Patients' memories of events during general anaesthesia

Abstract

SummaryAwareness remains a serious complication of general anaesthesia with potential adverse psychological sequelae. Even during seemingly adequate general anaesthesia, implicit memory may be retained along with the ability to subconsciously process auditory stimuli. As a result behaviour may be modified and postoperative progress influenced. We shall discuss the structure of memory and the effects of increasing doses of general anaesthesia on cognitive processes. In addition methods of assessing the depth of anaesthesia will be reviewed.

Absence of implicit and explicit memory during propofol/remifentanil anaesthesia

“…It is still unclear whether this implicit learning may occur when subjects are unconscious or whether short periods of awareness are responsible for this memory [1]. We have showed in a previous study [3] that implicit recollection was eliminated when young ASA I/II patients had lost consciousness when propofol was used alone in the absence of a surgical stimulus.…”

“…This recollection occurs when a subject remembers information without being aware of it. It is still unclear whether this memory can be processed by unconscious patients or whether it is caused by short periods of awareness [1]. In a previous experiment, implicit or explicit memory could not be found when consciousness was lost using propofol as sole anaesthetic agent [3].…”

“…Awareness during general anaesthesia can be responsible for the recollection of some intraoperative events [1]. This recollection can lead to psychological sequelae for the patient and medicolegal concerns for the anaesthetist [2].…”

Electroencephalogram-based pharmacodynamic measures: a review

“…This experimental paradigm involves placing a small audio speaker into the subject’s ear and repeatedly playing a brief clicking sound. Auditory evoked potential response is categorized as originating from the brainstem (earliest response), midlatency and long latency [74]. An example application is the use of mid-latency auditory EP response to monitor depth of anesthesia [35,75].…”

Sevoflurane in Paediatric Anaesthesia

“…Lower flow rates during maintenance reduce hourly and total costs of inhalation anaesthetics, as well as improving the maintenance of the anaesthetic's humidity and reducing atmospheric pollution (primarily from N 2 O). [115,116] Accumulating evidence, albeit preliminary, suggests that lowflow sevoflurane anaesthesia can provide a similar recovery profile [117] for half the cost of high-flow techniques. [117,118] Using an acquisition cost of $US0.72/ml, the cost per case for induction with sevoflurane 2.7 L/min (mean) and low-flow maintenance with sevoflurane 0.9 L/min (mean) was $US6.45 for a 30-minute procedure.…”