Anaphylaxis

• 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)"

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

• 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
• 

• Airway edema
• Pulmonary hyperinflation
• Myocardial ischemia
• Visceral congestion
• Eosinophilic inflammation
• Laryngeal edema

• 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)

• -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
•       -Arachidonic acid associated - NSAIDs

-Idiopathic

• Atopy - especially for food induced
• Exposure - occupation, medical procedure
• Mast cell disease - mastocytosis, mast cell release syndrome
• PAF hydrolase deficiency

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

• 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

• 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
• 

• Muscle relaxant--#1 in Europe
• Opiate
• Antibiotic --#1 in US
• Latex
• Induction agent
• Plasma expander
• Protamine

Exposure - gloves, surgical supplies, balloons, condoms

Incidence - 1-% of operative anaphylaxis

Risk factors - atopy, food allergy, multiple surgeries, spina bifida

• 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
• -Immunotherapy - long term therapy; primarily for venoms
• -Drug intervention: (prophylaxis, active acute therapy)

• ...
• -Avoid exposure
• -provide epinephrine