What is the treatment for an acute anaphylactic reaction?

Management of Acute Anaphylactic Reaction

Epinephrine is the first-line treatment for anaphylaxis and must be administered promptly via intramuscular injection in the mid-outer thigh at a dose of 0.01 mg/kg (maximum 0.5 mg) for optimal outcomes. 1, 2

Immediate Actions

1. Recognize anaphylaxis symptoms:

   • Respiratory: Difficulty breathing, wheezing, stridor, bronchospasm
   • Cardiovascular: Hypotension, tachycardia, dizziness, syncope
   • Cutaneous: Urticaria, angioedema, flushing
   • Gastrointestinal: Abdominal cramps, vomiting, diarrhea
   • Other: Feeling of impending doom, uterine cramps 2

2. Administer epinephrine immediately:

   • Route: Intramuscular injection in the lateral thigh (vastus lateralis)
   • Dosage: 0.01 mg/kg of 1:1000 concentration (1 mg/mL)
   • Maximum single dose: 0.5 mg for adults >50 kg
   • Autoinjector options: 0.3 mg for patients >25-30 kg, 0.15 mg for children <25-30 kg
   • May repeat every 5-15 minutes if symptoms persist 2, 1, 3

3. Position patient appropriately:

   • Place in supine position or Trendelenburg position if hypotensive
   • Elevate legs to improve venous return 2

4. Establish airway and provide oxygen:

   • Administer oxygen (8-10 L/min) via face mask for respiratory distress 1, 2

5. Establish IV access and administer fluids:

   • Rapid fluid resuscitation with normal saline (20 mL/kg bolus) for hypotension
   • May need repeated fluid boluses for persistent hypotension 2, 1

Second-Line Treatments

After epinephrine administration, consider:

1. Antihistamines (for cutaneous symptoms only):

   • H1 antagonist: Diphenhydramine 1-2 mg/kg or 25-50 mg IV/IM
   • H2 antagonist: Ranitidine 50 mg IV (adults) or 1 mg/kg (children)
   • Note: Antihistamines should never be used alone or before epinephrine 2, 1

2. For bronchospasm resistant to epinephrine:

   • Inhaled beta-2 agonists (albuterol 2.5-5 mg nebulized) 2, 1

3. For refractory hypotension:

   • Consider vasopressor infusion (e.g., dopamine 2-20 μg/kg/min)
   • Continuous hemodynamic monitoring is essential 2

4. For patients on beta-blockers with poor response:

   • Consider glucagon 1-5 mg IV over 5 minutes, followed by infusion (5-15 μg/min) 2

Monitoring and Observation

1. Monitor vital signs continuously until symptoms fully resolve 2

2. Observe for biphasic reactions:

   • Extended observation (4-6 hours minimum) after symptom resolution
   • Consider longer observation (up to 24 hours) for severe reactions requiring multiple epinephrine doses
   • Biphasic reactions can occur up to 72 hours later (mean 11 hours) 2, 1, 4

3. Transport to emergency department for proper observation, especially from outpatient settings 2

Special Considerations

1. No absolute contraindications to epinephrine in anaphylaxis, even with cardiac disease 1

2. Glucocorticoids have no proven role in acute anaphylaxis management and should not delay epinephrine administration 2

3. Intravenous epinephrine (1:10,000 concentration) should be reserved for profound hypotension or cardiac arrest under continuous monitoring 1, 2

Follow-up Care

1. Prescribe epinephrine autoinjector upon discharge 1, 4

2. Refer to allergist-immunologist for comprehensive evaluation 2, 1

3. Educate patient on trigger avoidance and proper use of emergency medications 4, 5

4. Provide identification (e.g., medical alert bracelet) for patients at risk 2

Common Pitfalls to Avoid

1. Delaying epinephrine administration - associated with increased mortality and biphasic reactions 2

2. Using antihistamines or corticosteroids as first-line treatment - these do not address life-threatening cardiovascular or respiratory symptoms 2, 1

3. Administering epinephrine intravenously as initial treatment - increased risk of cardiac adverse effects compared to IM route 6

4. Discharging patients too early - risk of biphasic reactions requires extended observation 2

5. Failing to prescribe autoinjector for future episodes 4