Abstract: An anaesthesia control system and a method of calculating an index representative of the depth of anaesthesia is disclosed. The method comprises subjecting a patient to a repetitive audio stimulus and monitoring and auditory evoked potentials (AEP) produced by the patient and then recording these auditory evoked potentials using EEG recording means and providing a signal corresponding to the coarseness of the monitored AEP signal and using this signal as an index indicative of anaesthetic depth. The raw AEP signal is divided into a series of sweeps and each sweep is synchronized with the repetitive audio stimulus and sweeps are recorded in sequence to produce a time averaged sweep from which the anaesthetic index is calculated. The anaesthetic index is constantly updated by repeatedly conducting a successive series of sweeps.

Abstract: A system and method to obtain (19) unipolar EEG signals from electrodes (13) attached to a patient's head (14). The EEG signals are detected by the electrodes and transmitted over a patient cable (16) to the EEG data acquisition and analysis system (12). The system (12) generates all power spectrum, bispectrum, and higher-order spectrum arrays. These arrays are then used in conjunction with clinically predetermined coefficient arrays to produce diagnostic indices. These indices are sent to the host computer (18) and are displayed on the graphics display (2). Printed output of the diagnostic index is also available on the hard copy output device (22) which is connected to the microcomputer (18). The operator interacts with the acquisition and analysis components of the system by means of a user input device (24) with feedback on the graphics display (20).