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BIS does not predict dreams reported after anaesthesia
Linköping University, Department of Medical and Health Sciences. Linköping University, Faculty of Health Sciences. Departments of Anesthesiology and Intensive Care, County Hospital, Kalmar, Sweden.
Linköping University, Department of Medical and Health Sciences. Linköping University, Faculty of Health Sciences. Department of Clinical Physiology, County Hospital, Kalmar, Sweden.
Department of Anaesthesia and Intensive Care, Länssjukhuset, Kalmar, Sweden and Department of Physiology and Pharmacology, Section for Anesthesiology and Intensive Care Medicine, Karolinska Institutet, Stockholm, Sweden.
2008 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 52, no 6, 810-814 p.Article in journal (Refereed) Published
Abstract [en]

Background: In earlier studies, between 1% and 57% of patients have been reported to dream during anaesthesia. Thus, dreaming is much more common than definite memories of real events. We wanted to examine whether dreaming during anaesthesia is related to insufficient hypnotic action, as indicated by BIS levels and, thus, may constitute a risk for awareness.

Methods: After IRB approval, 2653 consecutive surgical patients were included. BIS registrations were recorded continuously during the anaesthetic procedure. The patients were interviewed on three occasions after anaesthesia. Standard questions, according to Brice, to evaluate awareness and dreaming during anaesthesia were asked. The dreams were categorized as either pleasant/neutral or unpleasant without any further evaluation of the dream content. Episodes with a mean BIS below 40, above 60 and above 70 were identified and subdivided according to duration (1, 2, 4 and 6 min, respectively). The total time as well as number and duration of episodes for the three BIS-levels were used to analyze any relation to reported dreaming. The mean BIS was also analyzed.

Results: Dreaming during anaesthesia was reported by 211 of patients (8.0%) on at least one of the post-operative interviews. BIS data did not show any significant correlation with dreaming, and neither did any of the tested case-specific parameters (gender, age, ASA group, BMI, use of relaxants, induction agent, maintenance agent, length of procedure, omitting N2O and concomitant regional anaesthesia).

Conclusion: Dreaming during anaesthesia seems to be a separate phenomenon, not in general related to insufficient anaesthesia as indicated by high BIS levels.

Place, publisher, year, edition, pages
Malden, MA, USA: Wiley-Blackwell, 2008. Vol. 52, no 6, 810-814 p.
Keyword [en]
Dreams, general anaesthesia, BIS
National Category
Anesthesiology and Intensive Care
URN: urn:nbn:se:liu:diva-15407DOI: 10.1111/j.1399-6576.2008.01633.xISI: 000256683700013OAI: diva2:114125
Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2014-01-21Bibliographically approved
In thesis
1. Awareness and Dreaming during Anaesthesia: Incidence and Importance
Open this publication in new window or tab >>Awareness and Dreaming during Anaesthesia: Incidence and Importance
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The definition of awareness used consistently in this thesis is: Explicit recall of intraoperative events during general anaesthesia. Since there is no objective method to detect awareness, the patients must be interviewed after anaesthesia. The form and timing of the interview is crucial. To rely on spontaneous disclosure of awareness episodes is not sufficient. The total number of awareness-victims is considerable although the incidence may seem modest. A number of these patients look upon the awareness experience as the worst experience in their life. Suffering can include pain, mental distress and delayed psychological symptoms. However, the experience of awareness is not uniform and not all patients suffer.

A comprehensible definition for dreaming during anaesthesia is: Any recalled experience, excluding awareness, which occurred between induction of anaesthesia and the first moment of consciousness upon emergence. Some findings point in the direction that dreaming during anaesthesia may be related to light or insufficient anaesthesia, but other findings do not. Some patients find dreaming during anaesthesia distressing, but generally the overall impression is that consequences of dreaming during anaesthesia seem to be small and of minor importance to the majority of patients.

In this thesis I have found the following:The incidence of awareness is approximately 0.2% when neuromuscular blocking drugs are used and awareness also exists without these drugs, albeit to a lesser extent. These findings represent standard practice in an adult population at normal risk. 50% of awareness cases may have delayed recall of awareness.

Using a consecutive inclusion design we found initial awareness suffering comparable to previous studies, but a lower incidence and less pronounced severity of late psychological symptoms. The incidences found among the awareness-victims in our study were; experience of pain 46%, immediate mental distress 65%, any late psychological symptom 33%, and PTSD below 10%.

A memory of an intraoperative dream after general anaesthesia is not an early interpretation of delayed awareness, indicating that no routine follow up of dreaming-only patients is indicated.

Dreams reported after anesthesia are generally not related to insufficient anesthesia defined as high BIS, and should not be regarded as near awareness.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 53 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1082
National Category
Anesthesiology and Intensive Care
urn:nbn:se:liu:diva-15408 (URN)978‐91‐7393‐786‐3 (ISBN)
Public defence
2008-12-06, Eken, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 11:00 (Swedish)
Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2009-08-21Bibliographically approved

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