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Anaphylactic and atopic
- Hypersensitivity type I reactions
- antibody mediated
- - free antigen crosslinks IgE on pre-sensitized mast cells and basophils, triggering release of vasoactive amines that act at postcapillary venules (i.e. histamine).
-Reaction develops rapidly after antigen exposure because of preformed antibody
" First (type) and Fast (anaphylaxis)"
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Anaphylaxis
clinical manifestations
Acute onset (minutes to hours)... [type 1 to type 3 (mild to severe)]
-Cutaneous - flush 46%, urticaria/angioedema 88% (less common with ingested allergens)
-Respiratory - upper vs. lower airway (upper airway edema 56%) (dyspnea/wheeze 47%)
-Cardiovascular - BP (hypotension 10-30%), ECG, collapse.
-GI - 30%
-Other - metallic taste (response to histamine in the blood), impending doom
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Anaphylaxis
Pathophysiology
- CV:
- -Decline in LV systolic function is closely associated with histamine in the blood
- -Decrease blood volume: loss of fluid (plasma) into interstitial space
- -- Hct appears to go up...
- Heart rate increases
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Anaphylaxis
pathology
- Airway edema
- Pulmonary hyperinflation
- Myocardial ischemia
- Visceral congestion
- Eosinophilic inflammation
- Laryngeal edema
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Anaphylaxis
Dx and Ddx
- Dx:
- -history
- -physical exam
- -serum tryptase or carboxypeptidase levels (some individuals have elevated baseline of tryptase, predisposed to anaphylaxis)
- -Skin testing
- -In vitro testing
- Ddx:
- -Aspiration
- -Myocardial infarction
- -Cardiac arrythmia
- -Seizure
- -Pulmonary embolism
- -Vasovagal syncope - pt will have slow heart rate
- -Functional disorders - pt will intentionally ingest a known allergen (or by proxy)
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Anaphylaxis
Etiology
- -IgE mediated
- Foods, drugs, venoms, foreign proteins, therapeudic extracts, environmental allergens (rare), Exercise + food
- -Non-IgE mediated
- -Complement induced - radiocontrast media (rcm), transfusion reaction
- -Direct mast cell activation - rcm, opiates
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-Arachidonic acid associated - NSAIDs
-Idiopathic
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Anaphylaxis
Risk factors
- Atopy - especially for food induced
- Exposure - occupation, medical procedure
- Mast cell disease - mastocytosis, mast cell release syndrome
- PAF hydrolase deficiency
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Food induced anaphylaxis
Allergen - glycoproteins, acid resistant
- Children: milk, egg, peanut, soy
- Adults: nuts, peanuts, fish, shellfish
Fatalities are often associated with asthma, late use of adrenalin, peanuts
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Anaphylaxis
Skin testing
- Selecting patients:
- -history suggests IgE mediated process
- -reaction to stings (hymenoptera rxn)
- -Abx reaction
- -Food reaction
- -Patient not tolerating or responding to anti-allergic medication
- Testing:
- -Epicutaneous - prick puncture; look for wheal and flare. Only test for inhalant allergens. Size of reaction does NOT correlate to severity of anaphylaxis
- -Intradermal - Large volume of dilute allergen, best for drugs and hymenoptera
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In vitro allergy testing
- Pt selection:
- -strong suspect of allergic rxn - especially foods
- -Skin testing unavailable, contraindicated, or negative result (with strong suspicion)
- -dermatographism
- -pt taking anti-histaminic drug
- Testing:
- radio-allergo-sorbent test
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Anaphylaxis in surgery
- Muscle relaxant--#1 in Europe
- Opiate
- Antibiotic --#1 in US
- Latex
- Induction agent
- Plasma expander
- Protamine
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Latex allergy
Exposure - gloves, surgical supplies, balloons, condoms
Incidence - 1-% of operative anaphylaxis
Risk factors - atopy, food allergy, multiple surgeries, spina bifida
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Anaphylaxis treatment
- Acute:
- -Epinephrine - IM (not sub-Q)
- -B2 agonist
- -Corticosteroids - no studies to indicate their efficacy
- -Methylxanthines
- -Antihistamine - no studies to indicate their efficacy
- -Glucagon - reverses beta blockade; pts often vomit
- -Vasopressin
- Longterm:
- -Desensitization - must continue using the drug for effect to last
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Immunotherapy - long term therapy; primarily for venoms - -Drug intervention: (prophylaxis, active acute therapy)
- ...
- -Avoid exposure
- -provide epinephrine
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