Using the estimate of coherence to monitor the depth of anaesthesia

The mid-latency auditory evoked potential (MLAEP) has been used to indicate the depth of anaesthesia, and is usually analysed in the time domain. This work investigates an objective response detection technique in the frequency domain, the Magnitude Squared Coherence (MSC), for the assessment of propofol-induced anaesthesia based on EEG under auditory stimulation. The reduction of MSC(f) during the anaesthetic infusion reflects the protocol better than the two time-domain methods (Auditory Evoked Potential Index and Taxonomic Distance) taken for the sake of comparison. Furthermore, MSC allows a statistical inference (α=1%) of the auditory response absence during the anaesthetic process