What is the immediate management of anaphylaxis?

Immediate Management of Anaphylaxis

Intramuscular epinephrine 0.01 mg/kg (maximum 0.3 mg in children, 0.3-0.5 mg in adults) injected into the mid-outer thigh (vastus lateralis) is the first-line, life-saving treatment that must be administered immediately upon recognition of anaphylaxis. 1, 2, 3

Initial Assessment and Positioning

Upon recognizing anaphylaxis, immediately:

• Call for help (911/EMS in community; resuscitation team in hospital)
• Position the patient supine with legs elevated; if respiratory distress or vomiting present, allow sitting upright with legs extended and elevated 2, 4
• Assess airway, breathing, circulation, and mental status 1

Primary Treatment: Epinephrine

Route and dosing specifics:

• Intramuscular injection into the anterolateral thigh (vastus lateralis) produces higher and more rapid peak plasma levels compared to arm or subcutaneous routes 1, 3
• Dose: 0.01 mg/kg of 1:1000 dilution
  • Children: maximum 0.3 mg
  • Adults: 0.3-0.5 mg depending on severity 2, 3
• Repeat every 5-15 minutes as needed for persistent symptoms 1, 2, 4
• 6-19% of pediatric patients require a second dose; third doses are infrequent 2

Critical caveat: There is no absolute contraindication to epinephrine in anaphylaxis, even in patients with cardiovascular disease or on β-blockers—the risk of fatal anaphylaxis exceeds the risk of epinephrine administration 1, 3

Secondary Interventions (After Epinephrine)

These are adjunctive only and should never delay or substitute for epinephrine:

Airway and Breathing

• Supplemental oxygen at 6-8 L/min 1
• Nebulized albuterol 2.5-5 mg in 3 mL saline for bronchospasm resistant to epinephrine; repeat as necessary 1
• Establish definitive airway (endotracheal intubation or cricothyrotomy) if needed 1

Circulation

• Establish IV access immediately 1
• Aggressive IV fluid resuscitation with normal saline—may require 1-2 L in adults rapidly; children require proportional volumes 1
• For refractory hypotension after volume and epinephrine: dopamine 400 mg in 500 mL D5W at 2-20 mcg/kg/min, titrated to maintain systolic BP >90 mmHg (requires continuous hemodynamic monitoring) 1

Antihistamines (Second-Line)

• Diphenhydramine 1-2 mg/kg or 25-50 mg parenterally 1
• Ranitidine 1 mg/kg (or 50 mg in adults) diluted in D5W to 20 mL, given IV over 5 minutes 1
• The combination of H1 + H2 antihistamines is superior to H1 alone, but both have much slower onset than epinephrine 1

Corticosteroids (Consider for Specific Situations)

• Not helpful acutely but may prevent biphasic or protracted anaphylaxis 1
• Consider in patients with:
  • History of idiopathic anaphylaxis
  • Asthma
  • Severe or prolonged anaphylaxis 1
• Dosing: Methylprednisolone 1-2 mg/kg/day IV every 6 hours, or prednisone 0.5 mg/kg PO for less critical episodes 1

Special Circumstances

Patients on β-Blockers

• Glucagon 1-5 mg IV over 5 minutes (20-30 mcg/kg in children, maximum 1 mg), followed by infusion at 5-15 mcg/min 1
• Aspiration precautions essential—glucagon causes nausea and vomiting 1

Refractory Anaphylaxis or Cardiac Arrest

• Continue IM/IN epinephrine every 5 minutes while optimizing ABC resuscitation 4
• Prepare IV epinephrine infusion after 2 doses of IM epinephrine; initiate after third dose or earlier at provider discretion 4
• High-dose IV epinephrine for cardiac arrest: 1-3 mg (1:10,000) IV over 3 minutes, then 3-5 mg over 3 minutes, then 4-10 mg/min infusion 1
  • Children: 0.01 mg/kg (0.1 mL/kg of 1:10,000, max 0.3 mg) every 3-5 minutes 1
• Atropine and transcutaneous pacing for asystole/pulseless electrical activity 1
• Prolonged resuscitation efforts are encouraged—more likely successful in anaphylaxis, especially in young patients with healthy cardiovascular systems 1

Critical warning: IV epinephrine should only be used during cardiac arrest or profound hypotension unresponsive to volume and multiple IM epinephrine doses, with continuous hemodynamic monitoring when available 1

Observation and Disposition

• Observation periods must be individualized—no reliable predictors of biphasic reactions exist based on initial presentation 1
• Risk factors for biphasic reactions: severe initial anaphylaxis, need for >1 epinephrine dose 5
• Transport to emergency department or ICU for monitoring and potential additional interventions 1
• Provide epinephrine autoinjector and training before discharge 1
• Refer to allergist-immunologist for diagnostic evaluation and long-term management 1

Common Pitfalls to Avoid

1. Delaying epinephrine administration—fatal outcomes are associated with delayed or absent epinephrine 2, 3, 6
2. Using antihistamines or corticosteroids as first-line therapy—these should never substitute for epinephrine 1, 3
3. Subcutaneous or arm IM injection instead of thigh IM—suboptimal pharmacokinetics 1, 3
4. Allowing patient to stand or walk—can precipitate cardiovascular collapse 2
5. Premature IV epinephrine use—associated with fatalities when used injudiciously 1