Immuno - Anaphylaxis

Question 1

How are hypersensitivity reactions classified?

Answer 1

Classified into five groups:
Type I: Immediate hypersensitivity- IgE mediated- e.g Anaphylaxis, allergic rhinitis, asthma
Type II: antibody-mediated- IgG or IgM and complement- e.g. autoimmune haemolytic anaemia, Goodpasteur’s disease, rheumatic heart disease
Type III: immune-complex mediated- IgG and complement- e.g. Lupus nephritis, rheumatoid arthritis
Type IV: delayed (cellular) hypersensitivity- T cells, macrophages, histiocyte mediated- e.g. contact dermatitis, chronic transplant rejection, coeliac disease.

Question 2

What is anaphylaxis?

Answer 2

A severe, life-threatening, systemic hypersensitivity reaction.
Can be further subdivided into allergic or non-allergic.

Allergic:
- IgE mediated immunological reaction with histamine and pro-inflammatory cytokine release.
- leads to vasodilatation, capillary leak and bronchoconstriction.

Non-allergic:
- direct drug reaction
- Mast cell and basophil degranulation.

Question 3

What are the signs and symptoms of anaphylaxis?

Answer 3

Patient may complain of metallic taste or feeling very unwell (impending sense of doom).
Commonest clinical features are:
- Cardiovascular: hypotension from vasodilatation secondary to histamine
– Skin: skin rash/urticaria
- Respiratory: bronchoconstriction, upper airway oedema and swelling.

Question 4

What are some of the common triggers for anaphylaxis that are used in Critical Care?

Answer 4

Medications:
1. Antibiotics - predominantly pencillins and teicoplanin
2. Muscle relaxants
3. Anaesthetic induction agents - thiopentone

Equipment:
1. Latex - cross reactivity with strawberry and kiwi
2. Chlorhexadine
3. IV contrast, blue dye (breast surgery)

Question 5

How should you manage an acute anaphylactic reaction?

Answer 5

AAGBI guidance:Immediate management:
- Resuscitate in an A-E approach.
- Stop offending agents
- Secure airway
- 100% oxygen- Call for help
Specific management:- Give adrenaline 1:1000 IM 0.5ml (500mcg) OR 50mcg IV- Fluid bolus and vasopressors
- Once stable:- Mast cell tryptase investigations: - time 0, time 1 hr, time 6-24 hrs.
- Follow-up:- Reactions should be reported: yellow card, to GP, to patient in writing
- - Referral to Regional Allergy Centre

Question 6

What is the dose of adrenaline IM in anaphylaxis?

Answer 6

Adult or child >12= 500mcg or 0.5ml (1:1000) IM
Child 6-12 = 300mcg or 0.3ml (1:1000) IM
Child 6m to 6y = 150mcg or 0.15ml (1:1000)
IMRepeated again after 5mins if not effective.