What is the management of anaphylaxis?

Anaphylaxis Presentation and Management

Immediate Recognition and First-Line Treatment

Epinephrine 0.01 mg/kg intramuscularly (maximum 0.3 mg in prepubertal children, 0.5 mg in adults) injected into the mid-outer thigh is the drug of choice and must be administered immediately at the first recognition of anaphylaxis—delays in administration are associated with fatality. 1

Clinical Presentation

Anaphylaxis is an acute, life-threatening systemic reaction resulting from sudden release of mediators from mast cells and basophils. 2

Key presenting features include:

• Cutaneous manifestations: Urticaria and angioedema are the most common initial signs, though they may be delayed or absent in rapidly progressive cases 2
• Respiratory symptoms: Bronchospasm, wheezing, dyspnea, laryngeal edema, and upper airway obstruction 2
• Cardiovascular collapse: Hypotension, tachycardia (though bradycardia can occur via Bezold-Jarisch reflex), and vascular collapse 2, 3
• Gastrointestinal symptoms: Nausea, vomiting, abdominal cramping, diarrhea 2
• Neurological symptoms: Lightheadedness, feeling of impending doom, or loss of consciousness 2

Critical timing principle: The more rapidly anaphylaxis develops, the more likely it is to be severe and life-threatening. 2

Immediate Management Algorithm

Step 1: Epinephrine Administration (DO NOT DELAY)

• Administer intramuscular epinephrine 0.01 mg/kg using 1:1000 concentration into the anterolateral thigh 1
• Maximum dose: 0.3 mg in prepubertal children, 0.5 mg in adults 1
• For children: Use 0.15 mg auto-injector if 10-25 kg, or 0.3 mg if ≥25 kg 1
• Repeat every 5-15 minutes if symptoms persist or progress—there are no absolute contraindications to epinephrine in anaphylaxis 1, 4
• If in doubt whether this is anaphylaxis, administer epinephrine anyway—it is better to err on the side of caution 2

Step 2: Call Emergency Services and Position Patient

• Activate emergency medical services immediately 1
• Position patient supine with elevated lower extremities to prevent orthostatic hypotension and improve venous return 1, 3

Step 3: Establish IV Access and Oxygen

• Establish intravenous access 1
• Administer supplemental oxygen at 6-8 L/min 1, 4

Step 4: Aggressive Fluid Resuscitation

• Administer normal saline rapidly: 1-2 L in adults at 5-10 mL/kg in first 5 minutes 1
• Children: up to 30 mL/kg in first hour 1
• Up to 7 L of crystalloid may be necessary due to massive fluid shifts (50% of intravascular volume can shift to extravascular space within 10 minutes) 1

Step 5: Airway Management

• Maintain airway patency—consider endotracheal intubation or cricothyroidotomy if laryngeal edema is severe 1

Second-Line Adjunctive Therapies (ONLY AFTER EPINEPHRINE)

These should NEVER delay epinephrine administration:

• H1-antihistamine: Diphenhydramine 1-2 mg/kg or 25-50 mg parenterally 1
• H2-antihistamine: Ranitidine 50 mg IV in adults (1 mg/kg in children) diluted in 5% dextrose over 5 minutes 1
• Bronchodilators: For bronchospasm resistant to epinephrine—nebulized albuterol 2.5-5 mg in 3 mL saline, repeat as necessary 1
• Corticosteroids: Consider for patients with history of idiopathic anaphylaxis, asthma, or severe/prolonged anaphylaxis—these do NOT help acutely but may prevent biphasic reactions 1

Management of Refractory Anaphylaxis

Refractory anaphylaxis is defined as inadequate response after 10 minutes of appropriate treatment. 3

Escalation protocol:

1. Re-evaluate adequacy of initial treatment 3
2. Double the epinephrine bolus dose 1, 3
3. Start epinephrine infusion (0.05-0.1 μg/kg/min) after three bolus doses 1, 3
4. Add alternative vasopressors for persistent hypotension:
   • Norepinephrine infusion 0.05-0.5 μg/kg/min 1
   • Dopamine 2-20 μg/kg/min titrated to maintain systolic BP >90 mmHg 1
5. For patients on beta-blockers unresponsive to epinephrine: Administer IV glucagon 1-2 mg over 5 minutes, followed by infusion of 5-15 μg/min 3, 4

Cardiopulmonary Arrest During Anaphylaxis

• Initiate CPR and advanced cardiac life support immediately 1, 4
• Administer high-dose IV epinephrine rapidly: 1-3 mg (1:10,000 dilution) over 3 minutes, then 3-5 mg over 3 minutes, followed by 4-10 μg/min infusion 1

Observation Period

All patients must be observed for a minimum of 6 hours in a monitored setting, as biphasic reactions can occur in up to 20% of cases. 1, 4

• Biphasic reactions are recurrences without re-exposure that can occur up to 72 hours later (mean 11 hours) 3
• Risk factors for biphasic reactions include severe initial presentation and need for repeated epinephrine doses 5
• There are no reliable predictors of who will develop biphasic reactions 1

Post-Event Management

Before discharge, every patient must receive:

• Two epinephrine auto-injectors with comprehensive training on self-administration 1
• Referral to allergist-immunologist for diagnostic evaluation, trigger identification, and long-term management 1, 4
• Medical alert identification jewelry (e.g., Medic Alert) 2

Critical Pitfalls to Avoid

Pitfall #1: Confusing anaphylaxis with vasovagal reaction

• Vasovagal reactions present with bradycardia, absent urticaria, normal/increased blood pressure, and cool pale skin 2, 4
• Anaphylaxis typically presents with tachycardia (though bradycardia can occur), urticaria, and hypotension 2

Pitfall #2: Delaying epinephrine due to concerns about cardiac disease or age

• There are NO absolute contraindications to epinephrine in anaphylaxis 1, 4
• Delay in epinephrine administration is associated with increased mortality 4

Pitfall #3: Relying on antihistamines or corticosteroids as first-line therapy

• These agents should NEVER delay epinephrine administration 1
• They have no role in acute management and do not prevent biphasic reactions reliably 1, 5

Pitfall #4: Missing anaphylaxis due to absent cutaneous findings

• Urticaria may be delayed or absent in rapidly progressive anaphylaxis 2, 3
• Certain medications (beta-blockers, ACE inhibitors, antihistamines) may blunt initial manifestations 6

Pitfall #5: Inadequate observation period

• Discharging patients before 6 hours risks missing biphasic reactions 1, 4