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Correspondence NAP5 and depth of anaesthesia monitoring We read with interest the editorial by Avidan and Mashour [1] accompanying the National Audit Project (NAP)5 baseline report by Pandit et al. [2]. We are somewhat surprised at the criticism of the methodology of this study and the inference that this may lead to an underreporting of the true incidence of awareness. Considering that surgical procedures are commonly performed under regional anaesthesia or monitored anesthesia care in fully awake or sedated patients, we question the significance of awareness during surgery that is not reported. If it isn’t reported then it could be contested that it is not something that has distressed the patient, especially when this is a topic that is widely reported in the media and when UK patients do not appear reluctant to complain or even litigate. It is also important, from the same perspective, to differentiate between awareness with and without pain, the latter, as with regional anaesthesia, being unlikely to trouble patients. It is also difficult to understand how the results from the NAP5
baseline report support Avidan and Mashour’s elaboration on total intravenous anaesthesia (TIVA), bispectral index (BIS) and end-tidal anaesthetic concentration. Firstly, the assertion that TIVA is associated with a higher incidence of awareness with recall is based on a study from Spain (in which the interview details were not published) [3] and one from China [4]. In the former, the incidence of awareness with recall in TIVA was even less than the average US incidence reported in the AIM trial [5], and the latter reports exceptionally high incidences of awareness with recall no matter what technique of anaesthesia was used. Neither of these studies could provide details on the TIVA technique and the dose of anaesthetic. Such figures suggest serious problems with the way anaesthesia is being delivered generally and make it impossible to know whether TIVA was being used appropriately. Other studies suggest no difference in the incidence of awareness with TIVA compared with inhalation anaesthesia [6–8]. Secondly, TIVA has meanwhile gained in popularity. In many earlier audits, it was an uncommon
technique mainly performed by ‘enthusiasts’, hence the risk of awareness was difficult to quantify in comparison with inhalation anaesthesia techniques. Although TIVA requires careful monitoring of the intravenous infusion site there is, however, no other reason why TIVA should increase awareness risk. In fact, the ability to titrate to clinical effect at induction using target controlled infusions is a distinct advantage over inhalational anaesthesia, induction of which is usually with an intravenous drug and subsequently delivered according to minimum alveolar concentration (MAC), the statistically ‘mean’ dose. Although it is possible to measure end-tidal concentrations of inhalational agents, anaesthetic management based on concentration has not been shown to reduce awareness in itself. In the B-unaware study [9], awareness with recall occurred even when BIS values and end-tidal anaesthetic concentrations were within the target ranges. Indeed, the incidence of explicit recall was no different whether end-tidal anaesthetic concentration was used or not in a large prospective Scandinavian study [7]. The inherent
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variability of MAC [10] makes it, therefore, problematic to suggest protocols to reduce awareness with recall based on end-tidal anaesthetic concentration only. Thirdly, it is erroneous to recommend that a processed EEGbased monitor (pEEG) be used in order to decrease the likelihood of awareness with recall if TIVA is chosen. These monitors may be useful irrespective of the anaesthesic technique used but also have significant limitations. The only reason that they could be more useful with TIVA is for the same reason that TCI can be titrated. As for pEEG, for intravenous and volatile agents alike, at least with TCI this can be titrated during induction. Not only does pEEG show remarkable intraindividual variability at loss of consciousness, it also varies according to the anaesthetic drug(s) used [10]. With TIVA the same drugs are used during induction and maintenance. Consequently, if used, pEEG can be titrated to clinical signs of loss of consciousness, potentially increasing reliability and effectiveness. When intravenous induction is followed by volatile maintenance, this advantage is lost and, again, effectiveness is based on statistical probability. Bispectral index (BIS) monitoring is probably the most commonly used pEEG monitor. Only two relevant prospective, randomised, controlled trials, concluded that BIS monitoring was of benefit to high-risk patients, the Baware study (supported in part by the manufacturer) and the BIS cardiopulmonary bypass study, which was underpowered to detect an effect [11, 12]. 974
Correspondence
Although brain function monitors in general may add a certain value in titrating anaesthetic drugs, the low utilisation of these devices found in the NAP5 baseline report still appears to be associated with a lower incidence of awareness with recall than expected. Therefore, it seems that more evidence needs to be produced to promote their use solely to prevent awareness with recall. M. G. Irwin University of Hong Kong Hong Kong, China Email:
[email protected] S. Schraag Golden Jubilee National Hospital Glasgow, Scotland
No external funding and no competing interests declared. Previously posted on the Anaesthesia correspondence website: www.anaesthesia correspondence.com.
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1. Avidan MS, Mashour GA. The incidence of intra-operative awareness in the UK: under the rate or under the radar? Anaesthesia 2013; 68: 334–8. 2. Pandit JJ, Cook TM, Jonker WR, O’Sullivan E. A national survey of anaesthetists (NAP5 Baseline) to estimate an annual incidence of accidental awareness during general anaesthesia in the UK. Anaesthesia 2013; 68: 343–53. 3. Errano CL, Sigl JC, Robles M, et al. Awareness with recall during general anaesthesia: a prospective observational evaluation of 4001 patients. British Journal of Anaesthesia 2008; 101: 178–85. 4. Xu L, Wu AS. Yue. The incidence of intraoperative awareness during general anaesthesia in China: a multi-center observational study. Acta Anaesthesiologica Scandinavica 2009; 53: 873–82. 5. Sebel PS, Bowdle TA, Ghoneim MM, Rampil IJ, Padilla RE, Gan TJ, Domino KB. The incidence of awareness during anesthesia: a multicenter United States
Extubation over a bougie in difficult airways: are we missing a trick? Following publication of the Difficult Airway Society’s extubation guidelines [1], we performed an audit to evaluate extubation over a standard bougie for patients undergoing maxillofacial and ENT procedures. Although the use of Airway Exchange Catheters (AECs) to maintain access to the airway after extubation has been described [2], the use of simple bougies has not. Bougies may confer important advantages over AECs in that they
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