Patent Publication Number: US-11660460-B2

Title: Integrated pump control for dynamic control of plasma field

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 15/292,496, filed on Oct. 13, 2016, which claims the benefit of U.S. Provisional Patent Application No. 62/242,529, filed Oct. 16, 2015, the disclosures of all of which are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to pump systems and, more particularly, to pumps and pump controlling devices and methods for surgical procedures. 
     BACKGROUND OF THE INVENTION 
     Fluid management pump systems are employed during surgical procedures to introduce sterile solution into surgical sites. One such procedure in which a fluid management pump is employed is during an endoscopic surgical procedure. In endoscopic surgery, an endoscope is inserted into the body at the site where the surgical procedure is to be performed. The endoscope is a surgical instrument that provides a view of the portion of the body in which it is inserted. Other surgical instruments are placed in the body at the surgical site. The surgeon views the surgical site through the endoscope in order to manipulate the other surgical instruments. The development of endoscopes and their companion surgical instruments has made it possible to perform minimally invasive surgery that eliminates the need to make large incisions to gain access to the surgical site. Instead, during endoscopic surgery, small openings, called portals, are formed in the patient. An advantage of performing endoscopic surgery is that since the portions of the body that are cut open are minimized, the portions of the body that need to heal after the surgery are likewise reduced. Still another advantage of endoscopic surgery is that it exposes less of the interior tissue of the patient&#39;s body to the open environment. This minimal opening of the patient&#39;s body lessens the extent to which the patient&#39;s internal tissue and organs are open to infection. 
     The ability to perform endoscopic surgery is enhanced by the development of fluid management pumps. A fluid management pump is designed to pump a sterile solution into the enclosed portion of the body at which the endoscopic surgical procedure is being performed. This solution expands and separates the tissue at the surgical site so as to increase both the field of view of the surgical site and the space available to the surgeon for manipulating the surgical instruments. One type of endoscopic surgery in which fluid management pumps have proven especially useful is in arthroscopic surgery. In arthroscopic surgery, a specially designed endoscope, called an arthroscope, is employed to examine inter-bone joints and the ligaments and muscles that connect the bones. A fluid management pump is often employed in arthroscopic surgery to expand the space between the bones and adjacent soft tissue in order to increase the field in which the surgeon can perform the intended surgical procedure. Fluid management pumps are, during arthroscopic surgery, used to increase the surgical view of the joints that form an elbow, a knee, a wrist, or an ankle. Fluid management pumps are used both in endoscopic surgery and in other surgical procedures to remove debris generated by the procedure. 
     A fluid management pump system includes a number of different components. There is the pump unit that supplies the motive force for pumping the sterile solution through an inflow tube into the surgical site. The actuation of the pump is regulated by a control unit. The control unit receives as input signals both surgeon-entered commands and an indication of the liquid-state fluid pressure at the surgical site. Still another component of a fluid management pump system is the tube set. The tube set includes the fluid communication tubes that are connected between the pump unit, the control unit, and the surgical site in the patient which is infused with the distention fluid. The tube set includes the previously described inflow tube through which the solution is introduced into the surgical site. There is also an outflow tube through which the solution and any waste material carried therewith are removed from the surgical site. Fluid flow from the site can be regulated by a valve integral with the control unit that selectively opens and closes the outflow tube. The tube set also includes a pressure feedback tube. The pressure feedback tube provides a fluid communication path between the surgical site and the control unit so that a pressure transducer integral with the control unit can monitor the fluid pressure at the surgical site. The pressure signal the transducer supplies is used by the control unit to regulate the actuation of the pump unit and to control the open/closed state of the fluid outflow tube. 
     Most fluid management pump systems further include cannulae that are inserted into the patient. The cannulae function as the actual fluid communication paths between the surgical site and the tubes forming the tube set. In order to minimize the number of portals that need to be formed in the patient, a single cannula can be provided that provides both the fluid communication into the body for the inflow tube and the pressure feedback tube that functions as the guide bore through which the endoscope is inserted. These particular cannulae are called pressure sensing cannulae. An RF probe, shaver or other instruments may be used in the endoscopic surgical procedure, along with the fluid management pump. These instruments may provide information to the control unit of the pump, which can then be used to control one or both of the inflow or outflow to the pump, based on the desired conditions of the surgical site. One such condition is a plasma field which is advantageous when in a stable condition. An algorithm used by the control unit of the pump can control inflow and outflow rates to achieve a stable plasma field. 
     Other advantages, objects and/or purposes of the invention will be apparent to persons familiar with constructions of this general type upon reading the following specification and inspecting the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view of a pump system of the present invention illustrating flow paths through the pump system. 
         FIG.  2    is a block diagram showing inputs provided to the pump control processor and outputs from the pump control processor. 
         FIG.  3    is a flowchart of a portion of a pump system operating routine that includes obtaining information regarding a cutting accessory. 
         FIG.  4    is a flowchart of a portion of a pump system operating routine to adjust the suction in a surgical pumping system. 
     
    
    
     For purposes of description herein, it is to be understood that the invention may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
     Referring to  FIG.  1   , there is illustrated a pump system  10  and flow paths through the pump system  10 . The pump system  10  includes a pump  14  configured to provide a surgery washing fluid to a body cavity  12  (e.g., a joint) during surgery and to suction waste fluid out of the body cavity  12 . 
     As illustrated in  FIG.  1   , the pump  14  receives a surgery washing fluid from a source of surgery washing fluid  16 . The surgery washing fluid could be any washing fluid used in surgery and could be, for example, 0.9% saline or Ringer&#39;s lactate. The surgery washing fluid can provide irrigation to the body cavity  12 , provide distension in a joint to give a surgeon room to operate in certain joints, and/or provide tamponade to help with bleeding. Input tubing  18  is connected between the source of surgery washing fluid  16  and the pump  14  for supplying the surgery washing fluid to the pump  14 . As illustrated in  FIG.  1   , the pump  14  can have an inflow cassette  20  inserted therein for receiving the surgery washing fluid and for pushing the surgery washing fluid to the body cavity  12  through an inflow tube  22 . Typically, the inflow tube  22  is inserted into and/or connected to an inflow cannula  24  inserted into the body cavity  12 . 
     The illustrated pump  14  can also have an outflow cassette  26  inserted therein for suctioning the fluid out of the body cavity  12 . An outflow tube  28  extends between the body cavity  12  and the outflow cassette  26 , with the outflow tube  28  typically inserted into and/or connected to an outflow cannula  30  inserted into the body cavity  12 . The outflow cassette  26  can also have one or more surgery devices  32  connected thereto by device suction tubing  34 . The surgery devices  32  are configured to suction the fluid out of the body cavity  12  while the surgery devices  32  are being used within the body cavity  12 . The surgery devices  32  can include a shaver  36 , an RF device  38  or any other surgery device that can suction waste fluid out of the body cavity  12 . The RF device  38  has at least one electrode  38   a  which can generate a plasma field. The RF device  38  also preferably has a fluid port  38   b . An RF generator  39  is connected to the RF probe  38  and to the pump  14 . The RF generator  39  provides feedback to the pump  14 , which is used in determining the outflow from the pump  14 . 
     The outflow cassette  26  is connected to a waste receptacle  40  by waste tubing  41 . The outflow cassette  26  works with the pump  14  to suction the waste fluid out of the body cavity  12  and to push the waste fluid into the waste receptacle  40  through the waste tubing  41 . The input tubing  18 , the inflow tube  22 , the outflow tube  28 , the device suction tubing  34 , and the waste tubing  41  can have any length. 
     In the illustrated example, the pump system  10  can receive information from all elements of the pump system  10  to change the flow rate and/or pressure of the surgery washing fluid being provided to the body cavity  12  (i.e., inflow characteristics) and/or to change the flow rate and/or pressure of the waste fluid being suctioned from the body cavity  12  (i.e., outflow characteristics). In the illustrated example, the pump  14  and/or an integration system can contain an algorithm for altering the inflow and/or outflow characteristics. Therefore, while most of the information paths are illustrated as being between the pump  14  and other elements, the information paths could lead to the integration system instead of the pump  14 . In some embodiments, the integration system is disposed within a pump housing. The pump  14  and/or integration system can include information from the body cavity  12  (e.g., pressure and temperature within the body cavity  12 ), the surgery devices  32  (e.g., voltage, impedance, power, current at the surgical site via the shaver  36  and/or the RF probe  38 ), the RF generator  39 , a foot pedal, a remote control, inflow information measured within the pump  14  including pressure information of the fluid outputted from the pump  14 , and outflow information measured within the pump  14  including pressure information of the fluid suctioned by the pump  14 . The pump  14  can also include an input device for inputting information directly into the pump  14  (e.g., a keyboard or touch screen). 
       FIG.  2    illustrates various inputs, outputs and input devices that are provided with a pump control processor  100 . The pump control processor  100  uses various input data to determine and control the flow of solution from the pump  14 . The input devices include the multi-device operating room controller  42 , a foot pedal  44 , a remote control  46 , and a pump input device  48 . 
     In various embodiments, only some of the inputs shown in  FIG.  2    are provided to the pump control processor  100  and only selected ones of the outputs are output therefrom. For example, in some embodiments of the invention there is no outflow pump motor control. In other embodiments, an unidentified third party surgical device is provided, wherein the pump control processor  100  does not know device parameters of such a surgical device. Many embodiments of the invention do not include an in-joint pressure sensor or an in-joint temperature sensor, and thus such directly measured joint pressure values are not provided to the pump control processor  100 . In some embodiments, a multi-device operating room controller is not connected to the pump system  10 . Further, additional inputs and outputs for the pump control processor  100  that are not shown in  FIG.  2    are also contemplated. 
     Identified Components: 
     In one embodiment, the type of inflow cannula  24 , type of endoscope  25 , and the type of inflow tube  22  and length thereof are identified. Identification information for each of the components is input into the pump control processor  100  manually or automatically. The dimensions and length of the inflow and outflow tubing, along with other properties, is typically automatically read by RF communication or identified by the pump control processor  100  when inflow and outflow tubing, via cassettes or otherwise, is inserted into the pump  14 . 
     The pump control processor  100  utilizes stored or read dimensions and other values for the known identified components to calculate a pressure loss (P loss ) curve based on the dimensions and characteristics of the inflow tubing  22 , the inflow cannula  24  and the endoscope  25  that define an inflow path to the surgical site  12  in the joint. Details for the inflow tubing, the endoscope  25  and the inflow cannula  24  can be stored in pump memory. An algorithm or program executed by the pump control processor  100  calculates coefficients (COEF 1  and COEF 2 ) defining the P loss  curve from the properties including the dimensions and length of the tubing  22 , and properties including dimensions of both the cannula  24  and the endoscope  25 . The coefficients are provided in an equation including speed or velocity, typically revolutions per minute (RPMs) of an inflow pump motor to calculate a P loss  value at a point on the P loss  curve as defined for a given inflow pump motor speed. 
     Obtaining a P loss  value on the P loss  curve for an RPM value of the inflow pump motor requires an algorithm or program calculating a second order polynomial using the load coefficients COEF 1 , COEF 2  as set forth in the following equation:
 
 P   loss =COEF 1 ×(RPM value) 2 +COEF 2 ×(RPM value)
 
The above pressure loss equation results in a calculated P loss  value at a given RPM value for the inflow motor of the pump system.
 
     A measured head pressure (P head ) sensed by a pump inflow pressure sensor of the pump  14  disposed at or near the inflow pump cassette  20  may be used to calculate the in-joint pressure using the following equation:
 
 P   joint   =P   head   −P   loss  
 
Using the above calculation, the pump control processor  100  may control the inflow pump motor to maintain the P joint  value at a generally constant predetermined desired pressure value regardless of the outflow arrangement.
 
     The pump control processor  100  controls the inflow pump motor over a range in which there is a linear relationship between the flow rate and the inflow pump motor RPM value using the following equation:
 
Inflow=COEF INFL ×(RPM value)
 
The inflow coefficient COEF INFL  value is loaded from a look-up table for the identified hardware (cannula, inflow tubing, etc.) connected to the pump.
 
     In some embodiments, an inflow cannula provides fluid to a joint without an endoscope. In such an instance, the pump control processor  100  simply determines the load coefficients and inflow coefficient from the inflow tubing and the inflow cannula. In other embodiments the cannula is an outflow cannula or a different cannula. 
     Unidentified Components: 
     Another embodiment of an inflow pump control arrangement is utilized wherein the dimensions and other properties of the inflow tubing  22 , inflow cannula  24 , and the endoscope  25  are unknown. In this embodiment, the pump control processor  100  utilizes a calibration routine or an algorithm as a start-up pump priming routine to obtain data values that are used to calculate the pressure loss coefficients COEF 1  and COEF 2  that define a P loss  curve. At start-up, the pump priming routine begins. Such a routine is described in U.S. patent application Ser. No. 13/782,660, filed Mar. 1, 2013, which published as U.S. Publication No. 2013/0267779, and which is hereby incorporated by reference in its entirety. The pressure loss equation thus results in a calculated pressure loss P loss  for a pump system having an unidentified tubing size and length, an unidentified endoscope and an unidentified cannula disposed between the pump and the surgical site of a joint. 
     Unlike the first embodiment discussed above, wherein the hardware such as the endoscope, the cannula, and the tubing are identified, in this embodiment pump priming execution is necessary to determine the coefficients COEF 1 , COEF 2  for the second order polynomial equation defining a P loss  curve. 
     Unlike the first embodiment, wherein the inflow coefficient COEF INFL  is determined from the identified hardware, COEF INFL  is determined from a look-up table in view of the values of coefficients COEF 1 , COEF 2 . In some embodiments, properties of the inflow tubing  22  may be obtained by the pump control processor  100  from the inflow pump cassette before start-up. 
     Recognized Surgical Device: 
     Surgical devices  32  manufactured by the manufacturer of the pump system  10  recognize each other&#39;s signals and thus are capable of two-way communication. Thus, performance parameters of surgical devices  32  and cutting accessories can be communicated to the pump control processor  100 . In some embodiments for the shaver  36 , parameters including shaver identification information and identification information including the type and size of bur or other surgical device accessory disposed on the shaver is provided automatically to the pump control processor  100 . Further, the ON/OFF condition, the specific cutter or bur used, the type of operating mode selected for the shaver (examples are Forward, Reverse, Oscillation, etc.), the real-time RPM value of a shaver motor during operation, and other properties can be provided to the pump control processor  100  via the communication bus to optimize the performance of the pump  14 . Further, a window size and window position of a surgical device and/or cutting accessory can be provided to the pump control processor  100 . 
     In some embodiments, the dimensions of a flow path through a surgical device handpiece and the position of a lever controlling flow through the path can be provided over the communication bus to the pump control processor  100 . In some embodiments surgical device identifiers and cutting accessory identifiers are sent over the communication bus to the pump control processor  100  and values for the bur size, window size, and flow path dimensions that are previously stored in the pump memory can be retrieved. 
       FIG.  3    is a flowchart of the steps of a portion of a pump flow control routine  200  executed by the pump control processor  100  that emphasizes the identification of a cutting accessory. At step  202 , the type of joint, maximum and minimum flow rates, a desired or best flow rate that minimizes fluid consumption and maintains good visibility, a maximum pressure value, a desired pressure value and other types of information, including but not limited to the information or parameters listed and shown in  FIG.  2   , can be provided to the pump control processor  100 . The information can be manually entered into the pump control processor  100  via an input device, read or downloaded automatically from a memory card or the like, or provided by other means. Then the routine advances to step  204 . 
     At step  204  surgical device information, including identification information for a cutting accessory attached thereto, is provided to the pump control processor  100 . As discussed above, the information can be provided over a communication bus. The surgical device  32  can include an RF reader to identify an RF tag secured to the cutting accessory. In another embodiment, the pump includes an RF reader to identify RF tags secured to both the surgical device and the cutting accessory. The routine then advances to step  206 . 
     At step  206 , the routine or program executed by the pump control processor  100  compares pump settings with predetermined disposable fluid flow characteristics. An algorithm or program uses a look-up table, calibration curves, and in some embodiments additional information to determine ideal fluid inflow and fluid outflow rates for operation of the pump  14 . At step  208 , the pump inflow control signals, and in some instances outflow information, is provided to the inflow pump motor and to additional devices to obtain ideal in-joint pressures and fluid flow at the surgical site. 
     A feedback path (not shown) from step  208  returns to a program or routine whereat an algorithm recalculates pump flow rates based on one or more of real-time joint pressure, inflow head pressure, pump motor speeds, surgical device speed, and ON/OFF condition. Typically, the routine does not need to re-identify the surgical device or the cutting accessory. Further, the user joint settings, such as desired joint pressure, maximum and minimum joint pressure, maximum and minimum fluid flow through the joint, and desired fluid flow information typically do not change, and thus the routine typically does not return to step  202  until one cutting operation ends and another cutting operation begins. 
     In one example, for a shaver operating at a motor speed of 12,000 RPM with a 5.0 mm round bur attached thereto, and a desired pressure value of 70 mmHg, the algorithm or routine executed by the pump control processor  100  provides outputs to the inflow pump motor, the outflow pump motor, and in some instances to other devices including outflow pinch valves, to obtain the desired joint pressure of 70 mmHg, while maintaining desirable inflow and outflow rates for the pump output. 
     When the shaver  36  is operated, the pump control processor  100  receives the ON/OFF condition and the RPM output value of the shaver and calculates and controls the inflow pump RPM value that is output by the inflow pump motor, controls the outflow pump motor, and controls pinch valves provided with or near an outflow cassette by opening a valve for the outflow tubing  34  connected to the shaver while closing a separate outflow tubing  28  from the outflow cannula  30 . 
     The additional surgical device information, along with the joint pressure values calculated or sensed as described above, enable the pump control processor  100  of the pump  14  to more accurately control the P joint  value and fluid flow rates that result in surgical site conditions that closely correspond to the selections or inputs of an authorized medical user operating the pump system  10 . 
     As the shaver is identified, a non-linear outflow rate to RPM curve is provided with a look-up table containing coefficients to predict the outflow rate based on the outflow RPM for controlling the pump to provide a desired or best outflow rate. This is also the procedure for a recognized RF probe. 
     User preferences and other information from the pump control processor  100  can be provided to the surgical device  32 , such as the shaver  36  and RF ablation device  38 . The preferences can include surgical device settings preferred by the medical user that will be operating the surgical device  32  and the pump system  10 . 
     Unrecognized Shaver and RF Ablation Surgical Devices: 
     The pump  14  can be utilized with unrecognized third-party surgical devices  32  that are not identifiable by the pump control processor  100 . Such RF ablation devices and shaver devices are typically connected to power outlets located on the backside of the pump housing. Located within the pump housing are current and/or voltage sensing devices that sense a current waveform of the power drawn by the unrecognized surgical devices when operated. Instantaneous and past changes in the current waveform can be normalized to changes in the applied mains voltage and the pump control processor  100  can execute a linear-discrimination algorithm to optimally differentiate between times when the unidentified surgical devices are off and when the surgical devices are activated to treat or cut tissue. 
     As discussed above, the critical flow rate values and maximum pressure value for the surgical site  12  at the joint are typically different during operation of a surgical device  32  as compared to during non-operation of the surgical device. Therefore, sensing surgical device activation enables adjustments to the desired joint pressure value and fluid flow by control of the inflow pump motor, outflow pump motor and other devices while the surgical device is activated. 
     In-Joint Sensor: 
     In some embodiments an in-joint sensing device includes an in-joint pressure sensor and/or an in-joint temperature sensor that are disposed at or adjacent the surgical site. The in-joint sensing device can obtain and send a real-time pressure value from the surgical site  12  to the pump control processor  100 , thereby avoiding reliance on the calculated P loss  curves discussed above. The in-joint sensing device also reduces time delay in determining pressure changes in the joint. For instance, when pressure changes are measured upstream, there is a delay in the pressure change at the joint propagating through the inflow tubing to the sensor in the pump  14 . The in-joint pressure sensor also removes the upstream pressure measuring influence of hydrostatic head which occurs due to height differences between the pump and the cutting accessory located at the surgical site. Therefore, the pump need not be maintained at the same level or height as the surgical site. 
     Overpressure: 
     Regardless of the type of P joint  calculation or direct pressure measurement, a P joint  value must not exceed a predetermined pressure value. Thus, when an overpressure condition is calculated or measured, the pump control processor  100  performs at least one of operating outflow pinch valves, reducing the RPM value of the inflow pump motor, and other steps to reduce the joint pressure. 
     Plasma Field Stability: 
     It has been found that when certain electrical characteristics are not maintained at a threshold level (or within a certain range), significant instability in a plasma field can occur at the surgical site. The stability of the plasma field is significantly influenced by the suction rate through a probe. Higher flow rates tend to show more instability in the plasma field. Accordingly, stability thresholds can be determined for each different type of probe, and the pump  14  can dynamically control the suction rate in order to maintain the electrical characteristic value above the stability threshold, while having a goal of keeping the suction rate as high as possible while maintaining stability of the plasma field. 
     The pump control processor  100 , via the RF probe  38 , measures one or more of the electrical characteristic values of the RF probe  38  when activated. Through integration with the pump  14 , the electrical characteristics of the RF probe  38  can be delivered to the pump  14  in real time. 
     In one embodiment, an algorithm or routine, as shown in  FIG.  4   , is utilized to attempt to maintain a stable plasma field. The suction level achieved by the pump  14  starts at a low value when the RF probe  38  is activated, and the pump system  10  samples the electrical characteristic value(s) for the activated probe. 
     Specifically, once the algorithm is started, based on the probe type, the controller  100  sets variables of a base suction value, a lower threshold electrical characteristic value, an upper threshold electrical characteristic value, and a suction increment value (step  302 ). The algorithm then moves on to the step of determining whether it should hold the suction value below the maximum value (step  304 ). If the answer to this question is YES, then the algorithm moves to step  306  at which the max flow logic is held. If the answer to step  304  is NO, then the algorithm moves to step  308  at which the incoming probe electrical characteristic value is assigned to an array. The algorithm then moves to step  310 , at which if the probe has just been activated, the suction value is changed to a default low value, which may be zero. 
     The algorithm then moves on to step  312  at which it is determined whether the required length of time has been met for sampling data. If the answer to this question is NO, then the system continues to acquire data sampling until the required time value is met. Once the required time length has been achieved for sampling data, the algorithm moves to step  314 , at which an average electrical characteristic value is calculated for the sampled data. A standard deviation for the sampled data is also calculated. 
     Once the average electrical characteristic value and standard deviation are calculated, the algorithm moves to step  316 , at which it is determined whether the average electrical characteristic value is greater than the upper threshold voltage value and whether the hold max flow has been disabled. If the answer to both of these questions is YES, then the algorithm moves to step  318  at which the suction rate is increased by the suction increment value. The algorithm then goes back to step  308  to add the incoming electrical characteristic value to an array and the data is sampled again. If the answer to either of the questions of step  316  is NO, the algorithm moves to step  320 , at which it is determined whether the average electrical characteristic value is less than the lower threshold electrical characteristic value. If the electrical characteristic value average is less than the lower threshold electrical characteristic value, then the algorithm moves to step  322 , at which the suction is set to the base suction value. If the answer to the question of step  320  is NO, the algorithm moves to step  324  to maintain the suction at the same level. 
     In another embodiment, instead of at step  322  setting the suction to a low, base value, the suction rate is incrementally decreased based either on the suction increment value assigned at step  302 , or a second suction increment value. 
     In another embodiment, the suction rate may be increased depending on the actual value measured. Thus, instead of having a fixed incremental increase, the increase in flow rate is calculated using a particular function depending on the actual value of an electrical characteristic, such as voltage, which may allow the suction rate to increase more when needed, but not at other times. 
     The algorithm  300 , and in particular the electrical characteristic reading and sampling, could also be used to determine if the system is clogged with tissue and could help with declogging the system. When a probe is clogged, the sampled electrical characteristic sustains a value above an upper threshold which causes the algorithm to increase the suction to the maximum value very quickly. This sustained maximum value can be used as an indicator that the probe is clogged. 
     A similar algorithm could use the information that the probe is clogged to have the pump try a number of different methods to declog the probe, such as pulsing the outflow suction, increasing the joint pressure, and increasing the outflow motor RPMs beyond a set limit to attempt to achieve a higher suction. 
     The algorithms and system described herein improves the RF device performance and may reduce clogging. Performance of the system is improved by maintaining a more stable plasma field as the surgeon resects tissue. 
     Although particular preferred embodiments of the invention have been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.