70. Previous anaphylaxis Flashcards
A patient with a history of anaphylaxis during general anaesthesia
3 months ago now presents for an evacuation of retained products of
conception.
Discuss the anaesthetic management of this patient
The details of the episode must be established from the notes and the patient.
The reaction may have been
True anaphylaxis (Type I IgE mediated or Type III immune complex, IgG mediated)
Anaphylactoid (histamine release directly or by complement)
An alternative diagnosis that was misinterpreted either by the anaesthetist or the patient, such as:
Asthma
MH
Angio-oedema
Vaso-vagal episode.
All drugs given during the previous episode should be avoided if possible.
What would you use/avoid
Volatile anaesthetics have not been reported to cause anaphylaxis, so an
inhalational technique would be safe if the patient was not thought to be at
risk of regurgitation. A spinal anaesthetic may also be considered, although
local anaesthetic allergy is possible.
There is insufficient time to establish the cause of the anaphylaxis and the
surgery is urgent. The safest method of proceeding may be with a gas
induction and maintenance of anaesthesia with avoidance of colloids and
latex exposure.
Specific things to avoid
Avoid any drugs given in the initial anaesthetic if these can be identified,
unless a specific drug has been implemented.
There is significant cross over in related drugs,
especially non-depolarising
muscle relaxants (NDMRs)
Do not give cephalosporins or imipenem to those with suspected or
confirmed penicillin anaphylaxis.
There may be a history of non-pharmacological reaction. The quaternary
ammonium group of NDMRs are shared by some foods, cosmetics and
hair-care products.
There have been no reports of anaphylaxis to volatile anaesthetic agents, so
an inhalational technique is possible.
What investigations for anaphylaxis would this patient have undergone
post-operatively?
Serum tryptase:
Released by degranulating mast cells in an IgE reaction.
It should be measured ideally at 0, 1, 6 and 24 hours (in reality the zero
time means as soon as possible after resuscitation).
The half-life of tryptase is 2.5 hours.
Peak concentration at 1 hour (may be earlier in cases with associated
hypotension).
The peak may be missed if the early samples are not taken.
Skin prick testing
Gold standard
Remember all the possible allergens such as latex, chlorhexidine,
antibiotics, colloids and lidocaine.
If skin prick testing is negative and there remains a strong clinical
suspicion, then intradermal testing can be considered.
Radioallergosorbent test (RAST)
Involves laboratory exposure of antigen to patient serum to identify IgE
reactions. Coated allergen particle (CAP) is a newer test.
Only really useful for suxamethonium, latex and penicillin, although
many other RASTs exist (with lower specificity).
When should you perform skin testing?
Skin prick testing should be performed 4–6 weeks after the event to allow
IgE stores to regenerate.
It needs to be done at a centre experienced in the performance and
interpretation of such tests.
Resuscitation equipment should be available.
What is the evidence for pre-medicating this patient with an
antihistamine in these circumstances?
Some would advocate pre-medication with an antihistamine and
hydrocortisone, but there is no convincing evidence that this reduces the
incidence of anaphylaxis
Which induction agent is least likely to cause anaphylaxis?
Which induction agent is least likely to cause anaphylaxis?
There is not enough data to state which induction agent is more or less
likely to cause a reaction but thiopentone has the longest safety history of
all currently used agents.
Reactions to anaesthetic drugs are rare and the incidence in the UK is unknown.
The RCA estimates the risk of life-threatening anaphylaxis to be between 1
in 10 000 and 1 in 20 000 anaesthetics.
Further information regarding anaphylaxis
In France, the incidence of anaphylaxis to neuromuscular blocking
agents (NMBs) is 1 in 6500 anaesthetics.
In one study of 477 confirmed reactions, NMBs accounted for 62%,
latex 17%, antibiotics 8%, hypnotics 5% and colloids, opioids and
others approximately 3% each.
17% of allergies to NMBs had not had a previous anaesthetic.
With allergy to NMBs, previous exposure was found in less than 50%
of patients.
Previous exposure to the allergic agent is not necessary
How would you recognise anaphylaxis if the patient was anaesthetised?
88% present with signs of cardiovascular collapse related to distributive shock.
There may be:
Tachycardia
Hypotension
Low cardiac output state (seen as a reduced ET CO2).
Cardiovascular collapse is the only feature in 10% of cases.
36% present with bronchospasm due to histamine release.
Angio-oedema is present in 24% of cases.
Isolated cutaneous erythema is often seen due to local histamine release,
commonly after atracurium, morphine or thiopentone injections. This is
usually trivial but may represent the first sign of impending anaphylaxis.
If this patient presented for a peripheral limb operation, how would
you anaesthetise her?
A regional technique such as spinal, supraclavicular or interscalene block could
be performed, but care must be taken as the causative agent may have been
latex, chlorhexidine, local anaesthetic agent or colloid.
