Key Points
- Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
- Use system-specific risk tools to guide testing and disposition.
- Order high-yield tests first; escalate imaging when indicated.
- Start evidence-based initial therapy and reassess frequently.
Algorithm
- Primary survey and vitals; IV access and monitors.
- Focused history/physical; identify red flags and likely etiologies.
- Order system-appropriate labs and imaging (see Investigations).
- Initiate guideline-based empiric therapy (see Pharmacology).
- Reassess response; arrange consultation and definitive management.
Clinical Synopsis & Reasoning
Anaphylaxis is a rapid, systemic hypersensitivity reaction with airway, breathing, or circulatory compromise; diagnosis is clinical. Elicit exposures to foods, medications, stings, and latex; evaluate for biphasic potential and co‑morbid asthma which increases severity. Do not delay definitive therapy for testing.
Treatment Strategy & Disposition
Administer IM epinephrine in the mid‑anterolateral thigh promptly and repeat as needed; provide airway support, high‑flow oxygen, large‑bore IV access, and isotonic fluids for shock. Adjuncts (H1/H2 blockers, corticosteroids) do not replace epinephrine. Observe based on severity and risk for biphasic reaction; discharge with epinephrine auto‑injector, trigger avoidance counseling, and allergy referral.
Management Notes
Do not delay epinephrine for IV access or antihistamines. Provide trigger avoidance counseling and school/work plans.
Epidemiology / Risk Factors
- Risk factors vary by condition and patient profile
Investigations
| Test | Role / Rationale | Typical Findings | Notes |
|---|---|---|---|
| CBC | Baseline hematology | Abnormal counts | |
| BMP | Electrolytes/renal | Derangements |
Epinephrine At‑a‑Glance
| Scenario | Dose/Notes |
|---|---|
| Adult IM | 0.3–0.5 mg (1 mg/mL) lateral thigh |
| Pediatric IM | 0.01 mg/kg up to 0.3–0.5 mg |
| Infusion | 1–10 mcg/min titrate to MAP |
| β‑blocker patient | Add glucagon 1–2 mg IV |
| Autoinjectors | 0.1/0.15/0.3 mg strengths |
Pharmacology
| Medication | Mechanism | Onset | Role in Therapy | Limitations |
|---|---|---|---|---|
| Epinephrine (IM) | α/β agonist | Minutes | First-line life-saving | Arrhythmia; repeat dosing as needed |
| Diphenhydramine ± famotidine | H1 ± H2 antagonism | Hours | Symptom control adjunct | Sedation |
| Methylprednisolone | Glucocorticoid | Hours | Prevents protracted/biphasic symptoms (limited evidence) | Hyperglycemia |
| Albuterol (neb) | β2-agonist | Minutes | Bronchospasm | Tachycardia |
Prognosis / Complications
- Prognosis depends on severity, comorbidities, and timeliness of care
Patient Education / Counseling
- Explain red flags and when to seek emergent care.
- Reinforce medication adherence and follow-up plan.
References
- Anaphylaxis Guidelines — Link