Apparatus and method for rapid reliable electrothermal tissue fusion and simultaneous cutting

Pieces of tissue are fused together and simultaneously cut by compressing the pieces together at an interface, delivering an impulse of electrical power which is converted into sufficient thermal energy to fuse the pieces together at the interface and simultaneously cut the fused tissue pieces along a well-defined linear path. The impulse, and the fusion and the simultaneous cutting, occur within a preferable time of 1.5-2.0 seconds but no greater than 4.0 seconds. The temperature of the thermal energy is regulated between 220° C.-320° C. The force applied on the tissue pieces is sufficient to fuse the tissue at the interface followed by further compression to cut the fused tissue along the linear path as a result of the thermal energy and a zero distance gap between jaws which compress the tissue pieces. The jaws have smooth working surfaces with an Ra of 0.15 or less microns up to 0.40 microns.

CROSS REFERENCE TO RELATED APPLICATIONS

This invention is related to inventions for an Apparatus and Method for Rapid and Reliable Electrothermal Tissue Fusion, described in U.S. patent application Ser. No. 11/701,857, and for an Tissue Fusion Instrument and Method to Reduce the Adhesion of Tissue to its Working Surfaces, described in U.S. patent application Ser. No. 11/701,858, both filed concurrently herewith by the inventors hereof and assigned to the assignee of the present invention. The disclosures of these concurrently-filed U.S. patent application are incorporated herein by this reference.

FIELD OF THE INVENTION

This invention relates to electrothermal tissue fusion, and more particularly, to a new and improved electrothermal apparatus and electrothermal method that seals or fuses tissue while simultaneously cutting or separating the tissue with the application of a short time-duration impulse of electrical energy which creates relatively high temperature heat that is applied to squeezed-together tissue pieces. The tissue sealing and simultaneous cutting occurs quickly, and the seal is of high integrity to resist failure while the cut results is a well-defined, substantially linear separation of the tissue through the sealed area.

BACKGROUND OF THE INVENTION

Coaptive electrothermal tissue fusion or sealing involves the application of force and electrical energy to heat compressed tissue sufficiently to join together separate pieces of tissue. Electrothermal tissue fusion avoids the need to manually suture or tie-off tissues or vessels during a surgical procedure. The tissue is fused or sealed to prevent blood or other fluid loss so that thereafter the tissue may be cut or incised. Thus, the usual purpose of sealing or fusing tissue is to allow cutting of the tissue adjacent to the fused area during the surgical procedure.

In most cases, sealing the tissue and thereafter cutting the tissue adjacent to the sealed area is a desired and efficient way to perform a surgical procedure. Tissue cutting has therefore been combined with electrosurgical tissue fusion, in order to obtain efficiency and convenience. However, the tissue cutting is almost universally accomplished by use of a blade or other mechanical cutter rather than by cutting through the application of electrosurgical energy. The common types of mechanical tissue cutting devices have had the effect of compromising the effectiveness of the tissue seal or fusion. Without adequate tissue sealing or fusion, tissue cutting becomes substantially irrelevant because a failure to adequately seal or fuse the tissue offers no advantage over the typical manual procedures of suturing or tying off vessels or cutting tissue with a scalpel. Therefore, achieving and maintaining effective and reliable tissue fusion is a prerequisite to tissue cutting.

Although the exact details of the physical chemistry involved in tissue fusion are probably not completely understood, it is believed that the heat denatures chains or strands of tissue proteins in the separate pieces of tissue and the pressure causes the denatured protein chains to reconstitute or re-nature across the interface between the tissue pieces. The reconstituted proteins chains interact and intertwine with one another to hold the previously-separate tissues pieces together.

Collagen is one type of protein chain that appears to play an important role in tissue fusion. Collagen, also known as tropocollagen, consists of three polypeptide protein chains that form a triple helix. These protein chains are grouped or tangled together to establish significant tissue structure and strength, as is observed in blood vessels and ligaments. Applying heat to the tissue to raise the temperature to about 60-70° C. causes the protein chains to become disordered, disassociated, separated and untangled from the triple helix.

Elastin is another type of protein chain that appears to play an important role in tissue fusion. Elastin a collection of polypeptide protein chains that are individually and randomly cross-linked with each other to form a fibril. Fibrils are grouped or tangled together to form an elastin fiber. Upon the application of heat to raise the temperature to about 120° C., the elastin fiber becomes disassociated into a disordered collection of individual polypeptide chains, fibrils and fibers.

The heat which causes denaturation of the collagen and elastin chains also appears to create unfavorable molecular interactions among the components of the denatured proteins, resulting in a relatively high free energy state. Atoms with the same electrostatic charge, and hydrophobic and hydrophillic regions of the protein chains, begin to interact and create repulsive forces. Force must be applied at the interface between the tissue pieces during fusion to overcome the repulsive forces and to achieve more favorable interactions of the proteins chains thereby reducing the amount of free energy. Force must also be applied at the interface to maintain the denatured protein chains in physical proximity with each other so that they will reconstitute and join the tissue pieces together.

Although this theoretical model of tissue fusion is understandable, reliable tissue fusion is difficult to achieve on a consistent basis. Fusing blood vessels is of particular concern, because vessel fusion during a surgical procedure is the primary use of tissue fusion at the present time. Fused blood vessels that fail or leak after the conclusion of surgery lead to internal bleeding. Internal bleeding usually requires a second operation to gain access to and seal the leaking vessel, which induces further trauma and risk to the patient.

One prior art type of electrosurgical tissue fusion involves bipolar electrosurgery. The tissues are compressed between two jaws of a forceps-type instrument. The jaws also serve as electrodes to conduct high-voltage radio frequency (RF) current through the compressed tissue. Heat is generated from the RF current flowing through the resistance or impedance of the tissue, and that heat denatures the chains of protein.

Certain difficulties arise when using bipolar electrosurgical tissue fusion. The voltage between the jaws which compress the tissue and serve as electrodes is typically several thousand volts. The distance between the jaws is relatively small when the tissue is compressed. The relatively high voltage can create arcs which jump the small distance between the jaws and penetrate the tissue adjacent to the jaws, particularly toward the end of the fusion procedure when the tissue between the jaws dehydrates and its impedance increases. The arcs enter the tissue in minuscule spots and destroy or weaken the tissue at those spots. Under conditions of prolonged application of RF power in this manner, which is typical with bipolar electrosurgical tissue fusion, the arcing can actually perforate the tissue adjacent to the fused area, thereby rupturing the tissue and destroying any sealing effect from the sealed area if there are a significant number of ruptures. This is particularly the case when sealing vessels, because a typical failure mode of vessels sealed with bipolar electrosurgery is a leak or rupture in the wall of the vessel adjacent to the sealed area.

The RF current inherently flows through the tissue in a somewhat random or uncontrollable pattern depending on the point-to-point characteristics of the tissue and many other factors. As a consequence, uniform heating of the tissue is impossible to control. The non-homogeneous distribution of heat over the area to be fused causes the protein chains to denature and reconstitute in a variable and nonuniform manner. The nonuniform denaturation and reconstitution leads to fused tissue areas of variable, nonuniform and somewhat unpredictable strength.

Assessing when to stop the delivery of RF current during bipolar electrosurgical tissue fusion is difficult. Applying either too much or too little RF current leads to seals that are more likely to fail. The application of too much RF current creates an excessive amount of heat which drives chemical reactions that appear to oxidize or burn the tissue and change the nature of the protein chains, thereby diminishing their ability to reconstitute and create effective seals. Overly-heated tissue at the sealed area or adjacent to the sealed area increases the probability of a failure because the tissue has become brittle and lacks pliability due to excessive dehydration, thereby contributing to cracking and breaking. In contrast, prematurely stopping the delivery of RF current prevents an adequate amount of denaturing of the protein chains which, in turn, prevents an adequate amount of reconstitution of the proteins chains, thereby diminishing the strength of the seal.

Control systems have been developed to attempt to address the problem of applying too much or too little RF power during bipolar electrosurgical tissue fusion. Such control systems monitor some event associated with the application of electrical power to the tissue, typically the impedance. Monitoring the tissue impedance is based on an expectation that some change indicates the occurrence of appropriate sealing conditions. However, it is believed that no reliable relationship exists between tissue impedance and the formation of a consistently reliable seal.

Another problem with bipolar electrosurgical tissue fusion is that the alternating aspects of the RF electrical energy inherently results in less energy application per unit of time. The alternating aspects of the RF energy application is by nature a pulsed or alternating current (AC) energy application, as opposed to a continual energy application. The tissue must withstand relatively high voltages, but the amount of power transferred is not commensurate with the high voltage due to the pulsed or AC application of the RF current. The effect of the pulsed or alternating RF energy application is that more time is required to transfer an equivalent amount of energy compared to the transfer of energy delivered at a sustained peak value. The typical maximum power delivery with a widely used RF tissue fusion device is approximately 115 to 350 Watts per square inch (18-54 W/cm2).

Electrothermal instruments have also been used for tissue fusion. Electrothermal instruments have heating elements within jaws that grip and compress the tissue. Electrical current is conducted through the heating elements to generate the heat that is applied to the compressed tissue. As with bipolar electrosurgery, previous electrothermal instruments have produced varying and inconsistent tissue fusion results, possibly as a result of an ineffective control system or control functionality based on misperceptions relating to tissue fusion physiology, including the perceived limitation of not heating the tissue above the 120° C. point where elastin protein chains denature. The prevalent view is to avoid elevating the temperature of the tissue beyond the 120° C. point where elastin protein chains denature, because it is believed that temperatures beyond that point are destructive to the proteins chains. Consequently, all presently known tissue fusion technologies attempt to limit the tissue temperature to no more than approximately 120° C., and many tissue fusion technologies limit the temperature of the tissue to approximately 100° C. to avoid creating steam.

The typical approach used to combine tissue cutting and fusion is to incorporate a mechanical blade with the applicator of the RF or thermal energy. The electrodes of the RF applicator, or jaws of the electrothermal applicator, create the fusion. Once the fusion is complete, the blade is advanced in grooves or slots formed in the electrodes or jaws to sever the fused area of the tissue, usually while the electrodes or jaws maintain pressure on the tissue. Such mechanical cutting systems are prone to sticking or jamming. Usually the mechanical blade is relatively thin and therefore has a tendency to distort while cutting, which may cause friction and sticking as it advances in the grooves or slots. The fluid and small pieces of tissue at the surgical site may also interfere with the intended movement of the mechanical blade.

The mechanical action of the blade severing the fused area of tissue also has the tendency to induce forces on the sealed area and the adjacent tissue, which typically compromises the effectiveness of the seal. Advancing the mechanical blade through the sealed area can separate the sealed area sufficiently to create a fluid leak and may even crack or otherwise destroy the sealed area to create a fluid leak. In certain circumstances, the mechanical blade can become so stuck or jammed to prevent release of the tissue from between the electrodes or jaws. Such a circumstance is particularly serious in minimally invasive (endoscopic or laparoscopic) surgery because the closed minimally invasive procedure has to be converted to an open surgical procedure to gain access to the stuck applicator and release it from the tissue. Converting a closed minimally invasive surgical procedure to an open procedure induces substantial unexpected trauma on a patient, and unexpectedly prolongs the duration and risk associated with the surgical procedure.

A further disadvantage of mechanical cutting is that the blade must be advanced in a linear direction, making it impossible to cut on a curve. Many surgeons prefer to use instruments which are curved, particularly in minimally invasive procedures where visualization is difficult because of a lack of stereoscopic vision. A curved electrode or jaw is easier to observe from the monoscopic perspective of minimally invasive surgical procedures.

Attempts have been made to electrothermally cut tissue simultaneously while fusing the tissue, but all such known attempts have proved unsuccessful or impractical. In general, tissue cutting while simultaneously fusing the tissue has involved delivering energy into the tissue for a considerable length of time. The prolonged energy delivery has apparently heated the tissue to the point where essentially complete dehydration of the tissue occurs and causes the tissue to become crisp, brittle and friable, like a potato chip. The tissue simply reaches a point where the sealed area disintegrates or crumbles.

Such prolonged heating has the effect of inducing thermal spread into the adjacent tissue, which compromises the strength of the seal and the unsealed adjacent tissue areas. The brittleness of the tissue causes it to separate or crack in a non-defined or non-controllable manner, which may extend the crack to the adjacent tissue walls and compromise or destroy the seal and create a leak. Moreover, the separation through the sealed area is essentially non-defined because of the relatively large area of total dehydration and the inability to control where the dehydrated tissue will crack or disintegrate. Consequently, known tissue fusion and simultaneous cutting procedures result in cutting which is more of the nature of ill-defined tissue obliteration rather than linear cutting along a desired path which surgeons prefer in order to avoid damaging more tissue than is necessary during the overall surgical procedure.

Although the principal concern of tissue fusion and cutting in a single procedure is creating reliable seals that hold on a long-term basis, another very important practical consideration is an ability to create the seal and perform the cut quickly. A typical surgical procedure will involve sealing many blood vessels at the surgical site. The typical time required by known electrosurgical tissue sealing devices to create a single seal is about 5-12 seconds. When also simultaneously electrothermally cutting the tissue in the manner described, the entire energy application extends from 30 to 60 seconds. When mechanically cutting the tissue after it has been fused, an additional 5 to 10 seconds is required in order to advance the mechanical blade through the fused area, providing that no sticking or jamming occurs. A considerable amount of time is therefore consumed in making each single-procedure seal and cut. Considering that a typical surgical procedure may require sealing and cutting scores of vessels, a considerable amount of the total overall surgical procedure time is consumed by vessel sealing and cutting.

Moreover, because of concern about the reliability of the vessel seals, the typical practice is to create two sequential seals at each severed end of the vessel. The theory is that if the first or upstream seal fails, the second or downstream seal becomes a redundant backup to prevent fluid leakage. The time to create the primary and backup seals is more than twice the amount of time required to create a single seal when the time for repositioning and observing the quality of each seal is taken into account. Further still, double seals must be made at both ends of each severed vessel if there is concern about leaking from the seals created at opposite ends of the vessel which is cut. Thus, a considerable amount of time is consumed during the surgical procedure by sealing vessels and cutting them. The time consumed by cutting and sealing vessels extends the time required to accomplish the entire surgical procedure, or alternatively, detracts from the time available to accomplish other activities during the surgical procedure.

SUMMARY OF THE INVENTION

The present invention creates reliable seals of good integrity while simultaneously cutting the tissue, and does so in a considerably shorter amount of time than known single-procedure tissue sealing and mechanical cutting techniques or known tissue sealing and simultaneous cutting techniques. The present invention delivers a short impulse of a relatively high amount of electrical energy to create the heat applied to fuse or seal the tissue while simultaneously cutting the fused tissue. Creating a reliable seal having good structural integrity while simultaneously cutting the seal is achieved with an electrical power impulse having a typical duration of about 2.0 or less seconds, and in many cases about 1.5 seconds or less. In certain exaggerated circumstances, a time duration of the electrical power impulse may extend to about 4.0 seconds, but this circumstance is unusual. The amount of energy delivered is sufficient to elevate the jaw temperature at the interface between the sealed and cut tissues to between 220° C. and 320° C. The relatively short time duration of the energy impulse and the resulting high temperature quickly create an effective, reliable and consistent seal followed by severing the tissue along a well-defined path through the sealed area.

Cutting or separation of the tissue occurs along a well-defined separation or parting line or path that may be linear in a straight or slightly curved sense. The separation line is established by the configuration of the jaws which grasp and compress the tissue during sealing and simultaneous cutting. The linear nature of the separation path or parting line is displaced sufficiently from the adjoining fused tissue areas to avoid compromising the strength or integrity of the adjoining fused areas. The separation or parting is accomplished simultaneously with the tissue fusion, so adverse forces on a previously-formed fused tissue area are avoided, thereby avoiding the problem of weakening the integrity of the sealed area by subsequent cutting.

The short time duration of the high temperature application does not affect the ability of the protein chains to renature and thereafter reconstitute in a strong reliable bond, even though the temperature created is considerably higher than the typically-regarded appropriate temperature for tissue fusion. The short impulse of relatively high heat is believed to effectively dehydrate or desiccate polar water molecules from binding sites on the protein chains without so dehydrating the tissue as to substantially compromise its pliability, thereby permitting more and direct interactions between the protein chains at those binding sites, resulting in stronger direct interactions between the protein chains, increased affinity between the chains and increased strength of the fusion between the tissues at the interface. However, the short impulse of energy does not so dehydrate the sealed tissue to cause it to lose its pliability and strength and thereby contribute to a leak or seal failure. The cutting occurs while the tissue is sealed and remains slightly pliable, thereby facilitating well-defined separation while avoiding adverse forces on the sealed tissue areas that might negatively affect the strength of the seal.

The seal and simultaneous cut created by the relatively short impulse of high energy become effective immediately, allowing the compression force on the tissue to be released almost immediately after delivering impulse of energy, without requiring a cooling-off time period. The short amount of time required to create the simultaneous cut and seal, and the avoidance of a subsequent cooling-off period or a mechanical cutting time period, greatly diminish the amount of time required to complete each simultaneous cut and seal procedure.

The quick delivery of energy forms an effective seal without significantly destroying, cracking or substantially adversely affecting the strength of the tissue adjacent to the seal along the separation line where the cut occurs. Consequently, the sealed and other tissue adjacent to the separation line retains its natural strength and is unlikely to fail, unlike the typical prior art electrosurgical tissue sealing and cutting procedure which spreads considerable thermal energy to the adjoining tissue. The thermal spread to the adjoining tissue is believed to destroy or diminish the strength of the adjacent tissue and the sealed area, making them susceptible to rupture from physiological pressure and from mechanical severing.

The sealed areas have a consistent strength which is significantly greater than the normal physiological pressure applied on the sealed areas. The strength and integrity minimizes or virtually eliminates post-operative bleeding. The reliability and integrity of the seals diminishes or eliminates the need for double seals for redundancy purposes. However, under circumstances where double seals are preferred, the characteristics of the seal created assure that a failure of the primary upstream seal will still confine the fluid to the vessel so that the redundant downstream seal will have the opportunity to function as an effective backup.

In accordance with these and other features, one aspect of the invention is an apparatus for fusing together pieces of tissue at an interface and simultaneously cutting the fused tissue along a linear path through the interface. The apparatus comprises an instrument and a power control device. The instrument includes jaws with working surfaces and a movement mechanism which moves the jaws toward one another to compress the tissue pieces together at the interface between the working surfaces. The working surfaces are formed of ceramic material and have a smoothness defined by an Ra of 0.40 microns or less. The movement mechanism has a capability for transferring sufficient force to achieve a compressed tissue thickness sufficient to fuse the tissue pieces at the interface, which in the case of blood vessels is 0.05 mm to 0.10 mm, followed by further compressing the tissue pieces at the interface to a zero thickness to cut the fused together tissue pieces. The power control device delivers an impulse of electrical power to the jaws which contains sufficient energy to fuse and simultaneously cut the tissue pieces along the linear path at the interface within no greater than 4.0 seconds after the electrical power impulse is initiated. The power impulse creates thermal energy and maintains a temperature of the thermal energy applied to the interface in the range of 220° C. to 320° C.

Another aspect of the invention is an apparatus for fusing together pieces of tissue at an interface and simultaneously cutting the fused tissue along a linear path through the interface. The apparatus comprises an instrument and a power control device. The instrument includes jaws with working surfaces and a movement mechanism which moves the jaws toward one another to compress the tissue pieces together and to obtain a zero separation distance between the working surfaces of the jaws to simultaneously cut the compressed and fused tissue pieces along the linear path. The power control device delivers an impulse of electrical power to the jaws which contains sufficient energy to fuse the tissue pieces together and to simultaneously cut the fused tissue pieces at the interface by creating a temperature applied to the interface in the range of 220° C. to 320° C. within the time duration of the electrical power impulse.

A further aspect of the invention is a method of electrothermally fusing together pieces of tissue at an interface and simultaneously cutting the fused tissue along a linear path through the interface. The method involves compressing the tissue pieces together at the interface sufficiently for fusing the tissue pieces together and for cutting the fused tissue pieces in the linear path through the fused tissue at the interface, delivering an impulse of electrical power of no greater than 4.0 seconds time duration which contains sufficient energy to fuse the tissue pieces together at the interface and to simultaneously cut the fused tissue in a linear path through the fused tissue at the interface within the time duration of the electrical impulse, converting the electrical power impulse into thermal energy applied at the interface to fuse the tissue pieces and to simultaneously cut the fused tissue pieces in the linear path through the interface, and regulating the temperature of the thermal energy applied at the interface in a range of 220° C. to 320° C. while fusing and simultaneously cutting the tissue pieces at the interface by controlling characteristics of the electrical power impulse.

Preferably, the time duration of the electrical power impulse is no greater than 2.0 seconds. The invention is particularly applicable to fusing apposite walls of a vessel to form an occlusion in a lumen of the vessel while simultaneously cutting the vessel.

Certain further aspects of the invention involve one or more of the following features: releasing the interface immediately after termination of the electrical power impulse, elevating the temperature of the thermal energy applied at the compressed interface at a rate of between 150° C. per second to 500° C. per second from energy contained in the electrical power impulse, producing an energy density in the range of 388 W per square centimeter to 465 W per square centimeter of area of the compressed interface from the electrical power impulse, forming electrical power impulse from direct current and conducting the direct current power impulse to a heating element within each jaw, releasing compression of the interface after fusion and simultaneous cutting by moving the working surfaces away from the fused and cut interface with the working surfaces extending parallel to one another, releasing compression of the interface without inducing shear forces on the fused and cut interface, and separately regulating characteristics of the electrical power impulse delivered to the heating element within each jaw to regulate the temperature of thermal energy applied by the working surface from each jaw separately.

A more complete appreciation of the present disclosure and its scope, and the manner in which it achieves the above and other improvements, can be obtained by reference to the following detailed description of presently preferred embodiments taken in connection with the accompanying drawings, which are briefly summarized below, and to the appended claims.

DETAILED DESCRIPTION

The present invention is incorporated in an electrothermal apparatus20shown inFIG. 1. The electrothermal apparatus20is used to fuse or seal biological tissue, such as a vessel21, while simultaneously cutting or separating the biological tissue, by use of a handpiece or tissue fusion and cutting instrument22. Proximal handles24and26of the instrument22are moved or squeezed together, which causes a parallel movement mechanism28(FIG. 7) of the instrument22to move distal arms30and32of the instrument22toward one another with parallel closing movement. Jaws34and36are attached to the distal end of the arms30and32. Working surfaces38and40of the jaws34and36contact, squeeze, force and compress the vessel21when the jaws38and40and the distal arms30and32move toward one another, as shown inFIG. 2. Before compression, a lumen42within the vessel21is unobstructed and not occluded as shown inFIG. 3. Movement of the jaws34and36toward one another forces and compresses walls44of the vessel21into apposition with one another at a tissue interface46shown inFIG. 4.

An impulse of electrical energy from a power control device48, shown inFIGS. 1 and 2, is delivered to a heating element49(FIGS. 8 and 10-13) embedded in each of the jaws34and36, upon compressing together the apposite walls44of the vessel21at the tissue interface46. The heating element49converts the electrical power to heat, and the heat is conducted from the working surfaces38and40to elevate the temperature of the compressed apposite vessel walls44at the interface46. The temperature of the vessel walls44is elevated to a predetermined set point temperature within the range of 220° C. to 320° C. where tissue fusion and simultaneous cutting occurs while the jaws34and36compress the apposite vessel walls44against one another until the working surfaces38and40contact one another and thereby sever or cut the sealed vessel walls44at a well-defined line along the longitudinal dimension of the working surfaces38and40. The force applied from the working surfaces38and40in contact with the apposite vessel walls44is sufficient to squeeze the fully compressed and heated apposite vessel walls until an essentially zero dimension gap, i.e. complete contact, between the working surfaces38and40of the jaws34and36, respectively, is achieved. This force required to achieve an essentially zero space or gap between the working surfaces is usually greater than 150 Newtons (N), but may fall within the range of 110 N to 150 N.

The heat first denatures and disassociates the protein chains at the interface46of the compressed apposite vessel walls44at the interface46. The denatured protein chains immediately reconstitute or re-nature across the compressed tissue interface46to fuse or seal the vessel walls44together at a sealed area50(FIGS. 6 and 20). The sealed area50occludes the lumen42and prevents fluid normally confined within the lumen42from passing from the vessel21. Continued compression further squeezes the sealed area50until the heat essentially destroys the tissue in a well-defined separation line51through the sealed area50and causes the vessel21to separate or part at the separation line51(FIGS. 6 and 20). Immediately after the impulse of electrical power is terminated, the handles24and26are moved away from one another, which causes the arms30and32and the attached to jaws34and36to separate, releasing the vessel21which has been cut or severed at the parting or separation line51, as shown inFIGS. 6 and 20. The tissue fusion and simultaneous cutting procedure is typically complete in 1.5 to 2.0 seconds.

The heat is disbursed substantially uniformly throughout the jaws34and36and across the compressed tissue interface46(FIG. 4) at the sealed area50. The tissue walls44are continually compressed until a zero gap or contact is achieved between the working surfaces38and40. The heat and the continued compression destroys the tissue in a well-defined linear manner between the working surfaces38and40at the separation line51to separate the vessel21after it has been sealed and occluded in the sealed areas50adjoining the separation line51.

The jaws34and36are formed of high thermal conductivity material, preferably ceramic material such as aluminum nitride, thereby achieving a substantially uniform temperature on the tissue squeezed between the working surfaces38and40. The tissue interface temperature is approximately equal to the temperature of the jaws34and36due to the relatively thin amount of tissue compressed between the jaws.

The working surfaces38and40of the jaws34and36are smoothed or polished, preferably to an Ra of less than 0.15 microns. Jaws with working surfaces which have this degree of smoothness prevent the tissue from sticking to the jaws during fusion, despite the high relatively high temperature of the jaws against the tissue. By avoiding sticking, the integrity of the seal created is not damaged or its strength compromised from separating the jaws34and36after the seal has been formed, as would be the case if the tissue stuck to the jaws.

The impulse of electrical power delivered from the power control device48has a power density of greater than 1500 Watts per square inch (W/in2) (233 W/cm2) of the working surfaces of the jaws34and36, and preferably in the range of 2500 W/in2to 3000 W/in2(388 W/cm2to 465 W/cm2). This power density is considerably higher than the typical power density of 115-350 W/in2(18-54 W/cm2) obtainable from a prior art RF tissue fusion device that is presently widely used The impulse of electrical power raises the temperature of the jaws at a preferable rate of about 500° C. per second or more. An impulse of electrical power of this magnitude is sufficient to increase the temperature of the jaws34and36to about 220° C. to 320° C. very quickly after application of the impulse. The tissue fusion and cutting occurs over the 1.5-2.0 second preferred time duration of the electrical power impulse, allowing the jaws34and36to be separated or moved apart from one another to release the sealed area immediately after terminating the electrical power impulse.

The time required for achieving a reliable seal with high integrity against leaking and simultaneously cutting the tissue is related to the amount of tissue squeezed between the working surfaces, the type of tissue involved and the temperature applied to the tissue. Larger vessels, thicker walled vessels or larger amounts of tissue typically require longer sealing times and/or higher temperatures. Effective seals and cuts of typical small to medium vessels of 2-3 mm diameter are achieved with electrical impulses of less than 1.5 seconds duration, while seals of larger vessels in the neighborhood of 7-8 mm diameter are achieved with electrical impulses of about 1.5-2.0 seconds duration. Electrical impulses having a time duration of up to about 4.0 seconds are effective in some situations involving very large vessels, more massive amounts of high-density tissue, low thermal conductivity tissue, and/or lower temperatures.

Achieving consistent, reliable seals and simultaneous cuts on a wide range of different sizes and types of vessels provides a significant procedural advantage over known prior art tissue sealing apparatus. Known prior art vessel sealing techniques are believed to require at least 5-12 seconds of power application before a seal is formed and then the time required to advance a mechanical blade slowly through the sealed area and then withdrawn before the vessel can be released. The advancement of the mechanical blade must progress relatively slowly to avoid distorting the sealed area and compromising the integrity of the sealed area which could lead to a leak. In general, 5-10 seconds is required for manual advancement and retraction of the blade, provided that the blade does not become jammed or stuck. Those known prior art electrothermal systems which attempt sealing and simultaneously cutting require times of at least 30-60 seconds to perform both sealing and simultaneous cutting, and then the cutting is more akin to ragged obliteration rather than a well-defined linear separation. Thus, simultaneous cutting and sealing is accomplished with the present invention considerably more quickly compared to known prior art techniques. In addition, the seal created by the present invention has enhanced integrity and resistance to failure after cutting, compared to prior art seals.

The vessel21exemplifies biological tissue which is sealed and simultaneously cut with the present invention, and the lumen42of the vessel21exemplifies a lumen, duct, passageway, chamber or gap or separation which is to be permanently bonded, occluded, sealed, fused or joined. The actions of bonding, occluding, sealing, fusing or joining tissues are collectively referred to herein as fusion or sealing. The action of separating the tissue after it has been fused or sealed is referred to herein as cutting or separation. In addition to the vessel21, which may be an artery or a vein, other specific examples of biological tissue which may be fused or sealed and thereafter cut include fallopian tubes, bile ducts, tissue surrounding an aveoli or air sac in the lung, the colon or bowel, or any other tissue where surgical ligation might be performed. In most but not necessarily all of the cases where tissue fusion or sealing and simultaneous cutting is performed, the purpose of sealing or fusing the tissue is to confine a fluid or other bodily substance and its associated flow within a passageway which is either defined by or closed by fusing or sealing and the purpose of cutting the tissue is to excise tissue for surgical purposes. Therefore, in accordance with a naming convention followed in this detailed description, the walls44of the vessel21are examples of apposite pieces of biological tissue which are fused or sealed, the lumen42of the vessel21is an example of a passageway which is permanently occluded or closed or defined by sealing the apposite walls44at the interface46of the vessel21, and an example of cutting the tissue occurs through the sealed area50along the separation line51with the apposite walls44sealed at the interface46occluding the lumen of the vessel on opposite sides of the separation line51.

The smoothness of the working surfaces38and40of the high thermal conductivity jaws34and36contributes to creating seals of high integrity and cutting the tissue in a short amount of time. Smooth working surfaces38and40release the fused and separated tissue from the jaws34and36without sticking when the jaws separate (FIG. 6), despite the relatively high temperature of those jaws when compressing them against the tissue during fusion and simultaneous cutting. Preventing the tissue from sticking to the jaws as they separate avoids pulling the fused vessel walls apart, which could destroy or weaken the sealed area. Consequently, the fused interface of the vessel walls will have substantially all of the integrity and strength created by the fusion process, and that integrity and strength is not diminished by separation forces when the jaws separate. The smooth working surfaces38and40decrease the risk that the seal will ultimately fail.

Tissue sticking to the working surfaces of the heated jaws is a substantial problem in prior art devices. If the tissue sticks to the jaws as they separate, the integrity of the fused interface at the sealed area of the vessel will be compromised by the tendency to pull the sealed vessel walls apart at the fused interface46. Even if the fused apposite vessel walls are not separated at the fusion interface, the separation force may weaken the walls enough to allow the natural fluid pressure within the lumen or passageway to eventually separate the vessel walls and create a leak.

Quickly achieving seals of high integrity while simultaneously cutting the tissue is also facilitated by an even distribution of compression, force or pressure across the squeezed vessel walls44at the interface46(FIG. 4). The even force or pressure distribution across the tissue interface46is obtained by parallel movement of the working surfaces38and40toward one another when compressing the vessel21(FIGS. 4 and 5). The parallel movement mechanism28causes the jaws34and36and their respective working surfaces38and40to move parallel to each other when opening and closing and compressing and releasing the vessel. The parallel movement of the jaws34and36avoids introducing shear forces on the sealed tissue interfaces46of the separated vessel pieces (FIGS. 4 and 5) when the jaws separate. Shear forces have the effect of weakening the sealed tissue interface and diminishing the strength of the seal created on each of the separated vessel pieces.

Details of the parallel movement mechanism28of the instrument22are explained and shown mainly in conjunction withFIG. 7but also inFIGS. 1, 2 and 6. The proximal handles24and26pivot with respect to one another in opening and closing movements. The parallel movement mechanism28transfers the force created by the opening and closing movements of the handles24and26into parallel opening and closing movement of the distal arms30and32. The parallel opening and closing movement occurs over the range of movement where the tissue is compressed between the working surfaces of the jaws during tissue fusion to the point where the working surfaces38and40contact one another with a zero distance gap therebetween. The parallel movement avoids introducing adverse shear forces on the fused tissue and creates even force and pressure on the tissue when compressed for fusion and cutting.

The parallel movement mechanism28is enclosed within a housing52(FIGS. 1, 2 and 6). The housing52is formed by a rear wall member54and a front closure member56which includes integral top, bottom and side wall portions which enclose internal components of the parallel movement mechanism28. Openings are formed in the integral side wall portions of the front closure member56to allow the handles24and26and the arms30and32to extend into the housing52.

The top handle24is integrally attached at its distal end to a block62, and the block62is rigidly attached to the rear wall member54by pins64. The bottom arm32is formed integrally with the rear wall member54. Thus, both the top handle24and the bottom arm32are rigidly connected relative to the rear wall member54. Thus, the top handle24and the bottom arm32do not move relative to one another or relative to the rear wall member54or the housing52. Only the bottom handle26and the top arm30and jaw34move relative to the stationary top handle24and the bottom arm32.

The bottom handle26is pivotally connected to the rear wall member54at a pivot pin66. The bottom handle26pivots around the pivot pin66. When the top and bottom handles24and26are separated or moved toward one another, only the bottom handle26possesses the freedom to pivot. The pivot pin66is located slightly proximally from the distal end of the bottom handle26.

The top arm30has a flange68integrally attached to its proximal end. The flange68extends generally parallel to the rear wall member54. As the top arm30moves upward and downward, the flange68moves upward and downward with the top arm30within the housing52between the rear wall and front closure members54and56.

A rail70is rigidly attached to the rear wall member54by pins72. The rail70extends perpendicularly relative to the extension of the bottom arm32. The rail70projects outward from the rear wall member54toward the flange68. A guide block74is attached to the flange68by pins78. The guide block includes a center channel76which conforms to the cross-sectional shape of the rail70and which movably receives and surrounds the rail70. The size of the center channel76permits a slight clearance on each the three lateral sides of the rail70which extend outward from the rear wall member54. The guide block74, flange68and the attached top distal arm30are therefore movable along a path defined by the rail70and relative to the rear wall member54.

The rail70is oriented perpendicularly to both the top and bottom arms30, and therefore movement of the top arm30maintains the same parallel angular relationship with the bottom arm32. The rail70has substantial structure to withstand the torque applied to the distal end of the top arm30during tissue compression to maintain the same relative angular relationship of the top arm30with the bottom arm32.

One end of a link80is pivotally connected at the distal end of the bottom handle26by a pivot pin82. The other end of the link80is pivotally connected to the flange68by another pivot pin84. Upon the clockwise (as shown inFIG. 7) pivoting movement of the bottom handle26relative to the top handle24, the distal end of the bottom handle26transfers upward force through the link80to the flange68. The flange68moves upward along the rail70, and causes the connected top arm30to separate from the bottom arm32. Consequently, an opening movement of the bottom handle26relative to the top handle24causes an opening separation movement of the top arm30relative to the bottom arm32. A gap or separation is created between the working surfaces38and40of the top and bottom jaws34and36by the separation movement of the bottom arm32relative to the top arm30.

Closing the top and bottom handles24and26moves the distal end of the bottom handle26downward, causing the link80to move the flange68downward along the rail70. The top arm30moves downward toward the stationary bottom arm32, thereby closing the gap between the working surfaces38and40of the top and bottom jaws34and36.

The movement of the top arm30is restricted by the orientation of the rail70and the guide block74which is connected to the flange68. Because the guide block74can only move vertically as dictated by the rail70, the flange68and the integrally attached top arm30can only move vertically as well. The vertical motion requires the parallel angular relationship of the top and bottom jaws34and36to remain constant as the top arm30opens and closes relative to the bottom arm32.

The jaws34and36are attached to the top and bottom arms30and32so that the working surfaces38and40of the jaws34and36extend parallel with one another in a longitudinal dimension extending along the arms30and32. The transverse dimension of the working surfaces38and40may also be planar with respect to one another (FIG. 12), but preferably one of the working surfaces has a slight convex or crowned shape (FIG. 13) while the other working surface is planar.

The parallel movement of the top and bottom arms30and32and the top and bottom jaws34and36allows the working surfaces38and40to apply and distribute force evenly across the compressed interface46(FIG. 4) and until the compressed tissue is separated at the parting line51(FIG. 5). The even force application is important to obtain even and uniform reconstitution of the denatured protein chains during fusion and even and uniform parting of the tissue along the separation line51during cutting, all of which results in enhanced strength and integrity of the sealed interface46(FIG. 4) and the sealed areas50(FIGS. 6 and 20) adjacent to the separation line51. The parallel movement of the working surfaces38and40does not impart any shearing force on the sealed areas50(FIGS. 6 and 20) as the working surfaces38and40separate from one another. Such a shearing force could compromise the integrity of the fused interface46(FIG. 4), apart from whether the heated, compressed and cut vessel21has any tendency to stick to the working surfaces of the jaws as they separate.

The mechanical advantage resulting from closing the handles24and26, transferred through the parallel movement mechanism28, moves the arms30and32and jaws34and36to compress and cut the vessel21uniformly at each point on the interface46of the two apposite vessel walls44. The applied force results in compressing the heated pieces of tissue to a compressed tissue thickness sufficient to fuse the tissue pieces, which in the case of blood vessels is about 0.05-0.10 mm, at which point fusion occurs. Continued compression of the pieces of tissue until a thickness of approximately zero (no gap) is achieved between the working surfaces results in cutting the tissue, after it has been fused. In order to achieve this range of compression, the parallel movement mechanism28must obtain an adequate mechanical advantage to transfer a comfortable amount of force applied on the handles24and26to the tissue. The force is related to the pressure between the working surfaces38and40. The pressure is determined by the confrontational surface areas of the working surfaces38and40and the amount of force applied to the arms30and32.

In a preferred embodiment, the working surfaces have a length of about 25 mm and a transverse width of about 5 mm, creating an effective confrontational surface area of approximately 125 mm2. The mechanical advantage must therefore be capable of producing pressure of at least 1.2 Newtons per square millimeter (N/mm2) with comfortable squeezing pressure on the handles24and26. Producing a pressure of 1.2 N/mm2will assure a force of 150 N at each point of the compressed apposite tissue followed by severing of the tissue as a result of the force creating a zero gap between the working surfaces. Producing a pressure of 0.88-1.2 N/Mm2will assure a force of 110 N-150 N at each point of the compressed apposite tissue before it is severed. Because the pressure may vary according to the size of tissue squeezed between the working surfaces38and40, the force applied at each point to the two pieces of compressed tissue is a measure of the effectiveness of the compression necessary to achieve good tissue fusion and cutting. However, pressure must be considered to assure that an adequate amount of compression force is available to ultimately achieve the zero or no distance gap between the working surfaces38and40of the jaws34and36to cut the tissue following fusion.

Details of the jaws34and36are better understood by reference toFIGS. 3-5 and 8-13. Each jaw34and36is essentially of the same structure and configuration, although the top and bottom jaws may be of a mirror image configuration with respect to one another. Each jaw34and36is preferably formed of a ceramic material with a high thermal conductivity, such as aluminum nitride. The jaws34and36are secured to the arms30and32with an adhesive, such as epoxy, which is applied in a layer86between the jaws34and36and the arms30and32. Insulating spacers90are positioned near the distal and proximal ends of each of the jaws34and36between the jaws34and36and the arms30and32. The adhesive layer86occupies the spaces between the spacers90, the jaws34and36and the arms30and32.

The heating elements49are embedded in the ceramic material of the jaws34and36, as shown inFIGS. 8, 10 and 11. The heating element49in each jaw34and36is essentially the same. Similarly, both jaws34and36are essentially the same, except with respect to the possibility of one or both of the jaws having a crowned working surface (FIG. 13) and the two jaws being mirror image configurations with respect to one another. Because of the similarities, the heating element49and the jaw36are described in conjunction withFIGS. 9-13, with the understanding that the heating element49and the jaw34are essentially the same.

The heating element49is formed by a length of an electrically conductive resistance material which produces heat when conducting electrical current. The heating element49has a high thermal shock withstanding capability and a high power density conducting capability. An example of one such electrically conductive resistance material which offers these capabilities is molybdenum. The heating element49extends substantially over the area of the jaw36(FIG. 11) so that heat is produced relatively uniformly throughout the jaw. The heat from the heating element49is conducted substantially uniformly through the jaw36due to the high thermal conductivity of the ceramic material from which the jaw36is formed, resulting in approximately equal temperature from point to point along the working surface40of the jaw36.

Electrical wires96and98connect to opposite ends of the heating element49. Electrical current is supplied to the heating element49through the wires96and98. The wires96and98extend through shoulders100and102which are formed on a back side104of the jaw from the same ceramic material as the jaw36. The shoulders100and102surround and support the wires96and98and hold them in position as part of the jaw36. The ceramic material of the jaw36is an electrical insulator, thereby assuring that the current conducted through the wires96and98flows through the heating element49without short-circuiting to the arms30and32of the instrument22(FIG. 1).

To embed the heating element49within the jaw36, enough powdered ceramic material to form the working surface40and the outer portion of the jaw36is placed in a mold and sintered. Thereafter, the heating element49is placed on this outer partially-formed jaw portion, preferably by using conventional fluid deposition techniques such as inking. More powdered ceramic material is then placed on top of the sintered outer portion of the jaw and the heating element49to form the remaining inner portion of the jaw including back side104and the shoulders100and102. Thereafter, the powdered ceramic material which forms the inner portion of the jaw is sintered to form the ceramic inner portion of the jaw36while also sintering that inner portion of the jaw36to the previously-formed outer portion of the jaw36, thereby completing the integral ceramic structure of the jaw.

In addition to embedding the heating element49within the jaw in the manner described, the heating element can also be embedded by following the described procedure but without sintering the outer portion until the inner portion has also been formed. A single sintering occurs with respect to both the outer and inner portions simultaneously to hold the heating element in place.

The wires96and98are mechanically and electrically connected to the ends of the heating element49by drilling holes through the shoulders100and102until the holes contact the ends of the embedded heating element49. The wires96and98are inserted through the holes until the ends of these wires contact the ends of the heating element49. The ends of the wires96and98and the ends of the heating element49are permanently connected together by brazing in an oven. The wires96and98and the shoulders100and102therefore extend from the back side104of the jaw36.

When the jaws34and36are attached to the arms30and32, respectively, by the adhesive layer86, the wires96and98extend through openings105and107which are formed in each of the arms30and32to receive the wires96and98, as shown inFIGS. 8 and 10. The openings105and107are sufficiently large to avoid electrical contact with the wires96and98, although the wires96and98are insulated in the areas within the openings105and107. Conductors106and108connect to the ends of the wires96and98. The conductors106and108from each jaw34and36extend through the housing52of the parallel movement mechanism28and along the top handle24to the power control device48, as shown inFIGS. 1 and 2. The power control device48delivers the electrical current through the conductors106and108to the heating element49in each jaw34and36, thereby heating the jaws.

The current supplied by the power control device48(FIGS. 1 and 2) is regulated relative to the temperature of the working surfaces38and40of the jaws34and36. The temperature of each jaw is separately measured by a thermocouple110associated with each jaw, shown inFIGS. 3-5, 7 and 9. The thermocouple110associated with each jaw34and36is essentially the same. Therefore, only one thermocouple110is described in association with the jaw36shown inFIG. 10, since the other thermocouple is substantially identical.

The thermocouple110comprises an electrical node or junction112of two dissimilar metal wires116and118, as shown inFIG. 10. The junction of the two dissimilar wires116and118creates a conventional type JT/C thermocouple junction112. A slight voltage is developed at the junction112by the inherent electrical characteristics of the two dissimilar metal wires116and118, and the magnitude of that voltage varies in relationship to the temperature of the junction112. Thus, the voltage developed at the junction112is related to the temperature of the junction112. The wires116and118extend through an opening119formed in each arm30and32(FIGS. 3-5). The wires116and118may be insulated over that portion of their length which extends through the opening119.

The voltage developed at the junction112is conducted through the wires116and118to conductors120and122, which connect to the ends of the wires116and118, respectively. The conductors120and122extend from the thermocouple110of each jaw34and36through the housing52of the parallel movement mechanism28and along the top handle24to the power control device48, as shown inFIGS. 1 and 2. The voltage from the thermocouple110, conducted through the conductors120and122, is used by the power control device48as a feedback signal to control the amount of electrical current delivered through the conductors106and108and the wires96and98to the heating element49in the jaws34and36, thereby independently regulating the temperature of the working surfaces of the jaws.

The thermocouple110is permanently thermally and mechanically attached to the jaw by oven brazing the junction112of the dissimilar metal wires116and118within a recess114formed into the ceramic material on the back side104of each jaw, as shown inFIG. 10. The attachment of the junction112to each jaw establishes good thermal conductivity of the junction112with each jaw, thereby enabling the junction112to respond to the temperature of the jaw. The high thermal conductivity material of each jaw distributes the heat from the heating element49throughout the jaw relatively rapidly. The temperature of the working surface of the jaw is typically slightly different from the temperature of the junction112because the junction112is not exactly at the working surface and slight dynamic thermal gradients exist within the jaw despite the high thermal conductivity of the jaw material. However, the temperature measured by the thermocouple junction112is closely correlated to the temperature of the working surface of the jaw, to result in temperature measurements which closely represent the temperature of the jaw working surface. Moreover, because the tissue compressed between the jaws during tissue fusion is relatively thin, the thermal transfer to the thin tissue causes that tissue to assume a temperature which is very close to the temperature of the jaw working surfaces.

Both of the working surfaces38and40may be flat and planar as shown inFIG. 12. In such circumstances the planar working surfaces are maintained in a parallel relationship with one another by the positioning of the jaws34and36on the arms and by the parallel movement of the arms30and32. Longitudinal edges124of the jaws34and36are rounded or radiused to avoid imparting or concentrating pressure to the vessel21in such a way to weaken the vessel at the edge of seal formed or to cut the vessel at the edge of the sealed area, thereby creating a weakened sealed area.

A preferred alternative to the planar configuration of the working surfaces38and40is one flat planar working surface and a crowned working surface on the opposite jaw. Both working surfaces could also be crowned. A crowned working surface40is shown inFIG. 13. The working surface40possesses a slight outward convex shape when viewed transversely to the longitudinal dimension of the jaw36, as shown inFIG. 13. The crowned or convex curvature of the working surface is useful for applying more force to the vessel at the center of the working surface for cutting the sealed area, while simultaneously creating a slightly graduated variation in the extent of tissue compression from the center of the working surface to the longitudinal radiused edges124. The slight variation in compression is instrumental in achieving separation of tissue along the separation line51(FIGS. 6 and 20) while simultaneously achieving an optimal sealing force on the tissue squeezed between the working surfaces38and40. However, in most cases, once adequate pressure is obtained, it is not necessary to achieve optimal pressure to accomplish adequate fusion with the present invention, so long as sufficient force is ultimately applied to reduce the thickness of compressed tissue to zero between the working surfaces along the separation line51at the fused area.

The curvature of the crowned working surface40of the jaw is in the transverse direction across the working surface. The amount of curvature of the working surface40, as shown inFIG. 13, is such that the radius of curvature of the working surface40in the transverse dimension is approximately 21 mm at a point where the transverse width of the jaw is approximately 5 mm. This radius of curvature generally causes the center of the crowned working surface to be approximately 0.1 mm higher than the working surfaces near the longitudinal edges124of the 5 mm wide jaw36, before those longitudinal edges124are radiused.

Each of the jaws34and36also curves laterally to the side, in the general shape of the typical “Maryland” jaw shape which is frequently preferred by surgeons, as shown inFIGS. 1, 2, 6-9 and 11. Furthermore the most forward or distal end of each of the jaws34and36has a reduced transverse dimension compared to the transverse dimension of the proximal or rearward end. This “Maryland” jaw shape facilitates viewing the jaws monoscopically during minimally invasive surgery, and the lesser transverse dimension of the distal end is useful for blunt dissection. The point of maximum convex curvature of the crowned working surfaces of such “Maryland” jaws extends on a curve which is approximately equidistant transverse between the edges of the jaws. Cutting occurs along the curved array of linear points of maximum convex curvature, and it is through the curved shape of the jaws that electrothermal cutting is accomplished on a linear curve. The curved cutting is reflected in the curvature of the separation line51.

An important aspect of the present invention is that the working surfaces38and40, and preferably side surfaces123and125(FIGS. 9, 12 and 13) and the radiused longitudinal edges124of the jaws34and36, have a high degree of smoothness. A sufficiently high degree of smoothness is capable of preventing any sticking of the compressed and heated tissue to the jaws34and36after the vessel21has been sealed and cut. The smoothness of the side surfaces123in125similarly prevents any overhanging tissue adjacent to the working surfaces38and40from sticking to the jaws34and36when the vessel21is sealed and cut. Eliminating the occurrence of tissue sticking to the jaws is a substantial improvement because sticking tissue is responsible for destroying or substantially weakening the seal in a significant proportion of those incidents where the seal fails. Eliminating the occurrence of tissue sticking to the jaws also offers a substantial convenience to surgeons, because a considerable amount of time is consumed during the surgical procedure in cleaning the jaws of adhered tissue. By avoiding the necessity to clean the jaws, a time required to perform the surgical procedure is diminished, resulting in reduced risk and trauma to the patient.

The conventional measurement of smoothness is referred to as Ra. To achieve the degree of smoothness most desirable in accordance with the present invention, the working surfaces38and40, the side surfaces123and125and the longitudinally radiused edges124of the jaws34and36, are formed from a ceramic material, such as aluminum nitride, or a material having a surface microstructure like ceramic material, and such surfaces have an Ra of 0.15 microns or less. Jaws formed of aluminum nitride with surfaces having a smoothness represented by an Ra of 0.15 microns or less have been determined to result in no tissue sticking to the jaws after fusion and cut procedure has been completed and the jaws are separated.

For jaw surface smoothness in the Ra range of 0.15 to 0.40 microns, a spectrum of smoothness exists where the frequency of sticking increases in relation to decreasing smoothness, although the frequency of sticking is not in a linear relationship to decreasing smoothness. For a small increase in smoothness at the lower end of the range, a large reduction in the frequency of tissue sticking occurs. For an Ra of 0.15 microns or less, no sticking of the tissue has been observed, and the force required to separate the working surfaces from the vessel is not significantly different than if the vessel had not been present between the working surfaces. For an Ra range of 0.15 to 0.20 microns, sticking does not occur or only occurs with very minimal or virtually nonexistent frequency, and the force required to separate the working surfaces from the sealed and cut vessel is not significantly greater than the force required to separate the working surfaces from the sealed and cut vessel when the Ra is less than 0.15 microns. In the Ra range of 0.20 to 0.25 microns, sticking occurs with a slightly greater frequency, and the force required to separate the tissue from the working surfaces is slightly increased. In the Ra range of 0.25 to 0.40 microns, a moderate increase in the frequency of sticking occurs, and the force required to separate the tissue from the working surfaces is also moderately increased. Finally, in the Ra range of 0.40 to 0.50 microns, sticking becomes significantly more frequent and the force required to separate the tissue from the working surfaces is further increased. However, an Ra in the range of 0.40 to 0.50 microns provides less tissue sticking than with the known prior art jaws used for tissue fusion by itself, or tissue fusion and simultaneous cutting, or for those jaws which have an Ra of about 0.60 microns or greater.

The sticking of tissue described herein applies to that tissue upon which pressure has been applied from the working surfaces during tissue fusion and cutting. Sticking is not intended to apply to any tissue or fluid, such as blood, which remains on the working surfaces after the jaws have been separated and the sealed and cut tissue is removed from the working surfaces. Although tissue and fluid may remain on the working surfaces after the tissue is removed, such tissue and dried fluid may easily be wiped from the working surfaces.

A conventional profilometer is used to measure the roughness of the working surfaces and to obtain the Ra values described herein. One example of such a commercially available profilometer is a Pocket Surf® portable surface roughness gauge manufactured by Mahr Federal, Inc. of Germany. Prior to measuring the roughness of the working surfaces, the profilometer was calibrated using a reference that had a known Ra. The Ra reference was certified against a known standard in accordance with ISO or ANSI standard procedures. The exemplary profilometer employed to obtain the Ra measurements described herein had an accuracy of ±0.05 microns and a resolution of 0.01 microns.

One useful ceramic material from which to form the jaws34and36is aluminum nitride. Aluminum nitride has a relatively high thermal conductivity of about 140-180 W/m° K. Aluminum nitride can also be polished to a smoothness of an Ra of 0.15 microns or less. When removed from the sintering oven after formation in a smooth mold, aluminum nitride can have an Ra as low as 0.60 microns, but not significantly lower. Working surfaces with an Ra of 0.60 microns appear smooth, but that apparent smoothness is above the acceptable range of Ra in accordance with the present invention.

Any polishing or other smoothing technique that can achieve the desired degree of smoothness of the working surfaces may be employed in accordance with the present invention. A satisfactory level of smoothness of the working surfaces of aluminum nitride jaws has been achieved by polishing the working surfaces using various grits of diamond paper or diamond pastes. Finer grades of abrasives were used in succession as the polishing proceeded toward the desired smoothness. The desired degree of smoothness was achieved by polishing the working surfaces by hand, successively using diamond grit paper with particle sizes of 6, 3, 1, 0.50, 0.25 and 0.10 microns in that order.

If the polishing is initiated with a grinding wheel or grit paper having a too coarse particle size, the working surface may be damaged and roughened to the extent that the desired smoothness can not be achieved when finer grits are used subsequently in the polishing process. When starting the polishing with too coarse of a particle size, the highest degree of smoothness (Ra of 0.15 microns or less) is difficult or impossible to achieve on aluminum nitride ceramic surfaces.

A strictly uniform smoothness across the working surfaces38and40is not required. Only those portions of the working surfaces38and40which contact the vessel21(FIG. 2) must be smoothed to the desired degree to obtain reduced tissue sticking. Thus, to the extent that the side surfaces123and125do not touch tissue, they may not require the same degree of smoothness as the working surfaces38and40and the longitudinal radiused edges124.

The amount of force transferred from the working surfaces38and40of the jaws34and36to the vessel21is measured by a conventional strain gauge126attached to a section128of the top proximal handle24, shown inFIG. 7. The section128of the top handle24has a reduced cross-sectional area. The strain gauge126is attached to extend longitudinally along the reduced cross-sectional area section128. Attached in this manner, the strain gauge126measures the amount of deflection of the section128created by the force resulting from squeezing the handles24and26together. The extent of deflection of the section128is accurately correlated to the amount of force applied from the distal arms30and32to the tissue squeezed between the working surfaces38and40(FIG. 4) and as the tissue separates when the distance between the working surfaces38and40approaches zero (FIG. 5). The signals from the strain gauge126are conducted through two conductors, collectively referenced130, to the power control device48, where those force-related signals are used to create a display of the force imparted to the compressed tissue and to control the power control device48.

A handle locking and release mechanism131is connected to the proximal ends of the handles24and26, as shown mainly inFIG. 7, and also inFIGS. 1, 2 and 6. The handle locking and release mechanism131includes a curved extension132with ratchet teeth134that extends downward from the proximal end of the top handle24. The bottom handle26includes a ratchet pawl136that extends rearward from the proximal end of the bottom handle26. The ratchet pawl136is connected to a rod138which extends longitudinally within the interior of the bottom handle26. A spring140is connected between a proximal end of the rod138and a shoulder141of the bottom handle26. The spring140is compressed and normally biases the rod138in the rearward direction. The normal rearward bias from the spring140on the rod138extends the ratchet pawl136rearward from the proximal end of the bottom handle26.

When the handles24and26are squeezed together, the ratchet pawl136slides by and engages the individual ratchet teeth134in succession, until the handles24and26reach a squeezed-together position where the desired amount of force is applied on the compressed vessel21. The handles can not separate or open because the ratchet pawl136is engaged with the ratchet teeth134, thereby allowing the working surfaces38and40to maintain force on the compressed vessel21during fusion. The handle locking and release mechanism131allows an adequate and substantial amount of force or pressure to be maintained on the vessel21during fusion without requiring the surgeon to continually squeeze the handles24and26. The handle locking and release mechanism131also prevents the force or pressure on the compressed vessel from substantially decreasing during the tissue fusion and simultaneous cutting procedure. The interaction of the ratchet pawl136with the ratchet teeth134prevents the handles24and26from moving apart from their squeezed-together position, until the ratchet pawl136is separated from the ratchet teeth134.

The handle locking and release mechanism131includes a trigger142which, when squeezed, separates the ratchet pawl136from the ratchet teeth134and thereby allows the handles24and26to open with respect to one another. The trigger142includes a contact arm144which contacts and interacts with a shoulder146at the distal end of the rod138. The normal bias from the spring140on the rod138biases the shoulder146against the contact arm144, and causes the trigger142to assume the normal position shown inFIG. 2, with a release arm148of the trigger142extending generally parallel with the elongated dimension of the bottom handle26. To disengage the ratchet pawl136from the ratchet teeth134, the trigger142is squeezed which causes the release arm148to pivot counterclockwise as shown inFIG. 7. The counterclockwise movement of the contact arm144against the shoulder146moves the rod138in the distal direction, as shown inFIG. 7, and the distal movement of the rod136releases the engagement of the ratchet pawl136with the ratchet teeth134. With the ratchet pawl136released from the ratchet teeth134, the handles24and26are free to move away from one another.

The following example illustrates the utility of the smooth working surfaces38and40in tissue fusion and simultaneous cutting. In two separate laboratory experiments, tissue fusion and simultaneous cutting was performed on mesentery and spleen tissue. The tissue fusion and cutting instrument used in the experiment had aluminum nitride jaws which had been hand polished to an Ra of about 0.15 microns as determined by at least five measurements over the working surfaces. The aluminum nitride ceramic jaws had a width dimension of 5 mm and a length dimension of 25 mm and a thickness dimension of 1.5 mm. One of the working surfaces was crowned (FIG. 13) and the other working surface was flat or planar (FIG. 12). Each sample of tissue was compressed between the jaw working surfaces with a force sufficient to reduce the gap between the working surfaces to zero at the conclusion of the procedure, thereby cutting the tissue. An impulse of power having a power density of 1500 W/in2(233 W/cm2) was delivered by the power control device48(FIG. 1) to the heating elements in the jaws. The power impulse used in fusing and simultaneous cutting the mesentery had a 2.0 second time duration. The power impulse used in fusing and simultaneously cutting the spleen had a 1.5 second time duration. The power impulses produced in both instances contained enough thermal energy to successfully seal the tissue as well as simultaneously cut the tissue. The thermocouples of the jaws recorded peak temperatures of the jaw working surfaces of about 230° C. when fusing and simultaneously cutting the mesentery and recorded peak temperatures of the jaw working surfaces of about 240° C. when fusing and simultaneously cutting the spleen.

When cutting the mesentery, 5 consecutive cuts were performed for a total length of the cut of approximately 125 mm. The total time required to cut the entire 125 mm length was approximately 38 seconds. Following the mesentery cut procedure, a blue sheet was placed underneath the cut portion of the mesentery and the mesenteric vessels were inspected for bleeding. No bleeding was observed. When cutting the spleen, 5 consecutive cuts were performed on previously unaffected live tissue, with no adverse bleeding from the sealed areas adjoining the separation line. Eleven other cuts were performed at locations which overlap areas which had previously only been sealed. In other words, the 11 cuts were a second procedure performed on top of an area which had previously been sealed only without cutting. Again, under such circumstances, no adverse consequences or deterioration of the sealed areas was observed.

After each fusion and simultaneous cut procedure was performed, the jaws were separated to release the fused and cut tissue. The tissue was considered stuck to one of the working surfaces if the fused and cut tissue did not separate itself immediately from the working surface which contacted the tissue. Of the tissue samples which were fused and simultaneously cut in these experiments, none adhered to the working surfaces of the jaws using this sticking evaluation criteria. Moreover, on occasion, blood or other tissue was present on the working surfaces of the jaws before the tissue sample was compressed between the jaws. Even in these adverse situations, the tissue did not stick to the smooth working surfaces. The blood or other tissue initially present on the jaws adhered to the tissue sample which had been fused and simultaneously cut, thereby producing clean working surfaces, but there was no adherence between the fused and cut tissue and the smooth working surfaces. Use of the present invention subsequent to these experiments have also confirmed the non-stick performance of the polished working surfaces.

More details concerning the power control device48are shown inFIGS. 14-15. As shown inFIG. 14, the power control device48includes a controller150which includes a memory152and a processor154. The memory152stores data and information supplied by conventional input devices156and/or supplied from a touch screen (not shown) of a conventional monitor158. The information stored in the memory152includes criteria160which establish the parameters for one or more standard tissue fusion and simultaneous cutting procedures. The standard procedure criteria160includes information describing the temperature to be attained at the working surfaces38and40of the jaws34and36of the instrument22, the amount of force to be applied by the jaws34and36to the vessel21or other tissue during the procedure, and the amount of time during which electrical power is to be delivered to heat the jaws34and36to perform the procedure.

In addition, the memory152stores certain user-selected criteria162which can be used in place of some or all the standard procedure criteria160to accomplish tissue fusion and simultaneous cutting. The ability to select and alter the criteria162allows the user to adjust the fusion criteria to the surgeon's preferences or to perform procedures which may be better accomplished by using user-selected criteria rather than standard criteria.

The memory152also stores the instructional code which defines certain functional routines164. The functional routines164cause the processor154to control the power delivered to the jaws34and36. The functional routines164also contain control constants and gain factors that are used when the processor164executes certain functional routines, as illustrated by the examples described below.

One of the functional routines executed by the processor154is a temperature control feedback routine166. The temperature control feedback routine166is executed in response to temperature signals168and170obtained from the sensing of the temperatures of the top jaw34and the bottom jaw36by their respective thermocouples110(FIG. 10) and supplied over the conductors120and122. The processor154responds to the individual temperature signals168and170from each of the top and bottom jaws34and36and separately regulates the amount of electrical power supplied to each top and bottom jaw heating element49. In doing so, the processor154executes the same temperature control feedback routine166for each jaw34and36, thereby separately regulating the temperature of each jaw34and36. In most cases, it is desired that the temperatures of both jaws34and36be the same during the procedure, but different amounts of electrical power may be required to cause each jaw34and36to attain and maintain the desired temperature, due to different thermal loads imposed by different physiology of the tissue or vessel21contacted by each jaw34and36.

The processor154creates switching signals172and174which are supplied to conventional controllable switches176and178, such as solid-state relays. In response to the switching signals172and174, the controllable switches176and178conduct electrical power from a conventional adjustable low-voltage, high-current direct current (DC) power supply180to the heating element49of the top jaw34and to the heating element49of the bottom jaw36.

By separately controlling the characteristics of the switching signals172and174, the conductivity characteristics of the controllable switches176and178are also separately varied to separately control the amount of electrical power delivered to each heating element49of the top and bottom jaws over the conductors106and108. In this manner, the amount of electrical power, and consequently heat available at each of the jaws34and36, is varied independently in each jaw.

The processor154also executes a criteria comparison routine184. The criteria comparison routine184utilizes the temperature signals168and170from the top and bottom jaws and a force signal186supplied over the conductors130from the strain gauge126, as well as internally generated time duration information which is measured from the time that the impulse of electrical power is applied to the jaws34and36. Execution of the comparison routine184creates information which is presented on the monitor158as graphs or other presentations of the temperature signals168and170, the force signal186and the elapsed time. The temperature of each jaw34and36may be displayed separately on the monitor158, while the force and the time are presented singularly with respect to each separate fusion procedure.

Execution of the comparison routine184also compares the temperature signals168and170, the force signal186and the elapsed time to corresponding limits or values of the temperature, force and elapsed time established by the standard procedure criteria160or by the user-selected criteria162for the tissue fusion and simultaneous cutting procedure. The result of comparing the actual temperatures, force and elapsed time to the procedure criteria limits or values is information which is supplied to the monitor158and/or an annunciator188. Execution of the comparison routine184identifies if and when the actual operative values associated with the tissue fusion and simultaneous cutting procedure fall outside of the procedure criteria limits or values. Under circumstances where the actual operative values achieve or deviate from the established procedure criteria values, visual and/or audible signals are delivered from the annunciator188, and related signals may also be presented visually on the monitor158.

For example, execution of the comparison routine184establishes the time instant at which electrical power impulse is delivered to the jaw heating elements. The comparison routine184monitors the force signal186to determine when the vessel21has been compressed sufficiently to apply the electrical power impulse for heating the jaws34and36. A certain force limit must be exceeded by squeezing the handles24and26before the controller150recognizes that a tissue fusion and simultaneous cutting procedure is underway. Once the initial force limit value is attained, the controller150delivers the control signals172and174to the controllable switches176and178to apply electrical power to the heating element49of the top and bottom jaws, thereby heating the working surfaces of the jaws34and36. Simultaneously, the comparison routine184begins timing the time duration at which the electrical power is delivered at the selected temperature for the procedure.

As another example of the execution of the comparison routine184, once it is recognized that the temperature of the working surfaces38and40of the jaws34and36has reached the selected temperature, a signal is delivered from the annunciator188. Under circumstances where one or both of the top and bottom jaw temperatures exceed or fall below the temperature limits, or under circumstances where the force between the jaws34and36has not reached the desired final level or exceeds or falls below the desired final level, an out-of-criteria signal is delivered from the annunciator188. Such limit information may also be presented on the monitor158as well, and is used by the surgeon during use of the instrument22.

A temperature feedback power control routine166, which offers the well-known and significant advantage of predictive capability, is a proportional, integral, derivative (PID) computation, represented in functional block diagram form shown inFIG. 15by a temperature control feedback circuit190. The PID temperature control feedback circuit190is shown as interconnected individual functional devices, but the PID functionality represented by the circuit190may also be executed by the instructional code executed by the processor154of the controller150(FIG. 14).

The temperature signal168or170supplied by the top or bottom thermocouple110of jaw34or36(FIG. 15) is multiplied in an amplifier192by a scaling factor Kj which converts the value of the temperature signal168or170from the jaw itself to a scaled temperature signal194. The scale temperature signal194represents the temperature of the working surface of the jaw. The application of heat to the jaw from the heating element49(FIG. 11) causes slightly different temperatures at different locations in the jaws. A slight temperature gradient within the jaws causes the temperature at the working surfaces to be different from the temperature at other locations within the jaws, including the temperature at the location which is sensed by the thermocouple110, despite the fact that the jaws are made from high thermal conductivity material. Accordingly, the temperature sensed by the thermocouple is not typically equal to the temperature of the working surface of the jaw which contacts the vessel being sealed. The scaling factor Kj is used to convert the actual thermocouple-sensed temperature signal168or170to the scaled temperature signal194, by multiplying the scaling factor Kj and the actual thermocouple-sensed temperature signal168or170. The result is that the scaled temperature signal194closely approximates the actual temperature of the working surface of the jaw.

The value of the scaling factor Kj is developed empirically, under conditions where the walls44of the vessel21are contacted and squeezed between the jaws. To empirically develop the value of Kj, it is necessary to conduct an actual temperature measurement of the jaw working surface, which can be accomplished by using conventional infrared temperature measurement techniques, for example. The actual temperature measurement is then related to the temperature measurement from the thermocouple to obtain the scaling factor Kj.

The scaling factor Kj may be different depending upon the desired temperature of the working surface of the jaw during the procedure. For example, the selection of a lower working surface temperature for the tissue fusion and simultaneous cutting procedure may result in a lower value for the scaling factor Kj compared to the scaling factor applicable when a higher working surface temperature is selected for a different tissue fusion and simultaneous cutting procedure. The values of the scaling factor Kj are stored in the memory52as part of the standard procedure criteria160(FIG. 14).

The amplifier192supplies a scaled temperature signal194to a negative input terminal of a comparator196. A set temperature signal198is supplied to the positive input terminal of the comparator196. The set temperature signal196represents the desired temperature of the working surfaces of the jaws which is to be attained and maintained during the tissue fusion and simultaneous cutting procedure. The set temperature signal196is one of the standard temperature criteria160or the user-selected temperature criteria162stored in the memory152(FIG. 14).

The comparator196subtracts the scaled temperature signal194from the set temperature signal198, and the result is an error signal200. The error signal200represents the difference between the actual temperature of the working surfaces of the jaw (signal194) and the desired or set temperature of the working surfaces of the jaws for the procedure (signal198). It is the error signal200and the elapsed time that cause the predictive aspects of the proportional, integral and derivative functionality to create a control error signal202which will be used by the processor154to create the switching control signals172and174(FIG. 14). The switching control signals172and174regulate the temperature of the working surfaces38and40of the jaws34and36.

The proportional aspect of the PID functionality is achieved by multiplying the error signal200by a proportional constant Kp in an amplifier204. A proportionalized error signal206is created by the amplifier204and is supplied to one input terminal of a summer208. The value of the proportional constant Kp is established through selection of the standard criteria160or the user-selected criteria162stored in the memory152(FIG. 14).

The integral aspect of the PID functionality is achieved by integrating the error signal200in an integrator210. The integrator210supplies an integrated error signal212which is then multiplied in an amplifier214by an integration constant Ki to create an adjusted integrated error signal216. The adjusted integrated error signal216is applied to another input terminal of the summer208. The value of the integration constant Ki is established through selection of the standard criteria160or the user-selected criteria162stored in the memory152(FIG. 14).

The differential aspect of the PID functionality is achieved by differentiating the error signal200in a differentiator218to create a differentiated error signal220. The differentiated error signal220is then multiplied in an amplifier222by a differentiation constant Kd to create an adjusted differentiated error signal224. The differentiated error signal224is applied to a third input terminal of the summer208. The value of the differentiation constant Kd is established through selection of the standard criteria160or the user-selected criteria162stored in the memory152(FIG. 14).

Although the differentiator218is shown as receiving the error signal200, it is also possible for the differentiator218to respond to the scaled temperature signal194. Under such circumstances, the differentiation of the scaled temperature signal194results in a higher value of the signal220. Under these circumstances the value of the differentiation constant Kd is adjusted to represent the changed value of the signal220.

The proportionalized error signal206, the adjusted integrated error signal216and the adjusted differentiated error signal224are summed together in the summer208. The result of the addition is the control error signal202. The values of the proportional constant Kp, the integration constant Ki and the differentiation constant Kd are all selected to achieve the desired predictive capability resulting from the contribution of the proportionalized, integrated and differentiated error signals206,212and220in creating the control error signal202. Adjusting the values of the PID constants Kp, Ki and Kp in this manner allows the error signal202to achieve the desired degree of control to heat the jaws.

The values of the proportional constant Kp, the integration constant Ki and the differentiation constant Kd are different based upon the desired set temperature and the time for the fusion procedure. The amount of force applied during the fusion procedure may also have an effect on the value of the PID constants Kp, Ki and Kd, although that impact will generally be less than the effect from the desired temperature and time duration of the fusion procedure.

The values of the PID constants Kp, Ki and Kd may remain constant throughout the delivery of power during the course of a single procedure, or they may also be varied during the delivery of power in a single procedure. For example one set of PID constants may be used when increasing the temperature of the working surfaces of the jaws to the desired set temperature, and another set of PID constants may be used to maintain the temperature of the working surfaces at the desired set temperature during the tissue fusion and simultaneous cutting procedure. The criteria comparison routine184executed by the processor154(FIG. 15) substitutes the different proportional constants into the temperature control feedback routine166and the temperature control feedback circuit190according to the temperature of the jaw working surfaces, the elapsed time of the power impulse, and to a lesser degree, the force applied. All of the values of the PID constants are stored in the memory152(FIG. 14).

In response to the control error signal202, the power control device48, shown inFIGS. 14 and 15, delivers an impulse of electrical power which is sufficient to raise the temperature of the working surfaces of the jaws from room temperature to a sealing set point temperature of about 220° C. to 320° C. at a rate greater than 150° C. per second and preferably greater than 500° C. per second. The rate should be as high as possible without creating untoward side effects on the tissue. Of course, the power control device48also has the capability of maintaining the selected temperature for the time duration of the power impulse, which is preferably about 1.5 to 2.0 seconds but which may extend to approximately 4.0 seconds. In general, the impulse of power begins with the switching signals172and174causing the controllable switches176and178to deliver DC current from the power supply180until the temperature of the jaws approaches the set point temperature. Thereafter the switches176and178are turned on and off to maintain the set point temperature during the fusion procedure. In general the on-time decreases and the off time increases to maintain the set point temperature after it is initially achieved. Delivering the impulse of power is effective to quickly establish and maintain a set point temperature creates a strong and effective seal while simultaneously cutting the tissue.

To achieve these temperatures, a power density of about at least 1500 W/in2(2.33 W/mm2) and preferably greater than 2500 W/in2(3.88 W/mm2) is typically required, with the usual power density being in the range of 2500 W/in2to 3000 W/in2(3.878 W/mm2to 4.64 W/mm2). Higher power densities are required to achieve shorter procedure times and to seal and simultaneously cut larger vessels and more massive tissues. However, the power density is not always an accurate representation of the capability of raising and maintaining the working surfaces of the jaws at the desired tissue fusion temperature. The thermal load created by the compressed vessel or tissue is variable, and thus directly influences the power density. Moreover, the distal arms30and32of the instrument22(FIG. 1), the wires96and98and the conductors106and108connected to the jaw heating elements49(FIG. 13) and the dissimilar wires116and118of the thermocouple110and conductors120and122connected to the thermocouples110(FIG. 8) act as heat sinks to transfer thermal energy away from the jaws, thereby making it difficult to account accurately for the amount of energy delivered to the vessel21and that amount of energy dissipated to the instrument22. As a consequence, the temperature of the working surfaces of the jaws is a better indication of the important thermal variable for fusing tissue.

The temperatures of the working surfaces38and40must be sufficiently high to denature the collagen fibers at a temperature of about 60-70° C. and also high enough to denature the elastin fibers at a temperature of about 120° C., and to quickly obtain enough dehydration of the compressed tissue to achieve good reconstitution of the denature proteins chains and to maintain some resiliency or pliability of the sealed tissue while the cut occurs, all before the tissue becomes too dehydrated to permit good fusion. By delivering an impulse of power that can heat the working surfaces of the jaws to temperatures in the range of 220° C. to 320° C. and maintaining that temperature for a preferable time duration of about 1.5 to 2.0 seconds while the vessel is compressed for sealing and thereafter simultaneously cut, the collagen and elastin fibers are first denatured and then reconstituted across the interface46to create a strong seal and then the heat continues to force the sealed area to separate along the separation line51(FIG. 1).

Because the electrical power is delivered for a short period of time, the heat generated by this power does not diffuse appreciably into the surrounding walls of the vessel. As a result, the walls adjacent to the seal remain substantially unaffected by thermal energy spread. The strength and capability of the adjacent tissue is not compromised to the point where it may contribute to a failure of the seal.

Sealing a vessel with an impulse of electrical power which elevates the temperature of the working surfaces to a set temperature of approximately 220° C. and maintains that 220° C. sealing and simultaneous cutting temperature for a time of about 2.0 seconds is illustrated by the graph shown inFIG. 16. The temperature of the working surface on the upper jaw is referenced at226, and the temperature of the working surface of the lower jaw is illustrated at228. The temperatures in the upper and lower jaws are comparable to one another, due to the independent and rapid temperature control feedback of the controller150(FIG. 14).

The electrical power is applied by the controller to the jaw heating elements beginning at the 0.0 time reference. The energy applied for an initial ramp up time increases the temperature of the working surfaces for approximately 0.7 seconds, at which time the temperature of the jaw working surfaces is approximately at the desired 220° C. set point temperature for the tissue fusion procedure. Thereafter, between approximately 0.7 seconds and 2.0 seconds, the controller150manages the delivery of electrical power to maintain the temperature of the jaw working surfaces at the set point temperature of about 220° C. A slight amount of temperature overshoot and undershoot occurs immediately after the transition from the initial temperature ramp-up to the desired set point temperature, but that slight oscillation of temperature is within an acceptable range of the desired set point temperature.

After the delivery of power is stopped at 2.0 seconds, the impulse of electrical power is terminated and the jaws are opened immediately thereafter to release the severed vessel. The annunciator188or the monitor158(FIG. 14) indicates when the jaws can be opened to release the severed vessel. After the vessel is released from the jaws, the sealed areas50(FIGS. 6 and 20), which are adjacent to the separation line51, lack substantial mass to retain heat and cool rapidly when exposed to air. The jaws also quickly cool in the air after release of the tissue, but that cooling is not material to the invention and is therefore not shown inFIG. 16.

Sealing a vessel with a 1.5 second impulse of power which achieves a jaw working surface temperature of approximately 320° C. is illustrated inFIG. 17. Each of the top and bottom jaw working surface temperatures are separately referenced at230and232. The temperature rapidly increases from 0.0 seconds to the set temperature of about 320° C. in slightly more than 0.5 seconds. Thereafter, the delivery of electrical power to the jaw heating elements is controlled to maintain the working surface temperature at about 320° C. until 1.5 seconds have elapsed since the commencement of delivering the electrical power impulse. At that time, the electrical impulse is terminated and the jaws are opened to release the vessel. Again, the sealed areas, which are adjacent to the separation line51, cool rapidly upon being exposed to the air. The jaws also quickly cool in the air after release of the tissue, but that cooling is not material to the invention and is therefore not shown inFIG. 17.

At temperatures of 220° C. to 320° C., the time duration of the power impulse must be relatively short to avoid damaging, destroying or substantially weakening the vessel. For example, maintaining the temperature of approximately 320° C. for 5.0 seconds has the effect of so dehydrating the tissue between the working surfaces of the jaws so that it becomes friable and brittle. Such characteristics make the sealed areas prone to break or crack and develop a leak and cause the separation at the sealed areas of the vessel to break or crack along an ill-defined and nonlinear path.

The staircase nature of the curves226,228,230, and232shown inFIGS. 16 and 17result from a digital sampling routine of the PID controller. The discrete sampling points observed inFIGS. 16 and 17are separated by significant amounts of time, but higher sampling frequencies are possible. Increasing the rate of sampling by the PID controller allows for better system control over such variables as overshoot and rise time.

The strength and integrity of the seals adjacent to the separation line51(FIGS. 6 and 20) created by use of the present invention have been evaluated using burst tests. To evaluate the strength of the seal with a burst test, the lumen of the vessel is connected to a source of pressurized fluid, such as air, which inflates the vessel adjacent to the sealed area until a rupture or burst in the sealed area or the vessel wall occurs. The fluid pressure at the rupture point is measured, and the rupture pressure represents the strength of the seal. The test is repeated many times with different specimens of sealed tissue. A sufficient number of burst tests are conducted to achieve a statistically significant number of samples by which to evaluate the strength and integrity of the seals. The burst tests indicate that the seals formed have some range of variability in strength, and the seal strength is dependent upon the type and the size of the vessel sealed. Despite the variations in the seal strength, the burst pressures observed indicate that the seals formed have more than sufficient strength to reliably withstand the applicable physiological pressures, and in most cases, multiples of those pressures.

In addition to having a statistically higher and more consistent burst pressure, the typical failure mode of a seal made in accordance with the present invention is also substantially different from the edge-seal leak or mid-seal wall leak failure modes of seals made by use of the typical, known prior art tissue fusion devices which are presently in significant use. Typical edge-seal or mid-seal wall leaks are illustrated inFIGS. 17 and 18, respectively.

As shown inFIG. 18, a vessel234has been sealed at area236by a typical prior art technique. The view ofFIG. 18is orthogonal to the relatively large flat surface of the sealed area236. An edge238of the sealed area236delineates its boundary. An edge-seal leak occurs at location240when the edge238of the sealed area236ruptures through a wall242of the vessel234at a location adjacent to the sealed area236, under the influence of pressure applied in the lumen244on the left-hand side of the vessel (as shown). Usually the edge-seal leak240results from the application of excessive heat and compression concentrated at the edge238or over the entire sealed area236, or as a result of RF arcing which impacts the wall242of the vessel234and weakens the vessel at or near the edge238. The edge238may also be weakened by excessive compression from non-parallel jaws of a handpiece or from a shearing action on the tissue at the sealed area when separating the jaws, as described above. The edge-seal leak240diverts fluid from the lumen244to the outside of the vessel234.

The typical mid-seal wall leak is illustrated inFIG. 19where a vessel246was previously sealed at an area248by a typical prior art technique. The view ofFIG. 19is parallel to the flat surfaces of the sealed area248. The sealed area248was formed by compressing and fusing apposite walls250of the vessel246. Unsealed vessel walls250extend away from edges of the sealed area248. Under the influence of pressure applied in the lumen252on the left-hand side of the vessel246shown inFIG. 19, the sealed wall portions of the sealed area248have started to separate due to the fluid pressure against the sealed area248. A remaining portion254of the sealed area248remains intact with the walls of the vessel sealed together. A mid-seal wall leak256occurs when the separated vessel wall of the previously sealed area248ruptures at256and allows fluid to flow from the lumen252to the exterior of the vessel246.

Both edge-seal leak240(FIG. 18) and mid-seal wall leak256(FIG. 19) create difficult medical problems. Usually, the sealed area has enough initial integrity to withstand the pressure of the fluid in the lumen of the vessel for a short amount of time, but continued blood or fluid pressure variations within the body cause the edge-seal leak or the mid-seal wall leak to occur at a later time, usually after closure of the surgical incision and completion of the entire surgical procedure. Post operative internal bleeding will have severe consequences if the bleeding is not stopped quickly. Consequently, both an edge-seal leak240and a mid-seal wall leak256require undertaking a second surgical procedure to stop those leaks. Such second surgical procedures following immediately on the earlier procedure induce considerable additional trauma and risk to the patient.

The failure mode of seals created by use of the present invention when also simultaneously cutting the tissue, if failure occurs, is substantially different from the prior art edge-seal leak240and the mid-seal wall leak256shown inFIGS. 18 and 19. Practical use of the present invention within its defined and preferred parameters has never resulted in an edge-seal leak or a mid-seal wall leak, after creating many hundreds of seals. On a fundamental level, an edge-seal leak240or a mid-seal wall leak256results because the strength of at least part of the sealed area is greater than the strength of a part of the vessel adjacent to or within the sealed area, usually as a result of the adjacent vessel part or the sealed part being damaged during the tissue fusion procedure. The failure mode of the seals created by the present invention is considerably different, because the strength of the severed vessel adjacent to the sealed areas is not impacted to the point where the strength of the sealed areas is significantly less than the strength of the vessel adjacent to the sealed areas. The failure mode created by the present invention may be characterized as a mid-seal separation, and the mid-seal separation is of considerably less risk than either the edge-seal leak240or the mid-seal wall leaks256, for the reasons discussed below.

The mid-seal separation resulting from the present invention, if such a separation occurs at all, is illustrated inFIGS. 20-24. As shown inFIGS. 20 and 21, the vessel21is sealed at the sealed area50and simultaneously cut at the separation line51, according to the present invention. The sealed area50is formed by forcing portions258of the walls44of the vessel21into apposition with one another at the tissue interface46and by delivering heat to the compressed apposite portions258of the walls44at the interface46. The separation at the separation line51is caused by continued heat application and force on the still-pliable tissue immediately following but as a continuation of tissue sealing which is sufficient to force the working surfaces38and40into contact with one another and thereby sever the sealed area50at the separation line51. The temperature of the vessel wall portions258is sufficient to denature and coagulate the protein chains in the wall portions258at the interface46and then allow those denatured proteins chains to re-nature and reconstitute to form the high-integrity sealed area50while the continued force and temperature application causes the sealed area52separate along the separation line51. The fusion of the wall portions258at the tissue interface46occludes the lumen42of both severed parts of the vessel21.

After fusion of the wall portions258at the interface46in the sealed area50followed by simultaneous cutting of the sealed area50at the separation line51, the application of fluid pressure within the lumen42on the left-hand side (as shown) sealed area50causes the severed vessel21to expand as shown inFIG. 22. The walls44of the vessel21stretch and balloon outward from an edge260of the interface46. A characteristic of the seal created by the present invention is that the strength of the fusion at the interface46between the wall portions258at the sealed areas50is less than the strength of the unsealed walls44of the vessel21and is also less than the strength of the portions258of the wall after they have been fused together at the sealed areas50. Even though the strength of the wall portions258after sealing may be somewhat diminished as a result of the heat and pressure application, the strength of those wall portions258is still greater than the strength of the fusion between the wall portions258at the interface46, and the strength of the fused wall portions258at the interface46is still considerably greater than the normal amount of pressure applied within the lumen42by normal physiological events. These characteristics achieve a seal of substantial integrity which is capable of withstanding fluid pressures which are considerably greater than normal, as shown inFIG. 22, but which also provides safety and reliability if the sealed areas50at the end of the severed vessel should experience a mid-seal separation.

If the fluid pressure applied within the lumen is increased beyond the exaggerated level shown inFIG. 22, the fused apposed wall portions258at the interface46began to separate from one another at the edge260without rupturing the vessel walls44adjacent to the sealed area50and without rupturing the separated wall portions258which had previously been fused together at the sealed area50, as shown inFIG. 23. The pressure causes the sealed area50to experience a mid-seal separation, meaning that the previously-fused wall portions258separate at the interface46. The pressure may continue to separate the previously-fused, apposed wall portions258, with the separation continuing longitudinally along the interface46. The separation may continue along the interface46until the entirety of the previously-fused wall portions258have separated, at which point the occlusion of the vessel21is eliminated and the vessel21opens completely as shown inFIG. 24.

Because the previously-fused wall portions258retain substantial natural strength as a result of the present invention, a rupture through the wall44of the vessel21is avoided. The entire sealed area50will separate in the manner shown inFIG. 24under unusual circumstances, but neither the unaffected walls44nor the previously sealed wall portions258rupture to the exterior of the vessel21and create a leak from the lumen42to the exterior of the vessel, as is the case in a prior art edge seal leak240(FIG. 18) or a prior art mid-seal wall leak256(FIG. 19). The fluid-confining lumen42remains intact to confine the fluid within the vessel21. Thus, even if the wall portions258at the sealed areas50separate, such a mid-seal separation does not result in a rupture of the vessel wall44to permit fluid to flow from the lumen42to the outside of the vessel21. This type of mid-seal separation is the same as is created from simply fusing the tissue without simultaneously cutting the tissue, as is described in the first above-mentioned US patent application. The capability of sealing vessels in such a way to achieve a consistent and reliable mid-seal separation as a failure mode is thought to never before have been achieved from electrosurgical or electrothermal tissue fusion or from electrosurgical or electrothermal tissue fusion and simultaneous cutting.

The consistent and predictable mid-seal separation created by the present invention offers substantial advantages in redundancy. It is not unusual during surgery to create multiple sealed areas270and272which are slightly longitudinally spaced from one another along the length of a vessel274, as shown inFIG. 25. The belief is that if the primary or upstream sealed area270ruptures or fails, the remaining secondary backup or redundant downstream sealed area272will hold, thus preventing a leak. This belief is prevalent even though a significant number of instances of failure of the upstream or primary sealed area are edge-seal leaks240(FIG. 18) or mid-seal wall leaks256(FIG. 19), also shown respectively inFIGS. 26 and 27. Under circumstances of an edge-seal leak or a mid-seal wall leak, the secondary or downstream backup sealed area272is totally ineffective to prevent fluid loss due to the rupture through the wall of the vessel upstream of the backup sealed area.

Thus, the perceived benefit of sequential primary and backup seals270and272created by prior art tissue sealing techniques is almost always illusory. When the typical edge-seal leak240or the typical mid-seal wall leak256occurs at the primary sealed area270, as shown inFIGS. 26 and 27, respectively, the leaks240and256divert the fluid from a lumen276of the vessel274to the outside of the vessel. Under such circumstances, the secondary or backup sealed area272has no ability to restrain the fluid within the lumen276because the leaks240and256have diverted the fluid away from the backup sealed area272. The backup sealed area272therefore has no ability and no utility to restrain bleeding under typical prior-art sealed-area failure-mode circumstances. The significant occurrences of prior art edge-seal leaks or mid-seal wall leaks, even if as low statistically as 20%, does not provide effective redundancy or backup.

On the other hand as a result of using the present invention as shown inFIG. 28to fuse and simultaneously cut the tissue at a secondary or backup sealed area50b, a mid-seal separation at a primary sealed area50astill confines the fluid within the lumen42of the vessel21and conducts that fluid within the lumen42to the backup sealed area50b. The upstream primary fused area at50amay be conveniently created by use of the same instrument22, but only to fuse the upstream primary area50a. Tissue fusion without cutting is described in the first above-referenced US patent application. The strength of the vessel walls at the primary sealed area50ais sufficient to confine the fluid within the lumen42without rupture. Consequently, the fluid pressure is applied to the backup sealed area50bwhere that backup sealed area50bhas the opportunity to provide effective redundancy to prevent fluid leaks from the sealed vessel21. Practical use of the present invention within its defined and preferred parameters has never resulted in an edge-seal leak or a mid-seal wall leak, after creating many hundreds of seals. Effective redundancy and backup is therefore achieved by the present invention.

Although the sealed areas created by the present invention normally have sufficient strength and integrity as to achieve a relatively low probability of failure, the beneficial use of multiple seals substantially diminishes the risk of internal bleeding, even when the secondary or backup sealed area is also simultaneously cut. Moreover, the substantially diminished risk of internal bleeding is enhanced by the reliability of obtaining consistent seals of high integrity with each fusion procedure performed in accordance with the present invention.

Another benefit of the present invention relates to the common practice of forming overlapping seals. An overlapping seal is formed from a first seal on a vessel in the typical manner, coupled with forming a second seal in which the sealed area of the second seal overlaps a portion of the sealed area of the first seal. Overlapping sealing is typically applied to seal large vessels where the perception is that additional energy is required because of the size of the large vessel. The second seal may overlap the initially sealed area by approximately 50% up to 100%. To do so, the first sealed area is compressed and heated again, along with any previously unsealed adjoining tissue depending upon the degree of overlap. A 100% overlap involves performing second sealing procedure entirely coincidentally with the initial seal.

The present invention is beneficial in performing overlapped sealing combined with simultaneous cutting because the heat created from the impulse of electrical power does not dissipate to the surrounding vessel walls to a sufficient degree to damage the vessel. Reducing or minimizing the damage of the vessel walls adjacent to the seal allows subsequent applications of energy to be effective in reinforcing previous seals, because the vessel has not been previously damaged by the excessive application of heat. However, when the overlapping seal is created, the sealed area is also simultaneously severed by the application of heat. Thus, the present invention is effective in creating overlapping seals while simultaneously cutting the overlapped sealed areas.

The benefits and improvements of the present invention are numerous and significant. The efficiency of vessel fusion and simultaneous cutting procedures is increased by delivering the high power impulses which create the heat for fusion and cutting. Reliable vessel seals are created considerably faster than with the prior art tissue fusion techniques now commonly used, and the vessel is cut in such a way which does not compromise or negatively affect the strength of the seal created. The vessel seals are significantly stronger and more reliable than the seals created using common prior art tissue fusion or combined tissue fusion and cutting devices. The mid-seal separation failure mode confines the fluid within the vessel, thereby simplifying the process of re-sealing the vessel. Multiple sequential seals on a single vessel ensure that the probability of ultimate seal failure is extremely low because the mid-seal separation failure mode allows the multiple sequential seals to achieve effective redundancy, unlike known prior art tissue fusion or combined tissue fusion and cutting devices. Overlapping sealing and simultaneous cutting may also be beneficially applied because of the ability of the present invention to confine the energy to the sealed area without significantly spreading that energy to damage adjacent tissues and because the initial energy application has not substantially compromised the tissue strength or pliability of the sealed area. An immediate mid-seal separation allows the seal and simultaneous cutting procedure to be corrected.

The significance of these and many other improvements and advantages will become apparent upon gaining a full appreciation of the ramifications and improvements of the present invention. Preferred embodiments of the invention and many of its improvements have been described with a degree of particularity. The description is of preferred examples of implementing the invention, but the description is not necessarily intended to limit the scope of the invention. The scope of the invention is defined by the following claims.