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Emergencies: Allergic Reaction

A severe allergic reaction (anaphylaxis) can be life threatening. It is caused by exposure to insect and animal venoms (e.g., wasp sting or jellyfish sting), plant products, medications, or any other agent to which the victim's immune system has been previously sensitized.Signs and symptoms of an allergic reaction.Symptoms include low blood pressure (shock); difficulty breathing (severe asthma) with wheezing; swelling of the lips, tongue, throat, and vocal cords (leading to airway obstruction); itching; hives (red, raised skin welts that may occur singly or in large patches); nausea and vomiting; diarrhea; abdominal pain; seizures; and abnormal heart rhythms. Any or all of these symptoms may be present in varying severity.

Respiratory distress is the most common life-threatening problem. Facial swelling indicates that the airway may soon become involved. One must be ready at all times to protect and support the airway.How do I treat an allergic reaction?

For a mild reaction (itching, hives, no airway or breathing problems, normal blood pressure):

  1. Administer diphenhydramine (Benadryl) or an equivalent antihistamine by mouth. A mild reaction that does not require epinephrine may be managed with diphenhydramine (Benadryl) alone.
    • The adult dose is 50 to 75 mg every 4 to 6 hours; the pediatric dose is 1mg/kg. The major side effect of this medication is drowsiness.

For a severe reaction (severe facial swelling, breathing difficulty, wheezing, low blood pressure):

  1. Administer aqueous epinephrine (adrenaline) 1:1,000 in a subcutaneous injection.
    • Adult dose: 0.3 to 0.5 ml.
    • Pediatric dose: 0.01 ml per kg of weight, not to exceed a total dose of 0.3 ml. For weight estimation, 1 kg equals 2.2 lb.
    • Available in preloaded syringes in certain allergy kits, which include the Ana-KitO and the EpiPenO (for adults and children over 66 lb in weight ) and EpiPen Jr.O (for children 66 lb and under). Instructions for use accompany the kits.
  2. Take particular care to handle preloaded syringes properly, to avoid inadvertent injection into a finger or toe. Do not intentionally inject epinephrine into the buttocks or a vein.
  3. Epinephrine should not be exposed to heat or sun, but does not need to be kept refrigerated. If clear (liquid) epinephrine turns brown, discard it.
  4. Administer diphenhydramine (Benadryl) or an equivalent antihistamine by mouth. The adult dose is 50 to 75 mg every 4 to 6 hours; the pediatric dose is 1 mg/kg. The major side effect of this medication is drowsiness.
  5. If the victim is short of breath or wheezing, administer an inhaled (aerosol or "micronized") bronchodilator (airway opener). Bronchodilators are available in metered-dose hand-held nebulizers from which the victim inhales therapeutic puffs. An excellent drug for an acute attack is albuterol (Ventolin). The dose for an adult is 2 to 4 puffs initially, followed by 2 puffs every 3 to 6 hours.
  6. Transport the victim for medical evaluation.

Brought to you by Paul S. Auerbach, MD, author of Medicine for the Outdoors.
- Paul S. Auerbach

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