Chapter 72: Anaphylaxis

DEFINTION

• Etiology: An acute multisystem response caused by a severe reaction to any antigen, such as a drug, vaccine, food, toxin, plant, or venom

• Clinical Presentation:

  • Systemic vasodilation:

    • Hypotension

    • Tachycardia

  • Increased capillary permeability:

    • Angioedema – may lead to partial or complete airway obstruction

    • Worsens hypotension

  • Pulmonary vasoconstriction:

    • Decreased pulmonary blood flow

    • Increased right ventricular afterload

    • Decreased left ventricular preload

  • Bronchoconstriction/bronchospasm

    • Respiratory distress +/− stridor, wheezing, or both

  • Histamine release:

    • Urticaria

    • Nausea and vomiting

MANAGEMENT

REMOVE/DISCONTINUE OFFENDING AGENT

• Example: Discontinue medication infusion

INITIATE SUPPORTIVE CARE

• ABCs:

  • Administer 100% oxygen

  • Maintain airway:

    • Positioning: place patient supine

    • Stabilization (i.e., bag-mask ventilation and/or endotracheal intubation [ETT] if necessary)

  • Suction as needed

  • Pulse oximetry

  • Obtain intravenous/intraosseous (IV/IO) access

  • EKG monitoring

INITIATE MEDICATION ADMINISTRATION

• Epinephrine:

  • Intramuscular (IM):

    • 0.01 mg/kg/dose = 0.01 mL/kg/dose q10–15min prn

    • Max single dose 0.3 mg

    • 1 mg/mL; 1:1000 concentration

  • IM autoinjector:

    • Weight 10 to 30 kg = 0.15 mg

    • Weight ≥30 kg = 0.3 mg

  • IV/IO bolus dose:

    • 0.01 mg/kg/dose = 0.1 mL/kg/dose IV/IO q3–5min prn

    • Max single dose 1 mg

    • 0.1 mg/mL; 1:10,000 concentration

  • IV/IO continuous infusion:

    • 0.1 to 1 mcg/kg/min IV/IO infusion

    • If hypotension persists despite fluids and IM injection

• Albuterol:

  • Nebulizer:

    • Weight <20 kg: 2.5 mg/dose via inhalation q20min prn

    • Weight >20 kg: 5 mg/dose via inhalation q20min prn

  • Continuous nebulizer:

    • 0.5 mg/kg per hour via continuous inhalation

    • Max dose 20 mg/hr

    • Indicated for severe bronchospasm

  • Metered dose inhaler (MDI: 90 mcg/puff):

    • 4 to 8 puffs via inhalation q20min prn with spacer (or ETT if intubated)

• Corticosteroids:

  • Methylprednisolone (reduces late-phase reaction):

    • Load 2 mg/kg IV/IM/IO (max 60 mg); use only acetate salt IM

    • Maintenance: 0.5 mg/kg IV/IO q6hr or 1 mg/kg q12hr (max 120 mg/day)

• Antihistamine:

  • H₁-receptor antagonist: diphenhydramine

    • 1 to 2 mg/kg/dose IM/IV/IO over 5 min q4–6hr

    • Maximum single dose 50 mg

  • H₂-receptor antagonist: ranitidine or famotidine

    • Ranitidine: 1 mg/kg/dose IV

      • Maximum single dose of 50 mg

    • Famotidine: 0.25 mg/kg/dose IV

      • Maximum daily dose of 40 mg

  • The combination of both H₁ and H₂ blocker may be more effective than giving either alone.

• Hypotension:

  • Isotonic crystalloid infusion:

    • Rapid infusion 20 mL/kg – repeat as needed

    • Normal saline or lactated Ringer's

  • Epinephrine infusion (see earlier):

    • Initiate for hypotension that is unresponsive to fluid and IM epinephrine administration

    • Titrate to achieve normal blood pressure for the patient's age

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