Anesthesia adequacy monitor and method

• US 5,195,531 A
• Filed: 03/01/1991
• Issued: 03/23/1993
• Est. Priority Date: 03/01/1991
• Status: Expired due to Term

• Current Assignee: Patient Comfort LLC
• Original Assignee: Henry L. Bennett
• Inventors: Bennett, Henry L.
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): Tucker, Guy V.
• Application Number:
  US07/663,434
• Time in Patent Office: 753 Days
• Field of Search: 128/733, 128/731, 128/744, 128/745, 128/741, 128/639, 128/640, 128/641, 128/642, 128/643, 128/644
• US Class Current: 600/546
• CPC Class Codes: A61B 2505/05 Surgical care
• CPC Class Codes: A61B 5/03 Detecting, measuring or recording fluid pressure within the body other than blood pressure, e.g. cerebral pressure; Measuring pressure in body tissues or organs A61B5/205 takes precedence
• CPC Class Codes: A61B 5/1106 to assess neuromuscular blockade, e.g. to estimate depth of anaesthesia
• CPC Class Codes: A61B 5/224 Measuring muscular strength
• CPC Class Codes: A61B 5/296 for electromyography [EMG]
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61B 5/6814 Head
• CPC Class Codes: A61M 16/104 specially adapted for anaesthetics A61M16/18 takes precedence
• CPC Class Codes: A61M 2230/18 Rapid eye-movements [REM]
• CPC Class Codes: A61M 2230/60 Muscle strain, i.e. measured on the user

Abstract

The anesthesia adequacy monitor measures the level of consciousness of a patient as distinguished from merely the physical paralysis of the patient. Sensors attached to the patient'"'"'s face measure the micro-expression the patient is exhibiting which is normally undetectable by even a trained observer. This device amplifies the patient'"'"'s expression and thereby provides both a quantative and a qualitative measure of the patient'"'"'s reactions to various stimuli during apparent unconsciousness. A display is provided giving an operator a readily discernable representation of the patient'"'"'s awareness. An artifact detector further enhances the device'"'"'s utility by filtering out unwanted anomalies from the monitor'"'"'s output. During surgery, this device can be used to maintain an adequate level of patient awareness while the patient is under anesthesia. After an event resulting in apparent unconsciousness, this device can provide a measure of the patient'"'"'s true level of awareness. In this way, patient comfort is maximized and patient recovery time is minimized.

Claims

1. A device for monitoring the consciousness of a patient under anesthesia comprising, in combination:

an array of facial muscle sensors adapted to be strategically located on the patient to generate signals representing the activity of at least two facial muscles, said muscles being responsible for eliciting distinctive patterns of facial expressions,

a processor for interpreting the patient'"'"'s awareness from comparison of measurements made by said sensors and operatively coupled to said sensors, wherein said processor includes a means for determining the facial expression of the patient by interpreting a signal created by said sensors, and

a display with means receiving output from said processor for accurately communicating to an anesthesiologist the level of patient awareness and therefore consciousness;

whereby the anesthesiologist may monitor the patient'"'"'s consciousness and take corrective action to improve patient comfort when indicated.

2. The monitoring device of claim 1 wherein said sensors are surface electromyograms adapted to be physically attached to the patient'"'"'s face in positions allowing monitoring of multiple facial muscles.

3. The monitoring device of claim 2 wherein a signal pathway is interposed between said sensors and said processor whereby a signal originating in said sensor may be transported to said processor.

4. The monitoring device of claim 3 wherein said processor is a microcomputer which is programmed to determine the facial expression of the patient by interpreting said signal created by said sensors and include means to amplify said signal between said sensors and said processor.

5. The monitoring device of claim 4 wherein a signal filter is interposed between said sensors and said microcomputer for filtering out artifacts from said signal which represent muscle contraction caused by a known external electric stimulus device, said signal filter enabled by the electric stimulus device, whereby the signal may accurately represent the patient'"'"'s facial response to nerve sensation without distortion caused by the electric stimulus device used on the anesthetized patient during an operating procedure.

6. The monitoring device of claim 5 wherein said sensors include plural surface electromyograms all of which combine to create said signal for input to said microcomputer, whereby a more accurate representation of the patient'"'"'s expression may be determined.

7. The monitoring device of claim 6 wherein said surface electromyograms are adapted to be attached to Corrugator and Frontalis facial muscles, such that detailed patient awareness analysis may be performed.

8. The monitoring device of claim 6 wherein said surface electromyograms are adapted to be attached to Corrugator, Zygomatic, Frontalis, and Masseter facial muscles.

9. A consciousness detector for informing an anesthesiologist of the level of consciousness of a patient under anesthesia through detection of the patient'"'"'s facial expression comprising, in combination:

an array of facial muscle sensors adapted to be strategically located on the patient and generating signals relating to measurements of the activity of at least two facial muscles, said muscles being responsible for eliciting distinctive patterns of facial expressions,

a signal processing system for interpreting the patient'"'"'s awareness coupled to said sensor array said signal processing system including a means for comparing said sensor signals, said signal processing system determining the facial expression of the patient by interpreting said sensor signals and converting a first signal representing raw sensor output from said sensors into a second signal representing output from said signal processing system reflective of the patient'"'"'s facial expression, and

a display device operatively driven by said second signal;

whereby when an unexpectedly high or unexpectedly low level of patient consciousness is detected the anesthesiologist may take corrective action.

10. The consciousness detector of claim 9 wherein an artifact detector and signal compensator are interposed between said array of sensors and said signal processing system such that when external electrical or physical forces are applied to the patient under anesthesia said artifact detector and signal compensator filters out the direct effect of these external forces on the patient'"'"'s facial muscles and the indirect effect on said first signal;

whereby said first signal is shielded from distortion providing a more accurate representation of the patient'"'"'s facial expression in response to nerve stimulation.

11. The consciousness detector of claim 10 wherein said array of sensors is formed from a plurality of surface electromyographs.

12. A consciousness detector for informing an anesthesiologist of the level of consciousness of a patient under anesthesia through detection of the patient'"'"'s facial expression comprising, in combination:

an array of facial muscle sensors adapted to be strategically located on the patient,

a signal processing system coupled to said sensor array capable of converting a first signal representing raw sensor output from said sensors into a second signal representing output from said signal processing system reflective of the patient'"'"'s facial expression, and

a display device operatively driven by said second signal;

whereby when an unexpectedly high or unexpectedly low level of patient consciousness is detected the anesthesiologist may take corrective action,

wherein an artifact detector and signal compensator are interposed between said array of sensors and said signal processing system such that when external electrical or physical forces are applied to the patient under anesthesia the direct effect of these external forces on the patient'"'"'s facial muscles and the indirect effect on said first signal is filtered out of said first signal;

whereby said first signal is shielded from distortion providing a more accurate representation of the patient'"'"'s facial expression in response to nerve stimulation,

wherein said array of sensors is formed from a plurality of surface electromyographs,

wherein said display device is a monitoring screen which displays a human face with indicia communicating the expression represented by said second signal;

whereby the patient'"'"'s expression may be monitored providing the anesthesiologist with an indication of the patient'"'"'s level of consciousness.

13. The consciousness detector of claim 12 wherein said surface electromyographs of said array are adapted to be attached to the Corrugator and Frontalis facial muscles.

14. The consciousness detector of claim 12 wherein said surface electromyographs of said array are adapted to be attached to the Corrugator, Zygomatic, Frontalis and Masseter facial muscles.

15. A method for maintaining an appropriate level of patient unconsciousness under anesthesia, the steps including:

configuring an array of at least two sensors on a patient'"'"'s face,

creating a signal with the sensors,

processing the signal created by the sensors to determine what facial expression the signal represents by comparing the signals from different sensors, the signals being reflective of the patient'"'"'s facial muscle tonus,

displaying the processed signal for viewing by an anesthesiologist on a display,

anesthetizing the patient with an initial dosage of anesthetic to create muscle relaxation in a desired level of consciousness, and

controlling the patient'"'"'s level of consciousness.

16. The unconsciousness maintenance method of claim 15 wherein said controlling step includes:

monitoring the display to determine the patient'"'"'s level of consciousness through subtle changes in the patient'"'"'s facial expressions resulting from stimuli,

administering consciousness correcting means to the patient to correct the patient'"'"'s actual level of consciousness to the desired level of consciousness, and

maintaining the patient'"'"'s level of consciousness by repeating said monitoring step and said administering step.

17. The unconsciousness maintenance method of claim 16 wherein said configuring step includes:

selecting appropriate facial muscle sensors,

attaching the sensors to appropriate muscles on the patient'"'"'s face, and

sending the signal created by the sensors to a signal processor.

18. The unconsciousness maintenance method of claim 17 wherein said processing step includes:

detecting and filtering out artifacts unrepresentative of the patient'"'"'s expression through steps of;

detecting when an artifact generating device is in operation

quantifying the artifact generating device'"'"'s effect on the signal as measured by the facial muscle sensors, and

subtracting from the signal the portion caused by the artifact;

whereby the signal is left unaffected by the artifact.

19. A method for monitoring a patient'"'"'s level of consciousness through detection of a patient'"'"'s facial expression the steps including:

attaching facial muscle sensors to the patient'"'"'s face,

forming an electronic signal from the facial muscle sensor'"'"'s input,

transforming the electric signal into a pictorial display of a face with the facial expression of the patient superimposed thereon, and

magnifying the signal such that the facial expression experienced by the patient is easily noticeable by an operator.

20. The unconsciousness monitoring method of claim 19 wherein said attaching step includes:

placing a sensor on the Corrugator muscle,

placing a sensor on the Zygomatic muscle,

placing a sensor on the Frontalis muscle, and

placing a sensor on the Masseter muscle.

21. An anesthetized patient awareness and facial expression monitor comprising in combination:

an array of facial muscle sensors adopted to be strategically located on the patient to generate signals representing the activity of at least two facial muscles, said muscles being responsible for eliciting distinctive patterns of facial expressions;

signal processing means including awareness detection means and stress detection means, said signal processing means connected to said sensors and utilizing output from said sensors;

wherein said signal processing means includes a means for determining the facial expression of the patient by comparing the signals representing the activity of said at least two facial muscles, and

display means operatively coupled to receive the output from said sensors for communicating patients awareness and stress;

whereby an anesthetized patient may be monitored during surgery to determine the adequacy of the anesthesia through analysis of the patient'"'"'s awareness and stress.

22. The monitor of claim 21 wherein said stress detection means of said signal processing means utilizes quantitative data from said sensors to determine both the existence of and magnitude of the stress level of the patient.

23. A method for monitoring the depth and degree of anesthetization of a patient, the steps including:

segregating into two groups muscles of the patient based on the muscle'"'"'s ability to respectively reflect pain or the absence of pain by change in muscle tonus,

monitoring the activity of at least one muscle from each group,

establishing a baseline for each muscle monitored prior to performing an operatory procedure,

comparing the muscles monitored from each group for relative changes correlative of the patient experiencing pain during the operatory procedure said comparing step including quantifying muscle tonus values for each monitored muscle and calculating a difference between values of at least one muscle from each group to establish a measure of patient pain recognition, and

displaying the comparison.

24. The method of claim 23 including the step of modifying the anesthetic administered to the patient in response to anomalies in the comparison displayed by said displaying step.

25. The method of claim 23 wherein said monitoring step includes monitoring the activity of at least one facial muscle.

26. The method of claim 23 wherein said monitoring step includes monitoring the activity of at least one facial muscle for each group.

27. The method of claim 23 wherein said comparing step includes recognizing a difference between muscles from both groups.

28. The method of claim 23 wherein said monitoring step includes monitoring the activity of the corrugator and frontalis facial muscles.

29. The method of claim 23 wherein said monitoring step includes monitoring the activity of the corrugator, frontalis, masseter and frontalis facial muscles.

30. A method for monitoring the depth and degree of anesthetization of a patient, the steps including:

segregating into two groups muscles of the patient based on the muscle'"'"'s ability to respectively reflect pain or the absence of pain by change in muscle tonus,

monitoring the activity of at least one muscle from each group,

establishing a baseline for each muscle monitored prior to performing an operatory procedure,

comparing the muscles monitored from each group for relative changes correlative of the patient experiencing pain during the operatory procedure;

displaying the comparison; and

wherein said comparing step includes calculating a ratio for each monitored muscle and calculating a difference between values of at least one muscle from each group to establish a measure of patient pain recognition.

31. The method of claim 30 wherein said monitoring step includes monitoring the activity of the corrugator and frontalis facial muscles.

32. The method of claim 30 wherein said monitoring step includes monitoring the activity of the corrugator, frontalis, masseter and frontalis facial muscles.

33. An anesthesia monitor for measuring the depth and quality of patient anesthetization, comprising, in combination:

at least one first sensor adapted to be operatively coupled to at least one patient'"'"'s muscle selected from a first group of muscles having a tonus which changes when a patient experiences pain,

at least one second sensor adapted to be operatively coupled to at least one patient'"'"'s muscle selected from a second group of muscles having a tonus which changes when a patient experiences the absence of pain,

signals emanating from said sensors,

a signal processing means receiving said signals from said first sensors and said second sensors, said signal processing means having means to initialize said signals before said patient undergoes an operatory procedure, said signal processing means having means to measure changes in said signals, said signal processing means having means to compare said signals from said first sensors with said signals from said second sensors reflective of changes in the tonus and for determining the facial expression of the patient from said comparison; and

a display means operatively coupled to said signal processing means for communicating the depth of the patient'"'"'s anesthetization;

whereby a user may determine the depth and quality of patient anesthetization.

34. The monitor of claim 33 wherein at least one of said sensors from either said first group or said second group is a facial muscle sensor, whereby muscle activity related to facial micro-expressions may be monitored.

35. The monitor of claim 33 wherein at least one of said sensors from each said group is a facial muscle sensor, whereby muscle activity related to facial micro-expressions may be monitored.

36. The monitor of claim 33 wherein said means to compare said signals calculates a difference between changes in muscle tonus values of muscles from each said group.

37. The monitor of claim 33 wherein said means to compare said signals calculates a ratio between changes in muscle tonus values of muscles from each said group.

38. The monitor of claim 33 wherein at least two said sensors are adapted to be operatively connected to muscles including the frontalis facial muscle and the corrugator facial muscle.

39. The monitor of claim 38 wherein at least two sensors are adapted to be operatively coupled to the masseter facial muscle and zygomatic facial muscle, whereby said signal processing means may determine a detailed indication of patient facial expression reflecting the depth and quality of patient anesthetization.