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Chapter 18 Lecture 2 Type I (Immediate) Hypersensitivity (Prevention of…
Chapter 18 Lecture 2
Type I (Immediate) Hypersensitivity
Clinical signs of localized allergic reactions
Usually mild and localized
Site of reaction depends on portal of entry
Inhaled allergens may cause hay fever
Runny nose, sneezing, itchy throat and eyes
If inhaled allergens are small enough, and reach the lungs they can cause asthma
Wheezing coughing, excessive production of a thick, sticky mucus
Some allergens may cause inflammation of the skin called hives or urticaria
Latex, wool, venom of wasps, bees, deer flies, fleas, ect..
Clinical signs of systemic allergic reactions
After coming in contact with an allergen, many mast cells will degranulate, releasing a massive amounts of histamine and other inflammatory mediators
The release may exceed the body’s ability to adjust and it results in a condition called acute anaphylaxis or anaphylactic shock
Clinical s/s- rapid suffocation
Why? Bronchial smooth muscle (highly sensitive to histamine) contracts violently then increase of fluid from blood vessels causes swelling of the larynx and other tissues
Also, get contraction of smooth muscle of bladder and intestines
Common- bee stings, peanuts, vaccines containing egg proteins, antibiotics like PCN, iodine dyes, local anesthetics blood products and morphine
Must be treated promptly STAT with epinephrine
Diagnosis of type I hypersensitivity
Can diagnose with a test, called ImmunoCAP Specific IgE blood test, CAP RAST, or Pharmacia CAP
Suspected allergens are mixed with samples of the pts blood
These tests detects the amount of IgE directed against each allergen
Can also inject the skin very small amounts of a dilute solution of allergens being tests
Causes redness and swelling at the injection site.
Prevention of type I hypersensitivity
Begins with identifying the allergen and then avoiding them
Filter the air and avoiding rural areas during pollen season , encasing bedding, vacuuming and avoiding furniture that can trap dust.
Food allergies need to be identified and then avoid them
Healthcare workers need to assess patient's medical history for allergens
Immunotherapy “allergy shots” injections of dilute allergen once a week for many months and be repeated every two to three years.
Not effective in treating asthma
Immunotherapy reduces allergy s/s by 50% in 2/3 of pts.
Treatment of type I hypersensitivity
Administer drugs to counteract the inflammatory mediators when cells degranulate
Antihistamines neutralize histamine
Treat asthma with a glucocorticoid and a bronchodilator (counteracts effects of inflammatory mediators )
Epinephrine neutralizes many mechanisms of anaphylaxis
Relaxes smooth muscle tissue in lungs
Contracts smooth muscle of blood vessels thus reducing vascular permeability
That is why we use for emergency tx of severe asthma and anaphylactic shock