Abstract:
A fluid pump system having a first fluid pump for pumping fluid from a source to a surgical site and a second fluid pump for removing fluid from the surgical site at a first predetermined rate, wherein said fluid pump system intermittently operates in conjunction with a surgical tool which, when operational, removes fluid from the surgical site at a second predetermined rate greater than said first predetermined rate, the improvement including a sensor for sensing a predetermined parameter of the surgical tool and providing an output signal indicating that the surgical tool is operating; and an actuating means responsive to said output signal to actuate said second fluid pump to remove fluid from the surgical site at second predetermined rate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 14/061,992, filed on Oct. 24, 2013, which is a divisional of U.S. patent application Ser. No. 11/642,457, filed on Dec. 20, 2006, now U.S. Pat. No. 8,591,453. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to systems for the irrigation and/or aspiration of fluids into or from a surgical work site during an endoscopic procedure. More particularly, the invention relates to a multi-purpose irrigation/aspiration system for use during minimally invasive surgery for the purpose of performing any one of a variety of irrigation/aspiration functions such as, for example, tissue lavage, joint distension or uterine distension. Still more particularly, the invention relates to an irrigation/aspiration system having a common control system operating two separate pumps, one pump dedicated to irrigation and one pump dedicated to aspiration. Still more particularly the invention relates to controlling the outflow fluid when an aspirating surgical tool is used with the system. 
       BACKGROUND OF THE INVENTION 
       [0003]    Minimally invasive surgery also referred to herein as endoscopic surgery, often utilizes an irrigation system to force suitable biocompatible fluid into the area surrounding the surgical work site within a patient. The term “irrigation” is used broadly to mean any type of pressurized fluid flow whether it be for irrigation in particular or for other uses described below. Flexible plastic tubing is used to conduct the fluid from a source to the work site and from the work site to a drain or other receptacle. Flexible tubing is also sometimes used as a pressure monitoring line to convey fluid pressure information to a control mechanism. Depending upon the procedure, the irrigating fluid is useful for various purposes such as tissue lavage, hydro-dissection, joint distension, uterine distension, etc. Known irrigation systems include electrically driven pump systems, in which a suitable fluid is pumped through flexible tubes from a source to the work site, gravity-feed systems, in which the pump is replaced by merely adjusting the height of the fluid supply above the patient, and nitrogen powered systems. 
         [0004]    Irrigation systems generally utilize a means to set the pressure desired at the surgical work site. A feedback loop uses information from a pressure sensor to maintain the set pressure within a desired range. The invention described herein includes improvements in pressure control. 
         [0005]    Known aspiration systems employ a source of reduced-pressure (i.e. lower than that of the work site) and include vacuum systems, in which a vacuum source is simply connected via flexible tubes to the work site, and simple gravity controlled drain lines. Aspiration of the fluid serves to either simply remove it to improve visibility, prevent undesirable fluid accumulation or high pressure at the work site, or to regulate the flow rate to maintain a predetermined fluid pressure at the work site. 
         [0006]    Because the irrigation and aspiration functions are commonly used together, prior art irrigation/aspiration systems have been developed to perform both functions with one system, often combined in one console which provides power and control. The irrigation system is generally used in conjunction with an aspiration system which removes the fluid pumped into the work site at a controlled rate depending on the flow rate selected by the surgeon. Dual pump irrigation and aspiration systems are known where one pump is dedicated to the irrigating function and another pump is dedicated to the aspirating function. Each system utilizes a collection of flexible tubes to connect the fluid and vacuum sources to appropriate instruments inserted into the body. The collection of tubes includes a fluid inflow conduit, a fluid outflow conduit and, in some instances, a pressure monitoring conduit. All of the tubes are packaged together as a tubing set and each tubing set is produced as a unit containing all necessary tubes and connections required for performing a particular procedure with a particular system. This invention relates to improvements in dual pump irrigation/aspiration systems. 
         [0007]    Consequently, it is an object of this invention to produce an irrigation/aspiration system having an inflow pump and an outflow pump and a control system for operating each pump in accordance with predetermined characteristics defined for use during a selected one of several different surgical procedures. 
         [0008]    It is also an object of this invention to produce a multi-purpose irrigation/aspiration system capable of operating with a variety of specific types of tubing sets, each set intended for use only during a particular type of surgical procedure. 
         [0009]    It is also an object of this invention to produce a multi-purpose irrigation/aspiration system capable of operating with a variety of specific types of tubing sets which are each identified with a particular coding means associated with that tubing set type to identify the use for which the tubing set and/or the system associated therewith is intended. 
         [0010]    It is also an object of this invention to produce two tubing cassettes for use with a multi-purpose irrigation/aspiration system wherein one cassette is dedicated to and facilitates the engagement of the irrigation tubing with the system and the other cassette is dedicated to and facilitates the engagement of the aspiration tubing with the system. 
         [0011]    It is still another object of this invention to produce a dual pump irrigation/aspiration system having a flow control system which automatically changes the outflow of fluid based on whether another tool, such as a shaver blade handpiece is activated to withdraw additional fluid from a surgical work site. 
         [0012]    It is yet another object of this invention to produce a dual pump irrigation/aspiration system having varying size peristaltic rollers and associated tubing cassettes to facilitate proper assembly. 
         [0013]    It is also an object of this invention to produce a dual pump irrigation/aspiration system having a flow control system capable of controlling selectively pressure and flow on the basis of actual intra-articular pressure or a calculated/inferred pressure. 
         [0014]    It is also an object of this invention to produce a dual pump irrigation/aspiration system having a valve means and a control for the valve means capable of drawing outflow fluid from selected outflow tubes. 
         [0015]    It is yet another object of this invention to produce a dual pump irrigation/aspiration system having a software driven declogging feature. 
       SUMMARY OF THE INVENTION 
       [0016]    These and other objects of this invention are achieved by the preferred embodiment disclosed herein which is a dual pump multi-purpose irrigation/aspiration pump system. The system is designed with a first pump to pump fluid from a source of irrigating fluid and a second pump to provide a source of aspirating vacuum during an endoscopic surgical procedure at a surgical work site. The system comprises a common console and a pump flow control system for controlling both a peristaltic inflow pump and a peristaltic outflow pump. The flow control system utilizes inflow and outflow pressure sensors and inflow and outflow flow rate controls. A tubing set comprising an inflow cassette housing, an outflow cassette housing and a plurality of flexible conduits is used to connect the source of irrigating fluid and aspirating vacuum to the surgical work site. The tubing set contains inflow and outflow pressure transducers and connects them to pressure sensors in the console. The tubing set is adapted for use during a predetermined type of surgical procedure and contains a coding means which carries a code to identify the type of surgical procedure and selected predetermined fluid pressure and flow characteristics associated therewith. Decoding means is provided on the console for reading the coding means to determine the code. Retention means is provided for receiving and holding the tubing cassettes and operatively engaging them and portions of the flexible conduits with their respective (inflow or outflow) pump, the flow rate control means and the decoding means. Also provided is a control means responsive to the code and the pressure sensors for controlling the inflow and outflow fluid pressures and flow rates in accordance with the predetermined characteristic identified by the code. 
         [0017]    A further aspect of this invention is embodied in a system using two tubing cassettes, each for use with a respective one of the irrigation/aspiration pumps accessible on a single power/control console. The tubing cassettes comprise an inflow cassette housing which holds a first flexible tube for supplying irrigation fluid from a fluid source to the surgical work site and an outflow cassette housing which holds a second flexible tube for communicating a vacuum created by the outflow pump to the surgical work site. Additionally, the cassettes may also be provided with pressure transducers for communicating pressure data from inflow and outflow pressure transducers to pressure sensors on the console. The cassette housings for receiving the tubes comprise a code carrying means. The tubing cassettes are adapted to automatically align predetermined parts of the housing, code means and tubes with associated parts of the system console. 
         [0018]    In one aspect of this invention a fluid pump system is provided for supplying fluid to and removing fluid from a surgical site, the system comprising a first peristaltic pump for supplying fluid, the first peristaltic pump having a roller assembly of a first predetermined diameter, and a second peristaltic pump for removing fluid, the second peristaltic pump having a roller assembly of a second predetermined diameter, the second predetermined diameter not equal to the first predetermined diameter. 
         [0019]    Another aspect of this invention is an improvement in a fluid pump system which has a first fluid pump for pumping fluid from a source to a surgical site and a second fluid pump for removing fluid from the surgical site at a first predetermined rate wherein the fluid pump system intermittently operates in conjunction with a surgical tool which, when operational, removes fluid from the surgical site at a second predetermined rate greater than the first predetermined rate. The improvement comprises a sensor for sensing a predetermined parameter of the surgical tool and providing an output signal indicating that the surgical tool is operating. The improvement further comprises an actuating means responsive to the output signal to actuate the second fluid pump to remove fluid from the surgical site at second predetermined rate. 
         [0020]    Another aspect of this invention is an improvement in a fluid pump system which has a first fluid pump for pumping fluid from a source to a surgical site and a second fluid pump for pumping fluid from the surgical site to a fluid drain and for removing fluid from the surgical site at a first predetermined rate, wherein the fluid pump system intermittently operates in conjunction with a surgical tool which, when operational, removes fluid from the surgical site at a second predetermined rate greater than said first predetermined rate. The improvement comprises a first input tube joining the surgical site to the second pump and a second input tube joining the surgical tool to the second pump and a shuttle means for alternatively pinching one or the other of the first and second input tubes, or neither tube. The shuttle means comprises a movable pinching member, moving means for moving the movable pinching member between a first position in which neither of the first or second tubes is closed, a second position in which only the first input tube is closed and a third position in which only the second input tube is closed. The improvement also comprises a control means for sensing the position of the moving means and for producing signals alternatingly representing the first, second and third positions. 
         [0021]    Another aspect of the invention is a method for determining the pressure at a surgical work site in a variety of ways. Various pressure data sources are provided and a selected source is used in the feedback control loop to maintain the set pressure within a predetermined range. The system determines which pressure data sources are available and compares data to determine reliability of the data before selecting the pressure data source to be used. More specifically the invention includes a method for determining the pressure at a surgical work site during an endoscopic surgical procedure utilizing a fluid inflow pump, inflow tubing and an inflow cannula for conveying fluid from a fluid source to the surgical work site and a fluid outflow pump, outflow tubing and an outflow cannula for conveying fluid from the work site to a drain. The method further utilizes a pressure feedback control loop intended to maintain fluid pressure at the surgical work site at a pressure set point by determining actual pressure at the surgical work site and adjusting pressure and flow parameters to maintain the actual pressure at or near the set point pressure. The method comprises the steps of providing a first pressure determining means comprising a pressure sensor near the inflow pump to measure actual pressure at the output of the inflow pump; selectively providing a second pressure determining means comprising a pressure sensor at the surgical work site to measure actual pressure in the joint and providing a third pressure determining means comprising a joint pressure inferring system to calculate the actual pressure at the surgical work site using known and measurable pressure and fluid flow characteristics. The method further comprises selecting either the first, second or third pressure determining means as the source of the actual joint pressure to be used in the feedback control loop. The method may include the step of determining if a signal indicative of pressure is present at the surgical work site and, if so, using such signal to control operation of the pump. 
         [0022]    In yet another aspect of the invention the irrigation/aspiration system is provided with a means for declogging a surgical tool which may suffer a blockage. More specifically, this declogging feature is included within a fluid pump system having a first fluid pump for pumping fluid from a source to a surgical site and a second fluid pump for removing fluid from the surgical site at a first predetermined rate. The fluid pump system intermittently operates in conjunction with a surgical tool which, when operational, removes fluid from the surgical site at a second predetermined rate greater than the first predetermined rate. The declogging feature comprises the method of removing a blockage in the outflow fluid path of the surgical tool wherein the method comprises the steps of producing a declogging signal, communicating the declogging signal to the fluid outflow pump to thereby cause the pump to reverse flow direction for a predetermined period of time and subsequently to return to operation in the forward direction for a different predetermined time. During the period of reversed flow, the surgical tool may be withdrawn from the work site so the clog may be directed to a waste container. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a front elevation view of a dual pump irrigation/aspiration console constructed in accordance with the principles of this invention. 
           [0024]      FIG. 2  is a schematic view of the tubing set for use with the console of  FIG. 1 . 
           [0025]      FIG. 3  is a view of the console of  FIG. 1  assembled with the tubing set of  FIG. 2  and connected for use during an arthroscopic procedure. 
           [0026]      FIG. 4A  is a schematic diagram of the shaver sensor component of the system. 
           [0027]      FIGS. 4B and 4C  are top and bottom perspective views of the shaver sensor shown schematically in  FIG. 4A . 
           [0028]      FIG. 5  is a cross-sectional view of  FIG. 1  taken along the line A-A and omitting certain components for clarity. 
           [0029]      FIG. 6  is a front perspective view of a slidable shuttle valve member. 
           [0030]      FIG. 7  is a rear perspective view of  FIG. 6 . 
           [0031]      FIG. 8  is a cross-sectional view of  FIG. 1  taken along the line  8 - 8  with certain components omitted for clarity. 
           [0032]      FIGS. 9 a  and 9 b    are plan and elevation views, respectively, of  FIG. 5  showing the components in one particular state of operation. 
           [0033]      FIGS. 10 a  and 10 b    are plan and elevation views, respectively, of  FIG. 5  showing the components in another state of operation. 
           [0034]      FIGS. 11 a  and 11 b    are plan and elevation views, respectively, of the components of  FIG. 5  in yet another state of operation. 
           [0035]      FIG. 12  is a bottom perspective view of a portion of  FIG. 1  showing portions of the outflow cassette and shuttle valve. 
           [0036]      FIG. 13  is a flowchart of a portion of the control system incorporated into the console of  FIG. 1 . 
           [0037]      FIG. 14  is a schematic pressure/flow diagram describing various components of the system depicted in  FIG. 3 . 
           [0038]      FIG. 15  is a flowchart of the declogging procedure portion of the control system used in the console of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Referring now to  FIGS. 1 and 2  there is shown an exemplary dual pump irrigation/aspiration system  10  constructed in accordance with the principles of this invention and comprising pump console  12  and tubing set  14 . Pump system  10  is adapted to deliver irrigating fluid from a fluid source to a surgical work site, at a selected pressure and flow rate, in an exemplary set up as shown in  FIG. 3 . The pump is suitable for use during a variety of selected surgical procedures and is, therefore, designed to be operable over a wide range of pressure and flow as selected by the user on control panel display  11  by up/down pressure control buttons to set desired pressure and up/down flow rate control buttons to set desired flow. After being set, display  11  can show actual pressure and/or flow. In the preferred embodiment, the pressure is selectable in 5 mm Hg increments between approximately 0 and 150 mm Hg. The inflow flow rate is selectable between approximately 0 and 2,500 ml/min (milliliters/minute) in the laparoscopic mode and in discrete amounts of 50, 100 or 150 ml/min in the arthroscopic mode (with the outflow flow rate also being 50, 100 or 150 ml/min respectively). As will be understood below, the rates may increase when auxiliary devices are used to remove a greater amount of fluid. Pressure and flow rate are both controlled by a flow control system incorporated into system  10 , the flow control system being microprocessor controlled and menu-driven. Pump console  12  and tubing set  14  serve to communicate fluid from source  34  via irrigation or inflow tubing  16  to the work site  18  and from the work site via aspiration or outflow tubing  20  to a drain  22 . Pump console  12  comprises an inflow peristaltic pump  30  and an outflow peristaltic pump  40 . 
         [0040]    Tubing set  14  comprises a plurality of elongated flexible conduits (such as polyvinyl chloride (PVC) tubes) which are retained in predetermined relationships to each other by cassettes  36  and  44  (described below) situated at points intermediate the ends of the various tubes of the tubing set. Tubing cassettes  36  and  44  of the present invention facilitate the engagement of the tubing set to the console  12  by holding intermediate peristaltic roller tubes  50  and  60 , respectively, in predetermined open loop shapes (where the ends of the tubes are attached to laterally spaced bores on the cassette housings). This enables the user to easily and one-handedly place the two cassettes into position at their respective cassette receiving stations on pump console  12 . Tubing set  14  is representative of a disposable tubing set usable with pump system  10 . Each tubing set may be associated with a particular procedure and may have a differently colored cassettes or cassette labels and each separate tube attached to each cassette could be identified by different colors or markings to facilitate hooking up the system to the patient and fluid supplies. The different colors or other indicia could indicate that the code associated with the tubing set causes the system to be programmed to automatically limit flow and pressure ranges depending upon the procedure for which the tubing set is designed. 
         [0041]    Tubing set  14  comprising inflow tubing  16  and outflow tubing  20 . Inflow tubing  16  comprises inflow tubes  32   a ,  32   b  and  32   c , inflow cassette  36  and inflow tube  38 . Tubes  32   a ,  32   b  and  32   c  provide for communicating fluid from fluid source(s)  34  to inflow tubing cassette  36  attached to the inflow peristaltic pump  30  and then to inflow tube  38  connected to an endoscope sheath  39  or other appropriate inflow device to communicate the fluid to the work site  18 . Outflow tubing  20  comprises a main outflow tube  42 , outflow cassette  44 , auxiliary outflow tube  72  and outflow tube  46 . Outflow tube  42  is connected to a working cannula  43  and is adapted to provide a normal, relatively low flow fluid outflow path for fluid being aspirated from the work site  18 . Auxiliary outflow tube  72  is adapted to provide increased fluid outflow from the work site  18  as will be understood below. Both outflow tubes  42  and  72  are connected to the outflow peristaltic pump  40  as will be understood below. 
         [0042]    Inflow tubing  16  further comprises the aforementioned intermediate roller tube  50  (on inflow cassette  36 ) interposed between inflow tubes  32   a  and  38 . Cassette  36  and roller tube  50  are adapted to engage inflow peristaltic pump  30  at an inflow cassette receiving station  31  on the front of pump console  12 . Outflow tubing  20  further comprises outflow cassette  44  which is adapted to hold the aforementioned intermediate roller tube  60  interposed between outflow tubes  42 / 72  and  46 . Outflow cassette  44  and outflow intermediate roller tube  60  are adapted to engage outflow peristaltic pump  40  at an outflow cassette receiving station  41 . Each cassette  36  and  44  is provided with a pressure transducer member on its rear surface. Both cassette receiving stations  31  and  41  have pressure sensors  75  and  76 , respectively, on front panel  102  behind cassettes  36  and  44 , respectively, as best seen in  FIG. 1 . The sensors  75  and  76  are adapted to read the pressure when the associated cassette is properly installed. 
         [0043]    The operation and structure of cassettes  36  and  44  and pressure sensors  75  and  76  is best understood by reference to U.S. Design Pat. 513,801 (Stubkjaer) issued Jan. 24, 2006, U.S. Design  513 , 320  (Stubkjaer) issued Dec. 27, 2005 and U.S. Ser. No. 10/701,912 (Blight et al.)(Publication No. US2005/0095155), filed Nov. 5, 2003, all assigned to the assignee hereof and incorporated by reference herein. 
       Different Size Pump Heads 
       [0044]    Cassettes  36  and  44  facilitate the attachment of tubing set  14  to the input and output peristaltic pumps  30  and  40 , respectively. In the preferred embodiment the cassettes are further improved over the aforementioned references by making the sizes of certain components on the inflow side of the system different from the sizes on the outflow side to avoid improper installation of tubing set  14  on pump console  12 . Attachment of the tubing improperly could create an unsafe situation. While size variations may be achieved in a variety of ways, in the preferred embodiment as best seen in  FIGS. 1-3  the size of the loop formed by inflow intermediate roller tube  50  is different than the size of the loop formed by the outflow intermediate roller tube  60 . The relative sizes of the roller assembly of each peristaltic pump are also different and adapted to fit on and work with the chosen loop size. The size of the inflow and outflow cassettes and the tube lengths, i.e. the distances along the intermediate roller tubes between the loop ends  36   a  and  36   b , and  44   a  and  44   b , respectively (i.e. the length of the roller tubes), is varied to assure that cassettes  36  and  44  can only be installed one way on their respective receiving station. Furthermore, inflow cassette  36  has a loop length L between the top of the peristaltic roller and the top of cassette  36  when the latter is installed at its cassette receiving station. Outflow cassette  40  has a similarly defined loop length L′ at its receiving station. In the preferred embodiment the peristaltic rotor (roller assembly) of the inflow peristaltic pump  30  has a diameter (2.89 inches, 73.4 mm), larger than the rotor of the outflow peristaltic pump  40  (2.45 inches, 62.2 mm). The tube lengths of the intermediate roller tubes are chosen to avoid too little tension (i.e. too long a tube) or too much tension (i.e. too short a tube) on the rotor. In the preferred embodiment the inflow and outflow roller tubes  50  and  60  are made of 50A C-Flex® TPE from Consolidated Polymer Technologies, Largo, Fla., and each has an outside diameter of 0.440 inches (11.18 mm), an inside diameter of 0.305 inches (7.75 mm), and a wall thickness of 0.068 inches (1.73 mm). The inflow roller tube  50  is 8.75 inches (222.25 mm) long and the outflow roller tube  60  is 7.25 inches (184.15) long. These dimensions, when applied to cassettes having roller to cassette distances of L, approximately equal to 4.36 inches (110.74 mm), and L′ approximately equal to 3.54 inches (89.92 mm) enable the cassettes to be properly installed one-handedly onto their respective receiving stations with an acceptable amount of force. In the preferred embodiment the rotors may also be color coded to match the proper inflow or outflow cassette to further facilitate proper installation. Additionally, the intermediate tubes  50  and  60  may also be color coded. 
         [0045]    The loop and rotor size variations of the preferred embodiment have several advantages. Improperly reversing the inflow and outflow cassettes will be almost impossible since placing the larger loop on the smaller rotor (i.e. inflow cassette on outflow rotor) will not only be apparent to the user but will result in a failure to operate. The flexible intermediate tube will simply be too loose. Also, placing the smaller loop on the larger rotor (i.e. outflow cassette on inflow rotor) will also be apparent to the user because the intermediate tube will be stretched too tightly to operate properly, and the force required to place the outflow cassette on inflow rotor will be so high as to make it noticeable to the user that something is wrong. It has been found that there is a relationship between the force required to properly and easily place each cassette (using only one hand) at its respective cassette receiving station. For any given roller tube structure (i.e. diameter, wall thickness, length, etc.) the ratio of tube length to loop length is in the range of approximately 1.7 to 2.1, preferably about 1.9. 
       Shave Sensor and Shuttle Valve 
       [0046]    During a surgical procedure a shaver blade handpiece  70  may be used within cannula  43  in conjunction with a shaver blade  73  to resect tissue and otherwise remove debris from the work site  18 . The resected tissue and debris are aspirated from the work site  18  along with fluid via cannula  43  and main outflow tube  42 . This fluid path is normally open and the fluid flows at a relatively low rate during the surgical procedure to maintain pressure at the site and to clear debris. However, when handpiece  70  is operating fluid is made to flow at a higher rate via auxiliary outflow tube  72 . In the preferred embodiment of the invention, system  10  further comprises a means to identify when shaver handpiece  70  is operating so that the pump control system can automatically establish the higher rate of flow. This is accomplished by sensing a predetermined operating parameter of the handpiece and using this information to activate a fluid diverter. 
         [0047]    As shown in  FIG. 3 , to use a shaver handpiece a handpiece drive console  80  is connected via power line  82  to handpiece  70 . In the preferred embodiment a shaver sensor means  84  is used to sense operation of the handpiece by detecting a parameter associated with the power line attached to the handpiece. Sensor  84  is connected via signal line  86  to pump console  12 . As will be understood below, sensor  84  via associated circuitry in pump console  12  identifies when the handpiece  70  is activated and therefore when the fluid flow rate through inflow cassette  36  and outflow cassette  44  must increase to compensate for the fluid withdrawn from the work site by handpiece  70 . 
         [0048]    As schematically shown in  FIGS. 3, 4A, 4B and 4C , sensor  84  is removably mechanically clamped onto power cable  82 , preferably near the console  80  end in order to place it outside of the sterile field, and includes a resonant circuit/antenna  87 , an amplifier  89 , a comparator  88  and oscillator  90 . The signal detected by coil  87  is ultimately delivered to console  12  on signal line  86  as a frequency output of oscillator  90 . The input to the oscillator comprises three switches  92 ,  93  and  94 . Switch  92  is adapted to provide an input to oscillator  90  on the power-up of sensor  84  (i.e. connection to console  12 ). This causes the frequency output of oscillator  90  to be 10 kHz. Switch  93  is adapted to provide an input to oscillator  90  upon the application of power to power line  82 , thus indicating the shaver handpiece  70  is running. This causes the frequency output of oscillator  90  to be 20 kHz. Switch  94  is adapted to provide an input to oscillator  90  upon receiving a signal from Hall sensor  95  representative of the presence of magnet  96  near the Hall sensor. Magnet  96  is located in a pivoting clamp  97 , one end  98  of which is movable relative to a base  99  containing the Hall sensor. When the clamp is placed on power line  82  the magnet is no longer detected by the Hall sensor (thus leaving switch  94  open). Switches  93  and  94  are adapted to work together to provide a 30 kHz oscillator output. The 30 kHz output is used to increase the speed of inflow pump  30  and to turn outflow pump  40  to the high flow mode and to perform other necessary functions to accomplish this as will be understood below. 
         [0049]    An advantage of sensor  84  is its ability to operate with a variety of shaver systems because it is easily attachable and detachable. The sensing circuit detects near-field radio frequency (RF) leakage (wide spectrum noise) generated by the shaver power line and is, therefore, compatible with all shaver systems (although the method works better with AC powered shavers.) 
         [0050]    To achieve a high flow mode, in addition to increasing the flow rate through inflow cassette  36  the control signal from shaver sensor  84  is used to activate a fluid diverter in the form of a shuttle valve  100 , best seen and understood by reference to  FIGS. 1 and 5 through 12 . Shuttle valve  100  is placed on the front panel  102  adjacent outflow cassette  44  at the point near where outflow tubes  42  and  72  enter a manifold (not shown) on outflow cassette  44 . The manifold is an element having two fluid inputs and one common output which serves to join both tubes  42  and  72  to a common peristaltic outflow intermediate roller tube  60 . The flow to the input side of intermediate roller tube  60  is controlled by passing both of the two fluid input tubes (i.e. outflow tubes  42  and  72 ) through shuttle valve  100 . 
         [0051]    Shuttle valve  100  is a pinch valve that operates by alternatingly pinching one or the other of the outflow tubes  42  or  72  closed. Shuttle valve  100  is accessible on the front panel  102  of pump housing  12  adjacent the outflow peristaltic pump  40 . As best seen in  FIG. 5 , shuttle valve  100  is attached to the front panel  102  and comprises a hollow slide housing  104  extending away from front panel  102  and containing a sliding shuttle member  106 . Housing  104  essentially provides a track within which shuttle member  106  can slidingly reciprocate. Housing  104  has a central opening  108  wide enough to receive both outflow tubes  42  and  72  when the outflow cassette  44  is loaded onto its cassette receiving station on the front of the pump housing  12 . Sliding shuttle member  106  includes a central opening  110  also adapted to receive both outlet tubes  42  and  72 . 
         [0052]    The operation of shuttle valve  100  is best understood by reference to  FIGS. 8 through 11 . In each of these drawings the outflow tubes  42  and  72  have been omitted for clarity. It should also be understood that  FIGS. 9A, 10A and 11A  are plan views taken along the section line A-A in  FIG. 1  while  FIGS. 9B, 10B and 11B  are front elevation views taken along the section line B-B in  FIG. 8 . 
         [0053]    Referring first to  FIG. 10A , it is noted that this view is identical to  FIG. 5  except for the fact that  FIG. 10 a    is a view with the outflow cassette  44  in place while  FIG. 5  is a view with the outflow cassette  44  omitted. Outflow cassette  44  includes a cover tab  120  which is sized to cover openings  108  and  110  in the slide housing  104  and shuttle member  106  respectively. Tab  120  supports a backing plate  121  which extends perpendicularly from tab  120  toward front panel  102 . Tab  120  is adapted to fit between outflow tubes  42  and  72  to facilitate selectively covering these tubes. As shown in  FIG. 12 , housing  104  is a shell generally conforming to the shape of shuttle member  106 . The hollow base of housing  104  is notched at slot  123  to provide lateral support for the bottom of the distal end of backing plate  121 . Housing  104  may be provided with a similar slot (not shown) to provide lateral support for the top of the distal end of backing plate  121 . 
         [0054]    In  FIG. 5  shuttle member  106  is shown within slide housing  104  in a central position symmetrically situated around housing  104  opening  108  which is thereby aligned with shuttle  106  opening  110 . As will be understood below, this position is automatically presented to the user upon start-up of system  10  in order to facilitate loading of tubing set  14 . In this central position shuttle member  106  enables outflow cassette  44  to be loaded onto outflow peristaltic pump  40 , as shown in  FIG. 10A , with outflow tubes  42  and  72  both received within opening  110  of shuttle member  106  and tab  120  situated between the tubes (not shown). As will be understood below, shuttle member  106  is movable both to the left and right of the central position shown in  FIG. 10 a   . As best seen in  FIGS. 6 and 7  shuttle member  106  has a left body member  122  and a right body member  124  situated on either side of central opening  110 , each member  122  and  124  having opposed and inwardly facing pinching surfaces  122   a  and  124   a  adapted to concentrate a squeezing force on outflow tubes  42  and  72 , respectively, by alternatively pushing one tube or the other against backing plate  121 . Shuttle member  106  has a rear surface  126  that can slide along the front panel  102 , rear surface  126  having a vertical slot  128  at the rear of rear surface  126 . Vertical slot  128  is adapted to engage a pin  130  extending through a rectangular slot  132  formed in front panel  102 . Pin  130  is in turn attached to an arcuate cam  134  driven about its axis by a rotatable output drive shaft  136 , driven in turn by shuttle drive motor  140 . It will be understood that the rotating elements of this mechanism could be replaced by a linearly reciprocating mechanism or any other suitable device. 
         [0055]      FIG. 10B  shows the relationship of the components of  FIG. 10 a    (taken along the line B-B of  FIG. 8  at the point in time represented by  FIG. 10A ). Cam member  134  has a generally semi-circular profile and an outer partially cylindrical arcuate surface  142  situated at a fixed radius from the axis of drive shaft  136 . Surface  142  terminates at opposite edges  144  and  146 . An optical sensor  150 , for example a light (or other radiation) emitting diode situated a predetermined distance from surface  142 , is focused on surface  142  and adapted to sense the position of shuttle member  106  in a non-contact manner by detecting the presence and absence of surface  142  in the field of view of sensor  150 . The shuttle member  106 , cam member  134  and sensor  150  are physically correlated so that a given position of cam member  134  corresponds to define when the shuttle member is centered in the position shown in  FIGS. 5 and 10A . In the preferred embodiment this correlation is achieved by having the shuttle member  106  in the central position shown in  FIG. 10A  when edge  144  of cam member  134  is situated so as to trigger a signal from sensor  150  that arcuate surface  142  cannot be detected. This ‘no-detect” signal is equivalent to detecting edge  144  and indicates to the control system that the shuttle valve member  106  is in its central position thereby indicating that neither of the outflow tubes  42  and  72  is being pinched or occluded. This is the loading and unloading state of the system when neither peristaltic pump is operating. 
         [0056]    Because of the clockwise direction of rotation of the peristaltic roller assemblies, the left side of each cassette  36  and  44  is the input side to its associated pump and the right is the output side of the pump. The input of inflow cassette  36  is provided only by single inflow tube  32   c . However, as will be understood below, the input of outflow cassette  44  is provided by two sources: outflow tube  42  and outflow tube  72 . As shown in  FIG. 2 , the exterior surfaces of these tubes may be physically joined to each other and to inflow tube  38  along a predetermined length to facilitate installation of tubing set  14 . While outflow tubes  42  and  72  may be discrete tubes joined along their outer surfaces, they may also be a single tube (not shown) having two lumens. Each lumen would of course be joined by a suitable adapter (not shown) where necessary to connect the lumen to other components. For this reason, outflow tubes  42  and  72  are herein sometimes referred to as a dual lumen tube. 
         [0057]    The shuttle control system incorporates a self-learning protocol on each start-up of console  12 . This feature compensates for any reversal of the polarity of the wiring of motor  140  and determines the home or center position where the shuttle valve must be placed to enable loading and removal of tubing set  14 . This feature operates as follows: (1) on startup a direction of rotation is arbitrarily selected and voltage of an arbitrary polarity is applied to motor  140  to drive it to one extreme of motion at which point current to the motor will increase; (2) at this point the output of detector  150  is determined (it will be either high or low depending upon whether surface  142  is detected or not); (3) the results of steps  1  and  2  are correlated in software and the system thus ‘learns” that whatever extreme position (polarity) resulted from step  1  it is thereafter associated with the signal of step  2 ; (4) the opposite extreme position (polarity) is therefore automatically associated with the other possible signal of step  2 . The zero, center position is then determined by simply reversing direction of the motor until the edge  144  crossover is detected. 
         [0058]    If at some point in the operation of pump console  12  there is detected the operation of an auxiliary device such as handpiece  70  (i.e. via an appropriate signal on line  86 ), the control system will interpret the signal from sensor  84  as a requirement to increase flow through shaver outlet tube  72  (the tube on the right side in  FIG. 3  and on the right side of shuttle opening  110 ). This will result in a signal to motor  140  to move in direction  154  to the position associated with shuttle member  106  being in the right-most position as shown in  FIG. 11 a   . If, however, it is determined desirable to continue drawing fluid from the left outlet tube  42  while pinching off the right outlet tube  72  (for example when shaver handpiece  70  is not running so oscillator  90  does not produce the 30 kHz signal), a signal is sent to motor  140  to rotate cam member  134  in direction  152 . This will result in sensor  150  detecting the presence of cam surface  142 , simultaneously moving pin  130  to the left thereby causing shuttle member  106  to move to the leftmost position as shown in  FIG. 9 b    to leave open the left tube while pinching the right tube. 
       Inferred Pressure Sensing System 
       [0059]    Pump system  10  utilizes a unique pressure sensing system to control the operation of inflow and outflow peristaltic pumps  30  and  40 . System  10  monitors the pressure at the surgical site and increases or decreases fluid flow through tubing set  14  to maintain the surgeon requested pressure (i.e. set pressure) at the site while maintaining some outflow to clear debris, etc. from the site. As will be understood below the system uses sensed and/or calculated/inferred pressure information to adjust various parameters to maintain set pressure. The pump fluid control system can operate by receiving pressure information from either the inflow cassette sensor  75  alone, both inflow and outflow cassette sensors  75  and  76 , or from a separate pressure sensing tube  45  attached to sensor port  47 . 
         [0060]    As shown in  FIG. 3 , tubing set  14  may be set up as a “one-connection” arthroscopic tubing set or as a “two-connection” arthroscopic tubing set. (In a “two-connection setup, optional tube  45  and pressure port  39   b  would be utilized, but in a “one-connection set-up they would not be utilized.) The term “one-connection” refers to the number of irrigating fluid and pressure sensing connections at the work site. A one-connection tubing set utilizes one fluid inflow line such as tube  38  to supply fluid to a work site during a surgical procedure and provides pressure information to the pump flow control system within the console via a pressure transducer attached to the fluid inflow line and operative with sensor  75  to produce a pressure value. In this case the pressure transducer is on the back of cassette housing  36  and sensor  75  is on front panel  102  adjacent cassette  36 . Sensor  75  senses pressure in fluid tube  38  as described in the aforementioned Publication No. US 2005/0095155. As will be understood by those skilled in the art, in arthroscopic procedures, one-connection systems are used with a simplified inflow cannula or scope sheath which does not have a separate pressure sensing port. Alternatively, an optional “two-connection” tubing set could also be used. In this case scope sheath  39  is provided with a fluid inflow port  39   a  and a separate pressure sensing port  39   b . The pressure sensing port  39   b  is connected via optional pressure sensing tube  45  to a pressure sensor/transducer  47  on pump console  12 . A two-connection tubing set provides a way to determine pressure at the work site while a one-connection tubing set determines pressure at a given point in the fluid path. The pressure at the work site is herein referred to as True Intra-articular Pressure (“TIPS”). 
         [0061]    Since use of the TIPS system is optional, pump system  10  includes a method for determining the source of pressure information used to adjust the fluid flow and pressure produced by the system. Upon start-up, pump system  10  goes through a pressure determination sequence to identify the source of pressure data. As shown in the flowchart of  FIG. 13 , pump system  10  first determines at block  200  whether inflow pump  30  is operating (running) or not (stopped). In either case the sequence of events regarding identifying the source of pressure data is the same. If the pressure sensed by the inflow cassette sensor  75  is greater than a predetermined amount, chosen in the preferred embodiment to be 25 mm Hg, the control system will check at block  202  to see if sensor  47  is producing a signal, thus indicating the optional TIPS line  45  is being used. If the pressure is under the 25 mm Hg threshold the system will default to operating in the “10K” mode, i.e. with measured pressure data coming from sensor  75 . If the measured pressure data exceeds the threshold and a TIPS signal is detected, block  204  will assure that the pump flow control system will continue to use this TIPS pressure data to control the operation of pump console  12 . If no TIPS pressure signal is detected, block  206  will determine whether to use pressure data from the inflow cassette sensor  75  only (the 10K mode) or from an alternate known as the Inferred Pressure Sensing (“IPS”) mode. The IPS system will only be used as a source of pressure data if (1) there is no TIPS signal at port  47  and (2) there is pressure data at both inflow cassette sensor  75  and outflow cassette sensor  76  and (3) there is a difference between the pressures sensed by the inflow and outflow cassette sensors  75  and  76 . 
         [0062]    The pressure values used by the pump flow control system are monitored such that if the TIPS or IPS pressure data fails or if the TIPS and IPS pressure values are significantly different (e.g. by an order of magnitude) the system will revert to the 10K mode for pressure information. The pump flow control system is a servo control loop using, as inputs to a proportional integral derivative (PID) comparator, a set point equal to the pressure selected by a user on control panel  102  and a feedback signal equal to the actual pressure measured by the system (i.e. from the 10K mode, TIPS or IPS). 
         [0063]    The Inferred Pressure Sensing (“IPS”) system is used to indirectly calculate pressure at the surgical site without measuring pressure directly as is done by the TIPS tubing. The IPS system produces a pressure value based on sensed pressure and calculated flow at certain points in the tubing set and calculating the effect of pressure drops associated with certain components of the set. The sensed and calculated/inferred values are used in various equations to arrive at a calculated value representative of the pressure at the surgical site without having to actually measure pressure at the site. The advantage of this is that it enables the system to provide increased pressure measurement accuracy even with a wide variety of cannulas of different sizes. The IPS system is a method of accounting for fluid flow drops and pressure losses and compensating for these drops and losses to thereby maintain a more accurate pressure at the surgical site. 
         [0064]    The mathematical equation describing fluid flow and pressure drops through the various tubes of tubing set  14  is a complex polynomial, although it can be reduced in a first order approximation simply to 
         [0000]        P=R×F   (equation 1)
 
         [0000]    where R=flow resistance, F=flow rate and P=pressure. This simplified expression is deemed valid because of the magnitude of flow in the surgical procedures involved (about 1 to 2 liters per minute) and because the control system will sample data at very short time intervals thereby approximating a static system, as will be explained below. 
         [0065]      FIG. 3  has been redrawn as a pressure/flow diagram  FIG. 14  to explain the IPS system and the application of the aforementioned equation to this IPS system. The components of  FIG. 3  each have certain pressure, flow and resistance characteristics that are depicted schematically in  FIG. 14 . Thus, in  FIG. 14  the following values are measured by the system: P in , the inflow pressure sensed by cassette sensor  75  associated with the inflow cassette  36 ; P out , the outflow pressure sensed by cassette sensor  76  associated with the outflow cassette  44 ; F in , the inflow fluid flow rate going into the work site  18  as determined by an encoder (not shown) adapted to calculate the fluid volume moved by inflow peristaltic pump  30  per unit of time; and F out , the outflow fluid flow rate coming out of the work site as determined by a similar encoder (not shown) adapted to calculate the fluid volume moved by outflow peristaltic pump  40  per unit of time. Those skilled in the art will understand that the flow rates can be determined as a function of the inner diameter of the intermediate roller tubes, the distance between the rollers of the peristaltic rotor assemblies and the speed of rotation of the rotor assemblies. These pressure and flow values are known values which are sampled by the system at intervals such as 10 mm (in the preferred embodiment). The remaining data needed to use the equation P=F×R is the flow resistance of the tubes and cannulas used in the set-up of  FIG. 3 . 
         [0066]    To facilitate the explanation of  FIG. 14  the various resistances are identified by the name of the component in the flow direction. Thus, the resistance R inflow tube  is labeled with the subscript “inflow tube” because it is the resistance of tube  38 , the inflow tube encountered by the fluid after pump  30 . This resistance causes a pressure drop P drop  drop inflow tube across the tube. The resistance R inflow tube  is calculated during manufacture of system  10  and stored in memory. Thus, the pressure drop P drop inflow tube  across tube  38  is known and =F in ×R inflow tube . Therefore, the pressure at the inflow port of cannula  39  (i.e. point  300 ) can now be calculated as 
         [0000]    
       
      
       P 
       at inflow cannula 
       =P 
       in 
       −P 
       drop inflow tube  
      
     
         [0000]      which is rewritten as 
         [0000]        P   at inflow cannula   =P   in   −R   inflow tube   ×F   in . 
         [0000]    The fluid flowing through the inflow cannula undergoes a further pressure drop before reaching the joint so 
         [0000]        P   at inflow cannula   −P   drop inflow cannula   =P   joint . 
         [0000]    We know the pressure drop across inflow cannula  39  is 
         [0000]        P   drop inflow cannula   =R   inflow cannula   ×F   in . 
         [0000]      Therefore, 
         [0000]        P   at inflow cannula −( R   inflow cannula   ×F   in )= P   joint   (equation 2)
 
         [0000]    At this point R inflow cannula  is unknown.
 
On the outflow side, we know that
 
         [0000]    
       
      
       P 
       at outflow cannula 
       =P 
       out 
       +P 
       drop outflow tube  
      
     
         [0000]      and 
         [0000]    
       
      
       P 
       drop outflow tube 
       =R 
       outflow tube 
       ×F 
       out  
      
     
         [0000]    where P out  is the pressure sensed by sensor  76 .
 
Consequently, the pressure at point  302  is
 
         [0000]        P   at outflow cannula   =P   out +( R   outflow tube   ×F   out ). 
         [0067]    In the preferred embodiment, inflow tube  38  and outflow tube  20  are identical in length, inner and outer diameter and material composition and, therefore, R outflow tube  is the same as Rinflow tube. We know that the pressure in the joint can be expressed in terms of the parameters at the outflow side as 
         [0000]    
       
      
       P 
       joint 
       =P 
       at outflow cannula 
       +P 
       drop outflow cannula  
      
     
         [0000]      and therefore 
         [0000]        P   joint   =P   at outflow cannula ( F   out   ×R   outflow cannula )  (equation 3)
 
         [0000]      We know that 
         [0000]    
       
      
       F 
       loss 
       =F 
       in 
       −F 
       out  
      
     
         [0000]    to account for leakage of fluid. Because the data sample rate is fast (in the range of approximately 1 to 20 ms, preferably approximately every 10 ms) we assume no fluid loss so that 
         [0000]        F   in   =F   out . 
         [0000]      Therefore, equation 2 may be rewritten as 
         [0000]        P   at inflow cannula −( R   inflow cannula   ×F   out )= P   joint   (equation 4)
 
         [0068]    Combining equations 3 and 4 produces the following: 
         [0000]        P   at inflow cannula −( R   inflow cannula   ×F   out )= P   at outflow cannula +( F   out   ×R   outflow cannula )  (equation 5)
 
         [0000]      Rearranging equation 5 results in 
         [0000]        P   at inflow cannula   −P   at outflow cannula   =F   out ( R   outflow cannula   +R   inflow cannula )  (equation 6)
 
         [0000]    In the preferred embodiment the R outflow cannula  is very low because outflow cannulas are designed to easily drain fluid from the work site. (As noted below, this explanation requires additional calculations if the outflow cannula is restrictive to any appreciable degree.) Additionally, the outflow flow rate is relatively low so the pressure drop is low. Thus, equation 6 is simplified to 
         [0000]    
       
      
       P 
       at inflow cannula 
       −P 
       at outflow cannula 
       =F 
       out 
       ×R 
       inflow cannula  
      
     
         [0000]    and R inflow cannula  is now able to be determined as 
         [0000]        R   inflow cannula =( P   at inflow cannula   −P   at outflow cannula )/ F   out   (equation 7)
 
         [0000]    R inflow cannula  is now known. These results can now be used in equation 4 (since  Pat inflow cannula  is known) to predict the pressure in the joint and regulate the control loop using inflow pressure data. Combining equation 7 and equation 4 results in 
         [0000]        P   at inflow cannula −( R   inflow cannula   ×F   out )= P   joint  
 
         [0000]        P   joint   =P   at inflow cannula   −F   out [( P   at inflow cannula   −P   at outflow cannula   /F   out ] 
         [0000]    
       
      
       P 
       joint 
       =P 
       outflow cannula  
      
     
         [0069]    These results predict the pressure in the joint using outflow pressure data. The results of the P joint  calculation from the inflow side is compared to the P joint  calculation from the outflow side. If there is any difference between the two, outside of a predetermined range, the system will revert to a different pressure sensing mode. If the results are within the predetermined range, the P joint  calculated from the inflow side is used to control the joint pressure. It is noted that this method enables calculation of joint pressure through the use of calculated values and without the necessity for any direct measurements of the joint pressure. This solution holds for the simplest case where all assumptions made above are valid. Further calculations are necessary to account for a more restrictive outflow cannula than is used in the preferred embodiment. 
       Declogging 
       [0070]    Pump system  10  also incorporates a declogging method for facilitating automatic removal of a blockage of the shaver aspirating tubing line  72 . The declogging system comprises software driven steps which control the output pump  40  to activate this function. 
         [0071]    The declogging feature operates during use of handpiece  70  by sensing various characteristics of the operation of system  10  to determine the likelihood of a clog. If the outflow peristaltic rotor is working and the inflow peristaltic rotor is not working (or if the inflow rotor speed is significantly less than the outflow rotor speed) and if pressure at the work site (or pressure at cassettes) is not changing, it is probable that the shaver blade or aspiration line  72  is clogged. In this event, the user may activate a declog button (not shown) which causes the outflow rotor to be activated in the opposite direction for a time period sufficient to create a pressure pulse to move approximately 5-15 ml of fluid through outflow line  72 , handpiece  70  and shaver  73 . After this time period the outflow rotor resumes normal operation. In the preferred embodiment, 5-15 ml of fluid displacement is deemed sufficient for the size of the tubing used Approximately 5 ml of fluid (approximately 6.2 inches (157.48 mm) long in a 0.25 inch (6.35 mm) internal diameter tube) is an estimate of a volume sufficient to move the fluid back to the clog, and another approximately 5 ml is an estimate of the fluid required to push the clog out. In use, the surgeon would remove the shaver from the work site and aim it at a waste container. The declog button would cause the outflow rotor to be run in reverse as quickly as possible for approximately three revolutions and then forward for approximately six revolutions to push the clog out. 
         [0072]      FIG. 15  is a flowchart describing the operation of the declogging feature. 
         [0073]    It will be understood by those skilled in the art that numerous improvements and modifications may be made to the preferred embodiment of the invention disclosed herein without departing from the spirit and scope thereof.