Surgery – Instruments – Electrical application
Reexamination Certificate
1993-10-07
2001-04-03
Shay, David M. (Department: 3739)
Surgery
Instruments
Electrical application
C606S038000, C606S039000, C606S040000
Reexamination Certificate
active
06210403
ABSTRACT:
FIELD OF THE INVENTION
An automatic control for an electrosurgical generator measures energy delivered and, in particular, permits the operation of the electrosurgical generator during electrosurgical tissue desiccation. Surgeons find that manual operation by hand or foot activated switching can cause excessive surgical energy delivery resulting in over drying the tissue at the surgical site.
Surgeons have tried to deal with energy application by adjusting the basic power level of the electrosurgical generator and using the hand or foot switch to control the power applied over time. Unfortunately, that technique often leads to unintended power delivery or undesired duration of power delivery to the surgical site. Surgeons also experience difficulty in repeatably and/or consistently desiccating tissue to the desired levels due to the limits of their human reaction time or machine response time when manual or foot activated switches are used for manual control. In addition, during endoscopic procedures, surgeons lose some visual and tactile indications of desiccation progression.
BACKGROUND OF THE INVENTION
As a result of manual operation problems, several attempts to provide automatic generator operation when surgical forceps contact patient tissue have been patented. U.S. Pat. No. 2,827,056, German patent 1,099,658, German patent 28 23 291 describe circuits which place a direct current potential across the surgical forceps. Placement of the forceps across patient tissue causes a small DC current to flow therethrough. Direct current flow causes activation of a relay circuit enabling the higher power radio frequency energy to flow into the patient's tissue for surgical effect. Selecting fixed resistance values, within the circuits, determine the tissue impedance level below which radio frequency energy activation occurs.
German Patent DE 25 40 968 describes a circuit which uses a low-frequency measurement current to determine relative patient tissue impedance; low frequency current flow within a specified amplitude range turns on generator high frequency power for surgical effect. That circuit also includes a time delay relay for controlling time between application of forceps to patient tissue and subsequent generator operation.
Subsequent patents addressed the need for automatic turn off capability during bipolar desiccation procedures. German patent DE 31 20 102 A1 describes a circuit which monitors the differential quotient (time derivative) of patient tissue impedance to determine when to turn off radio frequency power delivery; a point of zero time derivative is selected to turn off power delivery. German patent DE 29 46 728 A1 describes a circuit which turns radio frequency power off after an adjustable, but fixed time delay. German patent DE 35 10586 describes a circuit which uses a low-frequency control current or low level generator radio frequency current source and a current level monitor to turn on generator radio frequency power for surgical effect. The circuit also monitors the generator output voltage for third harmonic content generated when desiccation completes and sparking begins to cause harmonic frequency generation to turn off generator radio frequency power. It is a device which measures current flowing through the tissue and forms a digitized signal of current level. The signal and the manual activation are combined to operate the device.
U.S. Pat. No. 4,860,745 discusses the problems encountered when turning off radio frequency power based upon measurements of the time derivative of patient tissue impedance and, instead, presents a circuit which turns off generator radio frequency power based upon fixed fractional changes in the amount of radio frequency current delivered to the patient tissue during desiccation or based upon generator sparking and harmonic frequency generation. A peak detector circuit examines the peak current at the forceps and a second circuit which monitors the decreasing current during coagulation. Measured current levels are converted to voltages within the circuits. The voltages, thus measured, control the electrosurgical generator which is turned off when a fraction of the peak current is greater than the current measured which flows through the tissue during coagulation. If the current flowing through the tissue is greater than the fraction, then the output of the electrosurgical generator is continued until it is less.
German patent 2,455,174 is directed to a switch and relay so when the doctor operates the switch, which is normally closed; it enables ESU control. Opening the switch activates a relay which operates the electrosurgical generator when the impedance value between the forceps is within a predetermined range. These claims are avoided since we have no switch and relay. Also required is a manually activated switch to operate the relay. The switch is on the handle of the forceps.
U.S. Pat. No. 4,658,819 discloses a circuit wherein the power delivered to the electrode is a function of the voltage from a DC supply and the load as measured by sensors of load voltage and current. A microprocessor controller digitizes the sensing signals and computes the load impedance and actual power being delivered. The microprocessor controller accordingly repeats the measurement, calculation and correction process approximately as long as the generator is operating. U.S. Pat. No. 4,372,315 discloses a circuit which measures impedances after delivering a set number of radio frequency pulses on a pulse burst by pulse burst basis. U.S. Pat. No. 4,321,926 has a feedback system to control dosage but the impedance sensing is not on a real time basis. U.S. Pat. Nos. 3,964,487, 3,980,085, 4,188,927, and 4,092,986 have circuitry to reduce the output current in accordance with increasing load impedance. In those patents voltage output is maintained constant while the current is decreased with increasing load impedance. U.S. Pat. No. 4,094,320 has a circuit that responds to impedance changes as measured by sensing current in the active and return leads. The sensed currents are subtracted from one another and it that exceeds a variable threshold the generator is turned off. The variable threshold is a function of power level and leakage current through stray capacitance.
No circuitry has been known to automatically control the energy applied by comparing a basic user setting of power level desired to the actual power delivered over time. No automatic control is responsive to actual and desired energy delivery which are a function of tissue impedance. It is desired to provide consistent desiccation levels.
SUMMARY OF THE INVENTION
An automatic control for an electrosurgical generator responds to the level of tissue impedance between active and return electrodes of the electrosurgical generator during tissue desiccation. An electrosurgical generator preferably has an active lead and a return lead to supply high frequency electrosurgical energy, the electrosurgical generator may include a user control for setting the level of energy desired for electrosurgery. A voltage sensing circuit may respond to high frequency electrosurgical energy supplied by the electrosurgical generator and flowing through the leads. The voltage sensing circuit is preferably capable of providing a signal of voltage level between the active and return leads. A current sensing circuit may responds to high frequency electrosurgical energy supplied by the electrosurgical generator and flowing through the return lead, the current sensing circuit capable of providing a signal of current level. A multiplier receives the signals from the voltage and current sensing circuits and multiplies those signals together for preferably calculating the power flowing through the leads of the electrosurgical generator.
A clock may establish units of time during which power flow calculated by the multiplier is considered. An integrator most preferably calculates the energy supplied through the leads per each unit of time established by the clock based on the instantaneous power calculation
Shay David M.
Sherwood Services AG
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