already done.

After the First Injection

1. Call 999 immediately — even if symptoms improve.
2. Lay the person down with legs elevated if they feel faint or their blood pressure appears low. If breathing is difficult, they may prefer to sit up.
3. If no improvement after 5–15 minutes: administer the second auto-injector if available.
4. If the person becomes unconscious and stops breathing: begin CPR.

Why must they go to hospital after epinephrine? Epinephrine is short-acting — it wears off in 15–30 minutes. Without hospital treatment (IV antihistamines, corticosteroids, further epinephrine if needed, monitoring), anaphylaxis can recrudesce as the epinephrine wears off. This is the "biphasic reaction" — symptoms returning hours later.

Position During Anaphylaxis

Condition	Position
Faint, hypotensive, no breathing difficulty	Lie down; raise legs
Breathing difficulty	Sitting up may be more comfortable; do not force flat
Pregnant	Lie on left side
Unconscious, breathing	Recovery position
Not breathing	CPR position

If No Epinephrine Is Available

Epinephrine is the treatment — there is no first aid substitute. If no epinephrine auto-injector is available:

1. Call 999 immediately — state it is anaphylaxis; paramedics carry epinephrine.
2. Antihistamines (e.g. cetirizine, loratadine, chlorphenamine) can be given for mild reactions — they are not a substitute for epinephrine in anaphylaxis; they take too long to act and do not address the cardiovascular and airway emergency.
3. Keep the person as calm and still as possible — reduce metabolic demand.
4. Be prepared to perform CPR if the person loses consciousness and stops breathing.

After the Episode — Prevention and Planning

Following any anaphylaxis episode:

1. Allergy specialist referral — to confirm the trigger; skin prick and blood tests
2. Epinephrine auto-injectors prescribed — carry two at all times
3. Medical alert bracelet — worn at all times
4. Written anaphylaxis action plan — provided to the person, family members, school, and workplace
5. Anaphylaxis training for close contacts — everyone who may be present during a reaction should know how to use the auto-injector

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Quick Reference

Situation	Action
Signs of anaphylaxis	Administer epinephrine immediately; call 999
Uncertain if anaphylaxis	Administer epinephrine — risk of giving when unnecessary is low
Position	Lie down, legs elevated; sitting up if breathing difficult
After epinephrine	Call 999; monitor; second dose if no improvement in 5–15 min
No epinephrine	Call 999; no alternative; prepare for CPR
Symptoms improve	Still go to hospital — biphasic reaction risk
Do not	Give antihistamines instead of epinephrine; wait to see if it improves