Key Points
- Use the highest‑yield diagnostic test early; do not let testing delay time‑critical therapy.
- Set objective targets and reassess frequently.
- Plan definitive source control or disease‑specific therapy when indicated; document follow‑up and patient education.
Algorithm
- Diagnose clinically; give IM epinephrine immediately; place supine with legs elevated; oxygen and IV access.
- Add fluids and adjuncts; monitor vitals and airway; prepare for intubation if progressing.
- Observe 4–24 h based on severity/risk; prescribe two auto-injectors and an action plan; refer to allergy specialist.
Clinical Synopsis & Reasoning
Anaphylaxis is a rapid, systemic hypersensitivity reaction. Inject IM epinephrine in the anterolateral thigh promptly; repeat every 5–15 min as needed. Position patient supine with legs elevated, give high-flow oxygen, IV fluids, H1/H2 blockers, bronchodilators, and steroids as adjuncts; observe for biphasic reactions.
Treatment Strategy & Disposition
Stabilize ABCs. Initiate guideline‑concordant first‑line therapy with precise dosing and continuous monitoring. Escalate to advanced/procedural interventions based on explicit failure criteria. Define ICU, step‑down, and ward disposition triggers; involve specialty teams early.
Epidemiology / Risk Factors
- Risk varies by comorbidity and precipitants; see citations for condition‑specific data.
Investigations
| Test | Role / Rationale | Typical Findings | Notes |
|---|
| Clinical diagnosis (skin, respiratory, cardiovascular, GI) | Recognition | Rapid onset after exposure | Do not delay epi for testing |
| Serum tryptase (within 1–3 h; optional) | Adjunct | Mast cell activation | Helps confirm later |
| Allergen evaluation (outpatient) | Prevention | Identify trigger | Action plan |
High-Risk & Disposition Triggers
| Trigger | Why it matters | Action |
|---|
| Hypotension, airway edema, stridor | Fatal progression risk | Repeat IM epi; start IV epinephrine infusion; ICU |
| β-blocker use with refractory hypotension | Epi resistance | Give glucagon; start infusion |
| Biphasic reaction risk (severe initial reaction) | Late deterioration | Observe 4–24 h based on severity |
| Known mast cell disorders | Severe/atypical courses | Longer observation; hematology/allergy input |
| Poor access to epinephrine or remote living | Safety | Discharge with two auto-injectors and action plan |
Pharmacology
| Medication/Intervention | Mechanism | Onset | Role in Therapy | Limitations |
|---|
| Epinephrine 0.3–0.5 mg IM (1 mg/mL) q5–15 min | α/β agonist | Minutes | First-line life-saving therapy | Peds: 0.01 mg/kg (max 0.3 mg) |
| Normal saline bolus 1–2 L (adults) | Volume support | Minutes | Treats distributive shock | Titrate to response |
| H1/H2 blockers, corticosteroids | Adjunctive | Hours | Symptom relief/reduce protracted reactions | Do not replace epinephrine |
| Albuterol nebulization | β2-agonist | Minutes | Bronchospasm | — |
| Epinephrine infusion or Glucagon (if β-blocked) | Rescue | Minutes | For refractory hypotension | Monitor closely |
Prognosis / Complications
- Outcome depends on timeliness of diagnosis and definitive therapy; monitor for complications.
Patient Education / Counseling
- Provide red‑flag education, adherence guidance, and explicit return precautions; arrange timely specialty follow‑up.
References
- AAAAI/WAO anaphylaxis guidance — Link