Anaphylaxis

Question 1

Define

Answer 1

Acute life-threatening multisystem syndrome caused by sudden release of mast cell- and basophil-derived mediators into the circulation

Question 2

Causes

Answer 2

• Immunogenic - IgE-mediated or immune complex/complement-mediated
• Non-Immunogenic - mast cell or basophil degranulation WITHOUT the involvement of antibodies (e.g. reactions caused by vancomycin, codeine, ACE inhibitors)

Pathophysiology

• Inflammatory mediators such as histamine are released leading to bronchospasm, increased capillary permeability and reduce vascular tone
• This leads to tissue oedema

Common Allergens

1. Drugs (e.g. penicillin)
2. Latex
3. Peanuts
4. Shellfish
5. NOTE: anaphylaxis can be caused by the repeat administration of blood products in a patient with selective IgA deficiency (due to the formation of anti-IgA antibodies)

Question 3

Epidemiology

Answer 3

more common in atopic individuals

Question 4

Symptoms

Answer 4

Wheeze

Shortness of breath and a sense of choking

Swelling of lips and face

Pruritus

Rash

NOTE: patients may have a history of other hypersensitivity reactions (e.g. asthma, allergic rhinitis)

Question 5

Signs

Answer 5

Tachypnoea

Wheeze

Cyanosis

Swollen upper airways and eyes

Rhinitis

Conjunctival infection

Urticarial rash

Hypotension

Tachycardia

Question 6

Investigations

Answer 6

Diagnosis is made clinically

↑Serum tryptase (15 mins –3 hours after onset of symptoms)↑Histamine levels (30 mins after onset)
↑Urinary metabolites of histamine (remain ↑ for several hours)

*Note: Normal levels of these mediators do not exclude possibility of anaphylaxis

After the attack

• Allergen skin testing – identify the allergen
• Only performed by a specialist due to risk of repeat anaphylaxis
• IgE immunoassays – Radioallergosorbent tests (RASTs) to identify food specific IgE in serum

Question 7

Management

Answer 7

ABCDE

Stop suspected drugs
Secure airway, 100% O2
IM Adrenaline (repeat every 10mins dependant on HR and BP) IV antihistamine (chlorpheniramine)
IV steroids (hydrocortisone)
IV crystalloid or colloid to maintain BP

Treat bronchospasm with salbutamol ±ipratropium

Advice

• Educate on use of IM adrenaline pen
• Provide MedicAlert bracelet
• Note in pt notes and drug charts
• Refer to allergy specialist

Question 8

Complications

Answer 8

Respiratory failure, shock, death

Question 9

Prognosis

Answer 9

Good if prompt tx given