Monitoring of the cerebral state of a subject

• US 20070010795A1
• Filed: 07/07/2005
• Published: 01/11/2007
• Est. Priority Date: 07/07/2005
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Salmi, Elina, Sarkela, Mika, Scheinin, Harry, Maksimow, Anu, Jaaskelainen, Satu, Langsjo, Jaako
• Granted Patent: US 7,805,187 B2
• Time in Patent Office: Days
• US Class Current: 604/503
• CPC Class Codes: A61B 5/18 for vehicle drivers or machine operators
• CPC Class Codes: A61B 5/369 Electroencephalography [EEG] devices for psychotechnics A61B5/16
• CPC Class Codes: A61B 5/389 Electromyography [EMG]
• CPC Class Codes: A61B 5/398 Electrooculography [EOG], e.g. detecting nystagmus; Electroretinography [ERG]
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61B 5/4839 combined with drug delivery

Abstract

The invention relates to a method and apparatus for monitoring the anesthetic state of a subject. Physiological signal data including EEG and possibly also EMG signal components is acquired from a subject and supplied to a monitoring process configured to derive, based on the said data, a state index indicative of the anesthetic state of the subject. In order to extend the applicability of present-day monitoring processes, the operation of the monitoring process is controlled according to whether at least one drug inducing high frequency EEG signal components is administered to the subject. The presence of the high frequency EEG signal components in the physiological signal data may be detected automatically.

Claims

1. A method for monitoring the cerebral state of a subject, the method comprising the steps of:

obtaining physiological signal data from a subject, the physiological signal data including EEG signal components;

supplying the physiological signal data to a monitoring process configured to derive a state index from the physiological signal data, the state index being indicative of the cerebral state of the subject; and

controlling the operation of the monitoring process according to whether at least one drug inducing high frequency EEG signal components is administered to the subject.

2. A method according to claim 1, wherein the at least one drug is an NMDA antagonists.

3. A method according to claim 1, wherein the at least one drug belongs to a group including ketamine, S-ketamine, nitrous oxide, and xenon.

4. A method according to claim 1, further comprising a step of detecting whether the at least one drug is administered to the subject.

5. A method according to claim 4, wherein the detecting step includes the sub-steps of:

monitoring whether high frequency EEG signal components are substantially present in the physiological signal data; and

performing the controlling step upon detecting that the high frequency EEG signal components are substantially present in the physiological signal data.

6. A method according to claim 5, wherein the monitoring sub-step includes the sub-steps of:

calculating, based on the physiological signal data, signal power values on two predetermined frequency bands, whereby two signal power values are obtained;

deriving a variable based on the two signal power values; and

comparing the variable with a predetermined threshold value to detect whether the high frequency EEG signal components are substantially present in the physiological signal data.

7. A method according to claim 6, wherein

the calculating sub-step includes calculating signal power on a first frequency band covering both EEG and EMG frequencies and on a second frequency band covering only. EMG frequencies;

and

the deriving sub-step includes calculating the ratio of the two signal power values.

8. A method according to claim 7, wherein the first frequency band extends from a frequency of about 32 Hz to a frequency of about 47 Hz and the second frequency band extends from a frequency of about 105 Hz to a frequency of about 145 Hz.

9. A method according to claim 1, wherein the controlling step includes indicating at least one frequency band value to be used in the monitoring process in order to derive the state index.

10. A method according to claim 1, wherein the controlling step includes controlling the monitoring process to determine the state index as the entropy of the physiological signal data calculated over a frequency range extending from a frequency of about 0.5 Hz to a frequency which is above 80 Hz.

11. A method according to claim 1, wherein the controlling step includes controlling the operation of the monitoring process through a user-operated actuator.

12. A method according to claim 1, further comprising a step of producing an indication informing whether the at least one drug is administered to the subject.

13. A method according to claim 12, wherein the producing step includes producing the indication, in which the indication is produced in a drug delivery system.

14. An apparatus for monitoring the cerebral state of a subject, the apparatus comprising:

first measurement means for obtaining physiological signal data from a subject, the physiological signal data including EEG signal components;

monitoring means for deriving a state index from the physiological signal data, the state index being indicative of the cerebral state of the subject; and

control means for controlling the operation of the monitoring means according to whether at least one drug inducing high frequency EEG signal components is administered to the subject.

15. An apparatus according to claim 14, wherein the control means are configured to:

monitor whether the high frequency EEG signal components are substantially present in the physiological signal data; and

control the operation of the monitoring means upon detection of a substantial presence of the high frequency EEG signal components in the physiological signal data.

16. An apparatus according to claim 15, wherein the controlling means are further configured to

calculate signal power values on two predetermined frequency bands, thereby to obtain two signal power values;

derive a variable based on the two signal power values; and

compare the variable with a predetermined threshold value.

17. An apparatus according to claim 14, wherein the control means include a user-operated actuator for controlling the operation of the monitoring means.

18. An apparatus for monitoring the cerebral state of a subject, the apparatus comprising:

a monitoring device configured to obtain physiological signal data from a subject, the physiological signal data including EEG signal components, and to derive a state index from the physiological signal data, the state index being indicative of the cerebral state of the subject; and

a first controller configured to control the operation of the monitoring device according to whether at least one drug inducing high frequency EEG signal components is administered to the subject.

19. A computer program product for monitoring the cerebral state of a subject, the computer program product comprising:

a first program code portion configured to receive a control instruction for controlling the operation of a monitoring process adapted to derive a state index indicative of the cerebral state of the subject; and

a second program code portion configured to control the operation of the monitoring process in response to the control instruction.

20. A computer program product according to claim 19, further comprising a third program code portion configured to determine whether high frequency EEG signal components are substantially present in physiological signal data obtained from the subject.