Abstract:
The present disclosure provides an electrosurgical return pad current detection system for use in monopolar surgery as well as a method of using the same. The detection system comprises a plurality of conductive pads which include a plurality of conductive elements. The detection system further includes a sensor which senses the current returning to each conductive pad as well as a comparator which determines the difference in current among a plurality of conductive pads. If the current differential is above or below a prescribed limit, the system will alert the user of potential hazards and/or alter the amount of energy delivered to a surgical device.

Description:
BACKGROUND 
   1. Technical Field 
   The present disclosure is directed to an electrosurgical apparatus and method, and, is particularly directed to a patient return electrode pad and a method for performing monopolar surgery and RF ablation using the same. 
   2. Background 
   During electrosurgery, a source or active electrode delivers energy, such as radio frequency energy, from an electrosurgical generator to a patient. A return electrode carries the current back to the electrosurgical generator. In monopolar electrosurgery, the source electrode is typically a hand-held instrument placed by the surgeon at the surgical site and the high current density flow at this electrode creates the desired surgical effect of cutting, ablating and/or coagulating tissue. The patient return electrode is placed at a remote site from the source electrode and is typically in the form of a pad adhesively adhered to the patient. 
   The return electrode typically has a relatively large patient contact surface area to minimize heat concentrations at that patient pad site (i.e., the smaller the surface area, the greater the current density and the greater the intensity of the heat.) Hence, the overall area of the return electrode that is adhered to the patient is generally important because it minimizes the chances of current concentrating in any one spot which may cause patient burns. A larger surface contact area is desirable to reduce heat intensity. The size of return electrodes is based on assumptions of the anticipated maximum current during a particular surgical procedure and the duty cycle (i.e., the percentage of time the generator is on) during the procedure. The first types of return electrodes were in the form of large metal plates covered with conductive jelly. Later, adhesive electrodes were developed with a single metal foil covered with conductive jelly or conductive adhesive. However, one problem with these adhesive electrodes was that if a portion peeled from the patient, the contact area of the electrode with the patient decreased, thereby increasing the current density at the adhered portion and, in turn, increasing the heat applied to the tissue. This risked burning the patient in the area under the adhered portion of the return electrode if the tissue was heated beyond the point where normal circulation of blood could cool the skin. 
   To address this problem, split return electrodes and hardware circuits, generically called Return Electrode Contact Quality Monitors (RECQMs), were developed. These split electrodes consist of two separate conductive foils arranged as two halves of a single return electrode. The hardware circuit uses an AC signal between the two electrode halves to measure the impedance therebetween. This impedance measurement is indicative of how well the return electrode is adhered to the patient since the impedance between the two halves is directly related to the area of patient contact. That is, if the electrode begins to peel from the patient, the impedance increases since the contact area of the electrode decreases. Current RECQMs are designed to sense this change in impedance so that when the percentage increase in impedance exceeds a predetermined value or the measured impedance exceeds a threshold level, the electrosurgical generator is shut down to reduce the chances of burning the patient. 
   As new surgical and therapeutic RF procedures continue to be developed that utilize higher current and higher duty cycles, increased heating of tissue under the return electrode may occur. Ideally, each conductive pad would receive substantially the same amount of current, therefore reducing the possibility of a pad site burn. However, this is not always possible due to patient size, incorrect placement of pads, differing tissue consistencies, etc. It would therefore be advantageous to design a return electrode pad which has the ability to detect and correct a current imbalance between pads, therefore reducing the likelihood of patient burns. 
   SUMMARY 
   The present disclosure provides an electrosurgical return pad current detection system for use in monopolar surgery. The detection system comprises a plurality of conductive pads which include a plurality of conductive elements. The detection system further includes a plurality of sensors which sense the current returning to each conductive pad as well as a comparator for sensing the difference in current between a plurality of conductive pads. 
   The present disclosure may also include an ablation generator which may regulate the amount of power delivered to a surgical device. In operation, the return pad current detection system is placed in contact with the patient. A generator enables the transfer of radio frequency current from an active electrode to at least one of a plurality of conductive elements. The plurality of sensors measures the amount of current returning to each pad. This information in then processed a comparator which detects any possible imbalances in current between the pads. If there is a substantial imbalance the user is warned of such a situation and the generator automatically corrects the imbalances. 
   In one embodiment of the present disclosure the current sensor of each conductive pad is a current sense transformer. Alternatively, the current sensor could be, inter alia, a non-inductive sense resistor. 
   In another embodiment of the present disclosure the comparator is a differential or instrumentation amplifier. 
   It is envisioned for the generator to utilize the information provided by the comparator to alert the user of potential hazardous conditions and to prevent injury. This may be achieved using a variety of differing methods including safety control, neural network, or fuzzy logic algorithms. 
   In one embodiment, a full-wave rectifier is connected to the current sensor in order to convert the returning current signal from alternating current to direct current. 
   The present disclosure also includes a method for performing monopolar surgery. The method utilizes the return pad current detection system as described above. The method also includes placing the return pad current detection system in contact with a patient; generating electrosurgical energy via an electrosurgical generator; supplying the electrosurgical energy to the patient via an active electrode; measuring the current returning to each conductive pad; detecting imbalances in current by comparing the current returning to one conductive pad with the current returning to each of the remaining pads; warning the user of possible hazardous conditions; and substantially correcting or regulating the imbalances among pads. 
   For a better understanding of the present disclosure and to show how it may be carried into effect, reference will now be made by way of example to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a schematic illustration of a monopolar electrosurgical system; 
       FIG. 2  is a plan view of an electrosurgical return electrode according to one embodiment of the present disclosure, illustrating a conductive pad having a grid of conductive elements of substantially equal sizes; 
       FIG. 3  is a plan view of an electrosurgical return electrode according to another embodiment of the present disclosure, illustrating a conductive pad having a grid of conductive elements of varying sizes; 
       FIG. 4  is an enlarged schematic cross-sectional view of a portion of the return electrodes; and 
       FIG. 5  is an electrical schematic of the multiple RF return pad current detection system. 
   

   DETAILED DESCRIPTION 
   Embodiments of the presently disclosed multiple RF return pad current detection system and method of using the same are described herein with reference to the accompanying drawing figures wherein like reference numerals identify similar or identical elements. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail. 
   Referring initially to  FIG. 1 , a schematic illustration of a monopolar electrosurgical system  100  is shown. The electrosurgical system  100  generally includes a surgical instrument (e.g., electrosurgical pencil, electrical scalpel, or other active electrode)  110 , a return electrode  200 , a connection device  300  for connecting the return electrode  200  to a generator  120 , and a current detection system  400  disposed on or operatively associated with the return electrode  200  ( FIG. 4 ). In  FIG. 1 , the return electrode  200  is illustrated placed under a patient “P.” Electrosurgical energy is supplied to the surgical instrument  110  by the generator  120  via a cable  130  to cut, coagulate, blend, etc. tissue. The return electrode  200  returns energy delivered by the surgical instrument  110  to the patient “P” back to the generator  120  via return path  140 . 
   The current detection system  400  is in operative engagement with the return electrode  200  and operatively connected to the connection device  300  via a cable  250 . The connection device  300  may be operatively connected to the generator  120  ( FIG. 1 ), may be operatively connected to the return electrode  200  ( FIGS. 2 and 3 ), may be disposed between the return electrode  200  and a generator  120  ( FIG. 4 ) or housed within generator  120 . 
     FIGS. 2 ,  3  and  4  illustrate various embodiments of the return electrode  200  for use in monopolar electrosurgery. Generally, the return electrode  200  is a conductive pad  210  having a top surface  212  ( FIG. 4 ) and a bottom surface  214  ( FIG. 4 ). The return electrode  200  is designed and configured to receive current during monopolar electrosurgery. While the figures depict the return electrode  200  in a general rectangular shape, it is within the scope of the disclosure for the return electrode  200  to have any regular or irregular shape, such as circular, polygonal, etc. 
   As illustrated in  FIGS. 2 ,  3  and  4 , the conductive pad  210  is comprised of a plurality of conductive elements (only conductive elements  220   a - 220   f  are labeled for clarity) arranged in a regular or irregular array. Each of the plurality of conductive elements  220  may be equally-sized or differently-sized and may form a grid/array (or be disposed in any other grid-like arrangement) on the conductive pad  210 . It is also envisioned and within the scope of the present disclosure for the plurality of conductive elements  220   a - 220   f  to be arranged in a spiral or radial orientation (not shown) on the conductive pad  210 . 
   As illustrated in  FIG. 4 , current detection system  400  includes an array of individual current sensors (illustrated as  402   a - 402   f , corresponding to conductive elements  220   a - 220   f , respectively), which are able to measure the amount of current returning to each pad, e.g.,  210   a . The current detection system  400  may be operatively connected to the plurality of conductive elements  220   a - f  on the top surface  212  or bottom surface  214  (or anywhere therebetween) of conductive pad  210 . For example, individual current sensors  402   a  may be operatively connected to conductive element  220   a . Moreover, each current sensor, e.g.  402   a  may be connected via a common cable  250  to a comparator  404  (see  FIG. 5 ), which may be housed in a multitude of different configurations, including within connection device  300  or generator  120 . Alternatively, a series of current detection systems, e.g.  402   a , maybe connected to a connection device  300  via a respective cable  250   a  ( FIG. 5 ). In the interest of clarity, each of the possible cable arrangements for cables  250   a - d  connected to each current detection system  402   a - d  are not illustrated. 
   Generally, the area of the return electrode  200  that is in contact with the patient “P” affects the current density of a signal that heats the patient “P.” The smaller the contact area the return electrode pad  210  has with the patient “P,” the greater the current density which directly affects tissue heating at the contact site. Conversely, the greater the contact area of the return electrode  200 , the smaller the current density and the less heating of tissue at the patient site. As can be appreciated, higher current densities lead to greater heating of tissue and greater probability of patient burn. It is therefore important to either ensure a relatively high amount of contact area between the return electrode pad  210  and the patient “P,” or otherwise maintain a relatively low current density on the return electrode pad  210 . 
   While there are various methods of maintaining a relatively low current density (including, inter alia, the use of electrosurgical return electrode monitors (REMs), such as the one described in commonly-owned U.S. Pat. No. 6,565,559, the entire contents of which are hereby incorporated by reference herein), the present disclosure ensures low current density at the patient site by sensing the amount of current returning to each of the plurality of conductive elements  220   a - f  of the return electrode  200  and adjusting the energy accordingly to reduce current densities at the patient site. 
   More particularly, the current detection system  400  of the present disclosure has the ability to measure the amount of current returning to each conductive element  220   a - 220   f . Each conductive element  220   a - f  is connected to the connection device  300  and may be activated and/or deactivated (or adjusted) as needed. For example, if a conductive element (e.g.,  220   a ) along the perimeter of the conductive pad  210  becomes relatively hot, that conductive element  220   a  may be disconnected from the connection device  300 , deactivated or adjusted to receive a lower amount of energy. In this example, the conductive element  220   a  would not receive any more energy or receive a reduced amount of energy and the current level in the area of the pad contacting the conductive element  220   a  would dissipate. It is envisioned and within the scope of the present disclosure for the disconnection/re-connection, deactivation/reactivation of the conductive elements  220   a - f  to occur automatically as a result of an algorithm (or the like) provided in the electrosurgical generator  120 . 
   It is also envisioned and within the scope of the present disclosure for a disconnected conductive element, e.g.,  220   a , to be reconnected to the connection device  300  when the current level of a particular conductive element or particular area of the pad  210  in contact with the corresponding current detection system  400  decreases. Utilizing these features, the current levels of the return electrode  200  can be relatively consistent throughout the entire surface thereof, thus reducing the possibility of “hot spots” and patient burns. For example, the grid-like arrangement of the pad  210  makes it easier for the generator  120  to identify and adjust current levels at different pad  210  locations depending upon the current build-up possibly reducing the likelihood of patient burns. 
   Referring now to  FIG. 5 , the current detection systems  400  may be operatively associated with a plurality of pads  210   a - d  which operatively connect to generator  140 . One or more algorithms controls the electrical energy associated with each pad to reduce patient burn. Current detection system  400  includes a sensing device  402   a  for sensing the current to each conductive pad  210   a - 210   d  as well as at least one a comparator  404   a - 404   f  which senses the difference in current between the plurality of conductive pads  210   a - 210   d . Current detection system  400  is connected to a plurality of conductive elements  220   a - 220   f  (see  FIGS. 2 and 3 ) on each pad  210   a - 210   d  and may be located in a variety of different areas including, on conductive pads  210   a - 210   d , inside connection device  300 , or within generator  120 . Other locations for current detection system  400  are envisioned and are within the scope of the present disclosure. 
   The current sensor(s), e.g.,  402   a  may take a number of different forms including, but not limited to, open loop sensors, closed loop sensors, digital current sensors, Hall-effect devices or a current sense transformer (not shown), the operation of which will be described hereinbelow. In use, the return current for each conductive pad e.g.,  210   a , is passed through a toroidal magnetic, which forms a 1:N current sense transformer comprised of 1 turn from the return wire and N turns of the toroidal core. The waveform representing the current can be converted to a voltage waveform by placing a resistor between the terminations of the toroidal core turns. This voltage waveform is substantially sinusoidal in nature and may require further modification. An AC/DC converter circuit, e.g.  408   a , may be utilized to substantially convert the alternating current signal of the return current into a direct current signal. This eliminates any phase or frequency modulation that could lead to inaccuracies in measurement. This DC response is representative of the amount of RF current flowing through each conductive pad  210 . AC/DC converter circuit may be operatively associated with each respective sensor  402   a - 402   d.    
   Once the DC response of each conductive pad  210   a  is obtained, the signal may then be fed into a comparator e.g.,  404   a . Each comparator  404   a  receives two distinct DC inputs, each from a separate conductive pad, e.g.,  210   a ,  210   b . It is envisioned that one possible type of comparator  404   a  is an instrumentation amplifier. Instrumentation amplifier receives a DC input from two different conductive pads  210   a ,  210   b  and calculates the current differential between the two. This difference is then multiplied by the gain of comparator or instrumentation amplifier  404   a  in order to obtain a scaled representation of imbalances between any two of the pads e.g.  210   a ,  210   b . Ideally, the current differential would be negligible with each pad receiving the same amount of return current. However, if a substantial imbalance is present, a warning is provided via a warning device (audible or visual) or safety control algorithms which are utilized to mitigate pad site burns which will be described hereinbelow. 
   Generator  120  may contain, inter alia, embedded software. It is envisioned that this embedded software may be utilized to develop safety control algorithms or similar warning mechanisms. Using the information provided by comparator(s)  404   a - 404   d , generator  120  may be able to modulate the amount of power delivered to each conductive pad  210   a - 210   d  therefore minimizing the chances of pad site burns. Moreover, this information may also be processed using a variety of different techniques, including but not limited to, neural networks or fuzzy logic algorithms. 
   It should be noted that a current sense transformer may be replaced with any current measuring device such as a non-inductive sense resistor. Similarly, comparator or instrumentation amplifier could be replaced with a number of different devices including, but not limited to, differential amplifiers. Moreover, AC/DC converter circuit(s)  408   a - 408   d  may take on a number of different forms such as a full-wave rectifier circuit. 
   During electrosurgical use of the return electrode pad  210 , portions of the perimeter of the return electrode pad  210  may become hot at a faster rate than the center of the return electrode pad  210 . In such a situation, as seen in  FIG. 3 , it may be desirable to have the conductive elements  220   a - 220   f  near the perimeter of the return electrode pad  210  be smaller than the remaining conductive elements  220   g - 220   i . Monitoring the returning current levels of each conductive pad(s)  210   a - 210   d  and each conductive element  220   a - 220   i  of each pad  210   a - 210   d  would allow greater control of the overall temperature of the portions of the patient “P” in contact with the entire return electrode pad or pads. Thus, the return electrode pad  210 , as a whole, would be able to receive a greater amount of current, as some new procedures necessitate. Moreover, and as illustrated in  FIG. 5 , a plurality of pads  210   a - 210   d  may be utilized each with a plurality of conductive elements  220   a - 220   i  which all may be individually regulated or controlled to reduce patient burns. 
   To further limit the possibility of patient burns, it is envisioned that an adhesive layer  500  may be disposed on the return electrode  200  about the periphery of pad  210 , as illustrated in  FIGS. 2 and 3 . The adhesive layer  500  may be conductive and may be made from materials that include, but are not limited to, a polyhesive adhesive; a Z axis adhesive; or a water-insoluble, hydrophilic, pressure-sensitive adhesive and is desirably made of a polyhesive adhesive. Such materials are described in U.S. Pat. Nos. 4,699,146 and 4,750,482, the entire contents of each of which are herein incorporated by reference. A function of the adhesive layer  500  is to ensure an optimal surface contact area between the return electrode  200  and the patient “P” thus limiting the possibility of a patient burn. 
   It is envisioned that the return electrode(s)  200  may be entirely disposable, entirely re-usable, or a combination thereof. In one embodiment, the conductive elements  220  are re-usable, while the adhesive layer  500  is disposable. Other combinations of disposable/re-usable portions of the return electrode  200  are envisioned and within the scope of the present disclosure. 
   It is envisioned that a multiplexer  260  may be employed to control switching of the plurality of conductive elements  220   a - 220   f , as illustrated in  FIG. 4 . For example, it is envisioned that the multiplexer  260  may be configured to regulate the current in any fashion by switching “on” and “off” various amounts of the plurality of conductive elements  220   a - 220   f . While the multiplexer  260  is illustrated between the generator  120  and the connection device  300 , other locations for the multiplexer  260  are envisioned and within the scope of the present disclosure. 
   The present disclosure also includes a method for performing monopolar surgery. The method utilizes one or more return pads operatively associated to one another which form a current detection system  400  as described above. The method also includes placing one or more return pads of the current detection system  400  in contact with a patient; generating electrosurgical energy via an electrosurgical generator  120 ; supplying the electrosurgical energy to the patient via a surgical instrument  110 ; measuring the current returning to each conductive pad  210   a - 210   d ; detecting imbalances in current by comparing the current returning to one conductive pad  210   a  with the current returning to each of the remaining pads  210   b - 210   d ; warning the user of possible hazardous conditions; and providing a means for substantially correcting the imbalances. 
   While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. For example, it is envisioned for the return electrode  200  to be at least partially coated with a positive temperature coefficient (PTC) material to help distribute the heat across the return electrode  200 , as described in commonly-owned U.S. Provisional Patent Application Ser. No. 60/666,798, the entire contents of which are hereby incorporated by reference herein.