What is the emergency treatment for a 12 kg child presenting with spreading hives from an unknown allergen?

Emergency Treatment for Spreading Hives in a 12 kg Child

For a 12 kg child presenting to the ER with spreading hives from an unknown allergen, administer intramuscular epinephrine 0.12 mg (0.12 mL of 1:1000 solution) into the mid-outer thigh immediately if there are ANY additional symptoms beyond skin involvement, or if the hives are rapidly progressive. 1, 2

Immediate Assessment and Risk Stratification

Rapidly evaluate for signs of anaphylaxis beyond isolated hives: 1

• Respiratory symptoms: wheezing, stridor, dyspnea, throat tightness, difficulty swallowing, persistent cough 1
• Cardiovascular symptoms: hypotension (systolic BP <70 mmHg for this age), tachycardia, syncope, dizziness, pallor 1
• Gastrointestinal symptoms: persistent crampy abdominal pain, vomiting, diarrhea 1
• Neurological symptoms: confusion, sense of impending doom 1

Critical point: Spreading or generalized hives can be the first manifestation of developing anaphylaxis, and cutaneous findings may be absent or delayed in rapidly progressive reactions. 2 The more rapidly symptoms develop, the more likely the reaction is severe and life-threatening. 2

Treatment Algorithm

If ANY of the following are present → Give epinephrine IMMEDIATELY:

• Respiratory compromise of any degree 1
• Cardiovascular symptoms 1
• Persistent gastrointestinal symptoms 1
• Rapidly spreading hives (progression over minutes) 2
• Known exposure to high-risk allergen (even with isolated hives) 2

Epinephrine Dosing for 12 kg Child:

Dose: 0.01 mg/kg = 0.12 mg (0.12 mL of 1:1000 epinephrine solution) 1, 3

Route: Intramuscular injection into the mid-outer thigh (vastus lateralis muscle) 1, 4

• The intramuscular route in the thigh achieves peak plasma concentrations in 8 ± 2 minutes, compared to 34 ± 14 minutes with subcutaneous injection 4
• Do NOT inject subcutaneously - this results in dangerously delayed absorption 4

Important consideration for 12 kg child: Standard epinephrine auto-injectors (EpiPen Jr 0.15 mg) may deliver epinephrine into bone in children <15 kg, particularly those <10 kg. 5 In the ER setting, use a standard syringe with measured dose of 0.12 mL for precise intramuscular delivery. 3

If Isolated Hives Without Progression:

Close observation is mandatory, but antihistamines can be initiated: 1, 2

• Diphenhydramine 1 mg/kg (maximum 50 mg) IV or PO 6
• However, antihistamines are NOT sufficient for anaphylaxis and should never delay epinephrine 1
• Antihistamines only relieve cutaneous symptoms and have onset of 30-40 minutes, during which life-threatening respiratory or cardiovascular symptoms can develop suddenly 1, 2

Post-Epinephrine Management

After epinephrine administration: 1

1. Call for additional help/activate emergency response 1
2. Position child supine with legs elevated (unless respiratory distress, then allow upright positioning) 1
3. Monitor continuously - vital signs every 5 minutes 1
4. Second dose of epinephrine may be given 5-10 minutes after first dose if symptoms persist or recur 1, 3
5. Administer supplemental oxygen 1
6. Establish IV access and give fluid bolus if hypotensive 1

Adjunctive medications (AFTER epinephrine, not instead of): 1

• H1-antihistamine (diphenhydramine) 1
• H2-antihistamine (ranitidine) - combination therapy superior to H1 alone 6
• Inhaled albuterol if wheezing present 1
• Corticosteroids (though no evidence they prevent biphasic reactions) 7

Observation Period and Discharge Planning

Minimum observation period: 4-6 hours after symptom resolution 7

• Biphasic reactions occur in up to 20% of cases, with symptoms recurring 6-12 hours after initial resolution 2, 7
• Higher risk for biphasic reactions with severe initial presentation or requirement for multiple epinephrine doses 6

Discharge requirements: 7

• Prescribe epinephrine auto-injector (0.15 mg for 12 kg child) 8
• Provide written anaphylaxis emergency action plan 1
• Refer to allergist for identification of trigger and long-term management 7
• Continue oral antihistamines for 2-3 days 6

Critical Pitfalls to Avoid

Do not wait for respiratory or cardiovascular symptoms to develop before giving epinephrine - isolated hives can rapidly progress to life-threatening anaphylaxis. 2 When in doubt, err on the side of giving epinephrine, as delayed administration is associated with increased mortality. 1

Do not rely on antihistamines alone - they are ineffective for treating anaphylaxis and have dangerously slow onset. 1, 2, 6

Do not use subcutaneous route - intramuscular injection in the thigh is essential for rapid absorption. 4

Do not assume absence of skin findings rules out anaphylaxis - 10% of anaphylaxis cases have no cutaneous manifestations. 1