CA2499855A1 - Multiple rf return pad contact detection system - Google Patents
Multiple rf return pad contact detection system Download PDFInfo
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- CA2499855A1 CA2499855A1 CA002499855A CA2499855A CA2499855A1 CA 2499855 A1 CA2499855 A1 CA 2499855A1 CA 002499855 A CA002499855 A CA 002499855A CA 2499855 A CA2499855 A CA 2499855A CA 2499855 A1 CA2499855 A1 CA 2499855A1
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- 238000001514 detection method Methods 0.000 title claims abstract description 28
- 238000005259 measurement Methods 0.000 claims abstract description 24
- 230000003993 interaction Effects 0.000 claims abstract description 13
- 239000004020 conductor Substances 0.000 claims abstract description 8
- 238000004804 winding Methods 0.000 claims description 12
- 239000003990 capacitor Substances 0.000 claims description 3
- 230000008878 coupling Effects 0.000 claims description 2
- 238000010168 coupling process Methods 0.000 claims description 2
- 238000005859 coupling reaction Methods 0.000 claims description 2
- 230000006870 function Effects 0.000 description 9
- 238000002847 impedance measurement Methods 0.000 description 7
- 238000010438 heat treatment Methods 0.000 description 6
- 238000012544 monitoring process Methods 0.000 description 6
- 230000004913 activation Effects 0.000 description 3
- 230000003044 adaptive effect Effects 0.000 description 3
- 210000001519 tissue Anatomy 0.000 description 3
- 238000002679 ablation Methods 0.000 description 2
- 210000000577 adipose tissue Anatomy 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 230000001939 inductive effect Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000001356 surgical procedure Methods 0.000 description 2
- 206010015150 Erythema Diseases 0.000 description 1
- 208000027418 Wounds and injury Diseases 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 231100000321 erythema Toxicity 0.000 description 1
- 231100001261 hazardous Toxicity 0.000 description 1
- 208000014674 injury Diseases 0.000 description 1
- 230000003902 lesion Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000002028 premature Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 231100000241 scar Toxicity 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
- A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
- A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
- A61B18/1206—Generators therefor
- A61B18/1233—Generators therefor with circuits for assuring patient safety
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
- A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
- A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
- A61B18/14—Probes or electrodes therefor
- A61B18/16—Indifferent or passive electrodes for grounding
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
- A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
- A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
- A61B18/14—Probes or electrodes therefor
- A61B18/16—Indifferent or passive electrodes for grounding
- A61B2018/165—Multiple indifferent electrodes
Abstract
A return pad contact detection system is provided. The return pad contact detection system includes two or more signal sources each generating an operating current to a corresponding pair of pairs of patient return pads. The operating current is conducted through conductors to the pairs of patient return pads. Two or more resonant circuits are provided and correspond to the pair of patient return pads and corresponding signal sources. Each of the resonant circuits is responsive to the operating current for producing a signal that is a function of the impedance between the two corresponding patient return pads. The two resonant circuits are tuned to different frequencies and tuned to substantially the same frequency as the corresponding signal source to minimize measurement interaction between the pairs of patient return pads when the operating currents are simultaneously applied to the corresponding pairs of patient return pads.
Description
MULTIPLE RF RETURN PAD CONTACT DETECTION SYSTEM
BACKGROUND
1. Technical Field The present disclosure is directed to electrosurgery and, in particular, to circuitry for measuring or sensing the contact resistance or impedance between the patient and pairs of RF
return pad contacts or electrodes employed in such surgery.
BACKGROUND
1. Technical Field The present disclosure is directed to electrosurgery and, in particular, to circuitry for measuring or sensing the contact resistance or impedance between the patient and pairs of RF
return pad contacts or electrodes employed in such surgery.
2. Description of the Related Art 1o One potential risk involved in electxosurgery is the possibility of stray electrical currents causing excess heating proximate the RF return pad contacts or patient return electrodes. The most common conditions which are thought to lead to excess heating include:
(1) Tenting: Lifting of the return electrode from the patient due to patient movement or improper application. This situation may lead to excess heating if the area of electrode-15 patient contact is significantly reduced;
(2) Incorrect Application Site: Application of a return electrode over a highly resistive body location (e.g., excessive adipose tissue, scar tissue, erythema or lesions, excessive hair) will lead to a greater, more rapid temperature increase. Or, if the electrode is not applied to the patient (i.e. electrode hangs freely or is attached to another surface), the current may seek 2o an alternate return path such as the table or monitoring electrodes; and (3) Gel drying either due to premature opening of the electrode pouch or use of an electrode which has exceeded the recommended shelf life.
Many monitor or detection systems have been developed in the past, but most cannot directly guard against all three of the above listed situations. In order to protect against these 25 potentially hazardous situations, the contact resistance or impedance between the return electrode and the patient should' be monitored in addition to the continuity of the patient return circuit.
Safety circuitry is known whereby split (or double) patient electrodes are employed and a DC current (see German Pat. No. 1,139,927, published Nov. 22, 1962) or an AC current 30 (see U.S. Pat. Nos. 3,933,157 and 4,200,104) is passed between the split electrodes to sense the contact resistance or impedance between the patient and the electrodes.
U.S. Pat. No.
3,913,583 discloses circuitry for reducing the current passing through the patient depending upon the area of contact of the patient with a solid, patient plate. A
saturable reactor is included in the output circuit, the impedance of which varies depending upon the sensed impedance of the contact area.
The above systems are subject to at least one or more of the following shortcomings:
(a) lack of sensitivity or adaptiveness to different physiological characteristics of patients and (b) susceptibility to electrosurgical current interference when monitoring is continued during electrosurgical activation.
U.S. Pat. Nos. 4,416,276 and 4,416,277 describe a split-patient return electrode monitoring system which is adaptive to different physiological characteristics of patients, and a return electrode monitoring system which has little, if any, susceptibility to electrosurgical to current interference when monitoring is continued during electrosuxgical activation. The entire contents of both U.S. Pat. Nos. 4,416,276 and 4,416,277 are incorporated herein by reference.
Still a need exists for a detection or monitoring system, which is: 1) adaptive to different physiological characteristics of patients; 2) has little, if any, susceptibility to 15 electrosurgical curxent interference, (including interference or measurement interaction between components of the detection system); 3) can measure or sense the contact resistance or impedance between the patient and pairs of RF return pads or electrodes where multiple pairs of RF return pads are utilized due to the high current frequently needed during electrosurgery, such as during tissue ablation; and 4) eliminates or minimizes the risk of 2o measurement interaction between the RF return pad pairs.
Therefore, it is an aspect of the invention to provide a multiple RF return pad contact detection system for use during electrosurgical activation which achieves the above obj ectives.
SUMMARY
25 A multiple 12F return pad contact detection system is disclosed which is adaptive to different physiological characteristics of patients, without being susceptible to electrosurgical current inter.Ference. The detection system includes interference or measurement interaction between components of the detection system which can measure or sense the contact resistance or impedance between the patient and pairs of RF return pads or electrodes when 3o multiple pairs of RF return pads are utilized. Due to the high current frequently needed during electrosurgery, such as during tissue ablation, the detection system advantageously eliminates or minimizes the risk of measurement interaction between the RF
return pad pairs.
_2_ The circuitry of the multiple RF return pad contact detection system is preferably provided within an electrosurgical generator for controlling the generator according to various measurements, such as the contact resistance or impedance between the patient and pairs of RF return pads or return electrodes. Advantageously, the system allows for the independent and simultaneous measurement of the pad contact impedance for each pair of RF
return pads.
If the impedance of any pad pair is above a predetermined limit, the system advantageously turns off or reduces the electrosurgical output of the electrosurgical generator to prevent excess heating.
The system eliminates or minimizes interference or measurement interaction between to the pad pairs by providing a different signal source frequency for each pad contact pair, but a frequency which matches an associated series resonant network frequency. The current that flows in the series resonant network is a direct reflection or function of the pad impedance of the corresponding pad pair. Since the two resonant networks are tuned to different w frequencies, there is minimal interaction, if any, within. the system, which advantageously reduces the chances of inaccurate measurements.
The system may advantageously include or be modified to include a multiplexer to multiplex the measurements corresponding to each pad contact pair to eliminate or minimize measurement interaction and also minimize hardware resources.
More specifically, the present disclosure relates to a return pad contact detection system for use with at least two pairs of patient return pads adapted for contacting a patient.
Each pair of the at least two pairs of patient return pads has two conductors attached to a corresponding patient return pad for connecting the pad to a source of a.c.
energy passing through the pad. The return pad contact detection system includes: at least two signal sources for generating an operating current for a corresponding pair of the at least two pairs of patient return pads; means for applying the operating current through the conductors to the at least two pairs of patient return pads; and at least two resonant circuits each corresponding to at least one pair of patient return pads and one of the at least two signal sources. Each of the at least two resonant circuits responsive to the current for producing a signal which is a function of the impedance between the two corresponding patient return pads. The at least two 3o resonant circuits are tuned to different frequencies and are tuned to the substantially the same frequency as the corresponding signal source for substantially minimizing measurement interaction between the at least two pairs of patient return pads when the operating currents are simultaneously applied to the corresponding pairs of patient return pads.
As can be appreciated from the present disclosure, in one embodiment the frequency of the electrosurgical current may be substantially different from that of the operating current.
Preferably, the at least two resonant circuits are RCL series resonant circuits having minimum impedance at the resonant frequency. Advantageously, the system may include means for establishing a desired range having at least an upper limit for the impedance the system may also include determining means responsive to said signal for determining whether the impedance is within the desired range. Preferably, the means for establishing a desired range includes means for generating a reference signal corresponding to the upper limit and wherein the determining means includes comparator means for comparing the signal which is to a function of the impedance with the reference signal.
Advantageously, the system may further include means for generating a control signal for controlling the operation of the electrosurgical generator according to the determination made by the comparator means.
The desired range may advantageously include a lower limit for the impedance and wherein the means for establishing a desired range includes means for generating a reference signal corresponding to the lower limit and wherein the determining means includes comparator means for comparing the signal which is a function of the impedance with the reference signal. Preferably, the lower limit for the impedance is about 20 ohms and the upper limit for the impedance is about 144 ohms.
Advantageously, the means for applying the operating current includes at least two transformers each for coupling the corresponding pair of patient return pads to the corresponding signal source. The secondary winding of each transformer is connected to the corresponding pair of patient return pads and the primary winding thereof is in circuit with the corresponding signal source and resonant circuit.
The present disclosure also relates to a return pad contact detection system for use with at least two pairs of patient return pads adapted for contacting a patient. Each pair of the at least two pairs of patient return pads having two conductors attached to a corresponding patient return pad for connecting the pad to a source of a.c. energy passing through the pad.
The return pad contact detection system includes: means for producing and applying a corresponding current signal for each of the at least two pairs of patient return pads; resonant circuitry means responsive to the impedance between the at least two pairs of patient return pads for producing at least one signal which is a function of the impedance;
and measurement means for receiving the at least one signal for determining the impedance between the at least two pairs of patient return pads, Advantageously, the frequency of the corresponding current signal for each of the at least two pairs of patient return pads is substantially equal to the frequency of at least a portion of the resonant circuitry means.
Preferably, the means for producing and applying the corresponding current signal includes at least two a.c. signal sources. Advantageously, the resonant circuitry means includes at least two RCL series xesonant circuits having minimum impedance at the resonant frequency.
The system may advantageously further include: means for establishing a desired range having at least an upper limit for the impedance and determining means responsive to to the at least one signal fox determining whether the impedance is within the desired range.
Much like the embodiment above, the means for establishing a des~_red _ra_n_ge includes means for.generating a reference signal corresponding to the upper limit and wherein the determining means includes comparator means for comparing the at least one signal.
which is a function of the impedance with the reference signal. Preferably, the system further 15 includes means for generating a control signal for controlling the operation of the electrosurgical generator according to the determination riiade by the compaxator means.
Advantageously, the desired range includes a lower limit for th:e impedance and wherein the means for establishing a desired range includes means for generating a reference signal corresponding to the lower limit and wherein the determining means includes 20 comparator means for comparing the at least one signal which is a function of the impedance with the reference signal. Preferably, the lower limit for said impedance is about 20 ohms and the upper limit for said impedance is about 144 ohms.
Advantageously, the means for producing and applying the corresponding current signal includes at least two transformers wherein the secondary winding of each transformer 25 is connected to a corresponding pair of patient return pads and the primaxy winding thereof is in circuit with a portion of the means for applying and producing the corresponding current signal and the portion of the resonant circuitry means.
Advantageously the system may include two capacitors connected in series connected in parallel with the secondary winding of each transformer.
3o Further features of the multiple RF return pad contact detection system of the invention will become more readily apparent to those skilled in the art from the following detailed description of the apparatus taken in conjunction with the drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of the invention will be described herein below with reference to the drawings wherein:
FIG. 1 is a schematic diagram of the multiple RF return pad contact detection system in accordance with a preferred embodiment of the invention; and FIG. 2 is a graph illustrating the operation of the pad contact impedance measurement subsystem of FIG. 1.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
to Reference should be made to the drawings where like reference numerals refer to similar elements. Referring to FIG. 1, there is shown a schematic diagram of the multiple RF
wreturn pad contact detection system 100 of the present invention wherein electrosurgical generator 10 includes known circuitry such as a radio frequency oscillator 12 and an output amplifier 14 which generate an electrosurgical current. This current is applied to a patient (not shown) via an active electrode 16. The electrosurgical current is returned to the generator 10 via pad contact pairs or return electrode pairs 18a, 18b having pads or electrodes 20a, 20b and 22a, 22b and a corresponding two conductor patient cable 24a, 24b having leads 26 and 28. Two capacitors 32 and 34 are connected across each of the secondary windings 40a, 40b of transformer 38a, 38b.
2o Each primary winding 36a, 36b is connected to a corresponding a.c. signal source 42a, 42b and a series resonant network 44a, 44b. The purpose of each series resonant network 44a, 44b is to produce a current (i.e., left and right current senses) which is a function of the impedance between pads or electrodes 20a, 20b and 22a, 22b.
The system 100 eliminates or minimizes interference or measurement interaction between the pads 20a, 20b and 22a, 22b, while allowing for the independent and simultaneous measurement of the pad contact impedance for each pair of RF
return pads by having each a.c. signal source 42a, 42b provide a different signal source frequency for its corresponding pad contact pair. The frequency of each series resonant network 44a, 44b is tuned to match the frequency of the current produced by its associated a.c.
signal source 42a, 42b.
Accordingly, the frequency of one of the series resonant networks 44a is different from the frequency of the other series resonant network 44b. Hence, there is minimal interaction, if any, between the left and right circuitry of the system 100, especially the two contact pad pairs 18a, 18b. This essentially eliminates inaccurate or confusing measurements.
Additionally, the frequency of the electrosurgical current produced by the electrosurgical generator 10 is substantially different from that of the current produced by the a.c. signal sources 42a, 42b.
The current that flows in each series resonant network 44a, 44b, i.e., left and right current senses, is a direct reflection or function of the pad impedance of the corresponding pad contact pair 18a, 18b according to the physics of~a series resonant network. Each series resonant network 44a, 44b is an RCL network or a combination of R
(resistance), L
(inductance) and C (capacitance). In a preferred embodiment of the series resonant networks 44a, 44b, the inductive component for each network is integrated into t_h_e respective transformer 38a, 38b.
The frequency response of a series resonant network has a maximum resonant frequency fR. At the resonant frequency, the series resonant network has the minimum impedance, as opposed to a parallel resonant network which has the maximum impedance at the resonant frequency, and the phase angle is equal to zero degrees. The total impedance of a series resonant network is ZT+jXL jX~=R+j(XL-X~). At resonance: XL=Xc, fR=1/(2~sqrtLC), 7~=R, and VL=Vc. The resonance of a series resonant network occurs when the inductive and capacitive reactances are equal in magnitude but cancel each other because 2o they axe 180 degrees apart in phase.
The left and right current senses are applied to pad contact impedance measurement subsystem 46 which determines whether the impedance measurements between pads or return electrodes 20a, 20b and 22a, 22b are within a desired range. The range is preferably adaptable to the physiological characteristics of the patient. If at least one of the impedance measurements is not within a desired range, an inhibit signal is applied over a line 48 to internally disable the electrosurgical generator 10 (or reduce the RF output therefrom) to prevent excess heating.
U.S. Pat. Nos. 4,416,276 and 4,416,277 describe a method for determining the desired range according to the physiological characteristics of the patient, the entire contents of these 3o patents is incorporated herein by reference.
Preferably, the desired range fox which the impedance must fall between return electrodes 20a, 20b and 22a, 22b is about 20 to about 144 ohms. If not, the electrosurgical generator 10 is disabled. Thus, in one method of operation of the present invention, the lower limit is fixed at the nominal value of 20 ohms, thus reducing the onset of patient injury as a result of stray current paths which may surface if a contact pad or electrode is applied to a surface other than the patient. The upper limit is set to avoid such problems as those mentioned hereinbefore, i.e., tenting, incorrect application site, gel drying, etc.
In accordance with an important aspect of the invention, the upper limit is adjustable from the absolute maximum (typically about 144 ohms) downward to as low as typically 20 ohms to thereby provide for automatic adaptiveness to the physiological characteristics of the patient. This provides the multiple RF return pad contact detection system 100 of the present invention with significantly more control over the integrity of the RF pad contact or electrode l0 connections without limiting the range of patient types with which the multiple RF return pad contact detection system 100 may be used or burdening the ope_rato_r with additional concerns.
That is, the physiological characteristics can vary significantly from patient to patient and from one location site for the pad pairs to another. Thus, patients may vary in their respective amounts of adipose tissue (which is one determining factor in the impedance measurement between the various pads) without effecting the detection system.
Further, for a particular patient, one location site may be more fatty, hairy or scarred than another. Again, this does not reduce the effectiveness of the system, i.e., all of these factors typically affect the impedance measured between pads 20a, 20b and 22a, 22b and thus concern the operator as to which site is optimal for a particular patient. Such concerns are eliminated in accordance with the present invention by providing for automatic adaptability to the physiological characteristics of the patient.
Reference should now be made to FIG. 2 which is a graph illustrating the operation of pad contact impedance measurement subsystem 46.
During operation, the desired impedance range (that is, the acceptable range of the impedance detected between pads 20a, 20b and 22a, 22b) is preset when the power is turned on to an upper limit of, for example, 120 ohms and a lower limit of, for example, 20 ohms as can be seen at time T=0 seconds in FIG. 2. If the monitored impedance for any pad contact pair is determined to be outside of this range (T=A seconds) by comparing the current sense signal (or a signal derived there from) with a reference signal (e.g., a signal equal to 120 ohms or 20 ohms) using comparator circuitry (e.g., when a pad pair or any single contact pad is not affixed to the patient) an alert will be asserted and the electrosurgical generator 10 will be disabled over line 48.
_g_ The impedance between two contact pads of a contact pad pair at any instant is designated the return RF electrode monitor (REM} Instantaneous Value (RIV) in FIG. 2.
When the 1ZEM impedance enters the range (T=B seconds} bounded by the Upper Limit (UL) and the Lower Limit (LL), a timing sequence begins. If after five seconds the RIV is still within range (T=C seconds), the alert condition will cease and the R.EM
impedance value is stored in memory. This is designated as 1ZEM Nominal Value (RNV). The upper limit is then reestablished as 120% of this amount. The 80 ohm 1ZIV shown in FIG. 2 causes the upper limit to be at 96 ohms. This feature of the invention is particularly important because it is at this time (T=C seconds) that adaptation is initially made to the physiological to characteristics of the patient. Note if the RIV were to exceed 96 ohms at a time between T=C
and T=F seconds (while the upper limit is 96 ohms), the alert will be asserted and t_he electrosurgical generator 10 disabled.
However, if the upper limit had not been adjusted to 96 ohms, the alert would not have been asserted until after the RIV exceeded the initial 120 ohms upper limit as determined by the comparator circuitry, thus possibly heating one or both of the pads 20a, 20b and 22a, 22b. This situation is of course exacerbated if the patient's initial RIV within the preset 20 to 120 ohm range is 30 ohms.
An initial RIV of 10 ohms within the preset range of 20 to 120 ohms sets an upper limit of 144 ohms.
2o In accordance with another aspect of the invention, it has been observed that the impedance between contact pads of contact pad pairs decreases over a relatively long period, such as a number of hours. Since many surgical procedures can extend a number of hours, this effect is also taken into consideration in the present invention.
Accordingly, RIV is continuously monitored and any minima in REM impedance (e.g., a downward trend followed by a constant or upward trend in REM impedance) initiates a new five second timing interval (T=E seconds) at the end of which the RNV is updated to the RIV if the RIV
is lower (T=F seconds). The REM upper limit of 120% of RNV is re-established at this time.
The five second interval causes any temporary negative change in R.EM
impedance (T=D
seconds) to be disregarded. Operation will continue in this manner provided RIV does not exceed the upper limit of 120% RNV or drop below the lower limit of 20 ohms.
Exceeding the upper limit (T=G seconds) causes an alert and the electrosurgical generator 10 is disabled.
It will remain in alert until the R1V drops to 115% of RNV or less (T=H
seconds) or until the system 100 is reinitialized. IZIV dropping to less than 20 ohms (T=I seconds) causes a similar alert which continues until either the RIV exceeds 24 ohms (T=J seconds) or the system 100 is reinitialized. The hysteresis in the limits of the REM range (that is, the changing of the upper limit to 115% of RNV and the lower limit to 24 ohms in the previous examples) prevents erratic alerting when RIV is marginal.
It should be noted in the example of FIG. 2 that the alert actually does not turn off when RIV returns to a value greater than 24 ohms because the pad pairs are removed before 5 seconds after T=J seconds elapse. Thus, the alarm stays on due to the removal of the pad contact pairs 18a, 18b.
Removing the pad contact pairs 18a, 18b from the patient or unplugging the cables 26, l0 28 from the electrosurgical generator 10 (T=K seconds) for more than one second causes the system 100 to be reinitialized to the original limits of 120 and 20 ohms. This perm?ts a pad to be relocated or replaced (T=L seconds) without switching the electrosurgical generator 10 off.
The RIV at the new location is 110 ohms and 120% RNV is 132 ohms. Thus, as described above, this is the one time (whenever RIV enters the 20 to 120 ohms range (either as preset during power on or as reinitialized as at T=K seconds) for the first time) that the upper limit can be raised during the normal REM cycle. Otherwise, it is continually decreased to adapt to the decreasing RIV impedance with the passage of time.
The preferred implementation of the foregoing FIG. 2 operation of the pad contact impedance measurement subsystem 46 is effected by a set of programmable instructions configured for execution by a microprocessor.
The system 100 could be~modified by providing a multiplexer to multiplex the measurements corresponding to each pad contact pair 18a, 18b to eliminate or minimize measurement interaction and also minimize hardware resources.
Other pad contact pair arrangements can be provided in the system 100 of the present invention besides the pad pair arrangements shown in FIG. 1. For example, ten pad contact pairs 18 can be provided and connected to electrosurgical generator 10 by cables 26 and 28, where the corresponding a.c. signal source 42 and series resonant network 44 corresponding to each pad contact pair 18 are tuned to the same frequency which is different from the frequency of the other a.c. signal sources 42 and series resonant networks 44.
It is provided that the system 100 of the present invention allows for impedance comparisons to be performed between pad pairs. Therefore, if the pad pairs are placed symmetrically on the patient, i.e., left leg and right leg, comparison of the contact impedance can provide another degree of detection and safety.
Although the subject apparatus has been described with respect to preferred embodiments, it will be readily apparent to those having ordinary skill in the art to which it appertains that changes and modifications may be made thereto without departing from the spirit or scope of the subject apparatus.
(1) Tenting: Lifting of the return electrode from the patient due to patient movement or improper application. This situation may lead to excess heating if the area of electrode-15 patient contact is significantly reduced;
(2) Incorrect Application Site: Application of a return electrode over a highly resistive body location (e.g., excessive adipose tissue, scar tissue, erythema or lesions, excessive hair) will lead to a greater, more rapid temperature increase. Or, if the electrode is not applied to the patient (i.e. electrode hangs freely or is attached to another surface), the current may seek 2o an alternate return path such as the table or monitoring electrodes; and (3) Gel drying either due to premature opening of the electrode pouch or use of an electrode which has exceeded the recommended shelf life.
Many monitor or detection systems have been developed in the past, but most cannot directly guard against all three of the above listed situations. In order to protect against these 25 potentially hazardous situations, the contact resistance or impedance between the return electrode and the patient should' be monitored in addition to the continuity of the patient return circuit.
Safety circuitry is known whereby split (or double) patient electrodes are employed and a DC current (see German Pat. No. 1,139,927, published Nov. 22, 1962) or an AC current 30 (see U.S. Pat. Nos. 3,933,157 and 4,200,104) is passed between the split electrodes to sense the contact resistance or impedance between the patient and the electrodes.
U.S. Pat. No.
3,913,583 discloses circuitry for reducing the current passing through the patient depending upon the area of contact of the patient with a solid, patient plate. A
saturable reactor is included in the output circuit, the impedance of which varies depending upon the sensed impedance of the contact area.
The above systems are subject to at least one or more of the following shortcomings:
(a) lack of sensitivity or adaptiveness to different physiological characteristics of patients and (b) susceptibility to electrosurgical current interference when monitoring is continued during electrosurgical activation.
U.S. Pat. Nos. 4,416,276 and 4,416,277 describe a split-patient return electrode monitoring system which is adaptive to different physiological characteristics of patients, and a return electrode monitoring system which has little, if any, susceptibility to electrosurgical to current interference when monitoring is continued during electrosuxgical activation. The entire contents of both U.S. Pat. Nos. 4,416,276 and 4,416,277 are incorporated herein by reference.
Still a need exists for a detection or monitoring system, which is: 1) adaptive to different physiological characteristics of patients; 2) has little, if any, susceptibility to 15 electrosurgical curxent interference, (including interference or measurement interaction between components of the detection system); 3) can measure or sense the contact resistance or impedance between the patient and pairs of RF return pads or electrodes where multiple pairs of RF return pads are utilized due to the high current frequently needed during electrosurgery, such as during tissue ablation; and 4) eliminates or minimizes the risk of 2o measurement interaction between the RF return pad pairs.
Therefore, it is an aspect of the invention to provide a multiple RF return pad contact detection system for use during electrosurgical activation which achieves the above obj ectives.
SUMMARY
25 A multiple 12F return pad contact detection system is disclosed which is adaptive to different physiological characteristics of patients, without being susceptible to electrosurgical current inter.Ference. The detection system includes interference or measurement interaction between components of the detection system which can measure or sense the contact resistance or impedance between the patient and pairs of RF return pads or electrodes when 3o multiple pairs of RF return pads are utilized. Due to the high current frequently needed during electrosurgery, such as during tissue ablation, the detection system advantageously eliminates or minimizes the risk of measurement interaction between the RF
return pad pairs.
_2_ The circuitry of the multiple RF return pad contact detection system is preferably provided within an electrosurgical generator for controlling the generator according to various measurements, such as the contact resistance or impedance between the patient and pairs of RF return pads or return electrodes. Advantageously, the system allows for the independent and simultaneous measurement of the pad contact impedance for each pair of RF
return pads.
If the impedance of any pad pair is above a predetermined limit, the system advantageously turns off or reduces the electrosurgical output of the electrosurgical generator to prevent excess heating.
The system eliminates or minimizes interference or measurement interaction between to the pad pairs by providing a different signal source frequency for each pad contact pair, but a frequency which matches an associated series resonant network frequency. The current that flows in the series resonant network is a direct reflection or function of the pad impedance of the corresponding pad pair. Since the two resonant networks are tuned to different w frequencies, there is minimal interaction, if any, within. the system, which advantageously reduces the chances of inaccurate measurements.
The system may advantageously include or be modified to include a multiplexer to multiplex the measurements corresponding to each pad contact pair to eliminate or minimize measurement interaction and also minimize hardware resources.
More specifically, the present disclosure relates to a return pad contact detection system for use with at least two pairs of patient return pads adapted for contacting a patient.
Each pair of the at least two pairs of patient return pads has two conductors attached to a corresponding patient return pad for connecting the pad to a source of a.c.
energy passing through the pad. The return pad contact detection system includes: at least two signal sources for generating an operating current for a corresponding pair of the at least two pairs of patient return pads; means for applying the operating current through the conductors to the at least two pairs of patient return pads; and at least two resonant circuits each corresponding to at least one pair of patient return pads and one of the at least two signal sources. Each of the at least two resonant circuits responsive to the current for producing a signal which is a function of the impedance between the two corresponding patient return pads. The at least two 3o resonant circuits are tuned to different frequencies and are tuned to the substantially the same frequency as the corresponding signal source for substantially minimizing measurement interaction between the at least two pairs of patient return pads when the operating currents are simultaneously applied to the corresponding pairs of patient return pads.
As can be appreciated from the present disclosure, in one embodiment the frequency of the electrosurgical current may be substantially different from that of the operating current.
Preferably, the at least two resonant circuits are RCL series resonant circuits having minimum impedance at the resonant frequency. Advantageously, the system may include means for establishing a desired range having at least an upper limit for the impedance the system may also include determining means responsive to said signal for determining whether the impedance is within the desired range. Preferably, the means for establishing a desired range includes means for generating a reference signal corresponding to the upper limit and wherein the determining means includes comparator means for comparing the signal which is to a function of the impedance with the reference signal.
Advantageously, the system may further include means for generating a control signal for controlling the operation of the electrosurgical generator according to the determination made by the comparator means.
The desired range may advantageously include a lower limit for the impedance and wherein the means for establishing a desired range includes means for generating a reference signal corresponding to the lower limit and wherein the determining means includes comparator means for comparing the signal which is a function of the impedance with the reference signal. Preferably, the lower limit for the impedance is about 20 ohms and the upper limit for the impedance is about 144 ohms.
Advantageously, the means for applying the operating current includes at least two transformers each for coupling the corresponding pair of patient return pads to the corresponding signal source. The secondary winding of each transformer is connected to the corresponding pair of patient return pads and the primary winding thereof is in circuit with the corresponding signal source and resonant circuit.
The present disclosure also relates to a return pad contact detection system for use with at least two pairs of patient return pads adapted for contacting a patient. Each pair of the at least two pairs of patient return pads having two conductors attached to a corresponding patient return pad for connecting the pad to a source of a.c. energy passing through the pad.
The return pad contact detection system includes: means for producing and applying a corresponding current signal for each of the at least two pairs of patient return pads; resonant circuitry means responsive to the impedance between the at least two pairs of patient return pads for producing at least one signal which is a function of the impedance;
and measurement means for receiving the at least one signal for determining the impedance between the at least two pairs of patient return pads, Advantageously, the frequency of the corresponding current signal for each of the at least two pairs of patient return pads is substantially equal to the frequency of at least a portion of the resonant circuitry means.
Preferably, the means for producing and applying the corresponding current signal includes at least two a.c. signal sources. Advantageously, the resonant circuitry means includes at least two RCL series xesonant circuits having minimum impedance at the resonant frequency.
The system may advantageously further include: means for establishing a desired range having at least an upper limit for the impedance and determining means responsive to to the at least one signal fox determining whether the impedance is within the desired range.
Much like the embodiment above, the means for establishing a des~_red _ra_n_ge includes means for.generating a reference signal corresponding to the upper limit and wherein the determining means includes comparator means for comparing the at least one signal.
which is a function of the impedance with the reference signal. Preferably, the system further 15 includes means for generating a control signal for controlling the operation of the electrosurgical generator according to the determination riiade by the compaxator means.
Advantageously, the desired range includes a lower limit for th:e impedance and wherein the means for establishing a desired range includes means for generating a reference signal corresponding to the lower limit and wherein the determining means includes 20 comparator means for comparing the at least one signal which is a function of the impedance with the reference signal. Preferably, the lower limit for said impedance is about 20 ohms and the upper limit for said impedance is about 144 ohms.
Advantageously, the means for producing and applying the corresponding current signal includes at least two transformers wherein the secondary winding of each transformer 25 is connected to a corresponding pair of patient return pads and the primaxy winding thereof is in circuit with a portion of the means for applying and producing the corresponding current signal and the portion of the resonant circuitry means.
Advantageously the system may include two capacitors connected in series connected in parallel with the secondary winding of each transformer.
3o Further features of the multiple RF return pad contact detection system of the invention will become more readily apparent to those skilled in the art from the following detailed description of the apparatus taken in conjunction with the drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of the invention will be described herein below with reference to the drawings wherein:
FIG. 1 is a schematic diagram of the multiple RF return pad contact detection system in accordance with a preferred embodiment of the invention; and FIG. 2 is a graph illustrating the operation of the pad contact impedance measurement subsystem of FIG. 1.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
to Reference should be made to the drawings where like reference numerals refer to similar elements. Referring to FIG. 1, there is shown a schematic diagram of the multiple RF
wreturn pad contact detection system 100 of the present invention wherein electrosurgical generator 10 includes known circuitry such as a radio frequency oscillator 12 and an output amplifier 14 which generate an electrosurgical current. This current is applied to a patient (not shown) via an active electrode 16. The electrosurgical current is returned to the generator 10 via pad contact pairs or return electrode pairs 18a, 18b having pads or electrodes 20a, 20b and 22a, 22b and a corresponding two conductor patient cable 24a, 24b having leads 26 and 28. Two capacitors 32 and 34 are connected across each of the secondary windings 40a, 40b of transformer 38a, 38b.
2o Each primary winding 36a, 36b is connected to a corresponding a.c. signal source 42a, 42b and a series resonant network 44a, 44b. The purpose of each series resonant network 44a, 44b is to produce a current (i.e., left and right current senses) which is a function of the impedance between pads or electrodes 20a, 20b and 22a, 22b.
The system 100 eliminates or minimizes interference or measurement interaction between the pads 20a, 20b and 22a, 22b, while allowing for the independent and simultaneous measurement of the pad contact impedance for each pair of RF
return pads by having each a.c. signal source 42a, 42b provide a different signal source frequency for its corresponding pad contact pair. The frequency of each series resonant network 44a, 44b is tuned to match the frequency of the current produced by its associated a.c.
signal source 42a, 42b.
Accordingly, the frequency of one of the series resonant networks 44a is different from the frequency of the other series resonant network 44b. Hence, there is minimal interaction, if any, between the left and right circuitry of the system 100, especially the two contact pad pairs 18a, 18b. This essentially eliminates inaccurate or confusing measurements.
Additionally, the frequency of the electrosurgical current produced by the electrosurgical generator 10 is substantially different from that of the current produced by the a.c. signal sources 42a, 42b.
The current that flows in each series resonant network 44a, 44b, i.e., left and right current senses, is a direct reflection or function of the pad impedance of the corresponding pad contact pair 18a, 18b according to the physics of~a series resonant network. Each series resonant network 44a, 44b is an RCL network or a combination of R
(resistance), L
(inductance) and C (capacitance). In a preferred embodiment of the series resonant networks 44a, 44b, the inductive component for each network is integrated into t_h_e respective transformer 38a, 38b.
The frequency response of a series resonant network has a maximum resonant frequency fR. At the resonant frequency, the series resonant network has the minimum impedance, as opposed to a parallel resonant network which has the maximum impedance at the resonant frequency, and the phase angle is equal to zero degrees. The total impedance of a series resonant network is ZT+jXL jX~=R+j(XL-X~). At resonance: XL=Xc, fR=1/(2~sqrtLC), 7~=R, and VL=Vc. The resonance of a series resonant network occurs when the inductive and capacitive reactances are equal in magnitude but cancel each other because 2o they axe 180 degrees apart in phase.
The left and right current senses are applied to pad contact impedance measurement subsystem 46 which determines whether the impedance measurements between pads or return electrodes 20a, 20b and 22a, 22b are within a desired range. The range is preferably adaptable to the physiological characteristics of the patient. If at least one of the impedance measurements is not within a desired range, an inhibit signal is applied over a line 48 to internally disable the electrosurgical generator 10 (or reduce the RF output therefrom) to prevent excess heating.
U.S. Pat. Nos. 4,416,276 and 4,416,277 describe a method for determining the desired range according to the physiological characteristics of the patient, the entire contents of these 3o patents is incorporated herein by reference.
Preferably, the desired range fox which the impedance must fall between return electrodes 20a, 20b and 22a, 22b is about 20 to about 144 ohms. If not, the electrosurgical generator 10 is disabled. Thus, in one method of operation of the present invention, the lower limit is fixed at the nominal value of 20 ohms, thus reducing the onset of patient injury as a result of stray current paths which may surface if a contact pad or electrode is applied to a surface other than the patient. The upper limit is set to avoid such problems as those mentioned hereinbefore, i.e., tenting, incorrect application site, gel drying, etc.
In accordance with an important aspect of the invention, the upper limit is adjustable from the absolute maximum (typically about 144 ohms) downward to as low as typically 20 ohms to thereby provide for automatic adaptiveness to the physiological characteristics of the patient. This provides the multiple RF return pad contact detection system 100 of the present invention with significantly more control over the integrity of the RF pad contact or electrode l0 connections without limiting the range of patient types with which the multiple RF return pad contact detection system 100 may be used or burdening the ope_rato_r with additional concerns.
That is, the physiological characteristics can vary significantly from patient to patient and from one location site for the pad pairs to another. Thus, patients may vary in their respective amounts of adipose tissue (which is one determining factor in the impedance measurement between the various pads) without effecting the detection system.
Further, for a particular patient, one location site may be more fatty, hairy or scarred than another. Again, this does not reduce the effectiveness of the system, i.e., all of these factors typically affect the impedance measured between pads 20a, 20b and 22a, 22b and thus concern the operator as to which site is optimal for a particular patient. Such concerns are eliminated in accordance with the present invention by providing for automatic adaptability to the physiological characteristics of the patient.
Reference should now be made to FIG. 2 which is a graph illustrating the operation of pad contact impedance measurement subsystem 46.
During operation, the desired impedance range (that is, the acceptable range of the impedance detected between pads 20a, 20b and 22a, 22b) is preset when the power is turned on to an upper limit of, for example, 120 ohms and a lower limit of, for example, 20 ohms as can be seen at time T=0 seconds in FIG. 2. If the monitored impedance for any pad contact pair is determined to be outside of this range (T=A seconds) by comparing the current sense signal (or a signal derived there from) with a reference signal (e.g., a signal equal to 120 ohms or 20 ohms) using comparator circuitry (e.g., when a pad pair or any single contact pad is not affixed to the patient) an alert will be asserted and the electrosurgical generator 10 will be disabled over line 48.
_g_ The impedance between two contact pads of a contact pad pair at any instant is designated the return RF electrode monitor (REM} Instantaneous Value (RIV) in FIG. 2.
When the 1ZEM impedance enters the range (T=B seconds} bounded by the Upper Limit (UL) and the Lower Limit (LL), a timing sequence begins. If after five seconds the RIV is still within range (T=C seconds), the alert condition will cease and the R.EM
impedance value is stored in memory. This is designated as 1ZEM Nominal Value (RNV). The upper limit is then reestablished as 120% of this amount. The 80 ohm 1ZIV shown in FIG. 2 causes the upper limit to be at 96 ohms. This feature of the invention is particularly important because it is at this time (T=C seconds) that adaptation is initially made to the physiological to characteristics of the patient. Note if the RIV were to exceed 96 ohms at a time between T=C
and T=F seconds (while the upper limit is 96 ohms), the alert will be asserted and t_he electrosurgical generator 10 disabled.
However, if the upper limit had not been adjusted to 96 ohms, the alert would not have been asserted until after the RIV exceeded the initial 120 ohms upper limit as determined by the comparator circuitry, thus possibly heating one or both of the pads 20a, 20b and 22a, 22b. This situation is of course exacerbated if the patient's initial RIV within the preset 20 to 120 ohm range is 30 ohms.
An initial RIV of 10 ohms within the preset range of 20 to 120 ohms sets an upper limit of 144 ohms.
2o In accordance with another aspect of the invention, it has been observed that the impedance between contact pads of contact pad pairs decreases over a relatively long period, such as a number of hours. Since many surgical procedures can extend a number of hours, this effect is also taken into consideration in the present invention.
Accordingly, RIV is continuously monitored and any minima in REM impedance (e.g., a downward trend followed by a constant or upward trend in REM impedance) initiates a new five second timing interval (T=E seconds) at the end of which the RNV is updated to the RIV if the RIV
is lower (T=F seconds). The REM upper limit of 120% of RNV is re-established at this time.
The five second interval causes any temporary negative change in R.EM
impedance (T=D
seconds) to be disregarded. Operation will continue in this manner provided RIV does not exceed the upper limit of 120% RNV or drop below the lower limit of 20 ohms.
Exceeding the upper limit (T=G seconds) causes an alert and the electrosurgical generator 10 is disabled.
It will remain in alert until the R1V drops to 115% of RNV or less (T=H
seconds) or until the system 100 is reinitialized. IZIV dropping to less than 20 ohms (T=I seconds) causes a similar alert which continues until either the RIV exceeds 24 ohms (T=J seconds) or the system 100 is reinitialized. The hysteresis in the limits of the REM range (that is, the changing of the upper limit to 115% of RNV and the lower limit to 24 ohms in the previous examples) prevents erratic alerting when RIV is marginal.
It should be noted in the example of FIG. 2 that the alert actually does not turn off when RIV returns to a value greater than 24 ohms because the pad pairs are removed before 5 seconds after T=J seconds elapse. Thus, the alarm stays on due to the removal of the pad contact pairs 18a, 18b.
Removing the pad contact pairs 18a, 18b from the patient or unplugging the cables 26, l0 28 from the electrosurgical generator 10 (T=K seconds) for more than one second causes the system 100 to be reinitialized to the original limits of 120 and 20 ohms. This perm?ts a pad to be relocated or replaced (T=L seconds) without switching the electrosurgical generator 10 off.
The RIV at the new location is 110 ohms and 120% RNV is 132 ohms. Thus, as described above, this is the one time (whenever RIV enters the 20 to 120 ohms range (either as preset during power on or as reinitialized as at T=K seconds) for the first time) that the upper limit can be raised during the normal REM cycle. Otherwise, it is continually decreased to adapt to the decreasing RIV impedance with the passage of time.
The preferred implementation of the foregoing FIG. 2 operation of the pad contact impedance measurement subsystem 46 is effected by a set of programmable instructions configured for execution by a microprocessor.
The system 100 could be~modified by providing a multiplexer to multiplex the measurements corresponding to each pad contact pair 18a, 18b to eliminate or minimize measurement interaction and also minimize hardware resources.
Other pad contact pair arrangements can be provided in the system 100 of the present invention besides the pad pair arrangements shown in FIG. 1. For example, ten pad contact pairs 18 can be provided and connected to electrosurgical generator 10 by cables 26 and 28, where the corresponding a.c. signal source 42 and series resonant network 44 corresponding to each pad contact pair 18 are tuned to the same frequency which is different from the frequency of the other a.c. signal sources 42 and series resonant networks 44.
It is provided that the system 100 of the present invention allows for impedance comparisons to be performed between pad pairs. Therefore, if the pad pairs are placed symmetrically on the patient, i.e., left leg and right leg, comparison of the contact impedance can provide another degree of detection and safety.
Although the subject apparatus has been described with respect to preferred embodiments, it will be readily apparent to those having ordinary skill in the art to which it appertains that changes and modifications may be made thereto without departing from the spirit or scope of the subject apparatus.
Claims (22)
1. A return pad contact detection system for use with at least two pairs of patient return pads adapted for contacting a patient, each pair of said at least two pairs of patient return pads having two conductors attached to a corresponding patient return pad for connecting the pad to a source of a.c. energy passing through the pad, said return pad contact detection system comprising:
at least two signal sources which each generate an operating current to a corresponding pair of said at least two pairs of patient return pads, the operating current being conducted through said conductors to said at least two pairs of patient return pads; and at least two resonant circuits each corresponding to at least one pair of patient return pads and one of said at least two signal sources, each of said at least two resonant circuits responsive to said operating current for producing a signal which is a function of the impedance between said two corresponding patient return pads, said at least two resonant circuits being tuned to different frequencies and being tuned to substantially the same frequency as the corresponding signal source for substantially minimizing measurement interaction between the at least two pairs of patient return pads when said operating currents are simultaneously applied to said corresponding pairs of patient return pads.
at least two signal sources which each generate an operating current to a corresponding pair of said at least two pairs of patient return pads, the operating current being conducted through said conductors to said at least two pairs of patient return pads; and at least two resonant circuits each corresponding to at least one pair of patient return pads and one of said at least two signal sources, each of said at least two resonant circuits responsive to said operating current for producing a signal which is a function of the impedance between said two corresponding patient return pads, said at least two resonant circuits being tuned to different frequencies and being tuned to substantially the same frequency as the corresponding signal source for substantially minimizing measurement interaction between the at least two pairs of patient return pads when said operating currents are simultaneously applied to said corresponding pairs of patient return pads.
2. A system as in Claim 1, wherein said at least two resonant circuits are RCL
series resonant circuits having minimum impedance at the resonant frequency.
series resonant circuits having minimum impedance at the resonant frequency.
3. A system as in any preceding claim, further comprising:
measurement circuitry responsive to said signal for determining whether said impedance is within a desired range having at least an upper limit for said impedance.
measurement circuitry responsive to said signal for determining whether said impedance is within a desired range having at least an upper limit for said impedance.
4. A system as in any preceding claim, wherein said measurement circuitry includes a reference signal generator for generating a reference signal corresponding to the upper limit and a comparator for comparing the signal which is a function of said impedance with the upper limit reference signal.
5. A system as in any preceding claim, wherein said system further comprises a control signal generator for generating a control signal for controlling the operation of said electrosurgical generator according to the determination made by said comparator.
6. A system as in any preceding claim, wherein said desired range includes a lower limit for said impedance and wherein said reference signal generator generates a reference signal corresponding to the lower limit and wherein said comparator compares the signal which is a function of said impedance with the lower limit reference signal.
7. A system as in any preceding claim, wherein said system further comprises a control signal generator for generating a control signal for controlling the operation of said electrosurgical generator according to the determination made by said comparator.
8. A system as in any preceding claim, wherein the lower limit for said impedance is about 20 ohms and the upper limit for said impedance is about 144 ohms.
9. A system as in any preceding claim, wherein said system further comprises at least two transformers each for coupling the corresponding pair of patient return pads to the corresponding signal source, the secondary winding of each transformer being connected to the corresponding pair of patient return pads and the primary winding thereof being in circuit with the corresponding signal source and resonant circuit.
10. A system as in any preceding claim, wherein the frequency of said electrosurgical current is substantially different from that of said operating current.
11. A return pad contact detection system for use with at least two pairs of patient return pads adapted for contacting a patient, each pair of said at least two pairs of patient return pads having two conductors attached to a corresponding patient return pad for connecting the pad to a source of a.c. energy passing through the pad, said return pad contact detection system comprising:
a current source for producing and applying a corresponding current signal for each of said at least two pairs of patient return pads;
resonant circuitry responsive to the impedance between said at least two pairs of patient return pads for producing at least one signal which is a function of said impedance;
and measurement circuitry for receiving said at least one signal for determining the impedance between said at least two pairs of patient return pads, wherein the frequency of said corresponding current signal for each of said at least two pairs of patient return pads is substantially equal to the frequency of at least a portion of said resonant circuitry.
a current source for producing and applying a corresponding current signal for each of said at least two pairs of patient return pads;
resonant circuitry responsive to the impedance between said at least two pairs of patient return pads for producing at least one signal which is a function of said impedance;
and measurement circuitry for receiving said at least one signal for determining the impedance between said at least two pairs of patient return pads, wherein the frequency of said corresponding current signal for each of said at least two pairs of patient return pads is substantially equal to the frequency of at least a portion of said resonant circuitry.
12. A system as in Claim 11, wherein the current source includes at least two a.c.
signal sources.
signal sources.
13. A system as in Claim 11 or 12, wherein said resonant circuitry includes at least two RCL series resonant circuits having minimum impedance at the resonant frequency.
14. A system as in Claim 11, 12 or 13, wherein said measurement circuitry is responsive to said at least one signal for determining whether said impedance is within a desired range having at least an upper limit for said impedance.
15. A system as in Claim 11, 12, 13 or 14, wherein said system further comprises a reference signal generator for generating a reference signal corresponding to the upper limit and wherein said measurement circuitry includes a comparator for comparing said at least one signal which is a function of said impedance with the upper limit reference signal.
16. A system as in Claim 11, 12, 13, 14 or 15, wherein said system further comprises a control signal generator for generating a control signal for controlling the operation of said electrosurgical generator according to the determination made by said comparator.
17. A system as in Claim 11, 12, 13 or 14, wherein said desired range includes a lower limit for said impedance and wherein said reference signal generator generates a reference signal corresponding to the lower limit and wherein said comparator compares said at least one signal which is a function of said impedance with the lower limit reference signal.
18. A system as in Claim 11, 12, 13, 14, 15, 16 or 17, wherein said system further comprises a control signal generator for generating a control signal for controlling the operation of said electrosurgical generator according to the determination made by said comparator.
19. A system as in Claim 11, 12, 13, 14, 15, 16, 17 or 18 wherein the lower limit for said impedance is about 20 ohms and the upper limit for said impedance is about 144 ohms.
20. A system as in Claim 11, 12, 13, 14, 15, 16, 17, 18 or 19, wherein said system further comprises at least two transformers, the secondary winding of each transformer being connected to a corresponding pair of patient return pads and the primary winding thereof being in circuit with a portion of said current source and the portion of said resonant circuitry.
21. A system as in Claim 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20, further comprising two capacitors connected in series connected in parallel with the secondary winding of each transformer.
22. A system as in Claim 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or 21, wherein the frequency of said electrosurgical current is substantially different from that of said corresponding current signal.
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2002
- 2002-09-25 US US10/254,956 patent/US6860881B2/en not_active Expired - Lifetime
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2003
- 2003-09-11 EP EP10180223.9A patent/EP2258295A3/en not_active Withdrawn
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- 2003-09-11 EP EP03798717A patent/EP1542603B1/en not_active Expired - Fee Related
- 2003-09-11 EP EP06008198.1A patent/EP1719471B1/en not_active Expired - Fee Related
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AU2008229843B2 (en) | 2011-06-30 |
JP4383536B2 (en) | 2009-12-16 |
US20070073284A1 (en) | 2007-03-29 |
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WO2004028385A1 (en) | 2004-04-08 |
WO2004028385A9 (en) | 2004-11-25 |
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DE60309901T2 (en) | 2007-10-31 |
EP1542603B1 (en) | 2006-11-22 |
US20040059323A1 (en) | 2004-03-25 |
US6860881B2 (en) | 2005-03-01 |
US20050021022A1 (en) | 2005-01-27 |
EP1719471B1 (en) | 2015-03-25 |
EP1719471A3 (en) | 2010-07-21 |
US7160293B2 (en) | 2007-01-09 |
AU2003266140B2 (en) | 2008-07-10 |
JP2006500165A (en) | 2006-01-05 |
AU2008229843A1 (en) | 2008-10-30 |
EP1542603A1 (en) | 2005-06-22 |
DE60309901D1 (en) | 2007-01-04 |
AU2003266140A1 (en) | 2004-04-19 |
US7938825B2 (en) | 2011-05-10 |
CA2499855C (en) | 2013-04-23 |
EP1719471A2 (en) | 2006-11-08 |
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