Anaphylaxis:

Question 1

Pathogenesis: what is the underlying cause?

Answer 1

IgE-mediated hypersensitivity leading to an exaggerated inflammatory response

Question 2

How does sensitisation to an allergen occur?

Answer 2

Due to a first exposure to an allergen that does not create signs or symptoms

• first exposure to an allergen causes the production of large quantities of IgE
• IgE molecules then bind to receptors on basophils and mast cells throughout the body

Question 3

What initiates this inflammatory response and what happens at the cellular level?

Answer 3

• Second or subsequent exposure
• Allergen binds to the IgE on the mast cells and basophils, which causes stimulation and degranulation of histamine
• newly synthesised mediators such as prostaglandins and leukotrienes

Question 4

What will happen in the airways in response to mediator release?

Answer 4

• hyperaemia and oedema
• bronchospasm in bronchioles
• excessive mucous production in conducting airways

Question 5

what will happen in the gut and skin in response to mediator release?

Answer 5

• muscle spasm
• hyperaemia and oedema
• hives/pruritis

Question 6

Signs and symptoms of anaphylaxis in the airway and gut?

Answer 6

• throat tightness, stridor, hoarse voice, wheeze, hypoxia, dyspnoea/tachypnoea/ increased effort of breathing
• swollen tongue, difficulty swallowing, abdominal cramps, nausea & vomiting, diarrhoea

Question 7

Signs and symptoms of anaphylaxis in skin and cardiovascular?

Answer 7

• erythema/rash, warmth, angioedema (lips, eyelids, hands, feet), itching/tingling
• tachycardia, hypotension, arrhythmias

Question 8

other neural signs and symptoms of anaphylaxis

Answer 8

-anxiety, sweating, dizzy/lightheaded, syncope

Question 9

How does adrenaline treat anaphylaxis?

Answer 9

• a1 receptors for vasoconstriction: increases peripheral resistance/BP and venous return, reduces oedema
• B2 receptors for smooth muscle relaxation: bronchodilation, GI relaxation
• B1 receptors for cardiac effects: increased force of contraction and rate (inotropic effects)

Question 10

How would you treat anaphylaxis?

Answer 10

• remove the trigger
• administer adrenaline (IM anterolateral thigh)
• manage hypotension: posture, fluids post-adrenaline
• manage respiratory compromise: oxygen and salbutamol if persistant wheeze
• steroids: reduces late phase/biphasic reactions