Anaphylaxis

Question 1

Definition

Answer 1

Life-threatening condition that in a severe, generalised or systematic hypersensitivity causing obstruction to the airway +/- breathing +/- circulation problems that is usually associated with skin and mucosal changes

Question 2

Pathophysiology

Answer 2

TYPE 1 HYPERSENSITIVITY REACTION: Exposure to allergens causes IgE-mediated activation of mast cells and basophils.

• Sensitisation phase: where allergen is taken up by the antigen-presenting cells that interact with Th2 cells which stimulates B cells to produce allergen-specific IgE
• If a patient is re-exposed to the same allergen and binds to IgE antibodies = cross-linking and aggregation = mast cell degranulation = histamine, typtase, cytokines, prostaglandins, and leukotrine release

Question 3

Epidemiology

Answer 3

Previous anaphylactic shock
History of atopy
Higher socioeconomic background

Question 4

Resus Council Triad

Answer 4

• Sudden onset and rapid progression of symptoms (<15 mins)
• A irway and/or B reathing and/or C irculation problems
• Skin and/or mucosal changes (flushing, urticaria, angioedema) – but these may be absent in up to 20% of cases

Question 5

Signs

Answer 5

Hypotensive/Tachycardic
Tachypnoiec
Urticarial rash

Question 6

Symptoms

Answer 6

Exposure to allergen
Angioedema: swelling of the face, tongue, larynx, resulting in difficulty in breathing
Stridor and wheeze
Pruitus and rash
Dizziness
Syncope

Question 7

Diagnosis

Answer 7

GOLD STANDARD = Mast cell tryptase:
- Measured on 3 occasions:
= immediately after treatment
= 1-2 hours post-reaction
= 24 hours post reaction
- Elevated levels seen up to 12 h after and return to baseline at 24 hr
Consider:
- Skin prick test
- Patch test
- Radioallergosorbent test (RAST)
- Challenge test

Question 8

Treatment

Answer 8

FIRST LINE = IM Adrenaline
- best in the anterolateral aspect of the middle third of the thigh
- repeat after 5 mins if ABC problems persist
Important to maintain supine position + avoid sudden changes in posture

Question 9

Refractory anaphylaxis

Answer 9

• Where there is no improvement in respiratory or cardiovascular symptoms despite two appropriate doses of IM Adrenaline
• IV fluids given early if hypotension or shock present
• IV adrenaline infusion

Question 10

Discharge

Answer 10

Fast track > 2 hours
- Good response 5-10 mins of single dose given with 30 min of onset AND
- Complete resolution of symptoms
- Px has un-used epipen (+trained) AND
- Adequate supervision following discharged
Min 6 hr obs
- 2 doses OR
- Previous biphasic response
12 hr obs - any one of:
- Severe reaction needing > 2 doses of adrenaline
- Px has severe asthma or reaction involved severe resp comp
- Possibility of continuing absorption of allergen (slow release meds)
- Patient presents late at night or may not be able to respond to any deterioration
- Patients in areas where access to emergency care is difficult

Question 11

Follow up

Answer 11

Referral to allergy specialist
Adrenaline auto-injector (2 devices)