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.
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 |
Key Medications
| Drug | Adult dose | Notes |
|---|---|---|
| Epinephrine IM (thigh) | 0.3–0.5 mg of 1 mg/mL | Repeat q5–15 min |
| Normal saline | 1–2 L bolus for hypotension | Titrate to response |
| Albuterol neb | Per protocol | For bronchospasm |
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.
Notes
Consider glucagon for patients on beta blockers with refractory hypotension. Avoid subcutaneous epinephrine due to delayed absorption.