Anaesthetists' attitudes towards awareness and ... - Wiley Online Library

Anaesthesia, 2003, 58, pages 11–16 .....................................................................................................................................................................................................................

Anaesthetists’ attitudes towards awareness and depth-of-anaesthesia monitoring P. S. Myles,1 J. A. Symons1 and K. Leslie2 1 Department of Anaesthesia and Pain Management, Alfred Hospital, P.O. Box 315, Melbourne, Victoria 3004, Australia 2 Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Melbourne, Victoria, Australia Summary

Advances in technology have resulted in the development of several depth-of-anaesthesia monitors. Whether any of these monitors can reduce the incidence of awareness is an important issue for anaesthetists and their patients. We therefore surveyed a random selection of anaesthetists, asking for their opinions of awareness and depth-of-anaesthesia monitoring in current clinical practice. Approximately half (52%) of the anaesthetists surveyed had experienced a patient with awareness. Anaesthetists considered that they had a lower incidence of awareness in their own practice when compared with others, 1:5000 vs. 1:10 000 (p < 0.001). Anaesthetists rated awareness on an 11-point scale as only a moderate problem, median (interquartile range) 5 (2–7). Older anaesthetists were less likely to rate the importance of awareness highly (p ¼ 0.009) and to use awareness monitoring (p ¼ 0.001). Anaesthetists are prepared to use depth-of-anaesthesia monitoring more widely if it can be shown to prevent most cases of awareness in routine practice. Keywords Anaesthesia; monitoring, depth of anaesthesia. Complications; awareness. . ......................................................................................................

Correspondence to: P. S. Myles Accepted: 4 September 2002

Awareness under general anaesthesia is a rare event, with an overall incidence of 0.1–0.2% [1–3]. Despite this, awareness is a major concern to patients [4–6] and can have potentially devastating psychological consequences [5–9]. The risk of awareness is higher in some types of surgery [10–14], including caesarean section (0.9%), cardiac surgery (0.4–1.1%), and trauma surgery (up to 20%). Most cases of awareness occur during general anaesthesia when muscle relaxants are used [1, 3, 8]. Other factors associated with an increased risk of awareness include: intermittent administration or inadequate dosage of hypnotic agents [3, 8, 12, 15], equipment failure [8], administering muscle relaxant prior to induction agent [3, 15], and lack of vigilance by the anaesthetist [3, 15, 17]. Factors thought to decrease the risk of awareness include maintenance of at least 0.5 minimum alveolar concentration (MAC) of a volatile agent [16], co-administration of benzodiazepines [8, 11] and continuous administration of anaesthesia [8, 11, 13]. Patient factors may also be associated with awareness. These include female gender 2003 Blackwell Publishing Ltd

[17], young age [12, 17] and possibly chronic use of alcohol and recreational drugs [1]. Advances in technology have resulted in the development of several depth-of-anaesthesia monitors [12, 17]. These include auditory-evoked potential signal processing, bispectral index (BIS; Aspect Medical Systems, Newton, MA), and a variety of other methods of electroencephalogram (EEG) processing, such as 95% spectral edge frequency and quantitative EEG (QEEG; Physiometrix, North Billerica, MA). Whether any of these monitors can reduce the incidence of awareness is an important issue for anaesthetists and their patients. The BIS monitor, in particular, has received much attention in anaesthesia journals and the popular press in relation to its ability to detect and prevent awareness [18–21], despite this not being a claim made by the manufacturer [22]. Whether such a monitor actually decreases the risk of awareness has yet to be proven [3, 21, 23]. There is some concern that depth-of-anaesthesia monitoring may in fact increase the risk of awareness if it leads to reduced administration of anaesthetic drugs and insufficient 11

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P. S. Myles et al. Awareness and depth-of-anaesthesia monitoring Anaesthesia, 2003, 58, pages 11–16 . ....................................................................................................................................................................................................................

anaesthesia [17, 19, 21, 23]. We therefore investigated anaesthetists’ attitudes regarding awareness and the value of depth-of-anaesthesia monitoring.

Table 1 Demographic characteristics of the study sample

(n ¼ 167). Anaesthetist

Methods

Following local ethics committee approval, a crosssectional survey of Australian anaesthetists was conducted. With the cooperation of the Australian and New Zealand College of Anaesthetists (ANZCA), a computer-generated random selection (n ¼ 220) of ANZCA Fellows (anaesthetists) was obtained. ANZCA assigned a unique identifier code to each anaesthetist in order for us to track non-responders. The survey, with a covering letter explaining the aims and relevance of the study, was sent to all participants with a reply paid coded envelope. The survey consisted of 22 questions and investigated anaesthetists’ attitudes towards awareness in anaesthesia and the role of depth-of-anaesthesia monitoring. Anaesthetists were asked to rate whether they believed awareness was a major problem in anaesthesia on an 11-point scale, where 0 represented Ônot a problem at allÕ, and 10 represented Ôa very serious problemÕ. The completed surveys were dealt with in the following way. The envelope containing the questionnaire was opened and the envelope discarded after recording its identification code in order to establish which questionnaires had been returned. After the envelope had been discarded, no link could then be established between the identity code of the anaesthetist and their responses, thus ensuring the respondent’s confidentiality and only allowing identification through ANZCA. Non-responders were sent a reminder letter. Survey data were entered onto a database and frequency distributions were generated. Summary statistics are presented as median (interquartile range [IQR]) or number (%, rounded to the nearest whole number). Cost data are presented in Australian dollars [UK exchange rate (UK:A) 0.40, Euro exchange rate (EUR:A) 0.60]. A number of predetermined comparisons were analysed using Chi-square test, Friedman test or Mann–Whitney U-test; associations were estimated using Spearman rank correlation coefficients. Some variables were categorised according to their distribution and ease of clinical interpretation. All analyses were performed using SPSS 10.0 (SPSS Inc. Chicago, IL). A p-value < 0.05 was considered significant. Results

Of the 220 anaesthetists surveyed, 186 questionnaires were returned (response rate 85%). 19 replies (10%) were not completed: there was one refusal and 18 who were 12

Age; years £ 35 36–45 46–55 56–65 > 65 Gender Male Female Practice location (Australian state) New South Wales* Victoria Queensland South Australia Western Australia Northern Territory Tasmania

%

11 38 31 16 4 81 19 35 23 19 10 6 4 2

*Including Australian Capital Territory.

practising exclusively in pain medicine, intensive care or had retired from clinical practice. The demographic characteristics of the respondents (Table 1) were equivalent to Australian anaesthetist workforce statistics of ANZCA [24, 25], indicating a representative sample. There was a significant difference between what anaesthetists thought the overall incidence of awareness was in Australian practice, compared with their own practice, 1:5000 vs. 1:10 000 (p < 0.001). Approximately half (52%) of the anaesthetists surveyed had experienced a patient with an episode of awareness under anaesthesia. Nearly all (99%) had occurred during general anaesthesia in which muscle relaxants had been administered, and benzodiazepines had been used in 35% of cases. Only 23% of anaesthetists had reported their case(s) of awareness to their medical defence organisation, and there were known medico-legal consequences in only 1%. Anaesthetists who had experienced patients with awareness rated their own incidence of awareness significantly higher than those who had not had a case of awareness, 1:10 000 vs. £ 1:50 000 (p < 0.001). Approximately half (56%) of the anaesthetists surveyed thought the public overestimated the incidence of awareness. This was not affected by anaesthetist gender (p ¼ 0.53) or age (p ¼ 0.13). Most rated awareness as only a moderate problem on an 11-point scale, median 5 (IQR 2–7). Older anaesthetists were less likely to rate the importance of awareness highly (p ¼ 0.009); other factors associated with anaesthesiologist rating of the importance of awareness are presented in Table 2. Only 11% of anaesthetists routinely informed their patients of the risk of awareness under anaesthesia and a similar number routinely interviewed their patients 2003 Blackwell Publishing Ltd

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Anaesthesia, 2003, 58, pages 11–16 P. S. Myles et al. Awareness and depth-of-anaesthesia monitoring . ....................................................................................................................................................................................................................

Table 2 Anaesthetist factors affecting

their rating (on an 11-point scale*) of the importance of awareness under anaesthesia.

Factor Age < 55 years Male gender Had experienced patient awareness Considered the public over-estimate awareness incidence Considered awareness a result of negligence in ‡ 60% of cases Willing to accept > $20 cost if monitoring prevents > 90% of awareness

Factor present vs. absent

p-value

5 5 5 3 7 7

0.009 0.70 0.54 0.008 0.11 0.02

(3–8) vs. 2.5 (1–7) (2–8) vs. 5 (3–8) (2.3–8) vs. 5 (2.3–8) (2–8) vs. 6 (3–8) (2–9) vs. 5 (3–7) (3–8) vs. 4 (2–7)

*Where 0 ¼ not a problem at all, to 11 ¼ a very serious problem. Median (IQR).

postoperatively about awareness, either in person or via a delegate (e.g. resident, nurse). Awareness was considered by anaesthetists to be a result of negligent or substandard anaesthetic practice in a minority (10–39%) of cases. Anaesthetists with experience of patient awareness were not more or less likely to think that awareness was due to negligent or substandard practice (p ¼ 0.63). Factors thought to increase the risk of awareness are presented in Table 3. Most anaesthetists identified patient movement and various autonomic signs as possible indicators of awareness. Most anaesthetists used some additional pharmacological measures to prevent awareness in their routine practice. No anaesthetists indicated that benzodiazepines always prevent awareness, but many anaesthetists (62%) thought that benzodiazepines prevented awareness on most occasions. Most (93%) anaesthetists thought that end-tidal volatile agent monitoring was a useful technique to reduce the likelihood of awareness. Most (78%) anaesthetists would alter their anaesthetic technique if told that their patient had experienced awareness in the past. Techniques identified included: increased end-tidal volatile agent concentration (81%), use of a benzodiazepine agent (79%), increased dose of the induction agent (44%), increased dose of opioid (30%), and increased vigilance (77%). Half (50%) of the anaesthetists surveyed have used depth-of-anaesthesia monitoring on at least one occasion. In most cases (92%) this was BIS monitoring, although 16% had used other EEG monitoring and 2% had used auditory-evoked potential monitoring. Approximately half (53%) of the anaesthetists surveyed reported they would use an awareness monitor for most or all of their cases, if it was validated (Table 4). Older anaesthetists were less likely to use an awareness monitor (p ¼ 0.001). Responses to specific clinical circumstances are presented in Table 4. The cost anaesthetists were willing to accept for routine use of an awareness monitor varied according to its proven ability to prevent awareness (p < 0.001, Table 5). Anaesthetists who had experienced patient awareness 2003 Blackwell Publishing Ltd

Table 3 Anaesthetists’ practices and opinions of awareness

(n ¼ 167). More than one response could be selected for each item. Item Clinical signs looked for as indicators of awareness Gross purposeful movement Unexplained tachycardia Unexplained hypertension Unexplained sweating Unexplained lacrimation None of the above Routine measures taken to decrease the risk of awareness Increase end-tidal volatile agent concentration Use a benzodiazepine agent Regional block, or increase the dose of the opioid agent Other (e.g. depth-of-anaesthesia monitoring) Factors considered to increase the risk of awareness Relaxant anaesthesia Lack of vigilance by the anaesthetist Equipment error Drug error Using too little induction agent Not using a co-induction agent (e.g. midazolam) Inadequate pre-operative assessment Total intravenous anaesthesia Not using nitrous oxide Performing tracheal intubation too early Lack of communication with the surgeon Lack of communication with other theatre staff Other Do benzodiazepines prevent awareness? Always On most occasions Occasionally Never

%

92 92 90 89 84 2 80 65 53 20 76 76 75 74 55 47 39 37 37 34 21 10 22 0 62 35 3

were not willing to accept more cost for the use of an awareness monitor than those who had not (p ¼ 0.67). Approximately half (45%) of the anaesthetists surveyed considered an awareness monitor would decrease the dose of anaesthetic drugs used. For those who had had a previous instance of patient awareness, 11% believed BIS monitoring would have prevented all such cases, 48% believed that BIS monitoring would have prevented 60–99% of such cases, 21% believed BIS monitoring would have prevented 30–59% of such cases, and 20% 13

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Table 4 Anaesthetists’

opinions

of

awareness

monitoring

(n ¼ 167). Item

%

How often would you use an Ôawareness monitorÕ? Always Most times Often Never When should an Ôawareness monitorÕ be used? If the patient has had an episode of awareness in the past If the patient has specifically requested it High-risk cases only (e.g. caesarean section, trauma, cardiac) All cases under relaxant general anaesthesia All cases under general anaesthesia None

17 36 43 4 71 57 54 44 17 4

Table 5 What cost anaesthetists are willing to accept for routine

use of an Ôawareness monitorÕ, according to its ability to prevent awareness. Cost (AUS$)

Item

25

If a monitor was shown to prevent: (i) > 90% of cases of awareness (ii) 50–90% of cases of awareness (iii) < 50% of cases of awareness

< 10 < 10 < 10

Percentile 50 (median)

10–20 < 10 < 10

75

21–40 10–20 < 10

believed BIS monitoring would have prevented fewer than 30% of such cases. Discussion

We surveyed a representative sample of Australian anaesthetists [24, 25]. Anaesthetists believe the incidence of awareness in Australia is 1:5000 (incidence 0.02%) which is 5- to 10-fold lower than that reported previously in the literature [1, 3, 8]. Myles et al. [2] reported an incidence of awareness of 0.11% in their survey of 10 811 patients in an Australian hospital. Moreover, anaesthetists thought that the incidence of awareness in their own practice was less than half that of other anaesthetists. The reasons for the perceived differences are not known. Interestingly, and perhaps not unexpectedly, anaesthetist age was shown to be related to attitudes of awareness and depth-of-anaesthesia monitoring. Possible explanations for this include older (more experienced?) anaesthetists being exposed to higher rates of awareness in the past, and placing greater reliance on standard monitoring and ⁄ or resistance to the use of new technology. About half of the anaesthetists surveyed believed that the public overestimates the incidence of awareness and are of the opinion that awareness under anaesthesia is only 14

a moderate problem. Previous reports [4, 26] have found that patients rate the importance of awareness more highly than the anaesthetists in this study. Such attitudes may partly explain the limited adoption of depth-ofanaesthesia monitoring in the UK and Australia. Currently BIS monitoring is routinely used in < 1% of cases within Australia (Steve Cramp, Aspect Medical Inc., personal communication). Some have argued that awareness does not lead to delayed neurotic symptoms [3], but others have found substantial psychological morbidity [5–7, 9]. A strong relationship has been shown between patient dissatisfaction with anaesthesia care and intra-operative awareness [2]. Although medico-legal consequences associated with awareness in the past were low in our study population, only 24% of anaesthetists had reported their case(s) of awareness to their medical defence organisation. Considering that patients are concerned about awareness [4, 6, 26], depth-of-anaesthesia monitoring is available and believed by some to reduce awareness [20], and awareness-related litigation is increasing [15], it would be prudent for all anaesthetists to report any suspected cases of awareness to their medical defence organisation. Similarly, very few anaesthetists inform their patients of the risk of awareness under anaesthesia or ask them about previous experiences with respect to awareness. Current patient expectations of being fully informed suggest that anaesthetists should provide some information about awareness to patients prior to surgery. Many Australian anaesthetists have used some type of depth-of-anaesthesia monitoring. There seems to be a general willingness of the anaesthetic community to use awareness monitoring, but it would need to be shown to prevent most cases of awareness in routine practice [19, 23]. This issue is currently being addressed in a large randomised trial (http://www.b-aware-trial.org.au). Even if the BIS monitor is shown to be a sensitive indicator of anaesthetic depth, the cost of using such a monitor to prevent such a rare event may limit widespread use [3, 21]. Theoretical calculations of the cost of an awareness monitor preventing one episode of awareness range from $4000 to 800 000, according to its incidence and the diagnostic utility of the monitor [21]. We found that most anaesthetists are only willing to accept a cost of $10–20 per case for the use of an awareness monitor, and only if it is shown to prevent at least 90% of awareness cases. In contrast, patients in a US study were willing to pay US$34 to avoid awareness after viewing a brief information video on awareness and being told it may occur at a rate of 5:1000, with 91% of respondents rating the avoidance of awareness a maximum score on an 11-point scale [4]. Our study suggests that anaesthetists do not rate awareness as a major 2003 Blackwell Publishing Ltd

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Anaesthesia, 2003, 58, pages 11–16 P. S. Myles et al. Awareness and depth-of-anaesthesia monitoring . ....................................................................................................................................................................................................................

problem, and this may explain their resistance to accepting large costs (> $20) to prevent its occurrence. This may in part be explained by the low rate (and cost) of litigation for awareness in the past [17]. Those that were prepared to pay more for routine awareness monitoring rated awareness more highly. In our study, the most accepted pharmacological measure used by anaesthetists to prevent awareness is maintaining > 0.5 MAC end-tidal concentration of volatile agent. This view is supported by recent literature [16]. Sandin et al. [3] found that end-tidal agent monitoring did not appear to prevent awareness in their large case series; information regarding volatile agent concentration was not available. Other pharmacological measures used to prevent awareness included the use of benzodiazepines, and opioids or a regional block. Benzodiazepines are recommended by some [8, 11], but not others [1]. Most anaesthetists thought that benzodiazepines prevent awareness on most occasions, but none thought that benzodiazepines always prevent awareness. The ability of benzodiazepines to prevent recall is dose-dependent [27], and the incidence of awareness in a recent large case series [3] was not affected by whether patients had received benzodiazepines. The unreliability of pharmacological measures and clinical signs of awareness highlight the need for a more sensitive monitor of awareness to be developed and our study found that anaesthetists are prepared to adopt such monitoring in their practice. A few respondents expressed concern that awareness monitoring might in fact lead to an increase in the risk of awareness if smaller amounts of anaesthetic drugs were used. This concern has been raised in the literature [17, 19, 21, 23], and highlights the importance of conducting trials into the effectiveness of such monitoring in routine practice [19, 23]. Currently, most anaesthetists would only use an awareness monitor for specific indications such as a history of awareness or in high-risk cases. In our study, most anaesthetists would alter their anaesthetic technique if informed that a patient has had a previous episode of awareness, mostly by increasing anaesthetic drug administration. This is a recommended approach [8, 12], but can be expected to delay recovery time and may be associated with a higher incidence of intra-operative hypotension. Given that many anaesthetists thought that awareness monitoring can decrease the dose of anaesthetic drugs they use, possibly in response to recent studies [28, 29], monitoring should have a favourable effect on the management of such patients. A majority of anaesthetists reported that they would also increase their vigilance. Lack of vigilance was considered by almost 80% of anaesthetists to be a factor in contributing to awareness. Human error is an important 2003 Blackwell Publishing Ltd

component of many critical incidents in anaesthesia [15, 30], including awareness [3, 8, 15, 17]. We have seen marked improvements in patient monitoring during anaesthesia, but not yet a valid and reliable monitor of awareness. This survey was limited to Australian anaesthetists and may not represent attitudes of those practising in other healthcare environments. The reasons for such attitudes could not be determined in most circumstances. We, like others [3, 20, 21], recognise that depth-of-anaesthesia monitoring may not necessarily equate with awareness monitoring, although the latter is of considerable interest to anaesthetists and patients [18]. Awareness is a difficult endpoint to study because of its low incidence, and partly explains why manufacturers have focused their attention on anaesthetic drug titration and recovery times. In conclusion, although rare, many anaesthetists have had a patient with awareness under anaesthesia, but most rated awareness as only a moderate problem. Anaesthetists considered they had a lower incidence of awareness in their own practice when compared with others, and lower than the published literature. This may partly explain the low rate of depth-of-anaesthesia monitoring in current practice. Anaesthetists are prepared to use depth-ofanaesthesia monitoring more widely if it can be shown to prevent most cases of awareness in routine practice. Acknowledgements

We would like to thank Karen Monette and Fellows of the Australian and New Zealand College of Anaesthetists (ANZCA) for their cooperation with this study. Conflict of interest statement: Paul Myles and Kate Leslie are principal investigators of the B-Aware Trial (http://www.b-awaretrial.org.au), an investigator-driven study part-funded by Aspect Medical Systems (Newton, MA). Kate Leslie has received support for travel and conference expenses from Aspect Medical Systems (Newton, MA). The concept, design, analysis and interpretation of this study was done by the authors. Financial support: Funded by the Alfred Hospital research trust. Dr Myles is supported by an Australian National Health and Medical Research Council Practitioner’s Fellowship. References 1 Liu WHD, Thorp TAS, Graham SG, Aitkenhead AR. Incidence of awareness with recall during general anaesthesia. Anaesthesia 1991; 46: 435–7. 2 Myles PS, Williams DL, Hendrata M, et al. Patient satisfaction after anaesthesia and surgery: results of a prospective survey of 10,811 patients. British Journal of Anaesthesia 2000; 84: 6–10.

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