Patent Publication Number: US-2023143878-A1

Title: Medical systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/858,231, filed Apr. 24, 2020, which is a continuation of U.S. application Ser. No. 15/887,390, filed Feb. 2, 2018, now U.S. Pat. No. 10,716,584; which is a continuation of U.S. application Ser. No. 14/247,649, filed Apr. 8, 2014, now U.S. Pat. No. 9,907,563, which claims priority to U.S. Provisional Application 61/809,681, filed on Apr. 8, 2013, the full disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to surgical fluid management systems and methods, for example for use in distending the uterine cavity to allow resection and extraction of abnormal uterine tissue such as fibroids and polyps. 
     BACKGROUND OF THE INVENTION 
     Uterine fibroids are non-cancerous tumors that develop in the wall of uterus. Such fibroids occur in a large percentage of the female population, with some studies indicating up to 40 percent of all women have fibroids. Uterine fibroids can grow over time to be several centimeters in diameter and symptoms can include menorrhagia, reproductive dysfunction, pelvic pressure and pain. 
     One current treatment of fibroids is hysteroscopic resection or myomectomy which involves transcervical access to the uterus with a hysteroscope together with insertion of a resecting instrument through a working channel in the hysteroscope. The resecting instrument may be a mechanical tissue cutter or an electrosurgical resection device such as a cutting loop. Mechanical cutting devices are disclosed in U.S. Pat. Nos. 7,226,459; 6,032,673 and 5,730,752 and U.S. Published Patent Application 2009/0270898. An electrosurgical resecting device is disclosed in U.S. Pat. No. 5,906,615. 
     In a myomectomy or hysteroscopic resection, the initial step of the procedure includes distention of the uterine cavity to create a working space for assisting viewing through the hysteroscope. In a relaxed state, the uterine cavity collapses with the uterine walls in contact with one another. A fluid management system is used to distend the uterus to provide a working space wherein a fluid is administered through a passageway in the hysteroscope under sufficient pressure to expand or distend the uterine cavity. The fluids used to distend the uterus are typically liquid aqueous solutions such as a saline solution or a sugar-based aqueous solution. 
     In some RF electrosurgical resection procedures, the distending fluid is a non-conductive aqueous solution to limit RF current conduction. 
     One particular concern is the fact that fluid management systems typically administer the fluid under a pressure of up to 100 mm Hg or more which results in a significant risk that the distending fluid may be taken up by a cut blood vessel exposed in the uterine cavity. Such unwanted fluid uptake is known as intravasation, which can lead to serious complications and even death. For this reason, fluid management systems have been developed to monitor the patient&#39;s fluid uptake on a continuous basis during a procedure, typically using complicated systems that capture, collect and weigh distending fluids that flow through the uterine cavity. 
     While hysteroscopic resection can be effective in removing uterine fibroids, many commercially available instrument are too large in diameter and thus require anesthesia in an operating room environment. Conventional resectoscopes require cervical dilation to about 9 mm. What is needed is a system that can effectively resect and remove fibroid tissue through a small diameter hysteroscope. 
     SUMMARY OF THE INVENTION 
     In a first aspect of the present invention, a fibroid treatment system comprises a controller, an inflow pump operated by the controller and configured to provide fluid inflow through a flow path to a patient&#39;s uterine cavity, an outflow pump operated by the controller and configured to provide fluid outflow through a flow path to the uterine cavity and a motor driven resecting device operated by the controller. The resecting device comprises an elongate introducer member having a tissue extraction channel therein with a diameter of no less than 2.4 mm and an outer sleeve having a diameter of no more than 3.8 mm. Further, the resecting device is adapted to remove fibroid tissue at a rate of at least 2 gm/min. In one variation, the controller can be configured to actuate the inflow and outflow pumps in response to signals of fluid pressure in the uterine cavity and to maintain the target pressure as described above. Additionally, the signal of fluid pressure can be provided by a pressure sensor coupled to a static fluid column communicating with the uterine cavity. In another variation, the controller can be configured to operate the resecting device in response to at least one parameter selected from a group consisting of an inflow pump speed, an outflow pump speed and signals of fluid pressure in the uterine cavity as will be described further below. 
     In a second aspect of the invention, a fluid management system comprises a controller. A first pump is operated by the controller and configured to provide a fluid inflow to a site in patient&#39;s body. A second pump is also operated by the controller and configured to provide a fluid outflow from the site in patient&#39;s body. The controller is configured to maintain at least one operating parameter selected from a group consisting of a first pump speed, a fluid inflow rate, a second pump speed, and a fluid outflow rate, and the controller is configured to provide a fluid loss warning if the first pump speed exceeds a predetermined level for a pre-selected time interval. 
     In exemplary embodiments of the second aspect, the pre-selected time interval may be at least 1 second, at least 5 seconds, or at least 10 seconds. The controller may be further configured to de-activate at least one pump if the first pump speed exceeds the predetermined level for the pre-selected time interval, and the controller may be still further configured to de-activate a powered resecting device positioned in the site if the first pump speed exceeds the predetermined level for the pre-selected time interval. 
     In a third aspect of the present invention, a fluid management system comprises a controller. An inflow pump is operated by the controller and adapted to provide a fluid inflow through a flow path to a site in a patient&#39;s body. An outflow pump is also operated by the controller and adapted to provide a fluid outflow through a flow path from the site in the patient&#39;s body. The controller is configured to maintain at least one operating parameter selected from a group consisting of a first pump speed, a fluid inflow rate, a second pump speed, and a fluid outflow rate, and the controller is configured to provide a blocked flow warning if a calculated power for driving the inflow pump exceeds a predetermined level for a pre-selected time interval. 
     In exemplary embodiments of the third aspect of the present invention, the controller may be further configured to de-activate at least one pump if the calculated power for driving the inflow pump exceeds the predetermined level for the pre-selected time interval. The controller may be still further configured to de-activate a powered resecting device positioned in the site if the calculated power for driving the inflow pump exceeds the predetermined level for the pre-selected time interval. 
     In a fourth aspect of the present invention, a fluid management system comprises a controller. A first pump is operated by the controller and configured to provide fluid inflow to a site in patient&#39;s body. A second pump is also operated by the controller and configured to provide fluid outflow from the site in patient&#39;s body. The controller is configured to maintain at least one operating parameter selected from a group consisting of a first pump speed, a fluid inflow rate, a second pump speed, and a fluid outflow rate, and the controller is further configured to provide a blocked flow warning if an input voltage to the inflow pump motor is below a predetermined threshold voltage for a pre-selected time interval. 
     In exemplary embodiments of the fourth aspect of the present invention, the pre-selected time interval may range from 5 seconds to 120 seconds. The controller may be further configured to de-activate at least one pump if the input voltage to the inflow pump falls below the predetermined level for the pre-selected time interval, and the controller may be still further configured to de-activate the powered resecting device positioned in the site if the voltage to the inflow pump motor exceeds the predetermined level for the pre-selected time interval. 
     In a fifth aspect of the present invention, a fluid management system comprises a controller. An inflow pump is operated by the controller and configured to provide fluid inflow through a flow path to a site in patient&#39;s body. An outflow pump is also operated by the controller and configured to provide fluid outflow through a flow path from the site in patient&#39;s body. The controller is configured to maintain at least one operating parameter selected from a group consisting of a first pump speed, a fluid inflow rate, a second pump speed, and a fluid outflow rate, and the controller is further configured to provide a blocked flow warning if a measured current to the outflow pump exceeds a predetermined threshold voltage for a pre-selected time interval. 
     In a sixth aspect of the present invention, a fluid management system for use in a tissue resection procedure comprises a controller. An inflow pump is operated by the controller and configured to provide a fluid inflow through a flow path to a site in patient&#39;s body. An outflow pump is also operated by the controller and configured to provide a fluid outflow through a flow path from the site in patient&#39;s body. A motor driven resecting device for resecting tissue at the site is also provided. The controller is configured to actuate an inflow pump and an outflow pump in response to signals of actual pressure at the site in the patient&#39;s body to provide respective fluid inflow and fluid outflow to maintain a target pressure at the site, and the controller is further configured to de-activate the motor driven resecting device upon sensing that the actual pressure in the site falls below a predetermined threshold pressure level. 
     In exemplary embodiments of the sixth aspect of the present invention, the controller may be further configured to de-activate a motor in the motor driven resecting device if actual pressure in the site falls below a predetermined threshold pressure level. The controller may be alternatively configured to de-activate at least one tissue resecting electrode in the motor driven tissue resection device if actual pressure in the site falls below a predetermined threshold pressure level. The threshold pressure level is 100 mmHg or less, 50 mmHg or less, or 25 mmHg or less. 
     In a seventh aspect of the present invention, a fluid management system for use in tissue resection comprises a controller. The controller is configured to (a) actuate an inflow pump and an outflow pump in response to signals of actual pressure in a site in patient&#39;s body to thereby provide respective fluid inflows and fluid outflows to maintain a target pressure at said site, (b) send a tissue-engagement signal to the controller after sensing a predetermined increase in the actual pressure within a pre-selected interval resulting from a resecting tool engaging targeted tissue in the site, (c) send a tissue-disengagement signal to the controller after sensing a predetermined decrease in the actual pressure within a pre-selected interval resulting from a resecting tool subsequently disengaging from the tissue, and (d) modulate an operating parameter of the fluid management system in response to a tissue-engagement signal or a tissue-disengagement signal. 
     In exemplary embodiments of the seventh aspect of the present invention, the controller may be further configured to place the inflow pump in a ready state to provide a selected high inflow rate in response to a tissue-engagement signal. The controller may also be configured to actuate the inflow pump to provide a selected high inflow rate in response to a tissue dis-engagement signal. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a plan view of an assembly including a hysteroscope and a tissue-resecting device corresponding to the invention that is inserted through the working channel of the hysteroscope. 
         FIG.  2    is a schematic perspective view of a fluid management system used for distending the uterus and for assisting in electrosurgical tissue resection and extraction. 
         FIG.  3    is a cross-sectional view of the shaft of the hysteroscope of  FIG.  1    showing various channels therein. 
         FIG.  4    is a schematic side view of the working end of the electrosurgical tissue-resecting device of  FIG.  1    showing an outer sleeve and a reciprocating inner sleeve and an electrode arrangement. 
         FIG.  5    is a schematic perspective view of the working end of the inner sleeve of  FIG.  4    showing its electrode edge. 
         FIG.  6 A  is a schematic cut-away view of a portion of outer sleeve, inner RF resecting sleeve and a tissue-receiving window of the outer sleeve. 
         FIG.  6 B  is a schematic view of a distal end portion another embodiment of inner RF resecting sleeve. 
         FIG.  7 A  is a cross sectional view of the inner RF resecting sleeve of  FIG.  6 B  taken along line  7 A- 7 A of  FIG.  6 B . 
         FIG.  7 B  is another cross sectional view of the inner RF resecting sleeve of  FIG.  6 B  taken along line  7 B- 7 B of  FIG.  6 B . 
         FIG.  8    is a schematic view of a distal end portion of another embodiment of inner RF resecting sleeve. 
         FIG.  9 A  is a cross sectional view of the RF resecting sleeve of  FIG.  8    taken along line  9 A- 9 A of  FIG.  8   . 
         FIG.  9 B  is a cross sectional view of the RF resecting sleeve of  FIG.  8    taken along line  9 B- 9 B of  FIG.  8   . 
         FIG.  10 A  is a perspective view of the working end of the tissue-resecting device of  FIG.  1    with the reciprocating RF resecting sleeve in a non-extended position. 
         FIG.  10 B  is a perspective view of the tissue-resecting device of  FIG.  1    with the reciprocating RF resecting sleeve in a partially extended position. 
         FIG.  10 C  is a perspective view of the tissue-resecting device of  FIG.  1    with the reciprocating RF resecting sleeve in a fully extended position across the tissue-receiving window. 
         FIG.  11 A  is a sectional view of the working end of the tissue-resecting device of  FIG.  10 A  with the reciprocating RF resecting sleeve in a non-extended position. 
         FIG.  11 B  is a sectional view of the working end of  FIG.  10 B  with the reciprocating RF resecting sleeve in a partially extended position. 
         FIG.  11 C  is a sectional view of the working end of  FIG.  10 C  with the reciprocating RF resecting sleeve in a fully extended position. 
         FIG.  12 A  is an enlarged sectional view of the working end of tissue-resecting device of  FIG.  11 B  with the reciprocating RF resecting sleeve in a partially extended position showing the RF field in a first RF mode and plasma resecting of tissue. 
         FIG.  12 B  is an enlarged sectional view of the working end of  FIG.  11 C  with the reciprocating RF resecting sleeve almost fully extended and showing the RF fields switching to a second RF mode from a first RF mode shown in  FIG.  12   . 
         FIG.  12 C  is an enlarged sectional view of the working end of  FIG.  11 C  with the reciprocating RF resecting sleeve again almost fully extended and showing the explosive vaporization of a captured liquid volume to expel resected tissue in the proximal direction. 
         FIG.  13    is an enlarged perspective view of a portion of the working end of  FIG.  12 C  showing an interior chamber and a fluted projecting element. 
         FIG.  14    is a sectional view of the working end of  FIG.  12 C  showing an interior chamber and a variation of a projecting element. 
         FIG.  15    is a sectional view of the working end of  FIG.  12 C  showing an interior chamber and a variation of a projecting element configured to explosively vaporize the captured liquid volume. 
         FIG.  16    is a schematic view of a system for fibroid removal including a fluid management system. 
         FIG.  17    is a schematic view of the fluid management system of  FIG.  16    with an enlarged view of the working end of a tissue-resecting probe as generally described in  FIGS.  1 - 12 C  in a position to resect and extract fibroid tissue. 
         FIG.  18    is a schematic view of a pressure sensor component of the fluid management system of  FIGS.  16 - 17   . 
         FIG.  19    is a cut-away schematic view of a filter module of the fluid management system of  FIGS.  16 - 17   . 
         FIG.  20    is a schematic view of an endoscope and fluid management system being used in a diagnostic mode. 
         FIG.  21    is a schematic view of the endoscope and fluid management system of  FIG.  20    together with a resecting probe with the assembly as used is a non-diagnostic or therapeutic mode. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates an assembly that comprises an endoscope  50  used for hysteroscopy together with a tissue resecting device  100  extending through a working channel  102  of the endoscope. The endoscope or hysteroscope  50  has a handle  104  coupled to an elongated shaft  105  having a diameter of 5 mm to 7 mm. The working channel  102  therein may be round, D-shaped or any other suitable shape. The endoscope shaft  105  is further configured with an optics channel  106  and one or more fluid inflow/outflow channels  108   a ,  108   b  ( FIG.  3   ) that communicate with valve-connectors  110   a,    110   b  configured for coupling to a fluid inflow source  120  thereto, or optionally a negative pressure source  125  ( FIGS.  1 - 2   ). The fluid inflow source  120  is a component of a fluid management system  126  as is known in the art ( FIG.  2   ) which comprises a fluid container  128  and pump mechanism  130  which pumps fluid through the hysteroscope  50  into the uterine cavity. As can be seen in  FIG.  2   , the fluid management system  126  further includes the negative pressure source  125  (which can comprise an operating room wall suction source) coupled to the tissue-resecting device  100 . The handle  104  of the endoscope includes the angled extension portion  132  with optics to which a videoscopic camera  135  can be operatively coupled. A light source  136  also is coupled to light coupling  138  on the handle of the hysteroscope  50 . The working channel  102  of the hysteroscope is configured for insertion and manipulation of the tissue-resecting and extracting device  100 , for example to treat and remove fibroid tissue. In one embodiment, the hysteroscope shaft  105  has an axial length of 21 cm, and can comprise a 0° scope, or 15° to 30° scope. 
     Still referring to  FIG.  1   , the tissue-resecting device  100  has a highly elongated shaft assembly  140  configured to extend through the working channel  102  in the hysteroscope. A handle  142  of the tissue-resecting device  100  is adapted for manipulating the electrosurgical working end  145  of the device. In use, the handle  142  can be manipulated both rotationally and axially, for example, to orient the working end  145  to resect targeted fibroid tissue. The tissue-resecting device  100  has subsystems coupled to its handle  142  to enable electrosurgical resecting of targeted tissue. A radiofrequency generator or RF source  150  and controller  155  are coupled to at least one RF electrode carried by the working end  145  as will be described in detail below. In one embodiment shown in  FIG.  1   , an electrical cable  156  and negative pressure source  125  are operatively coupled to a connector  158  in handle  142 . The electrical cable couples the RF source  150  to the electrosurgical working end  145 . The negative pressure source  125  communicates with a tissue extraction channel  160  in the shaft assembly  140  of the tissue extraction device  100  ( FIG.  4   ). 
       FIG.  1    further illustrates a seal housing  162  that carries a flexible seal  164  carried by the hysteroscope handle  104  for sealing the shaft  140  of the tissue-resecting device  100  in the working channel  102  to prevent distending fluid from escaping from a uterine cavity. 
     In one embodiment as shown in  FIG.  1   , the handle  142  of tissue-resecting device  100  includes a motor drive  165  for reciprocating or otherwise moving a resecting component of the electrosurgical working end  145  as will be described below. The handle  142  optionally includes one or more actuator buttons  166  for actuating the device. In another embodiment, a footswitch can be used to operate the device. In one embodiment, the system includes a switch or control mechanism to provide a plurality of reciprocation speeds, for example 1 Hz, 2 Hz, 3 Hz, 4 Hz and up to 8 Hz. Further, the system can include a mechanism for moving and locking the reciprocating resecting sleeve in a non-extended position and in an extended position. Further, the system can include a mechanism for actuating a single reciprocating stroke. 
     Referring to  FIGS.  1  and  4   , an electrosurgical tissue resecting device has an elongate shaft assembly  140  extending about longitudinal axis  168  comprising an exterior or first outer sleeve  170  with passageway or lumen  172  therein that accommodates a second or inner sleeve  175  that can reciprocate (and optionally rotate or oscillate) in lumen  172  to resect tissue as is known in that art of such tubular cutters. In one embodiment, the tissue-receiving window  176  in the outer sleeve  170  has an axial length ranging between 10 mm and 30 mm and extends in a radial angle about outer sleeve  170  from about 45° to 210° relative to axis  168  of the sleeve. The outer and inner sleeves  170  and  175  can comprise a thin-wall stainless steel material and function as opposing polarity electrodes as will be described in detail below.  FIGS.  6 A- 8    illustrate insulative layers carried by the outer and inner sleeves  170  and  175  to limits, control and/or prevent unwanted electrical current flows between certain portions go the sleeve. In one embodiment, a stainless steel outer sleeve  170  has an O.D. of 3.6 mm to 3.8 mm with an I.D. of 3.38 mm to 3.5 mm and with an inner insulative layer (described below) the sleeve has a nominal I.D. of about 3.175 mm″. In this embodiment, the stainless steel inner sleeve  175  has an O.D. of about 3.05 mm with an I.D. of about 2.84 mm″. The inner sleeve  175  with an outer insulative layer has a nominal O.D. of about 3.12 mm″ to reciprocate in lumen  172 . The inner diameters of the inner sleeve portions are described below. As can be seen in  FIG.  4   , the distal end  177  of inner sleeve  175  comprises a first polarity electrode with distal resecting electrode edge  180  about which plasma can be generated. The electrode edge  180  also can be described as an active electrode during tissue resecting since the electrode edge  180  then has a substantially smaller surface area than the opposing polarity or return electrode. In one embodiment in  FIG.  4   , the exposed surfaces of outer sleeve  170  comprises the second polarity electrode  185 , which thus can be described as the return electrode since during use such an electrode surface has a substantially larger surface area compared to the functionally exposed surface area of the active electrode edge  180 . 
     In one aspect of the invention, the inner sleeve or resecting sleeve  175  has an interior tissue extraction lumen  160  with first and second interior diameters that are adapted to electrosurgically resect tissue volumes rapidly--and thereafter consistently extract the resected tissue strips through the highly elongated lumen  160  without clogging. Now referring to  FIGS.  5  and  6 A , it can be seen that the inner sleeve  175  has a first diameter portion  190 A that extends from the handle  142  ( FIG.  1   ) to a distal region  192  of the sleeve  175  wherein the tissue extraction lumen transitions to a smaller second diameter lumen  190 B with a reduced diameter indicated at B which is defined by the electrode sleeve element  195  that provides resecting electrode edge  180 . The axial length C of the reduced cross-section lumen  190 B can range from about 2 mm to 20 mm. In one embodiment, the first diameter A is between 2.8 mm and 2.9 mm and the second reduced diameter B is between 2.4 mm and 2.5 mm. As shown in  FIG.  5   , the inner sleeve  175  can be an electrically conductive stainless steel and the reduced diameter electrode portion also can comprise a stainless steel electrode sleeve element  195  that is welded in place by weld  196  ( FIG.  6 A ). In another alternative embodiment, the electrode and reduced diameter electrode sleeve element  195  comprises a tungsten tube that can be press fit into the distal end  198  of inner sleeve  175 .  FIGS.  5  and  6 A  further illustrates the interfacing insulation layers  202  and  204  carried by the first and second sleeves  170 ,  175 , respectively. In  FIG.  6 A , the outer sleeve  170  is lined with a thin-wall insulative material  200 , such as PFA, or another material described below. Similarly, the inner sleeve  175  has an exterior insulative layer  202 . These coating materials can be lubricious as well as electrically insulative to reduce friction during reciprocation of the inner sleeve  175 . 
     The insulative layers  200  and  202  described above can comprise a lubricious, hydrophobic or hydrophilic polymeric material. For example, the material can comprise a bio-compatible material such as PFA, TEFLON™, polytetrafluroethylene (PTFE), FEP (Fluorinated ethylenepropylene), polyethylene, polyamide, ECTFE (Ethylenechlorotrifluoro-ethylene), ETFE, PVDF, polyvinyl chloride or silicone. 
     Now turning to  FIG.  6 B , another variation of inner sleeve  175  is illustrated in a schematic view together with a tissue volume being resected with the plasma electrode edge  180 . In this embodiment, as in other embodiments in this disclosure, the RF source operates at selected operational parameters to create a plasma around the electrode edge  180  of electrode sleeve  195  as is known in the art. Thus, the plasma generated at electrode edge  180  can resect and ablate a path P in the tissue  220 , and is suited for resecting fibroid tissue and other abnormal uterine tissue. In  FIG.  6 B , the distal portion of the resecting sleeve  175  includes a ceramic collar  222  which is adjacent the distal edge  180  of the electrode sleeve  195 . The ceramic  222  collar functions to confine plasma formation about the distal electrode edge  180  and functions further to prevent plasma from contacting and damaging the polymer insulative layer  202  on the resecting sleeve  175  during operation. In one aspect of the invention, the path P cut in the tissue  220  with the plasma at electrode edge  180  provides a path P having an ablated width indicated at W, wherein such path width W is substantially wide due to tissue vaporization. This removal and vaporization of tissue in path P is substantially different than the effect of cutting similar tissue with a sharp blade edge, as in various prior art devices. A sharp blade edge can divide tissue (without cauterization) but applies mechanical force to the tissue and may prevent a large cross section slug of tissue from being cut. In contrast, the plasma at the electrode edge  180  can vaporize a path P in tissue without applying any substantial force on the tissue to thus resect larger cross sections or slugs strips of tissue. Further, the plasma resecting effect reduces the cross section of tissue strip  225  received in the tissue-extraction lumen  190 B.  FIG.  6 B  depicts a tissue strip to  225  entering lumen  190 B which has such a smaller cross-section than the lumen due to the vaporization of tissue. Further, the cross section of tissue  225  as it enters the larger cross-section lumen  190 A results in even greater free space  196  around the tissue strip  225 . Thus, the resection of tissue with the plasma electrode edge  180 , together with the lumen transition from the smaller cross-section ( 190 B) to the larger cross-section ( 190 A) of the tissue-extraction lumen  160  can significantly reduce or eliminate the potential for successive resected tissue strips  225  to clog the lumen. Prior art resection devices with such small diameter tissue extraction lumen typically have problems with tissue clogging. 
     In another aspect of the invention, the negative pressure source  225  coupled to the proximal end of tissue extraction lumen  160  (see  FIGS.  1  and  4   ) also assists in aspirating and moving tissue strips  225  in the proximal direction to a collection reservoir (not shown) outside the handle  142  of the device. 
       FIGS.  7 A- 7 B  illustrate the change in lumen diameter of resecting sleeve  175  of  FIG.  6 B .  FIG.  8    illustrates the distal end of a variation of resecting sleeve  175 ′ which is configured with an electrode resecting element  195 ′ that is partially tubular in contrast to the previously described tubular electrode element  195  ( FIGS.  5  and  6 A ).  FIGS.  9 A- 9 B  again illustrate the change in cross-section of the tissue extraction lumen between reduced cross-section region  190 B′ and the increased cross-section region  190 A′ of the resecting sleeve  175 ′ of  FIG.  8   . Thus, the functionality remains the same whether the resecting electrode element  195 ′ is tubular or partly tubular. In  FIG.  8 A , the ceramic collar  222 ′ is shown, in one variation, as extending only partially around sleeve  175  to cooperate with the radial angle of resecting electrode element  195 ′. Further, the variation of  FIG.  8    illustrates that the ceramic collar  222 ′ has a larger outside diameter than insulative layer  202 . Thus, friction may be reduced since the short axial length of the ceramic collar  222 ′ interfaces and slides against the interfacing insulative layer  200  about the inner surface of lumen  172  of outer sleeve  170 . 
     In general, one aspect of the invention comprises a tissue resecting and extracting device ( FIGS.  10 A- 11 C ) that includes first and second concentric sleeves having an axis and wherein the second (inner) sleeve  175  has an axially-extending tissue extraction lumen therein, and wherein the second sleeve  175  is moveable between axially non-extended and extended positions relative to a tissue receiving window  176  in first sleeve  170  to resect tissue, and wherein the tissue extraction lumen  160  has first and second cross-sections. The second sleeve  175  has a distal end configured as a plasma electrode edge  180  to resect tissue disposed in tissue receiving window  176  of the first sleeve  170 . Further, the distal end of the second sleeve, and more particularly, the electrode edge  180  is configured for plasma ablation of a substantially wide path in the tissue. In general, the tissue extraction device is configured with a tissue extraction lumen  160  having a distal end portion with a reduced cross-section that is smaller than a cross-section of medial and proximal portions of the lumen  160 . 
     In one aspect of the invention, referring to  FIGS.  7 A- 7 B and  9 A- 9 B , the tissue extraction lumen  160  has a reduced cross-sectional area in lumen region  190 A proximate the plasma resecting tip or electrode edge  180  wherein said reduced cross section is less that 95%, 90%, 85% or 80% than the cross sectional area of medial and proximal portions  190 B of the tissue extraction lumen, and wherein the axial length of the tissue extraction lumen is at least 10 cm, 20 cm, 30 cm or 40 cm. In one embodiment of tissue resecting device  100  for hysteroscopic fibroid resecting and extraction ( FIG.  1   ), the shaft assembly  140  of the tissue resecting device is 35 cm in length. 
       FIGS.  10 A- 10 C  illustrate the working end  145  of the tissue resecting device  100  with the reciprocating resecting sleeve or inner sleeve  175  in three different axial positions relative to the tissue receiving window  176  in outer sleeve  170 . In  FIG.  10 A , the resecting sleeve  175  is shown in a retracted or non-extended position in which the sleeve  175  is at it proximal limit of motion and is prepared to advance distally to an extended position to thereby electrosurgically resect tissue positioned in and/or suctioned into in window  176 .  FIG.  10 B  shows the resecting sleeve  175  moved and advanced distally to a partially advanced or medial position relative to tissue resecting window  176 .  FIG.  10 C  illustrates the resecting sleeve  175  fully advanced and extended to the distal limit of its motion wherein the plasma resecting electrode  180  has extended past the distal end  226  of tissue receiving window  176  at which moment the resected tissue strip  225  in excised from tissue volume  220  and captured in reduced cross-sectional lumen region  190 A. 
     Now referring to  FIGS.  10 A- 10 C  and  FIGS.  11 A- 11 C , another aspect of the invention comprises “tissue displacement” mechanisms provided by multiple elements and processes to “displace” and move tissue strips  225  in the proximal direction in lumen  160  of resecting sleeve  175  to thus ensure that tissue does not clog the lumen of the inner sleeve  175 . As can seen in  FIG.  10 A  and the enlarged views of  FIGS.  11 A- 11 C , one tissue displacement mechanism comprises a projecting element  230  that extends proximally from distal tip  232  which is fixedly attached to outer sleeve  170 . The projecting element  230  extends proximally along central axis  168  in a distal chamber  240  defined by outer sleeve  170  and distal tip  232 . In one embodiment depicted in  FIG.  11 A , the shaft-like projecting element  230 , in a first functional aspect, comprises a mechanical pusher that functions to push a captured tissue strip  225  proximally from the small cross-section lumen  190 B of resecting sleeve  175  as the resecting sleeve  175  moves to its fully advanced or extended position. In a second functional aspect, the chamber  240  in the distal end of sleeve  170  is configured to capture a volume of saline distending fluid  244  from the working space, and wherein the existing RF electrodes of the working end  145  are further configured to explosively vaporize the captured fluid  244  to generate proximally-directed forces on tissue strips  225  resected and disposed in lumen  160  of the resecting sleeve  175 . Both of these two functional elements and processes (tissue displacement mechanisms) can apply a substantial mechanical force on the captured tissue strips  225  by means of the explosive vaporization of liquid in chamber  240  and can function to move tissue strips  225  in the proximal direction in the tissue extraction lumen  160 . It has been found that using the combination of multiple functional elements and processes can virtually eliminate the potential for tissue clogging the tissue extraction lumen  160 . 
     More in particular,  FIGS.  12 A- 12 C  illustrate sequentially the functional aspects of the tissue displacement mechanisms and the explosive vaporization of fluid captured in chamber  240 . In  FIG.  12 A , the reciprocating resecting sleeve  175  is shown in a medial position advancing distally wherein plasma at the resecting electrode edge  180  is resecting a tissue strip  225  that is disposed within lumen  160  of the resecting sleeve  175 . In  FIG.  12 A- 12 C , it can be seen that the system operates in first and second electrosurgical modes corresponding to the reciprocation and axial range of motion of resecting sleeve  175  relative to the tissue receiving window  176 . As used herein, the term “electrosurgical mode” refers to which electrode of the two opposing polarity electrodes functions as an “active electrode” and which electrode functions as a “return electrode”. The terms “active electrode” and “return electrode” are used in accordance with convention in the art—wherein an active electrode has a smaller surface area than the return electrode which thus focuses RF energy density about such an active electrode. In the working end  145  of  FIGS.  10 A- 11 C , the resecting electrode element  195  and its resecting electrode edge  180  must comprise the active electrode to focus energy about the electrode to generate the plasma for tissue resecting. Such a high-intensity, energetic plasma at the electrode edge  180  is needed throughout stroke X indicated in  FIG.  12 A- 12 B  to resect tissue. The first mode occurs over an axial length of travel of inner resecting sleeve  175  as it crosses the tissue receiving window  176 , at which time the entire exterior surface of outer sleeve  170  comprises the return electrode indicated at  185 . The electrical fields EF of the first RF mode are indicated generally in  FIG.  12 A . 
       FIG.  12    B illustrates the moment in time at which the distal advancement or extension of inner resecting sleeve  175  entirely crossed the tissue receiving window  176 . At this time, the electrode sleeve  195  and its electrode edge  180  are confined within the mostly insulated-wall chamber  240  defined by the outer sleeve  170  and distal tip  232 . At this moment, the system is configured to switch to the second RF mode in which the electric fields EF switch from those described previously in the first RF mode. As can be seen in  FIG.  12 B , in this second mode, the limited interior surface area  250  of distal tip  232  that interfaces chamber  240  functions as an active electrode and the distal end portion of resecting sleeve  175  exposed to chamber  240  acts as a return electrode. In this mode, very high energy densities occur about surface  250  and such a contained electric field EF can explosively and instantly vaporize the fluid  244  captured in chamber  240 . The expansion of water vapor can be dramatic and can thus apply tremendous mechanical forces and fluid pressure on the tissue strip  225  to move the tissue strip in the proximal direction in the tissue extraction lumen  160 .  FIG.  12 C  illustrates such explosive or expansive vaporization of the distention fluid  244  captured in chamber  240  and further shows the tissue strip  225  being expelled in the proximal direction the lumen  160  of inner resecting sleeve  175 .  FIG.  14    further shows the relative surface areas of the active and return electrodes at the extended range of motion of the resecting sleeve  175 , again illustrating that the surface area of the non-insulated distal end surface  250  is small compared to surface  255  of electrode sleeve which comprises the return electrode. 
     Still referring to  FIGS.  12 A- 12 C , it has been found that a single power setting on the RF source  150  and controller  155  can be configured both (i) to create plasma at the electrode resecting edge  180  of electrode sleeve  195  to resect tissue in the first mode, and (ii) to explosively vaporize the captured distention fluid  244  in the second mode. Further, it has been found that the system can function with RF mode-switching automatically at suitable reciprocation rates ranging from 0.5 cycles per second to 8 or 10 cycles per second. In trial, it has been found that the tissue resecting device described above can resect and extract tissue at the rate of from 2 grams/min to 8 grams/min without any potential for tissue strips  225  clogging the tissue extraction lumen  160 . In one embodiment, a negative pressure source  125  can be coupled to the tissue extraction lumen  160  to apply tissue-extracting forces to tissue strips in the lumen. 
     Of particular interest, the fluid-capture chamber  240  defined by sleeve  170  and distal tip  232  can be designed to have a selected volume, exposed electrode surface area, length and geometry to optimize the application of expelling forces to resected tissue strips  225 . In one embodiment, the diameter of the chamber is 3.175 mm and the length is 5.0 mm which taking into account the projecting element  230 , provided a captured fluid volume of approximately 0.040 mL. In other variations, the captured fluid volume can range from 0.004 to 0.080 mL. 
     In one example, a chamber  240  with a captured liquid volume of 0.040 mL together with 100% conversion efficiency in an instantaneous vaporization would require  103  Joules to heat the liquid from room temperature to water vapor. In operation, since a Joule is a W*s, and the system reciprocate at 3 Hz, the power required would be on the order of 311 W for full, instantaneous conversion to water vapor. A corresponding theoretical expansion of 1700x would occur in the phase transition, which would results in up to 25,000 psi instantaneously (14.7 psi×1700), although due to losses in efficiency and non-instantaneous expansion, the actual pressures would be less. In any event, the pressures are substantial and can apply expelling forces sufficient to the expel the captured tissue strips  225  the length of the extraction channel in the probe. 
     Referring to  FIG.  12 A , the interior chamber  240  can have an axial length from about 0.5 mm to 10 mm to capture a liquid volume ranging from about 0.004 mL to 0.010 mL. It can be understood in  FIG.  12 A , that the interior wall of chamber  240  has an insulator layer  200  which thus limits the electrode surface area  250  exposed to chamber  240 . In one embodiment, the distal tip  232  is stainless steel and is welded to outer sleeve  170 . The post element  248  is welded to tip  232  or machined as a feature thereof. The projecting element  230  in this embodiment is a non-conductive ceramic.  FIG.  13    shows the cross-section of the ceramic projecting element  230  which is fluted, which in one embodiment has three flute elements  260  in three corresponding axial grooves  262  in its surface. Any number of flutes, channels or the like is possible, for example from 2 to about 20. The purpose of this design is to provide a significant cross-sectional area at the proximal end of the projecting element  230  to push the tissue strip  225 , while at the same time the three grooves  262  permit the proximally-directed jetting of water vapor to impact the tissue exposed to the grooves  262 . In one embodiment, the axial length D of the projecting element  230  is configured to push tissue entirely out of the reduced cross-sectional region  190 B of the electrode sleeve element  195 . In another embodiment, the volume of the chamber  240  is configured to capture liquid that when explosively vaporized provided a gas (water vapor) volume sufficient to expand into and occupy at least the volume defined by a 10% of the total length of extraction channel  160  in the device, at least 20% of the extraction channel  160 , at least 40% of the extraction channel  160 , at least 60% of the extraction channel  160 , at least 80% of the extraction channel  160  or at least 100% of the extraction channel  160 . 
     As can be understood from  FIGS.  12 A to  12 C , the distention fluid  244  in the working space replenishes the captured fluid in chamber  240  as the resecting sleeve  175  moves in the proximal direction or towards its non-extended position. Thus, when the resecting sleeve  175  again moves in the distal direction to resect tissue, the interior chamber  240  is filled with fluid  244  which is then again contained and is then available for explosive vaporization as described above when the resecting sleeve  175  closes the tissue receiving window  176 . In another embodiment, a one-way valve can be provided in the distal tip  232  to draw fluid directly into interior chamber  240  without the need for fluid to migrate through window  176 . 
       FIG.  15    illustrates another variation in which the active electrode surface area  250 ′ in the second mode comprises a projecting element  230  with conductive regions and non-conductive regions  260  which can have the effect of distributing the focused RF energy delivery over a plurality of discrete regions each in contact with the captured fluid  244 . This configuration can more efficiently vaporize the captured fluid volume in chamber  240 . In one embodiment, the conductive regions  250 ′ can comprise metal discs or washers on post  248 . In other variation (not shown) the conductive regions  250 ′ can comprise holes, ports or pores in a ceramic material  260  fixed over an electrically conductive post  248 . 
     In another embodiment, the RF source  150  and controller  155  can be programmed to modulate energy delivery parameters during stroke X and stroke Y in  FIGS.  12 A- 12 C  to provide the optimal energy (i) for plasma resecting with electrode edge  180 , and (ii) for explosively vaporizing the captured fluid in chamber  240 . In one variation, the controller  155  can include an algorithm that activates the RF source  150  to delivery RF energy to working end as the resecting sleeve  175  moves in the distal direction towards its extended position to resect tissue but terminates RF energy delivery to the working end as the resecting sleeve  175  moves in the proximal direction towards its non-extended position. The termination of RF energy delivery during the proximal stroke of the resecting sleeve  175  eliminates energy delivery to electrode edge  180  when it is not resecting tissue which thus prevents unnecessary heating of distention fluid which would occur when RF energy is delivered during both the forward and backward strokes of the resecting sleeve. 
       FIGS.  16 - 18    illustrate a fluid management system  500  that can be used when treating tissue in a body cavity, space or potential space  502  ( FIG.  17   ). The fluid management system  500  is depicted schematically in a hysteroscopic tissue resecting system  510  that is adapted for resecting and extraction of fibroids or other abnormal intra-uterine tissue using an endoscope or hysteroscope  512  and tissue resecting probe  515  that can be similar to those described above.  FIG.  16    depicts the tissue resecting probe  515  with handle  516  and extending member including outer sleeve  518  with working end  520  ( FIG.  17   ) that can be introduced through working channel  522  extending through the body  523  and shaft  524  of the hysteroscope  512 .  FIG.  16    further shows a motor  525  in handle  516  of the tissue resecting probe that is coupled to a controller and power supply by power cable  526 .  FIG.  17    illustrates the working end  520  of the resecting probe  515  in a uterine cavity proximate a targeted fibroid  530 . 
     Referring to  FIGS.  16 - 17   , in general, the fluid management system  500  comprises a fluid source or reservoir  535  of a distention fluid  244 , a controller and pump system to provide fluid inflows and outflows adapted to maintain distension of a body space and a filter system  540  for filtering distention fluid  244  that is removed from the body cavity and thereafter returned to the fluid source  535 . The use of a recovered and filtered fluid  244  and the replenishment of the fluid source  535  is advantageous because (i) the closed-loop fluid management system can effectively measure fluid deficit to thereby monitor intravasation and insure patient safety, (ii) the system can be set up and operated in a very time-efficient manner, and (ii) the system can be compact and less expensive to thereby assist in enabling office-based procedures. 
     The fluid management system  500  ( FIG.  16   ) includes a computer control system that is integrated with the RF control system in an integrated controller  545 . The controller  545  is adapted to control first and second peristaltic pumps  546 A and  546 B for providing inflows and outflows of a distention fluid  244 , such as saline solution, from source  535  for the purpose of distending the body cavity. The first peristaltic pump may also be called an inflow pump or infusion pump herein. The second peristaltic pump may also be called an outflow pump or aspiration pump herein. The controller  545  and control algorithms are adapted to control the intra-cavity pressure during a tissue resecting and extracting procedure as depicted in  FIG.  17   . In one embodiment shown in  FIGS.  16 - 18   , the controller  545  controls the inflow pump  546 A to provide positive pressure at the outflow side  548  of the pump ( FIG.  17   ) to provide inflows of distention fluid  244  through inflow line  550  which is in communication with fitting  561  and fluid flow channel  108   a  in hysteroscope  515 . The flow channel  108   a  is described above in a previous embodiment and is illustrated in  FIG.  3    above. The controller  545  further controls the outflow pump  546 B to provide negative pressure to the outflow line  555  at the inflow side  552  of the pump ( FIG.  17   ) to provide outflows of distention fluid  244  from the body cavity  502 . As described above, the explosive vaporization of fluid in the working end  525  of resecting probe  515  functions to expel tissue strips  225  proximally in the extraction channel  160  of resecting sleeve  175 , which can operate in conjunction with negative pressure in line  555  provided by pump  546 B. In operation, the outflow pump  546 B also operates to provide positive pressure on the outflow side  556  of pump  546 B in the second outflow line portion  555 ′ to pump outflows of distention fluid  244  through the filter system  540  and back to the fluid source  535 . 
     In one system embodiment, the controller  545  operates to control pressure in cavity  502  by pressure signals from a pressure sensor  560  that is coupled to a fitting  562  in hysterocope  512  which communicates with a flow channel  108   b  (see  FIG.  16   ) that extends through the hysteroscope. In one embodiment, the flow channel  108   b  has a diameter of at least 1.0 mm to allow highly accurate sensing of actual intra-cavity pressure. In prior art commercially-available fluid management systems, the intra-cavity pressure is typically estimated by various calculations using known flow rates through a pump or remote pressure sensors in the fluid inflow line that can measure back pressures. Such prior art fluid management systems are stand-alone systems and are adapted for use with a wide variety of hysteroscopes and endoscopes, most of which do not have a dedicated flow channel for communicating with a pressure sensor. For this reason, prior art fluid management systems rely on algorithms and calculations to only estimate intra-cavity pressure. 
     In one embodiment, as depicted in  FIG.  16   , the pressure sensor  560  is disposable and is detachably coupled to the endoscope  512  and is in fluid communication with the body cavity through a flow channel  108   b  in the endoscope. The pressure sensor  560  is operatively coupled to controller  545  by cable  564 . The pressure sensor can be a biocompatible, piezoresistive silicon sensor of the type used in invasive blood pressure monitoring. For example, the sensor can be a piezoresistive silicon pressure sensor, Model No. 1620, available from Measurement Specialties. Ltd., 45738 Northport Loop West, Fremont, Calif. 94538. The sensor is designed with a pressure sensing element mounted on a ceramic substrate. A dielectric gel can be placed over the sensor element to provide electrical and fluid isolation. The sensor housing can have a Luer connection to couple to the endoscope  512 . Further, the sensor body can have a pressure relief valve for redundant overpressure protection (not shown). 
     As can be understood from  FIGS.  16  and  17   , the pressure sensor  560  is attached to the endoscope  512  to communicate with a fluid channel extending through the endoscope shaft to the body cavity. The fluid channel or sensor channel  108   b  used by the pressure sensor  560  is independent of flow channel  108   a  used for distention fluid inflows into the body cavity. In the absence of fluid flows in the sensor channel  108   b , the fluid in the channel  108   b  then forms a static column of incompressible fluid that changes in pressure as the pressure in the body cavity changes. With a sensor channel cross-section of 1 mm or more, the pressure within the pressure channel column and the pressure in the body cavity are equivalent. Thus, the pressure sensor  560  is capable of a direct measurement of pressure within the body cavity. In another variation shown schematically in  FIG.  18   , the pressure sensor  560  as indicated in  FIG.  16    can consist of two independent sensing elements  560 ′ and  560 ″ that both interface with fluid extending into the sensor  560  from the single fluid channel  108   b . The sensing elements  560 ′ and  560 ″ send pressure signals to controller  545  through cables  564 ′ and  564 ″ ( FIG.  18   ). At the initiation of a procedure, or during a procedure, the controller then can be configured to monitor or compare pressure signals from the independent sensing elements  560 ′ and  560 ″. If the two sensors&#39; pressure signals are not within a preselected range from one another, the controller  545  can provide a warning of sensor malfunction and/or terminate or modulate any ongoing operation of the fluid management system or resection device. 
       FIG.  17    schematically illustrates the fluid management system  500  in operation. The uterine cavity  502  is a potential space and needs to be distended to allow for hysteroscopic viewing. A selected pressure can be set in the controller  545 , for example via a touch screen  565 , which the physician knows from experience is suited for distending the cavity  502  and/or for performing a procedure. In one embodiment, the selected pressure can be any pressure between 0 and 150 mm Hg. In one system embodiment, the inflow pump  546 A can operate as a variable speed pump that is actuated to provide a flow rate of up to 850 ml/min through first line or inflow line  550 . In this embodiment, the outflow pump  546 B can operate at a fixed speed to move fluid in the second line or outflow line  555 . In use, the controller  545  can operate the pumps  546 A and  546 B at selected matching or non-matching speeds to increase, decrease or maintain the volume of distention fluid  244  in the uterine cavity  502 . Thus, by independent control of the pumping rates of the inflow and outflow pumps  546 A and  546 B, a selected set pressure in the body cavity can be achieved and maintained in response to signals of actual intra-cavity pressure provided by sensor  560 . 
     In one system embodiment, as shown in  FIGS.  17  and  19   , the fluid management system  500  includes a filter module or system  540  that can include a first filter or tissue capturing filter  570  that is adapted to catch tissue strips  225  that have been resected and extracted from the body cavity  502 . A second filter or molecular filter  575 , typically a hollow fiber filter, is provided beyond the first filter  570 , wherein the molecular filter  575  is adapted to remove blood and other body materials from the distention fluid  244 . In particular, the molecular filter  575  is capable of removing red blood cells, hemoglobin, particulate matter, proteins, bacteria, viruses and the like from the distention fluid  244  so that endoscopic viewing of the body cavity is not obscured or clouded by any such blood components or other contaminants. As can be understood from  FIGS.  16 - 19   , the outflow pump  546 B at its outflow side  556  provides a positive pressure relative to fluid flows into the filter module  540  to move the distention fluid  244  and body media through the first and second filters,  570  and  575 , and in a circulatory flow back to the fluid source  535 . 
     Referring to  FIG.  19   , in an embodiment, the first filter  570  comprises a container portion or vial  576  with a removable cap  577 . The inflow of distention fluid  244  and body media flows though line portion  555  and through fitting  578  into a mesh sac or perforate structure  580  disposed in the interior chamber  582  of the vial  576 . The pore size of the perforate structure  580  can range from about 200 microns to 10 microns. The lumen diameter of hollow fibers  585  in the second filter  575  can be from about 400 microns to 20 microns. In general, the pore size of perforate structure  580  in the first filter  570  is less than the diameter of the lumens of hollow fibers  585  in the second filter  575 . In one embodiment, the pore size of the perforate structure  580  is 100 microns, and the lumen size of the hollow fibers  585  in the molecular filter  575  is 200 microns. In one embodiment, the molecular filter  575  is a Nephros DSU filter available from Nephros, Inc., 41 Grand Ave., River Edge, N.J. 07661. In one variation, the filter  575  is configured with hollow fibers having a nominal molecular weight limit (NMWL) of less than 50 kDa, 30 kDa or 20 kDa. 
     In another aspect of the invention, the molecular filter  575  is configured to filter large volumes of distention fluid, since the fluid flows are circulating. Additionally, the molecular filter  575  is configured to filter significant potential volumes of distention fluid that may contaminated with blood, blood products and the like that will be mixed with the fluid. In one embodiment, the molecular filter  575  has a membrane surface area of at least 0.6 m 2 , 0.8 m 2 , 1.0 m 2 , 1.2 m 2  and 1.4 m 2 , wherein the membrane surface area is defined as the total surface area of the lumens of the hollow fibers  585  in the molecular filter  575 . In another aspect of the invention, a method of fluid management can include distending a body space and maintaining a flow rate of up to 850 ml/min of a distension fluid flow into and out of a body space and thereafter through a filter system  540  capable of removing at least 20 ml, 40 ml or 60 ml of blood from the distension fluid  244 . 
     Referring to  FIG.  19   , it can be seen that the filter module  540  includes detachable connections between the various fluid flow lines to allow for rapid coupling and de-coupling of the filters and flow lines. More in particular, flow line  555  extending from the tissue resecting probe  515  has a connector portion  592  that connects to inlet fitting  578  in the first filter  546 A. Flow line portion  555 ′ that is intermediate the filters  546 A and  546 B has connector portion  596   a  that connects to outlet fitting  596   b  in first filter  542 A. The outflow end of flow line  555 ′ has connector  598   a  that connects to inlet fitting  598   b  of the second filter  546 B. The return flow line  600  that is intermediate the second  546 B and fluid source  535  has connector portion  602   a  that connects to outlet fitting  602   b  in second first filter  546 B. In one embodiment, at least one check valve  605  is provided in the flow path intermediate the filters  546 A,  546 B which for example can be in line  555 ′, connectors  596   a ,  598   a  or fittings  596   b ,  598   b . In  FIG.  19   , a check valve  605  is integrated with the inlet end  608  of the second filter  546 B. In use, the operation of the system will result in substantial fluid pressures in the interior of the second filter, and the check valve  605  allows for de-coupling the first filter without escape of pressure and release of fluid media into the environment, for example, when the tissue resecting procedure is completed and the physician or nurse wishes to transport the vial  576  and tissue strips  225  therein to a different site for biospy purposes. In general, a one-way valve such as check valve  605  can be provided at one or more locations in flow lines  555  and  555 ′ to prevent back flows of pressure through line  555  to the resecting device  515 . For example, a one-way valve  605 ′, such as a float valve, can be provided at one or more locations in line  555  or fitting  578  as indicated by the dashed line in  FIG.  19    (see also  FIGS.  20 - 21   ). A float valve  605 ″ can also be provided in line  550  proximate the saline source  535 . 
     In one aspect, a fluid management system comprising a first fluid line  550  configured to carry distention fluid  224  from a fluid source  535  to a body space, a second fluid line  555 ,  555 ′ and  560  configured to carry fluid from the body space to a first filter  570  and then to a second filter  575  and then back to the fluid source  535 , an outflow pump operatively coupled to the second fluid line and at least one check valve  605  in the second fluid line intermediate the first and second filters  570  and  575 . 
     In one embodiment, the controller  545  of the fluid management system  500  is configured for calculation of a fluid deficit that is measured as a difference between a fluid volume delivered to the body space  502  and a fluid volume recovered from the body space during a medical procedure such as fibroid removal (see  FIGS.  16 - 19   ). A method of fluid management in a hysteroscopic procedure comprises providing a distention fluid source  535  ( FIG.  17   ) having a predetermined volume, introducing fluid (e.g., saline) from the source  535  through a first flow line or inflow line  550  into the uterine cavity and through a second flow line or outflow line  555  out of the cavity into a filter module  540  and through a further portion  600  of the second flow line back to the fluid source  535  wherein the interior volume of the first and second flow lines and the filter module when subtracted from the predetermined volume of the source  535  equals 2.5 liters or less. The instructions for use then can include the requirement that only a single 3 liter saline bag can be used in any fibroid or polyp removal procedure, which in turn will insure that saline intravasation can never exceed 2.5 liters. In this variation, the predetermined volume of the source  535  can be 3.0 liters, as in a standard 3 liter saline bag, and the interior system volume can be at least 0.5 liters. 
       FIGS.  20  and  21    are schematic diagrams relating to the integrated operation of an RF tissue resecting probe  515  of the type described above and a fluid management system  500  of the type described above. In general, the controller  545 , RF generator  670  and fluid management system  500  are adapted to provide controlled flows of distention fluid into and out of a body cavity  502  while maintaining a targeted pressure within the body cavity while at the same providing RF energy delivery to the resecting probe contemporaneous with fluid flows. In one system embodiment, the system can operate in three different modes, all controlled by the controller  545 : (i) a diagnostic mode for hysteroscopy, (ii) a resecting treatment mode for tissue resection and extraction; and (iii) and a coagulation treatment mode for tissue coagulation. 
     Referring to  FIG.  20   , in diagnostic mode, the inflow or infusion pump  546 A, the outflow or aspiration pump  546 B and the pressure sensor  560  and monitoring system are all activated. In one embodiment, the touchscreen  565  on controller  545  has a graphical user interface (GUI) with fluid control settings that can be adjusted by the physician ( FIG.  16   ). The inflow pump  546 A can be toggled ON/OFF by touching the inflow pump button on the GUI. The targeted intra-cavity pressure can be set on the touchscreen  565 , for example from 0 to 150 mmHg or more ( FIG.  16   ). 
     In a method of operation as shown in  FIG.  20   , the physician sets a target intra-cavity pressure on the GUI and then activates the inflow pump  546 A which causes a flow of distention fluid  244  through the inflow or infusion line  550  and endoscope  512  into the body cavity  502 . In one embodiment, the inflow pump  546 A in diagnostic mode can be actuated on the touchscreen  565 . In the diagnostic mode, the controller  545  is configured to not actuate the outflow pump  546 B until the set pressure is attained or there is an overpressure condition. Thereafter, in one variation, the outflow pump  546 A will then operate at a fixed rate and the inflow pump speed can be modulated in response to signals from the pressure sensor to stabilize the pressure around the targeted cavity pressure. The actual intra-cavity pressure measured by the pressure sensor  560  can be displayed on the controller GUI ( FIG.  16   ). 
     In order to stabilize fluid pressure in a body cavity, the controller  545  includes a pressure control algorithm that is configured as a feedback control loop. The controller microprocesser reads both the intra-cavity pressure set point and the actual cavity pressure based on signals from the pressure sensor  560 . In response to these two parameters, the algorithm calculates a delta value signal based on a generic proportional integral (PI) control algorithm. The delta value is sent to a digital to analog converter and fed into a motor amplifier that drives the inflow pump  546 A. The controller algorithm then minimizes the difference between the set pressure and the actual pressure by adjusting the speed of the inflow (infusion) pump  546 A. 
     In one embodiment, the system further includes an actuator and algorithm for providing a rapid fluid inflow and fluid outflow for flushing the body cavity  502 , which for example can be an actuator button  672  on a footswitch assembly  675 . In this flushing method, the outflow (aspiration) pump  546 B is actuated to provide an increased level of outflow and then the pressure algorithm modulates the speed of the inflow (infusion) pump  564 A to maintain the targeted pressure in the cavity. Thus, in the diagnostic mode, the system can be actuated to rapidly flush the body cavity with fluid inflows and outflows while the controller algorithm maintains intra-cavity pressure as described above. The flow rate through the system and body cavity can be pre-set at 100 ml/min or greater, for example at 200 ml/min or 300 ml/min. In another embodiment, the physician may select a rapid flow rate on the touchscreen from 200 ml/min to 800 ml/min. 
     In a non-diagnostic or therapeutic resecting mode for resecting tissue, referring to  FIG.  21   , the controller  545  delivers radiofrequency energy to the bi-polar electrode arrangement of the probe  515  (see  FIGS.  12 A- 12 C ) to resect tissue and also actuates the two pumps to provide fluid inflows and outflows as described above. To operate in the resection mode, the physician can use the touchscreen  565  ( FIG.  16   ) to enter a non-diagnostic (therapeutic) mode of operation. Thereafter, a first pedal  677   a  on the footswitch  675  can be used to actuate the system in resection mode to resect tissue. Actuation of the first pedal  677   a  results in the controller contemporaneously: (i) activating the outflow pump  546 B at a fixed speed to provide outflows at a rate of 400 ml/min to 850 ml/min; (ii) activating the inflow pump  564 A which has a rotation speed controlled and modulated by the controller  545  as described above to maintain a targeted pressure in the body cavity; (iii) delivering DC voltage to the motor  525  of the resecting probe  515  to reciprocate the resecting sleeve  175 ; and (iv) delivering RF energy to the bi-polar electrode arrangement of the resecting probe  515 . In one embodiment, the RF generator  670  and controller  545  provide a variable DC voltage from 5-20 volts to the motor  525  of the resecting probe, a peak RF power of  200  watts, and a peak RF voltage of 240 volts at a 148 kHz frequency. 
     In the resection mode, the controller&#39;s pressure algorithm operates in a dynamic flow condition wherein the outflow of distention fluid  244  from the body cavity  502  varies as it will be dependent on the rate of tissue resection and the speed at which resected tissue strips  225  and fluid  244  can move through the extraction channel  160 . The intra-cavity pressure is maintained at the set pressure by the feedback loop which operates in a similar manner as described above when the system operates in the diagnostic mode. Resected tissue strips  225  are moved through the system as described above and extracted from the body cavity and probe through the outflow line  555 . The outflows of fluid carries resected tissue, blood and other body fluids into the first filter  570  and then the second filter  575  as can be seen in  FIG.  21   . When the physician releases pressure on the first pedal  677   a , the resecting probe  515  is then de-activated and only the inflow  546 A will remain active in controlling the intra-cavity pressure as described previously. 
     In the coagulation mode, the controller  545  and controller algorithm activates the bi-polar electrode arrangement of probe  515  to coagulate tissue and also to intermittently actuate the fluid flow functions as described above. The motor  525  in the probe handle is not activated, and the resecting sleeve  175  is positioned in an intermediate position in the window  517  in the outer sleeve  518  (cf.  FIG.  12 A ). The intermediate position of the resecting sleeve  175  in the window  517  is a default position that occurs each time that DC current to probe motor  525  is terminated. 
     To initiate operation under the coagulation mode, it is assumed that the physician has previously selected the non-diagnostic (therapeutic) mode of operation using the touchscreen  565 . The physician then can actuate a second pedal  677   b  on the footswitch  675  to coagulate tissue. Actuation of the second pedal  677   b  results in the controller contemporaneously: (i) delivering RF energy to the bi-polar electrode arrangement of the resecting probe  515 ; and (ii) intermittently actuating the inflow and outflow pumps  546 A and  546 B to cause a circulating fluid flow while maintaining intra-cavity pressure as described above. In one embodiment, the dual pumps operate for 1 to 8 seconds after a continuous interval of RF energy delivery for greater than 10 seconds. The fluid flow rate can be from 100 to 600 ml/min. Further, each time the physician terminates RF energy delivery, the inflow and outflow pumps  546 A and  546 B can be activated for 1 to 10 seconds. The intermittent circulating flows in the coagulation mode are adapted to aid in visualization and further to prevent heating of distention fluid  244  in the body cavity  502  as a result of the RF energy application. In one embodiment, the RF generator  670  and controller  545  provide bi-polar radiofrequency outputs for coagulation at a peak RF power of  110  watts and a peak voltage of 200 volts at a 148 kHz frequency. 
     In operating the system in any diagnostic or therapeutic mode, the controller  545  has an over-pressure protection algorithm in the event that pressure exceeds the targeted intra-cavity set pressure. In one embodiment, if the intra-cavity pressure exceeds the set pressure by a predetermined amount for a pre-selected time interval, then the controller  545  can activate the outflow pump  546 B at a higher pumping rate than the inflow pump  546 A until the measured fluid pressure in the cavity drops below the set pressure. Optionally, the controller  545  can slow or stop the inflow pump  546 A until intra-cavity pressure drops to the targeted level. In one variation, the pump or pumps can be activated to reduce intra-cavity pressure if the measured pressure exceeds the set pressure by 5 mmHg for greater than 1 second, 2 seconds or 5 seconds. 
     Another mechanism for over-pressure protection is provided in the form a pressure relief valve  680  as depicted in  FIG.  18   . In one variation, the pressure relief valve  680  is coupled the housing  682  of sensor  560  and communicates with flow channel  108   b ′ in the sensor  560  to allow fluid venting and pressure relief through the sensor body. The pressure relief valve  680  can relieve pressure at a suitable pressure greater than 100 mm Hg, for example 100 mm Hg, 125 mmHg, 150 mmHg or another predetermined pressure. Thus, if intra-cavity pressure exceeds the targeted maximum level, the controller  545  provides an algorithm-based pressure relief mechanism by modulating the pumps while the check-valve  680  provides a back-up form of pressure relief ( FIG.  18   ). Further, the system can include a manual pressure relief valve  688  in a disposable fitting  712  coupled to the endoscope for additional safety redundancy ( FIG.  20   ). 
     In another aspect of the invention, the controller  545  includes an algorithm that is adapted to de-activate a powered resection device in the event that the actual pressure in the treatment site drops below a predetermined threshold level. The controller  545  is provided with continuous signals of actual pressure in the site from the pressure sensor assembly  560  ( FIG.  18   ). In one variation, if the actual pressure in the site drops below an allowable threshold pressure level, then the controller algorithm can automatically de-activate the motor that drives a reciprocating or rotating resecting member. In another variation, the controller algorithm can de-activate RF energy delivery to the working end of a resecting device  515  as shown in  FIGS.  16 - 17   . In this variation wherein RF energy delivery is de-activated, the algorithm may permit continued movement of the resecting sleeve  175  for a selected interval and then RF may be re-activated after the intra-cavity pressure level increases above the predetermined threshold either instantaneously or when such pressure exceeds the threshold level for a selected interval, for example of 1 to 10 seconds. In another variation, the controller algorithm can de-activate both the motor drive and RF delivery upon a fall in pressure below the threshold pressure level. The threshold pressure level in this algorithm can be any predetermined pressure, for example, 100 mmHg or less, 50 mmHg or less, or 25 mmHg or less. In one variation, the threshold pressure level is set at 15 mmHg. 
     In one aspect of the invention relating to treating tissue and directly sensing pressure in a body space, a method comprises (i) accessing a body space or potential body space with at least one system component configured to provide an inflow of distention fluid  244  to the space and an outflow of fluid from the space, the at least one component including an electrosurgical tissue resecting probe, (ii) providing a pressure sensor coupled to the at least one component configured to measure actual pressure in the space, (iii) sensing pressure within the space and modulating inflow and outflow rates in response to the sensed pressure to achieve or maintain a pressure set point in the space, and (iv) operating the electrosurgical probe at first RF parameters to resect tissue. The probe can be operated at second RF parameters to coagulate tissue. The step of modulating the inflow rates can provide inflows between 0 ml/min and 800 ml/min. The pressure set point can be between 30 mmHg and 200 mmHg. As described above, the step of sensing pressure is accomplished with a sensor coupled to an independent fluid channel that is separate from the flow channels carrying the distention fluid inflows and outflows. 
     In general, a fibroid treatment system corresponding to the invention comprises a controller, an inflow pump operated by the controller and configured to provide fluid inflow through a flow path to a patient&#39;s uterine cavity, an outflow pump operated by the controller and configured to provide fluid outflow through a flow path to the uterine cavity; and a motor driven resecting device operated by the controller. The resecting device comprise an elongate introducer having a tissue extraction channel ( 190 A,  190 B in  FIG.  6 A ) therein with a diameter of no less than 2.4 mm and an outer sleeve  170  having a diameter of no more than 3.8 mm. The resecting device is adapted to remove fibroid tissue at a rate of at least 2 gm/min. In this variation, the controller can be configured to actuate the inflow and outflow pumps in response to signals of fluid pressure in the uterine cavity and to maintain the target pressure as described above. More in particular, the signal of fluid pressure can be provided by a pressure sensor coupled to a static fluid column communicating with the uterine cavity. In another variation, the controller can be configured to operate the resecting device in response to at least one parameter selected from a group consisting of an inflow pump speed, an outflow pump speed and signals of fluid pressure in the uterine cavity as will be described further below. In another aspect of the invention, a fluid management system  500  and cooperating electrosurgical probe are provided that include an inflow pump  546 A configured for providing an inflow of a distention fluid into a site in a patient&#39;s body, a control system configured for operator selection of at least first and second flow control modes wherein the first flow control mode is configured for tissue resection and operates the inflow pump to provide a first peak inflow rate and wherein the second flow control mode is configured for tissue coagulation and operates the inflow pump to provide a second peak inflow rate. Typically, the first peak inflow rate is greater than the second peak inflow rate. In one variation, the first peak inflow is 1,000 ml/min, 800 ml/min, 600 ml/min or 500 ml/min. The fluid management and procedure system include a control system configured for operator-selection of a pressure set point at the site. As described above, the fluid management system and controller are configured to operate the inflow pump and an outflow pump to provide an outflow of distention fluid from the site to achieve or maintain the pressure set point in both the first and second flow control modes. 
     Referring to  FIGS.  16 - 21   , a fluid management system  500  of the invention comprises an inflow pump  546 A configured for providing an inflow of a distention fluid  244  into a site in a patient&#39;s body and an outflow pump  546 B configured for providing an outflow of fluid from the site, and a controller  545  configured for operator-selection of at least first, second and third flow control modes wherein the first flow control mode is configured for a diagnostic procedure and provides an inflow rate up to 800 ml/min, wherein the second flow control mode is configured for a tissue resection procedure and provides an inflow rate up to 1,000 ml/min, and wherein the third flow control mode is configured for a tissue coagulation and provides an inflow rate up to 800 ml/min with intermittent outflows at pre-selected time intervals. 
     Still referring to  FIGS.  16 - 21   , a fluid management and resection system corresponding to the invention comprises an elongated assembly configured for accessing and performing a procedure in a site in a patient&#39;s body, the system components including an endoscope, a tissue resecting probe, a fluid source and tubing set, inflow and outflow pumps and a controller wherein the inflow pump is configured for providing an inflow of fluid from the fluid source through a first channel in the assembly to the site, wherein the outflow pump is configured for providing an outflow of fluid through a second channel in the assembly from the site and wherein the controller is configured for contemporaneous control of the probe in at least one mode of operation and the inflow and outflow pumps to provide and maintain an operator-selected pressure set point at the site. 
     The system further includes a disposable pressure sensor detachably coupled to a system component, and in one variation, the pressure sensor is operatively coupled to a third channel in the system which typically is in the endoscope. In another variation, a pressure sensor is operatively coupled to the tubing set. Typically, the first channel described above is in the endoscope shaft  524  and the second channel is in the tissue resecting probe  515 . 
     In another aspect of the invention, referring to  FIGS.  20 - 21   , the fluid management system includes a fluid source  535 , typically a saline bag, with a sealed outflow port  702  and a inflow line tubing  550  that has a connector end  705  including at least one barb feature configured to permit said connector end  705  to advance into and spike the outflow port  702  but prevents withdrawal of said connector end  705  from the outflow port  702 . 
     In another aspect of the invention, the fluid management system  500  ( FIGS.  16 - 17   ) includes controller algorithms that are adapted to detect a significant fluid leak or loss within the system when deployed and in use in a diagnostic or therapeutic procedure. Such a leak can consist of fluid loss anywhere in the fluid path, such as at a connector in the inflow or outflow lines ( 550 ,  555 ) or through the cervical canal around the elongated shaft  524  of the endoscope  512  (see  FIG.  17   ). 
     In order to determine a leak or fluid loss, a controller algorithm continuously monitors the input voltage to the motor of the inflow or infusion pump  546 A wherein such input voltage corresponds directly to pump speed and thus corresponds to the fluid inflow rate. The algorithm further continuously monitors the input voltage to the motor of the outflow or aspiration pump  546 B which corresponds directly the fluid outflow rate. During such continuous monitoring, if the algorithm determines that the inflow pump motor is operating at an input voltage (inflow rate) that exceeds a predetermined threshold voltage level, then a timer is started. The threshold voltage level is a function of the set pressure, the actual intra-cavity pressure and which of the operational modes in operation at the time (diagnostic mode, resection mode, etc.). In each of the operational modes, the input voltage of the outflow pump (outflow rate) is different to meet the objectives of each mode. Thus, for each different mode and corresponding outflow rate, a different threshold voltage, inflow rate and time interval is used to determine if there exists an unwanted fluid loss. In another variation, a controller algorithm can detect a leak or fluid loss in the system using a linear fit curve that relates infusion motor voltage to an elapsed time interval to signal the leak or fluid loss. This type of algorithm may allow for faster detection of a fluid loss in operating modes in which the inflow pump motor operates at higher speeds, such as in a resection mode. In other words, the fluid loss could be detected earlier in cases in which there is a higher rate of loss. Test data can be collected to measure fluid loss at different motor speeds over a time interval to develop such a linear fit curve. 
     If the timer exceeds a pre-selected time interval during which input voltage of the inflow pump motor exceeds the predetermined voltage threshold, the controller then will display a notification warning and/or audible or visual alarm to indicate a leak or fluid loss. The length of the pre-selected interval also can vary depending on the severity of the fluid inflow rate, that is, the input voltage to the inflow pump motor, in any of the system&#39;s operating modes. As the inflow rate increases above the nominal inflow rate in any mode, the time interval preceding the fluid loss warning or alarm will be decreased. In one variation, the predetermined voltage threshold level can correspond to inflow rates of at least 25 ml/min, at least 50 ml/min or at least 100 ml/min and the pre-selected time interval can be at least 1 second, at least 5 seconds or at least 10 seconds. 
     In another aspect of the invention, the controller  545  includes algorithms that are adapted to detect kinks or clogs in the infusion tubing of inflow line  550  or the aspiration tubing of outflow line  555 . It is possible for the flexible tubing of either the inflow line  550  or outflow line  555  to be kinked which may remain temporarily unnoticed by the physician and the nursing staff. If the inflow line  550  is kinked, the decrease in fluid inflows into the treatment site will result in a loss of pressure in the site and the working space may collapse. A kink in the outflow line  555  can lead to an unwanted fluid pressure increase in the treatment site. 
     In order to rapidly detect a kink in the infusion line  550  on the positive pressure side of the inflow pump  564 A, a controller algorithm is adapted to provide a kinked tubing warning if the calculated power driving the inflow pump motor exceeds a predetermined value over a pre-selected time interval. Such a predetermined value depends on the motor, gear box, pump head, and a predetermined pressure limit. As can be understood from the above description of the dual pump system, the motor power directly corresponds to the pressure on the positive pressure side of the inflow pump  564 A. As the pressure in the inflow tubing increases as a result of a kink or clog in the tubing, the hydraulic load on the pump rollers from the tubing will increase, which transfers load to the inflow pump motor. This increase in load on the motor then results in an increase in the current which is required to drive the pump motor at the targeted speed. The controller  545  includes an algorithm for maintaining the pump speed (and corresponding flow rate) at a predetermined level, no matter the load, during use of the fluid management system in its various modes. The power value is measured by a controller algorithm, and at the predetermined limit, the algorithm can (i) display a warning of a blocked fluid flow which can relate to kinked tubing or a clog in the flow paths or filter  575 ; (ii) display a message or warning that the molecular filter  575  may be clogged; or (iii) display a message to exchange the filter  575 . The algorithm can further interrupt the procedure by de-activating the pumps  546 A,  546 B, and/or by de-activating the power to any tissue-resecting device  515  in use. 
     The fluid management system  500  further includes a controller algorithm for detecting a kink or clog in the outflow line  555  on the negative pressure side of the outflow pump  546 B. This kink detection is accomplished by monitoring the motor voltage of both pump motors. If the system is being operated in either the resection mode or diagnostic mode, the algorithm first checks to determine if the outflow pump  546 B is in an ON state, and then checks that voltage applied to the inflow pump  546 A. If the motor of inflow pump  546 A is operating at a voltage below a predetermined threshold level, then a timer is started. The predetermined voltage threshold of the inflow pump motor is selected based on the expected input motor voltage during the resection and diagnostic modes. The typical fluid outflow rate from the uterine cavity during the resection and diagnostic modes is 250 to 500 ml/minute, a flow rate which requires a minimum motor voltage input on the inflow pump motor to maintain pressure. If the outflow from the uterine cavity decreases or stops as a result of a kink in the outflow line  555 , then the actual intra-cavity pressure would remain at a relatively static level. In this static condition, the input voltage of the inflow pump motor would be below the predetermined threshold input voltage, and as such, the kink detection timer would be initiated. When the timer exceeds a pre-selected time interval ranging from 5 seconds to 120 seconds, the algorithm is adapted to provide a kinked tubing warning. Additionally, the algorithm can interrupt the procedure by de-activating the pumps ( 546 A,  546 B) and/or by de-activating the power to any resection device  515  in use. 
     The fluid management system  500  further includes a controller algorithm for detecting a kink in the tubing of outflow line  555  on the positive pressure side of the outflow pump  546 B. The controller algorithm detects such a kink in the outflow line  555  if the measured motor current on the motor driving the outflow pump  546 B exceeds a predetermined level. The predetermined level again depends on the motor, gear box, pump head, and a predetermined pressure limit. The motor current directly corresponds to the pressure on the positive pressure side of the pump  546 B. As the pressure in the tubing increases (as a result of a tubing kink or a clogged filter) the hydraulic load onto the pump rollers from the tubing increases, which transfers load to the motor. This increase in load to the motor increases the current required to drive the motor at the targeted speed and flow rate. As described previously, the controller  545  includes an algorithm that maintains the pump speed at a predetermined level during use of the fluid management system in various modes. Thus, the kink detection algorithm measures the current that drives the outflow pump motor, and at the predetermined current limit over a pre-selected time interval, the algorithm can (i) display a warning of kinked tubing; (ii) display a message or warning that the molecular filter  575  is clogged; or (iii) display a message to exchange the filter  575 . Additionally, the algorithm can automatically interrupt the procedure by de-activating the pumps ( 546 A,  546 B) and/or by de-activating the power to any resection device  515  in use in response to detection of the kinked tubing or clog in a flow path. 
     In another aspect of the invention, the controller  545  includes algorithms that are adapted to further control and optimize fluid pressure in a site during a tissue resection interval that uses a feedback control loop to maintain the targeted set pressure. The feedback control loop consists of utilizing the pressure sensor  560  to monitor actual pressure in the site, and then utilizing controller algorithms to modulate speeds of both the inflow pump  546 A and the outflow pump  546 B ( FIG.  21   ). More in particular, when the physician initiates tissue resection with a tissue resecting device  515  as shown in  FIGS.  16 - 17  and  21   , the tissue volume interfacing the window  517  ( FIG.  21   ) will at least partially block the window and thus begin to slow the fluid outflow through the extraction channel  160  in the inner sleeve  175 . As a result of the reduction in outflow, signals from the pressure sensor  560  to the controller  545  will indicate an increase in actual pressure in the site, which then under previously described algorithms will cause a reduction in the input voltage in the inflow pump motor to thus slow down the fluid inflow rate. If the condition of reduced outflow continues for a first pre-selected time interval, the controller algorithm then will recognize that the resecting device is resecting tissue and sends a tissue-engagement signal to the controller. After a subsequent or second pre-selected time interval, the algorithm will cause the controller  545  to reduce the input voltage of the outflow pump motor (and fluid outflow rate) from a higher voltage level (e.g., 15 to 30 volt range) to a lower voltage (e.g., 5 to 12 volt range) and contemporaneously will put the inflow pump into a “ready” state. In this ready state, if a sudden decrease in actual pressure in the site were signaled by the pressure sensor  560 , then the algorithm would cause delivery of a maximum voltage (e.g., 30 volts, instead of nominal voltage) to the inflow pump motor to thus cause the maximum fluid inflow into the site. Upon such a sudden decrease in pressure, the algorithm then sends a tissue-disengagement signal to the controller, which actuates the inflow pump at a maximum voltage as described above. In normal operating conditions, the nominal inflow pump voltage may be in the 10 to 20 volt range. The objective of this pressure maintenance algorithm is to anticipate a sudden decrease in pressure in the site when the window  517  in the resecting device is cleared of tissue while the resecting device is operating, or when tissue chips are cleared through the extraction channel  160  which then results in a rapid increase in outflow. The then ongoing decreased outflow pump voltage also reduces the outflow rate, and the “ready” state of the inflow pump insures that when the sudden tissue-clearing condition (tissue-disengagement signal) occurs, the inflow pump  546 A is activated at its maximum voltage and inflow rate to match or exceed the outflow rate which then will prevent any drop in actual pressure in the site. The maximum inflow rate and the reduced outflow rate will continue until the targeted set pressure is maintained for a pre-selected interval that can range from 0.1 second to 10 seconds. 
     Another method of operating a fluid management system and RF resecting probe as depicted in  FIGS.  16 - 21    comprises (i) accessing a site in a patient&#39;s body with a distal end of an endoscope and working end of an electrosurgical probe, (ii) delivering RF energy to the working end to apply energy to tissue at the site, (iii) contemporaneously operating a fluid management system to provide a selected rate of a fluid inflow to, and fluid outflow from, the site, (iv) detecting a change of a signal of an electrical parameter of the probe during operation and in response to detecting said change, switching at least one operational parameter of said fluid management system. Typically, the electrical parameter can include at least one of an impedance level, a power level, a voltage level and a current level. The operational parameter of the fluid management system that can be modulated includes at least one of a rate of fluid inflow to the site, a rate of fluid outflow through a system outflow channel from the site, a positive pressure level in communication with the fluid inflow channel, a negative pressure level in communication with the fluid outflow channel, a targeted pressure set point at the site and a rate of change of any of the preceding. In another variation, the at least one operational parameter can include an algorithm for operating a pressure sensing system configured to determine fluid pressure at the site. In the method described above, the applied energy can be adapted to ablate and resect tissue or to coagulate tissue. 
     While certain embodiments of the present invention have been described above in detail, it will be understood that this description is merely for purposes of illustration and the above description of the invention is not exhaustive. Specific features of the invention are shown in some drawings and not in others, and this is for convenience only and any feature may be combined with another in accordance with the invention. A number of variations and alternatives will be apparent to one having ordinary skills in the art. Such alternatives and variations are intended to be included within the scope of the claims. Particular features that are presented in dependent claims can be combined and fall within the scope of the invention. The invention also encompasses embodiments as if dependent claims were alternatively written in a multiple dependent claim format with reference to other independent claims.