awareness

Last reviewed 01/2018

Awareness in the context of anaesthesia is the state of the patient being alert and receptive to sensory information under general anaesthesia. It is a very rare phenomenon. It is a particular problem in the following situations:

• when muscle relaxants are used and the patient is unconscious or semi-conscious; they are unable to communicate their perception
• when minimal anaesthesia is deemed desirable:
• in obstetrics due to the risk of delivering a sedated baby
• victims of severe trauma
• cardiopulmonary bypass
• in recovery

There are believed to be four types of memory of events:

• that of pain
• recall of events with no pain
• subconscious recall of events
• recall of anaesthesia only

The indices of depth of anaesthesia may be poorly calibrated with respect to awareness, e.g. sympathetic responses may not be dramatically accentuated. Attempts at detecting awareness have entailed the use of EEG processing, evoked auditory stimuli and monitoring ECG R-R intervals.

If the patient reports awareness postoperatively, it must be taken very seriously. The recall of intraoperative pain is associated with great distress and psychosis has been reported. Early patient counselling is recommended.