1. Anaphylaxis

Question 1

What is it

Answer 1

Anaphylaxis is an acute, 
Type 1 hypersensitivity reaction 
caused by antigens binding 
to IgE immunoglobulin 
on mast cells and 
causing them to degranulate. 

These mast cells release ‘anaphylatoxins’,
mainly histamine, prostaglandins and leukotrienes.

It is these mediators that are
responsible for the physiological effects
of anaphylaxis –

vasodilatation,
increased capillary permeability
and smooth muscle constriction.

In order to undergo an anaphylactic reaction
the patient must have been previously sensitised
to the antigen
(in this context, a drug).

However, there are increasing reports
of cross-sensitivity between
environmental pathogens and
anaesthetic agents,

especially the non-depolarising muscle relaxants
such as rocuronium,
meaning that a patient
can undergo anaphylaxis
following their first exposure to the drug

Question 2

What are the signs in an

anaesthetised patient?

Answer 2

1. > Flushing and weals.

2. 
> Wheezing, 
bronchospasm and 
rising airway pressures, 
which can make ventilation difficult.

3
> Oedema of face,
lips and oropharynx,
which may precipitate airway obstruction.

4. > Pulmonary oedema may also
   develop compounding hypoxia.

5
> Hypotension, which may become
profound with complete circulatory collapse.

6
> Tachycardia

Question 3

Differential diagnosis:

Answer 3

Other causes of the same symptoms must be ruled out, for example:

> Haemorrhage

> Asthma

> High regional block

> Myocardial infarction

> MH

The temporal nature of events may aid diagnosis of anaphylaxis.

Question 4

How would you manage a case
of suspected anaphylaxis?

> Immediate management:

Answer 4

> Immediate management:

1 • State that this is an anaesthetic emergency
and that you need to call
for senior anaesthetic assistance.

2
• Stop giving the offending drug.

3
• Secure the airway and give 100% oxygen.

4
• If the patient is paralysed,
maintain anaesthesia using inhalational
agent (volatiles are not associated with anaphylaxis).

5
• Administer adrenaline 50–100 μg IV
(0.5–1 mL of 1:10 000 solution).

6
• Repeat this dose every minute 
until there is an improvement in
symptoms or deterioration to cardiac arrest, 
in which case move onto
the advanced life support algorithm.

7
• Give crystalloid or colloid IV
to increase circulating volume.

8. • If possible, elevate the patient’s legs to improve central blood volume.

Question 5

> Early management:

Answer 5

1. • Give antihistamines – chlorpheniramine 10 mg IV.

2
• Administer steroids – hydrocortisone 200 mg IV.

3
• Administer regular bronchodilators if necessary.

4
• Consider inotrope or vasopressor infusion
if indicated – adrenaline or noradrenaline.

5
• Administer bicarbonate if the
patient is severely acidotic.

6
• At 1 hour, take blood for serum tryptase levels.

7
• Admit to ITU and leave intubated
if the airway or ventilation is of concern.
8
• Check for a cuff leak prior to extubation.

Put 10 mL of blood into a plain glass tube and send straight to the laboratory where it needs to be stored at –20 °C.
An elevated serum tryptase level confirms mast cell degranulation and therefore anaphylaxis.

Question 6

Subsequent management:

Answer 6

Subsequent management:

1
• It is the responsibility of the anaesthetist
 involved in the case to refer
the patient to an immunologist 
for further allergy testing.

2
• A yellow card (found in the back of the BNF) should also be
completed to report the adverse reaction.

3
• Document events in the notes, inform the patient of events, send a
letter to the GP and complete a critical incident form.