Multiple element flat electrode useful for HF-surgery

A multi-element electrode comprises at least two flat partial electrodes which are arranged in juxtaposition to a pre-established direction. To simplify the fabrication of such an electrode and in particular to allow the use of cable conductors of equal length for attachment thereto, provision is made for the two partial electrodes to exhibit facing edges which are at an angle to the pre-established direction. Such a construction is advantageous in the case of a three-part electrode. The electrode is preferably the neutral electrode of an HF-surgical apparatus.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an electrode having at least two partial electrode 
elements, in particular a neutral electrode for HF-surgery (i.e., 
High-Freguency electrosurgery), in which the partial electrodes are 
arranged in juxtaposition in a pre-established direction. 
2. Description of the Prior Art 
A neutral electrode of the above-mentioned type operates with two flat 
electrodes, as described in German Registered Design Patent GM No. 82 05 
363, In this neutral electrode the electrical contact with the patient is 
monitored by means of a control circuit through which a low frequency 
control current flows. This control current flows from the contact surface 
of one partial electrode, through the skin of the patient, to the contact 
surface of the other partial electrode. 
Another two element neutral electrode is described in German Patent 
Publication DE-OS No. 28 49 422. 
Single element neutral electrodes are also employed in the present state of 
the art. HF-surgical apparatuses are frequently equipped with a monitoring 
circuit through which a check may be made to determine whether the single 
element electrode is in fact present in the circuit, i.e. is connected. 
For this purpose, a first and a second connecting lead is attached to the 
surface of the single element electrode. A control current is sent from 
the first connecting lead through the neutral electrode and the second 
connecting lead. If this control current exceeds a pre-established 
threshold, assurance is gained that the single element electrode is in 
fact present and does not have a defective electrical connection and/or 
has not become disconnected. The construction of the neutral electrode 
proposed herein is, in particular, to be capable of working in combination 
with a monitoring circuit of this type. 
lt has been demonstrated that a multi-element construction of the neutral 
electrode is also desirable, when an indication is to be provided by a 
monitoring circuit of whether such a neutral electrode makes large surface 
area contact or just a spot contact with the patient during the surgical 
procedure. Such a monitoring circuit is described in U.S. patent 
application Ser. No. 929,561, filed Nov. 10, 1986 and titled "Method and 
Apparatus for Monitoring the Surface Contact of a Neutral Electrode of an 
HF-Surgical Apparatus". 
In the construction of a neutral electrode, every effort must be made to 
design it in such a way that good surface contact with the patient is 
assured. In the case of two element electrodes (i.e., two partial 
electrodes), this has previously resulted in a rectangular shape. If the 
two partial electrodes are arranged in juxtaposition in a pre-established 
direction, and if the connecting cable conductor is led to the electrode 
in this pre-established direction, a condition results where the conductor 
or lead for one of the partial electrodes must be longer than that for the 
other of the partial electrodes. This requires particular care in the 
fabrication of the neutral electrode in order that no interchange of the 
conducting leads can occur. Moreover, conductors of different length must 
be kept on hand. 
An object of the present invention is to construct a multi-element 
electrode that will allow for simpler fabrication. In particular, 
assurance is to be provided that conductors of equal length may be 
connected to the partial electrodes. 
SUMMARY OF THE INVENTION 
The object is achieved according to the invention in that two partial 
electrodes exhibit edges facing one another at an angle to a 
pre-established direction. 
With this construction it is possible to connect conductors of equal length 
to both of the partial electrodes. The fabrication is thereby simplified 
as well as the guidance of the conductors. 
This construction results in particular advantage when a three element 
electrode is used. In such a construction three partial electrodes are 
provided. Two of the partial electrodes have an essentially trapezoidal 
shape and one is essentially rectangular. The three partial electrodes are 
arranged in juxtaposition in a pre-established direction and thereby form 
an essentially rectangular bearing surface having two short parallel 
sides, and two long parallel sides. An electrical termination is provided 
on that short side which is adjacent to the rectangular partial electrode. 
The two partial electrodes having the facing angular edges (i.e., those of 
trapezoidal shape) may to advantage have equa1 surface areas and be of 
identical shape. This simplifies their fabrication, as well as 
stock-keeping. 
It has been found, in the case of rectangular shaped single-element 
electrodes, that the four corners do not, as a rule, make especially good 
contact with the patient. This also applies to the outer four corners of a 
multi-element electrode. In order to assure an adequate contact surface in 
such cases, provision is made in the three element construction for the 
two outer partial electrodes to have somewhat larger surface areas than 
the surface area of the middle partial electrode. In particular they 
should be approximately 10% to 20% larger in order to achieve comparable 
results during measurement. 
These and other features and advantages of the invention will be apparent 
from the following description of the preferred embodiments, and from the 
claims. 
For a fuller understanding of the present invention, reference should now 
be made to the following description of preferred embodiments of the 
invention and to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
As shown in FIGS. 1 and 2, a neutral electrode 2 for HF-surgical apparatus 
comprises three flat surface partial electrodes 4, 6 and 8 of which two 
respective electrodes 4, 6 and 6,8 are separated from each other by an 
insulated strip having low electrical conductivity. The three partial 
electrodes 4, 6, 8 are arranged in juxtaposition e.g., lined up or located 
adjacent each other, in a pre-established direction x. They comprise a 
metal foil or a metal grid and are attached to a flexible base 10. Base 
10, which is preferably made to be self-bonding or self-adhesive, is 
essentially rectangular in shape, longer in the x-direction than in the 
y-direction, and its edges extend past the edges of the three partial 
electrodes 4, 6 and 8. Base 10 has two sides 10a which are shorter than 
and perpendicular to two sides 10b, which sides 10b lie parallel to the 
x-direction. 
Partial electrodes 4 and 6 are essentially of trapezoidal shape and partial 
electrode 8 is essentially of rectangular shape. It is to be noted that 
the length of the side of electrode 8 which is parallel to the x-direction 
is somewhat shorter than the length of the side parallel to the 
y-direction. It is to be further noted that partial electrodes 4 and 6 
exhibit facing edges 14 and 16 respectively, extending at an angle 
(90.degree.-.alpha.) with alpha not equal to 0.degree., 90.degree. to the 
pre-established x-direction. The edges 14 and 16 run parallel to each 
other and form one of the insulated strips. It should be noted that in the 
interest of clarity and contrary to the scale shown in FIG. 1, edges 14 
and 16 of two partial electrodes 4 and 6 are at an angle (alpha) of only a 
few degrees with respect to the perpendicular of the pre-established 
x-direction (i.e. the y-direction). This angle alpha may in particular be 
less than 10 degrees. It is also to be stressed that the insulated strips 
between the partial electrodes are actually substantially narrower than 
are illustrated, in the interest of clarity. 
As shown in FIGS. 1 and 2, the juxtaposed arrangement of partial electrodes 
4, 6, 8 results in an essentially rectangular conductive contacting 
surface assembly with two short and two long parallel sides, lying 
parallel to sides 10a and 10b, respectively. Thus, the two long sides run 
parallel to the pre-established x-direction. 
Base 10 is provided with a small end-piece or electrical terminal 20 on the 
side of rectangular base 10 which lies adjacent to partial electrode 8. 
Electrical terminal 20 contains three connecting leads 24, 26 and 28 for 
partial electrodes 4, 6, and 8 respectively. Terminal 20 is located 
approximately in the middle of short side 10a. As shown, conductors 24 and 
26 each run adjacent to one of the long sides 10b of base 10 and are 
connected adjacent said long sides 10b to the two trapezoidal partial 
electrodes 4 and 6, respectively. The points of connection are aligned 
with the y-axis. It is therefore possible to make connecting leads 24 and 
26 of equal length, which simplifies the fabrication and lowers the cost 
of stock-keeping. Connecting lead 28 is shorter than connecting leads 24 
and 26 and is in electrical contact with the outer edge of partial 
electrode 8 at its intersection with the x-axis. 
As shown in FIGS. 1 and 2, it is possible to arrange partial electrodes 4 
and 6 to have angular edges 14 and 16 in order to have equal surface 
areas. This has the advantage that identical partial electrode elements 
may be used during fabrication so that faulty construction due to changing 
one for the other is impossible. In contrast, it is also possible to 
arrange for at least one of the outer electrodes 4 or 8 to be formed with 
a larger surface area than middle electrode 6. In particular, the outer 
partial electrode 4 or 8 can be some 10% to 20% larger than middle partial 
electrode 6. Such a construction has the advantage that the contact 
surface of those partial electrodes that form the four corner points of 
the essentially rectangular surface are enlarged, so that a separation 
from the patient at these corner points--occasionally unavoidable--does 
not lead to undesirable consequences. 
It has already been pointed out that partial electrodes 4, 6 and 8 may be 
composed of a net or grid of good electrically conducting material. These 
nets are applied to a base 10 that is made of a rubberized layer. For 
monitoring electrode 2 for good surface contact, it is advantageous to 
make this rubberized layer of an electrically conducting rubber. Base 10, 
electrodes 4, 6 and 8 and terminal 20 are suitably overlaid with a 
covering 30 that may be cemented on. 
Terminal 20 may suitably comprise three adjacent contacts (not shown) to 
which a clamp of the alligator type may be connected. This means 
facilitates a rapid attachment of the side of electrode 2 having covering 
30 to the patient and rapid contact positioning is possible. 
FIG. 3 illustrates a portion of a monitoring circuit which generates a test 
current Ip. By means of test current Ip, the contact of the neutral 
electrode 2 to the patient 32, or where necessary, the separation of the 
electrode 2, may be ascertained. For example, a separate HF-generator 34 
in the HF-surgical apparatus may be employed for this purpose. As an 
alternative, the operating current of the HF-surgical apparatus may also 
be employed. 
Here, as illustrated, HF-generator 34 is employed to provide the operating 
current. Generator 34 has a terminal 36 for connection to an active 
electrode 38 and an additional terminal 40 for connection to neutral 
electrode 2. Neutral electrode 2 is attached to patient 32 in a suitable 
manner during the surgical procedure, e.g., to the upper thigh. The 
surgeon controls active electrode 38 during the surgical procedure and 
undertakes specific incisions and coagulations. 
Sufficiency of connection contact of neutral electrode 2 may also be 
monitored with a low frequency test current or, as shown here, with 
branching d.c test currents Ig.sub.1 and Ig.sub.3. Test currents Ig.sub.1 
and Ig.sub.3 are obtained from the output of a 1ow frequency transformer 
42 which currents are rectified via rectifier 44 and directed to partial 
electrodes 4 and 8 of neutral electrode 2 via relays 46 and 48, HF chokes 
50 and 52, through resistances 56 and 58 to middle electrode 6 and finally 
returned through a HF-choke 54 back to rectifier 44. Resistances 56 and 58 
are formed by the effect of the strip of conductive rubberized layer 10 
which separates the partial electrodes from each other. In an adequate 
contact of neutral electrode 2, relays 46 and 48 are energized. When 
neutral electrode 2 is detached, relays 46 and 48 activate an alarm system 
in the normal manner and/or actuate a safety means. 
Connecting leads 26 and 28 are connected to terminal 40 via capacitors 61 
and 63. Connecting lead 24 is directly connected to terminal 40. Current 
measuring devices 74, 76 and 78 are arranged in connecting leads 24, 26, 
28, respectively. These are preferably of identical construction. They are 
in the form of current transformers in the present invention and serve as 
a means of measuring the three partial currents I1, I2, I3. The evaluation 
of these three partial currents I1, I2, I3 can follow, in the manner more 
fully described in the previously noted U.S. patent application Ser. No. 
929,561. 
Thus, there has been shown and described novel apparatus for a neutral 
electrode which fulfills all the objects and advantages sought therefore. 
Many changes, modifications, variations and other uses and applications of 
the subject invention will, however, become apparent to those skilled in 
the art after considering this specification and the accompanying drawings 
which disclose a preferred embodiment thereof. For example, the presently 
described principle of the partial electrodes 4 and 6 with edges 14 and 16 
at an angle to the y-direction is applicable to standard electrodes, which 
as a rule are re-usable, as well as to electrodes that are designed to be 
disposable items. 
All such changes, modifications, variations and other uses and applications 
which do not depart from the spirit and scope of the invention are deemed 
to be covered by the invention which is limited only by the claims which 
follow.