Anaphylaxis

Background

• Anaphylaxis is an acute, systemic allergic reaction that may progress rapidly to airway obstruction, cardiovascular collapse, and death.
• Anaphylaxis may be associated with other allergic conditions.
• Common triggers include food allergens, drugs, insect stings, contrast media, and latex exposure and history is the most important tool in determining whether anaphylaxis occurred and the cause.

Evaluation

• Immediately assess the airway, breathing, circulation, and level of consciousness.
• Symptoms may include angioedema, urticaria, pruritus, flushing and rash, shortness of breath, dysphagia, palpitations, nausea, vomiting, diarrhea, abdominal cramping, feeling of impending doom, lightheadedness, fainting, and headache.
• Physical examination findings may include a reduced level of consciousness, hypotension, dyspnea, stridor, wheezing, diffuse or localized erythema, urticaria and/or angioedema.
• Diagnose anaphylaxis clinically in 1 of the following scenarios:
  • acute skin or mucosal tissue reaction (such as hives, pruritus, flushing, oral swelling, or angioedema) regardless of whether known allergen exposure has occurred and at least 1 of
    • respiratory compromise
    • reduced blood pressure or signs of end-organ hypoperfusion
    • symptoms of end-organ dysfunction (such as hypotonia, syncope, or incontinence)
  • after exposure to likely allergen, 2 or more of following reactions occurring rapidly (minutes to hours)
    • involvement of skin or mucosal tissue
    • respiratory compromise
    • reduced blood pressure or symptoms of end-organ dysfunction (such as hypotonia, syncope, or incontinence)
    • persistent gastrointestinal symptoms (such as vomiting, crampy abdominal pain)
  • after exposure to known allergen
    • reduced blood pressure - low systolic blood pressure (defined by age) or > 30% decrease in systolic blood pressure minutes to several hours after exposure to known allergen
• Specific testing to identify the cause may support diagnosis, with most important tests:
  • serum tryptase
    • obtain level within 5 hours (peak levels within 60-90 minutes of episode)
    • obtaining levels as soon as possible and second sample 1-2 hours (but no later than 4 hours) after symptom onset
      • recommended for patients > 16 years old with suspected anaphylactic reaction
      • suggested for children < 16 years old if venom-related, drug-related, or idiopathic anaphylaxis
    • tryptase > 1.2 times baseline tryptase plus 2 mcg/L may have best performance for diagnosis
  • plasma histamine within 30-60 minutes

Management

• Immediately give epinephrine 0.3-0.5 mg (0.01 mg/kg in children up to 0.3 mg) intramuscularly every 5-10 minutes as needed to control symptoms and maintain blood pressure.
• For hypotensive patients consider:
  • placing in a recumbent position and elevating the legs until the patients are hemodynamically stable and asymptomatic (Weak recommendation)
  • normal saline 1-2 L infused rapidly IV with 5-10 mL/kg in adults within first 5 minutes and then reassess; infuse up to 30 mL/kg IV in first hour in children and then reassess.
  • epinephrine IV if refractory hypotension or patient unresponsive to epinephrine IM
    • in adults and adolescents: epinephrine continuous IV infusion at starting rate of 1 mcg/min using 1 mcg/mL solution (1:1,000,000) to maximum of 10 mcg/min; may also be given by slow IV push in increments of 0.1 mg using 0.1 mg/mL solution (1:10,000)
    • in children: epinephrine continuous IV infusion at starting dose of 0.1 mcg/kg/minute using 1 mcg/mL solution (1:1,000,000)
  • vasopressor infusion (Weak recommendation)
• In addition to epinephrine, consider adjunctive treatment with:
  • antihistamines
    • should not be administered as initial therapy as they have slower onset than epinephrine, but may be considered as adjunctive therapy
    • options include H1 antihistamines diphenhydramine 1 mg/kg (maximum 50 mg) IV in children or 25-50 mg per dose in adults given by slow infusion IV or intramuscularly, or cetirizine 10 mg IV in adults over 1-2 minutes or 2-5-10 mg orally in children (dose depending on age) as single dose; or H2 antihistamines such as famotidine 20 mg IV or cimetidine 4 mg/kg IV
    • first-generation H1 antihistamines generally not suggested in children due to sedating effect; second-generation H1 antihistamines such as cetirizine preferred
  • corticosteroids - have slower onset than epinephrine and should only be used as adjunctive therapy to epinephrine (Strong recommendation)
• Consider observing the patient for 6-12 hours from the symptom onset, depending on the treatment response (Weak recommendation).
• Following acute treatment, provide an epinephrine autoinjector and patient education regarding the prevention and treatment of a recurrent attack.
• For infants, epinephrine is standard treatment and ongoing caregiver education is needed for identification and management of anaphylactic episodes.
• On follow-up, referral to an allergist to consider immunoglobulin E (IgE) or skin testing to determine the cause and potential for desensitization.