Elsevier

The Lancet

Volume 355, Issue 9205, 26 February 2000, Pages 707-711
The Lancet

Articles
Awareness during anaesthesia: a prospective case study

https://doi.org/10.1016/S0140-6736(99)11010-9Get rights and content

Summary

Background

Patients who are given general anaesthesia are not guaranteed to remain unconscious during surgery. Knowledge about the effectiveness of current protective measures is scarce, as is our understanding of patients' responses to this complication. We did a prospective case study to assess conscious awareness during anaesthesia.

Methods

11 785 patients who had undergone general anaesthesia were interviewed for awareness on three occasions: before they left the post-anaesthesia care unit, and 1–3 days and 7–14 days after the operation.

Findings

We identified 18 cases of awareness and one case of inadvertent muscle blockade that had occurred before unconsciousness. Incidence of awareness was 0·18% in cases in which neuromuscular blocking drugs were used, and 0·10% in the absence of such drugs. 17 cases of awareness were identified at the final interview, but no more than 11 would have been detected if an interview had been done only when the patients left the post-anaesthesia care unit. Four non-paralysed patients recalled intraoperative events, but none had anxiety during wakefulness or had delayed neurotic symptoms. This finding contrasts with anaesthesia with muscle relaxants, during which 11 of 14 patients had pain, anxiety, or delayed neurotic symptoms. After repeated discussion and information, the delayed neurotic symptoms resolved within 3 weeks in all patients. Analysis of individual cases suggests that a reduced incidence of recall of intraoperative events would not be achieved by monitoring of end-tidal anaesthetic gas concentration or by more frequent use of benzodiazepines.

Interpretation

The inability to prevent awareness by conventional measures may advocate monitoring of cerebral activity by neurophysiological techniques. However, the sensitivity of such techniques is not known, and in the light of our findings, at least 861 patients would need to be monitored to avoid one patient from suffering due to awareness during relaxant anaesthesia.

Introduction

Recall of intraoperative events in patients under general anaesthesia is rare (0·1–0·7%), although few prospective studies have assessed the incidence of awareness during surgical procedures.1, 2, 3, 4 Up to 54% of patients worry about the possibility of pain, paralysis, and mental distress during surgery.5 Previous studies have not recorded important background data, such as whether neuromuscular-blocking drugs were used or whether end-tidal anaesthetic gas concentration (ETAGC) was monitored. Also, memory for awareness may be delayed,1 and follow-up may have been too short to identify all cases.

We did a prospective study to assess patients' recall of awareness during surgery.

Section snippets

Patients and methods

This study, which was approved by the Ethics Committee of Linköping University Hospital, was done in two Swedish hospitals. Clinical routine at the two hospitals includes an interview for awareness on discharge from the post-anaesthesia care unit in all patients older than 15 years who have had general anaesthesia. This interview, modified from Brice and colleagues6 and described elsewhere,1 is given by the nurses who attended the patients, and is recorded in the anaesthesia record. Dedicated

Results

Baseline data of the 11 785 patients included in the study are shown in table 1.

Discussion

Our findings and our inability to find non-paralysed patients who had unpleasant effects during or after wakefulness suggest that awareness among patients without neuromuscular block is not a major concern, as long as conversation between operating-room staff remains respectful to the patient. Studies on awareness should therefore distinguish clearly between relaxant and non-relaxant anaesthesia.

If the first interview had been done after the patients had left the post-anaesthesia care unit, no

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