U.S. patent number 3,683,923 [Application Number 05/075,358] was granted by the patent office on 1972-08-15 for electrosurgery safety circuit.
This patent grant is currently assigned to Valleylab, Inc.. Invention is credited to Robert K. Anderson.
United States Patent |
3,683,923 |
Anderson |
August 15, 1972 |
ELECTROSURGERY SAFETY CIRCUIT
Abstract
A safety circuit suitable for use in electrosurgery apparatus to
prevent electrical burns is described herein. A current sensing
transformer having a pair of primary windings and a single
secondary or sense winding is provided. The primary windings are
connected so as to compare the input current applied to an active
electrode with the output current from an indifferent plate. When
the comparison is unequal, the sense winding generates an error
signal that warns the operator of the electrosurgery apparatus of a
possible electrical burn situation. Alternatively, the primary
windings are connected so as to sense the equality of output
currents from two indifferent plates. Lack of equality causes an
error signal to be generated to warn the operator.
Inventors: |
Anderson; Robert K. (Boulder,
CO) |
Assignee: |
Valleylab, Inc. (Boulder,
CO)
|
Family
ID: |
22125176 |
Appl.
No.: |
05/075,358 |
Filed: |
September 25, 1970 |
Current U.S.
Class: |
606/35; 361/45;
607/63; 128/908; 361/87 |
Current CPC
Class: |
A61B
18/16 (20130101); H02H 3/33 (20130101); A61B
18/1233 (20130101); Y10S 128/908 (20130101); A61B
2018/165 (20130101) |
Current International
Class: |
A61B
18/16 (20060101); A61B 18/14 (20060101); H02H
3/33 (20060101); H02H 3/32 (20060101); A61B
18/12 (20060101); A61b 017/36 (); A61n 003/00 ();
H02h 001/02 () |
Field of
Search: |
;128/2.1,303.14,303.17,303.18 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pace; Channing L.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A safety circuit suitable for use in determining the occurrence
of a break in the ground side of an electrical energy source having
an active side and a ground side, the active side of said
electrical energy source being adapted to apply current to an
active electrode and the ground side of said electrical energy
source being adapted to receive return current in equal amounts
from two indifferent electrodes, said safety circuit
comprising:
a current sensing transformer including:
a first primary winding connected between the ground side of said
electrical energy source and one of said indifferent
electrodes;
a second primary winding connected between the ground side of said
electrical source and the other of said indifferent electrodes,
said first and second windings being connected so that current
passing through them generate opposing magnetic fields; and,
a sense winding connected so as to sense when the magnetic fields
generated by said first and second primary windings are unbalanced;
and,
an alarm connected to said sense windings so as to provide an
indication when said sense winding senses that the magnetic fields
generate by said first and second primary windings are
unbalanced.
2. A safety circuit as claimed in claim 1 wherein said alarm
includes a means for preventing the further application of power
from said electrical energy source when said sense winding sense
that the magnetic fields generated by said first and second primary
windings are unbalanced.
3. In an electrosurgical apparatus wherein electrical energy from a
radio frequency source having an active side and a ground side is
applied via an active cable to an active electrode, suitable for
operating on a patient, and returns via at least one indifferent
electrode and a ground cable, a improvement comprising a safety
circuit suitable for sensing a discontinuity in the return portion
of said electrosurgical apparatus, said safety circuit being
connected between said radio frequency source and said
electrodes.
4. The improvement claimed in claim 3 wherein said safety circuit
comprises:
a current sensing transformer having a pair of primary windings
connected so as to be balanced when said electrosurgical apparatus
is operating in a normal manner and connected so as to be
unbalanced when a break occurs in said portion; and,
an alarm connected to said current sensing transformer so as to be
activated when said current sensing transformer is unbalanced
because of said break in said return portion.
5. The improvement claimed in claim 4 wherein said current sensing
transformer has first and second primary windings, said first
primary winding being connected between the active side of said
radio frequency source and said active electrode, said second
primary winding being connected between the ground side of said
radio frequency source and said at least one indifferent electrode,
said first and second primary windings being connected so that
current passing through them generates opposing magnetic fields,
said current sensing transformer further including a sense winding
connected so as to sense when the magnetic fields generated by said
first and second primary windings are unbalanced, said sense
winding being connected to said alarm.
6. The improvement claimed in claim 5 wherein said alarm includes
means for preventing the application of power from said radio
frequency source to said active electrode when said sense winding
senses said unbalanced condition.
7. The improvement claimed in claim 6 wherein said alarm includes
an alarm device and a triggerable solid state device that is
activated to pass current to said alarm device when said sense
winding senses said unbalanced condition.
8. The improvement claimed in claim 4 wherein said electrical
energy returns via two indifferent electrodes and wherein said
transformer includes first and second primary windings, said first
primary winding being connected between one of said indifferent
electrodes and the ground side of said radio frequency source, said
second primary winding being connected between the other of said
indifferent electrodes and the ground side of said radio frequency
source, said first and second primary windings being connected so
that currents passing through them generate opposing magnetic
fields, said current sensing transformer further including a sense
winding connected so as to sense when the magnetic fields generated
by said first and second primary windings are unbalanced, said
sense winding being connected to said alarm.
9. The improvement claimed in claim 8 wherein said alarm includes
means for preventing the application of power from said radio
frequency source to said active electrode when said sense winding
senses said unbalanced condition.
10. The improvement claimed in claim 9 wherein said alarm includes
an alarm device and a triggerable solid state device that is
activated to pass current to said alarm device when said sense
winding senses said unbalanced condition.
Description
BACKGROUND OF THE INVENTION
This invention relates to safety circuits and more particularly to
safety circuits suitable for use with electrosurgical
apparatus.
Electrosurgery has found widespread use in the medical field to
perform cutting and coagulating operations. In general, a patient
is laid on one or more indifferent electrode plates which are
connected to the ground side of a radio frequency (RF) source. The
active, or other side, of the RF source is connected to a cutting
or coagulating electrode. The RF source applies a high density
current to the cutting or coagulating electrode at a relatively
high voltage (in the range of 1,000 volts). The high density
current causes a localized cutting or coagulating action. The
current, after flowing through the operation point is returned via
the indifferent electrode plate or plates to the RF source. The
indifferent electrode plates contact the patient over a relatively
large area so that current density is low at all such contact
points. The low current density prevents the occurrance of
localized electrical burns at point where the indifferent electrode
plates contact the patient.
While electrical surgery apparatus of the foregoing nature has been
generally satisfactory, all such apparatus have one particular
disadvantage. More specifically, on occasion patients have been
electrically burned when they have been operated on by electrical
surgery apparatus. Such burns occur when either:
1. THE GROUND OR RETURN CABLE CONNECTING THE INDIFFERENT ELECTRODE
PLATES TO THE RF source is broken; or,
2. THE PATIENT MOVES OUT OF CONTACT WITH THE INDIFFERENT ELECTRODE
PLATES. When either of these conditions occurs and there is another
or secondary ground contact to the patient, current will flow
through the secondary ground contact and cause localized burning of
the patient at the point where the secondary ground contacts the
patient. Such secondary ground may be created, for example, by:
1. monitoring electrodes connected to the patient;
2. grounded adjacent metallic equipment; and,
3. vertical supports for supporting ancillary equipment, such as
overhead lights. In other words, when the normal ground return is
broken or separated from the patient, the electrical energy flowing
through the surgical electrode seeks other paths if they exist.
Because these other paths usually contact the patient over small
areas, the current densities at these areas may be very high. The
high current densities cause electrosurgical burns at these contact
points.
It will be appreciated by those skilled in the medical profession
that electrosurgical burns can be quite severe. While a patient
will react to them if he is conscious, he is often unconscious when
surgery is being performed. Hence, in most cases electrosurgery
burns go unnoticed until the operation is completed. And, because a
considerable length of time usually elapses during surgery, the
burns are more severe than they would be if the contact time
between the secondary ground and the patient were short.
Therefore, it is an object of this invention to provide a safety
circuit.
It is a further object of this invention to provide a safety
circuit suitable for use with electrosurgery apparatus to prevent
electrical burns.
It is yet another object of this invention to provide a safety
circuit suitable for use with electrosurgery apparatus to prevent
electrical burns at secondary ground points when an indifferent
electrode connection to a patient is broken either because of
inadequate patient contact to the indifferent electrode or because
of a break in the connecting line.
SUMMARY OF THE INVENTION
In accordance with principles of this invention a safety circuit
suitable for use with electrosurgery apparatus to prevent
electrical burns is provided. A current sensing transformer having
a pair of primary windings and a single secondary or sense winding
is mounted between a radio frequency (RF) source and a patient. The
two primary windings are connected so as to sense current flow
through predetermined portions of the electrosurgery apparatus.
When the current flow is balanced, the sense winding generates no
signal. However, when the current flow is unbalanced, the sense
winding generates a signal which can be utilized to operate a
light, an alarm, or a relay that de-energizes the RF source. The
primary windings are connected such that the sense winding only
generates a signal when the patient moves out of contact with the
indifferent electrodes or if the ground line from the different
electrodes to the RF source is broken.
In accordance with further principles of this invention, one of the
primary windings is connected between the active side of the RF
source and the operative surgical electrode (e.g. coagulating or
cutting). The second primary winding is connected between the
ground side of the RF source and the indifferent electrode. The
primary windings are connected such that current flow through them
generates opposing magnetic fields. Hence, when the same amount of
current is flowing through both windings, a balance condition
occurs. When this situation happens, the sense winding generates no
output signal. When a patient moves out of contact with the
indifferent electrode or if the ground line connected to the
indifferent electrode is broken, an unbalanced condition occurs.
When an unbalanced condition occurs, the sense winding generates a
signal. The signal can be used to cause the generation of a
suitable audible or visual alarm. Alternatively, the signal can
operate a relay to de-energize the active electrode.
In accordance with an alternate principle of the invention, the
patient is connected to two indifferent electrodes. Each of the
indifferent electrode is connected through one of the primary
windings of the current sensing transformer, to the ground side of
the RF source. Again, the windings are connected such that current
flow through them causes opposing magnetic fields. Hence, if either
of the electrodes comes out of contact with the patient or if
either of the connecting lines is broken, an unbalanced condition
occurs. The unbalanced condition causes the sense winding to
generate a signal. It will be appreciated that this principle may
be extended to electrosurgical systems that use more than two
indifferent electrodes to contact the patient.
In accordance with still further principles of this invention a
silicon controlled rectifier (SCR) is connected to the sense
winding. The SCR is triggered when the sense winding generates a
signal. An alarm or other indicator is connected in series with the
SCR so that it is energized when the SCR is triggered.
It will be appreciated from the foregoing brief summary of the
invention that a safety circuit suitable for use in a system that
has similar input and output currents, such as electrosurgery
apparatus, is provided. The use of a two primary winding, current
sensing transformer has various advantages over other systems. For
example, inexpensive current sensing transformers can easily handle
voltages in the 1,000 volt range while solid state devices that
will handle such voltages are expensive. Further, the current
sensing transformer isolates the sensing circuitry from the radio
frequency source to maintain 60Hz ground protection which is not
done by directly connected sensing circuits. In addition, to these
advantages, the invention has the additional advantage of being
relatively uncomplicated and, therefore, inexpensive to manufacture
and maintain. Moreover, the invention can be easily inserted into
presently used electrosurgical apparatus without requiring
extensive modifications of the apparatus.
It should be noted that while the preferred use of the invention is
with electrosurgical apparatus, it can be also used in other
systems. For example, the invention can be utilized to sense a
break in the ground line of an arc welding apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing objects and many of the attendant advantages of this
invention will become more readily appreciated as the same become
better understood from the following detailed description when
taken in conjunction with the accompanying drawings wherein:
FIG. 1 is a partially pictorial, partially schematic diagram
illustrating the dangers involved in the use of present
electrosurgical apparatus;
FIG. 2 is a partially schematic, partially pictorial diagram
illustrating one embodiment of the invention;
FIG. 3 is a schematic diagram illustrating an alternate embodiment
of the invention; and,
FIG. 4 is a schematic diagram of an embodiment of the invention
that includes an alarm system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates the coupling between an RF source and the
patient of a common prior art system. More specifically, FIG. 1
illustrates the secondary winding 21 of the output transformer of
an RF source (not shown). FIG. 1 also illustrates a patient 23
lying on a single indifferent electrode 25. The indifferent
electrode 25 is connected via a ground cable 27 to the ground side
of the secondary winding 21. The active or other side of the
secondary winding 21 is connected via an active cable 29 to a
surgical electrode 31. The surgical electrode 31 can be either a
cutting electrode or a coagulating electrode. FIG. 1 further
illustrates a secondary ground 33 shown as a wire 35 connected
through a resistance 37 to ground 39. The secondary ground 33 is
illustrated as contacting the patient 23 at a point 41. Also
illustrated in FIG. 1 is a break 43 in the ground cable 27.
As will be well understood by those skilled in the medical art, the
patient 23 residing on the indifferent electrode 25 may be operated
on by the surgical electrode 31 in many different manners. During
such operation, current I.sub.1 flows from the secondary winding 21
along the active cable 29 to the surgical probe 31. The dense
electrical current at the tip of the surgical probe 31 causes
localized cutting or coagulation of the patient's tissue. Current
flows from the surgical probe through the patient 33 to the
indifferent electrode 25. The current I.sub.2 at the indifferent
electrode returns through the ground cable 27 to the ground side of
the secondary winding 21. While a slight current flows through the
secondary ground 33, this current is very small because the major
area of ground contact is through the indifferent electrode 25. In
other words, I.sub.1 = I.sub.2 for all practical purposes.
When a break 43 occurs in the ground cable 27, current flow through
the ground cable 27 stops. However, because a secondary ground 33
exists in this example, a return path remains. This return path or
secondary ground now carries the entire return current flow to the
ground side of the secondary winding 21 of the RF source. Because
only a small area of the secondary ground 33 contacts the patient
23, a high density current passes through this small area and a
localized burn occurs at the contact point 41. It will be
appreciated that a similar situation will occur if the patient
moves off of the indifferent electrode 25 while remaining in
contact with the secondary ground 33.
It will be appreciated by those skilled in the art and others that
because most patients are under an anesthesia when they are being
operated on they are not able to communicate the fact that they are
being burned to the operator of the electrosurgery apparatus.
Further, because patients are usually almost totally covered during
an operation, such a burn is not readily self evident. Because of
these two factors in particular, electrical burns caused by
electrosurgery apparatus can be quite severe. That is, these two
factors allow the electrical burning situation to exist for a long
period of time. And, the length of burning time determines the
severity of the burn. It is elimination of such burns that is the
primary object of this invention.
FIG. 2 illustrates one embodiment of the invention which comprises
a transformer 51 having first and second primary windings 53 and 55
and a secondary or sense winding 57 all wound about a toroidal core
61. The active side of the secondary winding 21 of the output
transformer of the RF source is connected through the first primary
winding 53 to the surgical electrode 31. The ground side of the
secondary winding 21 is connected through the second primary
winding 55 to the indifferent electrode 25. As before, a patient 23
is illustrated as lying on the indifferent electrode 25 and a
secondary ground 33 is illustrated as connected between a point 41
on the patient and ground 39 via a connecting means 35 and a
resistor 37. The sense winding 57 is connected to a pair of output
terminals 59, 59.
Under normal conditions, the surgical electrode 31 applies the
radio frequency signal to the patient in the manner previously
described and the signal returns via the indifferent electrode 25.
Hence, as long as the system is operating correctly, the
transformer has no effect. However, if the patient moves off of the
indifferent electrode 25 or if a break occurs in the ground cable
27, the transformer becomes operative and the sense winding
generates a signal at the output terminals 59. More specifically,
the first and second primary windings 53 and 55 are wound around
the toroidal core 61 of the transformer 51 and connected in such a
manner that the magnetic fields generated by currents I.sub.1 and
I.sub.2 flowing through these windings are magnetically in
opposition. Hence, as long as the input current I.sub.1 is equal to
the output current I.sub.2, the sense winding 57 senses an
essentially zero magnetic field. However, if a break occurs or if
the patient moves off of the indifferent electrode 25, I.sub.2
reduces to zero. Under these conditions, I.sub.1 causes a current
to flow in the sense winding 57 whereby a voltage is created at the
output terminals 59, 59. The thusly created voltage can be utilized
to operate a visable alarm, an audiable alarm, or a relay which
will open circuit the output from the RF source. Or, two or all
three of these devices can be operated if desired.
FIG. 3 illustrates an alternative embodiment of the invention which
comprises a transformer 71 having first and second primary windings
73 and 75 and a single secondary or sense winding 77. In this case,
rather than the patient contacting a single indifferent electrode,
the patient (not shown) contacts two indifferent electrodes 79 and
81. The ground side of the output transformer (not shown) of the RF
source is connected to a ground terminal 83. The ground terminal 83
is connected to one side of each of the primary windings 73 and 75.
The other side of the first primary winding 73 is connected to the
first indifferent electrode 79 and the other side of the second
primary winding 75 is connected to second indifferent electrode 81.
The sense winding 77 is connected to sense output terminals 85, 85.
As illustrated in FIG. 3, the first and second primary windings 73
and 75 are wound and connected in series opposition. Consequently,
if the patient is equally contacting both of the indifferent
electrodes 79 and 81, as would occur under normal circumstances,
the return current I.sub.2 is split and half passes through each
primary winding. In other words, I.sub.2 /2 passes through each of
the primary windings 73 and 75. Because these currents flow in
opposite directions, the magnetic fields generated by the first and
second primary windings 73 and 75 are in opposition whereby they
tend to cancel one another. Hence, as long as one-half of I.sub.2
is passing through each of the primary windings, the secondary or
sense winding generates no output voltage. However, if one of the
return cables is broken or if the patient moves off of one of the
indifferent electrodes, the balance or current canceling condition
is broken. When either of these circumstances occurs, the sense
winding 77 generates a voltage across the sense terminals 85, 85
caused by the current flow through the other primary winding. This
voltage can be used in the manner previously described to cause an
alarm or operate a relay.
It will be appreciated from the foregoing description that the
invention provides a relatively uncomplicated apparatus for sensing
when the current flow applied to a surgical electrode is equal to
the current return from an indifferent electrode. As long as the
currents are relatively close to one another in magnitude, the
electrosurgical system operates in a conventional manner. However,
if the return line is broken or if the patient moves off of one or
more indifferent electrodes, a signal is generated that warns the
doctor or operator of the system that the patient is probably being
burned because there is a return through some other (secondary)
ground line. Hence, the doctor can stop the operation or the
operation can be automatically stopped through the operation of a
relay to prevent further burning of the patient. After the burn
situation is corrected, the operation can continue.
While various types of alarm systems can be connected to the sense
winding terminals, a preferred form of an uncomplicated alarm
system is illustrated in FIG. 4 and hereinafter described. For
purposes of illustration, FIG. 4 illustrates a current sensing
system of the type illustrated in FIG. 3. However, it will be
appreciated by those skilled in the art and others that the alarm
system can also be used with a current sensing system of the type
illustrated in FIG. 2. More specifically, FIG. 4 illustrates a
transformer 91 having first and second primary windings 93 and 95.
One end of the primary winding 93 is connected to a first
indifferent electrode 99 and one end of the second primary windings
95 is connected to a second indifferent electrode 101. In addition,
a ground terminal 103 is illustrated. The ground terminal 103 is
connected to the ground side of the output transformer (not shown)
of the RF source.
Rather than the ground terminal being directly directed to the
other sides of the first and second primary windings 93 and 95, it
is connected to those sides through a double pole, double throw
switch designated S. More specifically, the double pole, double
throw switch S is illustrated in FIG. 4 as having a pair of upper
terminals 105 and 107 and a pair of lower terminals 109 and 111
plus an upper common terminal 113 and a lower common terminal 115.
The upper common terminal 113 is connected to the other side on the
first primary winding 93 and the lower common terminal 115 is
connected to the other side of the second primary winding 95. The
ground terminal 103 is connected to the upper terminals 105 and 109
of both the upper and the lower pairs of terminals so that both the
first and the second primary windings are connected to the ground
terminal 103 when S is in its upper position.
One side of the sense winding 97 is connected to ground. The other
side of the sense winding 97 is connected to the anode of a diode
designated D. The cathode of D is connected to: a capacitor
designated C; a first resistor designated R1; and the cathod of a
zener diode designated ZD. The other terminals of R1 and C are
connected together and to ground. The other terminal of ZD is
connected to the lower terminal 111 of the lower pair of terminals
of S and through a second resistor designated R2 to ground. The
other terminal of ZD is also connected to the gate of a silicon
controlled rectifier designated SCR. The lower terminal 107 of the
upper pair of terminals of S is connected through a voltage source
designated V, a normally closed push button switch designated PS
and an alarm designated A, all connected in series, to the anode of
SCR. The cathode of SCR is connected to ground as is the other side
of V.
In normal operation, S is in the upper position illustrated in FIG.
4 and the system operates in a conventional manner. When a break
occurs or a patient moves off of one of the indifferent electrodes
99 or 101, the signal across the sense winding 97 is applied
through D to ZD. If the voltage level of this signal is
sufficiently high, ZD breaks down and SCR is gated on. When this
occurs, current flows from V through the push button switch to the
alarm A causing a audiable or visual signal to be generated
depending upon the nature of the alarm. That is, if desired, the
alarm A can be an audible alarm, a visual alarm or a combined
alarm. Moreover, the alarm can include a relay that, when
energized, prevents the application of further RF power to the
surgical electrode. Once SCR is gated on, the alarm continues to
operate until PS is opened. When this occurs, the alarm ceases to
operate because the cathode-anode terminals of SCR are open
circuited.
When S is in its lower position and the indifferent electrodes are
joined together via a patient represented by R3, the alarm circuit
illustrated in FIG. 4 can be tested. More specifically, when this
is done, a voltage flows from V through the first primary winding
93, the indifferent electrodes 99 and 101, the second primary
winding 95 and R2 to ground. This current flow causes a current in
the sense winding 97 which causes the application of a voltage to
the gate of SCR. This voltage gates SCR on whereby the alarm A is
energized if the alarm circuit is operating satisfactorily. Hence,
with S in its lower position, the integrity of all indifferent
electrode wires plus patient contact to the indifferent electrodes
is proven.
It should be noted that the arrangement illustrated in FIGS. 3 and
4 is intended to insure adequate patient contact (at a plurality of
points) to the indifferent electrodes whereas the FIG. 2
arrangement is intended to insure that all of the input current
comes out of the indifferent plate.
It will be appreciated from the foregoing description that the
invention provides a system for sensing when an electrosurgical
system is not operating in the desired manner. If the system is not
so operating, an alarm indicating that such undesirable operation
is occurring is provided. Such undesirable operation occurs when
the ground return line is broken or when the patient moves off of
the indifferent electrode. This mode of operation is undesirable
because a secondary ground may be connected to the patient. If so,
and the contact area of the secondary ground is small, a burn will
occur at the contact point. It is this type of harmful operation
that the invention is designed to prevent.
While the invention has been described in an electrosurgical
environment, it can be utilized in other environments. That is, it
can be utilized in other environments, such as welding, for
example, to detect when the input current is not equal to the
output current. Further, while one form of an alarm system has been
illustrated and described, various other types of alarm systems can
be utilized with the invention to carry out its basic objectives.
Moreover, while toroidal core transformers have been illustrated,
other types of current sensing transformers can be utilized by the
invention. Hence, this invention can be practiced otherwise than as
specifically described herein.
* * * * *