Allergic reaction

Question 1

What is the name of the rash associated with an allergic reaction?

Describe it.

Answer 1

Urticaria

Swollen, pale red bumps or wheals
They appear suddenly
They are itchy, burny and stingy

Question 2

Which systems are affected in an anaphylaxis reaction?

Describe how they’re affected?

Answer 2

Skin:

• flushing
• angioedema
• itching, burning

Resp:

• bronchospasm
• SOB, wheeze
• upper airway swelling causing stridor, hoarseness

CVS:

• coronary vasospasm leading to MI, arrest
• shock, low BP, high HR, pale, clammy, LOC

GI:

• cramps, colic
• nausea + vomiting

Question 3

What’s the difference between anaphylactic and anaphylactoid reactions?

Answer 3

Anaphylaxis: immunologic, IgE mediated, usually more serious and life threatening

Anaphylactoid: non-immunologic, not IgE mediated, complement mediated

Question 4

Describe the mechanism of anaphylactic reactions?

Answer 4

• IgE binds to the antigen the person is sensitive to to
• IgE-antigen complex activates receptors on mast cells and basophils causing them to degranulate
• leading to release of histamine + other inflammatory mediators
• these cause bronchial muscle contraction, vasodilation, fluid leakage from capillaries

Question 5

What are some common allergens for anaphylactic and anaphylactoid reactions?

Answer 5

Anaphylaxis: shellfish, buts, wheat, milk, eggs, venom

Anaphylactoid: contrast medium, drugs, opioids

Question 6

Describe the mechanism of anaphylactoid reactions?

Answer 6

• Complement mediated, causes degranulation of mast cells and basophils
• leading to release of histamine + other inflammatory mediators
• these cause bronchial muscle contraction, vasodilation, fluid leakage from capillaries

Question 7

How do patients having anaphylactic reaction usually present?

Answer 7

Sudden onset SOB, wheeze, stridor

Swelling of lips, airway

Urticaria

Nausea and vomiting

Anxiety, tachycardia

Question 8

How would you manage a non-anaphylactic but severe allergic reaction?

Answer 8

Anti-histamine: chlorphenamine

Steroid: hydrocortisone

Salbutamol nebs

You only give adrenaline if you think it is definitely anaphylaxis

Question 9

How would you know if an allergic reaction is true anaphylaxis?

Answer 9

Meeting these 3 criteria

1. sudden onset and rapid progression of symptoms
2. life threatening A, B, C problems
3. skin and mucosal changes (flushing, urticaria, angioedema)

Question 10

How would you manage an anaphylaxis?

Answer 10

Adrenaline IM
500mcg in adults
Less in children

IV fluid bolus to treat hypotension

Anti-histamine: chlorphenamine

Bronchodilators: salbutamol nebs

Sometimes:

• vasopressin
• noradrenaline
• meteraminol

Question 11

How can adrenaline be given?

Answer 11

IM (usually)

IV: good for peri-arrest situation, only by experienced specialists, as can cause harmful side effects (hypertension, tachycardia, arrhythmia)

Question 12

How does adrenaline help in anaphylaxis?

Answer 12

Agonist of a1, a2, b1, b2 receptors

Causes sympathetic effects

a1: vasoconstriction of vessels supplying skin, mucosa
b1: increases heart rate and strength of contraction
b2: vasodilation of vessels supplying heart and muscles

Question 13

What do these drugs do?

Vasopressin
Meteraminol

Answer 13

Vasopressin: synthetic antidiuretic hormone, causes body to retain water, increasing BP

Meteraminol: potent sympathomimetic amine used to raise BP

Question 14

What is a biphasic reaction?

How common?

Answer 14

When there’s recurrence of symptoms after an asymptomatic window

Up to 20%

Question 15

Who is at highest risk of a biphasic reaction?

Answer 15

Severe reaction with slow onset

Those with severe asthma

Presenting at evening or night (as less able to respond to deterioration)

History of biphasic reaction