Bipolar electrosurgical instruments

1. An electrosurgical system comprising:

a bipolar electrosurgical instrument comprising:

a body;

an elongate shaft (1) attached to the body and (2) having a distal end;

first and second elongate jaw members at the distal end of the elongate shaft, the first elongate jaw member carrying a first electrode and the second elongate jaw member carrying a second electrode, the first and second elongate jaw members being movable relative to one another between an open position in which the first and second electrodes are spaced apart from one another and a closed position in which the first electrode is adjacent the second electrode; and

a power cable having (1) a pair of electrically conductive elements, (2) a first end for connection with a source of radio frequency electromagnetic energy, and (3) a second end for connection to the first and second electrodes; and

a waveform generator which is the source of the radio frequency electromagnetic energy and is connected with the power cable of the bipolar electrosurgical instrument, and comprising:

a radio frequency signal generator configured to supply a radio frequency signal to the first and second electrodes via the power cable; and

a controller configured to control operation of the radio frequency signal generator, in dependence upon a received control input,

wherein the controller is configured to measure an electrical current supplied to the first and second electrodes to generate a measured current signal during an application process including, in seriatim, a first stage in which constant power is applied to tissue held between the first and second elongate jaw members for a predetermined period of time short enough to not alter substantially the characteristics of the tissue, a second stage in which a voltage across the first electrode and the second electrode is slowly ramped up from a starting voltage determined in the first stage at a first rate until an impedance of the tissue reaches a certain impedance, a third stage in which the voltage across the first electrode and the second electrode is ramped up from the voltage at the end of the second stage for a fixed time period at second rate larger than the first rate, and a fourth stage in which the tissue is sealed and to detect a short circuit between the first and second electrodes during the application process if the measured current signal exceeds a first predetermined value for at least a predetermined time period.

2. An electrosurgical system as claimed in claim 1 , wherein the first predetermined value is 4.5A RMS, and the predetermined time period is in a range of 400 ms to 800 ms.

3. An electrosurgical system as claimed in claim 1 , wherein the controller is configured to stop supply of the radio frequency signal to the first and second electrodes upon detection of the short circuit between the first and second electrodes.

4. A method of operating an electrosurgical system comprising (A) a bipolar electrosurgical instrument comprising a body; an elongate shaft (1) attached to the body and (2) having a distal end; first and second elongate jaw members at the distal end of the elongate shaft, the first elongate jaw member carrying a first electrode and the second elongate jaw member carrying a second electrode, the first and second elongate jaw members being movable relative to one another between an open position in which the first and second electrodes are spaced apart from one another and a closed position in which the first electrode is adjacent the second electrode; and a power cable having (1) a pair of electrically conductive elements, (2) a first end for connection with a source of radio frequency electromagnetic energy, and (3) a second end for connection to the first and second electrodes; and (B) a waveform generator which is the source of the radio frequency electromagnetic energy and is connected with the power cable of the bipolar electrosurgical instrument, and comprising a radio frequency signal generator configured to supply a radio frequency signal to the first and second electrodes via the power cable; and a controller configured to control operation of the radio frequency signal generator, in dependence upon a received control input, wherein the method comprises: measuring, by the controller, an electrical current supplied to the first and second electrodes to generate a measured current signal during an application process including, in seriatim, a first stage in which constant power is applied to tissue held between the first and second elongate jaw members for a predetermined period of time short enough to not alter substantially the characteristics of the tissue, a second stage in which a voltage across the first electrode and the second electrode is slowly ramped up from a starting voltage determined in the first stage at a first rate until an impedance of the tissue reaches a certain impedance, a third stage in which the voltage across the first electrode and the second electrode is ramped up from the voltage at the end of the second stage for a fixed time period at second rate larger than the first rate, and a fourth stage in which the tissue is sealed and detecting, by the controller, a short circuit between the first and second electrodes during the application process if the measured current signal exceeds a first predetermined value for at least a predetermined time period.

5. A method as claimed in claim 4 , wherein the first predetermined value is 4.5A RMS, and the predetermined time period is 400 ms.

6. A method as claimed in claim 4 , further comprising:

stopping supply of the radio frequency signal to the first and second electrodes upon detection of the short circuit.