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Created: 8/12/2005
Awareness remains a serious complication of general anaesthesia with potential adverse psychological sequelae. Even during seemingly adequate general anaesthesia, implicit memory (see below) may be retained, along with the ability to subconsciously process auditory stimuli. As a result, behaviour may be modified and post-operative progress influenced.


Awareness (explicit memory)
Explicit Memory refers to intentional or conscious recollection of prior experiences as assessed by tests or recall or recognition, which are also called direct memory test.

Awareness (implicit memory)
Perception without conscious recall. The patient denies recall, but may remember “something” under hypnosis. Psychologists are sceptical about the existence of this phenomenon.

Awareness (deliberate)
Surgery conducted under local or regional anaesthesia. During some neurosurgical procedures, the patient is woken up to assess whether surgery has affected, or will affect, important areas.

Stages of awareness

To accommodate the concept of gradual suppression of cognitive function by general anaesthesia, Griffith and Jones have described five stages of perception during general anaesthesia with memory of intra-operative events.

1. Conscious perception with explicit memory;
2. Conscious perception without explicit memory;
3. Dreaming;
4. Subconscious perception with implicit memory;
5. No perception and no implicit memory.

Checklist following a complaint of awareness during general anaesthesia

1. Visit the patient as soon as possible, along with a witness (Preferably a consultant)
2. Take a full history and document the patient’s exact memory of events
3. Attempt to confirm the validity of the account
4. Keep your own copy of the account
5. Give a full explanation to the patient
6. Offer the patient follow-up, including psychological support, and document that this has been offered
7. Reassure the patient that they can safely have further general anaesthetics, with minimal risk of a further episode of awareness
8. If the cause is not known, try to determine it
9. Notify your medical defence organisation
10. Notify your hospital administration
11. Notify the patient’s GP


[i] Increases in bispectral index lead to interventions that prevent possible intraoperative awareness. D. M. Mathews, S. S. Rahman, P. M. Cirullo and R. J. Malik. Br J Anaesth 2005 95(2):193-196;

[ii] Griffith D, Jones JB. Awareness and memory in anaesthesised patients. Br J Anaesth 1990; 65: 603-7

[iii] Schacter DL. Implicit knowledge: New perspectives on unconscious processes. Proc Natl Acad Sci USA 1992:89:1113-1117

[iv] Cobcroft MD, Forsdick C. Awareness under anaesthesia: The patient's point of view. Anaesth Intensive Care 1993; 21: 837-843

[v] Moerman N. Bonke B. Ossting J. Awareness and recall during general anesthesia. Facts and feelings. Anesthesiology 1993;79:454-464

[vi] Patients' memories of events during general anaesthesia. Bailey AR, Jones JG. Anaesthesia 1997; 52: 460-76

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