EEG operative and post-operative patient monitoring method

• US 6,067,467 A
• Filed: 12/21/1998
• Issued: 05/23/2000
• Est. Priority Date: 02/07/1994
• Status: Expired due to Term

• Current Assignee: New York University
• Original Assignee: New York University
• Inventors: John, Erwin Roy
• Primary Examiner(s): Dvorak, Linda C. M.
• Assistant Examiner(s): YARNELL, BRYAN KEITH
• Application Number:
  US09/217,010
• Time in Patent Office: 519 Days
• Field of Search: 600/483, 600/484, 600/544, 600/546, 600/545, 600/485, 600/529, 600/509
• US Class Current: 600/544
• CPC Class Codes: A61B 5/1106 to assess neuromuscular blockade, e.g. to estimate depth of anaesthesia
• CPC Class Codes: A61B 5/377 using evoked responses
• CPC Class Codes: A61B 5/383 Somatosensory stimuli, e.g. electric stimulation
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G16H 20/40 relating to mechanical, radiation or invasive therapies, e.g. surgery, laser therapy, dialysis or acupuncture
• CPC Class Codes: G16H 40/60 for the operation of medical equipment or devices
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems
• CPC Class Codes: G16H 50/30 for calculating health indices; for individual health risk assessment

Abstract

An electrocephalograph (EEG) method is provided to monitor patients during and after medical operations. An anesthesiologist administers sufficient anesthetics to cause the patient to attain the desired plane of anesthesia. The patient'"'"'s brain waves, both ongoing and evoked by stimuli, are amplified, digitized and recorded. That pre-operative set of brain wave data is compared to a set of the patient'"'"'s brain wave data obtained during the operation in order to determine if additional, or less, anesthesia is required, paying particular attention to the relative power in the theta band, as an indication of brain blood flow, and prolongations of the latency periods under brain stem stimuli, as an indication of the patient'"'"'s ability to feel pain. A set of neurometric features are extracted, converted into a normalized statistical score, a discriminant score is thereby developed and the discriminant score converted to a patient state index using probability functions.

Claims

1. An electroencephalograph (EEG) method for monitoring the plane of anesthesia of a patient undergoing a medical procedure, comprising:

(a) removably connecting a set of EEG electrodes to the scalp of the patient and administering sufficient anesthesia to the patient for the patient to attain the plane of anesthesia selected by the anesthesiologist;

(b) presenting a set of stimuli to the patient and amplifying and digitizing the brain wave evoked responses to the stimuli and the patient'"'"'s ongoing brain wave activity collected from the EEG electrodes to provide a first set of digital data representing a set of features of the patient'"'"'s brain waves in the patient'"'"'s pre-operative anesthetized state and recording the first set of digital data in computer system memory;

(c) during the operation, presenting the same set of stimuli to the patient and amplifying and digitizing the brain wave responses to the stimuli and the patient'"'"'s on-going brain wave activity to provide a second set of digital data regarding the same set of features as the first set;

(d) using the computer system to statistically compare the first and second sets of digital data on a feature-by-feature basis;

(e) deriving a discriminant score based on the comparisons of (d) by selectively weighting, selecting and combining a number of said feature-by-feature comparisons;

(f) combining the discriminant scores to derive probabilities that the patient is in a specific anesthetized state;

(g) applying selected guardbands (rule-out levels) to the probabilities to classify the anesthetized state of the patient on the basis of the probabilities; and

(h) providing a warning if the patient is not in a fully anesthetized state during the operation based on the classification of (g); and

(i) adjusting the anesthesia administered to the patient during the operation in response to the warning to restore the patient to the selected plane of anesthesia.

2. The method of claim 1 and including statistically comparing the second set of data with a normative reference database of features based on the successful outcomes of specific surgical procedures using specific anesthetic materials and deriving a second discriminant score based thereon.

3. The method of claim 2 in which the normative reference database of features are in the form of age-corrected Z-scores which are in the same dimensional unit.

4. The method of claim 1 and including statistically comparing the second set of data with a normative reference database based on post-operative reports of successful operative administration of anesthesia.

5. The method of claim 1 wherein the stimuli are auditory and the evoked responses are brain stem auditory responses (BSAR).

6. The method of claim 1 wherein the stimuli are sensory and the evoked responses are brainstem somatosensory evoked responses (BSER).

7. The method of claim 1 wherein a plurality of EEG electrodes are employed and the comparisons of (d) are displayed in a display corresponding to the locations of the EEG electrodes and displaying graphic trajectories representing changes in brain wave states at each EEG electrode.

8. The method of claim 1 wherein the measures of the ongoing EEG include absolute and relative power in the Delta, Theta, Alpha and Beta bands.

9. The method of claim 1 wherein the warning is a visual signal on a computer system monitor screen, a sound or a vibratory signal on a wrist band worn by the operator.

10. The method of claim 1 wherein the patient'"'"'s ongoing brain wave activity in (b) and (c) includes the relative brain wave power in the Theta band (3.5-7.5) as an indication of cerebral blood flow.

11. An electroencephalograph (EEG) method for monitoring the plane of anesthesia of a patient undergoing a medical procedure to determine the patient'"'"'s ability to feel pain, comprising:

(a) removably connecting a set of EEG electrodes to the scalp of the patient and administering sufficient anesthesia to the patient for the patient to attain the plane of anesthesia selected by the anesthesiologist;

(b) presenting a set of stimuli to the patient and amplifying and digitizing the brain wave evoked responses to the stimuli collected from the EEG electrodes to provide a first set of digital data representing a set of features of the patient'"'"'s brain waves in the patient'"'"'s pre-operative anesthetized state and recording the first set of digital data in computer system memory;

(c) during the operation, presenting the same set of stimuli to the patient and amplifying and digitizing the brain wave responses to the stimuli to provide a second set of digital data representing the same features;

(d) using the computer system to statistically compare the first and second sets of digital data including comparison features representing prolongations of the latency of periods of the brain stem and

(e) providing a warning if any latency periods are abnormal by being of a period shorter than a selected range and if the patient is classified in (g) in a non-fully anesthetized state;

(f) providing a discriminate score based on the comparisons of (d) by selectively weighting, selecting and combining a number of the feature-by-feature comparisons;

(g) combining the discriminant scores to derive probabilities that the patient is in a specific anesthesized state;

(h) applying selected guardbands (rule-out levels) to the probabilities to classify the anesthetized state of the patient on the basis of the probabilities;

(i) providing a warning if the patient is not in a fully anesthetized state during the operation based on the classification of (h); and

(j) adjusting the anesthesia administered to the patient during the operation in response to the warning to restore the patient to the selected plane of anesthesia.

12. The method of claim 11 and including statistically comparing the second set of data with a normative reference database based on the successful outcomes of specific surgical procedures using specific anesthetic materials.

13. The method of claim 11 and including statistically comparing the second set of data with a normative reference database based on post-operative reports of the successful operative administration of anesthesia.

14. The method of claim 11 wherein the stimuli are auditory and the evoked responses are brain stem auditory responses (BSAR).

15. The method of claim 11 wherein the stimuli are electrical or tactile and the evoked responses are brainstem somatosensory evoked responses (BSER).

16. The method of claim 11 wherein a plurality of EEG electrodes are employed and the comparisons of (d) are displayed in a display corresponding to the locations of the EEG electrodes and displaying graphic trajectories representing changes in brain wave states at each EEG electrode.

17. The method of claim 11 wherein the warning is a visual signal on a computer system monitor screen.

18. The method of claim 11 wherein the warning is a vibratory signal delivered by a wristband.

19. An electroencephalograph (EEG) method for monitoring the plane of anesthesia of a patient undergoing a medical procedure, comprising:

(a) removably connecting an EMG (electromyograph) and an EEG (electroencephalograph) electrode to the front of the scalp of the patient and administering sufficient anesthesia to the patient for the patient to attain the plane of anesthesia selected by the anesthesiologist;

(b) amplifying and digitizing the brainwaves in the Beta 2 band from the EEG electrode and amplifying and digitizing the patient'"'"'s facial muscle activity from the EMG electrode to provide a set of digital data representing the patient'"'"'s brain waves in the Beta 2 band and facial muscle activity during the patient'"'"'s pre-operative anesthetized state and displaying said first set to the anesthesiologist;

(c) providing a warning if the patient shows too much facial muscle activity and brain wave activity in the Beta band prior to or during the operation indicating insufficient anesthesia;

(d) adjusting the anesthesia administered to the patient in response to a warning to decrease the anesthesia and yet maintain the patient at the selected plane of anesthesia.

20. An electroencephalograph (EEG) method for monitoring the plane of anesthesia of a patient undergoing a medical procedure, comprising:

(a) removably connecting a plurality of EEG electrodes to the scalp of the patient;

(b) amplifying and digitizing the patient'"'"'s ongoing brain wave activity collected from the EEG electrodes to provide a first set of digital data representing mean total EEG power in the patient'"'"'s pre-operative and pre-anesthetized state;

(c) administering sufficient anesthesia to the patient for the patient to attain the plane of anesthesia selected by the anesthesiologist;

(d) and after (c), digitizing the patient'"'"'s ongoing brain wave activity to provide a second set of digital data representing mean total EEG power;

(e) using the computer system to statistically compare the first and second sets of digital data;

(f) providing a warning of burst suppression indicating an excess of anesthesia if the mean total power of the second set is significantly below the mean total power of the first set based on the comparison of (d); and

(g) administering less anesthesia to the patient in response to the warning.

21. An electroencephalograph (EEG) method for monitoring the plane of anesthesia of a patient undergoing a medical procedure, comprising:

(a) removably connecting an EMG (electromyograph) and EEG (electroencephalograph) electrode to the front of the scalp of the patient and administering sufficient anesthesia to the patient for the patient to attain the plane of anesthesia selected by the anesthesiologist;

(b) amplifying and digitizing the brainwaves in the Beta 2 band from the EEG electrode and amplifying and digitizing the patient'"'"'s facial muscle activity from the EMG electrode to provide a first set of digital data representing a set of facial muscle activity during the patient'"'"'s pre-operative anesthetized state and recording the first set of digital data in computer system memory;

(c) during the operation, amplifying and digitizing the brain wave responses in the Beta 2 band from the EEG electrode and the patient'"'"'s facial muscle activity from the EMG electrode to provide a second set of digital data;

(d) using the computer system to statistically compare the first and second sets of digital data;

(e) providing a warning if the patient shows excessive muscle activity during the operation indicting insufficient anesthesia based on the comparison of (d); and

(f) adjusting the anesthesia administered to the patient during the operation in response to the warning to decrease the anesthesia and yet maintain the patient at the selected plane of anesthesia.

22. An electroencephalograph (EEG) method for monitoring the plane of anesthesia of a patient undergoing a medical procedure, comprising:

(a) removably connecting a plurality of EEG electrodes to the scalp of the patient and administering sufficient anesthesia to the patient for the patient to attain the plane of anesthesia selected by the anesthesiologist;

(b) amplifying and digitizing the patient'"'"'s ongoing brain wave activity collected from the EEG electrodes to provide a first set of digital data representing mean total EEG power in the patient'"'"'s pre-operative anesthetized state and recording the first set of digital data in computer system memory;

(c) before or during the operation, amplifying and digitizing the patient'"'"'s ongoing brain wave activity to provide a second set of digital data presenting mean total EEG power;

(d) using the computer system to statistically compare the first and second sets of digital data;

(e) providing a warning of burst suppression indicating an excess of anesthesia if the mean total power of the second set is significantly below the mean total power of the first set based on the comparison of (d); and

(f) administering less anesthesia to the patient in response to the warning.

23. An electroencephalograph (EEG) method for monitoring the plane of anesthesia of a patient undergoing a medical procedure, comprising:

(a) removably connecting a plurality of EEG electrodes to the scalp of the patient, connecting a plurality of EKG electrodes to the chest of the patient, connecting at least one blood pressure (BP) sensor to the patient, connecting at least one respiration sensor to the patient, and administering sufficient anesthesia to the patient for the patient to attain the plane of anesthesia selected by the anesthesiologist;

(b) amplifying and digitizing the patient'"'"'s ongoing brain wave activity collected from the EEG electrodes, the patient'"'"'s heart beat rate from the EKG electrodes, the patient'"'"'s blood pressure from the blood pressure sensor and the patient'"'"'s respiration from the respiration sensor to provide in each case a self-norm comprising a first set of digital data representing the patient'"'"'s pre-operative anesthetized state and, in each case, recording the first set of digital data in computer system memory;

(c) before or during the operation, amplifying and digitizing the patient'"'"'s ongoing brain wave activity, EKG, BP and respiration to provide, in each case, a second set of digital data representing total EEG power, EKG, BP and respiration;

(d) using the computer system to statistically, in each case, to compare the first and second sets of digital data;

(e) providing a warning indicating an excess or lack of anesthesia if, in each case, the second set deviates significantly from the first set based on the comparison of (d); and

(f) administering less or more anesthesia to the patient in response to the warning.

24. An electroencephalograph (EEG) method for monitoring the plane of anesthesia of a patient undergoing a medical procedure, comprising:

(a) removably connecting a set of EEG electrodes to the scalp of the patient;

(b) amplifying and digitizing the patient'"'"'s brain wave activity collected from the EEG electrodes to provide a set of digital data and recording the set of digital data in a memory component of a computer system;

(c) using the computer system to extract a set of neurometric features from the digital data;

(d) removing artifacts from the set of neurometric features;

(e) using the computer system to convert the features by a transformation into a normalized statistical score;

(f) developing a discriminant score by applying a plurality of predetermined weighting factors to the normalized statistical scores and summing the products;

(g) converting the discriminant score to a patient state index (PSI) using probability functions;

(h) displaying the patient state index (PSI) on a monitor;

(i) repeating steps (b) through (h) at predetermined intervals and displaying the patient state index (PSI) in a time ordered sequence on the monitor;

(j) administering anesthesia to the patient so as to attain a plane of anesthesia selected by an anesthesiologist;

(k) performing steps (a) to (h) while the patient is at the selected plane of anesthesia of (i) to develop and display a patient state index (PSI) which is a self-norm of the patient at the selected plane of anesthesia;

(l) repeating steps (a)-(h) during the medical procedure and after step (j) while the patient is anesthetized to develop and display the patient state index; and

(m) providing more or less anesthesia to the patient in response to statistically significant changes of the PSI in step (l) compared to the self-norm of step (k).

25. The method of claim 24 and in step (b) amplifying and digitizing the patient'"'"'s ongoing brain wave activity.

26. The method of claim 25 wherein in step (e) the transformation is a logarithmic transformation and the normalized statistical score is a Z-score.

27. The method of claim 24 and in step (b) providing evoked potential stimuli to a patient and amplifying and digitizing the patient'"'"'s evoked brain wave activity.

28. The method of claim 24 and obtaining a self-norm of the patient prior to administering anesthesia to the patient by performing steps (a)-(h) prior to administration of anesthesia.

29. The method of claim 24 and in (d) removing artifacts by rejection of epochs of digital data in which (i) an EEG signal is too high, (ii) an epoch contains sharp waves, (iii) the voltage of an epoch is under a predetermined voltage, and (iv) an epoch contains a large voltage excursion.