What is the management of anaphylaxis?

Management of Anaphylaxis

Immediate First-Line Treatment

Administer intramuscular epinephrine 0.01 mg/kg (maximum 0.5 mg in adults, 0.3 mg in children) of 1:1000 solution into the anterolateral thigh immediately upon recognizing anaphylaxis—this is the only life-saving intervention and must never be delayed or substituted with antihistamines or corticosteroids. 1, 2, 3

Critical Initial Actions

• Inject epinephrine intramuscularly in the mid-outer thigh as the intramuscular route achieves peak plasma concentrations in 8 minutes compared to 34 minutes with subcutaneous injection 3
• For children, use epinephrine auto-injector 0.15 mg if weight is 10-25 kg or 0.3 mg if ≥25 kg 2
• Repeat epinephrine every 5-15 minutes if symptoms persist or recur—there is no maximum number of doses 1, 2, 3
• Call emergency services (911/EMS) immediately 2
• Position patient supine with lower extremities elevated, or in position of comfort if respiratory distress or vomiting present 2, 3
• Establish IV access, provide supplemental oxygen, and continuously monitor vital signs 1, 3

Why Epinephrine Works

Through alpha-adrenergic receptor action, epinephrine reverses vasodilation and vascular permeability that cause hypotension and intravascular volume loss 4. Through beta-adrenergic receptor action, it causes bronchial smooth muscle relaxation, alleviating bronchospasm, wheezing, and dyspnea 4. It also relieves pruritus, urticaria, angioedema, and gastrointestinal symptoms through smooth muscle relaxation effects 4.

Fluid Resuscitation

• Administer crystalloid fluid bolus: 500 mL for Grade II reactions, 1 L for Grade III reactions, escalating to 20-30 mL/kg for refractory cases 1, 3
• Volume replacement is crucial as anaphylaxis causes massive fluid shifts 1

Adjunctive Second-Line Therapies (Never Before Epinephrine)

Antihistamines

• H1 antihistamines (diphenhydramine 25-50 mg IV or 1-2 mg/kg) are adjunctive only for cutaneous symptoms—they have slow onset (≥1 hour) and do not relieve respiratory symptoms or shock 1, 3
• Consider H2 antihistamines (ranitidina 50 mg IV in adults, 1 mg/kg in children) as additional adjunctive therapy 1
• Never administer antihistamines before or instead of epinephrine 1, 2, 3

Bronchodilators

• For bronchospasm resistant to epinephrine, consider inhaled beta-agonists (albuterol nebulized 2.5-5 mg in 3 mL saline) 1, 3
• These are adjunctive only and do not replace epinephrine 2, 3

Corticosteroids

• Consider systemic corticosteroids for patients with history of idiopathic anaphylaxis, asthma, or severe/prolonged reactions 1, 3
• Corticosteroids are not useful in the acute phase but may prevent biphasic reactions 1
• Never administer as sole treatment or substitute for epinephrine 1, 3

Management of Refractory Anaphylaxis

Escalation Protocol

• If inadequate response after 10 minutes, double the epinephrine bolus dose 1, 3
• Start epinephrine infusion (0.05-0.1 μg/kg/min) when more than three boluses have been administered 1, 3

Intravenous Epinephrine (High-Risk Intervention)

• IV epinephrine should be reserved exclusively for cardiac arrest or profound hypotension unresponsive to multiple IM doses and aggressive fluid resuscitation 1, 3
• Dosing for severe hypotension: 20 μg for Grade II, 50-100 μg for Grade III, 1 mg for Grade IV (cardiac arrest) 3
• For cardiac arrest: administer 1-3 mg (1:10,000 dilution) slowly IV over 3 minutes, followed by infusion of 4-10 μg/min 1
• Continuous hemodynamic monitoring is mandatory with IV epinephrine, including continuous ECG, blood pressure every minute, and heart rate monitoring 3

Additional Vasopressors

• For hypotension refractory to volume and epinephrine, consider dopamine infusion 2-20 μg/kg/min (400 mg in 500 mL D5W) titrated to maintain systolic BP >90 mmHg 1, 3
• Consider norepinephrine infusion (0.05-0.5 μg/kg/min) for persistent hypotension 3
• Consider vasopressin 1-2 IU bolus with or without infusion (2 units/h) for refractory hypotension 3

Special Populations

• For patients on beta-blockers with refractory symptoms, administer IV glucagon 1-2 mg (20-30 μg/kg in children, maximum 1 mg) over 5 minutes, as these patients may be unresponsive to epinephrine 3

Observation Period and Monitoring for Biphasic Reactions

• Observe in monitored area for minimum 6 hours, as there are no reliable predictors of biphasic or prolonged anaphylaxis 1, 2, 3
• Monitor continuously for recurrence of symptoms without re-exposure to allergen 2, 5
• Obtain serum mast cell tryptase samples: first at 1 hour after reaction onset, second at 2-4 hours, and baseline at least 24 hours post-reaction 3

Post-Anaphylaxis Management and Discharge

• Prescribe epinephrine autoinjector before discharge 3
• Provide written personalized anaphylaxis emergency action plan 2, 3
• Train patient and family on autoinjector use and anaphylaxis recognition 3, 6
• Arrange allergist referral for trigger identification and consideration of allergen immunotherapy (e.g., venom immunotherapy) 3, 6
• Consider medical identification jewelry 2

Critical Pitfalls to Avoid

• Delayed epinephrine administration is the leading cause of anaphylaxis fatalities—administer immediately when anaphylaxis is suspected 3, 6, 5
• Never substitute antihistamines, corticosteroids, or bronchodilators for epinephrine as first-line treatment 1, 2, 3
• Do not place patients in upright position—this can precipitate cardiovascular collapse 6
• Do not administer IV epinephrine in non-arrest situations without appropriate monitoring and expertise 1, 3
• Avoid premature discharge without adequate observation for biphasic reactions 3, 5
• There are no absolute contraindications to epinephrine in anaphylaxis, even in high-risk patients with cardiovascular disease 1, 6

High-Risk Patients Requiring Extra Vigilance

• Patients with severe uncontrolled asthma are at higher risk for fatal anaphylaxis 3, 7
• Adolescents have particularly high risk for fatal anaphylaxis 3
• Patients on beta-blockers may have refractory symptoms requiring glucagon 3, 7
• Older age and underlying cardiovascular disease increase risk of severe reactions 5
• Peanut and tree nut allergies are associated with more severe reactions 5