ILA 2 - Anaphylaxis

Question 1

Define Anaphylaxis

Answer 1

Type 1 hypersensitivity.

Sudden onset and rapid progression of symptoms.
Life threatening airway/breathing/circulation problems, usually associated with skin/mucosal changes. Priming then reexposure

Question 2

Signs/symptoms of anaphylaxis

Answer 2

Hypotension
Vasodilation
Increased vascular permeability
Bronchoconstriction
Urticaria
Angiooedema

Question 3

Pathogenesis of anaphylaxis

Answer 3

• Initial exposure to antigen causes IgE antibodies to form, which bind to mast cells and basophils. Cells primed to react on reexposure
• Reexposure causes cross linking of IgE on cell surfaces, causing rapid mast cell degranulation.
• Release of histamine, leukotrienes, prostaglandins, platelet activating factor.

Question 4

Physiological responses to anaphylaxis mediators

Answer 4

• Smooth muscle spasm
• Vasodilation
• Increased vascular permeability
• Increased mucus secretion and bronchial smooth muscle tone. (resp symptoms)
• Decreased vascular tone and capillary leakage (CVD symptoms)

Hypotension, syncope, shock

Question 5

What do
H1
H2
H3
Receptors cause?

Answer 5

H1 - vasodilation/constriction, hypotension and flushing. Tachycardia, bronchospasm, rhinorrhoea
H2 - Atrial and ventricular chronotrophy and coronary artery vasodilation.
H3 - Importance unknown in humans.

Question 6

Treatment of anaphylaxis

Answer 6

IM Adrenaline 500mcg. Anterolateral aspect of the middle third of the thigh.

Lie patient on back with legs up.

Chlorphenamine can also be used (H1 receptor blocker)

Question 7

Effects of beta 1 and beta 2 stimulation

Answer 7

B1 - Positive ionotropic (heart contraction force) and chronotropic (heart rate) effects
B2 - Bronchodilation, reduces oedema. Increased C-AMP, reducing inflammation.

Question 8

Effects of alpha 1 and alpha 2 stimulation

Answer 8

A1 - Found in vascular smooth muscles. Stimulation causes vasoconstriction and increased BP.
A2 - Presynaptic neurones. Negative feedback for norepinephrine, decrease sympathetic activity. Also cause platelet aggregation.

Question 9

Why does adrenaline often need a second dose? What is the confirmatory blood test for anaphylaxis?

Answer 9

• 2nd dose needed as adrenaline has short half life.
• Serum mast cell tryptase, marker of degranulation. Levels peak 1 hour after, remain high 6 hours.

Question 10

What factors aid increased incidence of anaphylaxis

Answer 10

Family history
Increased pollution
Increased allergen exposure
Increased treatment/ cleanliness.