Patent Application
20150025529
All publications and patent applications mentioned in this specification are herein incorporated by reference into the present application to the same extent as if each individual publication or patent application were indicated specifically and individually to be so incorporated.
The present disclosure relates to systems and methods for electrosurgical technology. More particularly, the technology relates to impedance-mediated control of power delivery for electrosurgical systems and methods for tissue sealing.
Biopolar electrosurgical instruments apply high radiofrequency (RF) electrical current to a surgical site to cut, ablate, or coagulate tissue. A particular application of these electrosurgical effects is to seal luminal structures, such as blood vessels or gastrointestinal sites, or tissue edges. A typical electrosurgical instrument takes the form of a pair of forceps, with electrodes positioned on both jaws of the forceps. In an electrosurgical procedure, the electrodes are placed in close proximity to each other as the jaws are closed on a target site such that the path of current between the two electrodes passes through tissue within the target site. The mechanical force exerted by the jaws and the electrical current combine to create the desired surgical effect.
By controlling the level of mechanical pressure applied by the jaws, the gap distance between electrodes, and the intensity, frequency, and duration of the electrosurgical energy applied to the tissue, a surgeon can coagulate, cauterize, or seal tissue toward a therapeutic end. A typical goal of controlling the delivery of electrosurgical energy, more particularly, is to apply no more and no less than the precise amount of energy required to create the desired effect within the targeted sealing site, while minimizing deleterious effects to tissue peripheral to the target site. As tissue absorbs energy, such as radiofrequency energy, its impedance of radiofrequency energy increases. This increase in impedance is generally considered to be a measure of the degree to which the tissue has been “processed” toward a therapeutic endpoint state. Embodiments of the presently disclosed systems and methods are directed toward using target tissue impedance as a feedback signal to appropriately control the level of energy applied to a targeted sealing site.
Embodiments of the provided electrosurgical systems and methods include delivering energy from an electrosurgical device to a target tissue in a sealing cycle in the form of a series of pulses, each pulse being of a preset duration. The series of pulses begins with an initial pulse having a profile comprising a preset RF level start value that increases at a preset ramping rate to a preset RF end value. The methods may further include sending sensed tissue impedance values to a processor, or more specifically, to an impedance comparator element within a processor, throughout each pulse. Each pulse is either a preceding pulse to a subsequent pulse or a final pulse in a sealing cycle. The methods may further include comparing sensed impedance values to each of three preset impedance threshold values, including an impedance threshold value for RF setpoint, an impedance threshold value for cumulative time, and an impedance threshold value for energy cutback. The methods may further include controlling the delivery of energy during the sealing cycle by responding to the comparison of the sensed impedance values to the impedance threshold values.
In particular embodiments, controlling the delivery of energy includes ceasing the sealing cycle when the cumulative time of tissue showing an impedance value over the impedance cumulative time threshold value reaches a preset sealing cycle duration limit. Embodiments of the electrosurgical method may further include recording the cumulative time within an ongoing sealing cycle during which the sensed tissue impedance value exceeds the impedance threshold value for cumulative time.
Based on these comparisons of sensed impedance data to the impedance threshold values, various electrosurgical operating consequences may occur. When the sensed impedance value at the end of a preceding pulse is less than the impedance threshold value for RF setpoint, the methods may further include controlling the delivery of energy to the subsequent pulse such that it has substantially the same pulse profile as that of the initial pulse. When the sensed impedance value at the end of a preceding pulse exceeds the impedance threshold for RF setpoint, the methods may further include controlling the delivery of energy to the subsequent pulse such that it has an elevated profile. Such an elevated pulse profile may include stepping up at the outset of the pulse directly to the RF end value. An elevated pulse profile may also include ramping up from the RF start value to the RF end value at a rate greater than that of the preceding pulse.
When the sensed impedance at any time during a pulse exceeds the impedance threshold for energy cutback, the methods may include cutting back energy delivery. Such energy cutback may occur immediately, or it may include waiting for a preset elapsed amount of time to accumulate during which the sensed impedance exceeds the impedance threshold for energy cutback before cutting back energy delivery (up to about 2 seconds, for example).
Cutting back energy delivery may also include lowering any of an RF delivery level or a ramping rate. Lowering the amount of energy being delivered may include decreasing the energy delivery by an amount between about 1 and about 100 volts. Alternatively, lowering the amount of energy being delivered may include decreasing the energy delivery by a fractional percentage of that which is being delivered. More particularly, lowering the amount of energy being delivered may comprise decreasing the energy delivery by a fractional percentage of the amount of energy proportional to the extent to which the sensed impedance exceeds the impedance threshold for energy cutback value.
With regard to pulse duration and the RF values of pulses, in various embodiments of the electrosurgical method, the RF pulses, typically, are each of a constant duration that may range from about 0.5 sec to about 10 sec. The number of pulses in the series of pulses may range from 1 pulse to about 30 pulses. In various embodiments of the electrosurgical method, the cumulative sealing endpoint duration is between about 0.1 sec and about 5 sec. In various embodiments of the electrosurgical method, the RF start value is in the range of about 25 watts to about 150 watts, and the RF End Value is in the range of about 50 watts to about 150 watts.
With regard to the aforementioned impedance thresholds, in various embodiments of the method, the impedance threshold for RF setpoint is in the range of about 5 ohms to about 250 ohms, the impedance threshold for energy cutback value is in the range of about 100 ohms to about 900 ohms, and the impedance threshold for cumulative time value is in the range of about 100 ohms to about 750 ohms.
With regard to the transition from an RF start value to the RF end value of a pulse, in various embodiments of the electrosurgical method, delivering energy includes increasing the level of energy being delivered from the preset RF start value to a preset RF end value during a pulse. In some embodiments, increasing the level of energy during a pulse includes ramping up at a rate that ranges between about 1 watt/sec and about 100 watts/sec. In some embodiments, increasing the level of RF energy during a pulse includes ramping up in one or more steps. In some embodiments, increasing the level of energy during a pulse may include ramping up at a constant rate or at a changing rate. In still further embodiments, increasing the level of energy during a pulse comprises stepping up immediately to a preset RF end value upon initiation of a pulse.
In another aspect, an embodiment of an electrosurgical method includes delivering energy from an electrosurgical device to a target tissue site in a sealing cycle that includes a series of pulses, each pulse having a preset pulse duration. The series of pulses begins with an initial pulse having an initial pulse profile comprising a preset RF level start value that increases to a preset RF end value during the pulse. This embodiment of the method further includes sending a sensed tissue impedance value to a processor during each pulse, each pulse being either a preceding pulse to a subsequent pulse or being a final pulse. This latter embodiment of the method further includes controlling the delivery of energy during a sealing cycle such that: (A) a profile of a successor pulse relative to the profile of its preceding pulse has any of an identical profile or a higher energy profile, depending on a comparison of the impedance value shown by tissue during the initial or preceding pulse against a preset impedance threshold value for RF setpoint, (B) energy is cutback during a pulse when the sensed impedance value exceeds a preset threshold value for energy cutback; and (C) energy delivery ceases when a cumulative amount of time that sensed impedance has exceeded a preset impedance threshold value for cumulative time has accumulated a preset sealing cycle duration limit.
Further with regard to this latter embodiment of an electrosurgical method, when the sensed impedance exceeds the preset threshold value for RF set point, the energy profile of the succeeding pulse exceeds the energy profile of the preceding pulse, and when the sensed impedance is less than the preset threshold value for RF set point, the energy profile of the succeeding pulse is identical to the energy profile of the preceding pulse.
With respect to embodiments of an electrosurgical method, the energy profile of a pulse includes an RF start value, an RF end value, and a transition phase between the RF start value and the RF end value. In these embodiments, a lowered pulse energy profile of a successor pulse, with respect to the preceding pulse, may include any of a lowered RF start value, a lowered RF end value, and/or a lower rate of transition from the RF start value to the RF end value. A heightened energy pulse profile of a successor pulse, with respect to the preceding pulse, may include any of a higher RF start value, a higher RF end value, and/or a higher rate of transition from the RF start value to the RF end value. And finally, the transition from the RF start value to the RF end value comprises any of a sloped transition and/or a stepped transition.
The electrosurgical tissue sealing technology provided herein relates to applying the dynamics of the response of tissue to RF energy as feedback information to control the delivery of the energy during an electrosurgical procedure. Tissue sealing that is surgically optimal occurs when an appropriate level of energy is delivered to a target site at an optimal rate; too much energy, or energy delivered too quickly can damage the target site and surrounding tissue, and too little energy does not create a high integrity seal. Another consideration is that the effects of absorbing a given quantity of energy by a tissue sealing site is a function of the specifics of tissue type and total tissue volume receiving energy, both of which are variables at play in each sealing procedure. As tissue is being impacted or “processed” by RF energy, such as by coagulation, desiccation, or fulguration, or any combination thereof, impedance of the tissue to electrical current increases. The change in impedance is generally ascribed to a change in the “phase” or “state” of the tissue.
The relationship between energy input and the rate of change in the tissue state is affected by factors such as tissue composition, tissue density, water content, and electrolyte content. In these terms, an optimal rate of RF energy delivery is one that drives the change in tissue phase, as reflected in the rate of increase in impedance, at an optimal rate. The optimal rate of change in impedance can be learned empirically, from experimental and clinical experience. Accordingly, and as provided by embodiments of the method, the sensed change in tissue impedance during an electrosurgical procedure is an advantageous parameter to use as feedback in governing the rate of RF energy delivery to a targeted sealing site. A theoretical rationale of the method is offered to support of an understanding of its operation, but without any characterization that would limit claims to the method. It is considered advantageous to recognize when tissue is processing slowly, and, in response, to deliver energy to the tissue slowly. And, when tissue is processing quickly, in response, it is advantageous to deliver energy to the tissue quickly. The system is thus balanced so as to direct energy to a target site no more quickly than it can absorb the energy through tissue processing. Thus tissue is processed efficiently to an appropriate endpoint, and the spread of excess energy beyond the targeted tissue sealing site is minimized.
As described further below, impedance threshold values may be used to control the delivery of RF energy in a sealing cycle comprising a series of energy pulses delivered to a targeted tissue site. Sensed impedance may used to variously control energy delivery in real time, as during a pulse, or in a prospective manner, by controlling the delivery of energy in a succeeding pulse, as well as by terminating an energy delivery cycle at any point during a pulse.
Embodiments of the method and systems for operating method embodiments provided herein are suitable for both single channel and multiple channel electrosurgical system operation. Multi-channel systems typically include an RF generator with multiple outputs coupled to multiple electrodes or electrode pairs. In multi-channel systems that make use of the embodiments of the method described herein, a generator may be capable of addressing electrodes individually and independently, such that electrode firing may occur without constraint with respect to repetition of individual electrode firing or with respect to the sequential order of adjacent electrode firing. In other words, the firing parameters of each electrode may be based on settings and/or feedback associated solely with that electrode.
The effect of the electrosurgical device on the tissue is monitored at the site of tissue treatment by one or more sensors associated with the electrosurgical appliance. A signal produced by the one or more sensors is coupled to a sensor circuit 14. The sensors can monitor environmental factors and operating parameters such as temperature, impedance, RF voltage, RF current, elapsed time, and the like. In particular embodiments, at least some of the sensors monitor the parameters of tissue impedance and RF power.
A sensor circuit 14 generates an output signal that is conveyed to a processor 15. The processor, operating under control of a program per aspects of the presently described method, is configured to adjust the output of the RF generator by issuing control signals to the control circuit. In doing so, the processor may adjust the RF power delivered to the tissue in real time, in response to signal generation by the sensors. The program may be retained in a memory 17 and includes both instructions for operating the processor and parameters that determine how to respond to signals from the sensor, timing, and other information as may be utilized to control the delivery of energy per aspects of the method.
As the tissue is processed by application of energy, a phase or state change occurs in the tissue that, in turn, causes a change in the impedance of the tissue. A particular feature of the provided technology is the manner in which the processor operates the control circuit and, thus, the manner in which energy is supplied to the tissue, in response to signals provided to the processor from one or more types of sensors, such as impedance sensors, via sensor circuitry.
More particularly, embodiments of the method apply sensed impedance to changing aspects of the profile of an electrosurgical pulse, components of a profile include an initial RF start value, an RF end value, and either a step-wise or ramped increase in RF delivery over the course of the pulse from the RF start value to the RF end value. As used herein, a “ramp” of energy output refers to the difference between the output level at the start of a pulse of energy delivery and the output level achieved at the end of the pulse, while “slope” refers more specifically to the rate at which the energy output changes over time during the pulse. Energy is typically delivered in a series of pulses that may be of a preselected or preset constant duration, although in some embodiments of the, the pulses may vary in length.
Embodiments of the electrosurgical system and method monitor the sensed impedance that target tissue manifests when being exposed to a pulse of RF energy and compares impedance data to various preset impedance threshold values during a sealing cycle that includes a series of pulses. Embodiments of the system and method respond to these comparisons by variously adjusting the profile of the ongoing pulse, adjusting the profile of the immediately succeeding or subsequent pulse, and by tracking time toward a cumulative sealing cycle endpoint duration, at which point the sealing cycle is terminated. These various system responses, collectively, represent a method for controlling aspects of the performance of an electrosurgical system during a sealing cycle, including the amount of power delivered during individual RF pulses, and during the sealing cycle as a whole.
These impedance threshold values include an impedance threshold value for an RF setpoint, an impedance threshold value for cumulative sealing cycle duration timing, and an impedance threshold value for energy cutback. Although the impedance values for each of these three threshold values include regions of overlap, the thresholds within typical embodiments of the method are ordered such that the impedance threshold value for an RF setpoint is the lowest threshold value, the impedance threshold for cumulative sealing cycle duration is the intermediate threshold value, and the impedance threshold value for energy cutback is the highest threshold value. These impedance threshold values and their roles in controlling energy delivery are detailed and described further below. Tables 1 and 2, as well as
In one aspect, embodiments of the impedance-based power control method relate to controlling the profile of individual pulses within a series of pulses. Radiofrequency pulses, as delivered by embodiments of the method, have profile that includes a preset RF start value and a preset RF end value, typically higher than the RF start value. During the course of a pulse, the RF energy typically increases from the start value to the end value at a preset rate. In some pulses, per response to threshold impedance values as described further below, a pulse may step directly from the start value to the end value. Each of these parameters of a pulse profile is typically preset for a particular tissue sealing cycle, but each parameter may be adjustable within a range of values. The RF start value may range between about 25 and about 150 watts; a typical value, by way of example, is about 50 watts. The RF end value may range between about 50 and about 150 watts; a typical value, by way of example, is about 150 watts. The ramp rate or slope by which energy may increase from the RF start value to the RF end value may range between about 1 watt/sec and about 100 watts/sec; a typical value, by way of example, is about 50 watts/sec.
The impedance threshold value for RF setpoint is typically the lowest of the three impedance thresholds. This performance control mediating threshold has a preset value that ranges between about 5 and about 250 ohms; a typical value, by way of example, is about 50 ohms. Some embodiments of the system are configured to compare the tissue impedance at the conclusion of a pulse (or at its maximum) to this threshold value and to direct the profile of the succeeding pulse into one of two paths, depending on whether the pulse end impedance falls below or exceeds the RF setpoint threshold value. In the event that the end-pulse impedance (of a preceding pulse) is less than this threshold, the succeeding pulse is operated with the same profile as the preceding pulse.
In the event that the end-pulse impedance (of a preceding pulse) exceeds the impedance threshold value for RF setpoint, the succeeding pulse may be operated with a higher energy level profile. An elevated energy profile may occur by any approach that increases the integrated value of pulse duration multiplied by power; for example, in one embodiment, the pulse may initiate with the RF start value and then step directly (without an attenuated ramp) to the RF end value. In other embodiments, the slope of the energy delivery during the pulse may increase. In still other embodiments, the RF start value or the RF end value may be increased.
The impedance threshold value for cumulative sealing time duration is typically higher than the RF setpoint threshold value. In some embodiments, this performance control-mediating threshold has a preset value that ranges between about 100 ohms and about 750 ohms; a typical value, by way of example, is about 250 ohms. During the course of an electrosurgical procedure, as delivered by a series of pulses per aspects of the method, the impedance of target tissue increases. This increase is understood to be generally reflective of a tissue “processing” by RF energy to a level appropriate to serve a particular therapeutic end. Thus, the impedance shown by tissue may be considered a marker of tissue processing, and an optimal level of processing may be considered that rendered by absorbance of an optimal level of RF energy for an optimal duration of time. Accordingly, the system and method may be directed to record accumulated time at an impedance threshold value for cumulative time duration, which, upon being reached, causes the delivery of RF energy to cease. Cessation of energy delivery may occur immediately during an RF pulse upon accumulation of a preset sealing time duration. The cumulative sealing endpoint duration, per embodiments of the method, may range between about 0.1 sec and about 5 sec.
The impedance threshold value for energy cutback is typically the highest of the three impedance thresholds. This performance control-mediating threshold has a preset value that ranges between about 100 ohms and 900 ohms in some embodiments; a typical value, by way of example, is about 700 ohms. A high impedance level (see
The energy cutback, per embodiments of the method, occurs by decreasing the profile of energy pulses being delivered. Such energy cutback may occur immediately, at any point during a pulse, when the impedance threshold for energy cutback is exceeded. In alternative embodiments of the method, energy cutback may occur after the passage of a preset delay. In still other embodiments, the energy cutback may be initiated in a succeeding pulse. The amount of energy cutback may occur by way of cutting back on level of energy delivery, or by way of decreasing the rate of energy increase during a pulse. Any one or more of several approaches may adjust the level of energy delivery downward. For example, the energy delivery may be dropped by an absolute amount of wattage or voltage. Alternatively, the level of energy delivery may be dropped by a fractional percentage of the level of energy being delivered at the moment when the impedance threshold for energy cutback is exceeded. In another variation, the level of energy delivery may be dropped by the fractional portion that corresponds to the difference between the sensed impedance and the impedance threshold for RF energy cutback. It can be noted, merely for the purpose of understanding the rationale of aspects of the method, that an exceptionally fast increase in impedance which includes exceeding the impedance threshold for energy cutback is indicative of a small amount of tissue, rather than a normal amount of tissue, absorbing all of the delivered energy, and thus being processed more quickly than is desired.
Continuing with
Continuing with
Continuing further with
Finally, with regard to
As a result of these comparisons ongoing within the comparator (
Prior to the delivery of an RF pulse, an RF pulse selector 110 selects which pulse profile in the profile library (101, 102, or 103) to deliver to tissue 150. The pulse selector 110 makes the selection based on input from a threshold comparator 170 (see further, below). The RF pulse selector 110 has an output that drives the setpoint for the RF energy generator 120, which delivers an RF energy pulse 140 that is ultimately directed to a target tissue site 150. As energy is being delivered it passes through an intervening mechanism in the form of an RF energy attenuator or cutback block 130 that can attenuate the energy delivery, in real time, based on data from the threshold comparator 170.
The target tissue site 150 is both the recipient of RF energy 140 being delivered by the system via electrosurgical forceps 145, as well as the source for impedance data 160 that are conveyed back to the system, stored in a memory and processed by a processor, as represented by a threshold comparator 170. The threshold comparator performs constant surveillance of sensed impedance data from the target tissue and compares these data against three particular impedance thresholds, as outlined in
Briefly, these impedance thresholds include an impedance threshold for the RF setpoint 171, an impedance threshold for pulse duration cumulative timing 172, and an impedance threshold for energy cutback 173. It can be seen that the result of a comparison 171 of impedance data with respect to an RF setpoint threshold value is directed into the profile selector and adjuster 110, which then typically assigns either an elevated profile 102 or a lowered profile 103 for the subsequent pulse in response to the incoming data. The result of the comparison 172 of impedance data with respect to an impedance threshold for cumulative time is directed to the RF energy generator/delivery block 120; if the cumulative time is less than the preset duration, block 120 is enabled to generate RF energy. When the cumulative time achieves the preset sealing cycle duration, further delivery of energy from block 120 is stopped. The result of the comparison of impedance data with respect to an impedance threshold of energy cutback 173 is directed into the RF energy attenuator cutback block 130. If data from impedance comparison 173 indicates that the impedance is less than the impedance threshold for energy cutback, energy delivery proceeds without attenuation. If data from impedance comparison 173 indicates that the impedance exceeds the impedance threshold for energy cutback, energy delivery proceeds with attenuation in real time.
In some embodiments, in response to tissue impedance exceeding the impedance threshold for energy cutback, energy is cutback by an amount proportionate to the total amount of energy being delivered during the high impedance event. The fractional amount by which energy is cutback, in some embodiments, may be related to the proportional amount by which the sensed impedance is exceeding the impedance threshold for energy cutback. For example, if the impedance threshold for energy cutback is 300 ohms and sensed impedance is 450 ohms (50% greater than the impedance threshold of 300 ohms), the energy delivery may be cutback by 50%. In some embodiments of this proportional energy cutback procedure, the cutback is performed in a continuous real time manner, with the response to energy cutback immediately tracking the extent to which sensed impedance exceeds the threshold for energy cutback.
Table 1 summarizes the values of various parameters associated with the delivery of radiofrequency energy and the sensed target tissue impedance during an electrosurgical tissue sealing procedure, in accordance with aspects of the disclosed methods. The specific value drawn from within range (for RF values and impedance thresholds) is typically preset and fixed for any given electrosurgical procedure, however these preset values are adjustable within the range.
Table 2 summarizes the profile of the RF pulse that follows a preceding pulse, as controlled by the sensed tissue impedance during the preceding pulse, as well as other system responses to sensed impedance values during an exemplary sealing cycle.
An embodiment of the method by which sensed impedance controls the delivery of RF energy during an electrosurgical tissue sealing cycle is summarized below.
In the example provided by
Unless defined otherwise, all technical terms used herein have the same meanings as commonly understood by one of ordinary skill in the art of electrosurgery. Specific methods, devices, and materials are described in this application, but any methods and materials similar or equivalent to those described herein can be used in the practice of the present invention. While embodiments of the invention have been described in some detail and by way of illustrations, such illustration is for purposes of clarity of understanding only, and is not intended to be limiting. Various terms have been used in the description to convey an understanding of the invention; it will be understood that the meaning of these various terms extends to common linguistic or grammatical variations or forms thereof. It will also be understood that when terminology referring to devices or equipment, that these terms or names are provided as contemporary examples, and the invention is not limited by such literal scope. Terminology that is introduced at a later date that may be reasonably understood as a derivative of a contemporary term or designating of a hierarchal subset embraced by a contemporary term will be understood as having been described by the now contemporary terminology. Further, while some theoretical considerations have been advanced in furtherance of providing an understanding of the dynamics of tissue response to absorbing radiofrequency energy, consequences regarding tissue impedance, and exploiting these dynamics toward optimizing control of an electrosurgical system and method, the claims to the invention are not bound by such theory. Moreover, any one or more features of any embodiment of the invention can be combined with any one or more other features of any other embodiment of the invention, without departing from the scope of the invention. Still further, it should be understood that the invention is not limited to the embodiments that have been set forth for purposes of exemplification, but is to be defined only by a fair reading of claims appended to the patent application, including the full range of equivalency to which each element thereof is entitled.
This application is a continuation in part of U.S. patent application Ser. No. 12/748,229 of Koss et al., entitled “IMPEDANCE MEDIATED POWER DELIVERY FOR ELECTROSURGERY”, as filed on Mar. 26, 2010.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12907646 | Oct 2010 | US |
| Child | 14461559 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12748229 | Mar 2010 | US |
| Child | 12907646 | US |
