Surgery – Instruments – Electrical application
Reexamination Certificate
1998-10-06
2001-09-25
Peffley, Michael (Department: 3739)
Surgery
Instruments
Electrical application
C606S041000, C606S046000, C606S038000, C607S101000
Reexamination Certificate
active
06293941
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to the field of electro-surgical medical devices. More particularly, this invention relates to devices that deliver energy in the form of radio-frequency electrical current to tissue in order to perform surgical functions.
Description of Related Art
Various medical procedures rely on high-frequency electrical currents to deposit energy and thus heat human and animal tissues. During such procedures, a high-frequency current is passed through the tissue between electrodes. One electrode is located at the tip of a surgical probe. Another electrode is located elsewhere, and may be a ground pad or another surgical probe tip. The tissue to be treated lies between the electrodes.
When the electrode circuit is energized, the electric potential of the electrodes at the probe tips oscillates at radio frequencies about a reference potential. If one is used, a ground pad remains at a floating reference potential. As the electric potential of the probe electrodes varies, a motive force on charged particles in the tissue is established that is proportional to the gradient of the electric potential. This electromotive force causes a net flow of electric charge, a current, to flow from one electrode, through the tissue, to any other electrode(s) at a lower potential. In the course of their flow, the charged particles collide with tissue molecules and atoms. This process acts to convert electrical energy to sensible heat in the tissue and is termed Joule heating.
Upon heating, surgical functions such as cutting, cauterizing and tissue destruction can be accomplished. For example, tissues can be cut by heating and eventually vaporizing the tissue cell fluids. The vaporization causes the cell walls to rupture and the tissue to cleave. When it is beneficial to destroy tissue, comparatively higher rates of energy deposition can cause tissue ablation.
Ablation of cellular tissues in situ is used in the treatment of many diseases and medical conditions either alone or combined with surgical removal procedures. Surgical ablation is often less traumatic than surgical removal procedures and may be the only alternative where other procedures are unsafe.
Tissue ablation devices commonly utilize electromagnetic (microwave, radio frequency (RF), lasers) or mechanical (acoustic) energy. In the category of electro-surgical devices, microwave ablation systems utilize a microwave antenna which is inserted into a natural body opening through a duct to the zone of treatment. Electromagnetic energy then radiates from the antenna through the duct wall into the target tissue. However, there is often severe trauma to the duct wall in this procedure since there is a significant microwave energy flux in the vicinity of the intended target. The energy deposition is not sufficiently localized. To reduce this trauma, many microwave ablation devices use a cooling system. However, such a cooling system complicates the device and makes it bulky. Laser ablation devices also suffer the same drawback as microwave systems. The energy flux near the target site, while insufficient to ablate the tissue, is sufficient to cause trauma.
Application of RF electric currents emanating from electrode tips offers the advantage of greater localization of the energy deposition since the electrode tip is nearly a point source. However, these devices require consideration and monitoring of the effect of the energy deposition on the tissue since the electrical dissipation and storage characteristics of the tissue carrying the current may vary with time as a result of the current-induced heating. As a result, the tissue heating response could vary over the time of treatment due to changing values of the tissue's electrical properties.
In addition, the localization of energy flux in an RF electro-surgical device may require a number of electrodes to be included in the surgical probe to provide adequate area coverage. In the case of multiple probe electrodes, each electrode may not be at the same electric potential at each instant due to amplitude, frequency, or phase variations in their RF oscillations. In this instance, an electric current would flow between the probe electrodes, coupling them to an extent primarily determined by the difference in electric potential between the probe electrodes and the electrical properties of the tissue between the electrode tips. This coupling can confuse monitoring of applied power and tissue response.
With an electro-surgical device, the tissue heating response depends largely on the electrical impedance since impedance is a representation of energy dissipation and storage properties. As described, the impedance of the tissue lying between the electrodes is an important parameter in both in the case of a single electrode, as well as in the case of devices with multiple electrodes. In fact, tissue electrical impedance is often displayed to the medical practitioner during a procedure since large changes in tissue impedance are indicative of tissue drying, ablation, etc.. Thus, the efficacy of these devices is critically affected by the methods of tissue electrical impedance determination and power control.
Prior art methods for determining the electrical impedance of the tissue in the context of a device for electro-surgery are of questionable accuracy since the measurements are made at a comparatively low electric current. In the prior art methods, the electric current utilized to determine the impedance is insufficient to damage the tissue. However, the resulting measurements are prone to error since the electrical signals are not strong relative to the noise in the measurement circuit. Prior art methods also do not adequately eliminate electric coupling between the electrodes, termed crosstalk, in the case of a multiple electrode probe. Therefore, there is a need in the field of electro-surgical devices for improved methods and apparatae for tissue electrical impedance determination and electrical power control.
SUMMARY OF THE INVENTION
This invention is an improved method and apparatus for tissue electrical impedance determination and electrical power control in a surgical device. The tissue electrical impedance determination and associated power control is improved relative to the prior art methods in that the uncertainties in determining the actual tissue impedance are reduced in two ways. First, this invention makes the impedance determining measurements less prone to noise-related uncertainties. Second, this invention eliminates measurement uncertainties due to electrical cross-talk between multiple electrode channels.
In an embodiment of the invention, an apparatus for controlling power delivery in an electro-surgical instrument is disclosed. The electro-surgical instrument includes a first channel and a second channel for delivery of energy to a surgical site. The apparatus includes: a switch, a measuring unit, a processor and a drive unit. The switch electrically isolates the second channel during a first measurement interval and the first channel during a second measurement interval. The measuring unit is coupled to the first and the second channel. The measurement unit measures a first power level of the first channel during a first measurement interval and a second power level of the second channel during a second measurement interval. The processor is coupled to the measuring unit and to the switch. The processor adjusts the first power level and the second power level to minimize a difference between a measured value of a control parameter and a target value of the control parameter. The drive unit is controlled by the processor. The drive unit delivers the adjusted first and second power levels to the surgical site via respectively the first channel and the second channel during a heating interval.
In an alternate embodiment of the invention a method for controlling power delivery in an electro-surgical instrument is disclosed. The electro-surgical instrument includes a first channel and a second channel for deliv
Koenig Franklin R.
Strul Bruno
Peffley Michael
Ruddy David
Somnus Medical Technologies Inc.
Wilson Sonsini Goodrich & Rosati
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