Patent Description:
<FIG> is an illustrative partially cut-away cross-sectional side elevation view of an elongated tubular instrument shaft <NUM> enclosing an active electrode <NUM> of an electrosurgical instrument. The shaft <NUM> includes an elongated tubular safety shield conductor (shield) <NUM> that is surrounded by a non-conducting tubular outer insulating sheath <NUM>. The shield <NUM> surrounds the active conductor <NUM>, also referred to as an active electrode, to provide protection against unintended parasitic capacitive coupling of electrosurgical energy from active electrode <NUM> to metallic objects adjacent to instrument shaft <NUM>. A high dielectric insulator <NUM> is disposed between the shield <NUM> and the active electrode <NUM>.

<FIG> is an illustrative system level block diagram representing setup of a first monopolar electrosurgical system <NUM>. The system <NUM> includes a monopolar electrosurgical signal generator <NUM>, which delivers a high frequency electrical signal on the active conductor <NUM> of an electrosurgical instrument (ESI) <NUM>. A patient's biological tissue <NUM> is electrically coupled between the active conductor <NUM> and a return conductor <NUM>. During a surgical procedure, the active conductor <NUM> contacts a tissue portion <NUM> at a surgical site at which tissue is to be cut or ablated, for example. Electrosurgical instrument (ESI) current flows from the active conductor <NUM> to the patient tissue portion <NUM> at the surgical site and from there, to another patient tissue portion <NUM> that contacts a patient return conductor pad <NUM>. The ESI current flows from the return conductor pad <NUM> to the return conductor <NUM>. More particularly, an end effector tip portion <NUM> of the active conductor <NUM> extends beyond the end of the shaft <NUM> to impart energy at the surgery location to cut or remove biological tissue. Thus, ESI current flows from the active conductor tip <NUM>, to the patient tissue portion <NUM> at a surgical location, through patient anatomy <NUM>, to the patient tissue portion <NUM> at the return pad, and through the generator's return conductor <NUM> to the generator <NUM>.

Detection of certain electrical faults in electrosurgical instruments are known. <CIT> discloses an electrosurgical system that includes an electrosurgical generator to produce electrosurgical energy. The electrosurgical system also includes a capacitive return pad, a phase detector, and a control component. The control component is used to detect a fault in the capacitive return pad based upon a phase difference between a current component and a voltage component of the electrosurgical energy detected using the phase detector. <CIT> discloses a device and method to detect a fault in a shield of an electrosurgical instrument. The device monitors shield current. Monitoring circuitry compares a detected shield peak current value to a shield threshold peak current value. The monitoring circuitry compares a detected shield average current value to shield average threshold current value. However, neither of these published applications detects aberrant current flow due to breach of an insulative sheath surrounding a protective shield that surrounds an active electrode.

<FIG> is an illustrative block diagram representing setup of a second electrosurgical system <NUM>. The second electrosurgical system <NUM> includes a monopolar electrosurgical signal generator <NUM> and a first monitor circuit <NUM>. Components of the second system <NUM> that may be identical to those of the first system <NUM> are identified with the identical reference numerals and will be understood from the above description. A protective conductor <NUM> that couples a protective impedance Zp between the safety shield conductor <NUM> and the return conductor <NUM> provides a protective current path between them. <FIG> is an illustrative cross-sectional side elevation view of a portion of the instrument shaft <NUM> showing an electrical contact <NUM> between the shield conductor <NUM> and the protective electrical conductor <NUM>. The protective impedance Zp includes resistive and reactive elements, such as capacitive, (not shown) that couple the shield conductor <NUM> and the return conductor <NUM> to limit the high frequency energy that can be delivered from the safety shield conductor <NUM> to other instruments (not shown), for example. Capacitively coupled energy may potentially lead to electrical arcing or conduction to patient tissue <NUM> that may cause thermal injury to patient tissue <NUM>. For this protection to be maintained, the shield conductor must be electrically isolated from the patient tissue. If the insulation sheath <NUM> surrounding the shield conductor <NUM> is damaged and the underlying shield conductor <NUM> contacts patient tissue <NUM>, then the electrical conductor <NUM> and the protective impedance Zp may provide a conductive path for aberrant ESI current flow from the active conductor tip <NUM>, through patient tissue <NUM>, to the safety shield conductor <NUM>, and then to the return conductor <NUM> via the electrical conductor <NUM> and the protective impedance Zp resulting in a thermal injury to patient tissue <NUM>.

<FIG> are illustrative drawings of a portion of the second system <NUM> of <FIG> representing normal ESI current (IESI) path <NUM> through patient tissue <NUM> during a surgical procedure during normal operation (<FIG>) and representing aberrant ESI current path <NUM> through patient tissue <NUM> during operation with a breach in the insulation sheath <NUM> surrounding the conductor safety shield (<NUM> is also called "shield conductor") <NUM> (<FIG>). During normal operation, represented by <FIG>, ESI current flows from the active conductor tip <NUM> to the return pad <NUM>. The return pad <NUM> has a surface area that is large enough so that patient tissue <NUM> in physical contact with the pad has a large enough surface area so that the return ESI current spreads across a wide enough patient tissue area to limit the current density sufficiently to avoid tissue burns or other trauma due to the return ESI current, for example. As represented in <FIG>, a breach <NUM> in the insulation <NUM> may occur, for example, due to another instrument (not shown) physically contacting the shaft <NUM> during a surgical procedure. The insulation layer <NUM> may in some cases be damaged because of unintended or aggressive use during the surgical procedure. The aberrant ESI current <NUM> may flow from the active conductor tip <NUM>, which may contact the patient tissue portion <NUM> at a surgical site, to another patient tissue portion <NUM> that physically contacts an exposed portion <NUM> of the safety shield conductor <NUM> that is exposed to physical contact with the patient tissue portion due to a breach in the insulation layer <NUM>. Since an insulation breach dimension typically is small, much smaller than the dimensions of the contact pad <NUM>, the current density at the breach portion <NUM> of the safety shield conductor <NUM> may be larger than that at the contact pad <NUM>, creating a risk of thermal injury to the patient at the tissue portion <NUM> in contact with the shield conductor <NUM> due to the aberrant ESI current flow <NUM> from the active electrode tip <NUM>, through patient tissue portion <NUM>, to the exposed portion <NUM> of the shield conductor <NUM>.

Referring to <FIG> and <FIG>, the first monitor circuit <NUM> preferably deactivates the electrosurgical signal generator <NUM> in response to current on the protective conductor current path <NUM> exceeding a threshold level due to an abnormal condition such as aberrant current flow <NUM> due to a breach <NUM> in the insulation <NUM> that exposes a portion of the shield conductor <NUM> to contact patient tissue <NUM>, for example. Example monitor circuits are described in <CIT>; <CIT>; and <CIT>; and in <CIT>. A problem with monitoring current flow within a conductor <NUM> coupled to a protective impedance Zp to determine when to deactivate an electrosurgical signal generator <NUM> due to aberrant ESI current <NUM> is that there may be some desirable level of current passed through the conductor <NUM> to suppress a parasitic capacitance between the active conductor <NUM> and other instruments, for example. However, the magnitude of desired current flow to reduce parasitic capacitance may vary depending upon the generator settings and the instrument design, for example. Therefore, it may be difficult to select an appropriate threshold current that can allow for this intended current delivery, which may vary, and still provide an adequate margin of safety against aberrant ESI current <NUM> that may cause thermal injury in the event insulation breach, for example.

The invention is defined by the independent claims, with preferred features being defined in the dependent claims. In one aspect, there is provided an apparatus to detect electrical contact between an anatomical tissue portion near a surgical site and a protective shield conductor surrounding an active conductor, of an electrosurgical instrument, wherein the electrosurgical instrument comprises an elongated tubular instrument shaft including a non-conducting tubular outer insulating sheath surrounding the protective shield conductor surrounding the active conductor and including a dielectric insulator located between the protective shield conductor and the active conductor, the active conductor being used, in use, to deliver a high frequency electrical signal from an electrosurgical generator to a tissue portion at the surgical site, the apparatus comprising:.

In a second aspect, there is provided a method to protect a patient from injury due to electrical contact between an anatomical tissue portion near a surgical site and a protective shield conductor surrounding an active conductor of an electrosurgical instrument, the electrosurgical instrument comprising an elongated tubular instrument shaft including a non-conducting tubular outer insulating sheath surrounding the protective shield conductor surrounding the active conductor and including a dielectric insulator located between the protective shield conductor and the active conductor, the active conductor being used, in use, to deliver a high frequency electrical signal from an electrosurgical generator to a tissue portion at the surgical site, the method comprising:.

<FIG> is an illustrative schematic diagram representing setup of a third electrosurgical system <NUM>. The third system <NUM> includes a monopolar electrosurgical signal generator <NUM> and a second monitor circuit <NUM>. The electrosurgical signal generator <NUM> produces a high frequency ESI current to an active conductor <NUM> for use in electrosurgery. In some embodiments, the generator produces a <NUM> kV, <NUM> signal. The active conductor <NUM> extends within an elongated shaft <NUM>. An end effector tip <NUM> of the active conductor <NUM> extends beyond a distal end of the shaft <NUM> to impart energy to cut or remove patient's tissue <NUM> at a surgery location adjacent <NUM> to or in contact with the tip. The end effector tip <NUM> may be of various shapes such as needle-shape, hook-shape, spatula-shape, graspers, scissors, for example. During normal operation, high frequency ESI current flows between a proximal end of the shaft <NUM> adjacent the signal generator <NUM> and a distal end tip <NUM> of the shaft <NUM> adjacent to a patient tissue portion <NUM> at a surgical site. A patient return pad <NUM> physically contacts a patient tissue portion <NUM> at a location on the patient's tissue <NUM> that is outside of the surgical region. A return conductor <NUM> couples the return pad <NUM> to a return node of the signal generator <NUM>. A protective conductor path includes a protective impedance ZP coupled between a safety shield conductor <NUM> and the return conductor <NUM>. More particularly, first and second protective path conductors <NUM>, <NUM> couple the protective impedance ZP between first and second nodes N<NUM>, N<NUM>. The first conductor <NUM> couples the first node N<NUM> to the protective shield conductor <NUM>. The second conductor <NUM> couples the second node N<NUM> to the return path <NUM>. During normal operation, normal ESI current <NUM> may flow from the active electrode tip <NUM>, to patient tissue portion <NUM> at the surgical location, through patient tissue anatomy <NUM>, to patient tissue <NUM> at the patient return pad <NUM>, and then, through the return conductor <NUM> to the signal generator's return node, for example. The protective impedance ZP includes resistive and reactive elements (not shown) to limit potential inadvertent energy delivery due to capacitive coupling between the shield conductor <NUM> and other instruments (not shown) during normal operation i.e. in the absence of an insulation breach, for example.

<FIG> is an illustrative drawing showing portions of the third system <NUM> of <FIG> to illustrate current paths during normal and aberrant ESI current flow. In operation, if a breach <NUM> occurs in the protective insulation layer <NUM> due to damage, for example, then unwanted electrical contact between a patient tissue portion <NUM> and an exposed portion of the conductor shield <NUM>, may create a potentially harmful, aberrant current path <NUM> between patient tissue at a surgical site <NUM> and patient tissue <NUM> in contact with a portion of the conductive shield <NUM> exposed due to the breach in the insulation layer <NUM>. Moreover, the aberrant circuit path may include the protective current path formed by conductor <NUM> the protective impedance ZP and the second conductor <NUM>, which is coupled to the return lead <NUM>. Aberrant ESI current flow <NUM> may pose a risk of thermal injury to a patient, for example.

During normal ESI current flow, patient tissue <NUM> is not coupled in parallel with the protective impedance ZP between a node the first and second nodes N<NUM>, N<NUM>. However, during aberrant ESI current flow, patient tissue <NUM> is coupled in parallel with the protective impedance ZP between a node the first and second nodes N<NUM>, N<NUM>. Thus, parallel coupling of patient tissue <NUM> during aberrant current flow results in a patient body tissue impedance ZB coupled in parallel with the protective impedance ZP. More particularly, normal ESI current path <NUM> includes patient tissue <NUM> between a node NT where the tip <NUM> contacts patient tissue <NUM> in the surgical region and the patient contact pad <NUM>, which is electrically coupled via return conductor <NUM> and the second conductor <NUM> to the second node N<NUM>. During normal ESI current flow, there is no electrical coupling between the patient tissue <NUM> and the shield conductor <NUM> or the first node N<NUM>. However, during aberrant ESI current flow due to tissue contact with a shield conductor <NUM> resulting from a breach <NUM> in the insulation sheath <NUM>, for example, patient tissue <NUM> is coupled in an electrical path that includes the normal electrical path <NUM>, and that also includes a path that extends between the node NT where the active conductor tip <NUM> contacts the patent tissue <NUM>, a patient tissue portion <NUM> in contact with the shield <NUM>, the first conductor <NUM> and the first node N<NUM>. Thus, impedance across the first and second nodes N<NUM>, N<NUM> changes in response to inclusion of patient tissue <NUM> in contact with the shield conductor <NUM> due to a breach in the insulative shield <NUM>.

<FIG> is an illustrative circuit diagram showing portions of the third system <NUM> to illustrate parallel coupling of the protective impedance ZP and the body impedance ZB within the third system of <FIG>. A virtual switch <NUM><NUM> in an open position represents operation of the system <NUM> with no breach in the insulation sheath <NUM> when the body impedance ZB is not coupled in parallel with the protective impedance ZP during normal ESI current flow. The virtual switch <NUM> in a closed position represents operation of the system <NUM> with a breach <NUM> in the insulation sheath <NUM> resulting in coupling of the body impedance ZB in parallel with the protective impedance ZP during aberrant ESI current flow. The second monitor circuit <NUM> monitors impedance between nodes the first and second nodes N<NUM>, N<NUM> to detect an occurrence of a change impedance between them. The second monitor circuit <NUM> provides a detector control signal on an output node <NUM> that is coupled to cause the electrosurgical signal generator <NUM> system to transition to block ESI current flow to the active conductor tip <NUM> in response to detection of a change in impedance ZP that indicates coupling of the body impedance ZB in parallel with the protective ZP.

<FIG> is an illustrative drawing of the third system of <FIG> showing additional details of the second monitor circuit <NUM>. The second monitor circuit <NUM> includes an alternating current (AC) reference signal generator <NUM>, a transformer <NUM>, a current sensing circuit <NUM> and a phase match detector <NUM>. The AC reference signal generator <NUM> produces a reference signal at a reference signal frequency that is distinguishable from a frequency of an ESI signal produced by the electrosurgical signal generator <NUM>. In some embodiments, the reference signal has a reference signal frequency of <NUM>. The transformer <NUM> includes a primary winding <NUM> and a secondary winding <NUM>. The protective impedance ZP is coupled between a first node N<NUM> and a second node N<NUM>. A first capacitance C1 and a first resistance R1 are coupled in series between the first node N<NUM> and a first end <NUM>-<NUM> of the secondary winding <NUM>. A second capacitance C2 and a second resistance R2 are coupled in series between the second node N<NUM> and a second end <NUM>-<NUM> of the secondary winding <NUM>. The values of these components are selected to provide the intended amount of discrimination between the frequency of the reference signal and the fundamental frequency of the ESI signal.

The current sensing circuit <NUM> includes a differential amplifier circuit <NUM> that includes a first input <NUM> and a first input <NUM>. A current sensing resistor RCS is coupled between the first and second inputs <NUM>, <NUM> of the differential amplifier circuit <NUM>. More particularly, the first input <NUM> of the differential amplifier circuit <NUM> is coupled between a first node of the current sense resistor Res and a first end <NUM>-<NUM> of the primary winding <NUM>, and the second input <NUM> of the differential amplifier circuit <NUM> is coupled between a second terminal node of the current sense resistor Res and a reference potential <NUM>, which may be ground potential. An output <NUM> of die current sensing circuit <NUM> is coupled to a first input <NUM> of the phase match detector <NUM>. The AC reference signal generator <NUM> includes an AC reference signal output <NUM> coupled to a second end <NUM>-<NUM> of the primary winding <NUM>. The AC reference signal node <NUM> also is coupled to a second input <NUM> of the phase match detector <NUM>. The phase match detector <NUM> includes the output <NUM> to provide the detector control signal that has a value to indicate whether a body impedance ZB is coupled in parallel with the protective impedance ZP between the first and second nodes N1, N2.

<FIG> is an illustrative example aberrant ESI signal timing diagram. During a first example time interval, t0 to t1, no aberrant ESI current flows between the safety shield conductor <NUM> and the return lead <NUM>. During a second time interval, t1 to t2, aberrant ESI current flows between the safety shield conductor <NUM> and the return lead <NUM>.

<FIG> is an illustrative example detector control signal timing diagram. During the first example time interval, t0 to t1, the detector control signal on line <NUM><NUM> has a first value to indicate that no phase match indicative of no aberrant ESI current flows between the safety shield conductor <NUM> and the return lead <NUM>. During a second time interval beginning at time, t2, the detector control signal on line <NUM> has a value to indicate a phase match indicative of aberrant ESI current flows between the safety shield conductor <NUM> and the return lead <NUM>. Referring again to <FIG>, it will be understood that the electrosurgical signal generator <NUM> turns off in response to the control signal transitioning to the second value at time t2 resulting in halting of the aberrant ESI current flow.

Operation of the third electrosurgical system <NUM> that includes the second monitor circuit <NUM> of <FIG> is explained with reference to the signal timing diagrams of <FIG>. The AC reference signal generator <NUM> is coupled to inject an reference frequency signal at its output <NUM> to the primary winding. The injected reference frequency signal is magnetically coupled from the primary winding <NUM> to the secondary winding <NUM>. The coupled AC reference signal flows through the protective impedance ZP, which is coupled between the first and second nodes N<NUM>, N<NUM>. The capacitance C1 and first resistance R1 and the second capacitance C2 and a second resistance R2 act as low pass filters that are intended to filter out signals with frequencies above that of the AC reference signal. An AC reference frequency current that flows through the protective impedance ZP reflects back from the secondary winding <NUM> to the primary winding <NUM>. The reflected AC reference frequency current flows through current sense resistor RCS. The differential amplifier <NUM> produces an AC voltage value at its output <NUM> that is indicative of AC voltage drop across the current sense resistor Res due to the reflected AC reference frequency current.

The phase match detector <NUM> produces the control signal on control line <NUM> in response to an indication of the reflected AC reference frequency signal provided on its first input <NUM> and the AC reference frequency signal received at its second input <NUM>. In some embodiments, the phase match detector <NUM> produces a DC control signal on line <NUM> having a value indicative of the phase and frequency relationship of the AC voltage signal received at its first input <NUM>, which is indicative of the reflected AC reference frequency signal, and the AC reference signal received at its second input <NUM>. In response to absence of matching phase and frequency of the signals received at its first and second inputs <NUM>, <NUM>, the phase match detector <NUM> produces a first DC voltage value indicative of absence of a match. In response to matching phase and frequency of the signals received at its first and second inputs <NUM>, <NUM>, the phase match detector <NUM> produces a second DC voltage value indicative of a match.

In some embodiments, the phase match detector <NUM> includes a synchronous detector. In some embodiments, the synchronous detector includes an analog multiplication circuit that multiplies the signals at the first and second detector inputs <NUM>, <NUM> to produce the control signal at the detector output <NUM> that is indicative of whether the multiplied signals have matching phases and matching frequencies. Alternately, this could be determined by calculating the root-mean-square (RMS) value of each signal, and multiplying these together and then by the cosine of the phase difference between the two waveforms. The average product of the two waveforms ranges from <NUM> to <NUM> as the phase difference between the two signals ranges between <NUM> (purely resistive) e.g., during potential aberrant ESI current flow when ZB is coupled in parallel, and -<NUM> or <NUM> degrees (purely reactive) e.g., during normal ESI current flow when ZB is not coupled in parallel.

Referring to <FIG>, assuming that the phase match detector <NUM> includes a synchronous detector, during the first time interval, t0 to t1, an AC voltage signal provided at the first input <NUM> of the phase match detector <NUM> is phase shifted relative to phase of the AC reference signal provided at the second input node <NUM> of the phase match detector <NUM> detector <NUM>. During the first time interval, the virtual switch <NUM> is in an open state, the body impedance ZB is not coupled in parallel with the protective impedance ZP, and there is no aberrant ESI current flow. During the first time interval, a phase shift is imparted to the reflected AC reference frequency signal by reactive elements (not shown) within the protective impedance ZP. Thus, AC voltage signal at the first input <NUM> of the phase match detector <NUM> detector <NUM> is phase shifted relative to the AC reference signal at the second input node <NUM> of the phase match detector <NUM> detector 710As a result, during the first time interval t0 to t1, the phase match detector <NUM> detector <NUM> produces a DC control signal voltage on output line <NUM><NUM> having the first value indicative of absence of a phase and frequency match between the reflected AC frequency signal and the reference AC frequency signal, which is indicative of the absence of ZB coupling between the first and second nodes N<NUM>, N<NUM>.

During the second time interval, t1 to t2, an AC voltage signal provided at the first input <NUM> of the phase match detector <NUM> detector <NUM> is in phase (i.e. not phase shifted) with the reference AC signal provided at the second input <NUM> of the phase match detector <NUM> detector <NUM>. During the second time interval, the virtual switch <NUM> is in a closed state, the body impedance ZB is coupled in parallel with the protective impedance ZP, and there is aberrant ESI current flow. During the second time interval, has a different phase shift is imparted to the reflected AC frequency signal since the patient's body tissue <NUM> impedance ZB, which is coupled in parallel with protective impedance ZP, is generally resistive, not reactive, and therefore, results in the imparting of a different phase shift to the reflected AC reference frequency signal. Thus, during the second time interval t1 to t2, the phase match detector <NUM> detector <NUM> produces a DC control signal voltage on output line <NUM> having the first value indicative of a matched phase and frequency between the reflected AC frequency signal and the reference AC frequency signal, which is indicative of the presence of ZB coupled between the first and second nodes N<NUM>, N<NUM>.

It will be understood that the second monitor circuit <NUM> may operate independent of whether the electrosurgical signal generator <NUM> is operating to produce an ESI signal. Thus, even with the electrosurgical signal generator <NUM> turned off, the second monitor circuit <NUM> can operate to determine whether an aberrant ESI signal path exists. Moreover, during normal operation of the electrosurgical signal generator <NUM>, some portion of an ESI return signal that flows through the patient return pad <NUM> may be coupled from secondary winding <NUM> to the primary winding <NUM>. However, the phase and frequency of the ESI return signal do not match those of the AC reference frequency signal, and therefore, the coupling of an ESI frequency signal to the s phase match detector <NUM> does not cause false detection results, produces an output control signal at line <NUM> indicating no match. Moreover, the first and second capacitors and resistors C1, R1 and C2, R2 act to filter out the higher frequency ESI signal components that otherwise may be coupled from the secondary winding <NUM>. Thus, the presence of an ESI signal does not impact performance of the second monitor circuit.

Claim 1:
An apparatus to detect electrical contact between an anatomical tissue portion (<NUM>) near a surgical site and a protective shield conductor (<NUM>) surrounding an active conductor (<NUM>), of an electrosurgical instrument, wherein the electrosurgical instrument (<NUM>) comprises an elongated tubular instrument shaft (<NUM>) including a non-conducting tubular outer insulating sheath (<NUM>) surrounding the protective shield conductor (<NUM>) surrounding the active conductor (<NUM>) and including a dielectric insulator (<NUM>) located between the protective shield conductor (<NUM>) and the active conductor (<NUM>), the active conductor (<NUM>) being used, in use, to deliver a high frequency electrical signal from an electrosurgical generator (<NUM>) to a tissue portion (<NUM>) at the surgical site, the apparatus comprising:
a transformer (<NUM>) including a primary winding (<NUM>) and a secondary winding (<NUM>); an alternating current, AC, reference frequency signal generator (<NUM>) coupled to inject an AC reference frequency signal to the primary winding (<NUM>);a first reactive impedance (ZP) coupled in parallel with the secondary winding (<NUM>) between a first node (N<NUM>) and a second node (N<NUM>), wherein the first node (N<NUM>) is coupled, when in use, to the protective shield conductor (<NUM>) and the second node (N<NUM>) is coupled, when in use, to a return conductor (<NUM>) coupled to receive current from the tissue portion (<NUM>) to return to the electrosurgical generator (<NUM>);
wherein the primary (<NUM>) and secondary (<NUM>) windings are magnetically coupled such that the injected AC reference frequency signal in the primary winding (<NUM>) induces an AC reference frequency signal in the secondary winding (<NUM>) and the secondary winding (<NUM>) reflects back to the primary winding (<NUM>) a reflected AC frequency signal having a phase shift relative to the injected AC reference frequency signal that is indicative of an impedance between the first and second nodes (N<NUM>, N<NUM>); and
a phase match detector circuit (<NUM>) to detect a phase match between the AC reference frequency signal and the reflected AC frequency signal.