[EMed] Anaphylaxis

Question 1

what is anaphylaxis?

Answer 1

severe and life-threatening generalised type 1 hypersensitivity reaction

with airway +/- breathing +/- circulation compromise

usually associated with skin and mucosal changes (flushing, urticaria and oedema)

Question 2

what is the pathophysiology of anaphylaxis: (1) sensitisation phase?

Answer 2

• immune system encounters allergen and produces allergen-specific IgE
• asymptomatic
• most common allergens: foods, drugs and venom

Question 3

what is the pathophysiology of anaphylaxis: (2) reaction phase?

Answer 3

• re-exposure to the allergen → cross-links with IgE on surface of mast cells
• degranulation of mast cells and massive release of histamine

Question 4

what does histamine do?

Answer 4

• bronchoconstriction
• vasodilation
• increased capillary permeability
• tissue oedema

Question 5

the reaction phase is when the pt is symptomatic. what are the sx of anaphylaxis?

Answer 5

• airway oedema and constriction
• peri-oral swelling
• wheeze
• widespread urticarial rash
• hypotension
• shock

Question 6

you suspect a pt has anaphylaxis. what is your initial mx?

Answer 6

A-E assessment

IM adrenaline 0.5mg (0.5ml) 1:1000

remove source of reaction e.g. stop drug infusion, extract insect stings

Question 7

how often can you repeat IM adrenaline for?

Answer 7

repeat at 5 minute intervals if needed

Question 8

what do you give next after IM adrenaline?

Answer 8

IV fluid challenge 500-1000 ml bolus (crystalloid)

Question 9

what else can be given to the pt?

Answer 9

200mg IV hydrocortisone

10mg IV chlorpheramine

Question 10

after a suspected anaphylactic reaction, what is measured and when?

Answer 10

serum mast cell tryptase

• immediately post-resuscitation
• 1-2 hours later
• > 24 hours later (baseline tryptase)

Question 11

how long should pts be monitored for and why?

Answer 11

> 6 hours due to risk of biphasic reactions (>24 hours if high risk)

Question 12

what should all pts with a 1st anaphylactic reaction be referred to?

Answer 12

allergy specialist

Question 13

what is a type 1 hypersensitivity reaction?

Answer 13

(A)naphylaxis

IgE

histamine release from basophils and mast cells e.g. allergy / anaphylaxis

Question 14

what is a type 2 hypersensitivity reaction?

Answer 14

anti(B)ody

IgG

complement-mediated cell lysis e.g. Goodpastures syndrome

Question 15

what is a type 3 hypersensitivity reaction?

Answer 15

immune (C)omplex

IgG/IgM

Ag-Ab immune complex deposition e.g. SLE

Question 16

what is a type 4 hypersensitivity reaction?

Answer 16

(D)elayed

T-cell

e.g. contact dermatitis, Tuberculin skin test

Question 17

what is a type 5 hypersensitivity reaction?

Answer 17

autoimmun(E)

IgG/IgM

bind directly to cell receptors i.e. Graves disease / Myasthenia Gravis

Question 18

anaphylaxis to penicillin. what is the implication?

Answer 18

3% cross-reactivity to 3rd gen cephalosporins

Question 19

fever, rash, lymphadenopathy, deranged LFTs and eosinophilia. dx?

Answer 19

drug reaction with eosinophilia and systemic sx (DRESS)

Question 20

what confirms anaphylaxis?

Answer 20

elevated mast cell tryptase