Electrosurgical console for radiofrequency ablation

Abstract

An electrosurgical system for radio frequency ablation. The electrosurgical console includes a processor configured to determine an impedance threshold based on an initial tissue impedance value. The impedance threshold may vary based on a time-based characteristic. The temperature set point is reduced based on the occurrence of an impedance event where the tissue impedance value exceeds the threshold. The reduced temperature set point may be constant. The controller is configured to control the delivery of RF energy to drive the tissue temperature toward the temperature set point(s). The temperature set point may not be reduced and an alert may be displayed if an impedance event occurs during a ramp period. A secondary impedance threshold may be utilized to provide a slower ramp period later in the ablation procedure. A method of performing an ablation procedure using the electrosurgical system is also disclosed.

Description

[Technical field]

[0001] [Priority claim] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 227,387, filed July 30, 2021, which is incorporated by reference in its entirety. [Background technology]

[0002] Radiofrequency (RF) energy is commonly utilized to ablate diseased tissue to treat pain or pathology. The tissue can be a sensory nerve, an intraosseous nerve, or an intraosseous tumor, among other anatomical structures. Traditionally, an electrode is coupled to an electrosurgical console and RF energy is conducted from the electrode to the tissue across the electrode-tissue interface, resulting in a lesion at the treatment site. In the case of intraosseous tumors, the RF energy often heats the tissue to at least 90° C. (194° F.) to destroy the tumor cells.

[0003] Tissue has tissue impedance, a natural resistance to the conduction of RF energy. It has been observed that tissue impedance can rise rapidly when tissue becomes dehydrated or charred. In other words, charring can undesirably alter the electrical and thermal conductance of the tissue. Thus, detecting an increase in tissue impedance can signal a compromised effectiveness of the RF energy delivered to the treatment site. Thus, preventing or properly accounting for the increase in tissue impedance is an area of ​​interest and development.

[0004] It has been shown that injection of fluids such as saline into the treatment site can limit charring by improving conduction at the electrode-tissue interface and reducing tissue temperature. Known solutions have also included impedance-controlled systems in which delivery of RF energy is interrupted when tissue impedance rises above a certain threshold. The sudden interruption of RF energy disrupts the surgical procedure. Furthermore, because the effects of charring are only partially reversible, efforts to return the tissue to a previous temperature set point can often result in further repeated spikes in tissue impedance. A vicious cycle of significant disruptions and downtime during the ablation procedure can then ensue, making achievement of the desired lesion unfeasible. Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure is directed to an electrosurgical system, electrosurgical console, and computer-implemented method that overcomes the above-mentioned shortcomings. [Means for solving the problem]

[0006] The electrosurgical system includes an electrosurgical instrument(s) and, optionally, a cable accessory and / or a ground pad (i.e., the cable accessory or the ground pad or both). The cable accessory is configured to be removably coupled to an electrosurgical console, and the electrosurgical instrument is configured to be removably coupled to the electrosurgical console and / or the cable accessory (i.e., the electrosurgical console or the cable accessory or both). The injection module can be operable with the electrosurgical instrument to direct a fluid through the electrosurgical instrument. A thermocouple is disposed near a distal end of the electrosurgical instrument and configured to provide a temperature measurement of tissue near the electrode(s). The injection module includes an injection clamp configured to be actuated to selectively start and stop the flow of fluid. The electrosurgical console generates controlled radiofrequency electrical energy and passes the energy through the electrosurgical instrument and tissue, thereby heating the tissue to a temperature sufficient to destroy cells of the tissue. The electrosurgical console includes a display configured to display a graphical user interface (GUI) that enables a user to, among other actions, select operating parameters and navigate through different operating modes provided by software on the electrosurgical console.

[0007] The electrosurgical console includes a controller, one or more processors, and a memory. Computer executable instructions or code can be stored in the memory, for example, in a database in the memory. The instructions are accessible to the processor and executable by the processor to perform various functions of the electrosurgical console. The electrosurgical instrument is configured to be removably coupled to the electrosurgical console and to place the electrosurgical instrument in communication with the controller. Based on input to the GUI, the controller controls RF energy delivered to the electrosurgical instrument. The controller is further configured to receive or process one or more treatment parameters, such as tissue temperature. Another treatment parameter includes tissue impedance, which can be determined by the processor based on measured electrical parameters, for example, a supply voltage and a return voltage through the electrode across the electrode-tissue interface. The processor can be configured to determine an initial tissue impedance value. The initial tissue impedance value can be based on an initial supply voltage and a return voltage through the electrode across the electrode-tissue interface.

[0008] The processor can be configured to determine the impedance threshold based on the initial tissue impedance value. The impedance threshold varies based on an elapsed time-based characteristic of the ablation procedure. The elapsed time-based characteristic can be elapsed time since the beginning of delivery of RF energy or from another start or set time of the ablation procedure. The set time can be selected or predefined, for example, when the tissue temperature measured by the thermocouple is near or at a temperature set point. The elapsed time can be continuous or can be paused during a period when RF energy is not being delivered. The elapsed time-based characteristic can be a percentage of the total ablation time. The total ablation time can be entered by the user into the GUI or determined by the processor. The percentage of the total ablation time can be a ratio of elapsed time to the total ablation time. The elapsed time-based characteristic can be a percentage of the lesion that exceeds a threshold temperature. The threshold temperature can be a temperature set point, a percentage of the temperature set point, or another determined temperature based on any number of factors of the ablation procedure. The processor can be configured to determine the percentage as a ratio of the time the lesions exceed the threshold temperature to the total ablation time. The processor is further configured to determine a final threshold impedance value. The final threshold impedance value can be, for example, the last time-based characteristic impedance threshold at the end of the ablation procedure when the RF energy is terminated. This can correspond to 100 percent of the lesions exceeding the temperature threshold.

[0009] The impedance threshold can be determined from a function, for example according to a formula. The impedance threshold can define an impedance threshold curve. The impedance threshold curve can be linear or non-linear and can extend between an initial impedance value and a final impedance value. The impedance threshold curve can have a positive slope, the higher the value of the elapsed time-based characteristic, the higher the threshold. The slope of each one of the impedance threshold curves can decrease as the value of the initial tissue impedance value increases. The impedance threshold curves can have different slopes, the offset of the impedance threshold curve is greater where the value of the elapsed time-based characteristic is lower than where the value of the elapsed time-based characteristic is higher. A subsequent one of the impedance thresholds can be based on the occurrence of an impedance event, and the impedance threshold can deviate from a predefined function or curve. The impedance threshold can be predefined at each time of the ablation procedure.

[0010] The controller is configured to control RF energy delivered from the electrodes based on the temperature measurements of the thermocouples and a temperature set point at which the tissue is ablated. The processor is configured to reduce the temperature set point based on the occurrence of an impedance event. The electrosurgical console utilizes impedance-based control to drive the tissue temperature toward the temperature set point. The temperature set point can be predefined, determined, or user-selected. The predefined temperature set point can be based, for example, on the type of lesion being ablated. The determined temperature set point can be based, for example, on the type of lesion, total ablation time, tissue impedance, or another treatment parameter. The processor can be configured to determine the temperature set point. The user-selected temperature set point can be entered by the user into the GUI.

[0011] RF energy is delivered from the electrode to drive the tissue temperature to approximately or exactly at the temperature set point. During delivery of the RF energy, the processor is configured to determine subsequent tissue impedance values ​​during delivery of the RF energy by the electrosurgical instrument. The processor compares the subsequent tissue impedance values ​​to an impedance threshold. If the determined tissue impedance values ​​do not exceed the impedance threshold for a given elapsed time-based characteristic of the ablation procedure, the processor determines that an impedance event has not occurred. If the processor determines that an impedance event has occurred, the temperature set point is reduced. The above actions can be performed continuously and in real time throughout the ablation procedure. The reduction in the temperature set point can be permanent. In other words, the temperature set point is not increased for the remaining time of the ablation procedure.

[0012] The reduction in temperature set point may be a temperature offset. The temperature offset may be fixed, i.e., constant, or variable. The fixed temperature offset may be a value that reduces the temperature set point with each occurrence of an impedance event. The temperature offset may be constant or variable, and / or may be predefined, determined, or user selected, and combinations thereof. The processor may be configured to determine the temperature offset based on the initial tissue impedance, the initial temperature set point, the time elapsed between impedance events, the type of lesion, or any other treatment parameter. The determined temperature offset may be constant or may be determined iteratively after each occurrence of an impedance event. The user selected temperature offset may be entered into the GUI by the user.

[0013] The ablation procedure includes a ramp period during which the tissue temperature increases toward the temperature set point. The electrosurgical console limits instances when the temperature set point is reduced to impedance events occurring after the ramp period. The processor is configured to determine whether the impedance event occurs during or after the ramp period. The processor may compare the tissue temperature to the temperature set point or another temperature based on the temperature set point. The temperature may be a threshold temperature for a characteristic based on elapsed time. The threshold temperature may be a percentage of the temperature set point. The processor is configured to maintain the temperature set point if the occurrence of the impedance event occurs during the ramp period. The processor is further configured to reduce the temperature set point if the occurrence of the impedance event occurs after the ramp period. If the occurrence of the impedance event occurs during the ramp period, the processor is further configured to instruct the display to provide an alert. The display may also display a total ablation time, an operating mode, a graphical representation of temperature versus time of the ablation procedure, an indication of an electrosurgical instrument coupled to the electrosurgical console, among other treatment parameters.

[0014] The processor may generate a secondary impedance threshold to be utilized in conjunction with the impedance threshold. The secondary impedance threshold may be greater than the primary impedance threshold for all time-based characteristics. The secondary impedance threshold may be utilized when reductions in temperature setpoint are insufficient to prevent continued increases in tissue impedance. The secondary impedance threshold may have the same or a different slope as the primary impedance threshold. If tissue impedance exceeds the impedance threshold of the secondary impedance threshold, the processor may instruct the controller to discontinue delivery of RF energy to the electrosurgical instrument. The pause in delivery of RF energy provides time for fluid from the injection module to partially reverse effects such as charring of the tissue. After a predefined or required period of time, the controller is configured to resume delivery of RF energy to the electrosurgical instrument.

[0015] The processor is configured to increase the duration of a ramp period following the occurrence of an impedance event. Following a temporary cessation of delivery of RF energy in response to an impedance event, the rate at which the tissue temperature is driven towards the temperature set point is decreased. A slower ramp period results in a more uniform ablation volume, thereby allowing the tissue to heat more slowly following resumption at a later point in the ablation procedure. It is noted that "and / or" is used herein to cover one element, any combination, or the sum of two or more elements connected by the phrase. [Brief description of the drawings]

[0016] [Figure 1] 1 is a perspective view of an electrosurgical system including an electrosurgical console, a cable accessory, electrosurgical instruments, an injection module coupled to one of the electrosurgical instruments, and a grounding pad assembly. [Diagram 2]1 is a graphical representation of an impedance threshold trajectory in which impedance values ​​increase as a function of the percentage of treatment time that tissue exceeds a given temperature threshold. [Diagram 3] 1 is a graphical representation of impedance as a function of percent of lesion above temperature threshold, with several exemplary impedance threshold curves shown. [Figure 4] 1 is a graphical representation of tissue temperature (° C.) as a function of energy elapsed time (in minutes). The instances of temperature set point reduction are associated with the occurrence of impedance events. [Diagram 5] FIG. 1 is a diagram of a display of an electrosurgical console showing operating parameters of an ablation procedure. [Figure 6] FIG. 13 is another view of the display showing an alert in response to an impedance event occurring during the ramp period of the ablation procedure. [Figure 7] 1 is a graphical representation of tissue temperature (° C.) as a function of energy elapsed time (in minutes). The duration of the ramp period is shown as increasing at later points in the ablation procedure. [Figure 8] 1 is a graphical representation of tissue temperature (° C.) as a function of elapsed time (in minutes) of energy delivery. A suboptimal arrangement does not decrease the temperature set point after the occurrence of an impedance event, and charring of the tissue over time prevents the tissue from returning near the temperature set point. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 1 and 2, electrosurgical system 10 includes electrosurgical console 12, electrosurgical instrument(s) 16, 17, and optionally, cable accessory 14 and / or grounding pad 18. Cable accessory 14 is configured to be removably coupled to electrosurgical console 12, and electrosurgical instruments 16, 17 are configured to be removably coupled to electrosurgical console 12 and / or cable accessory 14. One embodiment of electrosurgical instrument 17 can be a monopolar electrode in which electrode 22 is operable with grounding pad 18 that is removably coupleable to electrosurgical console 12. Another embodiment of electrosurgical instrument 16 is a bipolar electrode, e.g., a self-grounding bipolar electrode, in which proximal electrode 22 and distal electrode 23 provide a path for electrical current through tissue to be ablated. Two or more bipolar electrodes can be used simultaneously, e.g., in a bipedicular approach through a vertebral body. The injection module 20 may be operable with the electrosurgical instrument 16 to direct fluid through the electrosurgical instrument 16 for ejection proximate the proximal and distal electrodes 22, 23. A thermocouple 24 is disposed near the distal end of the electrosurgical instrument 16, 17 and configured to provide a temperature measurement of tissue proximate the electrode(s) 22, 23. One preferred embodiment of the electrosurgical instrument 16 and injection module 20 is disclosed in commonly-assigned International Publication No. WO 2020 / 198150, published November 5, 2020, the entire disclosure of which is incorporated herein by reference. The injection module 20 includes an injection clamp 26 configured to be actuated to selectively start and stop the flow of fluid.

[0018] The electrosurgical system 10 is configured to treat tissue by radiofrequency (RF) ablation. The electrosurgical console 12 generates controlled radio frequency electrical energy and passes the energy through the electrosurgical instruments 16, 17 and the tissue, thereby heating the tissue to a temperature sufficient to destroy cells in the tissue. Ablation can be performed in a monopolar, parallel bipolar, or self-grounded bipolar configuration, as detailed in commonly owned International Publication No. WO 2018 / 200254, published November 1, 2018, the entire disclosure of which is incorporated herein by reference. In certain embodiments, the electrosurgical system 10 is utilized to ablate nerves for pain management. In other embodiments, the electrosurgical system 10 is utilized to ablate lesions, particularly intraosseous tumors. One exemplary procedure of particular interest is the ablation of tumors within vertebral bodies. An introducer assembly is deployed through one or both pedicles to facilitate access into the vertebral body, and the electrosurgical console 12 applies temperature controlled RF energy into the tumor. Associated nerves within or surrounding the tumor may also be ablated to provide pain relief. It should be appreciated that the electrosurgical system 10 of the present disclosure may be utilized to treat intraosseous tumors of the long bones, skull, mandible, ileum, etc.

[0019] Electrosurgical console 12 includes a display 30 configured to display a graphical user interface (GUI) 32 that allows a user to, among other actions, select operating parameters and navigate through different operating modes provided by software on electrosurgical console 12, as shown in FIGURE 1. Display 30, in one example, is a touchscreen, allowing selection of digital displays displayed on display 30 using contact locations that can be capacitively sensed on the touchscreen. Alternatively, display 30 can be paired with a separate touchscreen device or controlled by peripheral input devices connected to electrosurgical console 12, such as a mouse and / or keyboard (i.e., a mouse or keyboard, or both).

[0020] 2, electrosurgical console 12 includes controller 34, one or more processors 36, and memory 38. Computer executable instructions 40 or code may be stored in memory 38, such as in a database 42 of memory 38. The instructions 40 are accessible to processor 36 and executable by processor 36 to implement various functions of electrosurgical console 12. For example, instructions 40 are configured to implement GUI 32 on display 30. Other functions implemented by execution of instructions 40 are described below. Processor(s) 36 and memory 38 may have any suitable configuration and may be of any suitable type that enables implementation of the functions described herein. Moreover, following convention, this disclosure describes processor 36 executing instructions 40 and controller 34 controlling output from or actions of electrosurgical console 12, such as controlling RF energy delivered to electrosurgical instruments 16, 17. It should be understood that controller 34 may be implemented by processor 36 or may be a separate device from processor 36. The processor 36 is configured to communicate with the controller 34 or, if the controller 34 and the processor 36 are housed on separate devices, to be in wired or wireless communication with the controller 34. Any of the functions described herein may be performed by the controller 34, the processor(s) 36, or a combination thereof.

[0021] The electrosurgical instruments 16, 17 are removably coupled to the electrosurgical console 12 and configured to place the electrosurgical instruments 16, 17 in communication with a controller 34. Based on inputs to the GUI 32, the controller 34 controls the RF energy delivered to the electrosurgical instruments 16, 17. The controller 34 is further configured to receive or process one or more treatment parameters, such as tissue temperature. In particular, the controller 34 is configured to communicate with the thermocouples 24 of the electrosurgical instruments 16, 17 to receive signals indicative of the tissue temperature at the treatment site. Another treatment parameter includes tissue impedance, which may be determined by the processor 36 based on measured electrical parameters, such as the supply and return voltages through the electrodes 22, 23 across the electrode-tissue interface. The tissue temperature may also be used to determine an impedance value.

[0022] It is known that tissue impedance changes during ablation of a lesion, with higher tissue impedance values ​​being more tolerable after the ablation procedure. In other words, while the reduction in electrical and thermal conductivity of tissue becomes less important after the lesion has already been heated for an extended period of time, such reduction early in the procedure may impair the effectiveness of the procedure. Referring now to FIG. 3, the processor 36 may be configured to determine an initial tissue impedance value 44. The initial tissue impedance value 44 may be based on an initial supply voltage and a return voltage through the electrodes 22, 23 across the electrode-tissue interface. Thus, the electrosurgical instrument 16, 17 may deploy the electrodes 22, 23 at a target site near, at, or within the lesion, and a current path is created to obtain the initial supply voltage and the return voltage. In one embodiment, this may be done automatically when an input to initiate ablation is provided to the GUI 32. In other words, the initial tissue impedance value 44 may be determined in real time with the delivery of RF energy. Alternatively, after the electrosurgical instruments 16, 17 are deployed at the target site and before ablation begins, the user can select a tissue impedance acquisition mode on the GUI 32, after which subtherapeutic or sub-ablative magnitude current paths are created to obtain initial supply and return voltages from which an initial tissue impedance value 44 is determined.

[0023] The processor 36 can be configured to determine an impedance threshold 48 based on the initial tissue impedance value 44. The impedance threshold 48 can vary based on an elapsed time-based characteristic of the ablation procedure, reflecting that higher tissue impedance values ​​are more acceptable following the ablation procedure. In the broadest sense, the elapsed time-based characteristic can be the elapsed time since the start of delivery of RF energy or from another start or set time of the ablation procedure. The set time can be selected or predefined, for example, once the tissue temperature measured by the thermocouple 24 is near or at a temperature set point as described. The elapsed time can be continuous or can be paused during periods when RF energy is not being delivered. In another embodiment, the elapsed time-based characteristic can be a percentage of the total ablation time. The total ablation time can be entered by the user into the GUI 32 or can be determined by the processor 36. For example, based on the size of the lesion to be ablated and the temperature set point, the processor 36 is configured to determine the total ablation time. The percentage of the total ablation time can be the ratio of the elapsed time to the total ablation time, as previously described. In yet another embodiment, the time-based characteristic can be a percentage of the lesion above a threshold temperature, as shown in FIG. 3. The threshold temperature can be a temperature set point, a percentage of the temperature set point, or another determined temperature based on any number of factors of the ablation procedure. The tissue temperature of the lesion is sensed by the thermocouple 24 and transmitted to the processor 36. The processor 36 can be configured to determine the percentage as a ratio of the time the lesion has exceeded the threshold temperature to the total ablation time, as previously described. In such an embodiment, if the temperature remains above the temperature threshold, the percentage can increase despite the RF energy being paused.Experiments have shown that using the percentage of lesions above a threshold temperature as the basis for the impedance threshold more effectively provides a desired ablation profile while taking into account tissue impedance rises and / or transient spikes (i.e., rises or transient spikes or both).

[0024] In certain embodiments, the impedance threshold 48 may define an impedance threshold curve 46. The impedance threshold 48 may be determined according to a function, for example, the following equation: Z t (t)=Z s +(Z m -Z s )*t e Here, Z t (t) is the impedance threshold 48 at a given time during the treatment, and Z s is the initial impedance value of 44, Z m is the maximum impedance threshold, and t e is a characteristic based on elapsed time, e.g., a percentage of the total procedure time. A noise margin may be further considered. The maximum impedance threshold and noise margin may be fixed or variable values. The total procedure time may be variably determined prior to the procedure or may be determined based on a predefined default value stored in memory 38. The predefined default value may be based on the size of the probe of the electrosurgical instrument 16, 17.

[0025] The processor 36 is further configured to determine a final threshold impedance value 50. The final threshold impedance value 50 can be the last time-based characteristic impedance threshold 48, for example, at the end of the ablation procedure when the RF energy has ceased. This can correspond to the time-based characteristic of the above formula being equal to 1 and / or 100 percent of the lesions exceeding the temperature threshold (i.e., equal to 1 or 100 percent of the lesions exceeding the temperature threshold, or both). The final impedance threshold 50 can be based on the initial tissue impedance value 44 and can be determined according to the above formula. In an alternative embodiment, the memory 38 can store multiple impedance threshold curves, and the processor 36 is configured to determine the impedance threshold curve by selecting one of the impedance threshold curves 46 stored in the memory 38. One example is to compare the initial tissue impedance value 44 with the initial tissue impedance value of each of the impedance threshold curves 46 and select the impedance threshold curve 46 to which the initial tissue impedance value 44 is closest. Additionally or alternatively, a subsequent one of the impedance thresholds 48 can be based on the occurrence and / or characteristics of impedance events (i.e., the occurrence and / or characteristics) and the impedance threshold can be determined in real time and can deviate from a predefined function. As one example, a subsequent one of the impedance thresholds 48 can be higher or lower based on the amount by which the tissue impedance value 44 exceeds the impedance threshold 48.

[0026] FIG. 3 shows several exemplary impedance threshold curves 46 for illustration purposes. The impedance threshold curves 46 may be linear and may extend between an initial tissue impedance value 44 and a final impedance threshold value 50. The impedance threshold curves 46 may have a positive slope, with the higher the value of the elapsed time-based characteristic, the higher the threshold value. Additionally, the higher the value of the initial tissue impedance value 44, the lower the slope of each one of the impedance threshold curves 46. For example, as shown in FIG. 3, the impedance threshold curves 46 may have different slopes, with the offset of the impedance threshold curves 46 being greater where the value of the elapsed time-based characteristic is lower than where the value of the elapsed time-based characteristic is higher. More specifically, the initial tissue impedance values ​​44 are shown as being offset from each other by 100 ohms, while the final threshold impedance values ​​50 are shown as being offset from each other by 50 ohms. Other characteristics of the impedance threshold curves 46 are envisioned, such as nonlinear by having hyperbolic and logarithmic shapes, and stepped, among others.

[0027] With further reference to FIG. 4, the processor 36 is configured to control the RF energy delivered from the electrodes 22, 23 based on the temperature measurements of the thermocouple 24 and the temperature set point at which the tissue is ablated. Additionally, as described, the processor 36 is configured to reduce the temperature set point based on the occurrence of an impedance event, i.e., when the tissue impedance exceeds an impedance threshold 48. The presently disclosed electrosurgical console 12, which utilizes impedance-based control to drive the tissue temperature toward the temperature set point, advantageously improves the delivery of RF energy by reducing the risk of recurring uncontrolled spikes in impedance. In contrast, known systems in which impedance is driven toward an impedance trajectory may result in less than optimal temperature control. Similarly, FIG. 8 reflects a less than optimal arrangement in which the tissue temperature is driven toward the temperature set point, but without a reduction in the temperature set point following an impedance event, recurring impedance events would result in degradation of the electrode-tissue interface and insufficient deliverable RF energy for ablation. The presently disclosed electrosurgical console 12 overcomes such shortcomings.

[0028] The temperature set point may be predefined, determined, or user selected. The predefined temperature set point may be based, for example, on the type of lesion being ablated. An intraosseous tumor may be ablated with a temperature set point in the range of 90°C to 100°C, more particularly, in the range of 94°C to 96°C, or another temperature indicated to destroy cells of the tissue of the lesion. The determined temperature set point may be based, for example, on the type of lesion, the total ablation time, tissue impedance, or another treatment parameter. The processor 36 may be configured to determine the temperature set point. The user selected temperature set point may be entered by the user into the GUI 32. FIG. 5 shows a temperature set point 52 displayed on the display 30 as 95°C.

[0029] RF energy is delivered from the electrodes 22, 23 to drive or drive the tissue temperature 54 to approximately or exactly at the temperature set point 52. FIG. 5 shows the tissue temperature 54 displayed on the display 30 as 94° C. During delivery of the RF energy, the processor 36 is configured to determine subsequent tissue impedance values ​​during delivery of RF energy by the electrosurgical instruments 16, 17. The processor 36 compares the subsequent tissue impedance values ​​to an impedance threshold 48. If the determined tissue impedance value does not exceed the impedance threshold 48 at a given elapsed time-based characteristic of the ablation procedure, the processor 36 determines that an impedance event has not occurred. As an example, referring to FIG. 3, using an impedance threshold curve 46 where the initial tissue impedance value 44 is 150 ohms, and where the elapsed time-based characteristic is 60%, the first tissue impedance value shown at 56 is less than the impedance threshold 48 which is approximately 625 ohms. The processor 36 may take no action and the controller 34 continues to deliver RF energy to the electrodes 22, 23 to drive the tissue temperature 54 toward the temperature set point 52. When the elapsed time based characteristic is 75%, the second tissue impedance value shown at 58 is greater than the impedance threshold 48, which is approximately 750 ohms. The processor 36 determines the occurrence of an impedance event and reduces the temperature set point 52. The above actions may be performed continuously and in real time throughout the ablation procedure.

[0030] The reduction in temperature set point 52 may be permanent. In other words, the temperature set point 52 is not increased for the remainder of the ablation procedure. The underlying cause of the impedance event, e.g., tissue charring or suboptimal contact between the electrodes 22, 23 and the tissue, may remain, and as previously described, efforts to return the temperature set point 52 to the initial temperature set point may result in further impedance events. More specifically, FIG. 8 shows a first impedance event I1, after which the suboptimal configuration attempts to drive the tissue temperature to the initial temperature set point. This may be initially feasible, in some cases, due to the fact that tissue charring following a temporary drop in tissue temperature is partially reversible, or by improving contact between the electrodes and tissue. However, the characteristics of the lesion and / or the electrode-tissue interface (i.e., the lesion and / or the electrode-tissue interface) may make it impossible to maintain the initial temperature set point, after which a second impedance event I2 occurs. The suboptimal configuration again attempts to drive the tissue temperature to the initial temperature set point. Irreversible degradation of the electrode-tissue interface leads to the third impedance event, the fourth impedance event, and subsequent impedance events (I3, I4, ... I N ) occurs at lower tissue temperatures. In other words, not only is the initial temperature set point unattainable, but the impedance event results even at more moderate tissue temperatures. As a result, the tissue temperature to which RF energy can be delivered without an impedance event is insufficient for ablation, which effectively causes the ablation procedure to fail.

[0031] Referring now to FIG. 4, an embodiment of the present disclosure is shown in which the temperature set point 52 is reduced in response to the occurrence of an impedance event(s). Once delivery of RF energy begins, the tissue temperature is ramped to an initial or first temperature set point T1. In this example, the tissue temperature achieves the first temperature set point and a few minutes later, a first impedance event I1 occurs. The processor 36 reduces the first temperature set point T1 to a second temperature set point T2 and the controller 34 controls the RF energy to drive the tissue temperature to the second temperature set point T2. This may allow the lesion and / or electrode-tissue interface to be more likely to adapt to the level of RF energy associated with the second temperature set point, preferably without another impedance event occurring. For illustrative purposes, FIG. 4 shows the occurrence of a second impedance event I2 and a third impedance event I3. Based on the occurrence of the second impedance event I2, the processor 36 reduces the second temperature set point T2 to a third temperature set point T3, and the controller 34 controls the RF energy to drive the tissue temperature to the third temperature set point T3. Similarly, based on the occurrence of the third impedance event I3, the processor 36 reduces the third temperature set point T3 to a fourth temperature set point T4, and the controller 34 controls the RF energy to drive the tissue temperature to the fourth temperature set point T4. The remaining time of the ablation procedure proceeds with the lesion being ablated at the fourth temperature set point T4. In contrast to the suboptimal embodiment of FIG. 8, where the tissue temperature decays to approximately 40° C. due to repeated impedance events, the embodiment of the present disclosure of FIG. 8 remains running at 80° C., which is sufficient to ablate the lesion. In other words, this approach continues to output RF energy and expand the ablation zone, albeit at a slower rate, providing the user with confidence to proceed with the ablation procedure at a set point temperature known to result in the intended cell destruction.

[0032] The reduction in temperature set point 52 is a temperature offset. The temperature offset can be constant or variable. The constant temperature offset can be a value that reduces the temperature set point with each occurrence of an impedance event. The constant temperature offset can be in the range of 3°C to 7°C, more particularly approximately 5°C. Experiments have shown that the range of 3°C to 7°C significantly reduces the likelihood of subsequent occurrence of an impedance event. In the exemplary embodiment of FIG. 4, the constant temperature offset is 5°C, the initial and first temperature set point is 95°C, the second temperature set point is 90°C, the third temperature set point is 85°C, the fourth temperature set point is 80°C, and so on. It is further contemplated that the temperature offset can be constant or variable, and / or can be predefined, determined, or user selected, as well as combinations thereof. For example, the processor 36 can be configured to determine the temperature offset based on the initial tissue impedance, the initial temperature set point, the time elapsed between impedance events, the type of lesion, or any other treatment parameter. The determined temperature offset may be constant or may be determined iteratively after each occurrence of an impedance event. In other words, a first temperature offset may be 3° C., but if it is followed immediately by a subsequent impedance event within, for example, a predetermined or required elapsed time, a second temperature offset may be 5° C., 7° C., or more. Alternatively, a user-selected temperature offset may be entered by a user into the GUI 32. For example, a user-selected temperature offset may be selected as 15° C., and the second temperature set point is 80° C. because experiments have demonstrated that this results in very little impedance rise during testing.

[0033] With continued reference to FIG. 4, the ablation procedure includes a ramp period 60 during which the tissue temperature rises toward the temperature set point 52. Assuming a nominal body temperature of 37° C., the ramp period 60 may be the first minute, two minutes, three minutes, four minutes, or more of the ablation procedure before achieving the temperature set point 52, which may be, for example, 95° C. During the ramp period 60, when the tissue temperature is only 40° C., 50° C., 60° C., etc., the occurrence of impedance events may not be due to reduced electrical and thermal conductivity of the tissue (e.g., charring). Rather, the impedance events may be due to less than optimal contact between the electrodes 22, 23 and the lesion at the electrode-tissue interface. Thus, reducing the temperature set point during the ramp period 60 may be undesirable since the tissue remains likely to accommodate a level of RF energy that achieves the initial temperature set point. In other words, reducing the temperature set point during the ramp period 60 may be premature.

[0034] The presently disclosed electrosurgical console 12 advantageously limits instances in which the temperature set point is reduced to those in which the impedance event occurs after the ramp period 60. More specifically, the processor 36 is configured to determine whether the impedance event occurs during the ramp period 60 or later during the ramp period 60. To that end, the processor 36 may compare the tissue temperature to the temperature set point 52, or another temperature based on the temperature set point. The temperature may be a threshold temperature for a time-based characteristic, as previously described. In certain embodiments, the threshold temperature may be a percentage of the temperature set point. For example, if the tissue temperature has not reached 85%, 90%, or 95% of the temperature set point 52, the processor 36 determines that the ablation procedure is in the ramp period 60. Conversely, if the tissue temperature has reached the threshold temperature or the temperature set point 52, the processor 36 determines that the ablation procedure is no longer in the ramp period 60.

[0035] Processor 36 is configured to maintain temperature setpoint 52 if the impedance event occurs during ramp period 60. Continuing with reference to FIG. 4, the occurrence of a ramp impedance event during ramp period 60 is shown at 62. For ramp impedance event 62, processor 36 maintains temperature setpoint 52 as an initial or first temperature setpoint T1. Processor 36 is further configured to reduce temperature setpoint 52 if the impedance event occurs later during ramp period 60. One example of such an instance is the first impedance event I1 and the reduction from the first temperature setpoint T1 to the second temperature setpoint T2, as shown in FIG. 4 and described above.

[0036] As mentioned, an impedance event during the ramp period 60 may be due to less than optimal contact between the electrodes 22, 23 and the lesion at the electrode-tissue interface. The electrosurgical system 10 of the present disclosure includes an injection module 20 that directs fluid ejected near the proximal and distal electrodes 22, 23 through the electrosurgical instrument 16. The ejected fluid improves the conductivity of RF energy at the electrode-tissue interface, thereby limiting less than optimal contact between the electrodes 22, 23 and the lesion. Thus, an impedance event occurring during the ramp period 60 may be due to a user failing to activate the injection module 20 or failing to activate the injection clamp 26 to permit fluid flow. Thus, if an impedance event occurs during the ramp period 60, the processor 36 is further configured to instruct the display 30 to provide an alert 64. One exemplary alert 64 is shown as a pop-up notification in FIG. 6. Additional visual alerts, as well as audible and tactile alerts, are also envisioned. For example, FIG. 6 further illustrates tissue impedance 58 visually highlighted on display 30 to indicate that tissue impedance 58 exceeds an impedance threshold for a given elapsed time based characteristic 61 of the ablation procedure. Display 30 may also display total ablation time 66, operating mode 68, a graphical representation 70 of temperature versus time of the ablation procedure, an indication 72 of the electrosurgical instruments 16, 17 coupled to electrosurgical console 12, among other treatment parameters. It is further envisioned that more than one electrosurgical instrument 16, 17 may be simultaneously operable with electrosurgical console 12, and display 30 may include fields 74, 76 indicative of each of the electrosurgical instruments 16, 17 (see FIG. 1 ) coupled to electrosurgical console 12. Selection of fields 74, 76 on GUI 32 may enable a user to switch between the operating parameters of each of the electrosurgical instruments 16, 17.

[0037] In certain embodiments, the processor 36 can generate a secondary impedance threshold (not identified) that is utilized in conjunction with the impedance threshold 48, hereafter referred to as the primary impedance threshold. The secondary impedance threshold can be greater than the primary impedance threshold for all time-based characteristics. The secondary impedance threshold can be utilized when the reduction in temperature set point 52 is insufficient to prevent a continued increase in tissue impedance. In other words, the secondary impedance threshold can be considered a backup failsafe. The secondary impedance threshold can be a function, such as a curve with the same or different slope as the primary impedance threshold curve. In one example with a different slope, the secondary impedance threshold curve is a horizontal line at a constant maximum of acceptable tissue impedance. If the tissue impedance exceeds the impedance threshold of the secondary impedance threshold, the processor 36 can instruct the controller 34 to interrupt the delivery of RF energy to the electrosurgical instruments 16, 17. The pause in the delivery of RF energy provides time for fluid from the injection module to partially reverse effects such as charring of the tissue. After a predefined or required period of time, the controller 34 is configured to resume delivery of RF energy to the electrosurgical instruments 16 , 17 .

[0038] 7, another embodiment is shown in which instructions 40 are executed by the processor 36 to increase the duration of the ramp period following the occurrence of an impedance event. More specifically, following a temporary interruption in delivery of RF energy in response to an impedance event, the rate at which the tissue temperature is driven toward the temperature set point is decreased. In other words, a slower ramp period results in a more uniform ablation volume (i.e., less charring) and therefore the tissue heats more slowly following resumption at a later point during the ablation procedure. Thus, earlier in the procedure, a faster ramp period may be utilized and less aggressive ramping may be utilized if charring becomes an increasingly greater problem during the ablation procedure.

[0039] FIG. 7 illustrates that the tissue temperature is ramped to an initial or first temperature set point T1, where an initial ramp period 60 is defined as previously described. In response to a first impedance event I1, the processor 36 reduces the first temperature set point T1 to a second temperature set point T2. The controller 34 resumes delivery of RF energy at a power level configured to drive the tissue temperature toward the second temperature set point T2 in a second ramp period R2 having a slope of the temperature-time curve of FIG. 7. A second impedance event I2 occurs and the processor 36 reduces the first temperature set point T1 to the second temperature set point T2. The controller 34 resumes delivery of RF energy at another power level configured to drive the tissue temperature toward the third temperature set point T3 in a third ramp period R3. Because the third ramp period R3 is of greater duration than the second ramp period R2, the slope of the second ramp period R2 is less than the slope of the third ramp period R3. After delivering the additional RF energy, a third impedance event I3 occurs and the processor 36 reduces the second temperature setpoint T2 to the third temperature setpoint T3. The controller 34 resumes delivery of RF energy at yet another power level configured to drive the tissue temperature toward the fourth temperature setpoint T4 in a fourth ramp period R4. Because the fourth ramp period R4 is of greater duration than the third ramp period R3, the slope of the third ramp period R3 is smaller than the slope of the fourth ramp period R4. The remainder of the ablation procedure proceeds with the lesion being ablated at the fourth temperature setpoint T4.

[0040] The above disclosure is not intended to be exhaustive or to limit the invention to any particular form. The terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations are possible in light of the above teachings, and the invention can be practiced in other ways than as specifically described. It is understood that treatment parameters other than impedance and temperature can be utilized with the techniques described above. Furthermore, it is envisioned that treatment parameters can be controlled or defined in other ways than the techniques described. Furthermore, it is understood that the subject matter of the present disclosure can be used with microwave energy or electrical energy other than radio frequency energy.

[0041] With reference to the following clauses, an exemplary method of performing an electrosurgical procedure using the electrosurgical system 10 of the present disclosure is described.

[0042] Clause 1 - A method of operating an electrosurgical console to ablate tissue during an ablation procedure using an electrosurgical instrument, comprising: controlling electrical energy delivered from an electrode based on a temperature measurement of a thermocouple and a temperature set point at which the tissue is ablated; determining an initial tissue impedance value; determining an impedance threshold based on the initial tissue impedance value, the impedance threshold varying based on an elapsed time-based characteristic of the ablation procedure; determining subsequent tissue impedance values ​​during delivery of electrical energy by the electrosurgical instrument; determining an occurrence of an impedance event by comparing the subsequent tissue impedance value to the threshold; and reducing the temperature set point based on the occurrence of the impedance event.

[0043] Clause 2 - The method of clause 1, further comprising determining the elapsed time based characteristic by determining the percentage of the total treatment time during which the tissue exceeds a threshold temperature.

[0044] Clause 3 - The method of clause 1 or 2, wherein the ablation procedure includes a temperature set point at which tissue is ablated and a ramp period during which the tissue temperature rises toward the temperature set point, the method further including determining whether an impedance event occurs during or after the ramp period, and maintaining the temperature set point if the impedance event occurs during the ramp period.

[0045] Clause 4 - The method of clause 3, further comprising reducing the temperature setpoint if the occurrence of the impedance event is after the ramp period.

[0046] Clause 5 - The method of clause 4, further comprising reducing the temperature setpoint by a constant temperature offset upon occurrence of the impedance event and subsequent occurrence of an additional impedance event.

[0047] Clause 6 - The method of any one of clauses 3 to 5, further comprising displaying an alert if the occurrence of an impedance event occurs during a ramp period.

[0048] Clause 7 - The method of any one of clauses 3 to 5, further comprising interrupting delivery of electrical energy based on the occurrence of an impedance event after the ramp period, and resuming delivery of electrical energy after a period of time.

[0049] Clause 8 - The method of clause 7, further comprising upon resumption, delivering electrical energy with power that re-ramps the tissue temperature to a reduced temperature set point, optionally with the re-ramping being longer at a later point in the ablation procedure.

[0050] Clause 9 - The method of any one of clauses 1 to 8, further comprising determining a secondary impedance threshold and interrupting delivery of electrical energy based on a subsequent tissue impedance value exceeding the secondary impedance threshold.

[0051] Clause 10 - A method of operating an electrosurgical console to ablate tissue during an ablation procedure with an electrosurgical instrument, the ablation procedure including a temperature set point at which tissue is ablated and a ramp period during which the tissue temperature rises toward the temperature set point, the method including determining an impedance threshold, determining a tissue impedance value during delivery of electrical energy by the electrosurgical instrument, determining an occurrence of an impedance event by comparing the tissue impedance value to the impedance threshold, determining whether the occurrence of the impedance event is during or after the ramp period, and maintaining the temperature set point if the occurrence of the impedance event is during the ramp period.

[0052] Clause 11 - The method of clause 10, further comprising reducing the temperature setpoint if the occurrence of the impedance event is after the ramp period.

[0053] Clause 12 - The method of clause 11, further comprising reducing the temperature setpoint by a constant temperature offset upon occurrence of the impedance event and subsequent occurrence of an additional impedance event.

[0054] Clause 13 - A method as described in any one of clauses 9 to 12, further comprising receiving a tissue temperature value and determining whether an impedance event occurs during or after the ramp period by comparing the tissue temperature value to a temperature set point or a temperature threshold based on the temperature set point.

[0055] Clause 14 - The method of any one of clauses 9 to 13, further comprising controlling delivery of electrical energy from the electrosurgical instrument based on the occurrence of an impedance event.

[0056] Clause 15 - The method of any one of clauses 9 to 14, further comprising displaying an alert if the occurrence of an impedance event occurs during a ramp period.

[0057] Clause 16 - The method of any one of clauses 9 to 15, further comprising interrupting delivery of electrical energy based on the occurrence of an impedance event after the ramp period, and resuming delivery of electrical energy after a period of time.

[0058] Clause 17 - The method of clause 16, further comprising upon resumption delivering electrical energy with power to re-ramp the tissue temperature to a reduced temperature set point, optionally with the re-ramp being longer at a later point in the ablation procedure.

[0059] Clause 18 - A method of operating an electrosurgical console to ablate tissue during an ablation procedure with an electrosurgical instrument, the ablation procedure including a temperature set point at which tissue is ablated and a ramp period during which the tissue temperature rises toward the temperature set point, the method including determining a tissue impedance value during delivery of electrical energy by the electrosurgical instrument, determining an occurrence of an impedance event by comparing the tissue impedance value to an impedance threshold, and reducing the temperature set point by a constant temperature offset after the occurrence of the impedance event and subsequent occurrences of the impedance event.

[0060] Clause 19 - The method of clause 18, further comprising determining whether the occurrence of the impedance event is during the ramp period or after the ramp period, and reducing the temperature set point if the occurrence of the impedance event is after the ramp period.

[0061] Clause 20 - The method of clause 19, further comprising interrupting electrical energy delivered to the tissue and, optionally, upon resumption, delivering electrical energy with power that re-ramps the tissue temperature to a reduced temperature set point, the re-ramping being longer at a later point in the ablation procedure.

Claims

1. An electrosurgical console for ablating tissue during an ablation procedure using an electrosurgical instrument comprising an electrode for delivering electrical energy to the tissue and a thermocouple, a console configured to be coupled to the electrosurgical instrument, the console comprising a controller configured to communicate with the electrosurgical instrument coupled to the console, a processor configured to communicate with the controller, comprising, the processor is configured to, cause the controller to control the electrical energy delivered from the electrode based on the tissue temperature detected by the thermocouple and a temperature set point at which the tissue is to be ablated, determine an initial tissue impedance value, determine an impedance threshold based on the initial tissue impedance value, wherein the impedance threshold varies based on a characteristic based on the elapsed time of the ablation procedure, determine a subsequent tissue impedance value during delivery of the electrical energy by the electrosurgical instrument, determine the occurrence of an impedance event by comparing the subsequent tissue impedance value to the impedance threshold, reduce the temperature set point based on the occurrence of the impedance event, and is further configured to perform. An electrosurgical console.

2. The electrosurgical console according to claim 1, wherein the initial tissue impedance value is based on at least one of an electrical parameter related to the electrode and the tissue temperature.

3. The electrosurgical console according to claim 1, wherein the impedance threshold defines an impedance threshold curve that is linear, and the impedance threshold increases as a value of the characteristic based on the elapsed time increases.

4. The electrosurgical console according to claim 3, wherein the impedance threshold curve has a slope based on the initial tissue impedance value and a final impedance threshold, and the slope is different from another impedance threshold curve having a different initial threshold.

5. The electrosurgical console according to claim 1, wherein the processor is further configured to determine a characteristic based on the elapsed time by determining a percentage of a total treatment time that the tissue exceeds a threshold temperature.

6. The electrosurgical console according to claim 5, wherein the threshold temperature is the temperature set point or another temperature based on the temperature set point.

7. The ablation treatment includes the temperature set point at which the tissue is ablated and a ramp period during which the tissue temperature rises toward the temperature set point. The processor determines whether the occurrence of the impedance event is during the ramp period or after the ramp period, and is configured to maintain the temperature set point if the occurrence of the impedance event is during the ramp period. The electrosurgical console according to any one of claims 1 to 6.

8. The electrosurgical console according to claim 7, wherein the processor is further configured to reduce the temperature set point if the occurrence of the impedance event is after the ramp period.

9. The electrosurgical console according to claim 8, wherein the processor is further configured to reduce the temperature set point by a fixed temperature offset in accordance with the occurrence of the impedance event and subsequent occurrences of additional impedance events.

10. The electrosurgical console according to claim 9, wherein the fixed temperature offset is in the range of 3°C to 7°C.

11. The electrosurgical console according to claim 7, further comprising a display that communicates with the processor, and the processor is further configured to command the display to provide an alert if the occurrence of the impedance event is during the ramp period.

12. The electrosurgical console according to claim 7, wherein the processor is further configured to command the controller to interrupt the delivery of the electrical energy based on the occurrence of the impedance event after the ramp period and to resume the delivery of the electrical energy after a certain period.

13. The electrosurgical console according to claim 12, wherein the processor is further configured to command the controller to deliver the electrical energy with power for re-ramping the tissue temperature to the reduced temperature set point at the time of resumption.

14. The electrosurgical console according to claim 13, wherein the re-ramping control is longer at a point after the ablation treatment.

15. The processor is further configured to determine a secondary impedance threshold greater than the impedance threshold for each of the characteristics based on the elapsed time, and the processor is further configured to instruct the controller to interrupt the delivery of the electrical energy based on the subsequent tissue impedance value exceeding the secondary impedance threshold. The electrosurgical console according to any one of claims 1 to 6.

16. An electrosurgical console for an ablation procedure using an electrosurgical instrument comprising an electrode for delivering electrical energy to tissue and a thermocouple, wherein the ablation procedure includes a temperature set point at which the tissue is ablated and a ramp period during which the tissue temperature rises towards the temperature set point. The electrosurgical console is a console configured to be coupled to the electrosurgical instrument, and a processor configured to operably communicate with the electrosurgical instrument coupled to the console and comprising The processor is configured to determine a tissue impedance value during delivery of the electrical energy by the electrosurgical instrument, determine the occurrence of an impedance event by comparing the tissue impedance value with an impedance threshold, and reduce the temperature set point by a constant temperature offset after the occurrence of the impedance event and after a subsequent occurrence of the impedance event. The electrosurgical console is further configured to perform.

17. The processor is configured to determine whether the occurrence of the impedance event is during or after the ramp period, and reduce the temperature set point if the occurrence of the impedance event is after the ramp period. The electrosurgical console according to claim 16, which is further configured to perform.

18. The electrosurgical console according to claim 16, wherein the constant temperature offset is in the range of 3°C to 7°C.

19. The electrosurgical console according to claim 18, wherein the constant temperature offset is 5°C.

20. The console includes a controller configured to communicate with the processor and to communicate with the electrosurgical instrument coupled to the console, the controller being configured to control delivery of the electrical energy from the electrosurgical instrument based on occurrence of the impedance event. The electrosurgical console according to any one of claims 16 to 19.

21. The electrosurgical console according to claim 20, wherein the processor is further configured to instruct the controller to reduce or interrupt the electrical energy delivered to the tissue.

22. The electrosurgical console according to claim 21, wherein the processor is further configured to instruct the controller to deliver electrical energy with power to re-ramp control the tissue temperature to the reduced temperature set point upon resumption.

23. The electrosurgical console according to claim 22, wherein the re-ramp control is longer at a point after the ablation procedure.

24. The electrosurgical console according to any one of claims 16 to 19, wherein the reduced temperature set point is configured to remain unchanged for the remaining time of the ablation procedure in the absence of subsequent occurrence of the impedance event.

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