ABCs & initial assessment
- Assume anaphylaxis until proven otherwise — give epinephrine early
- Primary Survey
| System | Assessment | Actions |
|---|---|---|
| Airway | Stridor, voice change, tongue/lip swelling | Basic maneuvers → BVM if needed → call ICU/ENT early → prepare for intubation |
| Breathing | Wheeze, dyspnea, hypoxia | High-flow O₂ → nebulized salbutamol → consider epinephrine |
| Circulation | Hypotension, tachycardia | IV access → 1–2 L crystalloid → continuous monitoring |
| Disability | Confusion, dizziness | Suggests hypoperfusion/hypoxia → reassess frequently |
| Exposure | Urticaria, angioedema | Look for systemic involvement |
- Red Flags (Escalate Early)
- Persistent hypotension despite fluids + epinephrine
- Worsening airway compromise
- Biphasic reaction → monitor 6–24 hrs
- ACEi angioedema → often non-responsive → airway focus + ICU early
Diagnostic criteria
- Acute onset + ANY of the following:
- 1. Known allergen + hypotension SBP <90 mmHg OR ↓ ≥30% baseline
- 2. Skin/mucosa + ≥1 system
- Cardio: hypotension, syncope
- Resp: wheeze, stridor, dyspnea
- 3. Suspected allergen + ≥2 systems
- Skin → Urticaria, angioedema
- Respiratory → Wheeze, stridor
- GI → Vomiting, diarrhea
- Cardiovascular → Hypotension, collapse
HPI & examination
- History
- Trigger: Food, drugs, insect stings, environment
- Previous reactions/allergies
- Medications: Antibiotics, NSAIDs, contrast
- Examination
- Skin: urticaria, angioedema
- Airway: hoarseness, stridor, swelling
- Respiratory: wheeze, distress
- Cardio: hypotension, tachycardia
- Neuro: dizziness, syncope
Management
- Immediate Treatment
- IM Epinephrine 0.5 mg (1:1000) mid-thigh
- Repeat every 5–15 min if needed
- High-flow oxygen
- IV fluids: 1–2 L NS bolus
- Adjuncts
- Nebulized salbutamol (bronchospasm)
- Antihistamines:
- Cetirizine 10 mg PO
- OR Chlorpheniramine 10 mg IV
- Steroids:
- Hydrocortisone 100–200 mg IV
- OR Methylprednisolone 1–2 mg/kg
- Supportive:
- Stop offending agent
- Continuous monitoring
- Watch for a biphasic reaction
- IM Epinephrine 0.5 mg (1:1000) mid-thigh
- Investigations (Do NOT delay treatment)
| Test | Why |
|---|---|
| Serum tryptase | Confirms diagnosis (1–3 hrs peak) |
| ABG/VBG | Respiratory distress |
| ECG ± troponin | Persistent hypotension |
| Bloods / crossmatch | If unstable / preparing for escalation |
- Mild (isolated symptoms)
- Observe
- Oral antihistamines: Cetirizine 10 mg
- Loratadine 10 mg
- Moderate (more symptoms, not anaphylaxis)
- Add steroids
- Nebulized bronchodilators if needed
- Escalation
- Refractory hypotension → vasopressors + ICU
- Airway compromise → early intubation
- Unclear diagnosis → treat as anaphylaxis
Studying for R1? The IM Rapid Review covers this in the same format — see the sample chapter.
Last reviewed · May 2026