Slow-Wave Activity Saturation and Thalamocortical Isolation During Propofol Anesthesia in Humans

What is it about?

We used simultaneous EEG and FMRI to track changes in brain activity when individuals very slowly lost consciousness under propofol anesthesia. We found that the brain's electrical activity at slow wave frequencies (0.5-1.5Hz) saturates with increasing propofol anaesthetic dose. We called this slow wave activity saturation (SWAS). Our FMRI data show that at SWAS, thalamocortical isolation from sensory stimuli occurs and an alternative brain network persists. We believe this network, and the SWAS end-point, represents the key transition when an individual's brain becomes disconnected from the external world and sensory events.

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Why is it important?

Anaesthetists have no robust way of detecting when a patient under general anaesthesia stops perceiving the outside world. They typically infer a patient’s consciousness level by monitoring vital signs from the heart and lungs. Slow wave activity saturation (SWAS) is a potential new individualised biomarker for loss of perceptual awareness and therefore has great potential for depth of anesthesia monitoring. Knowledge of the precise point when an individual’s brain becomes unresponsive to external events would allow the delivery of the best anaesthetic dose for that person. This would reduce the risks associated with over- and under-anaesthesia particularly in vulnerable and at-risk patients.