Note: Descriptions are shown in the official language in which they were submitted.
2 ~ ~3 ~ (i r ~
ELECTROSURGICAL TROCA~ ASSEMBLY WITH BI~POLAR ELECTRODE
Cross Referenee to Related ApPlieation
This applieation is a continuation-in-part of our eo-
pending applieation Serial No. 07/853,149, filed March 17,
1992, and entitled ELECTROSURGICAL TROCAR ASSE~BLY.
Field of the Invention
The present invention relates to trocar devices or
assemblies used in surgery and, more partieularly, to an
electrosurgical trocar device or assembly.
Baekqround of~the Inven~ion
Surgieal proeedures such as laparoscopie proeedures
require the surgeon to ereate one or more punctures in the
anatomy of the patient to enable a yuide tube, referred to
as a eannula, to be sited and thereby enable surgical
instruments to be passed down through the eannula into the
patient in order to carry out the intended procedures.
One method of accomplishing this is the open or
"Hussan" method wherein an incision is made in the desired
area to aeeommodate the cannula and sutures are put around
the eannula to elose the gap left by ~he ineision. Sutures
are also made from the skin to cannula to assist in holding
the eannula in plaee. This technique is used primarily (but
not exelusively) in situations wherein other abdominal
surgeries pose potential adhesion complications~ Such
2~ eomplieations ean cause an unintended puncture in the bowel
or in other organs.
20~9~ ~
A second method involves the use of a mechanical trocar
device which comprises the combination of a trocar and a
cannula. The trocar basically comprises a rod or shaft
having a very sharp cutting edge or point at one end thereof
and is encl~sed within the tubular cannula. In some
devices, the cannula incorporates some kind of safety
mechanism, such as a shield, over the cutting tip prior to
use to reduce the chance of unintended punctures. Trocar
devices characteristically require substantial force to
drive the cutting end or tip through, e.g., the abdomen wall
and as a result, trocar devices can be hard to control. A
separate trocar device, i.e., comprising a trocar and
cannula, is used for each puncture site.
Summa~ the Invention
In accordance with the invention, a trocar device or
assembly is provided which overcomes the problems with prior
art trocar devices discussed above. The trocar device of
the invention comprises an electrosurgical cutting element,
which, in common with electrosurgical cutting instruments
commonly referred to as electrosurgical "blades," provides
cutting of tissue through the transmission of radio
frequency electrical energy to the area to be cut. The
trocar device of the invention uses electrosurgery to make
the guide hole for the cannula and thus enables the
remainder of the cannula assembly to enlarge the puncture.
This greatly reduces the force required as compared with
mechanical trocar devices. This reduction in force enables
an even, constant insertion pressure to be exerted, thereby
allowing substantially greater control and reducing the
chances of an unintended puncture. Further, the use of
electrosurgery eliminates the need for a sharp point as is
2 ~ 3
required in mechanical trocar devices, thereby allowing
multiple uses of the same trocar.
In accordance with a preferred embodiment of the
invention, the electrosurgical cutting element comprises a
S bi polar electrode assembly. The bi-polar electrode
- assembly comprises first and second independent, mutually
insulated electrodes, one of which carries the radio
frequency current and the other of which provides a return
path to ground. Although a single electrode arrangement can
be used wherein a single electrode carries the radio
frequ~ncy current and a return to ground is provided by,
e.g., a ground pad placed in a remote area of the body, the
bi-polar electrode assembly ensures that the ground circuit
is disposed in close proximity to the radio frequency
cutting point.
The electrosurgical cutting element is, in use,
connected to a conventional electrosurgical generator or
other source of radio frequency ~r.f.) power or energy (the
term electrosurgical generator being used herein to refer to
any suitable source for driving the electrosurgical cutting
element) and a further important feature of the trocar
assembly of the invention is in the provision of an
electronic control (cutoff or shutdown) circuit for sensing
current flow and, when the trocar breaks the wall of the
body cavity involved, for opening or cutting off the
connection to the electrosurgical generator. ~his feature
substantially eliminates any chance of an unintended
puncture.
In addition, further circuitry is preferably provided
which requires that the operator (surgeon~ release a control
s~itch for a predetermined time period prior to resuming
surgical operations so that power is again pYovided to the
electrosurgical cutting element only as thQ r~s~ ~ of a
conscious decision on the part of the operator. As a
result, inadvertent operation of the cutting elernent, and
thus possible inadvertent puncturing of an organ wall, are
combatted or avoided. Advantageously, an indicator such as
a light emitting diode (LED) ls used to indicate that the
generator is supplying power to the cutting element
(preferably by providing a continuous light output) and to
also indicate the predetermined ime period before
electrosurgery can be resumed (preferably by providing a
blinking or intermittent light output).
A further important feature of the invention involves
the provision of multiple trocars as part of a trocar
assembly or kit, independently of whether or not an
electrosurgical cutting element is used. The provision 3f
multiple trocars enables the same basic device to provide
punctures or openings of different diameters. The trocars
can be very simple in construction and thus can be made to
be low cost disposable items.
As discussed above, one aspect of the invention
concerns the provision of a control (shutoff) circuit for
shutting off the RF power supplied to the trocar, upon
penetration of the trocar through, e.g., the abdomen wall,
by sensing the change in load impedance when this happens.
This change can be detected in a number of ways including
monitoring the current, the voltage or the phase shift. As
is discussed below, for reasons of simplicity and economy it
is desirable to locate as much of the control circuitry as
possible in the electros~lrgical generator (ESU) or an
auxiliary control box. The disadvantage of doing this is
that, at the fre~uencies involved in electrosurgery, the
cable connected to the trocar presents a sizeable and
2 ~
varying "leakage" impedallce that complicates the task of
providing reliable detection of the shut-off point, as the
signal-to~noise ratio of the detected signal deteriorates.
In accordance with a further aspect of the invention,
in order to deal with this problem, means are provided for
counteracting the effects of the "leakage" impedan~e
described above. Various means can be used for this purpose
including the provision of a sample and hold circuit for
determining initial conditions prior to contact being made
(and, of course, the critical sensing elements can be
located close to the trocar end of the cable to minimize the
effect). However, according to a preferred embodiment of
this aspect of the invention, a reference wire or lead is
included in the connecting cable for the trocar which is
connected in parallel with the !'hot" wire or lead (i.e.,
that carrying the RF current to the cutting element of the
trocar) but which is not connected to the cutting element.
With this arrangement, the control circuit senses the
difference between the load conditions seen by the "hot"
(current carrying) wire and the reference wire. The
reference wire or lead can be a dedicated lead or can be a
wire or lead already used in the system to perform some
other function at the trocar end such as switching or
indication. In an advantageous implementation of this
embodiment, a current transformer is used to sense the
change in load impedance. In this embodiment, the current
carrying wire or lead and the reference wire or lead are
passed through the core of the current transformer,in such a
way as to oppose each other so that the leakage current is
substantially n~utralized.
In accordance with a further embodiment, the cutting
element, whether monopolar or bipolar, is provided with a
20~s~ ~
specialized high temperature resistant insulating portion,
made of Teflon (polytetrafluorethylene), a high temperature
ceramic or the like, adjacent to the distal tip of the
cutting element.
It is noted that a major advantage of the electronic
surgical device of the invention is that a cutoff or
protective action can be instituted as soon as the tip
emerges through the cavity wall in question based on sensing
the corresponding change in impedance. This cutoff is
substantially immediate and the danger of the cutting
element inadvertently puncturing an organ within the cavity
is substantially eliminated. This contrasts with mechanical
trocar devices which provide for release of a protective
sheath for covering the cutting blade only after the body of
the trocar device has fully penetrated the cavity wall.
Other features and advantages of the invention will be
set forth in, or apparent from, the following detailed
description of preferred embodiments of the invention.
Brief Description of the Drawinqs
Figure 1 is a side elevational view, partially in cross
section, of a trocar assembly in ac~ordance with a preferred
embodiment of the invention;
Figure 2 is a side elevational view of one of the
trocars of Figure 2, with the second trocar being shown in
phantom lines;
Figure 3 is a side elevational view of the second,
outer trocar of Figure l;
Figure 4 is a cross section view, to an enlarged scale,
of the distal or free end of the trocar assembly of Figure
1,
2 ~ f', fl.,
Figure 5 is a partial cross sectional view of the
cannula of the trocar assembly of Figure 1 s~lowing the
operation of the seal rollers;
Figure 6 is a cross sectional view taken generally
along line VI-VI of Figure 5;
Figure 7 is a schematic circuit diagram of circuitry
incorporated into the cannula of Figure li
Figure 8 is a schematic circuit diagram of the cutoff
circuit of Figurle l;
Figure 9 is a partial cross-sectional view similar to
that of Figure 4 illustrating a further embodiment of the
invention.
Figure 10 is a schematic circuit diagram of a further
embodiment of the invention; and
Figure 11 is a partial cross sectional view similar to
that of Figure 4 illustrating yet another embodiment of the
invention.
Description of the Preferred Embodiments
Referring first to Figure 1/ there is shown a schematic
side elevational view, partially in section, of a trocar
assembly whic:h is generally denoted 10. The trocar assembly
10 basically comprises a multi-element trocar 12 and a
cannula 14.
The multi-element trocar 12 includes a central or inner
trocar member 16 (perhaps best seen in Figures 2 and 4)
comprising a head portion 16a and a shaft or rod portion
16b, and an outer trocar member 18 (perhaps best seen in
Figures 3 and 4) which cc~mprises a head portion 18a and a
hollow shaft portion 18b and which slides onto and
releasably engages trocar member 16~ As shown, head portion
18a of trocar member 18 is affixed to head portion 16a while
h~
shaft portion 18b surrounds sha t or rocl portion 16h. The
cannula 14, which is also shown in Figures 5 and 5,
comprises a head or upper housing portion 14a and a guide
tube or cannula portion 14b. As shown, head portion 14a is
affixed to the head portion l~a of the outer trocar member
18 and the cannula portion 14b surrounds hollow shaft
portion 18a.
Considering the inner or central trocar member 16 in
more detail and referring to Figures 1, 2 and 4, head
portion 16a is generally cylindrical in shape and includes
an outwardly extending locking member or skirt 20 having a
shaped rim or circumferential lip portion which is adapted
to be received in a corresponding recess 22 in head portion
18a of outer trocar 18 (see also Figure 3) so as to provide
a releasable snap fit, as is indicated in phantom lines in
Figure 2. It will be understood that a similar releasable
connection can be provided between the trocar ~embers 16 and
18 using other suitable connecting arrangements.
~ead portion 16a is also provided with an indicator
light or lamp 24 for indicating the operating state of the
device as explained below and a reset pushbutton switch 26
which resets the electronic circuitry described below.
The shaft portion 16b of central trocar member 16
comprises a central metal rod 28 and an outer insulating
trocar shaft or tube 30. In a specific exemplary
embodiment, rod 28 is made of stainless steel and is about
.075 inches in diameter while trocar shaft 3Q is made of a
plastic, ceramic or any like material capable of providing
the appropriate temperature resistance as well as has a
3~ relatively low coefficient of friction and has an outside
diameter of about 3/16 of an inch or 5mm. The distal end of
trocar shaft 30 is tapered as illustrated so as ~o enable
2 o ~ 9 ~
ready insertion thereof into a small hole "burned" through
the wall in question by rod 2~.
Electrical power is provided to rod 28 through an
electrical circuit located in head portion 16a and discussed
; 5 in more detail below in connection with Figure 7. This
circuit, which is also shown in dashed lines in Figure 1
includes indicator lamp 24 and switch 26.
~ eferring to Figure 3~ the head portion 18a of the
second or outer trocar member 18 is also cylindrical in
sha~e and, as noted above, includes a circumferential recess
22 for receiving locking or latching member 20. A similar
locking or latching member or skirt 32 having rim or
circumferential lip is provided at the other end of head
portion 18a, as shown. The shaft portion 18h comprises a
tubular trocar shaft ~4 having a central bore 36 therein
through which the central trocar shaft 30 extends. The
distal end of trocar shaft 34 is tapered and as shown in
Figure 4 (and in Figure 1), the overall taper provided by
trscar shafts 30 and 34 is continuous or substantially
continuous. Trocar member 18 does not contain any active
components and in an exemplary embodiment has an outside
diameter of about 13/32 inches or lOmm and an inside
diameter about 7/32 inches, i.e., a diameter just slightly
larger than the outer diameter of inner trocar shaft 30.
However, it is to be understood that outer trocar members of
different sizes can be used and that a set of such trocar
members can be provided which would selectively be slipped
onto and over inner trocar shaft 30 to provide openings of
different sizes in the wall of the abdomen or other organ.
It will be appreciated that such outer trocars, which, as
noted above, contain no active parts, are quite simple in
construction and inexpensive to manufacture.
2~6~ L
~ eferring now to Figures 1, 5 and 6, it will be seen
that the head portion 14a of the cannula member 14 is hollow
in construction and includes a shaped circumferential recess
38 in the upper or proximal end thereof in which
reciprocally shaped circumferential loc~ing member 32 of
outer trocar member 18 is received so as to provide a snap
fit between members 14 and 18.
Disposed within the head portion 14a of cannula member
14 are a pair of sealing rollers or rolls 40 which are
suspended from the upper or proximal end wall of head
portion 14a by springs 42 that bias the rolls 40 toward each
other so as to close off an opening 44 in that proximal end
wall, as shown in solid lines in Figure 5. Inserting the
shaft portions 16b and 18b of trocar members 16 and 18 down
into opening 44 causes rolls 40 to be forced apart and to
assume the positions shown in Figure 1 and in dashed lines
in Figure 5. Reference is made to our commonly assigned co-
pending application Serial No. 07/846,386, filed on March 5,
1992, and entitled LAPAROSCOPIC CANNULA for a further
description of arrangement for permitting insertion of a
trocar while shutting off the opening for the trocar after
the trocar is removed.
A selectable seal device 46 is best seen io Figure 6.
The seal device 46 includes a flat sealing member 48 having
pull tabs 50 and 52 at opposite ends thereof and openings 54
and 56 of different sizes so as to accommodate trocars of
different diameters. In the exemplary embodiment
illustrated, the openings 54 and 56 are designed to receive
the 10mm trocar 18 and the 5mm trocar 16 and tabs 50 and 52
are marked accordingly. Thus, with 10mm tab 52 pulled out
so that sealing member 48 is moved to the right as shown in
Figure 6, the 10mm opening 54 is brought into alignment or
2~f~',J,'I
registration with opening 4~ so that the lOmm outer diameter
trocar 16 can be inserted therethrough as indicated in
Figure 1. Sealing member 48 is disposed in a slot in
housing portion 18a and is slidable therein as described
above. It will be appreciated that the embodiment just
described is exemplary only and that, for example, the
openings in sealing member 46 can be different in number and
sizes so as to accommodate surgical instruments of various
sizes during s~lrgery.
As shown in Figure 5, an opening 58 is ~rovided in head
or housing portion 14a which enables irrigation fluid to be
supplied to the puncture site through cannula shaft 14b,
when the trocars 16 and 18 are removed.
Referring to Figure 7, there is shown a schematic
circuit diagram of the electrical circuitry contained within
the head portion 16a of the main trocar 16 (this circuitry
also being shown in dashed lines in Figure 1). As
illustr~ted, four input leads or connections, denoted 60,
62, 64, and 66 are provided, one of which, lead 60 is the
"hot" lead directly connected to electrosurgical rod 28.
Leads 6~ and 66 provide a current input and return path for
switch 26 while lead 62 connects optional indicator lamp 24
to lead 64.
Referring to Figure 8, a preferred embodiment of the
cutoff circuit for the electrosurgical generator is shown.
As indicated in Figure 1, the cutoff circuit, which is
generally denoted 68, can be a separate package or unit
connected into the cable 70 or in another connection between
the electrosurgical generator (not shown) and the trocar
assembly 10. Alternatively, the circuit can be built into
the electrosurgical generator. The cutoff circuit 68 of
Figure 8 includes a current transformer 72 connected to the
3 ,~ ,3 ~ r~ ~'
generator output line (which ~c~n c~rrespoll~ to cahle 70 of
Figure 1) so as to sense or monitor the current flow from
the electrosurgical generator ~not shown) to the trocar
assembly 10. The secondary ~inding 72a of transformer 72 is
connected to a rectifier 74 which produces an output voltage
that is a function of the current level. Rectifier 74 is
connected to an adjustable voltage comparator 7G which
determines the cutoff current by comparing the output
voltage produce~ by rectifier 74 with a predetermined
reference level. The output of comparator 76 is connected
to one input of an OR gate 78 the output of which is
connected to an A~D gate 80. The functions of the qates 78
and 80 are described in more detail below.
A control switch 82 is provided for controlling
energizing of the electrosurgical generator. This switch
can correspond to switch 26 described above and is
controlled by the surgeon. A pair of delay networks, a
start delay cirCuit 84 and a reset delay counter circuit 86,
are connected to switch 82 in parallel with each other.
Start delay circuit 84 begins timing out its associated
delay when switch 82 is closed while reset delay counter
circuit 86 begins timing out its associated delay when
switch 82 is opened. The significance of delay circuits 84
and 86 is explained below.
The output of start delay circuit 84 is connected to
the other input of OR gate 78 and the delay provided allows
time for the surgeon to start a cut after activating the
switch 82. Thus, when switch 82 is closed the output of
start delay circuit 78 ~rovides for closing of a control
relay 88 for the electrosurgical generator so as to turn on
the electrosurgical generator. Relay 88 is connected to the
output of AND ga~e 80 throuqh an I~FElr switch 90 provided so
2 ,/3,~5) r~
as to ensure that the appropriate relay switching levels are
maintained. After delay circuit 84 times out, the operation
of relay 88 is controlled by the output of the current
sensor 72 and, more particularly, by the output of
5 comparator ~6. Thus, if this output drops below the level
set within comparator 76, relay 88 is opened and power to
the electrosurgical generator is cut off.
The cutoff circuit 68 also includes an inhibit latch 92
which includes a first, set input connected to the output of
OR gate 78, a second, reset input connected to the output of
reset delay counter circuit 86 and an output connected to
the other input of AND yate 80. When the sensed current
drops below the preset or predetermined reference value
dictated by comparator 76, this is reflected at the set
input o inhibit latch 90 and latch 90 is set (in addition
to the control relay 88 opening as mentioned above). Th~
inhibit latch 90 will remain set until the switch 82 is
opened for the reset delay period, i.e., the period of reset
delay counter circuit 86, which is approximately three
seconds in a specific exemplary embodiment. The reason for
this provision is that the normal current level will drop
when an initial puncture is made and the intention here is
to ensure that the electrosurgical cutting element rod 28
will not be used to cut again until the surgeon
intentionally provides for the electrosurgical generator to
be turned back on, i.e., after the three second delay
provided by reset delay counter circuit 86. As noted above,
opening of switch 82 starts the inhibit or reset delay
period, and during this delay period it is not possible to
turn the genera-tor on. In this regard, reactivating switch
82 resets the delay period, so that in order to turn on the
electrosurgical generator, switch 82 must be released or
opened, and left open for the full delay peri~ o~d'er to
reset the inhibit latch circuit 92. Of course, with inhibit
latch 92 reset, the circuit operates as set forth above and
the surgeon can begin cutting again.
In order to alert the surgeon to the fact that the
reset delay period is being timed out, an intermediate stage
of the counter of the reset delay counter circuit 86 is used
to cause an indicator light or lamp (e.g., a LED) 94 to
blink during the inhibit delay period. (Again, indicator
lamp 94 can correspond to indicator lamp 24 of Figure 1.)
Considering this operation in more detail, a negative OR or
NOR gate 94 is provided which has a first input connected to
the output of IGFET switch 9o, a second input connected to
the aforementioned intermediate stage of reset delay counter
86 and the output connected to the LED 94. When the output
of switch 90 is low, meaning that control relay 88 is
actuated and the electrosurgical generator is turned on, LED
94 will also be continuously on to provide an indication to
the surgeon that the generator is on. Further, as set forth
above, when the generator is off but the reset delay period
is being timed out, the intermediate stage of reset delay
counter 86 will provide a pulsed signal to NOR gate 96 which
will cause blinking of LED 94 during this period. As
explained previouslyr when this period is up, as indicated
by the fact that LED 94 is no longer blinking, the surgeon
will know that he can close s~ltch 82 and resume surgery.
Although the cutting element or electrode assembly of
the inner trocar can comprise a single electrode rod 28 as
illustrated in Figure 4, the electrode assembly can also
comprise a bi-polar electrode assembly as indicated at 28'
in Figure 9. More specifically, such a bi-polar electrode
assembly comprises, as illustrated in Figure 9, a pair of
14
~ ~().3
independent, mutually insulated electrodes 28a and 28b
separated by insulation 28c. As shown, electrode 28a is
connected to the electrosurgical generator (not shown) and
carries the r.f. current while electrode 2~b provides a
return path to ground. This is in contrast to the
embodiment of Figure 4, wherein rod electrode 28 carries the
r.f. current and the return to ground path could be
provided, e.g., by a conventional ground pad (not shown)
placed in a remote area of the body. The bi-polar electrode
assembly 28' of Figure 5 is advantageous in that the ground
circuit (provided by ground return electrode 28b) is in
close proximity to the r.f. cutting point and it is not
necessary to provide a ground return through the body and
thus risk the possibility of internal burning. However, it
is noted that such a conventional ground pad (not shown) can
also be provided with the embodiment of Figure 9, as a back-
up .
As discussed above in connection with Figure 8,
electronic trocar of the invention is adapted to shut off
the RF power supplied to the trocar upon penetration of the
trocar tip through the wall of the body cavity in question,
e.g., the abdominal wall, by sensing the change in load
impedance. As was also mentioned previously, this sensing
or detecting of a change in load impedance can be achieved
by monitoring current, voltage cr phase shift. The
associated control circuitry is advantageously incorporated
in the generator itself or in a separate control box or
control unit 68 as explained above, and one problem that is
encountered in doing this is that, at the frequencies
involved, the connecting cable (cable 70 of Figure l)
presents sizeable and varying "lea~age" impedance that makes
2 0 ~
reliable detection of the shut off point diffieult as the
signal to noise ratio of the detected signal deteriorates.
Referring to Figure 10, the "leakage" impedance problem
is solved by the illustrated circuit. Figure 10 illustrates
a system wherein a trocar assembly 100 corresponding to
troear assembly 10 or 10' described above is connected to an
eleetrosurgical unit or generator ~ESU) 102 which ineludes a
eutoff or shutdown eireuit 104 that can, e.g., correspond to
the circuit discussed above in connection with Figure 8. A
cable 106 connects ESU 102 to troear assembly 100 and
ineludes a eonnecting wire or eonductor 108 whieh
eorresponds to the "hot" wire of the embodiments diseussed
above (e.g., eonduetor 60 of Figure 7).
According to this embodiment of the invention, a
reference wire or conductor 110 is also provided in eable
106 in parallel with the wire 108 carrying the RF current to
the trocar 100 but is not connected to the eutting element
112. As a result, the control cireuitry will then sense the
difference between the load eonditions seen by the "hot"
wire or lead 10~ and the referenee wire or lead 110. In the
exemplary embodiment illustrated, a current transformer 114
is used to sense the change in load impedance and the
eurrent earrying wire 108 and reference wire 110 are passed
through the eore (not shown) of the current transformer in
sueh a manner as to oppose each other thereby essentially
neutralizing the leakage current. It is noted that the
reference wire or lead 110 can be a separate wire dedicated
to that purpose or can be a wire used for some other
function such as switching or indication at the trocar end
(and thus corresponding to the wires or conductors discussed
above).
16
2 ~ (3 ~
As mentioned above, otller tech~iques can be used to
counteract the effect of the leakage impedance, inclvding
the use of a sample ~nd hold circuit (not shown) for sensing
the initlal conditions before contact is made or by locating
the critical sensing elements close to the trocar end of the
cable.
Referring to Figure 11, a further embodiment of the
trocar tip is illustrated. This embodiment is similar to
that of Figure 4 and like elements are given the same
reference numerals with double primes attached. This
embodiment differs from that of Figure 4 tand Figure 9) in
that the tip, denoted 116, of the shaft portion 16b" of
central trocar member 16" is made of a high temperature
resistant material such as Teflon, a high temperature
ceramic or the like. Stated differently, shaft 16b" is of a
two part construction including a high temperature tip 116.
This construction enables the trocar tip to better withstand
the high temperatures generated during surgical procedures.
It will, of course, be appreciated that although this
embodiment has been described as a modification of the
embodiment of Figure 4, such a high temperature tip can also
be provided with the bi-polar embodiment of Figure 9.
In an implementation of the electronic trocar shutoff
circuit such as that of Figure 10 wherein a reference lead
is used in the cable to neutralize the effects of leakage,
it is important to ensure that the reference lead is
present, e.g., that, in Figure 10, lead 110 has not been
broken or pulled out from the trocar 100. One way of doing
this is by utilizing a current sensor such as that indicated
schematically at 118 in Figure 10 which monitors the leakage
current flowing in the reference lead 110. This will check
for an open lead. If the lead is shorted to the active wire
h.~;,i,
the shutoff sensor 118 will not sellse any current and will
turn off the electrosurgical generator. A short to the
abovementioned switch lead and/or indicator lead can also
upset the balance of the current sensor 118. Such a short
can be detected by sensing the presence of the generator
output voltage on these leads.
Although the present invention has been des~ribed
relative to specific exemplary embodiments thereof, it will
be understood by those skilled in the art that variations
10 and modifications can be effected in these exemplary
embodiments without departing from the scope and spirit of
the invention.
