Allergic emergencies

Anaphylaxis — adult recognition and response

Overview and approach

Anaphylaxis is a rapidly evolving systemic allergic reaction; skin findings may be absent.

  • ASCIA definition: a potentially life-threatening systemic allergic reaction, usually rapid in onset, with typical skin features (urticaria, erythema/flushing, angioedema) plus respiratory and/or cardiovascular and/or persistent severe gastrointestinal involvement; or any acute hypotension or respiratory impairment (bronchospasm, upper airway obstruction) where anaphylaxis is possible even without skin features (1).
  • Common triggers: foods, insect stings and drugs. Less common: latex, tick bites, exercise and cold. Radiocontrast, immunisation and idiopathic causes are rare (1).
Assessment and clinical features

Airway, breathing, circulation, exposure timing, GI symptoms and progression; position safely and call emergency support.

  • Any one of: difficult or noisy breathing, tongue swelling, throat tightness, wheeze or persistent cough, hoarse voice or difficulty talking, persistent dizziness or collapse (hypotension) (1).
  • Mild to moderate signs may precede anaphylaxis but need not: swelling of lips, face or eyes, hives, tingling mouth. Abdominal pain and vomiting are signs of anaphylaxis for insect allergy (1).
  • Cough in anaphylaxis is usually sudden and can resolve suddenly, unlike asthma. Severe vomiting alone is unlikely to be anaphylaxis (FPIES and gastroenteritis are alternatives) (1).
  • Positioning: lie flat or with legs elevated; left lateral if pregnant, vomiting or unconscious. Fatality can occur within minutes if the patient stands or walks, including after adrenaline. Do not stand until stable, usually at least 1 hour after one adrenaline dose and 4 hours if more than one was given (1).
Differentials and investigations

Diagnosis is clinical; selected tryptase helps later evaluation but must not delay treatment.

  • Differentials include life-threatening asthma, FPIES and gastroenteritis (vomiting without respiratory or skin features; these do not respond to adrenaline) (1)(2). Other mimics include vasovagal syncope and panic attack.
  • Anaphylaxis is a clinical diagnosis. 10-20% of reactions have no skin involvement (2).
  • Serum tryptase usually peaks 1-2 hours after onset and returns to baseline within 6-8 hours; a raised level versus baseline can retrospectively confirm the diagnosis. Never delay treatment for it (2).
Management and follow-up

Immediate IM adrenaline and supportive care under current local/ASCIA protocol, followed by monitored observation and prevention planning.

  • Adrenaline first, immediately: IM into the outer mid-thigh, 0.01 mg/kg of 1:1000 up to 0.5 mg per dose, repeated after 5 minutes if symptoms persist. Intranasal devices are also approved (1). Adrenaline is not withheld in pregnancy.
  • Adrenaline devices in Australia (as of July 2026): EpiPen Jr, EpiPen, Anapen 500, Jext Jr, Jext and neffy nasal spray (1).
  • Refractory anaphylaxis: if there is no response, organise transfer to advanced care, IV or IO access, 20 mL/kg normal saline bolus, oxygen, and an IV adrenaline infusion if available; otherwise repeat IM adrenaline (1).
  • Asthma: always give adrenaline first, then a reliever. Anaphylaxis with bronchospasm can look like life-threatening asthma (1).
  • Adjuncts only: salbutamol 8-12 puffs by spacer or 5 mg nebulised for persistent wheeze; nebulised adrenaline for upper airway obstruction; prednisolone 1 mg/kg (maximum 50 mg) or IV hydrocortisone 5 mg/kg (maximum 200 mg) (benefit unproven); non-sedating antihistamines for persistent skin symptoms only (1).
  • Observation: at least 4 hours after the last adrenaline dose. Overnight if severe or refractory, previous severe or biphasic reaction, concomitant severe asthma or arrhythmia, living alone or remote, or presenting late in the evening (1).
  • Before discharge: prescribe and dispense an adrenaline device, teach use, give an ASCIA Action Plan, refer to a clinical immunology/allergy specialist, and review asthma control (1).
Red flags and clinical pearls

Do not let antihistamines or steroids delay adrenaline. Sudden standing can worsen collapse; refractory reactions need expert escalation.

  • There are no contraindications to adrenaline in anaphylaxis. IV adrenaline boluses are not first line outside specialist settings (e.g. perioperative), and subcutaneous adrenaline is not recommended (2).
  • Risk factors for fatal anaphylaxis: upright posture, delayed adrenaline, concomitant asthma, delayed CPR; most deaths in Australia are from drugs and insect stings in men over 50 with comorbidities (2).
  • Give an IV 0.9% saline bolus (10-20 mL/kg) whenever there is cardiovascular compromise or after two doses of adrenaline without improvement (2). Do not forcibly remove a tick: freeze, don't squeeze (2).
  • Injectable promethazine should not be used (worsens hypotension, can cause necrosis); avoid oral sedating antihistamines because drowsiness can mimic deterioration (1).
  • The most common cause of death in food and drug anaphylaxis is respiratory arrest from bronchospasm in people with asthma or COPD (1).
  • Biphasic reactions occur in an estimated 3-20% within 48 hours (1).
References
  1. ASCIA: Guidelines for Acute Management of Anaphylaxis (2026)
  2. Medicine Today (Sept 2026): Updated anaphylaxis guidelines, a summary for primary care

Last updated from Sen’s notes on 9 October 2026.