Be wary of awareness – lessons from

NAP5 for Obstetric

anaesthetists

Editorial: International Journal of Obstetric Anesthesia (2015)

24, 1–4

Introduction

• 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 general anaesthesia."

History• Until the early 1970s it was standard practice

• To use doses of Thiopental in the region of 200–250 mg for induction

• 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 as 4%

• The recommendation by Moir in 1970 that 0.5% halothane should be added to the gas mixture reduced this to less than 2%

Present times

• 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.

NAP5• 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 routes.

• All reports were scrutinized and categorized by a panel that included representatives from the Obstetric Anaesthetists' Association (OAA).

Caveat 1

• 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 system;

• This meant that many of the cases happened outside the one-year study, sometimes many years or even decades previously.

Caveat 2

• 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 included.

• These latter cases, numerous though they were in the final report, have little or no impact on the obstetric data.

Caveat 3• The NAP5 audit relied solely on spontaneous

reporting of awareness.

• Modern interventional studies, in contrast, use some variation of the Brice Protocol, a structured postoperative questionnaire, to determine whether patients were aware during anaesthesia.

• 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 1:20 000.

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 caesarean sections.

• 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''.

Problem 1• 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 per month.

Thiopental • 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 obstetric cases.

• 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.

Problem 2

• 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

Problem 3• 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.

Other problems..

• 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.

Syringe swap• 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 resuscitation.

• 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 section.

Research suggestions• 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.

Consent

• 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 risk

• 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.

Conclusion • 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 techniques.

• 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.