Anaphylaxis

Question 1

Define anaphylaxis

Answer 1

An acute, severe, life-threatening allergic reaction in pre-sensitised individuals

Question 2

What happens in anaphylaxis?

Answer 2

release of immune and inflammatory mediators from basophils and mast cells (degranulation) = SYSTEMIC RESPONSE

Question 3

Aetiology of anaphylaxis

Answer 3

•	Caused by exposure to allergen in pre-sensitised individuals
o	Drugs, foods, insect stings, exercise
•	Sometimes a cofactor (e.g. NSAIDs, alcohol) is required to provoke anaphylaxis
•	Up to ½ triggered by food
•	Anaphylaxis more common in anaesthesia
o	Most often due to neuromuscular-blocking agents
o	IV anaesthetics
o	Opioid analgesics
o	NSAIDs
o	LAs
o	Colloids
o	Latex – more common in children

Question 4

Risk factors of anaphylaxis

Answer 4

• If <30 – food, exercise
• Atopy/asthma
• Anaphylaxis history
• Common sensitiser exposure (e.g. latex)
• If >30 – food, insect venom, medicine
• Female

Question 5

Epidemiology of anaphylaxis

Answer 5

• Lifetime prevalence of between 1-2%
• food allergic reactions higher in young children
• reactions to radiocontrast media, insect stings and anaesthetics higher in adults
• Slight female predominance

Question 6

Presenting symptoms of anaphylaxis

Answer 6

• Dyspnoea
• Rhinitis
• Pruritus = severe itching
• Bilateral conjunctivitis
• Nausea and vomiting
• Abdominal cramping and pain
• Anxiety/agitation
• Confusion/disorientation
• Dizziness
• Syncope
• Sense of impending doom
• Cardiac arrest
• Diarrhoea

Question 7

Signs of anaphylaxis on examination?

Answer 7

•	Urticaria = hives 
o	Rapid swelling of the upper dermis
o	Blanching, raised, palpable wheals which can be linear or annular
•	Angio-oedema
o	Rapid swelling of the dermis, subcutaneous tissue, mucosa and submucosal tissues
•	Flushing
•	Wheezing
•	Inspiratory stridor and hoarse voice
•	Tachycardia
•	Hypotension
•	Bradycardia
•	Tremor

• Seizures

Question 8

Investigations for anaphylaxis

Answer 8

•	1st line
o	Serum tryptase (Elevated)
•	Investigations to consider
o	In vitro IgE
	>0.35
o	Skin test
	>3mm diameter and greater than control
o	Challenge test

Question 9

Management plan for anaphylaxis

Answer 9

•	Acute onset
o	ABC - Cardiorespiratory assessment and supportive measures
o	0.5 – 1.0 mg IM epinephrine/adrenaline – 1:1000
o	Assess and secure airway
o	IV normal saline
•	IF cardiopulmonary arrest
o	CPR
o	IV epinephrine
•	IF severe hypotension
o	IV epinephrine
o	IV glucagon
•	IF persistent respiratory symptoms
o	Inhaled beta-2 agonist
•	IF hives and rhinorrhoea
o	Antihistamine
•	Post-emergency stabilisation
o	Corticosteroids
o	Serum tryptase

Question 10

Complications of anaphylaxis

Answer 10

• Recurrence
• MI - hypotension -> cardiac ischaemia -> MI
• Death

Question 11

Prognosis for moderate anaphylaxis

Answer 11

o High risk of reoccurrence

o Severity of previous reaction does not predict severity of the second

Question 12

Prognosis of severe anaphylaxis

Answer 12

o Diagnosis must be made early and management initated promptly to improve outcome
o Inadequate brain perfusion may occur with cardiac arrest
o Prognosis depends on comorbidities (e.g. asthma) and age
o Mortality rates around 0.5-2%
 Half are iatrogenic