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Awareness during anaesthesia: a prospective case study
Department of Anaesthesia and Intensive Care, Länssjukhuset, Kalmar, Sweden.
Department of Anaesthesia and Intensive Care, Vrinnevisjukhuset, Norrköping, Sweden.
Linköping University, Department of Medicine and Health Sciences. Linköping University, Faculty of Health Sciences.
Department of Anaesthesia and Intensive Care, Vrinnevisjukhuset, Norrköping, Sweden.
2000 (English)In: The Lancet, ISSN 0140-6736, Vol. 355, no 9205, 707-711 p.Article in journal (Refereed) Published
Abstract [en]


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.


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.


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.


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.

Place, publisher, year, edition, pages
Lancet , 2000. Vol. 355, no 9205, 707-711 p.
National Category
Anesthesiology and Intensive Care
URN: urn:nbn:se:liu:diva-15402DOI: 10.1016/S0140-6736(99)11010-9OAI: diva2:114120
Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2009-06-03Bibliographically 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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Enlund, GunnarLennmarken, Claees
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