What is the initial management of acute anaphylaxis in adults and children, particularly those with a history of asthma or other respiratory conditions?

Management of Acute Anaphylaxis

Immediately administer intramuscular epinephrine 0.01 mg/kg (1:1000 concentration) into the anterolateral thigh—up to 0.5 mg in adults and 0.3 mg in children—as the only first-line treatment for anaphylaxis, regardless of severity or patient age. 1, 2, 3

Immediate First-Line Treatment: Epinephrine

Epinephrine is the only medication that prevents and reverses life-threatening airway obstruction, bronchospasm, and cardiovascular collapse—there are no absolute contraindications to its use in anaphylaxis. 1, 2

Dosing and Administration

• Adults and children ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL of 1:1000) intramuscularly 1, 2, 3
• Children <30 kg: 0.01 mg/kg (maximum 0.3 mg) intramuscularly 1, 2, 3
• Route: Inject into the vastus lateralis (anterolateral thigh)—this achieves faster and higher plasma levels than subcutaneous or deltoid injection 4, 2, 5
• Repeat dosing: Every 5-15 minutes as needed if symptoms persist or progress, with no maximum number of doses 1, 2, 6

Critical Timing

Delayed epinephrine administration is directly associated with anaphylaxis fatalities—inject at the earliest sign of anaphylaxis, not after waiting to see if symptoms worsen. 4, 5, 7

Positioning and Supportive Care

• Place patient supine with legs elevated (unless respiratory distress prevents this position) 4, 2
• Administer supplemental oxygen to all patients with respiratory distress and those requiring additional epinephrine doses 1, 4
• Establish intravenous access immediately 4, 2
• Monitor vital signs continuously 1

Fluid Resuscitation

Aggressive crystalloid administration is imperative to combat vasodilation and capillary leak characteristic of anaphylaxis. 4, 2

• Grade II reactions (moderate): Initial bolus of 0.5 L crystalloids 4
• Grade III reactions (severe): Initial bolus of 1 L crystalloids 4
• Repeat boluses up to 20-30 mL/kg based on clinical response; large volumes (1-2 L in adults) may be required for persistent hypotension 4, 2, 6
• Administer IV fluids early with the first epinephrine dose in patients with cardiovascular involvement 1

Management of Respiratory Symptoms in Asthma Patients

Patients with lower respiratory symptoms (chest tightness, wheezing, shortness of breath) should receive inhaled beta-2 agonists (albuterol 2.5-5 mg nebulized) AFTER initial epinephrine treatment, not before or instead of it. 1, 2

This is particularly critical for patients with asthma or other respiratory conditions, as bronchospasm is a common manifestation and these patients are at higher risk for severe reactions. 1, 8

Refractory Anaphylaxis

For patients not responding to initial intramuscular epinephrine:

• After 3 intramuscular doses: Consider IV epinephrine infusion at 0.05-0.1 μg/kg/min 4, 2

  • Preparation: Add 1 mg (1 mL) of 1:1000 epinephrine to 250 mL D5W (concentration 4.0 μg/mL) 4, 2
  • Titrate to effect, maximum 10 μg/min in adults 4

• Alternative vasopressors for persistent hypotension despite epinephrine and fluids: norepinephrine, vasopressin, phenylephrine, dopamine 2-20 μg/kg/min, or metaraminol 4, 2

• Patients on beta-blockers: May require glucagon IV 1-2 mg 4

Second-Line Adjunctive Treatments (Never Replace Epinephrine)

Antihistamines and corticosteroids should NEVER be administered before or in place of epinephrine—they have no role in preventing or reversing life-threatening manifestations of anaphylaxis. 1, 6, 7

Antihistamines (for cutaneous symptoms only)

• H1 antihistamines: Diphenhydramine 25-50 mg IV in adults, 1-2 mg/kg in children (maximum 50 mg) 4, 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

Corticosteroids

• Methylprednisolone 1-2 mg/kg/day IV may be given to potentially prevent biphasic reactions, but has no proven role in acute treatment due to slow onset of action 1, 4, 2
• The American Academy of Allergy, Asthma, and Immunology recommends against using antihistamines and glucocorticoids to prevent biphasic anaphylaxis in adults 1

Post-Anaphylaxis Observation and Biphasic Reactions

Observe all patients for a minimum of 6 hours in a monitored area or until stable and symptoms are regressing. 4, 2

Risk Factors for Biphasic Anaphylaxis

Biphasic anaphylaxis (recurrence after appropriate treatment) occurs in approximately 15% of cases and can happen hours after initial symptom resolution. 1, 4

• High-risk patients requiring extended observation:

  • Severe initial presentation (Grade III-IV reactions) 4
  • Required >1 dose of epinephrine 1, 4
  • Wide pulse pressure 1
  • Unknown trigger 1
  • Drug trigger in children 1

• Grade III-IV reactions typically require ICU admission 4

Tryptase Sampling for Diagnostic Confirmation

• First sample: 1 hour after reaction onset 4, 2
• Second sample: 2-4 hours after onset 4, 2
• Baseline sample: At least 24 hours post-reaction for comparison 4, 2

Discharge Requirements

All patients who have experienced anaphylaxis must be discharged with two epinephrine autoinjectors and a written anaphylaxis emergency action plan. 4, 2

Autoinjector Dosing

• 0.1 mg: Infants >7.5 kg (where available) 4
• 0.15 mg: Children 10-25 kg 4, 2
• 0.3 mg: Individuals ≥25 kg 4, 2

Essential Discharge Components

• Written, personalized emergency action plan including common symptoms, clear instructions, and known triggers 4, 2
• Education on biphasic reactions: Symptoms can recur hours later, requiring immediate epinephrine use and return to emergency care 4, 2
• Referral to allergist for trigger identification, ongoing risk assessment, and long-term management 4, 2, 8
• Monitoring plan for autoinjector expiration dates 4

Critical Pitfalls to Avoid

• Never delay epinephrine for antihistamines or corticosteroids—this is the most common fatal error 6, 7
• Do not inject epinephrine into buttocks, digits, hands, or feet 3
• Do not use subcutaneous route—intramuscular injection into the thigh is superior 4, 2, 5
• Do not assume mild initial symptoms will remain mild—progression to severe, fatal reactions can occur within minutes 7
• Do not withhold epinephrine in elderly patients or those with cardiac disease—there are no absolute contraindications, and the risk of death from untreated anaphylaxis far exceeds any theoretical risk from epinephrine 2