24 - Hypersensitivity and Anaphylactic Shock

Question 1

What is shock

Answer 1

Failure to maintain adequate cardiac output

Question 2

What are the different types of shock

Answer 2

Hypovolemic
Obstructive
Cardiogenic
Distributive

Question 3

Hypovolemic shock causes

Answer 3

Haemorrhage

Severe fluid loss

Question 4

Obstructive shock causes

Answer 4

Pulmonary embolus or tamponade so fluid accumulates

Question 5

Causes of cardiogenic shock

Answer 5

Myocardial Infarction
Valvular disease
Myocarditis
Cardimyopathy

Question 6

Causes of distributive shock

Answer 6

Septic
Anaphylactic
Neurogenic

Question 7

IgG

Answer 7

can block pathogen binding, activate complement, & opsonise antigen for phagocytes. It is specially transported across the placenta

Question 8

IgM

Answer 8

block pathogen binding, activate complement

Question 9

IgA

Answer 9

block pathogen binding. present in secretions: tears, digestive juices, breast milk

Question 10

IgE

Answer 10

Activates mast cells

Question 11

IgD

Answer 11

not secreted, & function is unknown

Question 12

How are mast cells and basophils activated

Answer 12

1 - Cross linking of surface Ige by antigen
2 - Complement - C3a and C35
3 - Via nerves
4 - Direct contact with pathogen

Question 13

What is type 1 sensitivity

Answer 13

Mast cell activation and release of mediators

Question 14

What are some examples of mediators

Answer 14

Histamine
Leukotrienes
Prostaglandins

Question 15

What is the action of histamine

Answer 15

Increase in permeability of post capillary venules, vasodilation of arterioles, contraction of smooth muscles, itch

Question 16

What is the action of leukotrienes

Answer 16

Increase permeability of post capillary venules, chemotaxis

Question 17

What is the action of prostaglandins

Answer 17

Arteriolar dilation
Pain
Fever

Question 18

What is Atopy

Answer 18

the inherited predisposition to make IgE to common environmental antigens

Question 19

Clinical manifestations of type 1 hypersensitivity

Answer 19

• Local. Allergic rhinitis, asthma, atopic eczema, some urticaria, some angioedema
• Systemic: anaphylactic shock. patient does NOT have to be atopic to get anaphylactic shock.

Question 20

Clinical manifestations of anaphylactic shock

Answer 20

Drop in BP - redistribution (often warm peripheries)
Urticaria (hives)
Sore, red itchy eyes
Angiodema (swelling in SC tissue)
Bronchoconstriction - wheeze, respiratory obstruction
Nausea and vomiting 
Diarrhoea
Headache 
Feeling of impending doom
Cardiac arrest and death

Question 21

Antigens that trigger anaphylaxia

Answer 21

Drugs - B lactams have cross reactivity, NSAIDs, Insulin, local and general anaesthetics
Food - Peanuts, milk, eggs
Arthropod venoms - bee stings

Question 22

Acute treatment of anaphylaxia

Answer 22

Intramuscular adrenaline - 500micrograms in 0.5mls
Epipen can be self administered - 300micrograms in 0.3mls
Oxygen
IV Fluids
Antihistamines
Glucocorticosteroids

Question 23

Antihistamine example

Answer 23

Chlorpheniramine (10mg IM or IV)

Question 24

Glucocorticosteroid example

Answer 24

200mg hydrocortisone

Question 25

Differential diagnosis

Answer 25

Anaphylactoid shock - pseudo, non allergic

Idiopathic angiodema, hereditory angiodema (do not respond to adrenaline)

Question 26

What is anaphylactoid shock

Answer 26

Same as anyphylaxis but no IgE involved
Mast cells and basophils are activated by a different mechanism
IV contrast media

Question 27

What can you use to treat hereditary angiodema

Answer 27

C1 esterase inhibitor

Question 28

How to prevent anaphylaxis

Answer 28

Take careful history
Desensitisation
Omalizumab - IgE monoclonal antibody (too expensive and requires injections forever)