Method and apparatus for determining the cerebral state of a patient with fast response

Abstract

A method and apparatus for ascertaining the depth of anesthesia of the patient. In one embodiment, the entropy of the patient's EEG signal data is determined as an indication of the depth of anesthesia. A frequency domain power spectrum quantity is obtained from the patient's EMG signal data. The latter quantity can be updated more frequently than the EEG entropy due to its higher frequency. The EEG entropy indication and the EMG power spectrum indication can be combined into a composite indicator that provides an immediate indication of changes in the state of the patient. In a further embodiment, the frequency range over which the entropy of the biopotential signal from the patient is determined is selected to encompass both EEG signal data and EMG signal data and the entropy so determined used as an indication of the patients state. In addition, entropy of the EEG range alone can be used together with the entropy of the broadened range to indicate separately contributions from EEG and EMG. In a more generalized version of the further embodiment, a set of frequency components obtained from selected frequency ranges is utilized in determining entropy. The patient signal data from which the frequency components are extracted are obtained from time windows of differing lengths so that the resulting entropy indication will have optimally fast response times.