Apparatus for the Assessment of the Level of Pain and Nociception During General Anesthesia Using Electroencephalogram, Plethysmographic Impedance Cardiography, Heart Rate Variability and the Concentration or Biophase of the Analgesics

Abstract

Means and methods for measuring pain and adapted for calculating the level of nociception during general anesthesia or sedation from data including electroencephalogram (EEG), facial electromyogram (EMG), heart rate variability (HRV) by electrocardiogram (ECG) and plethysmography by impedance cardiography (ICG). In a preferred embodiment of this invention the parameters derived from the EEG, the HRV, the plethysmographic curve and the analgetics concentrations are either combined into one index on a scale from 0 to 100, where a high number is associated with high probability of response to noxious stimuli, while a decreasing index is associated with decreasing probability of response to noxious stimuli. Zero (0) indicates extremely low probability of response to noxious stimuli. In an alternative embodiment, only features from the EEG and ECG will be used or only features from EEG, ECG and ICG, to define the fmal index.

Claims

1. An apparatus equipped with means for estimating pain and nociception while awake, during general anesthesia or sedation from data including electroencephalogram (EEG), facial electromyogram (EMG), heart rate variability (HRV) by electrocardiogram (ECG) and plethysmography by impedance cardiography (ICG), the apparatus comprising the following features: (a) means for obtaining a signal containing EEG and facial EMG, said mean adapted for recording from a subjects scalp with three electrodes positioned at middle forehead, left (right) forehead and the left (right) cheek; (b) means for obtaining a three leads ECG signal and adaptations for calculating the R-R interval and the HRV from said ECG signal; (c) means for obtaining an ICG signal with four electrodes positioned at the chest of the patient; (d) means for obtaining the plethysmographic from the ICG; (e) adaptation for calculating the Fast Fourier Transform (FFT) and the Choi-Williams distributions for about 1-60 seconds of the EEG signal; (f) adaptations for calculating the frequency spectrum in about 1-10 seconds EMG signal; (g) adaptations for calculating the spectral edge frequency of the spectrum of the R-R interval of the ECG over about 2-6 minutes; (h) adaptations for calculating the Hilbert transform of the 1CG signal from which the number of peaks over a certain threshold in the 1st derivative of the Hilbert phase, is estimated; (i) means adapted for combining the extracted EEG, EMG, EGG, and ICG data into a final index of nociception represented by a scale from 0 to 99, where a value of 99 represents a high probability of response to light noxious stimuli and a value of close or equal to 0 corresponds to a total block of afferent noxious stimuli, for example obtained by local anesthetic drugs.

2. The apparatus according to claim 1 is further defined as the position of the electrodes can be either middle forehead (Fp, in the international 10-20 electrode positioning system), left forehead (F7) and the left cheek (temporal process) 2 cm below the middle eye line or the electrode position can alternatively be middle forehead, right forehead and the right cheek (temporal process) 2 cm below the middle eye line.

3. The apparatus according to claim 1 is further refined by calculating the HRV by doing a Fast Fourier Transform (FFT) of the signal defined as the R-R interval and the ninety-five percent Spectral Edge Frequency (SEF) of the spectrum is used for a subsequent calculation of the Index of nociception.

4. The apparatus according to claim 1 is further refined by calculating the Hilbert transform of the plethysmographic curve.

5. The apparatus according to claim 1 is further refined by estimating the Choi-Williams distribution over about at least 1-60 s and about at least 0-100 Hz, the variability of the energy of 1 s and 1 Hz squares are calculated.

6. The apparatus according to claim 1 which is further refined by calculating the mutual information and Fokker-Planck drift and diffusion coefficients between the EEG and impedance cardiography.

7. The apparatus according to claim 1 is further defined by calculating the energy in different frequency bands of the spectrum.

8. The apparatus according to claim 1 is further defined as the principle of Fast Fourier Transform (FFT) of the R-R intervals; from the spectrum the ninety-five percent Spectral Edge Frequency (SEF) is calculated and used for the subsequent calculation of the Index of nociception.

9. The apparatus according to claim 1is further refined as the ICG is measured with a sampling frequency of about 250 Hz whereafter the Hilbert transform is carried out on a signal of about 1 to 10 s duration; from which the number of peaks in the first derivative of the Hilbert phase which are over a certain threshold, is calculated; this parameter is used for the subsequent calculation of the Index of nociception.

10. The apparatus according to claim 1 describe parameters which are all included in a classifier, which could be but not necessarily a multiple linear or logistic regression, a quadratic equation or a fuzzy inference reasoner or a an adaptive neuro fuzzy inference system, where the output of the classifier is the Index of nociception, an index associated with the probability of response of the patient to noxious stimuli.

11. A method for estimating pain and for calculating the level of nociception while awake, during general anesthesia or sedation from data including electroencephalogram (EEG), facial electromyogram (EMG), heart rate variability (HRV) by electrocardiogram (ECG) and plethysmography by impedance cardiography (ICG), the method comprising the steps of: (a) obtaining a signal recording containing EEG and facial EMG from a subjects scalp with three electrodes positioned at middle forehead, left (right) forehead and the left (right) cheek; (b) obtaining a three leads ECG signal and calculating the R-R interval and the HRV from said ECG signal; (c) obtaining an ICG signal with four electrodes positioned at the chest of the patient; (d) obtaining the plethysmographic from the ICG; (e) calculating the Fast Fourier Transform (EFT) and the Choi-Williams distributions for about 1-60 seconds of the EEG signal; (f) calculating the frequency spectrum in a 1-10 seconds EMG signal; (g) calculating the spectral edge frequency of the spectrum of the R-R interval of the ECG over about 2-6 minutes; (h) calculating the Hilbert transform of the ICG signal from which the number of peaks over a certain threshold in the 1st derivative of the Hilbert phase is estimated; (i) combining the extracted EEG, EMG, ECG, and ICG data into a final index of nociception represented by a scale from 0 to 99, where a value of 99 represents a high probability of response to light noxious stimuli and a value of close or equal to 0 corresponds to a total block of afferent noxious stimuli, for example obtained by local anesthetic drugs.

12. The method according to claim 11, wherein said electrodes can be further positioned in a place selected from group consisting of: middle forehead (Fp, in the international 10-20 electrode positioning system), left forehead (F7) and the left cheek (temporal process) 2 cm below the middle eye line or the electrode position can alternatively be middle forehead, right forehead and the right cheek (temporal process) 2 cm below the middle eye line, and any combination thereof.

13. The method according to claim 11 further comprising a step of calculating the HRV by doing a Fast Fourier Transform (FFT) of the signal defined as the R-R interval; the ninety-five percent Spectral Edge Frequency (SEF) of the spectrum is used for the subsequent calculation of the Index of nociception.

14. The method according to claim 11 further comprising a step of calculating the Hilbert transform of the plethysmographic curve.

15. The method according to claim 11 further comprising a step of estimating the Choi-Williams distribution over about at least 1-60 s and about at least 0-100 Hz, the variability of the energy of 1 s and 1 Hz squares are calculated.

16. The method according to claim 11, wherein said method further comprises a step of calculating the mutual information and Fokker-Planck drift and diffusion coefficients between the EEG and impedance cardiography.

17. The method according to claim 11, wherein said step of calculating the frequency spectrum in a 1-10 seconds EMG signal further comprises a step of calculating the energy in different frequency bands of the spectrum.

18. The method according to claim 11, wherein said step of calculating the Hilbert transform of the ICG signal from which the number of peaks over a certain threshold in the 1.sup.st derivative of the Hilbert phase is estimated is further defined as the principle of Fast Fourier Transform (FFT) of the R-R intervals; from the spectrum the ninety-five percent Spectral Edge Frequency (SEF) is calculated and used for the subsequent calculation of the Index of nociception.

19. The method according to claim 11, wherein said step of calculating the Hilbert transform of the ICG signal from which the number of peaks over a certain threshold in the 1.sup.st derivative of the Hilbert phase is estimated is further refined as the ICG is measured with a sampling frequency of about 10-1024 Hz whereafter the Hilbert transform is carried out on a signal of 1 to 10 s duration from which the number of peaks in the first derivative of the Hilbert phase which are over a certain threshold are calculated to yield a parameter that is used for a subsequent calculation of the Index of nociception.

20. The method according to claim 1, wherein said method describes parameters which are all included in a classifier, which could be but is not necessarily a multiple linear or logistic regression, quadratic equation or a fuzzy inference reasoner or a an adaptive neuro fuzzy inference system, where the output of the classifier is the Index of nociception, an index associated with the probability of response of the patient to noxious stimuli.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0075] FIG. 1 showing a schematic flow chart of the present invention.

[0076] FIG. 2 showing a schematic graph of the evolution of the Composite Nociception Index (CNI) during infusion of an analgesic.

[0077] FIG. 3 showing a schematic graph of the sigmoidal curve showing the conceptual relationship between the Composite Nociception Index (CNI) and the probability of response to a noxious stimulus.

[0078] FIG. 4 showing a schematic flow chart of the spectral analysis of the R-R intervals which is estimated by a Fast Fourier transform. The Spectral Edge Frequency (SEF) is defined as the frequency where 95% of the area or energy of the spectrum is reached.