Anaphylactic Shock
Definition
Anaphylaxis is an acute systemic (multi-system) and severe Type I Hypersensitivity allergic reaction
Minute amounts of allergens may cause a life-threatening anaphylactic reaction.
Anaphylaxis may occur after ingestion, skin contact, injection of an allergen or, in rare cases, inhalation.
Anaphylactic shock
The most severe type of anaphylaxis
Due to quick release from mast cells of large quantities of immunological mediators (histamines, prostaglandins, leukotrienes)
Leading to systemic vasodilation and a sudden drop in blood pressure, and edema of bronchial mucosa → bronchoconstriction and difficulty breathing
Anaphylactic shock can lead to death in a matter of minutes if left untreated.
Causes
Allergens like bee sting - initial exposure - called sensitizing dose
Subsequent exposure - shocking dose
Immune system causes whole body reaction.
Some drugs (polymyxin, morphine, x-ray dye, and others)
cause an "anaphylactoid" reaction on the first exposure.
Antitoxins and antivenins may cause similar reactions.
Food allergies (peanuts and tree nuts)
Pollens and other inhaled allergens
Idiopathic.
Symptoms
Symptoms of anaphylaxis are related to the action of Immunoglobulin E (IgE)
Bronchospasm, respiratory distress
abdominal pain, cramps, vomiting, and diarrhea.
Hypotension
Shock
Pulmonary oedema
Polyuria
encephalitis
fainting
unconsciousness
urticaria (hives)
flushed appearance
angioedema (swelling of the lips, face, neck and throat): this can be life threatening
tears (due to angioedema and stress)
vomiting
itching
diarrhea
anxiety
Symptoms can appear immediately, or can be delayed by half an hour to several hours after ingestion.
Skin allergy testing (with or without patch testing)
Treatment
Emergency treatment
The primary treatment - epinephrine (adrenaline) - life-saving.
If the patient has previously been diagnosed with anaphylaxis, he or she may be carrying an EpiPen or Twinject for immediate administration of epinephrine.
0.3–0.5mL of a 1:1,000 dilution.
Antihistamines IM - such as chlorphenamine or Diphenhydramine (Benadryl)
Steroids, such as hydrocortisone or Dexamethasone (Decadron)
IV Fluid administration
Severe cases - pressor agents such as dopamine for hypotension
Administration of oxygen
Intubation during transport to advanced medical care.
Profuse laryngeal edema - cricothyrotomy or tracheotomy
Bronchospasm - bronchodilator drugs - salbutamol
Supportive care with mechanical ventilation may be required.
One to two days of medical care - needed
Rebound reactions - a few hours after the initial reaction or even after as much time as a week.
Beta-blockers may aggravate anaphylactic reactions and interfere with treatment.
Prevention
Immunotherapy with Hymenoptera venoms for allergy to bees, wasps, hornets, yellow jackets, white faced hornets, and fire ants
A vaccine to prevent anaphylaxis from peanuts and tree nuts - under research
