Surgical Instrument
An electrosurgical cutting blade ( 1 ) comprises a first electrode ( 2 ), a second electrode ( 3 ), and an electrical insulator ( 4 ) separating the first and second electrodes. The first and second electrodes have dissimilar characteristics (cross-sectional area, thermal conductivity etc.) such that the first electrode ( 2 ) is encouraged to become an active electrode and the second electrode ( 3 ) is encouraged to become a return electrode. The spacing between the first and second electrodes (between 0.25 mm and 3.0 mm) and the peak voltage supplied to the electrodes ( 2 and 3 ) are both selected such that arcing does not occur directly between the electrodes, but between the first electrode and the tissue at the target site. The arrangement is such that, in use, a thermal differential of at least 50° C. is established between the first and second electrodes ( 2 and 3 ), such that the second electrode is maintained below a temperature of 70° C. This is achieved either by thermally insulating the second electrode from the first electrode, and/or by transferring heat away from the second electrode, e.g. by conduction, forced cooling, or by means of a heat pipe ( 27 ).
1. A bipolar cutting blade comprising:
a first electrode,
a second electrode,
an electrical insulator spacing apart the first and second electrodes,
the first electrode having a characteristic which is dissimilar from that of the second electrode, such that the first electrode is encouraged to become an active electrode and the second electrode is encouraged to become a return electrode,
the spacing between the first and second electrodes being between 0.25 mm and 1.0 mm, such that when the first and second electrodes are in contact with tissue and an electrosurgical cutting voltage is applied therebetween, arcing does not occur directly between the first and second electrodes, and
a third electrode adapted for coagulating tissue, the third electrode being separated from the second electrode by an additional insulator,
wherein the firs electrode is substantially planar, and
wherein the electrical insulator spaces apart the first electrode from the second and third electrodes on the other side of the bipolar cutting blade.
2. The bipolar cutting blade according to claim 1 , wherein the second an third electrodes are provided in a side-by-side arrangement with the additional insulator therebetween.
3. The bipolar cutting blade according to claim 1 , wherein the characteristic of the first electrode which is dissimilar from that of the second electrode cornprises the cross-sectional area of the electrode, the cross-sectional area of the first electrode being substantially smaller than that of the second electrode.
4. The bipolar cutting blade according to claim 1 , wherein the characteristic of the first electrode which is dissimilar from that of the second electrode corn rises the thermal conductivity of the electrode, the thermal conductivity of the fir t electrode being substantially lower than that of the second electrode.
5. The bipolar cutting blade according to claim 1 , wherein the characteristic of the first electrode which is dissimilar from that of the second electrode corn rises the thermal capacity of the electrode, the thermal capacity of the first electrode being substantially lower than that of the second electrode.
6. The bipolar cutting blade according to claim 1 , wherein when the lade is used to cut tissue, the electrosurgical cutting voltage being applied between the first electrode and one of the second or third electrodes.
7. The bipolar cutting blade according to claim 1 , wherein when the blade is used to coagulate tissue, the electrosurgical cutting voltage being applied between the second and third electrodes.
8. The bipolar cutting blade according to claim 1 , wherein the first electrode is a longitudinal length of 8-20 mm.