What is the initial management of a hypersensitivity reaction in the Emergency Department (ED)?

Initial Management of Hypersensitivity Reactions in the Emergency Department

The two most important initial steps in managing hypersensitivity reactions in the ED are stopping the offending agent (if ongoing) and administering epinephrine as first-line treatment. 1

Immediate Assessment and Management

• Use the ABC (Airway, Breathing, Circulation) approach while calling for assistance and noting the time of reaction onset 1, 2
• Remove all potential causative agents immediately (including IV colloids, contrast media, latex, medications) 1
• Position the patient appropriately - supine or Trendelenburg if hypotensive 1
• Maintain airway and administer 100% oxygen; intubate if necessary 1, 2
• Establish or maintain IV access 2

First-Line Treatment: Epinephrine

• Administer epinephrine as the definitive first-line treatment - do not delay 1, 2
• For adults: Intramuscular epinephrine 0.01 mg/kg of 1:1000 concentration (1 mg/mL) into the vastus lateralis (anterolateral thigh), maximum single dose 0.5 mg 1
• For children >30 kg: 0.3 mg IM; for children <25-30 kg: 0.15 mg IM 1
• May repeat epinephrine dose every 5-15 minutes if symptoms persist 2
• No absolute contraindications exist for epinephrine in anaphylaxis, even with comorbidities like cardiac disease, age, or frailty 1

Fluid Resuscitation

• Begin immediate fluid resuscitation for hypotension with crystalloids (normal saline 0.9% or lactated Ringer's) 1
• Administer at a high rate via appropriate gauge IV cannula; large volumes may be required 1
• Initial bolus of 20 mL/kg, with additional boluses as needed 2

Secondary Management

• After epinephrine and fluid resuscitation, administer H1 antihistamines (e.g., chlorphenamine 10 mg IV for adults) 1
• Administer H2 antihistamines if available 1, 2
• Note that antihistamines only address cutaneous manifestations and are not life-saving 1
• Administer hydrocortisone 200 mg IV (adult dose) 1
• Note that glucocorticoids have no role in treating acute anaphylaxis due to slow onset of action and lack of evidence for preventing biphasic reactions 1

Management of Specific Complications

For persistent hypotension:

• Consider starting an epinephrine infusion if multiple doses required 1
• Consider alternative vasopressors if blood pressure doesn't recover despite epinephrine (e.g., norepinephrine, phenylephrine, metaraminol) 1
• Consider IV glucagon (1-2 mg) for patients on beta-blockers 1

For persistent bronchospasm:

• Administer inhaled bronchodilators (e.g., salbutamol) 1
• Consider IV bronchodilators (salbutamol infusion) 1
• Consider IV aminophylline or magnesium sulfate 1

Monitoring and Observation

• Monitor vital signs continuously until symptoms fully resolve 2
• Observe patient for minimum of 6 hours after stabilization and symptom regression 1, 2
• Consider 24-hour observation for severe reactions due to risk of biphasic anaphylaxis 2
• Biphasic reactions can occur up to 72 hours later (mean 11 hours) 1

Laboratory Testing

• Obtain blood samples for mast cell tryptase testing 1:
  • First sample as soon as feasible after resuscitation starts (do not delay treatment)
  • Second sample at 1-2 hours after symptom onset
  • Baseline sample at 24 hours or later

Common Pitfalls to Avoid

• Delaying epinephrine administration while waiting for antihistamines or corticosteroids to take effect 2
• Administering epinephrine intravenously instead of intramuscularly (except in cardiovascular collapse) 2
• Failing to recognize early warning signs before full reaction develops 2
• Discharging patients too early without adequate observation for biphasic reactions 2
• Confusing vasovagal reactions with anaphylaxis (vasovagal typically presents with bradycardia rather than tachycardia) 1, 2

Special Considerations

• Epinephrine autoinjectors may minimize errors and expedite delivery if staff experience in drawing epinephrine is limited 1
• For patients with contrast media reactions, consider sending to nearest emergency department for observation after initial management 1
• Distinguish between anaphylaxis and cytokine-release/hypersensitivity reactions, as management differs 2