SAFETY MONETORING DEVICE AND METHOD FOR ELECTROSURGICAL UNIT
FIELD OF THE INVENTION
[0001] The present invention relates in general to systems and methods for safety
monitoring of electrosurgical units and more particularly to safety monitoring
device and method for control of high frequency leakage current in electrosurgical
units.
BACKGROUND OF THE INVENTION
[0002] Electro surgery has widespread application in the medical field to perform
cutting and coagulating operations. The patient is placed in contact with a patient
electrode or plate connected to the patient terminal of a radio frequency (RF)
source. The active terminal of the RF source is then connected to the active
electrode of an electrosurgical instrument which is commonly utilized as a cutting
or coagulating electrode when brought into patient contact. The RF source applies
a high density current to the active electrode at a relatively high voltage and this
causes a localized cutting or coagulating action. The current, after flowing through
the active electrode, is normally returned through the patient plate to the RF
source.
[0003] If the return path connecting the patient plate to the RF source is broken,
however, or if the patient should move out of contact with a large area of the
patient plate, it has been found that electrical burns can result since there is no
longer a low current density connection for return of the RF energy. Such a burn
could occur, for example, where there is a secondary return contact to the patient
since current can flow through the secondary return contact and thus cause
localized burning of the patient at the point where the secondary return contacts the
patient.
[0004] Such secondary return contacts could exist, for example, where monitoring
electrodes are connected to the patient, where there is grounded adjacent metallic
equipment, or where vertical supports are utilized for supporting ancillary
equipment such as overhead lights. Since such secondary contacts with the patient

are commonly in localized areas, the cunent density at these areas can be high and hence result in electrosurgical burns at these contact points.
[0005] Basically, in Electro surgical units there is an upper limit on the high frequency leakage current which the instrument is not supposed to exceed under any circumstance for the safety of the doctor as well as the patient during surgery. [0006] But practical electro surgical units may have leakage currents more than this limit and in that situation there is a necessity to control and detect the leakage current through software. But while doing so the leakage current might be detected falsely by the software even in normal mode of operation with no physical possibility of leakage current in the hospital and the micro controller may falsely detect it and reduce the power in order to control it below the specified limits. [0007] Traditionally one can make use of the earth return path for monitoring the HF leakage current. Normally HF leakage current arises if the Type CF Applied Part of the ESU is delivering a power to the patient for Electro surgical purposes by the doctor and at the same time the patient who is supposed to be kept isolated from earth comes in contact with any metal part which is connected to earth for example a metal frame of the Operation theatre bed or even a pole of the inigation saline or it can be anything else, even a doctor who is not wearing a sleeper and doing surgery can connect the patient to earth.
[0008] In all the above situations the electro surgical unit will get the current, which is getting earthed, through its mains earth terminal and this can form the basis for leakage current detection by ESU. It is possible to monitor the HF leakage current coming or returning back to the ESU and doing so we can set a threshold limit wherein if the HF leakage current exceeds this limit it will be decided that the leakage current is exceeding the maximum limit.
[0009] But although this seems to be so simple the practical hospital situation is not to be underestimated. In a hospital in normal mode of operation, there will be some current which will be returning to the unit which will be small enough but if it exceeds the preset threshold limit it can lead to false detection of HF leakage current.

[0010] To make the situation more worse if the patient plate cable or any cable is so long enough that it is laid on the ground then in that case for low crest factor waveforms there will be dielectric heating due to which the return electrode current will be coupled capacitively to earth through the outer surface coating of the Neutral electrode cable due to inability to stop dielectric heating. In this scenario the cutoff will happen even in normal mode frequently.
[0011] Hence, there is a need to keep the threshold level much high enough during normal mode and low in leakage mode, without which there will be no solution from controller side. Also the set threshold needs to be properly defined for different modes of operation. Even noise spikes in the earth can affect the detection leading to false detection.
[0012] The present invention is an improvement to the existing product and is implemented in a new product. The invention helps to comply the ESU to international lEC standards.
SUMMARY OF THE INVENTION
[0013] The present invention relates to safety monitoring device and method for control of high frequency leakage current in electrosurgical units. [0014] The safety monitoring device for electro surgical unit according to one embodiment of the present invention comprises one Earth Conductor which carries a leakage current to the electro surgical unit, one leakage current detection circuit, one Isolated Signal Input block to keep the Earth Conductor isolated from the leakage current detection circuit and produce a replica of the leakage current flowing in the Earth conductor u'hich is a high frequency alternating signal, one High Frequency Refiner to refine the high frequency alternating signal and get an equivalent non-alternating signal, wherein the output further comprises an additional alternating ripple signal superimposed on the non-alternating signal, one Desegregator to remove the additional alternating ripple signal from the output of the High Frequency Refiner, a measuring circuit to measure the output of the Desegregator and take corrective action after correlating this value with a stored threshold reference data, a Common Reference Platform to act as a reference for

the measuring circuit to measure the output of the Desegregator, three Fine Tuned Routes to form potential gradient between the Desegregator output and the Common Reference Platform wherein each individual Fine Tuned Route represents a different mode of HF Leakage current, a common HF Leakage Platform to dynamically change the potential gradient when a particular mode is operated, such that each individual Fine Tuned Route will be connected to the common HF Leakage Platform and a corresponding individual Acquisition Base Link instead of connecting directly to the Common Reference Platform.
[0015] There are three Acquisition Base Links corresponding to different modes of HF Leakage current, an acquisition bridge to connect each acquisition base link to the Common Reference Platform, a bridge manager to control the acquisition bridge by sensing the mode of operation and shifting the Acquisition Bridge to the respective Acquisition Base link so as to connect the respective Fine Tuned Route of that mode to the Common Reference Platform and form a potential gradient across it, a mode value analyzer to find the mode of the signal for a predetermined time duration and give the mode value as first input to a correlator, and a correlator bridge comprising at least three correlator links to provide the stored threshold reference data corresponding to a particular mode as second input to the correlator such that if the correlator finds that the output of Mode Value Analyzer is higher than the Stored Threshold Reference Data then it will signal it out as a leakage and corrective action will be taken.
[0016] The safety monitoring method for Electrosurgical Units comprising the steps of producing a replica signal of leakage current flowing to the Electrosurgical Unit such that the signal is a high frequency alternating signal, refining the high frequency alternating signal and getting an equivalent non-alternating signal using a High Frequency Refiner, the output comprises an additional alternating ripple signal superimposed on the non-alternating signal, removing the additional alternating ripple signal from the output of the High Frequency Refiner using a Desegregator, forming a potential gradient between the Desegregator output and a Common Reference Platform, dynamically changing the potential gradient corresponding to the different modes of HF Leakage current, analyzing the mode

value to find the mode of the signal for a predetermined time duration and give the mode value as first input to a correlator and providing stored threshold reference data corresponding to a particular mode as second input to the correlator, wherein if the correlator fmds that the output of Mode Value Analyzer is higher than the Stored Threshold Reference Data then it will signal it out as a leakage and corrective action will be taken.
BRIEF DESCRIPTION OF DRAWINGS
[0017] So that the manner in which the above recited features of the present
invention can be understood in detail, a more particular description of the
invention, briefly summarized above, may be had by reference to various
embodiments, some of which are illustrated in the appended drawings. It is to be
noted, however, that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0018] FIG. 1 shows a schematic diagram of a traditional safety monitoring device
for electro surgical units.
[0019] FIG. 2 shows a schematic diagram of safety monitoring device for electro
surgical unit according to one embodiment of the present invention.
[0020] FIG. 3 shows a schematic diagram of safety monitoring method for electro
surgical unit according to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Referring to the drawings, FIG. 1 shows a schematic diagram of a traditional safety monitoring device 10 for electro surgical units. The Earth Conductor 12 is the component which carries a leakage current to the electro surgical unit 13 to take a corrective action. It needs to be isolated from our leakage current detection circuit which is done by the Isolated Signal Input block 14. The signal received at the output of the Isolated Signal Input block 14 being a replica of the signal flowing in the Earth conductor 12 is a high frequency signal which is alternating in nature.

[0022] The High Frequency (HF) Refiner 16 refines the high frequency signal in such a manner so as to get an equivalent format which is non-alternating with time and thus ideal for further analysis.
[0023] The output of the HF Refiner 16 being in an non-alternating signal format also have an additional alternating ripple signal superimposed on the non-alternating signal extracted from the HF Refiner. The HF Refiner is followed by a Desegregator 18 which removes this alternating signal and converts it to the same format obtained by conversion of the signal input of HF Refiner 16 to its signal output and adds this additional non alternating signal to the useful non alternating signal obtained at the output of the HF Refiner block. This is available at the output of the Desegregator 18.
[0024] The output obtained at the Desegregator is sufficient to detect and predict whether HF leakage current has happened or not and to take corrective action by reducing the power delivered to the patient.
[0025] In practical hospital condition, the circuit described till now wrongly detects leakage in normal condition also although no leakage current is present. The reason for this is not easy to predict because it has to do with the earthing of the hospital, also any transient signal in the earth terminal does matter. Also the long length of the patient plate cable which can be laid down on the ground can capacitively couple the HF signal flowing through it to earth which can return back to the unit through its earth terminal and lead to detection of HF leakage current wrongly although this has not happened through the patient's body. Fluids spilled in the operation theatre floor can add to make the situation still worse. [0026] FIG. 2 shows a schematic diagram of safety monitoring device 100 for electro surgical unit according to one embodiment of the present invention. The device 100 comprises one Earth Conductor 12 which carries a leakage current to the electro surgical unit, one leakage current detection circuit, one Isolated Signal Input block 14 to keep the Earth Conductor 12 isolated from the leakage current detection circuit and produce a replica of the leakage current flowing in the Earth conductor which is a high frequency alternating signal, one High Frequency Refiner 16 to refine the high frequency alternating signal and get an equivalent

non-alternating signal, wherein the output further comprises an additional alternating ripple signal superimposed on the non-alternating signal, one Desegregator 18 to remove the additional alternating ripple signal from the output of the High Frequency Refiner 16, a measuring circuit 19 to measure the output of the Desegregator and take corrective action after correlating this value with a stored threshold reference data, a Common Reference Platform 20 to act as a reference for the measuring circuit to measure the output of the Desegregator, three Fine Tuned Routes 22,23,24 to form potential gradient between the Desegregator output and the Common Reference Platform 20 wherein each individual Fine Tuned Route represents a different mode of HF Leakage current, a common HF Leakage Platform 26 to dynamically change the potential gradient when a particular mode is operated, such that each individual Fine Tuned Route will be connected to the common HF Leakage Platform 20 and a corresponding individual Acquisition Base Link instead of connecting directly to the Common Reference Platform 20.
[0027] There are three Acquisition Base Links 26,27,28 corresponding to different modes of HF Leakage current, an acquisition bridge 30 to connect each acquisition base link to the Common Reference Platform 20, a bridge manager 32 to control the acquisition bridge 30 by sensing the mode of operation and shifting the Acquisition Bridge to the respective Acquisition Base link so as to connect the respective Fine Tuned Route of that mode to the Common Reference Platform and form a potential gradient across it, a mode value analyzer 34 to find the mode of the signal for a predetermined time duration and give the mode value as first input to a correlator 36, and a correlator bridge 38 comprising at least three correlator links 40, 41, 42 to provide the stored threshold reference data corresponding to a particular mode as second input to the correlator 36 such that if the correlator finds that the output of Mode Value Analyzer 34 is higher than the Stored Threshold Reference Data then it will signal it out as a leakage and corrective action will be taken.
[0028] The Acquisition Base Links will be connected to the Common Reference Platform by an Acquisition Bridge which is under control of the Bridge Manager

who will sense the mode of operation and accordingly shift the Acquisition Bridge to the respective Acquisition Base link so as to connect the respective Fine Tuned Route of that mode to the Common Reference Platform and form a potential gradient across it which will give correct expected maximum signal in the leakage mode of operation and negligible unexpected signal in normal mode of operation. [0029] In a preferred embodiment of the present invention the different mode of HF Leakage current comprises cut and soft coagulation, spray and force coagulation and bipolar modes of operation.
[0030] The nature of the HF Leakage current is different for spray and force coagulation compared to cut, soft coagulation and bipolar modes. Hence, in the process of obtaining the signal at the HF Leakage Platform we need to tune the Fine Tuned Routes in such a way that we will get maximum signal when there is a leakage and negligible signal when there is no leakage during normal mode of operation.
[0031] But because of different nature of the HF Leakage current of Cut, Soft Coagulation and Spray, Force Coagulation, tuning of Fine Tuned Routes for one mode can Overtune the Fine Tuned Route for the other mode of operation if at all a single Fine Tuned Route is used, resulting in HF leakage current detection even in normal mode of operation for that mode.
[0032] The nature of waveform of HF leakage current for Cut, Soft Coagulation, Bipolar Modes is similar and also Spray, Force Coagulation both have similar waveform which is entirely different than the other modes available. This suggests for two Fine Tuned Routes differendy allocated for the two different kinds of waveforms.
[0033] Also the HF leakage limit prescribed as per the lEC 60601-2-2 Standard is 150 mA for Monopolar Modes of operation and 1% of the Maximum power setting produce in 200 Ohm resistor. Maximum setting of power in Bipolar modes is 120 watt Therefore, we get the Maximum current limit as 77 mA in Bipolar Modes of operation. Thus, if 77 mA is to be set for Bipolar Mode we need to provide a separate Fine Tuned Route for Bipolar Modes also.

[0034] Thus, now a need is witnessed to have a mechanism which will dynamically change the potential gradient for the Fine Tuned Route based on which particular mode is being operated, so as to detect HF leakage current without making any mode over tuned to detect HF leakage even in normal mode of operation.
Thus, taking this into consideration we need to provide three fine tuned routes as given below.
1) Cut and Soft Coagulation(for controlling HF leakage current below 150mA) (I)
2) Spray and Force Coagulation(for controlling HF leakage current belowl 50mA)
(11)
3) Bipolar Modes of operation(for controlling HF leakage current below 77mA)
(III)
[0035] The Bridge Manager also manages the Correlator Bridge which connects the Stored Threshold Reference Data to the Correlator Base links on Activation of a particular mode which is given as a threshold input to the Correlator. [0036] For different modes (I), (II),(III) the 3 cases described above, the Stored Reference Threshold Data will be different. The Stored Reference Threshold Data for Monopolar Cut & Soft Coagulation is stored in 45, for Spray & Force Coagulation is stored in 46 and that for Bipolar modes is stored in 47. The signal obtained at the HF Leakage Platform consists of noise signal which is Gaussian in nature and which can trigger wrong FIF leakage detection and so a Mode Value Analyzer is employed which finds the mode of the signal for a predetermined 250 mSec time duration and gives the Mode value as the second input to the Correlator. [0037] In a further preferred embodiment of the present invention the Bridge Manager 32 also manages the Correlator Bridge 38 which connects the Stored Threshold Reference Data 44 to the Correlator Base links 40, 41, 42 on activation of a particular mode which is given as a threshold input to the Correlator 36. [0038] In a further preferred embodiment of the present invention the device is capable of being controlled by a micro-processor. The invention includes a hardware and software, which in combination help the ESU to know whether the

mode of operation is normal mode or leakage mode and accordingly takes action on the decision that it has detected leakage current actually or falsely. [0039] FIG. 3 shows a schematic diagram of safety monitoring method 200 for electro surgical unit 13 according to one embodiment of the present invention. The method 200 comprises the steps of producing 202 a replica signal of leakage current flowing to the Electrosurgical Unit 13. The signal is a high frequency alternating signal.
[0040] Step 204 is refining the high frequency alternating signal and getting an equivalent non-alternating signal using a High Frequency Refiner 16, such that the output comprises an additional alternating ripple signal superimposed on the non-alternating signal. In step 206 the additional alternating ripple signal from the output of the High Frequency Refiner is removed by using a Desegregator 18. The signal obtained at the output of the Desegregator has a finite absolute potential, which needs to be given to a measuring circuit which will measure the value of the signal & take corrective action after correlating this value with specific stored constants.
[0041] Step 208 is forming a potential gradient between the Desegregator output and a Common Reference Platform. The measurement done by the measuring circuit will be with respect to the Common Reference Platform. The signal output of the Desegregator is measured with respect to the Common Reference Platform which is assumed to be at zero potential. But, while doing so we need to form a potential gradient in between the Desegregator output and the Common Reference Platform.
[0042] Step 210 is dynamically changing the potential gradient corresponding to the different modes of HF Leakage current. The potential gradient will be dynamically changed corresponding to a pardcular mode is operated. In step 212 the mode value is analyzed to find the mode of the signal for a predetermined time duration and give the mode value as first input to a correlator 36. [0043] Step 214 is providing stored threshold reference data 44 corresponding to a particular mode as second input to the correlator 36 and wherein if the correlator finds that the output of Mode Value Analyzer is higher than the Stored Threshold

Reference Data then it will signal it out as a leakage and corrective action will be
taken.
[0044] In a preferred embodiment of the present invention the different mode of
HF Leakage current comprises cut and soft coagulation, spray and force
coagulation and bipolar modes of operation.
[0045] The invention, as described herein and as illustrated by diagram provide a
safety monitoring device and method for control of high frequency leakage current
in electrosurgical units.
[0046] The forgoing description of the invention has been set for merely to
illustrate the invention and is not intended to be limiting. Since modifications of
the disclosed embodiments incorporating the spirit and substance of the invention
may occur to person skilled in the art, the invention should be constructed to
include everything within the scope of the appended claims and equivalents
thereof.

CLAIMS:
We claim:
I. A safety monitoring device for Electrosurgical Units, comprising:
- at least one Earth Conductor, which carries a leakage current to the electro surgical unit
- at least one leakage current detection circuit;
- at least one Isolated Signal Input block to keep the Earth Conductor
isolated from the leakage current detection circuit and produce a replica of
the leakage current flowing in the Earth conductor which is a high
frequency alternating signal;
- at least one High Frequency Refiner to refine the high frequency
alternating signal and get an equivalent non-alternating signal, wherein the
output further comprises an additional alternating ripple signal
superimposed on the non-alternating signal;
- at least one Desegregator to remove the additional alternating ripple signal from the output of the High Frequency Refiner;
- a measuring circuit to measure the output of the Desegregator and take corrective action after correlating this value with a stored threshold reference data;
- a Common Reference Platform to act as a reference for the measuring circuit to measure the output of the Desegregator;
- at least three Fine Tuned Routes to form potential gradient between the Desegregator output and the Common Reference Platform, wherein each Fine Tuned Route represents a different mode of HF Leakage current;
- a common HF Leakage Platform to dynamically change the potential gradient when a particular mode is operated, wherein the individual Fine Tuned Routes will be connected to the common HF Leakage Platform and a corresponding individual Acquisition Base Link instead of connecting directly to the Common Reference Platform;
- an acquisition bridge to connect each acquisition base link to the
Common Reference Platform;

- a bridge manager to control the acquisition bridge by sensing the mode of operation and shifting the Acquisition Bridge to the respective Acquisition Base link so as to connect the respective Fine Tuned Route of that mode to the Common Reference Platform and form a potential gradient across it;
- a mode value analyzer to find the mode of the signal for a predetermined time duration and give the mode value as first input to a correlator; and
- a correlator bridge comprising at least three correlator links to provide the stored threshold reference data corresponding to a particular mode as second input to the correlator, wherein if the correlator finds that the output of Mode Value Analyzer is higher than the Stored Threshold Reference Data then it will signal it out as a leakage and corrective action will be taken.
2. The device according to claim 1, wherein the different mode of HF Leakage
current comprises cut and soft coagulation, spray and force coagulation and bipolar modes of operation.
3. The device according to any of the preceding claims, wherein the Bridge
Manager also manages the Correlator Bridge which connects the Stored
Threshold Reference Data to the Correlator Base links on Activation of a
particular mode which is given as a threshold input to the Conelator.
4. The device according to any of the preceding claims, wherein the device is
capable of being controlled by a micro-processor.
5. A safety monitoring method for Electrosurgical Units, comprising the steps of:
- producing a replica signal of leakage current flowing to the
Electrosurgical Unit, wherein the signal is a high frequency alternating
signal;
- refining the high frequency alternating signal and getting an equivalent non-alternating signal using a High Frequency Refiner, wherein the output comprises an additional alternating ripple signal superimposed on the non-alternating signal;
- removing the additional alternating ripple signal from the output of the Ffigh Frequency Refiner using a Desegregator;

- forming a potential gradient between the Desegregator output and a
Common Reference Platform;
- dynamically changing the potential gradient corresponding to the different
modes of HF Leakage current;
- analyzing the mode value to find the mode of the signal for a
predetermined time duration and give the mode value as first input to a
correlator; and
- providing stored threshold reference data corresponding to a particular
mode as second input to the correlator, wherein if the correlator finds that
the output of Mode Value Analyzer is higher than the Stored Threshold
Reference Data then it will signal it out as a leakage and corrective action
will be taken.
6. The method according to claim 5, wherein the different mode of HF Leakage current comprises cut and soft coagulation, spray and force coagulation and bipolar modes of operation.