WO2001085012A2

WO2001085012A2 - Apparatus and method for controlling electrosurgical instruments using pressure feedback

Info

Publication number: WO2001085012A2
Application number: PCT/US2001/014540
Authority: WO
Inventors: Delfin Pelayo
Original assignee: Ethicon, Inc.
Priority date: 2000-05-09
Filing date: 2001-05-07
Publication date: 2001-11-15
Also published as: WO2001085012A3; AU2001259518A1

Abstract

The present invention provides for regulating power supplied to an electrosurgical instrument used in conjunction with a distension medium. The pressure of the distension medium is closely monitored. Vapor bubbles (60) that occur in normal operation in some instruments or unexpectedly occur in other electrosurgical instruments directly affect the pressure of the distension medium. If the pressure increases beyond normal levels as a result of the vapor bubble (60), the power supplied to the electrosurgical element may be reduced or simply terminated until the pressure returns to an acceptable level.

Description

APPARATUS AND METHOD FOR CONTROLLING ELECTROSURGICAL INSTRUMENTS USING PRESSURE FEEDBACK

5 CROSS REFERENCE TO RELATED APPLICATION

The present invention claims the benefit of earlier filed United States provisional patent, serial number 60/133,392, filed on May 10, 1999, which is hereby incorporated by reference in its entirety herein.

0 BACKGROUND OF THE INVENTION

This invention relates to a control method for electrosurgical instruments and heated balloon instruments used in conjunction with a distension medium for the treatment of tissue, and more particularly the use of a pressure feedback signal to control the operation of the electrosurgical instrument. 5 The use of electrosurgical instruments for the treatment of tissue is well known. Endoscopic electrosurgery is useful for treating tissues in cavities of the body, and is normally performed in the presence of a distension medium. When the distension medium is a liquid, this is commonly referred to as underwater electrosurgery. A gaseous medium is commonly employed with endoscopic o surgery is performed in a distensible body cavity of larger potential volume in which a liquid medium would be unsuitable, as is often the case in laparoscopic or gastroenterological surgery.

One such cavity that may be distended to perform endoscopic surgery is the uterus. Some disorders, such as myomas, or the endometrial lining of the uterus, 5 may be treated by passing a resectoscope through the cervix creating a seal. Clear fluid is then introduced into the uterus to expand it for visibility and to provide room to maneuver the resectoscope. The resectoscope can then be directed to remove myomas and/or the endometrial lining. As tissue is removed, blood vessels are severed and the ends of the vessels are exposed to the distention fluid. If the fluid o pressure is lower than the blood pressure, blood enters the distention fluid eventually blocking visibility. Clear distention fluid may be circulated through the uterus to continually remove blood and other visibility-reducing material. If the distension pressure is increased, visibility may be maintained; however, fluid pressure greater than the blood pressure results in the flow of distention fluid into the bloodstream. This can lead to cerebra edema with serious consequences for the patient.

Current electrosurgical instrumentation employ a pressure port at the controller for the instrument or at the fluid supply port of the instrument. This method can lead to errors in actual pressure values within the distended organ because of flow resistance and valving in the instrument. Another exemplary electrosurgery instrument to ablate tissue is disclosed in

International Publication No. WO 97/24994, incorporated herein in its entirety by reference. In a specific application, a cavity, such as the uterus, is distended with a liquid, such as normal saline. Generally, the distension medium is maintained at a constant pressure within a closed system. An electrode is inserted into the uterus and when RF power is applied to the electrode the fluid medium heats up. Increased power to the electrode causes a vapor pocket to form around the electrode. The electrode is then useful for cutting or vaporizing tissue. The amount of energy dissipation within the vapor pocket and the size of the vapor pocket depend on the output voltage. One drawback is that if the output voltage is too high the electrode assembly will be destroyed. Thus, in order to prevent destruction of the electrode, the power output of the generator must be closely monitored.

A still another electrosurgical instrument to cauterize the endometrium of a uterus is also well known. The use of a heated balloon to cauterize the lining of the uterus is disclosed in representative U.S. Patents 4,949,718 to Neuwirth et al. and 5,800,493 to Steven et al., both of which are incorporated herein in their entirety by reference.

One drawback with the heated balloon technology is the inability to accurately control the temperature of the distension fluid within the balloon. Thermocouples are incorporated into the balloon to provide temperature feedback to a controller that regulates an electrical heater within the balloon. However, it has been observed that the fluid temperature gradient within the balloon varies greatly from the distal portion of the balloon, where the heater is located, to the proximal portion of the balloon. This is particularly relevant when the balloon is in a retroverted position within a woman's uterus during the treatment process; that is, the balloon is in an incline position with the distal end lower than the proximal end. 5 After the deflated balloon is inserted into the uterus, a fluid, such as a 5% dextrose in water solution is inserted into the balloon until the balloon reaches a certain internally pressure as monitored by the controller. The fluid is heated by providing electric current to the resistive wire of the heating element. The method provides for heating the fluid to a desired temperature of about 82 to 85°C as indicated by 0 the thermocouples and maintaining the temperature and pressure within the distensible bladder for a desired time interval. Afterward, the distensible bladder is deflated and the distensible bladder and tubular member removed from the uterus of the patient.

During the fluid heating process, however, fluid having a higher temperature 5 accumulates at the proximal end of the balloon (the elevated portion in the retroverted position) and fluid having a cooler temperature accumulates at the distal end. The temperature differential may be appreciable, as much as 10°C has been observed. The temperature differential causes a problem since the thermocouples are located distally within the balloon. The fluid in the proximal portion of the o balloon heats to temperatures well above 85°C while the thermocouple provides temperature feedback of the cooler fluid in the distal portion. As this occurs, fluid in the proximal portion begins to evaporate, forming a vapor bubble within the balloon. The vapor bubble expands the fluid and causes the fluid pressure to rise. Even before the fluid in the distal end reaches the operating temperature, the vapor 5 bubble may cause the fluid pressure within the balloon to exceed the safety pressure limit of the system, causing the system to shutdown. If this happens, the process is terminated, and the physician must reset the process, all in conjunction with the increased anxiety of the patient.

One method to overcome this problem is to introduce fluid agitators within o the balloon to mix the fluid and eliminate temperature differentials. Fluid agitators are generally successful during the steady state process after the fluid has been elevated to operating temperature. The agitators are not, however, very useful during the quick heat-up stage at the beginning of the process. Slowing the heating process would add time to the overall heat treatment process, which is unacceptable to both the physician and the patient. Another option is to insert additional thermocouples at the proximal end of the balloon. This is unacceptable since it would add complexity and cost to the balloon apparatus.

Consequently, there is a need for a reliable control technique for use with electrosurgical instruments and ablation balloon systems that provides for the reliable control of energy supplied to the instruments, yet being efficient and economical.

This invention addresses that need.

SUMMARY OF THE INVENTION Briefly and in general terms, the present invention provides for regulating a process variable used in the operation of electrosurgical instruments or heated balloon apparatus, hereinafter, collectively referred to as electrosurgical instruments, through a pressure feedback signal. The regulated process variable may include, for example, the pressure of the distension fluid, the power supplied to an electrode tip or the power supplied to an electrical heater for heating a fluid.

Specifically, the pressure of a distension medium is closely monitored. For example, vapor bubbles that occur in normal operation in some instruments or unexpectedly occur in other electrosurgical instruments directly affect the pressure of the distension medium. If the pressure, however, increases beyond normal levels as a result of the vapor bubble, the power supplied to the electrical element may be reduced or simply terminated until the pressure returns to an acceptable level. In one embodiment of the invention a pressure port is located at the proximal end of an electrosurgical instrument that measures the actual pressure of the distension fluid. As an example only, the invention will be further summarized describing the use of the heated balloon electrosurgical instrument for endometrial ablation. The apparatus provides for heating of an inflation medium within a distensible bladder positioned within a uterus of a patient. The apparatus introduces the inflation medium under pressure into the distensible bladder so as to assure substantially uniform contact of the bladder with the endometrium. A resistive heater within the distensible bladder heats the inflation medium to a temperature necessary to ablate the endometrium. The system provides for regulating the temperature and pressure of the inflation medium while the distensible bladder is within the uterus for a desired period of time.

The system for performing endometrial ablation comprises a controller configured to regulate electric current to the heating element. The controller also includes a pressure sensor in fluid communication with the inflation lumen of the tubular member to provide a pressure signal to a pressure display for visualizing the pressure in the distensible bladder. The controller is electrically connected to the heating element and configured to generate electric current to the resistive wire. The controller includes a microprocessor configured to accept the pressure signal, the temperature signal and the elapsed time signal. The microprocessor is further configured to regulate the electric current generated by the heater controller as a function of the pressure.

Specifically, if the pressure caused by a vapor bubble within the distensibel bladder exceeds a certain threshold amount, the electrical current to the heater element is turned off until the pressure decreases to a certain level. Therefore, during the heating stage of the treatment process, the heater is modulated as a function of the fluid pressure.

These and other features and advantages of the present invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 depicts a distensible bladder utilized in the method of the present invention that has been inserted into and inflated within uterus of a patient;

FIGURE 2 is an elevation view of a distensible bladder illustrating the retroverted position and the formation of a vapor bubble;

FIGURE 3 is a perspective of an apparatus constructed in accordance with 5 the invention that illustrates the balloon catheter connections;

FIGURE 4 depicts the front panel of the system control unit; and

FIGURE 5 is a flow chart of the process control loop showing the monitoring of temperature, pressure to regulate the heater.

0 DESCRIPTION OF THE PREFERRED EMBODIMENT

By way of example only, the present invention will be explained in conjunction with heated balloon instrumentation useful for ablating the endometrium of the uterus. The invention, however, is useful in conjunction with any electrosurgical instrument used in a distension medium where the pressure of the 5 distension medium must be closely monitored or where the pressure of the distension medium provides an indication of other process variables that exist during the use of an electrosurgical instrument.

FIG. 1 shows an inflated distensible bladder or balloon 5 attached to an insertion tubing 3 located within a human uterus 6. Inflation of the distensible o bladder 5 with a fluid 25 assures uniform contact of the bladder with the endometrial tissue layer 27 of a uterus 6.

The insertion tubing 3 and the attached distensible bladder 5 must be sufficiently small, when the distensible bladder is deflated, so that it can be conveniently and safely inserted into the uterus 6 through a partially dilated cervix. 5 The insertion tubing 3 with the deflated bladder 5 is aligned with the cervical canal after the cervix is exposed with a speculum and grasped with a tenaculum. After the distensible bladder 5 has been inserted, the distensible bladder 5 should be inflated to a pressure sufficient to ensure firm contact against the endometrial tissue layer on the interior uterine surface. The bladder pressure should preferably be o maintained at or about 45 to 200 mmHg, and preferably about 120 to 160 mmHg, to minimize risk of rupture of the distensible bladder 5 and possible internal injury to the patient.

The distensible bladder 5 must be capable of withstanding high temperatures without rupturing, and preferably have as good a heat transfer characteristic as is obtainable in such materials to provide efficient heating action. 5 A distensible bladder of a heat curing rubber, such as latex rubber, or silicon has been found satisfactory. Inflation medium or fluid 25 preferably should be a sterile non-toxic fluid. A five- percent dextrose in water solution has been found satisfactory.

As shown in FIG. 2, bladder 5 is in a retroverted position within uterus 6. A 0 vapor bubble 60 may form in the proximal portion during the initial heating process as discussed below.

FIG. 3 depicts the arrangement of control unit 30 and balloon catheter 1 , comprising the distensible bladder 5, insertion tubing 3, catheter handle 10 and the interconnection of those elements. A fluid path comprises a fluid source such as a 5 syringe 14, connected to the proximal end of catheter handle 10 via a fluid fill port 16, insertion tubing 3, and distensible bladder 5. Manipulation of the syringe 14, by depressing a plunger 60 and fluid fill valve 18 at the same time, causes inflation medium to be introduced through the catheter handle 10 into the insertion tubing 3. The inflation medium 25 emerges from insertion tubing 3 and into distensible o bladder 5, forcing distensible bladder 5 to expand into contact with the endometrial tissue layer 27 of the uterus 6. The fluid is also directed along the flexible tubing 20 to the control unit 30 allowing measurement of the fluid pressure within the bladder as described below.

When the syringe 14 is attached to fluid fill port 16 of the catheter handle 10, 5 fluid can be introduced into the catheter by depressing the fluid fill valve 18 and the plunger 60 at the same time. The pressure display monitor located on the control unit 30 reads the pressure and if the pressure in the distendable bladder is below 70 or above 180 mmHg a warning signal and/or alarm alerts the user that the pressure is either too low or too high. A range of between 120 and 160 mmHg, o preferably 150 mmHg is considered to provide the acceptable range of operation.

The control unit 30 is also designed to regulate or control heat, operating times and monitor and display pressure values. FIG. 4 shows the front panel 500 of control unit 30. The control unit 30 includes a power switch 520, start button 540 and start button light 550. The temperature of fluid 25 in the distensible bladder 5 is shown at catheter heater temperature display 570. Similarly, the pressure of the 5 bladder is shown at display 560. These indicators allow the practitioner to readily reach the preset pressure range by varying the amount of fluid in the fluid path via manipulation of the syringe 14.

Fluid pressure within the bladder is monitored by displays located on the front of the control unit panel 500. The pressure connector 591 is designed for 0 receiving the pressure line and is directly connected to the pressure transducer (not shown) internal to the control unit 30. The pressure transducer measures the internal pressure of the fluid path including the pressure of the fluid inside the distendable bladder. The pressure transducer generates a signal indicative of the internal pressure of the fluid path including the pressure inside the distensible 5 bladder.

The control unit 30 is a software-controlled system with necessary hardware safety backups. The software controls the fluid temperature and pressure, while monitoring the elapsed time of the procedure. The elapsed time is shown in minutes and seconds at display 580. The software includes steps like priming and o filling the catheter and starting and stopping the heating therapy cycle. The temperature and pressure, however, are measured and read by both the hardware and the software.

FIG. 5 is a flow-chart showing the monitoring of pressure and temperature to control the heater on-off time. Process control loop of FIG. 5 monitors the 5 acceptable range of measurements for pressure and temperature. It is desirable for the temperature to reach 85 to 90 degrees Celsius during therapy session, preferably 87 degrees Celsius. When the fluid 25 is first introduced, it has a temperature equal to room temperature. The heat from the body cavity can elevate this temperature to slightly above the room temperature at the onset of the o procedure. When the measurements for temperature or pressure exceed a certain set point, the heater is de-energized. Step 100 shows that if the pressure exceeds a certain set point, here 210 mm Hg the heater is de-energized at box 102. As stated above, one cause of over pressure may be the formation of a vapor bubble within the balloon during initial heating. Effectively the energize time of the heater is modulated in accordance with the fluid pressure. In addition, step 108 requires that the temperature of the fluid within the balloon, as measured by the thermocouples, be below a certain set point before the heater is energized at 110. In this manner the heater is regulated not only by temperature of the distension fluid, but also by the pressure of the distension fluid. Preferably, control element 106 is added to the control loop. Element 106 prevents excessive modulation of the heater by requiring that the pressure dip below a second set point, here 207 mm Hg, before the heater is energized. In this manner, the fluid in the proximal end of the balloon is allowed to cool by mixing with the cooler fluid in the distal end of the balloon, as may be facilitated by agitators. During this cooling period, the vapor bubble shrinks and may ultimately disappear thereby reducing the fluid pressure. The control cycle continues until the fluid reaches the appropriate temperature for therapy without unwanted process shutdowns.

As is readily evident to those skilled in the art, the control process described in the above exemplary fashion would be equally applicable to other electrosurgical instrumentation used within a distension medium. The invention would be useful in the control of the apparatus disclosed in International Publication WO 97/24994 previously incorporated by reference. That is, as the vapor bubble increases as a result of the higher voltage, the pressure of the distension medium will increase. Here, the process control loop could be used to modulate the voltage to the electrode to prevent destruction of the electrode at high voltages. Although the present invention has been described in detail by way of illustration and example, it should be understood that a wide range of changes and modifications can be made to the preferred embodiments described above without departing in any way from the scope and spirit of the invention. Thus, the described embodiments are to be considered in all aspects only as illustrative and not restrictive, and the scope of the invention is, therefore, indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

CLAIMSWhat is claimed is:

1. An apparatus for endometrial ablation, the apparatus comprising: 5 an elongate tubular member having a proximal end and a distal end, said tubular member having a lumen in fluid communication with the proximal end and the distal end; a distensible bladder secured to the distal end of said elongate tubular member, said distensible bladder in fluid communication with the lumen of said o tubular member whereby a distension medium communicates through first lumen and into the bladder; a heating element secured to the distal end of said elongate tubular member and disposed within said distensible bladder; power means for supplying power to the heater; 5 pressure sensing means for sensing the pressure of the distension medium within the distensible bladder; and control means for modulating the power means as a function of the pressure.

2. The apparatus of claim 1 further comprising thermocouples disposed 0 in the bladder for sensing the temperature of the distension medium within the bladder.

3. The apparatus of claim 1 wherein the distension medium is a fluid.

5 4. The apparatus of claim 1 wherein the distension medium is a gas.

5. A method for ablating the endometrial lining of a uterus, the method comprising: inserting a distensible bladder into the uterus; o inflating the distensible bladder with an inflation medium; providing electric current to a heating element positioned within the distensible bladder; heating the inflation medium within the distensible bladder to a desired temperature as indicated by the thermocouple; and sensing the pressure of the inflation medium and comparing the pressure 5 against a first set point; and terminating the electric current to the heating element when the pressure exceeds the first set point.

6. The method of claim 5 further comprising the step of energizing the 0 heater element when the pressure falls below a second set point.

7. A method for controlling the power to an electrosurgical instrument used in conjunction with a distension medium to treat tissue within a body cavity, the method comprising: 5 inserting a distension medium within the body cavity; providing power to the electrosurgical instrument to treat tissue within the body cavity; sensing the pressure of the inflation medium and comparing the pressure against a first set point; and o adjusting the power to the electrosurgical instrument when the pressure exceeds the first set point.

8. The method of claim 7 wherein the distension medium is a liquid.

5 9. The method of claim 7 wherein the distension medium is a gas.

10. The method of claim 7 further comprising the step of adjusting the power to the electrosurgical instrument when the pressure falls below a second set point.