A review of the NAP 5 final report
Published on: Mar 3, 2016
Transcripts - NAP 5
Be wary of
lessons from NAP5
International Journal of Obstetric Anesthesia (2015) 24, 1–4
• The obstetric anaesthetist has become an integral
and respected player in the modern multidisciplinary
maternal care team.
• "Are we failing in what might be considered our most
basic task: keeping women unconscious during
• Until the early 1970s it was standard practice
• To use doses of Thiopental in the region of 200–250 mg for
• To maintain anaesthesia with nitrous oxide in oxygen alone,
• trying to avoid neonatal sedation and a loss of uterine tone
with concomitant increased blood loss.
• Under this regimen, awareness rates were reported to be as high
• The recommendation by Moir in 1970 that 0.5% halothane should
be added to the gas mixture reduced this to less than 2%
• That the problem still persists today was highlighted
in a recent epidemiological study carried out by the
Australian and New Zealand College of
Anaesthetists (ANZCA) who reported:
• An incidence of awareness in obstetric patients of
0.26%, albeit with rather small numbers.
• Carried out jointly in the UK and Ireland by the Royal College
of Anaesthetists and the Association of Anaesthetists of Great
Britain and Ireland.
• Largest study of its kind, anesthetic coordinators in all 329 UK
hospitals collated reports of AAGA and submitted them
monthly to the NAP5 panel
• The Royal Colleges of General Practitioners and of
Psychiatrists were also involved, along with other specialist
bodies, to try to capture patients who reported via other
• All reports were scrutinized and categorized by a panel that
included representatives from the Obstetric Anaesthetists'
• For a case to be included, it was not necessary
that the AAGA event had occurred during the
study period, only that it was the first time the
incident had ever been reported to the healthcare
• This meant that many of the cases happened
outside the one-year study, sometimes many
years or even decades previously.
• The definition of AAGA agreed from the out-set by
the panel involved a patient or their carer reporting
that they had been awake for a period of time when
they expected to be unconscious.
• Controversially perhaps, this means that sedation
cases where patients mistakenly believed that they
should have been fully anaesthetised were
• These latter cases, numerous though they were in
the final report, have little or no impact on the
• The NAP5 audit relied solely on spontaneous reporting
• Modern interventional studies, in contrast, use some
variation of the Brice Protocol, a structured postoperative
questionnaire, to determine whether patients were aware
• When interviewed using this tool, patients generally
report rates of awareness in the order of 1:600 (0.17%).
• The over-all incidence of spontaneously-reported AAGA
in NAP5 was around 30 times lower than this, at 1:20
NAP 5 : Obstetric data
• The overall rate of AAGA for all obstetric procedures in NAP5 – and
the reason we need to be concerned – was 1:1200 (0.08%) rising to
1:670 (0.15%) for caesarean section.
• We should bear in mind that the reported incidence of AAGA during
caesarean section when sought by Brice interview is 1:384.
• Some of the explanation for the difference between NAP5 rates for
obstetric and non-obstetric patients may be that mothers are more
likely to spontaneously report awareness when it occurs, because
many units operate a robust follow-up process, especially for
patients who required general anaesthesia.
• Obstetric cases represented only 0.8% of all general
anaesthetics in the Activity Survey but 10% of all reported
cases of AAGA.
Factors increasing AAGA
• Patient factors included female gender, young age group,
obesity and difficult airway.
• Organizational risk factors were junior anaesthetist, out-of-
hours and emergency surgery.
• Anaesthetic factors included use of thiopental, rapid-
sequence induction and the use of neuromuscular blockade.
• It is quite clear that many of these risks combine in obstetric
practice to produce a ‘perfect storm' for awareness. It may
even be that, as general anaesthesia becomes increasingly
reserved for only the most urgent of cases, this storm may
be gathering force rather than waning.
NAP 5 : Obstetric data
• There were 16 such accounts, 14 of which were
• All episodes of awareness were judged to have
occurred at, or very shortly after, induction of
anaesthesia, and all were short-lived.
• In all but one case, the duration was less than
five minutes, and in 10 cases awareness was felt
to have lasted only a few seconds.
"Mind the gap!"
• The problem seems to lie within that inherently
unstable period when the intra-venous agent is
wearing off, the volatile partial pressure is
building and, frequently, early surgical stimulation
is maximising afferent cerebral input.
• The NAP5 authors go to some lengths to warn
anaesthetists about the potential for awareness in
the intravenous-inhalational interval, using a
phrase borrowed from the London Underground:
‘‘Mind the gap''.
• The first of these – and perhaps the most
controversial – is the drug many of us choose to
use for induction.
• Thiopental is still the most commonly employed
induction agent in obstetrics in the UK, but its use
is increasingly rare for non-obstetric procedures.
• A survey of British anaesthetists shows that 55%
‘hardly or never' use the drug for indications other
than obstetrics and that 87% use it less than once
• While thiopental's association with AAGA is probably an indirect one
resulting from its use in rapid-sequence induction, it behoves us to
carefully reconsider whether the maternal and fetal benefits of this
drug outweigh its risks, especially as we become less familiar with it
in day-to-day practice and its availability diminishes outside the UK.
• If we do stick with thiopental, what dose should we use? Doses were
reported as being ‘low' or less than 4 mg/kg in 50% of the NAP5
• The need for a higher dose in obstetric patients has long been
recognized and, in one study, increasing the dose from 3–4 mg/kg
to 5–7 mg/kg contributed to a reduction in incidence of awareness
from 1.3% to 0.4%.
• The authors of NAP5 suggest that a dose of at least 5 mg/kg should
be used for the healthy parturient.
• The other end of the gap is, of course, the time
taken to achieve adequate partial pressures of
gaseous agents after tracheal intubation.
• High initial concentrations of volatile agent
(‘overpressure') with high gas flows can be of
help here, and the authors also stress the role of
nitrous oxide – another agent falling out of favour
in general anaesthetic practice – in achieving this
• Anything that prolongs the gap between administration of
intravenous induction and delivery of volatile agent is likely
to increase the risk of AAGA, such as difficulty in
managing the airway which was a feature of 64% of the
NAP5 obstetric cases.
• The authors recommend that
• Anaesthetists should decide before induction what steps
will be taken if intubation is unsuccessful and,
• Where it is felt beforehand that general anaesthesia
should be maintained if this situation arises, a second
syringe of intravenous agent should be prepared before
induction for this purpose.
• Two other ‘gap'-related cases in NAP5 arose
from failure to turn on the volatile agent vaporiser
after tracheal intubation.
• In another two cases, retrograde flow of the
induction agent along the intravenous giving set
was considered to be contributory.
• There were, in addition, two syringe-swap incidents.
• One of these was complex and unlikely to recur, involving a
large dose of intravenous lidocaine given in place of an
antibiotic; the patient had some recall of the subsequent
• The other patient received cefuroxime instead of thiopental and
so was awake when the muscle relaxant took effect.
• This latter issue may be more likely to arise as a result of recent
UK guidance to administer antibiotics for caesarean section
before skin incision and, of course, the stressful and time-limited
nature of induction of general anaesthesia in obstetric practice
provides fertile soil for any syringe-swap error
Failed neuraxial block
• Of interest, four of the cases of AAGA occurred in
patients in whom spinal or epidural anaesthesia
had been the first choice but had failed.
• The authors highlight the fact that patients needing
conversion from neuraxial to general anaesthesia
are exposed to the risks of both of these
techniques, and that conversion appears to be a
risk factor in its own right for airway complications
and for AAGA.
• Perhaps the inherent stress of such situations
adversely impacts performance.
Depth of Anaesthesia monitoring
• No information could be gleaned about the effect
of the use of depth of anaesthesia (DOA)
monitoring as none of the obstetric cases of
awareness was recorded as having such a
monitor in place.
• It is difficult to imagine how DOA monitoring could
be usefully employed in a cate-gory 1 caesarean
• Obstetric chapter of NAP5 carries suggestions for a number of
areas of research which could help to provide much-needed
evidence in this field.
• Suggested research topics
• Thiopental doses
• Thiopental vs Propofol debate,
• Optimum use of opioids
• Determining safe minimum inspired oxygen levels (thus
allowing additional nitrous oxide)
• Maintenance of uterine tone after delivery in the presence of
effective partial pressures of volatile agent.
• Given that the risk of AAGA remains relatively
high for Caesarean section, the NAP5 chapter on
consent is clear that any patient undergoing
general anaesthesia should be informed of this
• Prior to a category 1 caesarean section, a brief
mention of possible sensations during induction
along with a description of cricoid pressure might
be all that is possible.
• In our pursuit of greater safety through the increased
use of neuraxial techniques, we may have taken our
eye off the ball:
• NAP5 suggests that it is time we redirected our
attention and update our obstetric general anesthetic
• Whether it is further evidence that the obstetric
patient is inherently high risk and thus should be
anaesthetised by specialists who are either
consultants or who are directly supervised by
consultants is open for discussion.