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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electrode consisting of at least three
elements, and in particular to a neutral electrode for a High Frequency
(HF) surgical instrument in which the electrode elements are arranged on a
common flexible carrier.
2. Description of the Prior Art
A neutral electrode of the above mentioned kind which includes three planar
electrode elements is known, for example, from U.S. patent application
Ser. No. 929,561 filed Nov. 10, 1986 (corresponding with the present
Assignee's German Patent Publication DE-OS No. 35 44 443), now U.S. Pat.
No. 4,754,757.
In connection with HF surgical instruments it has been found that a
multiple element design for the neutral electrode is desirable if the
intent is to ascertain with a monitor circuit whether, during the HF
surgical procedure, the neutral electrode is in contact with the patient
over a large area and not only in some points. Such a monitor circuit for
a three-element neutral electrode is shown in FIG. 4 of the
above-mentioned DE-OS No. 35 44 443 and described in greater detail in the
related text.
If a multi-element planar electrode having rectangular electrode elements
is used and if this planar electrode is applied on the thigh of a patient,
two application directions, in principle, are possible. In one application
direction the three electrode elements are aligned in the direction of the
longitudinal axis of the thigh. This case should be called one of improper
application, for the high frequency going out from the surgical field, for
example in the abdominal area, will reach the three electrode elements
with different intensities. With respect to monitoring the proper contact
of the neutral electrode with the patient, this can lead to erroneous
measurements. In the other case, the three electrode elements are applied
transversely to the longitudinal direction of the thigh. This case can be
referred to as one of proper application, because in this case, the three
electrode elements are reached by the high frequency going out from the
surgical field approximately with the same intensity, given identical
surface areas.
In hospitals, the application of the neutral electrode is frequently
carried out by auxiliary personnel. In order to avoid the possibility of
committing an error and, hence, loss of time in preparing a patient for
the surgical procedure, a possible solution should be sought as to how the
individual electrode elements, independently of the orientation of the
neutral electrode with respect to the longitudinal axis of, for example,
the thigh, can be impressed with the same HF intensity (power). As a first
approximation it should be assumed that all of the electrode elements have
the same surface area.
An object of the invention, therefore, is to develop an electrode of at
least three elements so that a substantially uniform distribution of the
high frequency energy going out from the surgical field onto the electrode
elements is achieved. In this connection it is basically irrelevant in
which orientation with respect to its normal the neutral electrode is
applied on the patient.
SUMMARY OF THE INVENTION
This problem is solved by the invention wherein the neutral electrode
elements are arranged symmetrically with respect to an axis of symmetry
which is perpendicular on the electrode carrier and, with respect to the
axis of symmetry, displaced in a circumferential direction.
In order to achieve easy application, each electrode element should have at
least partially curved edges. The electrode elements can be,in particular,
round, but can also be sector-shaped.
In the general case one will proceed with the electrode elements being of
identical surface area. In special cases it may, however, be best to build
one or the other electrode elements of a different size. This will depend
on the geometric configuration.
Other features and advantages of the invention will be apparent from the
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 detailed description of the preferred embodiments
of the invention and to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an improper application of a neutral electrode on a
patient according to the state of the art;
FIG. 2 illustrates a first embodiment of an electrode according to the
invention with three symmetrically distributed circular electrode elements
shown in perspective; and
FIG. 3 illustrates a second embodiment of a neutral electrode according to
the invention with three sector-shaped electrode elements shown in
perspective.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to FIG. 1 an HF instrument 2 comprises a connection 4 for an
active electrode 6 and a further connection 8 for a neutral electrode 10,
which is shown fastened to the thigh of a patient P. The neutral electrode
10 is, in the present case, subdivided into three electrode elements 12,
14, and 16. During the operation the surgeon guides active electrode 6 and
carries out directed coagulations or sections upon patient P.
A circuit arrangement 18 is associated with HF surgical instrument 2 for
monitoring neutral electrode 10. Circuit arrangement 18 is a safety
circuit, which permits determination of whether neutral electrode 10 is in
contact with the patient P over a sufficiently large area so as to allow
proper operation of the HF surgical apparatus. If this is not the case, it
transmits a warning signal at an output 20. Safety circuit 18 can be built
according to the techniques shown in the forenoted United States Patent
Application, incorporated herein by reference.
In FIG. 1 it is assumed that electrode elements 12, 14 and 16 have
rectangular cross sections and are arranged on a carrier 11 in the
longitudinal direction of the patients thigh. In this case, upon turn-on
HF surgical instrument 2, no uniform distribution of the HF energy onto
three electrode elements 12, 14 and 16 can be expected. As a consequence
of this unsymmetrical flow through electrode elements 12, 14 and 16 of the
HF energy, reliable monitoring of the proper contact of neutral electrode
10 is potentially not possible.
In order to resolve this difficulty, and in accordance with the invention,
a three-element electrode 10 is designed in which the three electrode
elements 12a, 14a and 16a, (FIG. 2) and 12b, 14b and 16b (FIG. 3) are
arranged symmetrically with respect to a rotational axis of symmetry (A)
which extends perpendicular from the carrier 11 and, with respect to each
other, the electrode elements are rotationally displaced.
According to FIG. 2, three identical electrode elements 12a, 14a and 16a,
which are fastened on a carrier 11 of flexible electrically insulating
material, are of essentially circular shape. Each element includes a metal
foil or metal netting. Carrier 11, which preferentially is self-adhesive
and/or consists of a rubber, is likewise essentially circular. The
external connecting wires of the three electrode elements 12a, 14a and 16a
form essentially a triangular contact surface for the patient P. The
electrode elements 12a, 14a and 16a are, thus, each displaced by
120.degree. with respect to the axis of symmetry (A) in the
circumferential direction with respect to each other. The axis (A) is
central in and perpendicular to carrier 11.
At the right part of round carrier 11 a small support or link 21 for a wire
connection is provided. This wire connection accepts three connecting
wires 22, 24 and 26 for electrode elements 12, 14 and 16, respectively. As
is evident, three wires 22, 24 and 26 are closely adjacent in the link and
parallel to each other. It becomes thereby possible to permit a clamp to
fasten around the link so as to establish a connection of three wires 22,
24 and 26 to safety circuit 18. In addition is noted that the two outer
connecting wires 22 and 26 are of equal length, which simplifies their
production and keeps the cost of storage down. Due to the equally long and
symmetrical structure, identical parasitic capacitances are obtained and
largely independent production tolerances result therefrom.
It should be pointed out that electrode elements 12a, 14a, and 16a in FIG.
2 are built with equal surface areas.
If the neutral electrode 10 illustreated in FIG. 2 is applied on the thigh
of patient P (cf. FIG. 1), then it is largely irrelevant which positioning
with respect to a rotation around the axis of symmetry (A) this takes
place. In all positionings a largely uniform distribution of the HF energy
onto the electrode elements 12a, 14a and 16 is achieved. The difference is
maximally given by an angle of 60.degree.. If more electrode elements are
present, for example four instead of three, the differential angle becomes
even smaller, for example 45.degree..
In the embodiment of three-element electrode 10 according to FIG 3, a total
of three sector-shaped electrode elements 12b, 14b, and 16b are arranged
on the electrically insulating carrier 11. The three electrode elements
12b, 14b and 16b consist here of three circle-shaped sectors of equal
size, with each sector having an angle of 120.degree.. Hence, each
electrode element has one curved and two straight edges. Here too, a
rotationally symmetrical arrangement with respect to the axis of symmetry
(A) which is perpendicular to the carrier 11, is provided. The angle of
the rotational displacement here, too, is again 120.degree.. This
electrode 10 is also preferably self-adhesive.
With respect to the application of electrode 10 to the patient P, the same
advantages are obtained here as were obtained with the electrode 10 of
FIG. 2.
Thus, there has been shown and described novel multi-element neutral
electrodes which fulfill 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 preferred embodiments thereof. For example, the rotational
symmetry in the FIG. 2 and FIG. 3 embodiments were achieved by the
electrode elements having at least partially uniformly curved
circumferential lines. Further geometric forms of a multi-element
electrode 10 with equally-sized or physiologically determined
differently-sized electrode element surface areas 12, 14 and 16 are
conceivable. The electrode 10 could also consist of four, five or six etc.
elements, so that the angle of the rotational displacement of the discrete
electrode elements in those cases, would be 90.degree., 72.degree. or
60.degree., respectively, etc. 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.
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