Surgery – Truss – Pad
Patent
1987-03-30
1989-09-26
Wayner, William E.
Surgery
Truss
Pad
128741, 128745, A61B 504
Patent
active
048692646
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an anaesthetic monitor.
More particularly the invention relates to a method and apparatus for monitoring the level of consciousness of a subject who has been subjected to a general anaesthetic. Information concerning anaesthetic depth and the level of consciousness would be of considerable usefulness to the person administering the anaesthetic so that the administration of the anaesthetic can be controlled so as to give a desired anaesthetic depth and level of consciousness.
According to the present invention there is provided a method of testing anaesthetic depth or consciousness of a subject comprising the steps of applying a stimulus signal including at least one component of a predetermined frequency to a sensory organ of the subject, obtaining an electroencephalographic (EEG) signal from the subject whilst said stimulus signal is being applied, analysing the EEG signal so as to determine the magnitude and/or phase of that component of the EEG signal which has said predetermined frequency, and assessing the anaesthetic depth or consciousness of the subject with reference to said magnitude and/or phase of the component.
Preferably, the method includes steps for applying a stimulus signal having a plurality of predetermined frequency components therein and the analysis of the EEG signal is carried out to determine the magnitude and/or phase of the respective components in the EEG having the same frequencies as the stimulus signal.
Preferably further, the method includes the step of simultaneously applying selected groups of said frequency components.
Preferably further, the stimulus signal comprises electromagnetic radiation. Preferably further, the radiation comprises visible red radiation modulated in amplitude so as to have components at said plurality of predetermined frequencies. Preferably further, the frequency components are in the range of 4 to 72 Hz. The method may be used to test the consciousness of a subject under anaesthetic and, in this application, the method includes the step of administering anaesthetic in accordance with the magnitude and/or phase of the components.
In this case, the preferred method of treating the subject is to subject the subject to the method prior to administration of the anaesthetic so as to determine a pre-anaesthetic magnitude and/or phase response of the selected component of the EEG signal (hereinafter called a normal response). The anaesthetic is then administered and the method includes the step of comparing the magnitude after administration of the anaesthetic to the normal response. The comparisons are preferably carried out and displayed as a function of frequency of the stimulus signal.
The invention also provides apparatus for testing consciousness of a subject, said apparatus comprising generator means for generating a stimulus signal having at least one component of a predetermined frequency, coupling means for coupling the stimulus signal to a sensory organ of the subject, EEG electrodes for deriving an EEG signalf rom the subject and discriminating means for obtaining the magnitude and/or phase of that component of the EEG signal which has said predetermined frequency.
Where the apparatus is to be used for testing the consciousness of a subject under anaesthetic, it is important that the apparatus yields the information quickly regarding the magnitude and/or phase of the selected frequency component of the EEG signal so that personnel administering the anaesthetic will be in a position to monitor the results and thereby control the rate of administration of the anaesthetic to the subject.
The invention will now be further described with reference to the accompanying drawings, in which:
FIG. 1 is a block diagram showing the basic components of the anaesthetic monitoring system of the invention;
FIG. 2 is a schematic plan view showing EEG electrodes and Light Emitting Diode (LED) arrays relative to a subject;
FIGS. 3A to 3D illustrate graphical output displays of the system;
FIG. 4 is a block diagram showing the stimulus gen
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patent: 3513834 (1970-05-01), Suzuki et al.
patent: 3689135 (1972-09-01), Young et al.
patent: 4201224 (1980-05-01), John
patent: 4570640 (1986-02-01), Barsa
"Proceedings of the Eleventh Annual Northeast Bioengineering Conference", 14th-15th Mar. 1985, Worcester, MA, pp. 128-134, IEEE, NY, US; J. H. Strickland, Jr., et al.: Visual Evoked Response Phase Spectrum as Measure of Latency.
"Measuring the Level of Anesthesia by Automatic Analysis of Spontaneous EEG Activity", McEwen et al., IEEE Transactions on Biomedical Engineering, Jul. 1975, pp. 299-305.
Swineburn Limited
Wayner William E.
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