title: "Anaphylaxis"

Anaphylaxis

Key Facts

First-line treatment: IM adrenaline 0.5 mg (0.5 mL of 1:1000) into lateral thigh. Repeat every 5 minutes if no improvement.

Source: ASCIA; ANZCOR.

Warning

Refractory anaphylaxis: No improvement after 2 doses of IM adrenaline. Seek expert help early - may need IV adrenaline infusion.

Recognition

Anaphylaxis is a severe, potentially life-threatening allergic reaction. Diagnose when any ONE of:

Airway

Tongue/throat swelling
Hoarse voice, stridor
Difficulty swallowing

Breathing

Wheeze, persistent cough
Difficulty breathing
Respiratory distress

Circulation

Hypotension (pale, floppy in children)
Dizziness, collapse
Reduced consciousness

Other Features

Urticaria, angioedema
Abdominal pain, vomiting
Known allergen exposure

Clinical Pearl

Skin signs (hives, swelling) may be absent in up to 20% of anaphylaxis cases. Don't wait for skin changes if respiratory or cardiovascular signs present.

Source: ASCIA.

Algorithm

1. Remove trigger if possible
2. Call for help / activate emergency response
3. Position patient:
   - Lie FLAT (legs elevated)
   - Sit up only if breathing difficulty
   - DO NOT stand or walk
4. Give IM ADRENALINE (lateral thigh)
5. Give oxygen if available
6. If asthma symptoms → bronchodilator
7. Repeat adrenaline every 5 min if needed
8. If unresponsive → start CPR

Adrenaline Dosing

Age	IM Dose	EpiPen
Adult	0.5 mg	EpiPen (300 mcg)
Child over 5 years	0.3 mg	EpiPen (300 mcg)
Child 1-5 years	0.15 mg	EpiPen Jr (150 mcg)
Infant under 1 year	0.01 mg/kg	Draw from ampoule

Route: Always IM into lateral thigh (not deltoid, not subcutaneous).

Preparation: 1:1000 adrenaline = 1 mg/mL. So 0.5 mg = 0.5 mL.

Source: ASCIA.

When to Repeat

Repeat IM adrenaline every 5 minutes if:
- Airway/breathing/circulation problems persist
- No clinical improvement
After 2-3 doses without improvement → refractory anaphylaxis

Refractory Anaphylaxis

Warning

Definition: No improvement after 2 doses of IM adrenaline (10 minutes).

Action:

Call for senior/ICU help
Prepare for IV adrenaline infusion
Continue supportive care

IV Adrenaline (Specialist Use Only)

Only by those experienced in its use
Bolus: 10-20 mcg, doubling if no response
Infusion: 0.05-0.5 mcg/kg/min

Adjunct Treatments

Treatment	Role	Notes
IV fluids	Treat hypotension	20 mL/kg bolus
Bronchodilators	Wheeze/bronchospasm	Salbutamol nebulised
Antihistamines	Skin symptoms only	NOT first-line, doesn't treat anaphylaxis
Corticosteroids	Prevent biphasic reaction	Hydrocortisone 200mg IV

Clinical Pearl

Antihistamines and steroids do NOT treat anaphylaxis - they only help with skin symptoms and may prevent biphasic reactions. ADRENALINE is the only life-saving treatment.

Biphasic Reactions

Second wave of symptoms hours after initial reaction
Occurs in ~5% of cases
Observe for 4-6 hours after anaphylaxis (longer if severe)
Treated the same way: IM adrenaline

Post-Anaphylaxis

Observation: Minimum 4 hours (6+ if severe, biphasic risk)
Adrenaline autoinjector: Prescribe for discharge
Action plan: Provide written anaphylaxis action plan
Referral: Allergist/immunologist for investigation
Education: Trigger avoidance, when to use EpiPen

Sources

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