Treatment of anaphylaxis

[CEACCP 2004 Vol 4(4) "Anaphylaxis"]

Immediate management

1. Stop administration of all agents likely to have caused the anaphylaxis
2. Call for help
3. Maintain airway, give 100% O2, lie patient flat with leg elevated
4. Give epinephrine
   * IM dose = 0.5 - 1mg (0.5-1mL of 1:1000)
   * IV dose = 50 - 100mcg (0.5 - 1 mL of 1:10,000) over 1 min in case of CVS collapse
   * Never give undiluted 1:1000 epinephrine IV
5. Give IVF
   * Adults may require 2 - 4 L

Subsequent management

1. Give antihistamines
   * Role of H2 antagonist is controversial
2. Give corticosteroid (100 - 500 mg hydrocortisone slowly IV)
3. Consider bronchodilator if necessary
4. Catecholamine infusion
   * CVS instability may last several hours
   * Epinephrine infusion = 0.05 - 0.1 mcg/kg/min = 3 - 6 mcg/kg/hr
   * For 70kg adult, roughly 4 mL of 1:10,000 per hour
5. Check ABG
6. Consider bicarbonate 0.5 - 1 mmol/kg
   * 8.4% of NaHCO3 = 1 mmol/mL

Investigation

3 blood samples to be taken:

1. Immediately after the reaction has been treated
2. About 1 hour after the reaction
3. About 6 hours or up to 24 hours after the reaction

These bloods are to be stored at 4C if analysis within 48 hours, otherwise store at -20C

Tryptase

• Tryptase is found almost exclusively in mast cells
• Released during anaphylaxis and anaphylactoid reaction
• Peak after about 1 hour
• Blood test needs to be taken at about 1 hour after the reaction to confirm the presence of tryptase

Later investigations

• Full investigation and referal to allergist

For example,

• Skin prick tests
• Measurement of specific IgE
  * By radio-allergosorbent test (RAST) or by CAP test (??)

Screening

Screening for anaphylaxis has no value
* History of previous exposure is often not necessary

Management of patient with previous anaphylaxis

• Avoid causative agent
• Consider inhalational induction
• Premedication
  * Hydrocortisone
  * Inhaled beta-agonist
  * H1 and H2-receptor antagonists
• Preoxygenation
• Vasopressor immediately available