what is type I hypersensitivity?
IgE mediated immediate hypersensitivity
what are signs and symptoms of an allergy?
urticaria swelling nausea vomiting cramps
during an allergy what happens with cells?
- allergen binds to IgE
- cross linking through allergen exposure leads to mast cell activation
- degranulation and inflammatory mediator release
histamine and leukotriene relase
what is the effect of histamine?
endothelial cells: vessel permeability
smooth muscle: contraction of smooth muscle and airway vasoconstriction
mucosal epithelial lining: increased secretion of mucus
what is anaphylaxis?
a severe systemic allergic reaction
- respiratory difficulty
- hypotension
what blood tests can be done for allergy?
serum allergic specific IgE concentrations
what is a useful measurement after suspected anaphylaxis/
serum tryptase
released during mast cell degranulation
should be taken between 15 minutes and 3 hours after the reaction
what does skin prick testing test?
the response to the allergen being tested
what are advantages of skin prick testing?
painless
low risk of side effects
good patient complience
what are disadvantages of skin prick testing?
if the pt has took antihistamines it may suppress wheal and flare reaction
less reliable for food allergens compared to inhaled
discomfort
why might an oral food challenge be offered
unclear history of food allergen
blood test and skin tests are inconclusive
what is the management of hayfever?
- non sedating long acting oral antihistamines: loratidine or cetirizine
- aq steroid spray
eye drops
pollen avoidance
what are the three criteria to anaphylaxis?
- sudden onset and rapid progression of symptoms
- life threatening compromise of airway/breathing/circulation
- skin or mucosal changes: flushing/ urticaria/angiodema
what are the actions of adrenaline?
smooth muscle relaxation
vasoconstriction
what is the management of anaphylaxis?
- remove allergen
2, preserve airway and give high flow oxygen - adrenaline 0.5ml of a 1:1000 solution ie 0.5mg IM
repeat after 5 minutes if needed - fluid challenge 500-1000ml
- chlorphenamine 10mg
- hydrocortisone 200mg
observe for 6-12 hours
measure mast cell treatment after emergency treatment and again 2 hours later
what are types of hypersensitivity reaction?
- immediate IgE allergy mediated
- Cytotoxic IgG/IgM complement activity
- immune complex IgG
- delayed hypersensitivity t cell mediated
what is the correct dose of anaphylaxis medications in <6 months, 6 months-6 years, 6-12 years and >12 and adults?
<6 months:
150 micrograms adrenaline
25mg hydrocortisone
250micrograms/kg chlorphenamine
6months-6 years:
150 micrograms
50mg hydrocortisone
1.5mg chlorphenamine
6-12 years:
300 micrograms adrenaline
100 mg hydrocortisone
5 mg chlorphenamine
> 12 and adults:
500 microgrames adrenaline
200mg hydrocortisone
10mg chlorphenamine
where do you teach patients to used an epipen?
anteriolateral aspect of the middle thigh
