Management of Anaphylaxis

Diagnosis

1. Acute onset of an illness with skin/mucosal involvement AND at least one of: respiratory compromise or reduced BP/end-organ dysfunction
2. Two or more of the following occurring rapidly after exposure to a likely allergen: skin/mucosal symptoms, respiratory compromise, reduced BP, or persistent GI symptoms
3. Reduced BP after exposure to a known allergen for that patient

Immediate Emergency Management (Box 106.7, Rosen's EM)

Step 1 - Simultaneous Emergency Measures

• Remove the triggering agent if identifiable (e.g., stop IV drug infusion, remove insect stinger)
• Position: Place patient supine; elevate legs if hypotensive. Sitting the patient upright at onset is associated with worse outcomes
• Begin cardiac monitoring, pulse oximetry, and BP monitoring
• Establish large-bore IV access (16-18 gauge preferred)
• Administer supplemental oxygen
• Prepare for endotracheal intubation (early intubation is critical if angioedema threatens the airway - delay risks complete obstruction)
• Begin rapid infusion of isotonic crystalloid (normal saline):
  • Adults: 1000 mL IV in first 5 min (several liters may be required)
  • Pediatrics: 20-30 mL/kg IV increments

Drug Treatment

First-Line: Epinephrine (IMMEDIATE - No Absolute Contraindications)

• IM into the anterolateral thigh achieves higher, faster, and more consistent peak plasma levels than deltoid or SC injection
• SC injection is no longer recommended - IM is superior
• IV epinephrine carries risk of dysrhythmia; requires careful cardiac monitoring and dilution
• Central venous access is preferred for IV infusion to avoid tissue necrosis from extravasation
• There is no absolute contraindication in anaphylaxis, including in patients with cardiovascular disease - benefits far outweigh risks
• Most patients need only a single IM dose

Second-Line Agents (After Epinephrine - Never Instead of It)

H1 Antihistamines

H2 Antihistamines

Corticosteroids

For Bronchospasm (In Addition to Epinephrine)

• Adults: 2.5-5 mg nebulized (diluted to 3 mL NS), or 4-6 puffs MDI, q20 min as needed
• Pediatric: 1.25-2.5 mg nebulized q20 min

• Adults: 0.5 mg in 3 mL NS nebulized

For Refractory Anaphylaxis

Refractory to IM Epinephrine + Fluids

Patients on Beta-Blockers

• Dose: 1-5 mg IV bolus slowly over 5 min, then 5-15 mcg/min IV infusion, titrated to clinical response
• Monitor for nausea and vomiting (side effects of glucagon)

Airway Management

• Early intubation is preferred if there is evidence of angioedema-related respiratory distress - any delay risks complete obstruction
• Prepare for adjunct airway techniques: awake fiberoptic intubation, surgical airway (cricothyrotomy)
• If laryngeal edema is not rapidly responsive to epinephrine, cricothyroidotomy or tracheotomy may be required
• Maintain O2 saturation >90%

Positioning

• Supine with legs elevated (Trendelenburg) is standard
• If respiratory distress or vomiting, modify to semi-recumbent
• Never allow the patient to stand or sit suddenly - "empty caval syndrome" (positional cardiovascular collapse) can cause fatal cardiac arrest when moving from supine to upright

Disposition and Observation

• Protracted anaphylaxis or refractory hypotension
• Airway involvement
• Unknown trigger
• IV epinephrine required
• More than one dose of IM epinephrine given
• Poor social support or lives alone far from medical care

Discharge Planning

1. Epinephrine autoinjector (at least 2 prescribed; carry at all times and store at multiple locations - home, vehicle, work)
2. Antihistamines: Diphenhydramine 25-50 mg PO q6-8h for 3-5 days
3. Corticosteroids: Prednisone 40-60 mg PO daily (or 20-30 mg BID) for 3-5 days
4. Written emergency action plan
5. Education on: recognizing anaphylaxis, allergen avoidance, proper use of autoinjector (fewer than 1/3 of patients can demonstrate correct use without instruction), wearing a MedicAlert bracelet
6. Referral to allergist/immunologist for trigger identification and desensitization planning
7. Patients on beta-blockers should have their antihypertensive switched to a different drug class

Special Situations

Perioperative Anaphylaxis

• Frequency: ~1 in 2,000-10,000 cases
• Common triggers: neuromuscular blocking agents, antibiotics, latex, chlorhexidine, induction agents
• Management is the same; maintain high index of suspicion intraoperatively

Radiocontrast Anaphylaxis - Pre-medication Protocol

• Prednisone 50 mg PO at 13, 7, and 1 hour before procedure
• Diphenhydramine 50 mg PO 1 hour before procedure
• Consider ephedrine 25 mg PO 1 hour before
• Consider famotidine 20 mg PO 3 hours before

Non-histaminergic Angioedema (Hereditary Angioedema / ACE-inhibitor angioedema)

• Does not reliably respond to epinephrine and antihistamines (though these should still be tried initially)
• Specific agents for hereditary angioedema (HAE):
  • Icatibant (bradykinin B2 receptor antagonist)
  • Ecallantide (plasma kallikrein inhibitor)
  • Human or recombinant C1 esterase inhibitor
  • Fresh frozen plasma (FFP) as an alternative

Summary: Priority Hierarchy

ANAPHYLAXIS SUSPECTED
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1. EPINEPHRINE IM (anterolateral thigh) - IMMEDIATELY
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2. Supine position + O2 + IV access + fluids
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3. Monitor: cardiac, SpO2, BP
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4. Airway: early intubation if angioedema threatens
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5. If refractory: IV epinephrine infusion ± vasopressors
   If on β-blocker: add Glucagon
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6. Second-line: antihistamines + corticosteroids + bronchodilators
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7. Observe 4-6h minimum; admit if severe
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8. Discharge: EpiPen + steroids + antihistamines + allergist referral