What is the acute management of anaphylaxis?

Acute Management of Anaphylaxis

Intramuscular epinephrine 0.01 mg/kg (maximum 0.3 mg in prepubertal children, 0.5 mg in adults) injected into the anterolateral thigh is the only first-line treatment for anaphylaxis and must be administered immediately—delays in epinephrine administration are directly associated with fatalities. 1, 2, 3

Immediate First-Line Treatment: Epinephrine

Epinephrine has no absolute contraindications in anaphylaxis. 1, 2 The theoretical risks of adverse cardiac effects are vastly outweighed by the risk of death from untreated anaphylaxis. 1

Dosing and Administration

• Dose: 0.01 mg/kg using 1:1000 concentration (1 mg/mL) 2, 3, 4
  • Maximum 0.3 mg in prepubertal children 1, 2
  • Maximum 0.5 mg in adults 2, 3
• Route: Intramuscular injection into the mid-anterolateral thigh (vastus lateralis) 1, 2
  • This site achieves faster absorption and higher plasma levels than subcutaneous or deltoid injection 2, 3, 5
• Autoinjector dosing for children: 1, 2
  • 0.15 mg for weight 10-25 kg
  • 0.3 mg for weight ≥25 kg
• Repeat dosing: Every 5-15 minutes if symptoms persist or progress, with no maximum number of doses 1, 2, 3

Critical Timing

Do not delay epinephrine to obtain IV access, administer antihistamines, or perform other interventions—immediate administration is life-saving. 2, 5 The more rapidly anaphylaxis develops, the more severe and life-threatening the presentation. 2

Concurrent Supportive Measures

Positioning and Emergency Activation

• Position patient supine with legs elevated to prevent orthostatic hypotension and improve circulation to vital organs 1, 2
• Call emergency medical services immediately 2

Airway and Oxygen

• Establish and maintain airway patency—consider endotracheal intubation or cricothyroidotomy if severe laryngeal edema is present and clinicians are trained in these procedures 1, 2
• Administer supplemental oxygen at 6-8 L/min, especially for prolonged reactions, pre-existing hypoxemia, or patients requiring multiple epinephrine doses 1, 2

Vascular Access and Fluid Resuscitation

• Establish IV access immediately 1, 2
• Administer normal saline rapidly for volume replacement: 1, 2, 3
  • Adults: 1-2 L at 5-10 mL/kg in first 5 minutes
  • Children: up to 30 mL/kg in first hour
  • Up to 7 L of crystalloid may be necessary due to massive fluid shifts—increased vascular permeability can transfer 50% of intravascular volume to extravascular space within 10 minutes 1, 2

Second-Line Adjunctive Therapies (Only After Epinephrine)

Antihistamines

• H1-antihistamine (diphenhydramine): 25-50 mg IV/IM in adults, 1-2 mg/kg in children—for cutaneous symptoms only 2, 3
• H2-antihistamine (ranitidine): 50 mg IV in adults, 1 mg/kg in children, diluted in 5% dextrose over 5 minutes—may provide additional benefit when combined with H1 blockers 1, 2, 3

Bronchodilators

• Nebulized albuterol 2.5-5 mg in 3 mL saline for bronchospasm resistant to adequate epinephrine doses, repeat as necessary 1, 2, 3

Corticosteroids

• Systemic corticosteroids (methylprednisolone 1-2 mg/kg/day IV or prednisone 0.5 mg/kg PO) for patients with history of idiopathic anaphylaxis, asthma, or severe/prolonged reactions 1, 2, 3
• Important caveat: Corticosteroids have no acute benefit (onset 4-6 hours) but may prevent biphasic or protracted reactions 1, 2, 3

Management of Refractory Anaphylaxis

Escalating Epinephrine

• If inadequate response after 10 minutes or 2-3 doses: Double the epinephrine bolus dose 2, 3
• Consider continuous epinephrine infusion at 0.05-0.1 μg/kg/min when more than three boluses have been administered 2, 3
  • Preparation: Add 1 mg epinephrine to 250 mL D5W (concentration 4 μg/mL) 2, 3

Additional Vasopressors

• For hypotension refractory to epinephrine and fluids: 2, 3
  • Norepinephrine infusion 0.05-0.5 μg/kg/min, OR
  • Dopamine 2-20 μg/kg/min titrated to maintain systolic BP >90 mmHg

Special Considerations for Beta-Blocker Patients

• Glucagon 1-5 mg IV in adults (20-30 μg/kg in children, maximum 1 mg) over 5 minutes for patients on beta-blockers who are resistant to epinephrine 1
• Beta-blockers can render patients less responsive to epinephrine and cause refractory hypotension and bradycardia 1

Cardiac Arrest During Anaphylaxis

• Initiate CPR and ACLS immediately 1, 2, 3
• High-dose IV epinephrine: 1, 2, 3
  • 1-3 mg (1:10,000 dilution) slowly over 3 minutes
  • Then 3-5 mg over 3 minutes
  • Followed by 4-10 μg/min infusion
  • Children: 0.01 mg/kg (0.1 mL/kg of 1:10,000) repeated every 3-5 minutes; higher doses (0.1-0.2 mg/kg) for refractory asystole 1
• Prolonged resuscitation is encouraged—survival is more likely in anaphylaxis-related arrest than other cardiac arrests 1, 2
• Critical warning: IV epinephrine should never be given in non-arrest situations without appropriate monitoring due to fatal complications 2

Observation and Monitoring

• Observe all patients for minimum 6 hours in a monitored setting 2, 3, 6
• No reliable predictors exist for biphasic reactions based on initial presentation 1, 2, 3
• Biphasic reactions (recurrence without re-exposure) can occur in up to 20% of cases 2

Discharge and Follow-Up

• Prescribe two epinephrine autoinjectors with comprehensive training on self-administration 1, 2, 3
  • 0.15 mg for 10-25 kg
  • 0.3 mg for ≥25 kg
• Provide written, personalized anaphylaxis emergency action plan with trigger identification and clear instructions 2, 3
• Refer all patients to an allergist-immunologist for diagnostic evaluation, trigger identification, consideration of desensitization or immunotherapy, and long-term management 1, 2, 3
• Recommend medical identification jewelry (e.g., Medic Alert) 1, 2
• Educate on biphasic reactions—symptoms can recur hours later, requiring immediate epinephrine use and return to emergency care 2, 3

Common Pitfall

Approximately 90% of anaphylaxis cases require only one epinephrine dose 7, but the inability to predict which patients will need multiple doses mandates that all patients receive prescriptions for at least two autoinjectors and clear instructions to use a second dose if symptoms persist or recur. 2, 3