Anaphylaxis and allergic reactions

What hypersensitivity reaction?

there is an antigen on the cell surface that attracts IgM or IgG ab, this promotes cell lysis via the complement system

type II hypersensitivity

What hypersensitivity?

the antigen is freely circulating and binds to the antibody, then the complex is deposited in vessel walls and causes an inflammatory reaction

type III hypersensitivity

What hypersensitivity?

a previosly sensitized T helper cell recognizes an antigen and relases cytokines to recruit more T1 helper cells and mononuclear cells causing inflammatory reactions

type IV hypersensitivity

Explain the two phases of a type I hypersensitivity

The first phase involves an initial exposure to an allergen, leading to IgE antibody production and mast cell sensitization. The second phase occurs upon re-exposure, where the allergen cross-links IgE on mast cells, resulting in degranulation and the release of histamines and other mediators, causing allergic symptoms.

What is a biphasic reaction?

a reaction meeting anaphylacti criteria within 48 hours of previosu recation wihtout re-exposure to an antigen

What is the mechanism of a type I hypersensitivity reaction?

1st exposure: exposed to allergen, IgE is produced and it binds to the surface of mast cells and basophils

2nd exposure: once re-exposed, the already primed IgE-mast cell combo crosslinks with the antigens and causes the reaction

What are some common skin, respiratory, GI, ENT, neuro, and CV symptoms of an allergic reaction/anaphylaxis?

skin: flushing, prutitis (itching), uticaria (hives)

respiratory: rhinitis, stridor, wheexing

GI: n/v, diarhhea

ENT: uvula, tongue, or oral pharyngeal swelling

neuro: ha, seizure

CV: chest pain, hypotension

What are the 3 different routes of criteria for anaphylaxis?

(the slide is long, just read it and understand the basics)

1. acute inset of mucocutaneous symptoms (flushing, pruritis, angioedema) plus 1+:

   • wheezing, stridor, or hypoxia

   • hypotension or end-organ damage

2. 2+ that occur after known or suspected allergen

   • mucocutaneous involvement, respiratory symtoms, hypotension or end-organ hypoperfusion, GI symptoms (pain, n/v)

3. hypotension within minutes to hours after exposure to a known allergen

What is the determining factor for anaphylaxis vs anaphylactic shock?

shock = hypotension

What are the two most important things for the treatment of anaphylaxis?

maintain airway

admin epi: 0.3-0.5 mg IM in the thigh (0.01 mg/kg for peds)

Why is epi good for anaphylaxis? 3 things

increases peirpheral vascular resistance and cardiac output (increases BP)

stabilizes mast cells

reverses bronchconstriction and mucosal edema

Besides epi and maintaining airway, what are some other aspect of the treatment of anaphylaxis?

decontamination (remove allergen, stinger, etc)

albuterol if wheexing only

IV crystalloid infusion if hypotensive

corticosteroids (may prevent biphasic rxn)

What role do antihistamines play in anaphylaxis treatment

there is no evidence that they support the life-threatining apsects of anaphylaxis but they can help with the cutaneous symptoms

If you patient is on a beta-blocker, what else should we adminster for the epi to work in treating anaphylactic shock?

glucagon

What do we do for a low risk patient with resolved anaphylaxis

observe and discharge

rx for epi pen

consider rx for symptoms relief (anti-histamine)

f/u with PCP or allergist

What do we do for a high risk pt with a mild to moderate anaphylaxis? (they have persistent symptoms or increased risk of death from anaphylaxis)

prolonged ED observation or admit

What do we do for patients with severe anaphylaxis?

ICU admission:

• intubate

• IV epi

• airway monitoring

What is the most common sign we see with a non-anaphylactic allergic reaction?

urticaria (also seen in anaphylaxis)

we should ask them about potential exposures: foods, meds, soaps, fam hx of allergic rxns, etc.

remember: not all rashes are allergic reactions

How do we treat non-anaphylactic allergic reactions?

anithistamines (H1 and H2 together works better then just H1)

monitor for progression to anaphylaxis

consider corticosteroids (they decrease itch, but need to look at risk vs benefit — if severe give steroids)