Anaphylaxis

1. Anaphylaxis
Beyond the Epipen
From Trigger to Treatment
30th April 2025 1
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2. Anaphylaxis is characterised by:
Sudden Onset
Rapid progression of symptoms
after exposure to allergen
ABC Problems
Airway and/or Breathing and/or
Circulation problems
Skin Changes
Usually accompanied by skin
and/or mucosal changes
(flushing, urticaria, angioedema)
Anaphylaxis is a severe, life-threatening allergic reaction. It occurs rapidly after exposure to an allergen.

3. PATHOPHYSIOLOGY
Antigen-Antibody Binding
• Type 1 hypersensitivity reaction
• Antigen binds antibodies
• Triggering mast cell activation
Mediator Release
Mast cells and basophils release
• histamine
• leukotrienes,
• tumor necrosis factor
• various cytokines.
Physiological Effects
1. Increased bronchial smooth
muscle contraction
2. Decreased vascular tone
3. Increased capillary permeability
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4. Common Triggers
Food Allergens
• Tree nuts and peanuts
• Shellfish and fish
• Milk and eggs
• Wheat and soy
Insect Venom
• Bees and wasps
• Hornets and yellow jackets
• Fire ants
Medications
• Antibiotics (penicillin)
• NSAIDs
• Contrast dyes
• Anesthetics
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5. DIFFERENTIAL DIAGNOSIS
Life-threatening conditions
• Asthma (can present with similar symptoms and signs to
anaphylaxis, particularly in children)
• Septic shock (hypotension with petechial/purpuric rash).
Non-life-threatening conditions
• Vasovagal episode
• Panic attack or hyperventilation syndrome
• Breath holding episode in a child
• Systemic mast cell disorders
• Idiopathic (non-allergic) urticaria or angioedema.
Remember and avoid pitfalls 1
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6. INVESTIGATION
The Resuscitation Council recommend that
three tryptase levels are taken:
• As soon as resuscitation has started
• 1-2 hours after symptoms have started
• 24 hours later or in convalescence (some people have raised
baseline tryptase levels)
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8. MCQ
A 6-year-old child presents to the ED with acute onset
breathing difficulties, severe wheeze and an urticarial rash
after eating peanuts. He is hypotensive and tachycardic at
front door triage and you are called to assist.
After requesting to move the child to resus, your first priority at triage is:
A. High flow oxygen
B. Intramuscular adrenaline
C Intravenous fluids
D Lie patient flat
E Salbutamol nebuliser
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10. ADRENALINE
When to administer adrenaline?
What affect does it have?
Any contraindications?
How much to give?
The best site for IM injection is the anterolateral
aspect of the middle third of the thigh.
Use 1 mg/mL [1:1000] adrenaline
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How to administer adrenaline?

11. • Fluid challenge
• Give a crystalloid fluid bolus
• Adults: 500-1000ml intravenously
• Children: 10ml/kg intravenously
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12. THE DONTS
There is no role for anti-histamine use in the
immediate treatment of anaphylaxis.
The routine use of corticosteroids to treat
anaphylaxis is not advised.
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13. REFRACTORY ANAPHYLAXIS
Refractory anaphylaxis is defined as anaphylaxis requiring ongoing treatment (due to persisting respiratory or
cardiovascular symptoms) despite two appropriate doses of IM adrenaline.
Rapid ABCDE assessment should be undertaken, critical care support.
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14. 1 mg (1 mL of 1 mg/mL [1:1000]) adrenaline in 100 mL of
0.9% sodium chloride
In both adults and children, start at 0.5–1.0 mL/kg/hour
SIDE EFFECTS?
What is used as the prime differentiator between
anaphylactic shock and adrenaline overdose?
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15. SPECIAL CIRCUMSTANCES

16. BIPHASIC REACTION
Anaphylaxis can appear to resolve but then cause a
recurrence of symptoms several hours later in the
absence of further allergen exposure.
Risk factors for biphasic reactions following anaphylaxis include:
• more severe initial presentation of anaphylaxis
• initial reaction requiring more than one dose of adrenaline
• delay in adrenaline administration (> 30 – 60 min
from symptom onset)
• patients with a history of a previous biphasic
reaction may also be at an increased risk.
REMEMBER THE DISCHARGED ADVISE? Safety netting.
Give clear instructions to return to hospital if symptoms recur 16
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17. ANAPHYLAXIS MIMICS
ACE inhibitor induced-angioedema Hereditary angioedema Scombroid poisoning
• May occur years after starting the
drug therapy
• Swollen tongue and oral mucosa
typical
• Urticaria unlikely
• Hypotension unlikely
• Swollen tongue, lips, oropharynx
and extremities
• Urticaria unlikely
• Episodes usually begin in
childhood, becoming more
frequent in adolescence
• C1 esterase inhibitor deficiency
• Abdominal symptoms common
• Unresponsive to adrenaline
• 2 units FFP
• 1000-1500 units of C1 esterase
inhibitor
• Supportive therapy
• Flushing, occasional urticaria
• Follows ingestion of improperly
preserved fish essentially causing
ingestion of excessive histamine
• Hypotension quite possible
• Unresponsive to adrenaline
• Antihistamines
• Supportive therapy
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18. THANKYOU!
Valuable resources for anaphylaxis management:
RCEM Learning
Resus Council UK
OHEM
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