Patent Application
20220395310
Electrosurgery involves the use of electricity to buildup heat within biological tissue to cause thermal tissue damage through one or more of desiccation, coagulation, or vaporization, resulting in incision, removal or sealing of the tissue. High frequency electrosurgery involves heating biological tissue by imparting radio frequency (RF) alternating current (AC) to biological tissue such that the current is converted to heat by resistance as it passes through the tissue. Benefits include the ability to make precise incisions with limited blood loss during surgical procedures in hospital operating rooms or in outpatient procedures.
An electrosurgical instrument creates a relatively high voltage potential between an active electrode and the target tissue. This high voltage quickly dessicates the tissues and in many cases, creates a vapor barrier between the electrode and the tissue surface. With a high enough voltage, an electrical plasma is created in this vapor barrier, and the ionized elements of this plasma allow RF current conduction from the electrode to the tissue, which causes vaporization of the target tissue that results in mechanical separation or dissection.
Electrosurgery can be performed with either a monopolar or a bipolar electrosurgical instrument each of which includes two electrodes to contact biological tissue. In some cases, an active electrode can make contact with non-target conductive surfaces such as other instruments, staples or fluids such as blood or saline, which can result in a sudden breakdown in impedance across the vapor barrier. The sudden reduced impedance can result in an electrical arc at the active electrode or can result in an electrical arc between the active electrode and the return electrodes of a bipolar device. An arc event can cause excessive tissue damage or damage to the electrodes themselves.
Thus, there is a need to rapidly detect an onset of an arc event and to control the application of RF current to avoid occurrence of the arc event or to reduce intensity of the arc event.
In one aspect, a method to control delivery of heat to biological tissue. An RF electrical signal is imparted to the biological tissue over a circuit that includes a first electrode and a second electrode, wherein the biological tissue is electrically coupled between the first electrode and the second electrode. Frequency content of the RF electrical signal is measured. The RF electrical signal is adjusted based upon the measured frequency content of the RF electrical signal.
In another aspect, an electrosurgical system is provided to deliver heat to biological tissue. A radio frequency (RF) electrical signal source is operable to impart an RF electrical signal to the biological tissue. A digital sampling circuit is coupled to digitally sample the RF electrical signal imparted to the biological tissue. Frequency content logic is coupled to determine frequency content of the RF electrical signal based upon digital samples of the RF electrical signal. Control logic is coupled to control the RF electrical signal source based upon the determined frequency content of the RF electrical signal.
In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. Some embodiments are illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which:
A. Overview
Thus, during electrosurgery, the frequency content of the current flow through target biological tissue and the voltage across the target biological tissue are indicative of the severity of arc event. A clinically minor arc event often occurs in the normal course of a medical procedure and can contribute to a successful outcome. However, a clinically unacceptable more severe arc event can occur that, if not properly managed, can have deleterious consequences. As illustrated in
A system and method are provided to distinguish between a clinically acceptable minor arc event and a clinically unacceptably more severe arc event. By comparing frequency content of an RF voltage imparted to the biological tissue with frequency content of a corresponding RF current imparted to the biological tissue, a determination is made whether an aberrant arc event is occurring or is about to occur. RF energy delivery by the generator 102 is adjusted based upon the comparison. For example, a voltage level at which an RF current signal is delivered to tissue is reduced to reduce RF energy delivery to the tissue, and conversely, a voltage level at which an RF current signal is delivered to tissue is increased to increase RF energy delivery to the tissue. In response to a difference in frequency content of the current and voltage components that is within a clinically acceptable threshold limit, an example generator 102 is caused to continue generating RF energy delivery according to a predetermined clinical procedure protocol. In response to a difference in frequency content of the current and voltage components that exceeds the clinically acceptable threshold limit, the example generator 102 is caused to adjust RF energy delivery to stop or to limit the aberrant arc event.
B. Electrosurgical Signal Generator
The ESG 200 includes an AC-to-DC power supply 214 to convert an AC line voltage to a DC voltage on a voltage bus line 26216. The voltage bus line 26216 is coupled to provide a DC input voltage signal to the sealing stage circuit 202. The voltage bus line 26216 also is coupled to provide the DC input voltage signal to the cutting stage circuit 204. In some embodiments, the DC input voltage signal is approximately 48V, for example.
The sealing stage 202 includes a first RF signal source that includes a first buck regulator circuit 218 to convert the DC input voltage signal to a first controlled DC voltage signal and includes a first output transformer 220 coupled to produce the AC sealing signal based upon the first controlled DC voltage signal. The first output transformer 220 is coupled to provide the sealing signal to the set of sealing electrodes 206, 208. More particularly, the first output transformer 220 includes a first output terminal 222 electrically coupled to the first sealing electrode 206 and includes a second output terminal 224 electrically coupled to the second sealing electrode 208. In some embodiments, the first output stage includes a first H-bridge switch circuit. The first and second sealing electrodes 206, 208 are electrically coupled via an output socket 228 to opposed first and second jaws 303, 304 described below with reference to
Similarly, the cutting stage 204 includes second RF signal source that includes a second buck regulator circuit 248 to convert the DC input voltage signal to a second controlled DC voltage signal and includes a second output transformer 250 coupled to produce the cutting signal based upon the second controlled DC voltage signal. The second output transformer 250 is coupled to provide the AC cutting signal to the set of cutting electrodes 210, 212. More specifically, the second output transformer 250 includes a first output terminal 252 electrically coupled to the first cutting electrode 210 and includes a second output terminal 254 electrically coupled to the second cutting electrode 212. The set of cutting electrodes 210, 212 are electrically coupled via the output socket 228 to opposed first and second jaws 303, 304 described below with reference to
A user interface circuit (UI) block 270, is configured to receive user input commands to start and stop sealing and cutting activities and to indicate parameters to use for sealing and cutting signal waveforms such as voltage, current, signal frequency, and dwell time, for example. The UI circuit block 270 also may provide feedback information to the user such as amount of power delivered, whether a seal was successfully completed, whether an error condition occurred. A surgeon may use the UI to provide user input to select voltage and current levels or sealing signal patterns and cutting signal patterns based upon requirements of a particular patient or surgical procedure, for example. A main controller 271 is coupled to exchange information with the UI block 270 and to communicate with the first and second micro-controllers 232, 262. The main controller 271 may be configured to produce control signals to determine waveforms of the sealing and cutting signals under control of the first and second micro-controllers, including current and voltage levels, for example. The main controller 271 also may produce control signals to determine parameters such as, RF pulse duration, RF pulse repetition rate, and total number of RF pulses during a sealing or cutting procedure, which may be controlled by the first and second micro-controllers.
In operation, an AC sealing signal is provided via the first output transformer 220 across the set of sealing electrodes 206, 208, and an AC cutting signal is provided via the second output transformer 210 across the set of cutting electrodes 210, 212. In some embodiments, the first and second micro-controllers 232, 262 cooperate to provide a single PWM master signal to the first and second H-bridge switches 226, 256 to produce in-phase periodic sealing and cutting signals. Although the sealing and cutting signals are periodic signals that are in phase with each other, they typically have different peak-to-peak voltage potentials. The first and second output transformers 220, 250 may have different turn ratios to produce different voltage levels for the sealing and cutting voltages, for example. In general, impedance is lower during a sealing activity than during a cutting activity due to the higher impedance associated with the plasma discharge required to resect tissue. Thus, in general, a lower voltage ordinarily may be used during sealing than is used during a cutting. In some embodiments, for example, the peak-to-peak voltage for a sealing activity is approximately 71-210V and the peak-to-peak voltage for a cutting activity is approximately 300-600V. Conversely, in general, a higher current may be used during sealing than is used during a cutting.
The first jaw 302 includes first and second electrically conductive tissue sealing surfaces 306, 308 that are electrically coupled at the socket 228 to the active sealing electrode 206 and that extend longitudinally along outer portions of the first jaw 302. The first jaw 302 also includes an electrically conductive tissue cutting surface 314 that is electrically coupled at the socket 228 to the active cutting electrode 210 and that extends longitudinally along the first jaw 202 between the first and second tissue sealing surfaces 306, 308. The second jaw 304 includes third and fourth electrically conductive tissue sealing surfaces 310, 312 that are electrically coupled at the socket 228 to the shared return sealing electrode 208 and that extend longitudinally along outer portions of the second jaw 204 so as to align with the first and second tissue sealing surfaces 306, 308 when the first and second jaws 302, 304 are in the closed position. The second jaw 304 also includes a passive/insulative surface 316 that extends longitudinally along the second jaw 304 between the third and fourth tissue sealing surfaces 310, 312 so as to align with the first tissue cutting surface 314 when the first and second jaws 302, 304 are in the closed position.
Referring to
In general, the voltage and current density applied to a biological tissue determines whether cutting or sealing of the tissue occurs, as a higher voltage and current density is required to achieve the plasma discharge required for resection. A lower current density typically results in less rapid tissue heating, which may result in sealing, which as used herein, refers to tissue dehydration, vessel wall shrinkage and coagulation of blood constituents and collagen denaturatization and bonding. A higher current density typically results in the creation of a plasma discharge, which may result in cutting, which as used herein, refers to dissecting of tissue through vaporization, for example. Although electrosurgical sealing signals and electrosurgical cutting signals may deliver the same power, they ordinarily use different voltage and current levels to do so.
A typical electrosurgical procedure that involves both sealing and cutting activities may involve a sequence of “bites” in which a pair of jaws grasp a tissue portion, the electrosurgical generator provides sealing and cutting signals to seal it and cut it, and then a next portion of tissue is grasped, sealed and cut, etc. Each bite of sealing activity and each cutting activity may require only a short time interval, such as two seconds to seal and two seconds to cut, for example. The overall time required for an electrosurgical procedure increases with an increasing number of bites. For example, an electrosurgical procedure involving 5-6 bites in which sealing and cutting activities are performed in sequence may require 20-24 seconds. Moreover, if a single stage electrosurgical generator is used, then an additional time delay of perhaps 4-5 seconds per bite may be required, for example, to reconfigure the generator to generate a different signal pattern at each transition between a sealing and a cutting activity, which can further increase the overall time for an electrosurgical procedure by an additional 20-30 seconds, for example. Thus, there is need for simultaneous sealing and cutting to shorten the time required for an electrosurgical procedure.
C. Sealing and Cutting Signals
D. Adjusting RF Energy Delivery to Biological Tissue Based Upon Frequency Content of Voltage and Current Waveforms
During an electrosurgical sealing procedure an RF energy delivery operation 702 imparts an RF electrical signal to deliver RF energy at a predetermined clinical level to a biological tissue portion electrically coupled between first and second electrode conductors located at an electrosurgical instrument end effector. In an example ESG, a voltage measurement operation 704 continuously measures frequency content of a voltage waveform across the electrodes. In an example ESG, a current measurement operation 706 continuously measures frequency content of a current waveform at the first and second conductors. In an example ESG, an arc detection operation 708 continuously evaluates whether there is an occurrence aberrant arc event, based upon a combination of the measured frequency content of the voltage waveform and the frequency content of the current waveform. As explained below, an alternate example arc detection operation detects an occurrence of an arc event based upon measured current content. An adjustment operation 710 adjusts delivery of RF energy based upon outcome of the arc detection operation 708. Following adjustment operation 710, control next flows back to operation 702 so that the process 700 runs continuously throughout a electrosurgical procedure.
Referring to the example ESG 200 of
Still referring to the example ESG 200 of
E. Detecting an Arc Event Based Upon Frequency Content of Electrical Signals Measured Across a Biological Tissue Electrical Load
In the example ESG 200 (sealer stage 202 or dissection stage 204), of
A first example arc detection operation 708 evaluates total harmonic distortion (THD) of a waveform of an RF electrical current signal flowing through a biological tissue electrical load to evaluate whether there is an occurrence of an aberrant arc event. THD is a mathematical calculation that compares the output of higher order resonant frequencies in a signal to its fundamental frequency and that can be represented as percent deviation from a pure sine wave, with an increasing percentage as the signal becomes more deviated. More particularly, detection operation 708 evaluates THD by detecting magnitude of signal at the fundamental frequency and by determining magnitude of individual harmonics above the fundamental frequency. The signal magnitude content for the higher order harmonics is summed, typically up to the Nyquist sampling rate. The sum of the magnitudes of the higher order harmonics is compared with the magnitude of the original signal, to determine a THD value. Stated differently, operation 708 determines a THD of the current signal waveform as a ratio of noise introduced by arcing, measured in terms of the sum of magnitudes of higher order harmonics, divided by magnitude of fundamental frequency, the larger the value of THD, the higher the noise due to arcing. For example, a pure sine wave has a THD of 0%, a slightly distorted sine wave could have a THD of 10%, and a sine wave sufficiently distorted to become a square wave has a THD of about 50%. In an example ESG 200 in which the RF output signal is essentially sinusoidal, a simple evaluation of the THD of the RF current waveform could be adequate detect whether the energy delivery at the electrode was purely resistive, had some non-linearities as a result of the plasma discharge, or has significant non-linearities as a result of an arc discharge. During an arc event, the frequency content of current flow through biological tissue generally experiences more significant perturbation and corresponding harmonic distortion due to an arc event than does the frequency content of voltage across the biological tissue. Accordingly, the first example operation 708 evaluates presence of an arc event based only upon the measured current waveform. The first example detection operation 708 detects whether the THD of the electrical current signal waveform meets a threshold limit, for example, that is indicative on an aberrant arc event. For instance, a first example detection operation detects whether the THD of an electrical current signal wavefrom increases by ten per cent or greater from a baseline value for that waveform, which is indicative of an aberrant event. In such example instance, if the baseline value is 20, then the threshold for detection would be 22. Alternatively, the first example arc determination operation 708 can use signal to noise ratio (SNR) of the electrical current signal waveform instead of THD. SNR is the ratio of the signal frequency versus noise. Alternatively, the first example arc detection operation 708 can use signal to noise and distortion ratio (SINAD) of the electrical current signal waveform instead of THD. SINAD is the ratio of magnitude of signal frequency in RMS to the RMS of magntides of noise and/or harmonic frequencies.
A second example arc detection operation 708 is used with an alternative example ESG 200 that produces an RF output signal that is not sinusoidal. The second example arc detection operation determines a ratio of a THDI of an electrical current signal waveform to a TDHV of an electrical voltage signal waveform, which provides an indication of the non-linearity of the biological tissue load. More particularly, the ratio, THDI/THDV, provides an indication of the extent to which the electrical current signal waveform deviates from an electrical voltage signal waveform imparted by the ESG, due to non-linear component of the load. In general, nonlinearity of a tissue load due to an arc event has a greater impact upon frequency content of the measured current signal wavefrom than upon the measured voltage signal waveform. The second example detection operation 708 determines whether the THDI/THDV, meets a threshold limit of that is indicative on an aberrant arc event. For instance, a second example detection operation detects whether THDI/THDV>1.1. Alternatively, the second example arc determination operation 708 can evaluate whether a ratio of SNRI of the electrical current signal waveform to SNRV of the electrical voltage waveform (SNRI/SNRV) meets a threshold to detect an aberrant arc event. Alternatively, the second example arc detection operation 708 can evaluate whether a ratio of SINADI of the electrical current signal waveform to SINADV of the electrical voltage signal waveform (SINADI/SINADV) meets a threshold to detect an aberrant arc event.
The first and second example detection operations 708 can use specific frequency ranges above the fundamental frequency to determine values for THD, SNR, and SINAD. The noise caused by an arc event often occurs in a specific frequency range. Even in the absence of an arc event, some noise exists at some frequencies above the fundamental frequency in current and voltage signal waveforms measured across a tissue. Moreover, an arc event typically has a greater impact upon some frequencies than others. Including frequencies that are not as much influenced by unwanted arc events can dilute the effectiveness of THD, SNR or SINAD evaluations in detecting aberrant arc events. Thus, focusing THD, SNR or SINAD determinations on the frequency ranges most impacted by an arc event can provide a better indication of an occurrence of an arc event. In general, higher frequencies are less influenced by an arc event, and therefore, THD, SNR and SINAD determinations focus on lower frequency harmonics above the fundamental frequency. In an example arc determination operation 708, magnitude of one or more of the third through fifth harmonics above the fundamental are used in evaluating THD, SNR and/or SINAD to detect aberrant arc events.
A third example detection operation 708 uses a Q-factor (quality factor) to detect an occurrence of an aberrant arc event. A Q factor represents a ratio of a central frequency to the bandwidth around that frequency. A Q-factor often is used to determine the damping of a circuit. The high frequencies of an arc discharge generally increase the bandwidth of both the fundamental and resonant frequencies, which decreases the Q factor and making a resonator appear more overdamped. The calculated Q factor can be used in combination with or independently of THD, SNR, or SINAD or ratios involving THD, SNR, or SINAD, as described above, to determine an occurrence of an arc event.
A third example detection operation 708 determines a Q-factor based upon an FFT of a measured RF signal waveform (current or voltage) based upon the equation: Q=resonant frequency/bandwidth at −3 dB from peak. Thus, a Q-factor looks at the fundamental frequency resonance of the system instead of the harmonic frequencies. A larger value of Q-factor is indicative of an occurrence of an arc event. In an example ESG 200, an increase in Q-factor value by ten per cent is indicative of an arc event. Thus, for example, the threshold would be a Q factor increasing from 20 to 22.
F. Control of RF Energy Delivery Based Upon Arc detection of an Occurrence of an Arc Event
An example energy level adjustment operation 7101 adjusts the energy level delivered during a sealing or cutting procedure based upon information produced by the arc detection operation 708. For example, an example energy level adjustment operation 7101 can be selectably configured to interrupt delivery of RF energy level in response to the detection operation 708 providing information indicating that an arc event that exceeds a prescribed threshold. An example energy level adjustment operation 7101 can interrupt delivery for a prescribed time interval. An alternative example RF energy level adjustment operation 7101 is selectably configured to adjust RF energy delivery level as a function of frequency content of a measured an electrical current or voltage waveform or combination of the two to maintain a frequency content within a range indicative of absence of an aberrant arc event. Another alternative example energy level adjustment operation 7101 is configured to regulate RF energy level as a function of a selected high frequency harmonics of an electrical current signal waveform. For example, an example energy level adjustment operation 7101 can be configured to regulate RF energy level to maintain a prescribed frequency range of the electrical current signal waveform selected to ensure adequate clinical performances such as sealing or cutting, and to exclude frequency content indicative of an occurrence of an aberrant arc. Yet another alternative example energy level adjustment operation 7101 is configured to regulate RF energy level to maintain a prescribed value of the ratio of the current and voltage wave forms such as THDI/THDV SNRI/SNRV or SINADI/SINADV) selected to ensure adequate clinical performances such as sealing or cutting, and to exclude frequency content indicative of an occurrence of an aberrant arc. Still another alternative example energy level adjustment operation 7101 is configured to regulate RF energy level to maintain a prescribed value for a Q-factor selected to ensure adequate clinical performances such as sealing or cutting, and to exclude frequency content indicative of an occurrence of an aberrant arc.
An example protocol adjustment operation 7102 adjusts the clinical procedure protocol for an electrosurgery procedure during a sealing or cutting procedure based upon information produced by the arc detection operation 708. An example protocol adjustment operation 7102 adjusts the clinical procedure protocol for an electrosurgery procedure as a function of the RF energy level delivered in response to detection of an aberrant arc event. For instance, an example sealing or cutting protocol may require a prescribed number of RF energy pulses at a prescribed RF energy level during a prescribed time interval. However, in response to information received from the arc detection operation indicating detection of an aberrant arc event, one or more of the energy pulses might be skipped during or may have a reduced energy level, during an occurrence of the aberrant arc event. An example protocol adjustment operation 7102 adjusts the clinical procedure protocol for the procedure on-the-fly to make up for the missed or reduced-energy level pulses, to achieve desired clinical result such as sealing or cutting, despite the aberrant arc event. For example, a typical sealing or cutting operation involves a prescribed procedure-dependent number of pulses. Each typically has a duration in a range 100-200 milliseconds. For instance, in an example protocol adjustment operation 7102, if an aberrant arc is detected during a scheduled delivery of one or more sealing or cutting pulses, those pulses may be skipped in response to the energy level adjustment operation 7101 , but the protocol adjustment operation 7102 may add one or more pulses to the sequence of pulses in the clinical procedure protocol to make up for the skipped one or more pulses.
Although illustrative examples have been shown and described, a wide range of modification, change and substitution is contemplated in the foregoing disclosure and in some instances, some features of the examples may be employed without a corresponding use of other features. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. Thus, the scope of the disclosure should be limited only by the following claims, and it is appropriate that the claims be construed broadly and in a manner consistent with the scope of the embodiments disclosed herein. The above description is presented to enable any person skilled in the art to create and use electrosurgical signals to simultaneously seal and cut biological tissue. Various modifications to the examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. In the preceding description, numerous details are set forth for the purpose of explanation. For example, the ESG may include an FPGA circuit to evaluate frequency content of electrical signal waveforms at a target tissue and a separate processor circuit configured to adjust RF energy level and clinical procedure protocol. However, one of ordinary skill in the art will realize that the invention might be practiced without the use of these specific details. In other instances, well-known processes are shown in block diagram form in order not to obscure the description of the invention with unnecessary detail. Identical reference numerals may be used to represent different views of the same or similar item in different drawings. Thus, the foregoing description and drawings of embodiments in accordance with the present invention are merely illustrative of the principles of the invention. Therefore, it will be understood that various modifications can be made to the embodiments by those skilled in the art without departing from the spirit and scope of the invention, which is defined in the appended claims.
This application claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Patent Application Ser. No. 63/209,751, filed on Jun. 11, 2021, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63209751 | Jun 2021 | US |
