Method and system for monitoring a nerve

• US 9,084,551 B2
• Filed: 12/08/2008
• Issued: 07/21/2015
• Est. Priority Date: 12/08/2008
• Status: Active Grant

• Current Assignee: Medtronic Xomed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Xomed Incorporated (Medtronic Plc)
• Inventors: Brunnett, William C., Hacker, David C., Meyer, John A., McFarlin, Kevin Lee, Murphy, John Murdock, Yamasaki, Dwayne S., Gardi, John N.
• Primary Examiner(s): Dougherty, Sean
• Assistant Examiner(s): Stout, Michael C
• Application Number:
  US12/329,848
• Publication Number:
  US 20100145222A1
• Time in Patent Office: 2,416 Days
• Field of Search: 600/547, 600/554, 600/546
• US Class Current: 1/1
• CPC Class Codes: A61B 2505/05 Surgical care
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/389 Electromyography [EMG]
• CPC Class Codes: A61B 5/4041 Evaluating nerves condition
• CPC Class Codes: A61B 5/4893 Nerves
• CPC Class Codes: A61B 5/6877 Nerve
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 5/741 using synthesised speech
• CPC Class Codes: A61B 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B
• CPC Class Codes: A61N 1/0556 Cuff electrodes
• CPC Class Codes: A61N 1/3605 Implantable neurostimulators for stimulating central or peripheral nerve system

Abstract

A nerve monitoring system facilitates monitoring an integrity of a nerve.

Claims

1. A nerve monitoring system comprising:

an apparatus including;

a nerve stimulator configured to automatically and periodically apply an electrical stimulation signal to the nerve of a patient'"'"'s body to elicit an evoked potential, wherein the nerve stimulator is configured to be connected to a nerve stimulation cuff electrode;

a response measurement unit configured to automatically measure, in at least one of a nerve or a muscle of the patient'"'"'s body, a neurogenic response signal of the evoked potential, the response measurement unit including;

an identification function configured to automatically identify potential nerve impairment based on observable differences between the measured neurogenic response signal and a baseline neurogenic response pattern when the observable differences exceed a threshold, the identification function including an impairment sorter to differentiate multiple, different types of identified potential nerve impairment from each other according to the observable differences, which include at least a relative change in at least a nerve response latency parameter and a nerve response amplitude parameter, and

an alarm configured to automatically audibly announce, upon the identified potential nerve impairment, a verbal expression indicative of the identified type of the potential nerve impairment with a different verbal expression for each of the respective different types of nerve impairment; and

a controller configured to generate control signals, based on executable instructions stored in a memory of the controller, to direct operation of the nerve stimulator and the response measurement unit.

2. The system of claim 1, wherein the measured neurogenic response signal comprises at least one of:

a direct response signal measured at a location of the nerve spaced apart from a location at which the stimulation signal is applied;

an indirect response signal measured at a muscle of the patient'"'"'s body innervated by the nerve;

a chemical-based neurogenic response signal;

or

a smooth muscle-based neurogenic response signal.

3. The system of claim 1 wherein, in cooperation with the identification function, the response measurement unit comprises:

a nerve stimulation saturation function to identify an increase or decrease a nerve stimulation saturation of the measured response signal relative to a nerve stimulation saturation parameter of the baseline response pattern.

4. The system of claim 1, comprising:

a nerve stimulation cuff electrode removably securable to the nerve to maintain a continuous electrical pathway from the nerve stimulator of the apparatus to the nerve throughout the surgical procedure; and

a response measurement electrode removably securable relative to at least one of the nerve or an innervated muscle to maintain a continuous electrical pathway from the respective nerve or the innervated muscle to the response measurement unit throughout the surgical procedure.

5. The system of claim 1 wherein, in cooperation with the identification function, the response measurement unit comprises:

a nerve stimulation threshold function to identify an increase or decrease a nerve stimulation of the measured response signal relative to a nerve stimulation parameter of the baseline response pattern.

6. The system of claim 1 wherein in the identification function, the identified potential nerve impairment is selected from a group including at least a tension impairment and a compression impairment, and wherein in the alarm, the different verbal expressions include at least a tension impairment-related verbal expression, and a compression impairment-related verbal expression.

7. The system of claim 1 wherein the different verbal expressions include a general impairment-related verbal expression and a composite impairment-related verbal expression.

8. The system of claim 1, wherein the response measurement unit comprises:

a radiofrequency input connectable to an electrically conductive element and configured to detect a potential electrocautery-based nerve impairment via tracking an intensity of radiofrequency signals associated with an electrocautery instrument, and

wherein the alarm is configured to automatically audibly announce, upon detection of the potential electrocautery-based nerve impairment occurring substantially synchronous with another respective type of potential nerve impairments, an electrocautery-related verbal expression.

9. The system of claim 8, wherein the electrically conductive element comprises at least one of the electrocautery instrument and a medical lead electrically connectable to a patient body.

10. The system of claim 1, wherein the multiple different types of nerve impairment include a general impairment, a tension impairment, a compression impairment, and a composite impairment.

11. The system of claim 10, wherein the identification function is configured to identify an electrocautery impairment of the nerve as indicated by a detected electrocautery event occurring substantially synchronous with at least one of the types of the minor tension impairment, the tension impairment, the compression impairment, and the composite impairment.

12. The system of claim 10 wherein the general impairment is indicated by an increase in the nerve response latency parameter and an increase in the nerve response amplitude parameter, the tension impairment is indicated by an increase in the nerve response latency parameter and a decrease in the nerve response amplitude parameter, the compression impairment is indicated by a decrease in the nerve response amplitude parameter and a stable response latency, and the composite impairment of the nerve including at least two of the types of the general impairment, the tension impairment, and the compression impairment.

13. The system of claim 12, wherein the general impairment corresponds to the increase in the nerve response latency parameter beyond a first latency limit and the increase in the nerve response amplitude parameter beyond a first amplitude limit, wherein the tension impairment corresponds the increase in the nerve response latency parameter beyond a second latency limit and the decrease in the nerve response amplitude parameter beyond a second amplitude limit, and wherein the compression impairment corresponds to the decrease in the nerve response amplitude parameter beyond the second amplitude limit with the stable response latency.

36. The system of claim 1 wherein, in cooperation with the identification function, the response measurement unit comprises at least one of:

an amplitude function to identify a decrease in the amplitude of the measured response signal relative to an amplitude parameter of the baseline response pattern;

a latency function to identify an increase in the latency of the measured response signal relative to a latency parameter of the baseline response pattern;

or

an amplitude-based energy function to identify a decrease in an energy of the measured response signal relative to an energy parameter of the baseline response pattern.

14. A nerve monitoring system comprising:

an apparatus including;

a nerve stimulator configured to automatically and periodically apply an electrical stimulation signal to the nerve of a patient'"'"'s body to elicit an evoked potential, wherein the nerve stimulator is configured to be connected to a nerve stimulation cuff electrode;

a response measurement unit configured to automatically measure, in at least one of a nerve or a muscle of the patient'"'"'s body, a neurogenic response signal of the evoked potential, the response measurement unit including;

an identification function configured to automatically identify potential nerve impairment based on observable differences between the measured neurogenic response signal and a baseline neurogenic response pattern when the observable differences exceed a threshold, and wherein the identification function includes an impairment sorter to differentiate multiple, different types of identified potential nerve impairment from each other according to the observable differences with such differentiation being at least partially determined via;

a nerve refractory recovery parameter of the baseline response pattern, a change in at least one of a double response time, an amplitude, or a latency of a nerve refractory recovery waveform associated with the neurogenic response signal, wherein the nerve refractory recovery waveform is produced in response to a series of the stimulation signals applied according to a paired difference stimulus protocol; and

an alarm configured to automatically audibly announce a verbal expression indicative of the identified type of potential nerve impairment with a different verbal expression for each respective different type of nerve impairment; and

a controller configured to generate control signals, based on executable instructions stored in a memory of the controller, to direct operation of the nerve stimulator and the response measurement unit.

15. The system of claim 14, wherein the response measurement unit determines the baseline response pattern as an identification of an initial neurogenic status of the nerve according to multiple evoked responses via at least one of:

a statistical mean of the multiple evoked responses;

or

a variance measurement of the multiple evoked responses.

16. The system of claim 14, wherein the response measurement unit determines the baseline response pattern as an identification of an initial neurogenic status of the nerve via sorting a variability of the multiple evoked responses according to a Poisson distribution.

17. The system of claim 14, wherein the response measurement unit determines the baseline response pattern as an identification of an initial neurogenic status of the nerve according to multiple evoked responses via at least one of:

an exclusion of a portion of the multiple evoked responses based on a variability of the multiple evoked responses;

an exclusion of at least one of a maximum value or a minimum value of the multiple evoked responses;

or

an exclusion of non-evoked responses.

18. The system of claim 14, wherein the response measurement unit determines the baseline response pattern as an identification of an initial neurogenic status of the nerve according to multiple evoked responses via at least one of:

a rate of change of at least one parameter of the multiple evoked responses;

or

a rolling window of multiple evoked responses.

19. The system of claim 14, wherein the first nerve refractory recovery function is configured to apply the series of stimulation signals according to the paired difference stimulation protocol by:

initially applying a time delay, between a first stimulus pulse and a second stimulus pulse of the pair difference stimulation protocol, that is greater than a natural refractory recovery time period; and

decreasing the time delay, with each subsequent iterative application of the respective first and second stimulus pulses of the paired difference stimulation protocol, at least until the time delay becomes less than the natural refractory recovery time period.

20. The system of claim 14, wherein the differentiation is at least partially determined via at least a relative change in a nerve response latency parameter and a nerve response amplitude parameter.

21. A nerve monitoring system comprising:

a response measurement unit configured to automatically measure, in at least one of a nerve or a muscle of a patient'"'"'s body, a neurogenic response signal of an evoked potential of the nerve in response to electrical stimulation of the nerve, wherein the response measurement unit is configured to be connected to a nerve response electrode and wherein the response measurement unit includes;

an identification function configured to automatically identify potential nerve impairment based on differences between the measured neurogenic response signal and a baseline neurogenic response pattern, wherein the potential impairment is identified according to a plurality of different types of potential impairment selected from the group of a general impairment, a tension impairment, a compression impairment, and a composite impairment,

wherein the identification function includes an impairment sorter configured to differentiate the respective different types of identified impairment via;

identification of the general impairment of the nerve as an increase in the latency beyond a first latency limit and an increase in the amplitude beyond a first amplitude limit;

identification of the tension impairment on the nerve as an increase in the latency beyond a second latency limit and a decrease in the amplitude beyond a second amplitude limit;

identification of the compression impairment on the nerve as a decrease in the amplitude beyond the second amplitude limit with a stable response latency; and

identification of the composite impairment on the nerve as both compression and tension on the nerve; and

an alarm configured to automatically audibly announce, upon the identified potential nerve impairment, a verbal expression indicative of a type of the identified potential impairment with a different verbal expression for each of the respective different types of potential nerve impairment, including at least a tension impairment-related verbal expression, a compression impairment-related verbal expression, and a composite impairment-related verbal expression; and

a controller configured to generate control signals, based on executable instructions stored in a memory of the controller, to direct operation of the response measurement unit.

22. The system of claim 21 wherein identification function is configured to classify the impairment via application of at least one a correlation process, a wavelet transform, or a Fourier transform to the measured response signal and the baseline response pattern to identify one or more signal features of the measured response signal that substantially differ from the baseline response pattern.

23. The system of claim 22 wherein the identification function is configured to identify, via application of the Fourier transform, one or more signal features of the measured neurogenic response signal and the identification function includes at least one of:

a differentiation function configured to differentiate, in a frequency domain, a first signal feature in the measured neurogenic response signal from noise in the measured neurogenic response signal;

or

a comparison function configured to compare, in the frequency domain, the first signal feature of the measured neurogenic response signal relative to a corresponding first signal feature in the baseline response pattern.

24. The system of claim 21 wherein the alarm is configured to automatically provide the audible announcement via a communication of the intensity of impairment via at least two different verbal expressions, with each respective verbal expression indicating a different intensity of impairment.

25. The system of claim 21 wherein the audible alarm includes:

a graduated type of notification in which a volume of the audible announcements are in proportion to a degree of deviation of the measured response from the baseline response pattern.

26. The system of claim 21, wherein the identification function includes:

a first nerve refractory recovery function configured to identify, relative to a nerve refractory recovery parameter of the baseline response pattern, a change in at least one of a double response time, an amplitude, or a latency of a nerve refractory recovery waveform produced in response to a plurality of the stimulation signals, and

wherein the first nerve refractory recovery function is configured to apply the series of stimulation signals according to the paired difference stimulation protocol by;

initially applying a time delay, between a first stimulus pulse and a second stimulus pulse of the pair difference stimulation protocol, that is greater than a natural refractory recovery time period; and

decreasing the time delay, with each subsequent iterative application of the respective first and second stimulus pulses of the paired difference stimulation protocol, at least until the time delay becomes less than the natural refractory recovery time period.

27. The system of claim 21, wherein the identification function includes:

a second nerve refractory recovery function configured to identify, relative to a nerve refractory recovery parameter of the baseline response pattern, a change in at least one of a neurogenic response morphology waveform or a neurogenic response synchrony pattern produced in response to a plurality of the stimulation signals, and

wherein the second nerve refractory recovery function is configured to apply the series of stimulation signals according to the paired difference stimulation protocol by;

initially applying a time delay, between a first stimulus pulse and a second stimulus pulse of the pair difference stimulation protocol, that is greater than a natural refractory recovery time period; and

decreasing the time delay, with each subsequent iterative application of the respective first and second stimulus pulses of the paired difference stimulation protocol, at least until the time delay becomes less than the natural refractory recovery time period.

28. A nerve monitoring system comprising:

an apparatus including;

a nerve stimulator configured to automatically and periodically apply an electrical stimulation signal to the nerve of a patient'"'"'s body to elicit an evoked potential, wherein the nerve stimulator is configured to be connected to a nerve stimulation cuff electrode;

a response measurement unit configured to automatically measure, in at least one of a nerve or a muscle of the patient'"'"'s body, a neurogenic response signal of the evoked potential, the response measurement unit including;

an identification function configured to automatically identify potential nerve impairment based differences between the measured neurogenic response signal and a baseline neurogenic response pattern when the identified differences exceed a threshold, and wherein the identification function includes an impairment sorter to differentiate among a plurality of different types of nerve impairment with such differentiation being at least partially determined according via;

a second nerve refractory recovery function configured to identify, relative to a nerve refractory recovery parameter of the baseline response pattern, a change in at least one of a neurogenic response morphology waveform or a neurogenic response synchrony pattern produced in response to a series of the stimulation signals applied according to a paired difference stimulus protocol; and

an alarm configured to automatically audibly announce, upon the identified potential nerve impairment, a verbal expression indicative of each of the different respective types of the identified potential nerve impairment with a different verbal expression for each different respective type of nerve impairment; and

a controller configured to generate control signals, based on executable instructions stored in a memory of the controller, to direct operation of the nerve stimulator and the response measurement unit.

29. The system of claim 28, wherein the second nerve refractory recovery function is configured to apply the series of stimulation signals according to the paired difference stimulation protocol by:

initially applying a time delay, between a first stimulus pulse and a second stimulus pulse of the pair difference stimulation protocol, that is greater than a natural refractory recovery time period; and

decreasing the time delay, with each subsequent iterative application of the respective first and second stimulus pulses of the paired difference stimulation protocol, at least until the time delay becomes less than the natural refractory recovery time period.

30. The system of claim 28, wherein the differentiation is at least partially determined via at least a relative change in a nerve response latency parameter and a nerve response amplitude parameter.

31. A nerve monitoring system comprising:

a response measurement unit configured to automatically measure, at least one of a nerve or a muscle of a patient'"'"'s body, a neurogenic response signal of an evoked potential of the nerve in response to electrical stimulation of the nerve, wherein the response measurement unit is configured to be connected to a nerve response electrode and wherein the response measurement unit includes;

an identification function configured to automatically identify first potential nerve impairment based on differences between the measured neurogenic response signal and a baseline neurogenic response pattern, wherein the first potential nerve impairment is identified according to a plurality of different types of first potential nerve impairments selected from the group of a general impairment, a tension impairment, a compression impairment, and a composite impairment;

a radiofrequency input connectable to an electrically conductive element and configured to detect a potential electrocautery-based nerve impairment via tracking an intensity of radiofrequency signals associated with an electrocautery instrument; and

an alarm configured to automatically audibly announce, upon the identified first potential nerve impairment, a verbal expression indicative of a type of the identified first potential nerve impairment with a different verbal expression for each of the respective different types of first potential nerve impairment, including at least a tension impairment-related verbal expression, a compression impairment-related verbal expression, and a composite impairment-related verbal expression; and

a controller configured to generate control signals, based on executable instructions stored in a memory of the controller, to direct operation of the response measurement unit,

wherein the alarm is configured to automatically audibly announce, upon detection of the potential electrocautery-based nerve impairment occurring substantially synchronous with a respective one of the first potential nerve impairments, an electrocautery-related verbal expression.

32. A nerve monitoring system comprising:

an apparatus including;

a nerve stimulator configured to automatically and periodically apply an electrical stimulation signal to the nerve of a patient'"'"'s body to elicit an evoked potential, wherein the nerve stimulator is configured to be connected to a nerve stimulation cuff electrode;

a response measurement unit configured to automatically measure, in at least one of a nerve or a muscle of the patient'"'"'s body, a neurogenic response signal of the evoked potential, the response measurement unit including;

an identification function configured to automatically identify potential nerve impairment based on differences between the measured neurogenic response signal and a baseline neurogenic response pattern, wherein the identification function includes a nerve refractory recovery function configured to identify, relative to a nerve refractory recovery parameter of the baseline response pattern, a change in at least one of a neurogenic response morphology waveform or a neurogenic response synchrony pattern produced in response to a plurality of the stimulation signals applied according to a paired difference stimulation protocol;

a radiofrequency input connectable to an electrically conductive element and configured to detect a potential electrocautery-based nerve impairment via tracking an intensity of radiofrequency signals associated with an electrocautery instrument; and

an alarm configured to automatically audibly announce, upon identification of a potential nerve impairment, a verbal expression indicative of a type of the identified potential nerve impairment with a different verbal expression for each different type of a plurality of types of nerve impairment; and

a controller configured to generate control signals, based on executable instructions stored in a memory of the controller, to direct operation of the nerve stimulator and the response measurement unit,

wherein the alarm is configured to automatically audibly announce, upon detection of the potential electrocautery-based nerve impairment occurring substantially synchronous with a respective one of the first potential nerve impairments, an electrocautery-related verbal expression.

33. The system of claim 32 wherein the response module includes:

an impairment sorter module configured to differentiate the respective different types of impairment as at least one of a general impairment, a tension impairment, a compression impairment, a composite impairment, and an electrocautery impairment and wherein the different verbal expressions audibly announced via the alarm include at least one of the following terms general, tension, compression, and composite,

wherein the impairment sorter module is configured to differentiate the respective different types of identified impairment via at least one of;

identification of the general impairment of the nerve as an increase in the latency beyond a first latency limit and an increase in the amplitude beyond a first amplitude limit;

identification of the tension impairment on the nerve as an increase in the latency beyond a second latency limit and a decrease in the amplitude beyond a second amplitude limit;

identification of the compression impairment on the nerve as a decrease in the amplitude beyond the second amplitude limit and without a change in response latency; and

identification of the composite impairment on the nerve as both compression and tension on the nerve.

34. A nerve monitoring system comprising:

a response measurement unit configured to automatically measure, in at least one of a nerve or a muscle of a patient'"'"'s body, a neurogenic response signal of an evoked potential of the nerve in response to electrical stimulation of the nerve, wherein the response measurement unit is configured to be connected to a nerve response electrode and wherein the response measurement unit includes;

an identification function configured to automatically identify a first potential nerve impairment based on the measured neurogenic response signal according to a plurality of different types of potential impairment selected from a group including at least a general impairment, a tension impairment, a compression impairment, and a composite impairment;

a radiofrequency input connectable to an electrically conductive element and configured to detect a potential electrocautery-based nerve impairment via tracking an intensity of radiofrequency signals associated with an electrocautery instrument; and

an alarm configured to automatically audibly announce, upon detection of the potential electrocautery-based nerve impairment occurring substantially synchronous with a respective one of the first potential nerve impairments, at least an electrocautery-related verbal expression; and

a controller configured to generate control signals, based on executable instructions stored in a memory of the controller, to direct operation of the response measurement unit.

35. The system of claim 34, wherein the electrically conductive element comprises at least one of the electrocautery instrument and a medical lead electrically connectable to a patient body.