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[Intraoperative awareness and auditory evoked potentials]
D Schwender1, M Daunderer, S Klasing
1Institut für Anästhesiologie, Ludwig-Maximilians-Universität München.
Abstract:
Midlatency auditory evoked potentials (MLAEP) are suppressed dose-dependently during anaesthesia with a variety of general anaesthetics. Therefore, MLAEP have been proposed to measure depth of anaesthesia and to indicate intraoperative awareness. Several studies give evidence of a close relationship between MLAEP and motor signs of wakefulness, intraoperative awareness, and explicit and implicit memory functions during general anaesthesia. Summarising these data, one may conclude that there is a close hierarchical relation between cognitive function, memory and wakefulness during anaesthesia, and MLAEP latencies. A short Nb latency below 45 ms is consistent with conscious awareness and unimpaired memory function with explicit recall and adequate response to commands. When Nb latency increases to 45-50 ms, it may be associated with conscious awareness. Patients still respond to commands, but memory formation is impaired and explicit recall is lost. A further increase of Nb latencies seems to be consistent with unconscious awareness, characterised by implicit memory of intraoperative events; 60 ms seems to be the threshold value for motor signs of wakefulness during anaesthesia. With a further increase of MLAEP latency during anaesthesia, conscious awareness and memory formation, explicit and implicit recall, response to commands, and spontaneous purposeful movements during anaesthesia are blocked. The new volatile anaesthetic sevoflurane leads to a dose-dependent increase in MLAEP peak latencies and a decrease in MLAEP amplitudes. At about 1.5 vol.% end-expiratory sevoflurane concentration, MLAEP are significantly suppressed and Nb latency is in the range of 68-80 ms. Therefore, from the present data and those from the literature, one may expect that sevoflurane at concentrations greater than 1.5 vol.% for general anaesthesia would be able to suppress awareness phenomena such as purposeful movements, auditory perception, intraoperative wakefulness and awareness, memory formation, and explicit and implicit recall of intraoperative events.
Insights
Midlatency auditory evoked potentials (MLAEP) can indicate depth of anesthesia and intraoperative awareness. Sevoflurane anesthesia at concentrations above 1.5 vol.% suppresses MLAEP, blocking awareness and memory.
Area of Science:
- Neuroscience
- Anesthesiology
- Cognitive Science
Background:
- Midlatency auditory evoked potentials (MLAEP) are suppressed by general anesthetics, suggesting their utility in monitoring anesthesia depth.
- Studies indicate a strong correlation between MLAEP, wakefulness, intraoperative awareness, and memory functions under anesthesia.
Purpose of the Study:
- To investigate the relationship between MLAEP latencies and cognitive functions during general anesthesia.
- To evaluate the effect of sevoflurane on MLAEP and its implications for intraoperative awareness and memory.
Main Methods:
- Analysis of existing literature on MLAEP and general anesthetics.
- Review of studies correlating MLAEP latencies with motor signs, awareness, and memory recall.
- Examination of sevoflurane's dose-dependent effects on MLAEP amplitudes and latencies.
Main Results:
- MLAEP latencies correlate hierarchically with cognitive function, memory, and wakefulness during anesthesia.
- Specific Nb latency ranges are associated with different states of awareness and memory.
- Sevoflurane increases MLAEP latencies and decreases amplitudes in a dose-dependent manner, with significant suppression at ~1.5 vol.%.
Conclusions:
- MLAEP serve as reliable indicators of anesthesia depth and intraoperative awareness.
- Sevoflurane concentrations exceeding 1.5 vol.% are expected to suppress awareness, memory, and motor responses during anesthesia.
- Understanding MLAEP provides insights into the neurophysiological effects of anesthetics on consciousness and memory.