ELECTROSURGICAL INSTRUMENT WHICH
REDUCES THERMAL DAMAGE TO
CROSS REFERENCE TO RELATED 5
The present application claims the benefit of priority to U.S. Provisional Application Ser. No. 60/467,027 filed on May 1, 2003 by Chapman et al., the entire contents of which 10 being incorporated by reference herein.
The present disclosure relates to electrosurgical instru- 15 ments used for open and endoscopic surgical procedures for sealing or fusing tissue. More particularly, the present disclosure relates to a bipolar forceps for sealing vessels, vascular tissues and soft tissues having an electrode sealing assembly which is designed to limit and/or reduce thermal 20 spread to adjacent tissue structures.
Electrosurgical forceps utilize both mechanical clamping 25 action and electrical energy to effect hemostasis by heating the tissue and blood vessels to coagulate and/or cauterize vessels or tissue. However, certain surgical procedures may require sealing blood vessels or vascular tissue rather than just simply effecting hemostasis. "Vessel sealing" or "Tissue 30 Fusion" is defined as the process of liquefying the collagen, elastin and ground substances in the tissue so that it reforms into a fused mass with significantly-reduced demarcation between the opposing tissue structures. In contrast, the term "cauterization" is defined as the use of heat to destroy tissue 35 (also called "diathermy" or "electrodiathermy") and the term "coagulation" is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. Coagulation of small vessels is usually sufficient to permanently close them. Larger vessels or tissue need to be "sealed" to assure 40 permanent closure.
Numerous electrosurgical instruments have been proposed in the past for various open and endoscopic surgical procedures. However, most of these instruments cauterize or coagulate tissue and are normally not designed to provide 45 uniformly reproducible pressure on the blood vessel or tissue which, if used for sealing purposes, would result in an ineffective or non-uniform seal. For example, U.S. Pat. No. 2,176,479 to Willis, U.S. Pat. Nos. 4,005,714 and 4,031,898 to Hiltebrandt, U.S. Pat. Nos. 5,827,274, 5,290,287 and 50 5,312,433 to Boebel et al, U.S. Pat. Nos. 4,370,980, 4,552, 143, 5,026,370 and 5,116,332 to Lottick, U.S. Pat. No. 5,443,463 to Stern et al, U.S. Pat. No. 5,484,436 to Eggers et al. and U.S. Pat. No. 5,951,549 to Richardson et al, all relate to electrosurgical instruments for coagulating, cauter- 55 izing, and cutting vessels or tissue.
Many of these instruments include blade members or shearing members which simply cut tissue in a mechanical and/or electromechanical manner and are relatively ineffective for vessel sealing purposes. Other instruments generally 60 rely on clamping pressure alone to procure proper sealing thickness and are often not designed to take into account gap tolerances and/or parallelism and flatness requirements which are parameters which, if properly controlled, can assure a consistent and effective tissue seal. For example, it 65 is known that it is difficult to adequately control thickness of the resulting sealed tissue by controlling clamping pressure
alone for either of two reasons: 1) if too much force is applied, there is a possibility that the two poles will touch and energy will not be transferred through the tissue resulting in an ineffective seal; or 2) if too low a force is applied, a thicker less reliable seal is created.
Commonly-owned U.S. Application Ser. Nos. PCT Application Ser. No. PCT/US01/11340 filed on Apr. 6, 2001 by Dycus, et al. entitled "VESSEL SEALER AND DIVIDER", U.S. application Ser. No. 10/116,824 filed onApr. 5, 2002 by Tetzlaff et al. entitled "VESSEL SEALING INSTRUMENT" and PCT Application Ser. No. PCT/US01/11420 filed on Apr. 6, 2001 by Tetzlaff et al. entitled "VESSEL SEALING INSTRUMENT" teach that to effectively seal tissue or vessels, especially large vessels, two predominant mechanical parameters must be accurately controlled: 1) the pressure applied to the vessel; and 2) the gap distance between the conductive tissue contacting surfaces (electrodes). As can be appreciated, both of these parameters are affected by the thickness of the vessel or tissue being sealed. Accurate application of pressure is important for several reasons: to reduce the tissue impedance to a low enough value that allows enough electrosurgical energy through the tissue; to overcome the forces of expansion during tissue heating; and to contribute to the end tissue thickness which is an indication of a good seal.
It has been found that using electrosurgical instruments to seal tissue may result in some degree of so-called "thermal spread" across adjacent tissue structures. "Thermal spread" refers generally to the heat transfer traveling along the periphery of the electrically conductive surfaces. This can also be termed "collateral damage" to adjacent tissue. As can be appreciated, reducing the thermal spread during an electrical procedure reduces the likelihood of unintentional or undesirable collateral damage to surrounding tissue structures which are adjacent to an intended treatment site. Reducing the collateral damage to surrounding tissue or maintaining the viability of surrounding tissue after the sealing process is known to promote tissue healing and decrease overall healing time by stimulating/improving healing response.
Instruments which include dielectric coatings disposed on the outer surfaces are known and are used to prevent tissue "blanching" at points normal to the sealing site. In other words, these coatings are primarily designed to reduce accidental burning of tissue as a result of incidental contact with the outer surfaces of the end effectors. So far as is known these coating are not designed or intended to reduce collateral tissue damage or thermal spread to adjacent tissue (tissue lying along the tissue plane).
Commonly-owned U.S. patent Ser. No. 10/474,168 entitled "ELECTROSURGICAL INSTRUMENT WHICH REDUCES COLLATERAL DAMAGE TO ADJACENT TISSUE" filed on Oct. 3, 2003 by Buysse et al. relates to an instrument which is configured to control or regulate the electrical field around the electrically conductive sealing surfaces to reduce stray current concentrations which can result in thermal spread to adjacent tissue structures.
Thus, a need exists to develop an electrosurgical instrument which includes an electrode sealing assembly which can seal vessels and tissue consistently and effectively and reduce the undesirable effects of thermal spread across or to adjacent tissue structures by utilizing a thermally conductive, electrically non-conductive material.