3. Awareness Flashcards
Awareness
Awareness is currently
one of the most common
pre-operative anxieties
expressed by patients
for whom awareness under general anaesthesia
is a terrifying experience that
can result in debilitating psychological sequelae
and even post-traumatic stress disorder.
For the anaesthetist, it can also lead to serious consequences with medico-legal claims for awareness constituting 2% of all claims made against American anaesthetists.
The 5th National Audit project (NAP 5), published in 2012, is the largest study in the world that looked at the incidence and mechanism of accidental awareness under general anesthesia (AAGA).
Figures quoted here are from the NAP
5 data.
What do you understand by the term awareness?
Awareness under general anaesthesia
is the ability to
perceive,
feel or
be consciously aware
of one’s surroundings;
this may or may not be
accompanied by the
experience of pain.
There are two types of awareness:
> Explicit memory (or recall).
This is the intentional recollection of events
with conscious perception.
> Implicit memory (or recall).
This is the non-intentional recollection of
events with subconscious perception (i.e. these patients may remember events under hypnosis).
What is the incidence of
awareness?
NAP 5 data gave an estimated
overall incidence of AAGA of 1:19 000 anaesthetics.
The incidence varied considerably
depending on the setting:
1:670 for obstetric rapid sequence inductions,
1: 8000 when a neuromuscular blockade was used
(vs. 1:136 000 without it)
and 1:8600 in cardiothoracic anaesthesia.
What are the risk factors associated with awareness?
> Phase of anaesthesia:
> Phase of anaesthesia:
• Induction and emergence
account for two-thirds
of all reported AAGA cases.
• Interrupting delivery of anaesthesia
to transfer patients from the
anaesthetic room into theatre
is also a time of risk.
> Anaesthetic drugs and techniques:
1
• Neuromuscular blocking drugs-incidence
increases
from
1:136 000
to 1:8000.
On emergence,
failure to use a nerve stimulator
to ensure adequate return of muscle power
before turning off anaesthetic
is a major contributory factor to AAGA.
2 • Total intravenous anaesthesia – no real-time plasma concentration of intravenous agent can be made and therefore pharmacokinetic models are relied upon to ‘predict’ plasma and effect site concentrations.
3
• Thiopental is associated with
an increased incidence.
4
• Rapid sequence induction.
5
• Inadequate administration of volatile agent –
MAC is the minimum alveolar concentration,
at one atmosphere ambient pressure,
required to prevent movement in 50%
of subjects in response to a surgical stimulus.
The definition does not encompass the concept
of awareness, only movement.
There is now substantial evidence
to suggest a correlation between
MAC and recall, with explicit recall
being extremely unlikely at MAC > 1.
However, MAC is influenced by a variety of factors and published data for MAC is typically quoted for healthy, unmedicated subjects. All of these factors must be taken into consideration when interpreting MAC values.
6
• Drug error –
this accounted for 10% of the reports of AAGA to NAP5.
> Patient factors
1
• Female
2
• Younger adults (but not children)
3
• Obesity
4
• Previous AAGA
5
• Patients who are unexpectedly difficult to intubate
6 • Patients with increased resistance to anaesthetic agents including those that are febrile, hyperthyroid, alcoholic and or use recreational drugs
7
• Moribund patients for emergency procedures
> Subspecialities:
• Obstetrics (includes most of the risk factors: emergency, rapid sequence induction, thiopental, neuromuscular blockade, high incidence of obesity and difficult intubations)
• Cardiothoracics
(patients on cardiopulmonary
bypass or those
undergoing bronchoscopies)
> Equipment:
• Faulty or malfunctioning equipment
• Equipment not used or programmed
correctly by the anaesthetist
> Monitoring:
• Failure to monitor concentration of
inspired and expired volatile agents
and MAC
• Failure to monitor peripheral cannula
and infusion line with TIVA
• Failure to use specific
depth of anaesthesia monitoring
(e.g. entropy, BIS etc.)
• Failure to look for clinical signs of awareness
(heart rate, blood
pressure, tachypnoea,
sweating and lacrimation)
• Absence of clinical signs of awareness
due to drugs (
e.g. β-blockers
will mask a tachycardia and hypertension,
anti-muscarinic agents
will mask sweating and tear production,
opioids will mask
pupillary dilation and
neuromuscular blockers will
mask movement and
tachypnoea)
What would you do if a patient complains they were aware under general anaesthesia?
This is a serious situation with
potentially devastating consequences to
both the patient and anaesthetist involved.
NAP 5 suggested that 41%
of patients reporting AAGA
experienced moderate or severe long-term
sequelae.
Early reassurance and
support often led to good outcomes.
Seek advice from a consultant.
1
> Visit the patient as soon as possible with a witness (preferably a consultant).
2
> Take a full history and elicit
exactly what the patient sensed
and whether they were in pain.
3
> Document all conversations.
4 > Review the medical notes and anaesthetic records and try to ascertain the cause.
5
> Be sympathetic and
if true awareness is suspected, apologise.
6
> Give a full explanation to the patient.
7
> Offer a follow-up appointment and
psychological support.
Reassure patient that this is very
unlikely to happen again.
8
> Inform patient’s GP,
the hospital administrators and
your medical defence organisation.
9
> Complete a critical incident form.
10
> Debrief with your consultant to
try to determine what, if anything, could
have been done differently.
