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The University of Southampton

Research project: Anaesthesia and awareness

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Using the response of the brain to see if people are awake in operations

Depth of anaesthesia
Depth of anaesthesia

A reliable monitor of awareness could prevent rare, but highly disturbing cases of surgical awareness where people are awake but cannot move to tell anyone. They could also help to improve the accuracy with which anaesthetic agents are given. Anaesthetics such as Propofol have associated health risks, particularly for the elderly and they are very costly for the NHS

One way to monitor anaesthesia is to measure the response of the brain to sound known as the middle latency response (MLR). Research dating back to the 1980s has shown that the MLR changes as you fall asleep. However, the MLR is very small (about a millionth of a volt) and it is hard to measure such a small signal accurately in an operating theatre where there are often many sources of electrical interference. This means that the result of the measurement can be unreliable and so it might be difficult to tell if a patient is awake or asleep.

A chirp is a sound that can help to produce a large response in the brain
A Chirp

We have been looking at new mathematical techniques to better measure evoked potentials during anaesthesia. To improve signal acquisition we have used high rate maximum length sequences and chirp stimuli designed to compensate for frequency dispersion on the basilar membrane. Putting the two techniques together, we have found that we can improve the measurement of the small signal from the brain many times compared to previous acquisition methods in normal hearing subjects. However, the pattern of changes we found with anaesthetic differs from that found in previous studies and data quality for surgical monitoring still remains a challenge. This work was funded by EPSRC grant EP/D505593 and was featured on the Radio 4 programme ‘Sounds of Science’.We now want to explore how brain connections change during anaesthesia and if this gives us more information than the MLR. The new approach is supported with funding from the National Institute of Academic Anaesthesia and the Gerald Kerkut Charitable Trust.

Ultimately we hope to better understand the effects of anaesthetic on the brain.

Associated research themes

Bioengineering and human factors

Related research groups

Signal Processing, Audio and Hearing Group

Key Publications

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