Anaphylaxis

Diagnostic Criteria

Definitive: Skin or mucosal changes such as urticaria, flushing or angioedema plus one of the following

• Respiratory compromise: Wheeze, cough, stridor or throat tightness

• Cardiovascular compromise: Hypotension, pallor, tachycardia or bradycardia, collapse

• Gastrointestinal symptoms: Vomiting, diarrhoea, or abdominal pain

Alternatively, acute onset with hypotension, bronchospasm or upper airway obstruction even without skin changes

Management

Immediate Measures

• Remove the trigger if identified

• Position the patient supine with legs elevated and avoid sudden movements

• Create a calm environment to minimise stress

Pharmacological Management

• Intramuscular adrenaline at 10 mcg/kg (maximum 0.5 mL of 1:1000 solution) with repeats every 5 minutes as needed

• Administer high-flow oxygen to maintain SpO₂ above 94%

• Give intravenous fluids: Adults receive 1 L normal saline bolus (repeat as required); children receive 20 mL/kg saline bolus

• Use antihistamines such as cetirizine to relieve pruritus and urticaria (not effective for airway or cardiovascular compromise)

• Consider corticosteroids, e.g. prednisolone 1 mg/kg (maximum 50 mg) for 2 days in severe or protracted cases, though not first-line

Refractory Anaphylaxis

• Repeat intramuscular adrenaline every 5 minutes if inadequate response

• Initiate intravenous adrenaline infusion at 0.05–0.1 mcg/kg/min if necessary

• Add vasopressors such as noradrenaline if hypotension persists despite fluid resuscitation

Symptom-Specific Treatment

• For stridor, administer nebulised adrenaline 5 mL of 1:1000 solution

• For wheezing, use MDI salbutamol (12 puffs via spacer) or nebulised salbutamol 5 mg for severe cases

Post-Event Care

• Observe the patient for at least 4 hours after the last adrenaline dose due to biphasic reaction risk

• Prescribe an adrenaline auto-injector and provide a demonstration of correct use

• Provide a personalised anaphylaxis action plan and educate on early administration of adrenaline in future episodes

Non-Pharmacological Management

• Identify common triggers such as foods (nuts, shellfish, dairy), medications, insect stings, and latex

• Arrange referral for skin prick tests or specific IgE testing for confirmation

• Advise on allergen avoidance strategies including proper food handling, label reading, and minimising exposure during high-risk activities

• Ensure emergency preparedness by prescribing an adrenaline auto-injector and recommending a MedicAlert bracelet

Specialist Referral and Follow-Up

• Refer to an allergy specialist for further evaluation and desensitisation (e.g. venom immunotherapy) if indicated

• Consider immunologist referral if anaphylaxis is frequent or the trigger remains uncertain

• Schedule annual reviews to update the action plan, check auto-injector expiry and reassess avoidance strategies

Additional Notes

• Adjust medication doses in elderly patients or those with cardiac comorbidities

• Document any objective findings such as hypotension as they confirm anaphylactic shock

• Emphasise caregiver education on early recognition of symptoms and the importance of prompt adrenaline administration

• Remain vigilant for biphasic reactions and advise medical review even if symptoms initially resolve