Abstract:
An ultrasonic medical treatment device has a casing, an elongate probe, a transducer assembly, a sheath and at least one electrode member. The probe is mounted to and extends from the casing and has an axis and a free end serving as an operative tip. The transducer assembly is mounted to the casing and is operatively connected to the probe for generating vibrations of at least one ultrasonic frequency in the probe. The sheath surrounds the probe. The electrode member is connectable to an RF voltage source and is mounted at least indirectly to the casing so as to permit relative motion between the electrode member and the probe.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 10/141,789 filed May 8, 2002, now U.S. Pat. No. 6,648,839, as a continuation in part of application Ser. No. 10/086,508 filed Feb. 28, 2002 U.S. Pat. No. 6,736,814. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a medical device and more specifically to an ultrasonic tissue ablation instrument. Even more specifically, this invention relates to an ultrasonic medical treatment device with electrocautery. This invention also relates to an associated medical treatment method. 
     BACKGROUND OF THE INVENTION 
     Many diseases of the brain and spine require surgery to provide the patient with relief. These could include cancer, non-malignant lesions and trauma induced by accidents or physical attack. As a procedure, neurosurgery has been practiced for several millennia. Archeologists have discovered evidence of sophisticated cranial surgery in relics and skulls dating back to Roman times. The tools found have been shown to be remarkably similar to today&#39;s designs. Of course, modern science has substantially improved upon the techniques and results obtained in those days. 
     One of the biggest steps forward occurred approximately 30 years ago with the invention and marketing of the ultrasonic surgical aspirator. This device utilizes a hollow probe or tool that vibrates at frequencies at or above 20 kc with tip amplitudes of up to 300 microns. When the vibrating tip is placed against viable or diseased tissue, the moving tip ablates the cells and causes them to fragment or otherwise emulsify in the irrigation fluid that is being added simultaneously. The emulsified fluid is then aspirated through the hollow probe and deposited in a canister for histological examination or disposal. 
     The advantage of excising tissue with this device is that the surgeon can remove the lesion in layers almost 5 cells thick. By slowly removing the tumor from the top down, he can clearly see when he is reaching healthy tissue allowing him to stop before substantial collateral damage occurs. This is extremely desirable in brain and spine surgery, where tissue does not regenerate. Gastrointestinal surgeons have used the device as well for lesions of the liver and spleen, for the same reasons. 
     The required specifications, designs and engineering elements of such ultrasonic aspirators have become well known to the art in the intervening time. Although the technology is mature, several improvements can be made to enhance the ease of use and applicability to a wider range of procedures. 
     One side effect of any surgery is bleeding when the veins, arteries or capillaries are severed. Ultrasonic surgery is more sparing of blood vessels than knives because the collagen content of the vessels is more resistant to ultrasonic emulsion. However, the capillaries and small vessels will be compromised upon exposure to high amplitude ultrasonic tools. When these vessels are severed or punctured bleeding will of course occur. The surgeon will then be forced to pause the procedure, remove the ultrasonic tool from the site and generally reach for a cauterizing device of some type to close off the bleeder. Once coagulation has been achieved, then the surgeon can grab the ultrasonic tool, reposition it in the wound site and continue the removal of tissue. This situation repeats itself often in the course of the operation, lengthening the time of the procedure and coincidently the risk to the patient. It is therefore desired to find a way to cauterize tissue with the ultrasonic tool in place so the surgeon can stop bleeding with minimal downtime caused by switching tools and positions. 
     Several improvements to the basic design of the ultrasonic aspirator have been disclosed over the years which allows some degree of cauterization subsequent to or simultaneously with ultrasonic ablation. Most center on the application of RF cautery currents to the tool or probe itself. This has the effect of turning the ultrasonic tool into a monopolar RF cauterizer. 
     In a non-ultrasonic RF cauterizer, the tip of the tool is energized with a voltage sometimes exceeding 3000 volts RMS. The frequency of the voltage is very high, in order to prevent cardiac arrest in the patient. These frequencies are generally greater than 500,000 hertz. In monopolar RF, the tool is one pole of the electrical circuit. The second pole is generally a large piece of metal foil which the patient lays on during the procedure. The bare skin touching the foil makes an effective electrical contact. As the tool touches the tissue and the RF voltage is energized, a complete circuit path is created. The currents are very high, reaching 5 amps in some cases. At these currents, significant joule heating occurs in the tissue, raising the temperature higher than the burning temperature of 42° C. Continued operation dries the tissue by evaporating the water content. Cauterization then occurs. Since the back plate is very large in relation to the tool tip, the current “fans out” as it leaves the tool tip and thereby lowers the current density in the tissue to a point where the temperature rise in the tissue is reduced to that below burning. This minimizes collateral burning and tissue damage. 
     However, as large as the plate is, some collateral damage occurs away from the bleeder site. This collateral damage cannot be controlled reliably by the physician and is of great concern when operating on the brain. If the damage is two widespread, mental capacity or memory may be affected negatively. In addition, electrical current is forced to flow through viable tissue to the ground plate. Again, neurological damage may occur in some organs that are susceptible to damage due to this current, such as the brain, heart and nerve bundles. Other organs, such as the liver or spleen, are less susceptible to current effects. 
     Researchers have found a way to minimize or eliminate this current path by designing a tool that includes two electrical poles or contacts. This is called bipolar RF cauterization. Here the current flows between the two poles through the intervening tissue. No current path to the back is allowed. Therefore, the tissue that is damaged is only that caught between the two contacts, which can be very small. 
     Designers have found a way to add monopolar cautery to ultrasonic devices by connecting one electrical contact to the vibrating tip of the ultrasonic device. Several patents have disclosed concepts and techniques for this, such as U.S. Pat. No. 4,931,047 to Broadwin, et al. Here, the tip of the ultrasonic tool is the single pole that touches the tissue. The surgeon will generally stop ultrasonic vibration and turn on the cautery voltage. Current leaves the tip of the probe and goes through the body to the back plate. This has been shown to be effective in eliminating the need for switching tools to stop bleeding, saving time and effort on the doctor&#39;s part. However, all of the detriments of monopolar cautery still exist. Neurosurgeons are especially reticent to allow significant current to flow through brain or spinal cord tissue for fear of inducing neurological damage. In addition, the piezoelectric crystals of the ultrasonic transducer stack must be isolated from the cautery voltage or damage to the transducer or electronics will occur. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide an ultrasonic treatment device or instrument having electrocautery capability. 
     Another object of the present invention is to provide such a device that eliminates the above-described deficiencies in conventional systems. 
     A further object of the present invention to provide such a device or instrument which is easy to use and which provides reliable cautery effects while minimizing patient risk during an ultrasonic aspiration procedure. 
     Yet another object of the present invention is to provide such a device or instruments with a capability of grasping and clamping tissue or vessels prior to and concurrent with electrocautery. 
     A related object of the present invention is to provide an associated method which combines ultrasonic ablation with electrocautery in a manner that is easy to use. 
     SUMMARY OF THE INVENTION 
     An ultrasonic medical treatment device pursuant to the present invention comprises a casing, an elongate probe, a transducer assembly, a sheath and at least one electrode member. The casing is generally in the form of a handpiece that facilitates manipulation by a surgeon. The probe is mounted to the transducer assembly and particularly to a front driver thereof and extends from the casing, and has an axis and a free end serving as an operative tip. The transducer assembly is mounted to the casing and is operatively connected to the probe (via the front driver) for generating vibrations of at least one ultrasonic frequency in the probe. As is well known, the ultrasonic vibration frequency is a resonant frequency of the probe, whereby standing waves are produced in the probe. The sheath surrounds the probe. The electrode member, which is connectable in an RF circuit, is mounted directly to the sheath or casing and thus indirectly to the probe. Where the instrument is to be utilized in a monopolar mode of operation, the electrode member may be the only electrode on the instrument. Where the instrument is to be utilized in a bipolar mode of operation, at least one other electrode member is provided. This other electrode member may be the probe itself or another electrode member fixed to the sheath or casing. In the case of piezoelectric transducers, the crystals may be isolated from the metal front driver and probe by insulating washers or other means know to the art. If sufficient electrical isolation exists between the circuitry of the ultrasonic electronic generator and the RF generator circuitry, these washers or other insulation means may be eliminated. 
     In a preferred embodiment of the invention, the sheath is movably mounted to the casing. It is also preferred that the electrode member or members which are fixed to the sheath are substantially embedded in the sheath. These embedded electrode member have exposed portions disposed proximately to the operative tip of the probe for forming electrically conductive contact with organic tissues at a surgical site in a patient. 
     More particularly, the sheath is movably mounted to the casing for reciprocatable motion along the axis of the probe, whereby the tip of the probe may be alternately covered and exposed. Where the probe can function as an electrode in a bipolar mode of operation, of the instrument, the shiftability of the sheath enables the surgeon to juxtapose the tip of the probe with one or more exposed electride tips. Thus, during an ultrasonic use of the instrument, the sheath is retracted to expose the operative tip of the probe, which is energized by a predetermined ultrasonic vibration produced by the transducer assembly. Should a blood vessel become severed by ultrasonic ablation, the action of the transducer assembly may be interrupted and the sheath slid forward, in a distal direction, to move an exposed tip of the electrode member into proximity with or over the tip of the probe and to facilitate contact between the exposed tip of the electrode member, and the region about the severed blood vessel. More specifically, where the electrocautery is bipolar and the probe functions also as an electrode, the exposed tip of the electrode member is brought into proximity with the probe tip to facilitate the placement of bleeding tissues between the exposed electrode tip and the tip of the probe. Where there are more than one electrode member mounted to the sheath for a bipolar cauterization procedure, the tip of the probe may be covered and therefore spaced from the surgical site during the cauterization procedure. The electrodes, possibly including the probe, are then connected to a radio-frequency current source to generate a current flow between the exposed portions of the electrode members and probe. 
     The electrode members can be exactly one in number. In that case, the exposed portions of the electrode member either is fixed in reference to the circumference of the tip of the probe or can be rotated around the circumference at the discretion of the surgeon. 
     In another embodiment of the invention, there are two or more electrode members, with the members of each being disposed along the circumference of the sheath. In this embodiment, a manually operable switching circuit may be operatively connected between the power source and the electrode members for determining which electrode member or members are to be energized. The operating surgeon selects those electrode members which are most closely located to a bleeding site. Where the probe itself can function as an electrode in a bipolar electrocautery procedure, the switching circuit is used to determine which of the circumferentially disposed electrodes is to be connected in an RF circuit with the probe. It is to be noted that the probe may continue to vibrate ultrasonically during the application of RF electric current. Alternatively, the ultrasonic vibration of the probe may be interrupted either automatically or optionally under the control of the surgeon during the conduction of RF electrical current. 
     Pursuant to another feature of the present invention, the electrode members are movable in parallel to the axis of the probe. 
     A medical surgical method in accordance with the present invention utilizes an ultrasonic medical treatment device having a casing and an elongate probe mounted to and extending from the casing, the probe having an axis and a free end serving as an operative tip, a transducer assembly mounted to the casing being operatively connected to the probe, at least one electrode member being mounted at least indirectly to the casing. The method comprises inserting a distal end portion of the probe into a patient, thereafter energizing the transducer assembly to generate a standing wave of an ultrasonic frequency in the probe, ablating tissues of the patient at the operative tip of the probe during the generating of said standing wave, shifting the electrode member or members relative to the probe, connecting the electrode member or members to an RF voltage source, and cauterizing tissues in the patient owing to the conduction of current via the electrode members. 
     Where there is a single electrode member, the mode of operation of the medical treatment device is monopolar. For a bipolar mode of operation, there must be at least one additional electrode on the medical device. This additional electrode may be the probe itself or a dedicated electrode member. In the former case, shifting of the electrode member brings it into juxtaposition with the probe, whereas in the latter case, both electrodes are shifted to place the exposed tips of the electrodes distally of the probe tip. In either case, the shifting of the electrode(s) facilitates the performance of an electrocautery procedure. Where the electrode members are connected to a sheath, the moving of the electrode members may be accomplished by shifting the sheath relative to the probe. 
     In a further embodiment, the electrode may be hinged nearer the proximal end of the sheath. A protuberance may be provided, extending outside the outer sheath assembly, which contact the rigid metal electrode. By sliding the sheath forward, the distal end of the electrode is exposed. The electrode may be manipulated by the surgeon to allow tissue to fill the gap between said electrode and the probe. By squeezing the protuberance, the surgeon may apply a pinching force on the tissue to help close severed vessels while applying electrocautery current to the probe and the electrode. 
     It is to be noted that the electrodes may be used to ablate tissues of the patient in addition to cauterizing the ablated tissues. It should also be noted that the ultrasonic energy may be used simultaneously with the application of RF current or independently of the RF current. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a partial longitudinal cross-section view of an ultrasonic tissue ablation instrument with electrocautery, in accordance with the prior art. 
         FIG. 1B  is a side elevational view of a transducer assembly used in the prior-art surgical instrument of FIG.  1 A. 
         FIG. 2A  is a schematic side-elevational view of a human subject, showing an electrocautery plate and, in phantom lines, a possible current path where the instrument of  FIG. 1A  is used in neurosurgery. 
         FIG. 2B  is another schematic side-elevational view of a human subject, showing an electrocautery plate and, in phantom lines, another possible current path where the instrument of  FIG. 1A  is used in neurosurgery. 
         FIG. 3A  is a partial longitudinal cross-sectional view of a distal end portion of an ultrasonic tissue ablation instrument with electrocautery, in accordance with the present invention. 
         FIG. 3B  is an end elevational view of the instrument of  FIG. 3A , taken from the right side in FIG.  3 A. 
         FIG. 4A  is a partial longitudinal cross-sectional view, taken along line IVA—IVA in  FIG. 4B , of a distal end portion of another ultrasonic tissue ablation instrument with electrocautery, in accordance with the present invention. 
         FIG. 4B  is an end elevational view of the instrument of  FIG. 4A , taken from the right side in FIG.  4 A. 
         FIG. 5A  is a partial longitudinal cross-sectional view of the tissue ablation instrument of  FIGS. 3A and 3B , depicting one structure for shifting a sheath and electrodes relative to an ultrasonic probe and showing the sheath in a retracted position to expose a free end of the probe. 
         FIG. 5B  is a partial longitudinal cross-sectional view similar to  FIG. 5A , showing the sheath in an extended position to cover a free end of the probe and place operative ends of the electrodes in contact with organic tissues at a surgical site. 
         FIG. 6A  is a partial longitudinal cross-sectional view of the tissue ablation instrument of  FIGS. 3A and 3B , depicting another structure for shifting the sheath and electrodes relative to the probe and showing the sheath in a retracted position to expose the free end of the probe. 
         FIG. 6B  is a partial longitudinal cross-sectional view similar to  FIG. 6A , showing the sheath in an extended position to cover a free end of the probe and place operative ends of the electrodes in contact with organic tissues at a surgical site. 
         FIG. 7A  is a perspective view of a distal end portion of yet another ultrasonic tissue ablation instrument with electrocautery, in accordance with the present invention, showing a pair of electrodes hingedly mounted to a movable sheath disposed in a retracted position to expose an operating tip of an ultrasonic ablation probe. 
         FIG. 7B  is a perspective view of the instrument of  FIG. 7A , depicting the movable sheath slid forward to cover the operating tip of the ultrasonic ablation probe and to expose the distal ends of the electrodes. 
         FIG. 8A  is a partial longitudinal cross-sectional view of a distal end portion of another ultrasonic tissue ablation instrument with electrocautery, in accordance with the present invention. 
         FIG. 8B  is an end elevational view of the instrument of  FIG. 8A , taken from the right side in FIG.  8 A. 
         FIG. 9A  is a partial longitudinal cross-sectional view, taken along line IXA—IXA in  FIG. 9B , of a distal end portion of yet another ultrasonic tissue ablation instrument with electrocautery, in accordance with the present invention. 
         FIG. 9B  is an end elevational view of the instrument of  FIG. 9A , taken from the right side in FIG.  9 A. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Disclosed herein are various hardware configurations that will allow bipolar RF cautery to be used on organic tissues at a surgical site simultaneously with or immediately after ultrasonic ablation of tissue. The electrical connections are isolated from the ultrasonic tool thereby allowing the piezoelectric crystals to be floating with respect to this potential. 
     In the prior art, as shown in  FIG. 1A , an ultrasonic probe  12  is connected one pole of an RF cauterizer (not shown) by a wire  14 . Alternatively, an electrode member, conductive O rings or other methods known to the art (none shown) may be used. In the embodiment of  FIGS. 1A and 1B , a front driver  16  of the transducer is also rendered live, which necessitates that the metal parts be insulated from the grip or handle  17  of the instrument. If the transducer assembly  18  is of the electrostrictive type with piezoelectric crystals  20 , the crystals must be electrically isolated from the front driver  16  by methods known to the art such as using ceramic washers  22  and  24  as insulation in the crystal stack (FIG.  1 B). A disadvantage of using isolators is that they generally reduce the electromechanical coupling efficiency, thereby leading to transducer heating and higher power requirements for a given output amplitude. 
     The other pole of the RF cauterizer is attached to a back plate  26  that contacts the patient&#39;s bare skin, as shown in  FIGS. 2A and 2B . Then the entire body becomes part of the electrical connection. Possible current paths  28  and  30  are shown in  FIGS. 2A and 2B . 
     As depicted in  FIGS. 3A and 3B , both electrical poles or electrode members  32  and  34  of an electrocautery system are attached to and, more specifically, embedded in, a flexible silicone sheath  38  that surrounds an elongate ultrasonic probe  40 . Ultrasonic aspirators require the addition of a sterile solution of saline into the wound site to irrigate the area and improve ablation. Sheath  38  serves to define, with probe  40 , an annular conduit  42  for this saline solution. 
     In the embodiment of  FIGS. 3A and 3B , electrode members  32  and  34  in the form of wires are molded into the silicone sheath or flue  38 . The distal ends or tips  44  and  46  of the electrodes members  32  and  34  protrude from the distal end of sheath  38 , forming two electrodes. 
     By utilizing the sheath  38  as a holder for the two electrode members  32  and  34  of the bipolar device, the electrical connector is do not touch the tool itself. The close proximity of electrode members  32  and  34 , and particularly exposed tips  44  and  46  thereof, allows a very short circuit path ( FIG. 3B ) for the cauterizing current. To use of the cauterizing capability of the instrument of  FIGS. 3A and 3B , the instrument is rotated about a longitudinal axis  48  by the surgeon in order to approximate the exposed tips  44  and  46  of the electrode members  32  and  34  to bleeding tissues at a surgical site inside a patient. 
       FIGS. 4A and 4B  depict an alternative configuration of electrodes  50 - 53  in a flexible silicone sheath  54  surrounding an ultrasonic probe  56 . Electrodes  50 - 53  are circumferentially equispaced about the sheath  54 . Electrodes  50 - 53  are ring segments (i.e., arcuate about an axis of sheath  54 ) molded into the end of sheath  54 . Electrodes  50 - 53  have gaps between them for insulation purposes. Electrodes  50 - 53  are connected to electrode wires  58  and  60  that are embedded in sheath  54 . The wires  58  and  60  are each connected to two electrodes or segments  50 - 53  disposed 180° apart. During an electrocautery operation, current is conducted between each pair of adjacent electrodes, thus producing four zones of possible tissue cauterization corresponding to the four gaps between electrodes  50 - 53 . 
     In the embodiment of  FIGS. 4A and 4B , a finer control of cauterization location may be achieved by having electrodes  50 - 53  connected to respective wires. Wires  5 . 8  and  60  are thus each connected to a single electrode  50 ,  51 ,  52 , or  53 . In this embodiment, a single pair of adjacent electrodes  50 - 53  is selected for energization at any one time. Generally, a pair is selected that is considered closest to bleeding tissues at a surgical site in a patient. When the RF current is energized, the segments will allow current to flow between the gaps of the segmented ring around the periphery of the sheath end. It can be envisioned by those schooled in the art that logic circuitry may be provided to energize only two segments of a multi-segmented ring to allow current to pass through only one or two gaps and not all of the gaps provided. 
     The configurations of  FIGS. 3A ,  3 B and  4 A,  4 B have been developed to provide physicians with designs that can be used without losing dexterity or visibility of the operation site. The electrode member configurations of  FIGS. 3A ,  3 B and  4 A,  4 B allow for bipolar cauterization without energizing the tool tip itself. 
     In order to allow the surgeon the best visualization of the operative field, mechanisms have been developed for use with the devices of  FIGS. 3A ,  3 B and  4 A,  4 B that provide for a longitudinal translation of sheaths  38  and  54  alternately in a distal direction and a proximal direction. While the ultrasound is active, sheath  38  or  54  is slid back to expose the distal end or operative tip  78  or  79  of the probe  40  or  56 . When RF cautery is needed, the surgeon uses one finger (e.g., a thumb) to slide the sheath  38  or  54  forward to place the electrodes  44 ,  46  or  50 - 53  in contact with the tissue.  FIGS. 5A and 5B  show a first embodiment of this mechanism, constructed of molded or machined plastic, while  FIGS. 6A and 6B  show an alternative embodiment of the slide mechanism. Although  FIGS. 5A ,  5 B,  6 A, and  6 B depict the electrode configuration of  FIGS. 3A and 3B , it is to be understood that the electrode configuration of  4 A and  4 B could be used instead. 
     As illustrated in  FIGS. 5A and 5B , probe  40  is connected at a proximal end to a piezoelectric transducer assembly  62 , while sheath  38  is affixed to the distal end of a polymeric inner tubular member  64  telescopingly cooperating with an outer tubular member or casing  66 . 
     Casing  66  extends in a rearward or proximal direction to form a handgrip or handpiece for a surgeon or other user of the ultrasonic/electrocautery instrument. Annular conduit  42  communicates at a proximal end with an annular passageway  68  formed by probe  40  and inner tubular member  64 . Passageway  68  communicates with a saline source (not shown) via a nippled coupling  70  and an aperture  72  formed in inner tubular member  64 . Inner tubular member  64  is provided with a projection  76  serving as a manually operable control knob for sliding sheath  38  and electrode members  32  and  34  (a) in the distal direction prior to the energization of electrode members  32  and  34  and electrode tips  44  and  46  in an electrocautery operation and (b) in a proximal direction prior to an ultrasonic ablation procedure in which probe  40  is vibrated by transducer assembly  62 . During an ultrasonic ablation procedure, a free end or operative tip  78  of probe  40  vibrates with a maximized displacement (at an antinode of the standing wave generated in probe  40 ). 
     The telescoping cooperation of inner tubular member  64  and casing  66  enables a reciprocating motion of sheath  38  and electrode members  32  and  34  along the axis  48  of probe  40 , whereby the operative tip  78  of the probe may be alternately covered and exposed. Thus, during an ultrasonic use of the instrument, sheath  38  is retracted to expose the operative tip  78  of the probe  40 , which is energized by a predetermined ultrasonic vibration produced by the transducer assembly  62 . Should a blood vessel become severed by ultrasonic ablation, the action of transducer assembly  62  is interrupted and sheath  38  is slid forward, in a distal direction, to cover tip  78  of probe  40  and to facilitate contact between the exposed portions of the electrode members, i.e. electrode tips  44  and  46 , and the region about the severed blood vessel. Electrode members  32  and  34  are then connected to a radio-frequency current source (not illustrated) to generate a current flow between the exposed portions of the electrode members  32  and  34 . 
     As depicted in  FIGS. 6A and 6B , probe  40  is connected at a proximal end to a piezoelectric transducer assembly, while sheath  38  is affixed to the distal end of a polymeric tubular member  82  attached via an annular bellows  84  to a handpiece casing  86 . Annular conduit  42  communicates at a proximal end with an annular passageway  88  formed by probe  40  and tubular member  82 . Passageway  88  communicates with a saline source (not shown) via a nippled coupling  90  and an aperture  92  formed in tubular member  82 . Tubular member  82  is provided with a projection  96  serving as a manually operable control knob for sliding sheath  38  and electrode members  32  and  34  (a) in the distal direction prior to the energization of electrode members  32  and  34  and electrode tips  44  and  46  in an electrocautery operation and (b) in a proximal direction prior to an ultrasonic ablation procedure in which probe  40  is vibrated by transducer assembly  62 . 
     The distensible connection of tubular member  82  and casing  86  via bellows  84  enables a reciprocating motion of sheath  38  and electrode members  32  and  34  along the axis  48  of probe  40 , whereby the operative tip  78  of the probe may be alternately covered and exposed, as discussed hereinabove with reference to  FIGS. 5A and 5B . Bellows  84  provides the mechanism with a seal against the transducer housing (tubular member  82 ) to prevent fluid leaks. 
     As illustrated in  FIGS. 7A and 7B , two electrodes  102  and  104  may be spaced 180° apart and hinged (e.g., via a flexible joint) nearer the proximal end of a sheath  106 . Sheath  106  is provided with two pairs of longitudinal parallel slots  108  defining respective fingers  110  and  112  in which electrode wires (not separately illustrated) are embedded. Two actuators in the form of protuberances  114  and  116  are provided, extending through respective opposed apertures  118  (only one shown) in a casing  120 . Protuberances  114  and  116  are connected to fingers  110  and  112 , respectively, near the proximal ends thereof. Pushing one or both protuberances  114  and  116  in a longitudinal direction, along an axis (not indicated) of the instrument, slides sheath  106  either forward to cover an operating tip of an ultrasonic probe  122 , as depicted in  FIG. 7B , or rearwards to expose the probe tip, as depicted in  FIG. 7A. A  surgeon may also manipulate electrodes  102  and  104  to insert target organic tissues between the electrodes prior to an electrocautery operation. By squeezing protuberances  114  and  116  towards one another, the surgeon may apply a pinching force on the tissue to help close severed vessels while applying electrocautery current via electrodes  102  and  104 . In an application of compressive pressure to protuberances  114  and  114 , electrodes  102  and  104  function as tweezers, exerting a squeezing force on trapped tissue, thereby enhancing the vessel sealing effect of the electrodes and minimizing collateral damage. 
       FIGS. 8A and 8B  illustrate another ultrasonic tissue ablation instrument with electrocautery where the electrocautery may be of the monopolar and/or the bipolar type. The instrument includes a single electrode member  132  in the form of a wire embedded or molded in a flexible silicone sheath  138  that surrounds an elongate ultrasonic probe  140 . Sheath  138  and probe  140  together define an annular conduit  142  for a saline irrigant solution. A distal end or tip  144  of electrodes member  132  protrudes from the distal end of sheath  138 , forming a single electrode. In a monopolar mode of operation of the instrument of  FIGS. 8A and 8B , an RF A-C power supply or current source  124  is connected, as indicated by a lead  126  to electrode member  132  and to a sheet metal electrode (not shown) placed along an outer skin surface of a patient. In a bipolar mode of operation, power supply  124  is connected to both electrode member  132  and probe  140 , as indicated by a phantom line  128 . The instrument of  FIGS. 8A and 8B  may be configured with either monopolar electrocautery or bipolar electrocautery or both. In the latter, case, a switch (not shown) may be provided for selecting either the monopolar or the bipolar alternative. 
     As discussed above with reference to sheath  38 , sheath  138  functions in part as a holder for electrode member  132 , so that the electrical connections do not touch the tool itself. In the case of a bipolar instrument, the close proximity of electrode member  132 , and particularly exposed tip  144  thereof, to a tip  178  of probe  140  allows a very short circuit path ( FIG. 813 ) for the cauterizing current. To use of the cauterizing capability of the instrument of  FIGS. 8A and 8B , whether in the monopolar or the bipolar mode of operation, the instrument is rotated about a longitudinal axis  148  by the surgeon in order to approximate the exposed tips  144  and  178  of electrode member  132  and probe  140  to bleeding tissues at a surgical site inside a patient. 
       FIGS. 9 and 9B  depict another alternative of an ultrasonic tissue ablation instrument with electrocautery where the electrocautery is of the bipolar type. Multiple electrodes  150 - 153  are mounted to a flexible silicone sheath  154  surrounding an ultrasonic probe  156 . Probe  156  itself functions as an electrode, either concurrently with ultrasonic mechanical energization or alternately therewith. Electrodes  150 - 153  are circumferentially equispaced about the sheath  154 . Electrodes  150 - 153  are connected to respective electrode wires  158  and  160  (only two shown) that are embedded in sheath  154 . During an electrocautery operation, current from a power supply  162  is conducted between probe  156  and a single one of electrodes  150 - 153 , depending on the angular location of a bleeding site. To that end power supply  1652  is provided with a manually operable switching circuit (not separately illustrated) controlling the conduction of current between probe  156 , on the one hand, and electrodes  150 - 153 , on the other hand. 
     The tissue ablation instruments of  FIGS. 8A ,  8 B and  9 A,  9 B are preferably used as possible substitutes for the tools of  FIGS. 3A ,  3 B and  4 A,  4 B in the assemblies of  FIGS. 5A ,  5 B and  6 A,  6 B. 
     It is to be noted that, in a monopolar mode of utilization of the assembly of  FIGS. 9A and 9B , electrodes  150 - 153  (and even probe  156 ) may be used alternately as the monopolar electrode. In that case, a switching circuit is provided for enabling a manual selection by the surgeon of the monopolar electrode from among electrodes  150 - 153  (and possible probe  156 ). 
     It is to be noted further that the instrument of  FIGS. 7A and 7B  may be used in a monopolar operating mode in which only one electrode  102  or  104  is connected to the RF power supply (together with a sheet electrode, not illustrated). If that is the only mode of operation needed, then the other electrode  104  or  102  may be omitted. Alternatively, the embodiment of  FIGS. 7A and 7B  may be used in a bipolar mode of operation where probe  122  is energized together with one or both of electrodes  102  and  104 . Preferably, in this bipolar mode of operation, only one electrode  102  or  104  is active. Again, the inactive electrode  104  or  102  may be omitted from the design altogether. 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. It is to be noted, for instance, that the electrocatuery portion of a combined ultrasonic ablation and electrocautery tool as disclosed herein may be used for ablation, as well as cautery. It is to be noted, in addition, that the electrodes may be attached to the probe casing or frame by means other than the sheath. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.