Electromyography system
A system and methods that can be used to monitor and detect nerve status and/or proximity by determining relative neuro-muscular response onset value thresholds for a nerve. The nerve status and/or proximity may be determined by delivering and increasing a stimulation signal to depolarize the nerve and measuring the current intensity level at which a neuro-muscular response to the depolarization of the nerve is detected.
1. A method of determining at least one of a change in nerve status and a change in nerve proximity, comprising the steps of:
(a) applying a first stimulus signal to a stimulus electrode communicatively linked to a controller that directs application of electrical stimulus signals, said stimulus electrode being situated on a medical device and located a distance from a nerve;
(b) detecting with a sensor communicatively linked to said controller an EMG response generated by a muscle physiologically coupled to said nerve in response to said first stimulus signal;
(c) increasing said first stimulus signal and repeating steps (a) and (b) until said controller determines said detected EMG response associated with said nerve reaches a predetermined minimum EMG value representing an evoked muscle action potential;
(d) identifying the level of said first stimulus signal required to obtain said predetermined minimum EMG value;
(e) storing in a non-transitory fashion on the controller the identified level of said first stimulus signal required to obtain said predetermined minimum EMG value;
(f) repeating steps (a) through (d) with a second stimulus signal to identify the level of said second stimulus signal required to obtain said predetermined minimum EMG value associated with said nerve; and
(g) recalling on the controller the identified level of said first stimulus signal level and determining at least one of a change in nerve status and a change in nerve proximity based on a comparison of said first stimulus signal level required to obtain said predetermined minimum EMG value and said second stimulus signal level required to obtain said predetermined minimum EMG value.
2. The method of claim 1 , wherein said first and second stimulus signals each have a fixed current level.
3. The method of claim 1 , wherein said medical device includes at least one of a cannula, a pedicle probe, a needle, a catheter, RF ablation device and a medical laser.
4. The method of claim 1 , wherein said EMG response is detected through the use of at least one EMG electrode.
5. The method of claim 4 , wherein said at least one EMG electrode comprises at least one of a needle electrode disposed within said muscle and a surface electrode located above said muscle.
6. The method of claim 1 , wherein step (c) includes the sub-steps of measuring a magnitude of said detected EMG response and comparing said magnitude with said predetermined minimum EMG value.
7. The method of claim 6 , wherein predetermined minimum EMG value is a predetermined peak-to-peak voltage.
8. The method of claim 7 , wherein the predetermined peak-to-peak voltage is between 60 mV and 80 mV.
9. The method of claim 1 , wherein the controller includes a display and an indicator of said determined change in at least one of said nerve status and nerve proximity is displayed for a user.
10. The method of claim 9 , wherein the display is an LCD display.
11. The method of claim 9 , wherein the display is a series of LEDs.
12. The method of claim 9 , wherein the display also displays an indication of the determined first stimulus signal level.
13. The method of claim 9 , wherein the indication of said determined first stimulus signal level comprises a first color and the indicator of said change in at least one of said nerve status and nerve proximity comprises a different color.