Recollection of dreams after short general anaesthesia: influence on patient anxiety and satisfaction

Abstract

A reply EDITOR: We are grateful for the opportunity to respond to the comments of Drs Knight and Hardman on our investigation on the recollection of dreams after short general anaesthesia [1]. Working on a rarely noted scientific aspect of anaesthesia has clearly provoked questions, and we thank Knight and Hardman for their interest and comments. A comparison of propofol with a methohexital-isoflurane combination is an unusual choice for the UK, where methohexital has not been available since 1999. As Knight and Hardman state, it is widely used in Central Europe and North America for the induction of anaesthesia and long-term sedation in specific cases. The alternative barbiturate to methohexital would be thiopental. However, this has a long elimination half-life (12 h) and therefore is not the choice for short surgical procedures. Anaesthesia is not the effect of one single substance but of the combination of induction agent, maintenance agent and analgesia. Moreover, satisfaction with the anaesthetic procedure is one of the major measures of the quality of anaesthesia [2]. The primary aim of our study was to investigate the effect of the recollection of dreams on the anxiety and satisfaction of patients after an anaesthetic procedure, and not to compare two single agents. We therefore compared two common anaesthetic procedures for short surgical interventions. According to the literature, the propofol group of patients should have experienced a high incidence rate of dreaming [3,4]. It was a surprise to find that the methohexital-isoflurane group of patients also reported a high incidence rate of dreaming. We agree with Knight and Hardman that a therapeutic final plasma concentration does not indicate plasma concentrations at all stages of anaesthesia. The online electroencephalographic (EEG) monitored by specialist staff guaranteed control of the depth of anaesthesia in this study [4]. The control of propofol plasma concentration was a second parameter to prove the reliability of online EEG control and should have ensured a sufficient depth of anaesthesia after the last operative stimulus. The EEG data showed a significantly deeper anaesthesia among the propofol group of patients at defined points and no difference in the depth of anaesthesia between dreaming and non-dreaming patients. Therefore, our data gave no hint about the roles of different susceptible states on the activation of subconscious perception associated with shallow anaesthesia. We cannot strictly exclude the possibility that such a susceptible state was not evident. There are data from Oddby-Muhrbeck and Jakobsson about a higher susceptible state during propofol anaesthesia in comparison with inhalational anaesthesia using isoflurane, but their patients differed in their recollection of dreaming and their inclination to state that they had been exposed to music [5]. Knight and Hardman remark that there were no standardized intra- or postoperative stimuli. These were not reported as such in our paper because they did not form explicit parts of the study protocol, but there was a nearly standardized operating environment in that all patients had undergone a prior tumour removal several weeks beforehand. The same operating room was always used and the same group of staff always worked with the patients. None of the content of the reported dreams had any obvious relation to the operative setting. One major limitation of this study was the effect of opioid rescue analgesia given later in the recovery ward. Immediately after the procedure, there was no rescue analgesia allowed because pain levels after removal of brachytherapeutic applicators are very low and normally controlled immediately after awaking by the induction dose of fentanyl. Only five patients suffered postoperative side-effects (two in the propofol group, three in the methohexital-isoflurane group), so there was no significant influence on results. Finally, we agree with Knight and Hardman that the absence of evidence does not equate with evidence of absence. All such single studies must be viewed cautiously until they are reviewed and repeated by other investigators. K. Hellwagner A. Holzer B. Gustorff K. Schroegendorfer M. Greher M. Weindlmayr-Goettel B. Saletu F. X. Lackner University of Vienna; Vienna, Austria