Abstract:
A system and method for controlling electrosurgical snares are disclosed. The system includes an electrosurgical instrument having an elongate tubular sheath having proximal and distal ends, the sheath having a longitudinal axis defined therethrough and a shaft having proximal and distal ends. The shaft extends through and is axially movable relative to the sheath. A snare loop is provided at the distal end of the shaft and is configured for encircling tissue. Movement of the shaft relative to the tubular sheath changes the diameter of the exposed snare loop. A feedback sensor operatively connected to the elongated tubular sheath which determines at least one condition of the snare loop, and an electrosurgical generator provides electrosurgical energy to the electrosurgical snare instrument. The generator is configured to receive feedback measurements from the electrosurgical snare instrument and to adjust electrosurgical energy as a function of the measurements.

Description:
BACKGROUND 
   1. Technical Field 
   The present disclosure relates generally to an electrosurgical snare instrument and, more particularly, to a system and method for controlling energy delivered by an electrosurgical generator to the electrosurgical snare instrument based on diameter and pressure of the snare. 
   2. Background of Related Art 
   Snare instruments are electrosurgical devices that are primarily used for removing small growths from the lining of internal body cavities (e.g., polyps within the bowels), such as during polypectomy procedures. These snares include a wire loop configured to encircle the small growth, and then electrosurgical energy is applied to the tissue to cut and/or coagulate. Generally, snare instruments include an elongate tubular member having a handle, such as a sheath, a shaft extending through the tubular member having a wire loop connected to the distal end (“distal” refers to that portion that is further from the user, while “proximal” refers to that portion that is closer to the user or surgeon) thereof. The loop is opened by pushing the shaft toward the distal end thereby moving/extracting the loop outside the tubular member and is closed by pulling the shaft toward the proximal end thereby moving/retracting the loop inside the tubular member. 
   The snare instrument is generally inserted into internal body cavities through an endoscope. In the case of a polypectomy, the instrument is inserted through the gastrointestinal tract and moved toward the polyp(s) marked for removal. During insertion, the loop is retracted into the shaft, and once at the removal site, it is extracted and is expanded around the polyp. The surgeon then constricts the loop around the polyp and electrosurgical energy is applied thereto. 
   Currently, snare instruments are used without providing any sensory feedback to the generator. The surgeon has to manually adjust the energy delivered to the snare while simultaneously adjusting the pressure exacted on the polyp by the loop. For instance, as the surgeon increases the pressure, the energy must also increase so that the energy increases proportionally with pressure. The contiguous increase in pressure and energy allows for the polyp to be removed only after the stalk portion thereof has been cauterized. Increasing energy too slowly may detrimentally affect removal of the polyp causing bleeding. Increasing energy too rapidly may result in damage to the surrounding tissue. Presently, the success of these surgical procedures depended on the experience of the surgeon to control the pressure and energy delivered to the snare instrument. Such manual control of these operating factors is not infallible. 
   SUMMARY 
   The present disclosure provides for a system and method of controlling delivery of electrosurgical energy supplied by a generator to an electrosurgical snare instrument based on the position and pressure of the snare loop. The snare instrument is configured for removal of polyps and includes a position sensor configured to determine diameter of the snare loop and a pressure sensor configured to determine the pressure exacted on the polyp. The position and pressure feedback signals are transmitted to the generator, which then automatically adjusts the power of output, mode, and other factors affecting electrosurgical energy. 
   According to one embodiment of the present disclosure, an electrosurgical snare instrument is disclosed. The instrument includes an elongate tubular sheath having proximal and distal ends, the sheath having a longitudinal axis defined therethrough. The instrument also includes a shaft having proximal and distal ends, the shaft extending through and axially movable relative to the sheath. A snare loop is provided at the distal end of the shaft and is configured for encircling tissue. Movement of the shaft relative to the tubular sheath changes the diameter of the exposed snare loop. A feedback sensor operatively connected to the elongated tubular sheath determines at least one condition of the snare loop. 
   According to another embodiment of the present disclosure, a system for controlling an electrosurgical snare instrument is disclosed. The system includes an electrosurgical instrument having an elongate tubular sheath having proximal and distal ends, the sheath having a longitudinal axis defined therethrough and a shaft having proximal and distal ends. The shaft extends through and is axially movable relative to the sheath. A snare loop is provided at the distal end of the shaft and is configured for encircling tissue. Movement of the shaft relative to the tubular sheath changes the diameter of the exposed snare loop. A feedback sensor operatively connected to the elongated tubular sheath determines at least one condition of the snare loop, and an electrosurgical generator provides electrosurgical energy to the electrosurgical snare instrument. The generator is configured to receive feedback measurements from the electrosurgical snare instrument and to adjust electrosurgical energy as a function of the measurements. 
   According to a further embodiment of the present disclosure, a method for controlling an electrosurgical snare instrument is disclosed. The method includes the step of inserting an electrosurgical snare instrument into a body cavity. The instrument includes an elongate tubular sheath having proximal and distal ends, the sheath having a longitudinal axis defined therethrough. The instrument also includes a shaft having proximal and distal ends, the shaft extending through and axially movable relative to the sheath. A snare loop is provided at the distal end of the shaft and is configured for encircling tissue. Movement of the shaft relative to the tubular sheath changes the diameter of the exposed snare loop. The method further includes the steps of positioning the snare loop to encircle a portion of the tissue and collecting feedback measurements through a feedback sensor operatively connected to the elongated tubular sheath for determining at least one condition of the snare loop indicative of at least one condition of the snare loop. The method further includes the steps of transmitting feedback measurements to an electrosurgical generator, which provides electrosurgical current and adjusting electrosurgical energy as a function of the feedback measurements. 

   
     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 diagram illustrating an electrosurgical system including a snare instrument according to the present disclosure; 
       FIG. 2  is a schematic diagram illustrating a snare loop; 
       FIG. 3  is a block diagram of the electrosurgical system of  FIG. 1 ; 
       FIG. 4  is a cross sectional view of the snare instrument including a position sensor; 
       FIG. 4A  is a cross sectional view of an alternate snare instrument; 
       FIG. 4B  is a cross sectional view of an alternate snare instrument; 
       FIG. 4C  is a cross sectional view of an alternate snare instrument; 
       FIG. 5  is a diagram illustrating an alternate embodiment of an electrosurgical system according to the present disclosure; and 
       FIG. 6  is a diagram illustrating another alternate embodiment of an electrosurgical system according to the present disclosure. 
   

   DETAILED DESCRIPTION 
   Embodiments of the present disclosure are described below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. As used herein, the term “distal” refers to that portion that is further from the user while the term “proximal” refers to that portion that is closer to the user or surgeon. 
     FIG. 1  shows an electrosurgical system including a generator  10  that supplies electrosurgical energy to an electrosurgical snare instrument  11  through electrical wiring within a cable  12 . The generator  10  also includes processing means (e.g., one or more microprocessors, storage, memory, etc.) configured to analyze control and input signals as discussed in more detail below. The snare instrument  11  includes an elongate tubular sheath  13  having a proximal end  14  and a distal end  16  formed preferably from a suitable medical grade plastic, such as Teflon, polyurethane, polyethylene and the like. The sheath  13  has an outside diameter sufficiently small enough to allow the sheath  13  to fit through a working lumen of an endoscope (not explicitly shown). 
   The snare instrument  11  also includes an electrically conductive shaft  18  having a proximal end  20  and a distal end  22  extending through and axially movable within the sheath  12 . The shaft  18  may be in a form a multifilament twisted and drawn or swaged cable where the filaments are metallic, such as stainless steel, a nickel-titanium alloy, and the like. It is envisioned that the shaft  18  may be formed from a suitable plastic material, such as the plastic used to form the sheath  13 , wherein the plastic includes an electrically conductive surface (e.g., coating, foil, etc.). 
   A snare loop  24  is mechanically and electrically coupled to the distal end  22  of shaft  18  via a connector  30  near distal end  16  of the sheath  12  as illustrated in  FIG. 2 . The snare loop  24  is formed from suitable wire, such as multifilament wire used to form the shaft  18 . In the illustrated embodiment, the snare loop  24  includes two sides  40 ,  42  with corresponding two ends attached to the distal end  22  of the shaft  18  to form a loop by welding, soldering, or crimping. Alternatively, the shaft  18  may be formed from two cables or wires twined together from the proximal end  20  and the distal end  22  and untwined after the distal end to form the loop  24 . In an alternative embodiment, the two sides  40 ,  42  may be formed from separate wire or cable elements coupled together at the distal end  22  of the shaft  18  and the distal end  44 . 
   The snare instrument  11  further includes a handle assembly  26  having a distal end  30  and a proximal end  29 . The sheath  13  is connected to the assembly  26  at the distal end  30 . The assembly  26  may have tubular structure and may be formed by molding from an inflexible plastic material or formed by other processes from other inflexible medical grade materials (e.g., stainless steel). The assembly  26  may also be formed from elastic medical grade materials (e.g., high durometer urethane). 
   Within the assembly  26  is a plunger  27  having a distal end  34  and a proximal end  32 . The plunger  27  is electrically conductive and inflexible. The plunger  27  may be formed entirely from metal (e.g., steel rod) or from an inflexible plastic having an electrically conductive surface. The shaft  18  is connected to the plunger  27  at the shaft&#39;s proximal end  20  and plunger&#39;s distal end  34 . The plunger  27  includes a first handle  36  at the proximal end  32  thereof, which allows the surgeon in conjunction with a second handle  38  disposed at the proximal end  29  of the assembly  26  to manipulate the shaft  18  and the loop  24  by moving the shaft  18  along the longitudinal axis. The second handle  38  includes finger rests adapted to receive the forefinger and index finger of the surgeon whereby the thumb is inserted into the first handle  36  to facilitate the manipulation of the plunger  27  and the shaft  18 . 
   Disposed on the surface of the assembly  26  is a cautery connector  28  that is conductively coupled via a brush connector  39  to the shaft  18  through the plunger  27  so that the plunger  27  and the shaft  18  can be and moved longitudinally while maintaining such conductive coupling. 
   The snare instrument  11  can be adapted for monopolar and bipolar electrosurgical procedures. In monopolar configuration, the loop  24  serves as an active electrode through which electrosurgical energy will be applied to the tissue. In such a configuration, a return electrode (not shown) will be attached to a patient to return the current supplied through the loop  24  to the generator  10 . 
   In bipolar configuration, the active and return electrodes are incorporated into the loop  24 . One of the two sides  40 ,  42  serves as an active electrode while the other serves as a return electrode being separated by an insulative material (e.g., ceramic tip) at the distal end  44 . 
   Referring back to  FIG. 1 , the loop  24  is shown surrounding a stalk of a polyp  46  extending outward from the surface of a hollow organ  48  in the gastrointestinal tract (e.g., bowel). During an operating procedure, the snare instrument  11  is inserted into the organ through an endoscope channel and the endoscope is used to visually locate and assess the shape and type of the polyp  46  as is well known in the art. Thereafter, the surgeon positions the snare instrument  11  within the organ and places the loop  24  around the polyp  46 . Then, the surgeon retracts the loop  24  by pulling the plunger  27  toward the proximal end  32  to close the loop  24  around the polyp  46 . Once the loop  24  is closed and in contact around polyp  46 , the surgeon applies the coagulation current to desiccate the cells of the polyp  46 , thereby severing the growth. After the severing, the surgeon switches the generator  10  into coagulating mode and places the closed loop  24  in contact with severed blood vessels of the polyp  46  to close the vessels and stop the blood flow. It is known that the loop  24  in a closed configuration may also be used to remove polyps too small to be encircled by the loop  24 . Those skilled in the art will appreciate that the surgeon may also use coagulating current initially to coagulate the blood vessels within the polyp  46  and then use the cutting current to cut across or proximate the coagulated portion. 
   To aid the surgeon in adjustment of various parameters (e.g., intensity, waveform, etc.) of the electrosurgical energy, the present disclosure provides a position sensor  50  and a pressure sensor  60  disposed within the snare instrument  11 , as shown in  FIG. 3 , which provide feedback to the generator  10  upon which the generator  10  makes adjustment to operating parameters, such as power output, power versus impedance curves, operating mode, duty cycle, etc. The pressure sensor  60  senses the pressure exerted by the loop  24  on the polyp  46 . The position sensor  50  senses the diameter of the loop  24  (i.e., perimeter and/or size of the loop  24 ) and reports the measurements to the generator  10 , which then makes a determination based on the measurements and makes corresponding adjustments to electrosurgical energy. 
   More particularly, when the loop  24  is not fully closed but in contact with the polyp  46  the position sensor  50  and the pressure sensor  60  report that fact to the generator  10 , which then communicates electrosurgical energy through the loop  24  so that the polyp  46  can be severed. When the loop  24  is fully closed, e.g., the polyp  46  has been fully severed, that information is forwarded by the sensors  50 ,  60  to the generator  10 , which then switches into coagulation mode to coagulate the blood vessels. Those skilled in the art will appreciate that the generator  10  may be programmed to respond in different ways than those discussed above (e.g., coagulate when loop  24  is in contact with tissue and cut when the loop  24  is closed). The snare instrument  11  may include either one of, or both, the position sensor  50  and the pressure sensor  60  allowing the generator  10  to make power and other adjustments based on diameter and/or pressure measurements. 
   With reference to  FIG. 4 , the position sensor  50  is shown disposed within the assembly  26 . In one embodiment, the position sensor  50  includes a film-type potentiometer  52  coupled to the inner surface of the tubular structure of the assembly  26  and a contact nub  54  in contact therewith. The nub  54  is positioned on the outer surface of the plunger  27  directly opposite the potentiometer  52 . The potentiometer  52  and the nub  54  may be relocated (e.g., their positions reversed) as long as these components of the position sensor  50  are kept in contact with and are positioned opposite each other. Furthermore, the potentiometer  52  may be disposed on the inner surface of the sheath  13  with the nub  54  being located on the shaft  18 . The nub  54  may also be disposed (e.g., embedded) within the second handle  38  and the potentiometer  52  may be placed on the outer surface of sheath  13 , as shown in  FIG. 4A . 
   The spring sensor  60  may be constructed in the following manner. The sheath  13  and other components of the snare instrument  70  may be made from elastic materials and thereby be used to spring-load the loop  24 . The spring-loading produces a signal from the position sensor  50  embedded in the second handle  38  and measures both the snare size of the loop  24  and the pressure exerted thereby. 
   With reference to  FIG. 4B , a pressure sensor  60  is shown that includes the nub  54  disposed within the sheath  13  and in contact with a second potentiometer  53 . The nub  54  is coupled to the second handle  38  through a suitable elastic member  61  (e.g., a spring) connected in series thereto. The position of the nub  54  and its contact with the potentiometer  53  is directly proportional to the force with which the second handle  38  is pushed pack (e.g., counterbalanced by the elastic member  61 ). Therefore, the pressure exerted by loop  24  may be determined by measuring the signal generated by the nub  54  contacting the potentiometer  53 . The pressure sensor  60  may also be a piezoelectric crystal. The piezoelectric crystal converts pressure applied thereto into corresponding voltage that can then be converted into a digital signal and be processed by the processing means of the generator  10 . 
   As shown in  FIG. 4C , the pressure and position sensors  50 ,  60  are disposed within the snare instrument  70 . The position sensor  50  measures the diameter of the loop  24  using the position of the nub  54  and the pressure sensor  60  measures the pressure exerted by the loop  24  by determining the position of the nub  54  as affected by the elastic member  61 . 
   The feedback concerning the diameter of the loop  24  is reported to the generator  10  through control wires disposed within the cable  12 . As the plunger  27  is moved longitudinally within the handle assembly  26 , the nub  54  slides longitudinally across the surface of the potentiometer  52 . When the nub  54  is in contact with the potentiometer  52  near a proximal end  55  thereof, a corresponding voltage is transmitted to the generator  10 . The voltage is analyzed by the generator  10  to determine the control signal, which when the nub  54  is near or at the proximal end  55 , denotes that the loop  24  is in closed position (e.g., shaft  18  is fully retracted). When nub  54  is in contact with the potentiometer  52  near a distal end  56 , the voltage transmitted to the generator  10  signals that the loop  24  is fully opened. Positions of the nub  54  in between the proximal and distal ends  55 ,  56  can be configured to denote other corresponding control signals (e.g., partially closed loop  24 ). After analyzing the control signals and determining the position of the loop  24 , the generator  10  makes appropriate changes to the output of the electrosurgical energy, such as output power, waveform, voltage, impedance, mode, etc. 
   In addition to providing feedback on the position and diameter of the loop  24 , the present disclosure also provides for a system and method to determine the pressure exerted by the loop  24  on the polyp  46  using the pressure sensor  60 , as shown in  FIG. 3 . Determining the snare loop  24  pressure may be important in determining when power must be applied to the polyp  46 . As discussed above, initially power is applied to the polyp, more specifically, a coagulation mode is used. Conventionally, surgeons had to figure out when to sever the polyp based on experience. The pressure sensor  60  allows for automatic adjustment by providing feedback to the generator  10  concerning the pressure applied to the polyp  46 . When the pressure sensor  60  senses that the pressure is at its highest, it denotes that the loop  24  is firmly fitted around the polyp  46 . This information is transmitted to the generator  10  which increases power or switches operational modes (e.g., cutting mode) and supplies electrosurgical energy to the snare instrument  11 . As soon as the polyp  46  is severed, the pressure applied by the loop  24  dissipates since the physical obstruction (e.g., polyp  46 ) has been removed. This change in pressure is also transmitted to the generator  10  which then modifies the operating mode and supplies coagulating current to the snare instrument  11  to coagulate the blood vessels. 
   The pressure sensor  60  may enable the surgeon to regulate the pressure such that the surgeon can effectively seal the blood vessels prior to resection of the polyp  46 . For example, the surgeon may be able to control the pressure applied around the polyp  46  to within an ideal parameter known to effectively seal tissue rather than simply coagulate tissue. Other features may also have to be properly controlled to create an effective seal, such as gap distance between opposing surfaces of the loop  24  and energy control. 
   Where elastic compliance of the materials comprising the components of the snare instrument  70  are known, a single position sensor may be used to sense position as well as the pressure of the snare. In particular, the position measurement signal in conjunction with the elastic properties may be used to calculate the pressure and position of the snare based on a single signal. Conventional materials used in construction of snare instruments are prone to compress and stretch when force is applied to the handle. Therefore, placing the position sensor  50  at the handle  38  allows for measuring the position and the pressure of the snare. A single pressure sensor  60  may be used to determine both the position and the pressure of the snare from the pressure signal based on the elastic compliance of the flexible snare materials. 
   The snare instrument  70  may include an impedance sensor (not explicitly shown) that measures impedance of the tissue at the polyp  46 . Using a sensing current the impedance sensor determines when sufficient energy has been communicated to the polyp  46  to signal the polyp  46  has been coagulated and may be severed. Impedance measurements may also be used to determine when other stages of the procedure have been accomplished, since as energy is applied to the polyp  46  impedance of the tissue changes, which allows for measurements and/or determinations regarding the state of the polyp  46 . 
   Those skilled in the art will appreciate that the generator  10  includes a specific operating mode designed for snare procedures. Snare procedures differ from other electrosurgical operations (e.g., sealing blood vessels, cutting tissue, etc.) because the electrode in snare procedures (e.g., loop  24 ) is in continuous tissue contact. As a result snare procedures are characterized by low impedance of the tissue and low voltage requirements. The generator  10  of the present disclosure includes a new operating mode that changes output power, waveform, and voltage relative to the tissue impedance. This operating mode may be also useful in other electrosurgical procedures having same characteristics as snare procedures where an active electrode is in continuous tissue contact. 
   Pressure and loop diameter feedback can also be used to fully automate snare procedures by using a snare instrument  70  as shown in  FIG. 5 . The application of electrosurgical energy as well as diameter control of the loop  24  may be controlled by the generator  10  based on the feedback received from the sensors  50 ,  60 . The snare instrument  70  includes an actuator  62 , such as a piston cylinder which is electrically controlled by the generator  10  or a cable controller actuated by a pulley system. An algorithm for controlling the actuator  62  is programmed in the generator  10  and may be activated by scanning a barcode  64  attached to a plug  65 . It is well known in the art to identify devices by scanning barcodes and loading preprogrammed algorithms into the electrosurgical generators based on that information. The generator  10  may include a reader for scanning barcodes and other identifying means. 
   The snare instrument  70  also includes a button  66  that activates the snare instrument  70  once it is in position (e.g., the loop  24  is placed around the polyp  46 ). Once the proper positioning is achieved, the surgeon presses the button  66  to activate the generator  10  algorithm. The generator  10  adjusts the diameter of the loop  24  by decreasing the diameter gradually. More particularly, the generator  10  signals the actuator  62  to contract, thereby pulling the shaft  18  and contracting the loop  24 . The contraction continues until the pressure sensor  60  reports to the generator  10  that the loop  24  is in tight contact with the polyp  46 . The generator  10  then checks the tissue impedance and delivers electrosurgical energy of predefined operating mode and power level to the loop  24  based on pressure feedback and measured impedance. Impedance measurement may be carried out by supplying a measuring current to the polyp  46  to determine is impedance as is known in the art. 
   Once the energy is supplied to the polyp  46  and it is severed, the position sensor  50  reports to the generator  10  of this occurrence and the generator  10  responds to the position feedback by changing operating modes (e.g., switch to coagulation mode). The mode and power settings can be changed during the procedure as a response to measured tissue impedance and loop diameter. Once the resection of the polyp  46  is complete, the energy is turned off to reduce the possibility of affecting surrounding tissue. During various stages of the procedure one or more audio and/or visual indicator may be used to signal to the surgeon that a particular stage of the procedure is completed. The audio and/or visual indicators can be disposed on the generator  10  or snare instrument  70 . 
     FIG. 6  shows another embodiment of the snare instrument  70  that is automatically activated and monitored by the generator  10 . The snare instrument  70  includes a drive motor  62  that is controlled by the generator  10 . The drive motor  62  actuates a gear mechanism  72  that rotates a lead screw  74 , which in turn is connected to a block  76  that includes the shaft  18 . The drive motor  62  may rotate the lead screw in two directions (e.g., clockwise and counterclockwise), which then moves the block  76  and the shaft  18  backwards and forwards. The block  76  includes the nub  54  that is in contact with the potentiometer  52  to measure the diameter of the loop  24 . In addition, the block  76  also includes a piezoelectric crystal  63 , which converts pressure applied thereto into a corresponding voltage signal. The voltage signal may then be analyzed by the processing means of the generator  10 . 
   The generator  10  measures pressure and size of the loop  24  and includes suitable algorithms that control the drive motor  62 , through which the generator  10  controls snare pressure, snare exposure (e.g., size of the loop  24 ), generator mode, and generator power to optimize cautery and resection procedures. 
   The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Various modifications and variations can be made without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.