Incidence of Slow Delta EEG Frequencies (0.1-1 Hz) Before Burst Suppression

The electroencephalogram (EEG) measures brain waves during general anaesthesia via an electrode placed on the forehead. These brain waves show the different stages of natural sleep as well as the state of the brain when a patient is put under general anaesthesia for an operation. In this research project, the investigators aim to find out if the EEG signal shows slow wave activity (where an EEG wave repeats every 10 to 1 seconds) just before the onset of the burst suppression pattern, where the EEG waveform alternates between very small (suppression) and very large (burst) signals over a period of a few seconds. It is not currently known if and how often this occurs, but if it does, it would be a useful signal to help anaesthetists administer just the right dose of anaesthesia to patients.