What is the initial management of anaphylaxis in adults and children?

Initial Management of Anaphylaxis

Immediately administer intramuscular epinephrine 0.01 mg/kg (maximum 0.3 mg in children, 0.5 mg in adults) into the anterolateral thigh—this is the only first-line treatment and must never be delayed for antihistamines, corticosteroids, or other medications. 1, 2, 3

Immediate First Steps (Within Seconds)

• Inject epinephrine intramuscularly into the lateral thigh (vastus lateralis) using 1:1000 concentration—this route achieves faster and higher plasma levels than subcutaneous or deltoid injection 4, 1, 2
• Dosing:
  • Adults and children ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL) IM 4, 2, 3
  • Children <30 kg: 0.01 mg/kg (maximum 0.3 mg) IM 4, 3
  • Autoinjector dosing: 0.15 mg for 10-25 kg; 0.3 mg for ≥25 kg 4, 1
• Repeat epinephrine every 5-15 minutes as needed if symptoms persist or progress—there is no maximum number of doses 4, 2, 3
• Position the patient supine with legs elevated (unless respiratory distress prevents this) to combat hypotension from vasodilation 1, 2
• Administer supplemental oxygen at 6-8 L/min 4, 2
• Establish intravenous access immediately for fluid resuscitation 4, 1, 2

Fluid Resuscitation (Critical for Hypotension)

• Administer rapid crystalloid boluses to counteract vasodilation and capillary leak 1, 2
  • Grade II reactions: 0.5 L initial bolus 1
  • Grade III reactions: 1 L initial bolus 1
  • Repeat boluses up to 20-30 mL/kg based on response 1
• Large volumes (1-2 L in adults) may be required for persistent hypotension 4, 2

Refractory Anaphylaxis (After 2-3 Epinephrine Doses)

• Consider IV epinephrine infusion at 0.05-0.1 μg/kg/min when more than three IM boluses have been given 1, 2
  • Prepare by adding 1 mg epinephrine to 250 mL D5W (concentration 4 μg/mL), infuse at 1-4 μg/min, titrate up to 10 μg/min 2
• Alternative vasopressors for persistent hypotension despite epinephrine and fluids 1, 2:
  • Dopamine 2-20 μg/kg/min titrated to maintain systolic BP >90 mmHg 4, 2
  • Norepinephrine, vasopressin, phenylephrine, or metaraminol may be used 1
• For patients on beta-blockers: administer glucagon 1-2 mg IV (or 1-5 mg over 5 minutes), followed by infusion of 5-15 μg/min, as these patients may not respond adequately to epinephrine 1, 2

Second-Line Adjunctive Treatments (NEVER First-Line)

These medications treat only specific symptoms and do NOT prevent cardiovascular collapse or airway obstruction—they must never delay or replace epinephrine. 1, 2

• H1 antihistamines (diphenhydramine 25-50 mg IV in adults, 1-2 mg/kg in children) for cutaneous symptoms only 4, 1, 2
• H2 antihistamines (ranitidine 50 mg IV in adults, 1 mg/kg in children) may provide additional benefit when combined with H1 blockers 4, 2
• Nebulized albuterol 2.5-5 mg for persistent bronchospasm despite adequate epinephrine 4, 2
• Corticosteroids (methylprednisolone 1-2 mg/kg/day IV) may prevent protracted or biphasic reactions but have no role in acute management 2

Cardiac Arrest Management

• Implement standard BLS/ACLS protocols immediately 2
• Administer high-dose IV epinephrine: 1-3 mg (1:10,000) slowly over 3 minutes, then 3-5 mg over 3 minutes, followed by 4-10 μg/min infusion 2
• Prolonged resuscitation efforts are more likely to succeed in anaphylaxis compared to other causes of cardiac arrest 2

Post-Resuscitation Observation

• Observe all patients for minimum 6 hours in a monitored area or until stable and symptoms are regressing 1, 2
• Grade III-IV reactions typically require ICU admission 1
• Obtain mast cell tryptase samples at 1 hour, 2-4 hours, and baseline (≥24 hours post-reaction) for diagnostic confirmation 1

Critical Pitfalls to Avoid

• Never delay epinephrine for antihistamines or corticosteroids—delayed epinephrine is directly associated with anaphylaxis fatalities 1, 2, 5
• Never inject epinephrine into buttocks, digits, hands, or feet due to risk of tissue necrosis 3
• Never use IV epinephrine boluses in non-arrest situations without extreme caution—several fatalities have been attributed to injudicious IV use 4, 2
• Never discharge patients without two epinephrine autoinjectors and a written anaphylaxis action plan 1
• There are no absolute contraindications to epinephrine in anaphylaxis—even in elderly patients with cardiac disease, the benefits far outweigh risks 1, 5

Discharge Requirements

• Prescribe two epinephrine autoinjectors (0.15 mg for 10-25 kg; 0.3 mg for ≥25 kg) 4, 1
• Provide written, personalized anaphylaxis emergency action plan with trigger identification and clear instructions 1
• Refer to allergist for trigger identification and ongoing risk assessment 1, 2
• Educate on biphasic reactions—symptoms can recur hours later, requiring immediate epinephrine use and return to emergency care 1