Abstract:
A system and method for detecting perforations in a body cavity. In accordance with the method of the invention, a fluid (liquid or gas) is delivered into a body cavity to slightly pressurize the cavity. A pressure sensing system monitors the pressure within the cavity for a predetermined test period. If cavity pressure is not substantially sustained during the test period, the physician is alerted to further assess the cavity for perforations before initiating treatment within the cavity. In a preferred form of the system, a medical treatment system such as an RF ablation system is provided with perforation detection functionality. The system preferably includes a pre-test and post-test lockout system. The lockout system prevents RF power delivery unless, during a predetermined test period, the pressure sensing system determines that no perforation exists, or unless a previously performed perforation detection procedure determined a perforation was present but the lockout system was subsequently overridden by the physician.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the field of systems of methods for detecting the presence of perforations in body cavities. More particularly, the present invention relates to a system and method that pressurizes and body cavity and detects whether the body cavity can maintain a pressurized condition.  
         BACKGROUND OF THE INVENTION  
         [0002]    Background of the Invention  
           [0003]    There are certain medical procedures that are carried out within a body cavity. One example of such a procedure is tissue ablation. Ablation of the interior lining of a body organ is a procedure which involves heating the organ lining to temperatures which destroy the cells of the lining or coagulate tissue proteins. Such a procedure may be performed as a treatment to one of many conditions, such as chronic bleeding of the endometrial layer of the uterus or abnormalities of the mucosal layer of the gallbladder. Existing methods for effecting ablation include circulation of heated fluid inside the organ (either directly or inside a balloon), laser treatment of the organ lining, and resistive heating using application of RF energy to the tissue to be ablated.  
           [0004]    Ablation procedures are often carried out without direct endoscopic, visualization. For example, ablation of the endometrium typically involves insertion of an elongate ablation device into the patient&#39;s cervix without the use of a hysteroscope. As can be appreciated, the presence of a perforation in the uterus could result in inadvertent passage of the ablation device through the perforation and out of the uterus into the bowel. Although events of this nature are rare, the injury that could result from such occurrences make it highly desirable to provide a mechanism by which a physician can evaluate whether perforations are present in a body cavity before a treatment device such as an ablation device is used to deliver power.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is a system and method for detecting perforations in a body cavity. In accordance with the method of the invention, a fluid (either liquid or gas) is delivered into a body cavity to slightly pressurize the cavity. A pressure sensing system monitors the pressure within the cavity for a predetermined test period. If cavity pressure is not substantially sustained during the test period, the physician is alerted to further assess the cavity for perforations before initiating treatment within the cavity. In a preferred form of the system, a medical treatment system such as an RF ablation system is provided with perforation detection functionality. The system preferably includes an interlock that prevents RF power delivery unless a perforation detection procedure has been performed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a schematic representation of a perforation detection system utilizing principles of the present invention.  
         [0007]    [0007]FIG. 2A is a side elevation view of an ablation device that may be used with the system of FIG. 1.  
         [0008]    [0008]FIG. 2B is a plan view of the RF applicator head of the ablation device of FIG. 2A.  
         [0009]    [0009]FIG. 3 is a schematic representation of the pneumatic subsystem of the system of FIG. 1.  
         [0010]    [0010]FIG. 4 is a simplified state diagram illustrating a mode of operation utilizing the perforation detection and interlock features of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]    A perforation detection system  10  (also referred to as a “body cavity assessment system”) utilizing principles of the present invention will be described herein as forming part of an RF ablation system used to ablate tissue within a body cavity such as a uterus. However, it should be appreciated that the perforation detection system  10  may be provided with another type of system used for treatment, or it may be provided independently of a larger treatment system.  
         [0012]    Generally speaking, perforation detection system  10  includes a medical ablation device  12  of a type used for tissue ablation, and an RF generator system  14  of the type used to deliver RF ablation energy to an electrode array on ablation device  12 . The RF generator unit, however, is provided with additional components that are used for the body cavity assessment function of the present invention. In particular, the RF generator unit is provided with a fluid/gas source  16  and a body cavity assessment interlock  20 . Fluid/gas source  16  is fluidly coupled to ablation device  12  via a source line  22 . The ablation device is positionable within a body cavity BC so as to deliver fluid/gas from source  16  through the source line  22  and the ablation device and into the body cavity.  
         [0013]    Body cavity assessment interlock  20  includes a pressure sensing system  24  fluidly coupled to the medical device via pressure detection/signal line  26 . Pressure sensing system  24  monitors the pressure within the body cavity BC while fluid/gas is being (or after it has been) delivered to the body cavity, and detects whether elevated pressure can be maintained over a predetermined period of time, within a predetermined window of time. If it cannot, the user is alerted that there may be a perforation in the organ.  
         [0014]    Body cavity assessment interlock  20  further includes an interlock system  28  that prevents treatment with the ablation device  12  unless body cavity assessment has been performed. The RF generator system  14  is additionally provided with a vacuum system  30  coupled to pressure detection/signal line  26 , RF circuitry  27 , and other components needed to perform the ablation function. A footswitch  32  or other input device controls operation of the RF generator system  14 . A microprocessor or programmable logic device  34  within the RF generator system  14  governs various functions, including the body cavity assessment, interlock, and RF ablation procedures.  
         [0015]    Ablation Device  
         [0016]    An example of an RF ablation device  12  that may be used with the system  10  is shown in FIGS. 2A and 2B. Ablation devices of this type are shown and described in U.S. Pat. No. 5,769,880 and U.S. application Ser. No. 09/103,072, each of which are incorporated herein by reference. A similar device is the NovaSure ablation device available from Novacept, Inc., Palo Alto, Calif. Naturally the perforation detection system may be provided in combination with the other medical devices as well such alternative devices include thermal ablation devices in which heated liquid is circulated through a balloon positioned within the body cavity of interest, or other device used for procedures besides ablation. Alternatively, the system may be provided with two medical devices, one for use in delivering inflation medium and another for use in treating body tissue. As a further alternative, a treatment device may be provided independent of the system  10 .  
         [0017]    Ablation device  12  is configured to deliver RF ablation energy to the interior surface of a body cavity, while causing moisture (e.g. steam) generated during ablation to be withdrawn away from the body tissue—preferably using suction. This moisture transport feature of the device  12  is advantageous in that removing steam from the ablation site minimizes the amount of thermal ablation would otherwise be caused by the steam. Greater control over ablation depth is thus achieved by allowing ablation to occur only (or primarily) by RF energy rather than by thermal conduction.  
         [0018]    The device  12  includes an RF applicator head  36 , a sheath  38 , and a handle  40 . The applicator head  36  is slidably disposed within the sheath  38  to give the applicator head  36  a streamlined profile (FIG. 2A) to facilitate insertion of the device into a body cavity (e.g. the uterine cavity). Once the applicator head  36  has been inserted into the body cavity, handle  40  is manipulated to cause the applicator head  36  to extend from the distal end of the sheath  38  and to expand into the position shown in FIG. 2A as to make contact with body tissue.  
         [0019]    Referring to FIG. 2B, in which the sheath  38  is not shown for clarity, applicator head  36  extends from the distal end of a length of tubing  42  which is slidably disposed within the sheath  38 . Applicator head  36  includes an external electrode array  44  and an internal deflecting mechanism  46  used to expand and tension the array for positioning into contact with the tissue.  
         [0020]    The array  44  is preferably formed of a stretchable metallized fabric mesh which is preferably knitted from a nylon and spandex knit plated with gold or other conductive material. In one array design, the knit is formed of three monofilaments of nylon knitted together with single yarns of spandex. Each yarn of spandex has a double helix of five nylon monofilaments coiled around it.  
         [0021]    When in its expanded state, the array  44  includes a pair of broad faces  48  (one of which is shown in FIG. 2B) spaced apart from one another, and narrower side faces (not shown) extending between the broad faces  48  along the sides and distal end of the applicator head  36 , and a distal face  52  extends between the broad faces  48  at the distal end of the applicator head  36 .  
         [0022]    Insulating regions (not shown) formed by etching other techniques on the applicator head to divide the mesh into electrode regions.  
         [0023]    The array may be divided by the insulated regions into a variety of electrode configurations. In a preferred configuration the insulating regions divide the applicator head into four electrodes by creating two electrodes on each of the broad faces.  
         [0024]    Deflecting mechanism  46  and its deployment structure is enclosed within electrode array  44 . External hypotube  58  extends from tubing  42  and an internal hypotube  60  is slidably and co-axially disposed within hypotube  58 . Flexures  62  extend from the tubing  42  on opposite sides of external hypotube  58 . Hypotube  60  is a dual lumen tube that is coupled to the pneumatic subsystem as will be described below.  
         [0025]    A plurality of longitudinally spaced apertures (not shown) are formed in each flexure  62 . During use, these apertures allow moisture to pass through the flexures and to be drawn into exposed distal end of hypotube  58  using a vacuum source located in the RF generator system  14  and fluidly coupled to hypotube  58 .  
         [0026]    Each flexure  62  preferably includes conductive regions that are electrically coupled to the array  44  for delivery of RF energy to the body tissue. For example, strips of copper tape (not shown) or other conductive material may extend along opposite surfaces of each flexure. Conductor leads (not shown) are electrically coupled to the strips and extend through tubing  42  to an electrical cable which is attachable to the RF generator.  
         [0027]    During use, one conductive strip on each conductor is electrically coupled via the conductor leads to one terminal on the RF generator while the other strip is electrically coupled to the opposite terminal, thus causing the array on the applicator head to have regions of alternating positive and negative polarity.  
         [0028]    It is important to ensure proper alignment between the conductive regions of the flexures (e.g. the copper strips) and the electrodes in order to maintain electrical contact between the two. Strands of thread (which may be nylon) are preferably sewn through the array and around the flexures in order to prevent the conductive regions from slipping out of alignment with the electrodes.  
         [0029]    During use of the ablation device, the applicator head  36  is inserted into the uterus with the sheath  38  covering the array  44  to compress the applicator head  44  into a streamlined condition. Once the applicator head is within the uterus, the handle is used to withdraw the sheath and to open the array into its deployed position. Vacuum source  30  (FIG. 1) is activated, causing application of suction to hypotube  60 . Suction helps to draw uterine tissue into contact with the array  44 .  
         [0030]    Ablation power is supplied to the electrode array  44  by the RF generator system  14 . The tissue is heated as the RF energy passes from electrodes  56   a - d  to the tissue, causing moisture to be released from the tissue. The vacuum source helps to draw moisture from the uterine cavity into the hypotube  60 . Moisture withdrawal is facilitated by the apertures formed in flexures, by preventing moisture from being trapped between the flexures and the lateral walls of the uterus.  
         [0031]    Pneumatic Subsystem  
         [0032]    The fluid/gas source  16 , pressure sensing system  24 , and associated components are shown in FIG. 3. Each of the components of the pressure sensing system  24  is preferably coupled to microprocessor  34  of the RF generator system  14  although for clarity the microprocessor is not shown in FIG. 3. All pressure transducers, solenoid valves, and the vacuum pump are controlled by the microprocessor.  
         [0033]    It is also important to note that in the embodiment described below the roles of the two lines (source line  22  and pressure detection/signal line  26 ) play different roles during RF ablation than for perforation detection. Specifically, the signal line  26  for perforation detection serves as a suction line for ablation. The source line  22  for perforation serves as a vacuum signal line for ablation.  
         [0034]    Components along the source line  22  will first be described. Fluid/gas source  16  is preferably a disposable CO 2  cylinder, and may be a 16 gm cylinder providing approximately 850 psi at 25 C. One such example is the Linde medical grade 16 gm cylinder. The cylinder is removably attached to a pressure regulator  68  such as the Leland Model 50033 or equivalent. Regulator  68  includes a main shutoff valve  70  and pressure regulation component  72  which has a control pressure of approximately 60 psi. A pressure gauge  74  such as SenSym model ASCX100DN or equivalent is fluidly coupled to source line  22 . Pressure gauge  74  monitors the pressure remaining in the fluid/gas source  16  so as to detect when a low volume of fluid/gas remains, or when the user has failed to open the valve  68 .  
         [0035]    A solenoid valve  76  is positioned along the source line  22 , downstream of the pressure regulator  68 . Valve  76  remains in a closed condition, preventing flow of gas through the line  22 , except when a cavity assessment procedure is being carried out. A second pressure regulator  78 , such as an Airtrol R-920 series regulator, is positioned downstream of the valve  76  so as to reduce pressure in line  22  down to approximately 90+/−10 mmHg during a cavity assessment procedure. A flow control orifice  80 , positioned downstream of regulator  78 , limits flow in line  14  to 100+/−10 scc/min (standard cc/min). A pressure sensor upstream of orifice  80  monitors whether the pressure limit (of, for example, approximately 100 mm Hg) has been exceeded. If the limit has been exceeded, an output signal from this sensor causes an audible alarm to be triggered and the solenoid valve  76  is turned off. Downstream of orifice  80 , source line  22  is coupled, using a flexible Tygon tubing for example, to the introducer sheath  38  (FIG. 2B) of the ablation device  12 . The introducer sheath is located at the internal surface of the body cavity BC (the internal os, for example, in the case of a uterine cavity) so as to deliver gas into the body cavity BC that is to be treated.  
         [0036]    Turning to the components along the pressure detection line  26 , the pressure signal line  26  is fluidly coupled, using a Tygon tubing for example, to the lumen of hypotube  60 . Downstream of the medical device  12  is a pressure sensor  84 , such as the SenSym ACSX05DN. During a cavity assessment procedure, sensor  84  monitors pressure in the pressure signal line  26  and delivers the signal to microprocessor  34 . Microprocessor  34  then determines if pressure in the body cavity BC has failed to achieve a predetermined threshold (indicating a perforation in the body cavity) or if it has and maintained the threshold for a predetermined time period (indicating that the body cavity has no perforation).  
         [0037]    Further downstream of the pressure sensor  84  is a vacuum pump  86 . While not needed for perforation detection, vacuum pump  86  is used to carry out the moisture transport function of the medical device  12  described in the section entitled Ablation Device above.  
         [0038]    A second solenoid valve  88  lies upstream of the vacuum pump  86 . Valve  88  remains open at all times except during cavity assessment. Because the exhaust line of the vacuum pump may not be air-tight when it is not operating (including during the cavity assessment procedure) the valve  88  is provided to close the pressure signal line against leaks through the vacuum pump.  
         [0039]    A simplified state diagram illustrating operation of the system is shown in FIG. 4. Operation begins with valve  76  in the closed condition, and with valve  88  in the opened condition. In preparation for use of the system, a CO2 cylinder  16  is connected to the appropriate receiving device on the RF Generator&#39;s pneumatic subsystem (FIG. 3). The power to the generator is switched on. Pressure gauge  74  detects the pressure in the portion of pressure/monitoring line  22  extending between CO 2  cylinder  16  and valve  76 . If the user has failed to open the main CO 2  shutoff valve  70 , or if the pressure detected by gauge  74  is less than the specified pressure, an audible alert will sound, indicating a low-gas condition. Assuming no low-gas condition is detected, the user will connect the ablation device  12  to the. RF generator system  14 .  
         [0040]    The system remains in a “WAIT FOR CONNECT” condition, step  102 , until the user connects the ablation device  12  to the RF generator system. When the ablation device is plugged in, it actuates a microswitch or similar feature, which alerts the microprocessor that the ablation device has been connected. Connection of the device automatically starts the “CO2 PURGE” cycle, step  104 . During the purge cycle, valve  76  is opened to permit the flow of CO 2  through the device to drive air from the device. The purge cycle lasts for a duration sufficient to purge the air from the system, approximately 10 seconds. During the purging cycle the user is alerted by audible and visual indicators not to insert the device into the body cavity in order to prevent air from being delivered into the body. As a safety precaution, the vacuum pump that is part of the RF Controller is pulsed every few seconds during purging. If the user has inserted the ablation device into a body cavity during purging, the vacuum pump will draw out air that is delivered to the body.  
         [0041]    During the purge cycle and device insertion into the body cavity, the ablation device is closed, such that the poles of the electrode array are in contact with each other. A low voltage signal is applied to the ablation device which senses that the poles are in contact by detecting a DC short. After the completion of the purging cycle the system waits for the device to be deployed within the patient, step  106 , by monitoring for the end of the DC short condition. Once the user inserts the device into the uterine cavity and opens the array, the system detects that a DC short condition is no longer present. As a safety precaution, the perforation detection cycle cannot be initiated until the DC short condition is eliminated. In this way the last operation to be performed before the application of RF energy is the perforation detection cycle.  
         [0042]    From the completion of the purge cycle to the initiation of the perforation detection test, a continuous, low level flow of CO2 is circulated through the ablation device to keep the source and pressure signal lines open and free from blockage.  
         [0043]    Next, the system waits for the user to depress the footswitch  32 , “WAIT FOR FOOTSWITCH”, step  108 . Once the footswitch has been depressed, a 30-second timer is initialized (“RESET TIMER”) and the perforation detection test, (“PERFORM PRESSURE TEST”)  110  begins. Valve  88  is energized to close off the vacuum pump  86  to avoid loss of pressure through it. If it was not already opened, valve  76  is opened, allowing CO 2  to flow into the body cavity via medical device  12 . When the pressure at gauge  84  rises and remains above 50 mmHg for 4 seconds, the test has passed and the system moves to a “PASSTHROUGH” state. (It should be noted that the system may alternatively pressurize the cavity and then detect whether the monitored pressure falls below a predetermined level within a predetermined time period, indicating that a perforation may be present.)  
         [0044]    In the “PASSTHROUGH” condition the CO 2  is turned off and the vacuum pump is re-enabled by re-opening valve  88 . If the ENABLE button  33  has been pressed (automatic mode), RF power  114  (“APPLY RF POWER”) will be delivered automatically to the array  44  once the cavity assessment cycle has been completed and passed. If the ENABLE button has not been depressed (semiautomatic mode), the system moves through the “PASSTHROUGH” state and waits for footswitch actuation  112  (“WAIT FOR FOOTSWITCH”). The user must press the button to enable the RF generator and then press the foot switch  32  to deliver RF power  114 .  
         [0045]    In the event the cavity assessment test is not passed after the 30 second timer has expired, an audible tone sounds and visual indicators flash. The system remains in a TEST FAIL state, step  116 , and awaits further action by the user. If the user presses the foot switch, the system is re-sets to the initial ready state, step  108 , with the CO 2  flow off. The user may attempt the cavity assessment sequence as many times as desired.  
         [0046]    Alternatively, after one or more cavity assessment procedures has been performed and failed, the user may choose to override the system and cause the system to deliver RF energy despite the cavity assessment test having been failed. To do so, the user will press and hold the ENABLE button  33  for six seconds. Note that the pressure check must be attempted at least one time before this feature is available. If the user overrides the cavity assessment, the system moves to the “PASSTHROUGH” state to wait for footswitch step  112 .  
         [0047]    If at any time during the above sequence, the user should close the ablation device, a DC short will be detected in the electrode array by the RF generator&#39;s DC short detection circuitry. Closing the device causes the state of the perforation test to change to fail, and the system resets to the “WAIT FOR DEPLOY” state, step  106 . The system will then require that cavity assessment be performed again once the array is reopened. This assures that the last step performed before the application of RF energy is the perforation detection test: if the user, after having successfully completing the test, decides to close and remove the device for any reason, the perforation detection test must be performed again-once the device is deployed in the body cavity. This requirement also prevents a user from abusing the system by running cavity assessment with the device outside the body, and then inserting the device, overriding the test, and ablating without having every performed cavity assessment within the body cavity.  
         [0048]    For additional safety, the perforation detection system preferentially uses CO2, though other gases or liquids, such as normal saline, may be used. The pressure and flow limits follow well known guidance documents for insufflators. In the case of uterine perforation detection, the limits follow hysteroflator guidance documents. Though other configurations are possible, the cavity to be assessed should be in series between the source and pressure signal lines. In this manner, any kinked tubing or other problems will not lead to a false test result. Additionally, the system is capable of detecting perforations exceeding the range of sizes of devices normally inserted into body cavities (from say 15 mm down to less than 1 mm diameter).  
         [0049]    In order to reliably detect perforations in uterine cavities, the pressure threshold in that case is preferentially kept below the average cracking pressure of the fallopian tubes.  
         [0050]    There are several features that improve the system&#39;s ease of use. Firstly, the physician can start or stop the perforation test at any time in the sequence. Secondly microprocessor  34  is capable of distinguishing the difference between a device that is closed versus a device that is undergoing slight motion in the body cavity, thus reducing the likelihood that a passed test condition will be overturned. Finally, the system includes a collar assembly  63  in FIG. 2 a  which is capable of sealing the entry into the body cavity BC if leaks are determined to exist, thus reducing the likelihood of a false test failure.  
         [0051]    Although the forgoing description is with reference to a perforation detection system having a device usable to ablate tissue within a uterus, the present invention is applicable to perforation detection within other body cavities, and to perforation detection systems having medical devices useful for procedures other than ablation. In addition, although the system is described with reference to a particular embodiment, many other configurations are suitable for implementing the teachings of the invention. Those having ordinary skill in the art will certainly understand from the embodiment disclosed herein that many modifications are possible without departing from the teachings hereof. All such modifications are intended to be encompassed within the following claims.