Surgery – Instruments – Heat application
Reexamination Certificate
1997-09-22
2001-04-10
Shay, David M. (Department: 3739)
Surgery
Instruments
Heat application
C606S034000, C606S039000, C606S041000
Reexamination Certificate
active
06213999
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to surgical devices which incorporate electrosurgical energy and gas plasmas, and more specifically to an improved apparatus and method for igniting the plasma.
BACKGROUND OF THE DISCLOSURE
A gas plasma is an ionized gas that is capable of conducting electrical energy. Plasmas are used in surgical devices to conduct electrosurgical energy to a patient. The plasma conducts the energy by providing a pathway of low electrical resistance. The electrosurgical energy will follow this path and can therefore be used to cut, coagulate, desiccate, or fulgurate blood or tissue of the patient. One of the advantages of this procedure is that no physical contact is required between an electrode and the tissue being treated.
A plasma is created by ionizing a gas. Some electrosurgical systems have a source of regulated ionizable gas which is directed in a steady flow toward a patient. A gas that is typically used in this manner is argon, however other gasses can also be used. One advantage of having a directed flow of gas is that the plasma arc can be accurately focused and directed by the flow.
Electrosurgical systems that do not incorporate a source of regulated gas can ionize the ambient air between the active electrode and the patient. The plasma that is thereby created will conduct the electrosurgical energy to the patient, although the plasma arc will typically appear more spatially dispersed compared with systems that have a regulated flow of ionizable gas.
One of the difficulties in using a plasma is its initiation. A strong electrical field is required to accelerate enough free electrons within the gas such that a cascade of ionizing collisions is initiated which creates the plasma. This is sometimes called “igniting” the plasma. Once a plasma is ignited, it may be sustained at lower electrical field potentials.
Several techniques are presently used to create strong electrical fields that can ignite the plasma. One technique is to move the tip of an electrode very close to the surgical site. The electric field along a path between an electrode and the surgical site increases as their separation decreases, and may reach a level sufficient to ignite the plasma. The drawback of this method is that a surgeon must carefully manipulate the electrode to move it close to the surgical site without actually touching the tissue. If the electrode comes in contact with the tissue it may stick, causing eschar to deposit on the electrode. During laparoscopic procedures, it is often difficult for a surgeon to sense the proximity of the electrode to the tissue.
Another technique to ignite plasma is to use a pointed electrode which will generate a stronger electrical field at the tip of the electrode. However, a pointed electrode may be undesirable if the surgeon requires a blade-shaped electrode for cutting and other tissue manipulation. Yet another technique is to provide high voltage spikes to the surgical electrode until a detector has indicated a closed circuit with the return electrode. Once a closed circuit is detected, the high voltage spikes are terminated and the electrosurgical generator returns to its normal waveform output. While this technique is effective, it requires complicated electronics and components capable of withstanding the high voltages.
U.S. Pat. No. 4,060,088 relates to an electrosurgical method and apparatus for coagulation by fulguration. The apparatus has a source of inert ionizable gas which surrounds a tubular electrosurgical electrode. A source of periodic bursts of electrosurgical energy is disclosed which is used to initiate the plasma. Also disclosed is an auxiliary discharge to aid in the initiation of the plasma, where the auxiliary discharge results from the electric field established between the doctor's finger and the active electrode.
U.S. Pat. No. 4,781,175 has an ionizable gas jet to clear bodily fluids and coagulate or achieve fulguration in the form of an improved eschar. Circuitry and computer logic are shown to control the gas jet flow and the electrosurgical energy.
U.S. Pat. No. 4,901,720 and the reissue thereof Re. U.S. Pat. No. 34,432 deal with the rate of burst energy pulses, applied to maintain leakage current within acceptable limits while having sufficient energy to initiate ionization. Circuit and logic diagrams are provided to control the burst energy by pulse width, resonance, waveform and output.
U.S. Pat. No. 4,040,426 has a method and apparatus for initiating a plasma by the use of charged particles which are generated as the inert gas flows along a tube. This charge bleeds off of the tube through inwardly pointed tips on the tube, and is used to aid in the initiation of the plasma.
U.S. Pat. No. 4,901,719 has an electrosurgical unit in combination with an ionizable gas delivery system, where there is also an improvement relating to the gas conducting means.
The disclosures of the aforesaid references are incorporated by reference and made a part hereof.
The present state of the art has not completely overcome the difficulties associated with ignition of a plasma in surgical systems. A more simple and reliable apparatus and method for igniting a plasma will make it possible for plasma-based systems, and hence surgeons, to work more effectively.
SUMMARY OF THE INVENTION
An apparatus and method for igniting plasma in a surgical system is disclosed. The advantages which can be realized by this disclosure include greater reliability and repeatability of plasma ignition. This represents a significant advance over the present state of the art because current plasma ignition techniques often require difficult manipulations by the surgeon or complicated electronics.
A basis of this disclosure is the creation and use of two different types of plasma discharges: a “corona”, and a “plasma arc.” The plasma arc is meant to refer to the plasma discharge that is used for surgical purposes on the patient. A corona is a low current plasma discharge that occurs around pointed or wire electrodes where the electric field is greatly enhanced. It is sometimes associated with losses in electrical power transmission. References to “plasma ignition” are to the initiation of the plasma arc. An objective of this disclosure is to generate and use the corona to aid plasma ignition.
Gas discharges operate on the principle of electron avalanche ionization of a background gas. In surgical systems, the background gas is typically argon, however other gasses are also known to be effective. The process of electron avalanche ionization is started when seed electrons are accelerated in an applied electric field to energies sufficient to ionize a gas atom or molecule upon collision. The result of the collision is an ion and two free electrons that are available to ionize two more gas atoms resulting in four free electrons, and so on.
The growth in electron density is exponential with distance traveled by the seed electrons, and a thus a plasma is generated which is capable of conducting electrical energy. This is the principle mechanism of plasma ignition. Surgical systems make use of the plasma to conduct electrosurgical energy to the tissue of a patient without having to touch the tissue with a solid electrode. The electrosurgical energy can be used to cut, coagulate, desiccate, or fulgurate the blood or tissue of the patient.
This simplified description of electron avalanche ionization neglects electron loss mechanisms. Before the plasma is ignited, the primary electron loss mechanism is through single species diffusion. The presence of electronegative atoms or molecules also is a loss mechanism. A strong electric field is required to overcome these losses. After the plasma ignites, the diffusion becomes ambipolar and the electron diffusion loss rate is reduced significantly. Thus, once the plasma is ignited, a weaker electric field can sustain the plasma arc.
For surgical systems, this means that the surgeon must have a strong electric field to ignite the plasma. In certain systems, the surgeon may see this as a requirem
Bek Robin Badih
Platt, Jr. Robert C.
Shay David M.
Sherwood Services AG
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