Awareness and anaesthesia
Perth, Australia
* E-mail: grahamhocking{at}optusnet.com.au
Editor—We were interested to read the study by Errando and colleagues1 describing their experience of awareness with recall (AWR). While the figure of 1% is undoubtedly concerning, there are multiple methodological problems with their paper, which may influence the results, and limit any conclusions to be drawn from it.
We note the audit commenced in 1995, but was not completed until 2001 after recruiting only 4001 patients. Does this reflect that the population was merely a sample and therefore subject to potential sampling bias. Can the authors explain the role that ASPECT Medical Systems had in this project? Was the project actually studying the use of BIS-guided anaesthesia, which may have affected the way anaesthesia was delivered over this period? We note the anaesthetic techniques described in their paper contained some with a high likelihood of awareness. As such, the results may lack external validity because their findings may be non-representative. There are also discrepancies in totals within their tabulated data, which have not been adequately explained.
We performed an almost identical prospective audit in an Australian tertiary referral hospital in 20012 but found a much lower incidence of awareness. Our figures were in keeping with the established literature discussed in a recent editorial in this journal.3 A research nurse interviewed every consecutive surgical patient operated on in our institution during a full 12 month period. Data were collected on 5371 patients of whom 4899 received general anaesthesia. Using the same definition as Errando and colleagues,1 we had two cases of AWR-yes making our incidence of intraoperative awareness 0.04% (95% confidence interval 0–0.1%). Both cases occurred during balanced general anaesthesia with volatile agents. Since we interviewed consecutive patients in a full 12 month period, our incidence of 0.04% is a true rate of awareness in our institution. The techniques used in our hospital for general anaesthesia during the audit period were balanced anaesthesia (87%) and total i.v. anaesthesia (13%). No anaesthetist was using solely O2/N2O for maintenance.
Both of these audits were performed during a similar time period over 7 yr ago. We can only speculate why the incidences are so different. We suggest the validity of their results be considered in the light of these points.
Valencia, Spain
* E-mail: c.l.errando{at}carloserrando.com
Editor—Thank you for your interest in our article on AWR during general anaesthesia.1 Some of the suggested methodological problems in our work are discussed in our article. In addition, space constraints in this type of article (data rich) preclude the inclusion of all the information and this can introduce apparent biases. The timescale of patient recruitment, and the number of patients involved, was described in the Methods section. To extend the explanation, we blindly recruited patients in the post-anaesthesia care unit (PACU) (4–8 per day) on the days a participating anaesthetist was available. Unfortunately, our PACU was closed due to staff shortages for 1.5 yr. Thus, the patients were consecutively recruited, but not all patients anaesthetized during these years were entered in the database (20 000 patients per year anaesthetized in our hospital). No other considerations were taken into account in recruiting and we did not consider this as ‘sampling’.
The participation of a member of Aspect MS was declared on submission of the manuscript. At the time the study was performed, BIS was not available to us. Dr Sigl's participation was in the post-retrieval analysis of the data, contribution in the explanation of the findings related with this, and participation in the ‘discussion’ related to these aspects. There was no influence on the anaesthetic techniques, and the anaesthetist in charge was free to choose premedication, anaesthetic technique, drugs, and doses. The variety of anaesthetic techniques can be explained, in part, by the different anaesthesia training of the doctors, and because, at that time, we had a non-standardized method of work at our hospital.
I congratulate the authors for their low incidence of AWR, but, in my opinion, the way and timing of the patient's interview, together with the definition of AWR, are both important. Comparison with the paper by Hennessy and colleagues2 is not possible as it is an Abstract without complete information. Finally, as stated in our Discussion,1 the true figures of AWR quoted in the recent, large studies may need to be increased by a factor of 2–3 if the definition of AWR used in our study, or if ‘possible’ awareness cases, had been included.
References
1 Errando CL, Sigl JC, Robles M, et al. Awareness with recall during general anaesthesia: a prospective observational evaluation of 4001 patients. Br J Anaesth (2008) 101:178–85.
2 Hennessy B, Gibbs N, Long K. Quality of recovery from anaesthesia: patient satisfaction survey. Anaesth Intensive Care (2003) 31:695–6.
3 Sneyd JR, Matthews DM. Memory and awareness during anaesthesia. Br J Anaesth (2008) 100:742–4.
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