High-frequency surgery has been used for many years in both human and veterinary medicine to coagulate and/or cut biological tissue. With the aid of suitable electrosurgical instruments, high-frequency current is passed through the tissue to be treated so that said tissue becomes changed due to protein coagulation and dehydration. The tissue contracts such that the vessels become closed and bleeding is stopped. A possible subsequent increase in current density can cause explosive evaporation of the tissue fluid and rupturing of the cell membranes, so that the tissue is completely parted.
For the thermal treatment of biological tissue, both bipolar and monopolar techniques are employed. In monopolar arrangements, the HF current fed by an HF generator to the electrosurgical instrument is applied via a ‘different’ electrode, while the current path through the body of a patient leads to an ‘indifferent’ neutral electrode and from there back to the HF generator.
However, bipolar instruments, which are configured with two electrode portions that are electrically insulated from one another, are becoming increasingly more important. The current path between the electrode portions is calculable and does not lead via extended routes through the body of the patient. This reduces the influence on heart pacemakers or other equipment that may be connected to the patient during the operation.
Bipolar instruments of this type are generally configured as clamping forceps which usually comprise, at their distal end, two clamping parts, which can be moved toward one another via an associated actuating device to grasp a tissue. In a clamping position or a “coagulation position,” current flows from one clamping part, through the tissue, to the other clamping part, so that tissue grasped between the clamping parts can be treated by HF surgical means.
In the case of bipolar clamps for thermofusion or coagulation, used for example, during hysterectomy, when large volumes of tissue are grasped, the attempt is made to ensure that the emission of heat energy for coagulation is essentially limited to the region between the grasping surfaces of the clamping parts. In this way, undesirable heating of other sites (e.g., lateral thermal damage, heating with coagulation effects at the back of the jaws) is minimized. Particularly in the case of thin, small volume structures (e.g. parenchyma tissue, exposed blood vessels, etc.), the output of precisely dosed heat energy is also necessary, and this can only be ensured if the tissue volume during coagulation remains securely grasped and is not appreciably increased by involving additional material, e.g. due to thermal shrinkage.
A device for HF surgery is disclosed by EP 0 875 209 B1. What is described is a pair of clamping forceps for tissue coagulation, having, at the distal end thereof, two clamping parts joined to one another and movable relative to one another via an articulated connection. The two clamping parts delimit a grasping region in which the tissue to be treated can be firmly clamped. In order to enable particularly effective fixing of the tissue in the grasping region, one clamping part has movable fixing elements, which are movable into and out of the clamping part. Arranged at the other clamping part are two bipolar electrodes which are separated from one another by an electrical insulation layer. The first electrode protrudes out of this clamping part, while the second electrode surrounds this first electrode, being essentially laterally recessed. As soon as tissue is grasped between the two clamping parts and the HF generator is activated for coagulation current generation, current flows between the first protruding electrode, the grasped tissue, and the second electrode, wherein the coagulation process takes place in the tissue.
Disadvantageously, it has herein been found that, in this device, the whole clamping part heats up during the coagulation, resulting, inter alia, in undesirable vessel changes, such as spurious coagulation in the lateral and rear regions of the clamping part.
WO 2004-082495 A1 also discloses a bipolar clamp of this type for HF surgery, wherein two clamping parts are provided which are joined to one another into a jaw part for grasping the tissue to be coagulated. As before, the bipolar electrodes are arranged at one clamping part such that, following grasping of the tissue, current flows between the first electrode and the second electrode. The electrodes are configured as platform-like elevations, wherein the first electrode is arranged in the center and the second electrode is arranged as a ring-electrode surrounding the first electrode at the edge of the platform. In this case also, however, it has been found that due to a reduction in the conducting away of heat, heating of the clamping part carrying the electrodes cannot be prevented, so that undesirable tissue changes also take place in the side and rear region of the clamping part. Such a configuration can also only be realized with high cost and, due to the small bipolar electrode separations, is highly prone to faults in production.
US 2002/0013583 A1 also discloses a clamp for HF surgery, wherein, inter alia, the bipolar electrodes are provided on different clamping parts, so that a current flows between one electrode of one clamping part and another electrode of the other clamping part. In this case, the electrodes are laid on conducting paths which are arranged, in particular, on clamping surfaces of the clamping parts which face one another. The electrodes themselves are configured as electrode tips and are constructed so that, on grasping the tissue, they penetrate into the tissue to be coagulated. The intention of this is that the coagulation areas can be more precisely delineated by the individual bipolar electrodes penetrating the tissue. However, it has here again been found that heating of the tissue takes place in the side and rear regions of the clamping parts and that this heating is the cause of undesirable tissue changes in these regions. Furthermore, the production of such clamping parts involves technical manufacturing difficulties, since the fixing of the electrodes to the clamping part may not be able to withstand the very great mechanical and thermal loading.