U.S. patent application number 13/896244 was filed with the patent office on 2013-09-26 for single and multi-needle electromyographic (emg) recording electrode configurations for intraoperative nerve integrity monitoring.
The applicant listed for this patent is Richard L. PRASS. Invention is credited to Richard L. PRASS.
Application Number | 20130253296 13/896244 |
Document ID | / |
Family ID | 42319545 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130253296 |
Kind Code |
A1 |
PRASS; Richard L. |
September 26, 2013 |
SINGLE AND MULTI-NEEDLE ELECTROMYOGRAPHIC (EMG) RECORDING ELECTRODE
CONFIGURATIONS FOR INTRAOPERATIVE NERVE INTEGRITY MONITORING
Abstract
An electromyographic recording electrode assembly for
intraoperative nerve integrity monitoring includes cables enabled
for connection to a nerve integrity monitor; an electrode hub
connected to the one or more cables; and a needle electrode
connected to the electrode hub. The needle electrode extends
perpendicularly from an undersurface of the hub, and along a line
of insertion into a patient. The needle electrode extends from the
electrode hub to a first bend in a first direction, and extends
from the first bend in a second direction to an end of the
electrode, defining a proximal needle segment from the hub to the
first bend, and a terminal needle segment from the first bend to
the end of the electrode. The terminal needle segment and at least
a portion of the proximal needle segment are insertable into a
patient along the line of insertion.
Inventors: |
PRASS; Richard L.;
(Nashville, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PRASS; Richard L. |
Nashville |
TN |
US |
|
|
Family ID: |
42319545 |
Appl. No.: |
13/896244 |
Filed: |
May 16, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12686893 |
Jan 13, 2010 |
8452370 |
|
|
13896244 |
|
|
|
|
61144195 |
Jan 13, 2009 |
|
|
|
61144196 |
Jan 13, 2009 |
|
|
|
61144198 |
Jan 13, 2009 |
|
|
|
61144201 |
Jan 13, 2009 |
|
|
|
61144202 |
Jan 13, 2009 |
|
|
|
61144205 |
Jan 13, 2009 |
|
|
|
61144209 |
Jan 13, 2009 |
|
|
|
Current U.S.
Class: |
600/373 |
Current CPC
Class: |
A61B 5/0492
20130101 |
Class at
Publication: |
600/373 |
International
Class: |
A61B 5/0492 20060101
A61B005/0492 |
Claims
1. An electromyographic (EMG) recording electrode assembly for
intraoperative nerve integrity monitoring, comprising: one or more
cables enabled for connection directly or indirectly to a nerve
integrity monitor; an electrode hub connected to the one or more
cables; and one or more needle electrodes connected to the
electrode hub, each of the one or more needle electrodes extending
perpendicularly from an undersurface of the hub, each of the one or
more needle electrodes extending along a line of insertion into a
patient from the electrode hub to a first bend in a first
direction, and extending from the first bend in a second direction
to an end of the electrode, defining a proximal needle segment from
the hub to the first bend and a terminal needle segment from the
first bend to the end of the electrode, wherein the terminal needle
segment and at least a portion of the proximal needle segment are
insertable into a patient along the line of insertion.
2. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein an angle between an undersurface of the electrode
hub and the proximal needle segment is approximately 90
degrees.
3. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein an angle between the proximal needle segment and
the terminal needle segment is approximately 90 degrees.
4. The electromyographic (EMG) recording electrode assembly of
claim 1, the one or more needle electrodes being configured wherein
a depth of an initial insertion by the one or more needle
electrodes when inserted into a patient's skin is approximately
equal to a length of the proximal needle segment.
5. The electromyographic (EMG) recording electrode assembly of
claim 1, the one or more needle electrodes being configured wherein
a depth of an initial insertion by the one or more needle
electrodes when inserted into a patient's skin is approximately
equal to a length of the proximal needle segment or a half a length
of the terminal needle segment.
6. The electromyographic (EMG) recording electrode assembly of
claim 1, the assembly being configured wherein an angle of an
insertion by the one or more needle electrodes into a patient's
skin is approximately equal to 90 degree with respect to the
patient's skin.
7. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein the first bend is a depth guide for guiding a
depth of initial insertion.
8. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein the one or more needle electrodes and the
electrode hub being configured wherein when the one or more needle
electrodes are inserted into a patient's skin, the electrode hub is
enabled to lay flat on and parallel to the patient's skin
surface.
9. The electromyographic (EMG) recording electrode assembly of
claim 1, comprising at least a portion of the proximal segment
having a coating comprising polytetrafluoroethylene.
10. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein an angle between the proximal needle segment and
the terminal needle segment is greater than 90 degrees and less
than 180 degrees.
11. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein an angle between the electrode hub and the
proximal needle segment is greater than 90 degrees and less than
180 degrees.
12. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein the electrode hub has at least one concave groove
and at least one upper ridge.
13. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein one of the one or more needle electrodes is a
ground electrode.
14. The electromyographic (EMG) recording electrode assembly of
claim 1, further comprising: a cable hub, the cable hub being
configured for attaching one or more electrode leads, the cable hub
being configured to interpose the electrode hub and the nerve
integrity monitor when the one or more cables are connected to the
monitor.
15. The electromyographic (EMG) recording electrode assembly of
claim 14, wherein the one or more cables are attachable and
removable from the cable hub.
16. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein the terminal needle segment is longer than the
proximal needle segment.
17. The electromyographic (EMG) recording electrode assembly of
claim 14, wherein the cable hub is contoured.
18. The electromyographic (EMG) recording electrode assembly of
claim 14, wherein the cable hub is rounded.
19. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein the one or more cables are oriented perpendicular
to the one or more needle electrodes.
20. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein the electrode hub has an indented portion where a
user's thumb may be positioned to facilitate insertion of the
electrode into a patient's skin.
21. The electromyographic (EMG) recording electrode assembly of
claim 14, wherein the cable hub is connected to one or more cables
that are attachable to and removable from the patient.
22. The electromyographic (EMG) recording electrode assembly of
claim 14, wherein the cable hub serves as an active ground
electrode.
23. The electromyographic (EMG) recording electrode assembly of
claim 1, comprising: a plurality of ground electrodes, the
plurality of ground electrodes being consolidated in a single-point
connection to the electrode hub.
24. The electromyographic (EMG) recording electrode assembly of
claim 1, the one or more needle electrodes further comprising: a
stimulator anode electrode; a ground electrode; and a connection
between the stimulator anode electrode and the ground
electrode.
25. The electromyographic (EMG) recording electrode assembly of
claim 1, wherein the one or more cables are attachable and
removable from the electrode hub.
Description
PRIORITY APPLICATION INFORMATION
[0001] This application is a divisional of co-pending U.S. patent
application Ser. No. 12/686,893, filed Jan. 13, 2010, the entire
disclosure of which is hereby incorporated herein by reference in
its entirety. U.S. patent application Ser. No. 12/686,893 claims
priority from U.S. Provisional Patent Application No. 61/144,195,
filed Jan. 13, 2009, U.S. Provisional Patent Application No.
61/144,196, filed Jan. 13, 2009, U.S. Provisional Patent
Application No. 61/144,198, filed Jan. 13, 2009, U.S. Provisional
Patent Application No. 61/144,201, filed Jan. 13, 2009, U.S.
Provisional Patent Application No. 61/144,202, filed Jan. 13, 2009,
U.S. Provisional Patent Application No. 61/144,205, filed Jan. 13,
2009, and U.S. Provisional Patent Application No. 61/144,209, filed
Jan. 13, 2009; the entire disclosure of each provisional
application is hereby incorporated herein by reference in their
entireties.
BACKGROUND OF THE DISCLOSED EMBODIMENTS
[0002] 1. Field of the Disclosed Embodiments
[0003] The disclosed embodiments may relate to medical equipment
and in particular, to configurations of single and multi-needle
electromyographic (EMG) recording electrodes for nerve integrity
monitoring.
[0004] 2. Introduction
[0005] Intraoperative nerve integrity monitoring involves sonic and
graphic display of EMG activity from target muscles of nerves at
risk for surgical injury. The technique may be applied to any motor
nerve at risk for surgical injury, providing that its target
muscles are accessible for EMG recording. Sonic feedback, elicited
by electrical stimulation or mechanical manipulations of the
monitored nerve, allows the surgeon to be more aware of the
location and physical contour of the monitored nerve(s), as well
as, the possible injurious effects of surgical manipulations.
[0006] Largely due to the general effectiveness of nerve integrity
monitoring, its use during surgical procedures has significantly
expanded. This expansion has increased the number of new and
inexperienced end users. In addition, changes in reimbursement for
monitoring procedures have caused a shift from physician to allied
medical personnel-based equipment setup. The inexperience of end
users and the lack of standardized initial recording and stimulus
setup procedures for nerve integrity monitoring may lead to severe
medical consequences for patients.
SUMMARY OF THE DISCLOSED EMBODIMENTS
[0007] A several configurations for single and multi-needle
electromyographic (EMG) recording electrodes for intraopertaive
nerve integrity monitoring are disclosed. One possible embodiment
may concern a modification of single or multi-needle electrodes
with a single hub. The proposed modification may incorporate two
bends in the needle portion of the electrodes along the line of
needle insertion. The first bend may occur at the hub in a purely
downward direction. The magnitude of the first bend may be 90
degrees or more. The second bend is in the opposite direction of
the first bend, the angle of which may vary, depending upon the
intended orientation and depth of the terminal needle segment. In
order for proper insertion, the depth of initial insertion of the
terminal needle segment may be equal to the length of the portion
of the proximal needle segment below the lower border of the hub.
The full length of the terminal segment may be equal to or longer
than the depth of initial insertion.
[0008] The disclosed embodiments may also concern a modification
for single and multi-needle EMG electrodes with an offset
configuration. The modification may include a concave groove and a
relatively prominent upper ridge along the sides of the hub. The
ridge and groove along the upper side-edges of the hub may improve
the ability to manually manipulate the hub when it is parallel
with, and close to, the skin. The ridge and groove may be
particularly helpful in maintaining a slight elevation of the
electrode tip, in order to maintain the hub in a plane parallel to
the skin surface, as the electrode is advanced forward to its final
position. The ridge along the upper edge of the sides of the
electrode hub may be a possible alternative to increasing the hub
thickness in order to achieve better tactile feedback and
manipulative control during placement.
[0009] The disclosed embodiments may further concern a modification
of the ground electrode, where the electrode hub is physically, but
not necessarily electrically, attached to the lead wires of the
recording electrode(s). The attachment may be fixed, detachable or
adjustable in position along the length of the lead wires,
depending upon the requirements of individual applications. With
such an attachment, the recording electrode lead wires may be
supported and organized around a strategic placement position for
the ground electrode.
[0010] The disclosed embodiments may further concern a modification
of a modified ground electrode, where the electrode leads may be
attached to the hub of the ground electrode. In this case, however,
there may be hard electrical connections within the hub of the
ground electrode, connecting the terminal and proximal portions of
the recording electrode leads. In this manner, the delicate and
stable attributes of hooked-wire electrodes and the robustness of
standard electrode leads may be combined. The inserted portion of
the electrode may be a bipolar fine hooked-wire electrode, the lead
length of which may be limited to only that required for
unencumbered insertion into the target muscle tissue and subsequent
placement of the hub at a particular location.
[0011] The disclosed embodiments may further concern a modification
of needle electrodes with "offset" configuration, specifically with
regard to the positioning of the electrode needles on the hub. The
"offset" needle electrodes may be constructed so that the front
edge of the hub can serve as a guide to the proper insertion depth
for individual applications. Placement of the needle on the hub may
vary for different depths of insertion, depending upon the specific
application. For example, intramuscular placement may require a
greater insertion depth than subdermal placement.
[0012] The disclosed embodiments may further concern a modification
of a paired electrode design where a third needle electrode may be
located symmetrically between the paired recording electrodes and
serves as the ground electrode. The needle electrodes may be
straight or modified with an offset configuration. The electrode
leads may be taped together at intervals, twisted together or
braided in order to minimize the antenna-like qualities of the
electrode leads themselves.
[0013] The disclosed embodiments may further concern the
elimination for the need for a separate stimulus anode electrode
during monopolar electrical stimulation and reduces possible
localization ambiguity during bipolar stimulation. A separate anode
electrode connection to the patient may be eliminated by connection
of the ground electrode to the anode in the stimulus circuit. This
can be accomplished before or after the electrical isolation
circuitry, but not across it. For example, an exemplary electrical
connection between the ground electrode and the anode terminal
before the isolation circuit, which may be enclosed inside the
electrode connection ("head") box. An alternative embodiment may
involve making the connection between the ground and anode "after"
the electrical isolation circuit and within the main unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In order to describe the manner in which the above-recited
and other advantages and features of the disclosed embodiments can
be obtained, a more particular description of the disclosed
embodiments briefly described above will be rendered by reference
to specific embodiments thereof which are illustrated in the
appended drawings. Understanding that these drawings depict only
typical disclosed embodiments and are not therefore to be
considered to be limiting of its scope, the disclosed embodiments
will be described and explained with additional specificity and
detail through the use of the accompanying drawings in which:
[0015] FIG. 1A is a side view of needle modification of single or
multi-needle electrodes with 90 degree angles at A1 and A2 in
accordance with one possible embodiment of the disclosure;
[0016] FIG. 1B is a top view of needle modification of single or
multi-needle electrodes with 90 degree angles at A1 and A2 in
accordance with one possible embodiment of the disclosure;
[0017] FIG. 2 is a "special" embodiment of needle modification of
single or multi-needle electrodes with 90 degree angles at A1 and
A2 in accordance with one possible embodiment of the
disclosure;
[0018] FIG. 3 is a "special" embodiment of needle modification of
single or multi-needle electrodes with open angle at A2 in order to
achieve increased depth of insertion in accordance with one
possible embodiment of the disclosure;
[0019] FIG. 4 is a "special" embodiment of single or multi-needle
electrodes with open angles at A1 and A2 in accordance with one
possible embodiment of the disclosure;
[0020] FIG. 5A is a side view of modified electrode hub for use
with "offset" needle modifications in accordance with one possible
embodiment of the disclosure;
[0021] FIG. 5B is a rear view of modified electrode hub for use
with "offset" needle modifications in accordance with one possible
embodiment of the disclosure;
[0022] FIG. 6A is a bottom view of modified ground electrode that
employs a standard electrocardiogram (ECG) snap lead in accordance
with one possible embodiment of the disclosure;
[0023] FIG. 6B is a top view of modified ground electrode that
employs a standard ECG snap lead in accordance with one possible
embodiment of the disclosure;
[0024] FIG. 6C is a side view of modified ground electrode that
employs a standard ECG snap lead in accordance with one possible
embodiment of the disclosure;
[0025] FIG. 7A is a top view of hybrid recording electrodes with
hook wire electrodes electrically connected to standard electrode
leads within the hub of a modified ground electrode in accordance
with one possible embodiment of the disclosure;
[0026] FIG. 7B is a side view of hybrid recording electrodes, with
hook wire electrodes electrically connected to standard electrode
leads within the hub of a modified ground electrode in accordance
with one possible embodiment of the disclosure;
[0027] FIG. 8A is a side view of modification of the needle
positioning on the electrode hub in order to provide a depth guide
for electrode placement in accordance with one possible embodiment
of the disclosure;
[0028] FIG. 8B is a top view of modification of the needle
positioning on the electrode hub in order to provide a depth guide
for electrode placement in accordance with one possible embodiment
of the disclosure;
[0029] FIG. 9A is a side view of modified ground electrode
incorporating modified needle positioning on the hub in accordance
with one possible embodiment of the disclosure;
[0030] FIG. 9B is an opposite side view of modified ground
electrode incorporating modified needle positioning on the hub in
accordance with one possible embodiment of the disclosure;
[0031] FIG. 9C is a front view of modified ground electrode
incorporating modified needle positioning on hub in accordance with
one possible embodiment of the disclosure;
[0032] FIG. 10A is a top view of three-needle electrode
incorporating a ground electrode between two active recording
electrodes in accordance with one possible embodiment of the
disclosure;
[0033] FIG. 10B is a side view of three-needle electrode
incorporating a ground electrode between two active recording
electrodes and a straight needle configuration in accordance with
one possible embodiment of the disclosure;
[0034] FIG. 10C is a side view of three-needle electrode
incorporating a ground electrode between two active recording
electrodes and modified ("offset") needle configuration in
accordance with one possible embodiment of the disclosure;
[0035] FIG. 11 is a single-point connection of ground electrodes
when multiple three-needle electrodes are used in accordance with
one possible embodiment of the disclosure;
[0036] FIG. 12 is a "virtual anode" achieved by connecting the
ground electrode to the anode connection before an electrical
isolation circuit in accordance with one possible embodiment of the
disclosure; and
[0037] FIG. 13 is a "virtual anode" achieved by connecting the
ground electrode to the anode connection, after an electrical
isolation circuit in accordance with one possible embodiment of the
disclosure.
DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS
[0038] Additional features and advantages of the disclosed
embodiments will be set forth in the description which follows, and
in part will be obvious from the description, or may be learned by
practice of the disclosed embodiments. The features and advantages
of the disclosed embodiments may be realized and obtained by means
of the instruments and combinations particularly pointed out in the
appended claims. These and other features of the disclosed
embodiments will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of the disclosed embodiments as set forth herein.
[0039] The disclosed embodiments are discussed in detail below.
While specific implementations are discussed, it should be
understood that this is done for illustration purposes only. A
person skilled in the relevant art will recognize that other
components and configurations may be used without parting from the
spirit and scope of the disclosed embodiments.
[0040] The disclosed embodiments may relate to a modification of
single and multi-needle electromyographic (EMG) recording
electrodes, intended to improve reliability and stability of
intramuscular placement during intraoperative nerve integrity
monitoring. An aim of this technology is to achieve design-driven
improvements in standardization and ease of performing setup
procedures, regardless of experience and training among end users
and support personnel. The disclosed embodiments are intended to
facilitate and standardize the initial recording and stimulus setup
procedures for nerve integrity monitoring. The disclosed
embodiments are set forth as follows:
1. Modification of Needle EMG Electrodes for Intraoperative Nerve
Integrity Monitoring
[0041] The disclosed embodiments may relate to a modification of
single and multi-needle electromyographic (EMG) recording
electrodes, intended to improve reliability and stability of
intramuscular placement during intraoperative nerve integrity
monitoring. Intraoperative nerve integrity monitoring may involve
sonic and graphic display of EMG activity from target muscles of
nerves at risk for surgical injury. The technique may be applied to
any motor nerve at risk for surgical injury, providing that its
target muscles are accessible for EMG recording. Sonic feedback,
elicited by electrical stimulation or mechanical manipulations of
the monitored nerve, may allow the surgeon to be more aware of the
location and physical contour of the monitored nerve(s), as well
as, the possible injurious effects of surgical manipulations.
[0042] The most effective method of recording EMG activity for
nerve integrity monitoring may be achieved with intramuscular
electrode placement. Intramuscular recording may afford sensitive
detection of large, small, time-concerted and time-dispersed EMG
signals with a relatively narrow dynamic range. Such dynamic range
compression characteristics may be ideal for sensitive detection of
a wide variety of mechanically and electrically stimulated
responses at a single equipment setting. Intramuscularly recorded
EMG signals may typically be polyphasic and relatively readily
distinguishable from most electrical artifacts.
[0043] Intraoperative nerve integrity monitoring is most commonly
used for facial nerve monitoring during ear, parotid and skull base
surgery. Because facial muscles are located close to the skin
surface, intramuscular placement may be achieved with relatively
short needle electrodes. Standard 1 cm subdermal needle electrodes
have been commonly used successfully for this purpose.
[0044] A limitation of uninsulated needle electrodes is that a
significant proportion of the needle electrode may be in contact
with inactive tissue, such as skin and underlying subcutaneous fat
and connective tissue. Due to a typically shallow, 20-30 degrees,
angle of needle insertion, the length of contact with inactive
tissue may be 2-3 times the 1.5 mm skin thickness itself. Thus,
nearly 25-30% of 10-12 mm subdermal electrodes may be in contact
with electrically inactive skin tissue. The thickness of underlying
subcutaneous tissue and fat is more variable, but may be an
additional 2-4 mm.
[0045] Depending upon the thickness of underlying subcutaneous
tissue and fat, a minority of the electrode length may actually be
in contact within electrically active intramuscular tissue. Contact
of recording electrodes with inactive tissue degrades recording
quality for nerve integrity monitoring by dampening/reducing the
amplitude of recorded EMG signals. A polytetrafluoroethylene
coating such as a TEFLON coating of the proximal portion of the
electrode needles has been used in a paired- needle electrode
design (U.S. Pat. No. 5,161,533), in order to reduce or eliminate
electrode contact with inactive skin and subcutaneous tissue.
[0046] Straight needle electrodes are most securely held with the
index finger under, and the thumb positioned over the top of the
electrode hub. However, the index finger under the hub makes is
awkward to achieve an acute 20-30 degree insertion angle. Longer
needle length has been employed in order to facilitate a secure
grip of straight needle electrodes for placement at a shallow angle
(see e.g., U.S. Pat. No. 5,161,533, the contents of which are
incorporated by reference in its entirety). However, sales patterns
suggest that consumers prefer the shorter electrode lengths.
[0047] Once placed, straight needle electrodes are typically
secured by placing adhesive tape over the hub. Depending upon the
angle of placement, the needle hub may stick up to a greater or
lesser degree. The angle is usually greater with shorter needles.
Taping over a needle hub that is sticking up may locally distort
tissues in the recording area, possibly causing the needle to cut
through small blood vessels, especially in the orbicularis oculi
muscle area. The lack of a flat relationship with the skin surface
may also destabilize the placement, rendering the electrode more
likely to slide under the adhesive tape. In practice, a small coil
of lead-wire is often taped to the skin, close to the electrode
placement site, in order to provide "strain relief" as a
preventative measure against dislodgement with inadvertent
electrode lead manipulations.
[0048] The disclosed embodiments may concern a modification of
needle EMG electrodes that may be intended to improve the ease, as
well as, the reliability and stability of intramuscular placement.
The needle electrodes of the disclosed embodiments may effectively
appear shorter to the end user, which may aid in user comfort and
acceptance.
[0049] In particular, the disclosed embodiments may concern a
modification of single or multi-needle electrodes with a single hub
110. The single hub may be connected using one or more cables 140
directly or indirectly to a nerve integrity monitor (not shown)
(NOTE: for the purposes of further discussions concerning the
remaining embodiments, it will be assumed that any hub that is
shown in any of the figures may be connected using one or more
cables directly or indirectly to a nerve integrity monitor).
Conventional EMG needle electrodes for intraoperative nerve
integrity monitoring are straight. The modification in the
disclosed embodiments may incorporate one or more electrodes that
each comprises a proximal needle segment 120 and a terminal needle
segment 130 and each having two bends in the needle portion of the
electrodes along the line of needle insertion, as shown in FIGS. 1A
and 1B, for example. The first bend A1 may occur at the hub 110 in
a downward direction and may create the proximal needle segment
120. The magnitude of A1 may be substantially 90 degrees from the
hub (the hub being positioned horizontally as in the figure) or may
be at some other lesser angle, for example. The second bend A2 is
in the opposite direction of A1 which may create the terminal
needle segment 130, the angle of which may vary, depending upon the
intended orientation and depth of the terminal needle segment
130.
[0050] In order for proper insertion, the depth of initial
insertion d2 of the terminal needle segment 130 should be equal to
the length of the portion of the proximal needle segment 120 below
the lower border d1 of the hub 110. The full length d3 of the
terminal segment 130 may be equal to or longer than d2.
[0051] A "special" embodiment incorporates equal lengths of d1, d2,
and d3. With equal lengths of proximal needle segment 120 and
terminal needle segments 130, the entire terminal segment 130 may
be inserted into the skin. FIG. 2 shows such an embodiment with
both A1 and A2 at substantially 90 degree angles. The terminal
segment 230 of the needle electrode may be inserted at an angle
with the skin surface equal to the angle at A1 (e.g., substantially
90 degrees). The terminal needle segment(s) 230 may be completely
inserted to the level of A2, with the bend at A2 serving as a depth
guide. The hub 210 may then be rotated backward so that its
undersurface is roughly parallel with the skin surface. Final
positioning of the electrode may be achieved by advancing the hub
210 forward, while maintaining the "parallel with the skin"
orientation of the hub 210. This may be best achieved with the
index finger and thumb on opposite sides of the hub 210. Pressure
may be applied to the sides of the hub 210 so as to tip the
electrode slightly upward as the hub 210 is advanced forward.
During forward advancement of the hub 210, the applied force should
be exclusively parallel with the skin surface. When the hub 210 has
been advanced adequately, the electrode may drop into place, as the
proximal needle segment 220 enters the initial needle tract.
[0052] There are several potential advantages of this electrode
needle modification. When the electrode is properly inserted, the
hub 210 may lie flat on, and parallel to, the skin surface. The
"flat, parallel to the skin" post-placement positioning may provide
a quality assurance guide for proper electrode placement and, thus,
may increase consistency and reliability of placement. When the
electrode is properly placed, the intended depth and orientation of
the needle terminus may be assured.
[0053] This modification may be relatively self-securing. The
electrode hub must move backward and outward to become dislodged.
The closer A1 is to 90 degrees, the greater such resistance to
dislodgement by lead manipulation. Taping over the hub 210 may
provide additional stabilization of the electrode placement against
disruption with inadvertent electrode lead manipulations.
[0054] In contrast to straight needle electrodes, which cross
electrically inactive skin and subcutaneous tissue at a rather
shallow angle after full insertion, the needle modification
including, for example, proximal segment 220 traverses inactive
skin and subcutaneous tissue at a steeper angle. This maximizes the
depth of insertion that may be achieved relative to a straight
needle of comparable length. Also, this minimizes a portion of the
needle (proximal segment 220) that contacts inactive muscle tissue,
and maximizes a portion of the needle electrode (terminal segment
230) that is situated within active muscle tissue. While
polytetrafluoroethylene coating, such as TEFLON coating, of the
proximal needle segment 220 may be additionally advantageous in
order to limit the relative proportion of needle contact with
inactive tissue, it may be less important with the
modification.
[0055] Because of the two needle bends A1, A2, the modification may
appear significantly shorter than a straight needle of the same
length. The shorter appearance may aid in end user comfort. The
flat-to-the-skin positioning of the hub 210 after placement may
also be aesthetically pleasing and may also enhance end user
acceptance.
[0056] The A2 angle may be chosen to best align the active portion
of the electrodes, including proximal segment 220 and terminal
segment 230 within the target muscle. Since facial muscles are
oriented parallel to the skin, A2 should be roughly equal and
opposite to A1, so that the active portion of the electrode may be
parallel to the skin and the plane of the facial muscles. For
deeper, non-planar or thicker target muscles, a more obtuse angle
of A2 may be chosen, so that the active portion of the electrode
may course more deeply into the target muscle.
[0057] FIG. 3 shows an embodiment with an open angle at A2, which
enables a greater depth of insertion. In particular, FIG. 3 shows
an embodiment 300 including a hub 310. A proximal needle segment
320 extends from the hub 310 at a first bend to define an angle A1
therebetween of 90 degrees. The proximal needle segment 320 extends
to a second bend. A terminal needle segment 330 extends from the
second bend to an end of the needle, wherein the terminal segment
defines with the proximal segment 320 an angle A2 of greater than
90 degrees. Cables 340 extend from the hub 310 for connection to a
monitoring device (not shown). Straight needle electrodes are
typically inserted at a shallow angle with the skin. During needle
insertion, the skin facilitates initial skin penetration by
providing resistance along its surface. The above modified needle
embodiments 100, 200, and 300 may be inserted at a steeper angle,
relative to the skin surface. To achieve a proper overall insertion
of a needle, the terminal segment must be inserted at an initial
insertion angle that approximately corresponds to an angle between
a proximal segment and a hub from which the needle extends.
Therefore, an insertion angle of the terminal segment of
embodiments 100, 200, and 300 should be 90 degrees relative to the
skin. With a 90 degree insertion angle, however, there is no force
vector along the skin surface, and resistance tension along the
skin surface cannot aid in initial skin penetration. As such, in
alternative embodiment, an angle A1 that is greater than 90 degrees
may be implemented, so that at least some insertion force will be
applied parallel to the skin surface wherein skin tension aids in
skin penetration.
[0058] FIG. 4 shows an embodiment with A1 at 115 degrees and A2 at
125 degrees, for example. The terminal segment of this electrode
may be inserted at a 115 degrees angle (equal to A1) with skin in
order that the hub 410 will end up flat on top of the skin surface.
The slightly open angle of A1 may provide that there will be a
force vector along the skin surface. The proximal needle segment
420 may traverse skin and subcutaneous tissue at a mildly open
angle, versus a perpendicular orientation. Thus, it may achieve
less depth after insertion than with A1 and A2 at 90 degrees, given
a proximal needle segment of the same length. The larger angle at
A2, relative to A1, may provide a (compensatory) deeper penetration
of the terminal segment 430. Thus, within the "special" embodiment,
A1 and A2 parameters may be coordinated in order to achieve the
proper angle of insertion, as well as, the depth and orientation of
the terminal needle segment 430.
2. Hub Modification of EMG Needle Electrodes with "Offset"
Configuration
[0059] Subdermal (single needle) and multi-needle EMG electrodes
are widely used during various intraoperative biophysiological
monitoring procedures. A proposed modification of straight needle
electrodes, incorporates two bends (angles A1 and A2) of the needle
portion of EMG electrodes (FIG. 1). The modification is intended to
increase stability and reliability of placement. A "special"
embodiment of the general design incorporates equal lengths of the
proximal and distal needle segments d1 and d3 and the initial
insertion depth d2. With such embodiments, the entire terminal
segment is inserted into the skin, so that the second angle A2
serves as a depth guide (FIGS. 2-4).
[0060] The terminal segment of the needle electrode is inserted at
an angle with the skin surface, equal to the first angle A1. For
"special" embodiments, the terminal needle segment(s) is/are
completely inserted to the level of A2. The hub is then rotated
backward so that its undersurface of the hub is parallel to the
skin surface. Final positioning of the electrode is achieved by
advancing the hub forward, while maintaining the "parallel with the
skin" orientation of the hub. This is best achieved with the index
finger and thumb on opposite sides of the hub. Pressure is applied
to the sides of the hub so as to tip the electrode slightly upward
as the hub is advanced forward. During forward advancement of the
hub, the applied forward force should be exclusively parallel with
the skin surface. When the hub has been advanced adequately, the
electrode will drop into place, as the proximal needle portion
enters the initial needle tract. When properly inserted, the
electrode hub lies flat, immediately on top of the skin surface.
This final physical relationship, between the electrode hub and the
skin surface, provides quality assurance feedback to the end user
regarding the fidelity of electrode placement.
[0061] The placement procedure for single and multi-needle
electrodes with such an offset configuration involves different
manual manipulations than for straight needle electrodes. Straight
needle electrodes are typically placed with the index finger and
the thumb positioned below and on top of the hub, respectively, or
with the thumb and index finger on either side. Insertion is a
simple forward advancement along the needle alignment.
[0062] By contrast, the proposed modified needle electrodes are
placed with an initial orientation of the needle terminus at an
angle to the skin surface, which is equal to A1. The index finger
may initially be on top of the hub and the thumb on the bottom. The
next step in the placement procedure is to rotate the electrode hub
downward until the hub is roughly parallel to the skin surface. The
final step is the forward advancement of the electrode hub, while
tipping the needle end slightly upward, so that the hub maintains
is orientation parallel to the skin surface.
[0063] Present, low-profile, rounded-rectangular electrode hubs are
rather difficult to manipulate, when they are close to the skin
surface. It is a premise of the disclosed embodiments that the hub
shape may be modified in order to aid in the ability to manipulate
electrodes with an offset-needle modification during the placement
procedure.
[0064] The disclosed embodiments may concern a modification for
single and multi-needle EMG electrodes with an offset configuration
500. The modification may include a concave groove 560 and a
relatively prominent upper ridge 550 along the sides of the hub
510, as shown in FIGS. 5A and 5B. The ridge 550 and groove 560
along the upper side-edges of the hub 510 may improve the ability
to manually manipulate the hub 510 when it is parallel with, and
close to, the skin. The ridge 550 and groove 560 may also be
particularly helpful in maintaining a slight elevation of the
electrode tip, in order to maintain the hub 510 in a plane parallel
to the skin surface, as the electrode is advanced forward to its
final position. With the ridge 550 along the upper edge of the
sides of the electrode hub 510 may serve as a possible alternative
to increasing the hub thickness in order to achieve better tactile
feedback and manipulative control during placement.
[0065] Further refinements of the basic features might include
multiple small vertical grooves along the lateral edges of the
ridges 550 and/or in the grooves 560, in order to enhance the
positive tactile feel of the sides of the hub 510.
3. Modified Ground Electrode for Intraoperative Nerve Integrity
Monitoring
[0066] EMG recording during intraoperative nerve integrity
monitoring may be performed using differential bipolar
amplification, which incorporates a ground electrode in addition to
a differential pair of active recording electrodes. The ground
electrode is usually placed in or around the field of recording,
separately from placement of the recording electrodes. The ground
electrode is separate from the recording electrodes and is not
presently used in any fashion to help facilitate the electrode
setup.
[0067] The most common application of nerve integrity monitoring is
facial nerve monitoring. Currently available facial nerve
monitoring electrodes are in packages containing multiple
electrodes. Individual electrodes are individually coiled up and
lie free within the package. The end user must uncoil each
electrode and place them separately. It is up to the end user to
organize the electrodes in a manner that will minimize the
possibility of electrode dislodgement and interference by
mechanical or electrical artifacts.
[0068] In the case of facial nerve monitoring, the ground electrode
has been variously placed in the hairline, the upper chest area or
contralateral shoulder, with no consensus with regard to a
preferred or "standard" location of the patient-ground electrode
placement. Because the electrodes are packaged individually, with
no design elements to imply a preferred setup arrangement of
electrodes, there may be significant variability in setup among end
users. The relative lack of standardization may result in untoward
inconsistency in recording quality.
[0069] This disclosed embodiment may concern that the design and
positioning of the ground electrode may be tailored to facilitate,
organize and standardize the setup procedure.
[0070] In particular this disclosed embodiment may concern a
modification of the ground electrode, where the electrode hub is
physically, but not necessarily electrically, attached to the lead
wires of the recording electrode(s). The attachment may be fixed,
detachable or adjustable in position along the length of the lead
wires, depending upon the requirements of individual applications.
With such an attachment, the recording electrode lead wires may be
supported and organized around a strategic placement position for
the ground electrode.
[0071] During ear, parotid and skull base procedures, for which
facial nerve monitoring is commonly employed, the head is typically
turned away from the side to be operated. In this position, the
contralateral shoulder is in reasonably close physical proximity to
the ipsilateral (surgical) side of the face. This location is also
in the general path of the electrode leads, as they course toward
the point of connection with recording equipment at the "head box."
In the interest of setup standardization, the contralateral
shoulder may be elected as a possible site for the ground electrode
placement. The ground electrode hub may be modified to attach the
recording electrode leads at that site. This will support and
organize the electrode leads during the setup and "standardize" the
ground location. In the package, the electrodes may be arranged in
a single coil, in a more easily-managed fashion, so that uncoiling
the electrodes and their placement may be facilitated.
[0072] The ground electrode itself may include a needle electrode
with a curved, straight, angled, or "offset" configuration. The
needle hub may be modified to allow a fixed, detachable or
adjustable (sliding) attachment to single or multiple recording
electrode leads. The rather generous skin surface available at the
contralateral shoulder site for facial nerve monitoring may also be
amenable to the use of a "snap lead" style of surface electrode to
which the recording electrode leads may be attached. FIGS. 6A-6C
show an exemplary snap electrode lead 640 with a typical round disk
hub 610 and a female snap 620 on the undersurface.
[0073] On the side opposite of the snap 620, a single or set of
multiple recording electrode lead(s) 640 are attached to the hub
610. The attachment is at 630. In this embodiment, the electrode
leads 640 are fixed to the hub 610. However, the leads 640 may be
otherwise attached by a plastic or metal loop extending from the
snap-lead hub 610 that may allow the electrode leads 640 to slide
through, but not escape the hub attachment 630. Additional
embodiments may involve detachable connections of the electrode
leads 640 to the ground electrode hub 610, such as with Velcro dots
or magnetic chips, for example.
[0074] The distance "d" from the recording electrode hub(s) 610 and
the attachment point 630 to the ground electrode 650 may be elected
to best support the electrode leads 640 in a possible location and
orientation, proximate to the field of recording and where
manipulations of surgical drapes are less/least likely to provoke
mechanical artifacts. For facial nerve monitoring the distance may
be approximately 12-15 inches for placement of the ground at the
contralateral shoulder. In other applications, the positioning of
the attachment of the patient-ground to the recording electrode
lead wires may vary widely, depending upon the needs of individual
setups. In some cases, the distance "d" may be much shorter in
order to best organize the electrode leads 640 "out of the way" of
the surgical procedure or in a manner so as to reduce potential
electrical or mechanical artifacts. This configuration may be
especially helpful for applications during which the recording
electrodes 660 may be placed "on the field" in sterile fashion in
or around the surgical field.
[0075] From the patient-ground electrode hub 610, the recording
electrode leads 640 and the ground electrode lead 650 may run to
their termination at the recording equipment "head box". The leads
may 640, 650 may be organized or held together by braiding the
ground lead 650 with a single electrode pair 640 or by taping or
shrink wrapping multiple leads at selected intervals, for example.
Such organization may facilitate the setup in that there is only
one coil of electrode wires to unwind out of the package. Color
coding or employ of a single proprietary terminal connector may
facilitate proper connections to the recording equipment.
4. Multi-Application (Hybrid) Recording Electrode for
Intraoperative Nerve Integrity (EMG) Monitoring
[0076] Standard single or paired needle recording electrodes are
simple and robust for use in most common applications in nerve
integrity monitoring. However, their rigid construction may cause
instability of placement and possible injury when needle electrodes
are used to record EMG activity from delicate musculature or when
there may be significant movement around the recording site
area.
[0077] Hooked-wire electrodes have been used to record from
delicate muscles in the pharynx and larynx. They have also been
used to record from extremity musculature during active exercise,
due to their stability of placement and minimal tendency for
migration.
[0078] This disclosed embodiment may concern a modification of a
modified ground electrode 750, where the electrode leads may attach
to the hub 710 of the ground electrode 750. In this case, however,
there may be hard electrical connections 720 within the hub 710 of
the ground electrode, connecting the terminal 745 and proximal 740
portions of the recording electrode leads, as shown in FIG. 7A.
This disclosed embodiment may combine the delicate and stable
attributes of hooked-wire electrodes 760 and the robustness of
standard electrode leads. The inserted portion of the electrode 760
may be a bipolar fine hooked-wire electrode 760, the lead length of
which d1 may be limited to only that required for unencumbered
insertion into the target muscle tissue and subsequent placement of
the hub 710 at a possible location.
[0079] FIGS. 7A and 7B show an iteration of hooked-wire electrode
760 with the leads threaded through the entire length of the
insertion hypodermic needle. This configuration may be for
illustrative purposes to show the staggered arrangement of the bare
portions of the wire electrodes. A possible embodiment may include
having the terminal ends of the wires being backed into the
terminal end of the hypodermic needle (Parker). This may allow for
the needle to be completely removed after insertion.
[0080] The connection to existing nerve integrity monitoring
equipment may be made by a supplemental length L2 of standard
electrode leads 745 with standard or proprietary terminal
connectors. The two wire types may be electrically connected 720 at
the hub 710. After placement, the hub 710 may be taped or sewn into
place near the recording site in order to secure the electrode
placement. Paired notches or grooves or small tabs with holes may
be incorporated in order to aid in securing the hub with a single
suture.
[0081] A possible hub embodiment may be that of a modified ground
electrode incorporating a modified ("off-set") needle electrode, as
discussed below for example. Incorporation of a ground electrode at
the hub may aid in supporting the delicate hooked wire electrodes
and may standardize the relative positioning of the recording and
ground electrodes.
5. Strategic Needle Positioning on Electrode Hub as an Aid and
Quality Assurance Guide to Proper Depth of Placement
[0082] Subdermal (single) and multi-needle EMG electrodes are
widely used during various intraoperative biophysiological
monitoring procedures. Previous modifications of these electrodes
involve an "offset" configuration of the needle portion, which is
intended to increase stability and reliability of placement (FIGS.
1-4). Insertion of so-modified electrodes is performed by initially
entering the skin with the distal (sharp) portion of the needle at
an angle to the skin surface, equal between the undersurface of the
hub and the proximal needle segment A1. The needle is inserted to
the desired (final) depth, after which the electrode is rotated
backward so that the hub is roughly parallel to the skin surface.
Electrode insertion is continued by forward advancement of the hub,
parallel with the skin surface, while tipping the electrode
slightly upward. Insertion is completed as the proximal segment of
the needle drops into the track made during initial insertion.
[0083] When properly placed, the electrode hub lies flat,
immediately on the skin surface. This final physical relationship,
between the electrode hub and the skin surface, provides quality
assurance feedback to the end user regarding the fidelity of
electrode placement.
[0084] In conventional needle electrode designs, the needles
originate from the anterior face of the hub. In order that the
underside of the hub is positioned flat and on top of the skin
surface, the depth of initial insertion must be of equal length to
the proximal needle segment. For "special" embodiments of the
"offset" needle modification, where proximal and distal needle
segments are of equal length (FIGS. 2-4), the second needle bend at
A2 serves as a depth guide. However, if the terminal needle segment
is longer than the proximal segment (as in FIG. 1), the end user
must match the initial insertion depth to the length of the
proximal needle segment. If the initial insertion is too shallow,
the hub will sit off of the skin surface. If the initial insertion
is too deep, the hub will place pressure in the skin surface and
will not sit flat on the skin surface.
[0085] The special embodiment cannot be used for shallow insertion
depths, in that the overall needle length must be at least a
centimeter in order to achieve the desired electrical impedance.
Also, shorter needle lengths will not be as resistant to
dislodgement with inadvertent lead manipulation.
[0086] This disclosed embodiment may concern a modification of
needle electrodes with "offset" configuration, specifically with
regard to the positioning of the electrode needles on the hub. The
"offset" needle electrodes may be constructed so that the front
edge of the hub can serve as a guide to the proper insertion depth
for individual applications. Placement of the needle on the hub may
vary for different depths of insertion, depending upon the specific
application. For example, intramuscular placement may require a
greater insertion depth than subdermal placement.
[0087] FIG. 8A shows the modification of the "offset" needle
electrode 800. The needle 820, 830 may originate perpendicularly
from the undersurface of the hub 810, which obviates the need for
the first needle bend at A1. The length d1 of the proximal needle
segment 820 may be elected to be the final depth.
[0088] In order that the underside of the electrode hub sits flat
on top of the skin at the end of placement, the depth of initial
needle insertion d2 may be equal to the length dl of the proximal
needle segment 820. This possible embodiment may position the
origin of the needle along the hub 810, so that the needle terminus
(sharp end) may extend a strategic distance, equal to d1 (and d2),
from the front edge of the hub 810.
[0089] During the insertion procedure, the needle terminus 830 may
be inserted, perpendicular to the skin surface, until the front
edge of the hub 810 meets the skin surface. Thus, the front edge of
the hub 810 may serve as a guide for initial insertion depth. The
electrode placement is completed by rotating the hub 810 backward
until it is oriented parallel with the skin surface. With the
anterior aspect of the hub 810 tipped up slightly, so that the hub
810 is roughly parallel to the skin surface, the hub 810 may be
advanced forward until the proximal needle segment enters the
initial insertion path. The distance of forward advancement may be
the length d3 of the terminal needle segment 830.
[0090] FIGS. 9A-9C may combine an alternative embodiment 900 of a
modified ground electrode and the modified placement of the needle
on the hub. The length d1 of the proximal needle segment 920 may be
equal to the length d2 of the portion of the terminal needle
segment 930, beyond the anterior edge of the needle hub. The
recording electrode leads 940 and the ground lead 950 may be
oriented perpendicular to the needle, in order to allow the
mechanical manipulations required for needle placement. The needle
hub 910 may be modified from a typical rounded rectangular
configuration. There may be a ridge 911 and groove 912 on the back
aspect of the hub, as well as a ridge and flat anterior surface 913
on the front aspect of the hub. These hub 910 features may
facilitate placement of the electrode, with the thumb on the back
and index finger on the front of the hub. The electrode leads 940,
950 may interfere with placing the thumb and index finger along the
sides of the hub.
[0091] The ridge 911 on the back of the hub 910 may extend backward
at approximately a 45 degrees angle, which facilitates working the
back of the hub up and down with the thumb. The front ridge 913 may
be vertical and flat with the front face of the hub. The prominent
front edge of the hub may aid in keeping the electrode tipped up
slightly, with the index finger, during the final horizontal and
forward movement of electrode insertion. The flat portion may also
help the user establish insertion depth d2.
[0092] The modification may render the anterior edge of the needle
hub 910 as a guide to proper depth of placement. It is expected to
facilitate proper electrode placement by the end user and further
reduce untoward variability of recording quality.
6. Three-Needle Electrode, Low-Noise EMG Recording Electrode for
Intraoperative Nerve Integrity Monitoring and its Method of
Connection with Recording Equipment
[0093] Intraoperative nerve integrity monitoring provides auditory
feedback, which increases the surgeon's awareness of the physical
contour of the monitored nerve and the possible injurious effects
of ongoing surgical manipulations. The procedure involves use of
differential amplification of EMG signals, employing a pair of
recording electrodes and a ground electrode. While the recording
electrodes have been incorporated in a paired configuration with a
single hub, the ground electrode is placed separately in relative
proximity to the field of recording. The ground electrode, used in
differential amplification, helps control electrical artifacts,
such as DC offset and common electrical noise.
[0094] As the use of intraoperative nerve integrity monitoring
expands into other applications, maintenance of high quality
recording with a minimum of electrical artifacts remains an
important concern. False-positive electrical and mechanical
artifacts may confound recording electrodes appear the most
symmetrically and identically with the ground electrode positioned
between the two electrodes. The disclosed embodiments extend from
that concept and should adapt well to any application.
[0095] In conventional systems, ground and recording electrodes are
available in packages with two or more recording electrodes. The
end user must choose appropriate placement sites for the individual
electrodes. There is likely to be significant variability in the
setup with regarding to the placement and organization of electrode
leads.
[0096] This disclosed embodiment may include a product design that
may strongly leverage toward standardization of recording setup and
reduction of electrical artifacts during intraoperative nerve
integrity monitoring in a variety of possible future applications.
From the perspective of a differential amplifier, the recording
electrodes within a differential pair may appear the most
identical/symmetric, when the ground electrode is positioned
between them. The disclosed embodiments may derive from this
concept and may aid in setup standardization and in maintaining
high recording quality.
[0097] In this manner, the disclosed embodiments may concern a
modification of a paired electrode design where a third needle
electrode 1030, as shown in FIGS. 10A-10C, may be located
symmetrically between the paired recording electrodes 1020, and may
serve as the ground electrode in the electrode 1000 of FIGS.
10A-10C. The needle electrodes 1020, 1030, housing with a hub 1010,
may be straight, as shown in FIG. 10B or modified with an offset
configuration 1021, as shown in FIG. 10C. The electrode leads 1040,
1050 may be taped together at intervals, twisted together or
braided in order to minimize the antenna-like qualities of the
electrode leads themselves.
[0098] Conventional methodology may employ a single ground
electrode with single or multiple recording electrodes. The
disclosed embodiments may employ a ground electrode 1030 for each
differential pair of recording electrodes 1020, for example. If
multiple electrodes are used, there may be multiple ground
electrodes, for example. All ground electrodes may be tied together
electrically at one point, in order to avoid "ground loop" issues.
Such a connection may be accomplished with external adaptor
(Y-connecter) devices, for example.
[0099] Alternatively, internal modifications of the patient "head
box" or within the main monitoring unit itself may provide an
"internal" single-point connection. FIG. 11 shows a "single point"
connection 1110 within the patient isolation "head box" 1150, which
connects all needle ground electrodes 1130 of recording electrode
1140, and is located ahead of the input amplifiers 1120 within the
main recording unit. Electrode leads 1140, 1150 may be terminated
with proprietary three-lead terminal connectors to the headbox 1150
to further facilitate the setup by reducing the number of
connections to be made. Additional circuitry may be implemented for
adjusting the relationship between the chassis ground, patient
ground, and the ground at individual input (initial gain stage)
recording amplifiers 1120.
7. "Virtual" Anode Electrode for Intraoperative Nerve Integrity
Monitoring
[0100] The disclosed embodiments may concern a modification of the
method by which the anode ("return") electrode connection is
achieved for the purposes of electrical stimulation during
intraoperative nerve integrity monitoring.
[0101] Electrical stimulation is frequently performed during
intraoperative nerve integrity monitoring in order to locate and
map the physical contour of the monitored nerve. Stimulation is
achieved by a flow of current through the nerve of sufficient
intensity to produce nerve depolarization. Current flows from the
cathode (negative) electrode to an anode (positive) electrode. The
surgeon uses a handheld electrical stimulus probe, connected to the
cathode, in order to deliver current the nerve contour. In
monopolar applications, the anode may be placed at some distance,
such as at the ipsilateral shoulder. For bipolar applications, the
anode is positioned in close proximity to the cathode. Close
pairing of the cathode and anode, confines current flow to a small
area, enhancing spatial selectivity of electrical stimulation.
[0102] In possible applications, both the anode and cathode are
active, electrically distinct from patient and chassis ground
connections. If monopolar electrical stimulation is to be used, a
separate anode electrode must be placed. If the need for electrical
stimulation was not anticipated prior to the surgical procedure,
but is found necessary sometime during the case, placement of the
anode electrode "after the fact" under the surgical drapes may be
difficult and disruptive to the flow of the surgical procedure.
[0103] The cathode electrode is has greater "stimulus adequacy"
than the anode electrode, but current flow around an active anode
electrode may also provoke nerve stimulation, when the anode is in
physical proximity to the nerve. Stimulation around the anode may
result in some ambiguity in locating the nerve contour, relative to
the contact surfaces of the cathode and anode stimulus
contacts.
[0104] Current flow around the anode can be eliminated by
connecting the anode electrode to the ground, eliminating the
possibility of nerve stimulation at the anode electrode. Use of the
ground electrode as the stimulus anode connection obviates the need
to place a separate anode electrode, which streamlines the
setup.
[0105] The disclosed embodiments may eliminate the need for a
separate stimulus anode electrode during monopolar electrical
stimulation and may reduce possible localization ambiguity during
bipolar stimulation. FIG. 12 shows a virtual anode 1200 in
accordance with an embodiment. The virtual anode includes a
connection 1210 interposing a ground electrode circuit (within
headbox 1280) to an anode of a stimulus source 1220. A handheld
cathode stimulus probe 1230 is used to stimulate tissue in a
probing fashion. A separate anode electrode connection to the
patient (not shown) may be eliminated by connection of a ground
electrode hub 1240 to the anode in the stimulus circuit. This may
be accomplished before (e.g., on the patient side) or after (e.g.,
on the monitoring equipment side) the electrical isolation
circuitry, but may not be across it. FIG. 12 also shows a recording
electrode 1250. FIG. 12 shows an exemplary electrical connection
1210 between the ground electrode 1240 and the anode terminal.
Connection 1210 is located before (e.g., on the patient side) the
isolation circuit 1290. FIG. 12 shows additional filter and
amplification components 1270 for minimizing stimulus and other
artifacts, and amplifying signal to loudspeaker audio level. The
headbox 1280 may contain both the isolation circuit 1290 and said
connection 1210 as shown.
[0106] A possible disadvantage of making the ground-anode
connection before isolation may be that the harness 1215,
containing multiple wires from the terminal electrode connections
and the main monitoring unit, must include a connection 1210 such
as a wire that ultimately connects to the anode terminal of the
stimulus source 1220. FIG. 13 shows an alternative embodiment of a
virtual anode 1300. The embodiment shown in FIG. 13 includes a
connection 1310 between the ground electrode circuit and anode of
stimulus source 1320 "after" (e.g., on the monitoring equipment
side) the electrical isolation circuit 1390, within the main unit.
The possible interference from the stimulator circuit in the
recording side of the monitoring function may be accomplished with
a filter 1380, which separates the anode of the stimulus source
1320 from the ground of the differential amplifier 1360. Further,
existing designated nerve integrity devices 1370 may mute the EMG
recording signal during stimulus presentation, so that the end user
cannot hear the stimulus itself. FIG. 13 shows a handheld stimulus
probe 1330 for locating nerve structure of a patient connected
directly to the electrical isolation circuit 1390. FIG. 13 shows a
ground electrode hub 1340, and a recording electrode 1350 connected
directly to the electrical isolation circuit 1390.
[0107] An advantage of making the connection between the anode and
ground electrode in this location may be that no wire for the anode
connection 1310 is required in the patient connection harness 1315
between the main monitoring unit and the terminal electrode
connections. A possible disadvantage might be the ability to
prevent audible interference in the recording circuit and possibly
more difficulty in satisfying FDA safety issues.
[0108] Either of the above embodiments may convert the electrical
stimulation circuit from a "double-ended" to a "single-ended"
configuration, through connection of the anode electrode to the
ground electrode. This may result in neutralization of the anode
electrode with regard to stimulus adequacy. This configuration may
improve the spatial selectivity of bipolar stimulation. It may also
obviate the need for separate placement of an anode electrode for
monopolar stimulation. One may only need to connect the monopolar
(cathode) stimulus probe to complete the circuit for monopolar
stimulation, at any time during the surgical procedure.
[0109] Although the above description may contain specific details,
they should not be construed as limiting the claims in any way.
Other configurations of the described embodiments of the disclosed
embodiments are part of the scope of this disclosure. For example,
the principles of the disclosed embodiments may be applied to each
individual user where each user may individually deploy such a
system. This enables each user to utilize the benefits of the
disclosed embodiments even if any one of the large number of
possible applications do not need the functionality described
herein. In other words, there may be multiple instances of the
features in the disclosed embodiments each processing the content
in various possible ways. It does not necessarily need to be one
system used by all end users. Accordingly, the appended claims and
their legal equivalents should only define the disclosed
embodiments, rather than any specific examples given.
* * * * *