Bipolar electrosurgical instruments

1 . An electrosurgical system comprising:

a bipolar electrosurgical instrument comprising:

a body;

an elongate shaft (i) attached to the body and (ii) 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 (i) a pair of electrically conductive elements, (ii) a first end for connection with a source of radio frequency electromagnetic energy, and (iii) a second end for connection to the first and second electrodes; and

a waveform generator that is the source of radio frequency electromagnetic energy and comprising:

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

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

wherein:

in a preheating stage, prior to a tissue heating stage, the controller is operable to:

control the radio frequency signal generator to supply the radio frequency signal of a predetermined initial power level of up to 20 Watts to the first and second electrodes for a predetermined initial time period of up to 200 milliseconds, such that characteristics of a target vessel are not substantially altered, the predetermined time period having an end time;

measure a voltage level between the first and second electrodes at the end time to determine a starting voltage to be used at a heating start time;

and

in the tissue heating stage after the preheating stage and before a tissue sealing stage, the controller is operable to:

control the radio frequency signal generator to supply the radio frequency signal at a controlled voltage level to the first and second electrodes, the controlled voltage level starting at the starting voltage, at the heating start time, then increasing the controlled voltage level to a final voltage at a heating end time;

measure an impedance between the first and second electrodes during the supply of the controlled voltage level;

detect a minimum measured impedance between the first and second electrodes during the supply of the controlled voltage; and

declare the heating end time when a measured impedance is greater than the minimum measured impedance by a first predetermined amount.

2 . The electrosurgical system according to claim 1 , wherein the controller is operable to increase the controlled voltage level linearly between the starting voltage and the heating end time voltage.

3 . The electrosurgical system according to claim 1 , wherein:

in the tissue sealing stage, the controller is operable to:

increase the controlled voltage level linearly from the heating end time voltage to a predetermined sealing voltage level applied at a constant level for a predetermined sealing time period having a sealing end time, a rate of the controlled voltage level increase during the tissue sealing stage being larger than a rate of the controlled voltage increase during the tissue heating stage;

measure an impedance level between the first and second electrodes at the sealing end time;

compare a measured sealing impedance at the sealing end time with a predetermined reference impedance; and

declare the sealing end time to end the tissue sealing stage when the measured sealing impedance is greater than or equal to the predetermined reference impedance.

4 . The electrosurgical system according to claim 3 , wherein the controller is operable such that, in response to the measured sealing impedance at the sealing end time being greater than a predetermined value, the controlled voltage level is held at a maximum voltage level for a predetermined hold time.

5 . The electrosurgical system according to claim 1 , wherein the first predetermined amount is a predetermined portion of a minimum value of the measured impedance.

6 . An electrosurgical system comprising:

a bipolar electrosurgical instrument comprising:

a body;

an elongate shaft (i) attached to the body and (ii) 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 (i) a pair of electrically conductive elements, (ii) a first end for connection with a source of radio frequency electromagnetic energy, and (iii) a second end for connection to the first and second electrodes; and

a waveform generator that is the source of radio frequency electromagnetic energy and comprising:

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

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

wherein:

in a preheating stage, prior to a tissue heating stage, the controller is operable to:

control the radio frequency signal generator to supply the radio frequency signal of a predetermined initial power level of up to 20 Watts to the first and second electrodes for a predetermined initial time period of up to 200 milliseconds, such that characteristics of a target vessel are not substantially altered, the predetermined time period having an end time;

measure a voltage level between the first and second electrodes at the end time to determine a starting voltage to be used at a heating start time for the tissue heating stage;

and

in the tissue heating stage after the preheating stage and before a tissue sealing stage, the controller is operable to:

control the radio frequency signal generator to supply the radio frequency signal at a controlled voltage level to the first and second electrodes, the controlled voltage level starting at the starting voltage, at the heating start time, then increasing the controlled voltage level to a heating end time voltage level at a heating end time;

measure an impedance between the first and second electrodes during the supply of the controlled voltage level;

and

in response to the measured impedance at the heating end time being greater than a predetermined value, holding the controlled voltage level at a maximum value of the controlled voltage level for a predetermined hold time.

7 . An electrosurgical system comprising:

a bipolar electrosurgical instrument comprising:

a body;

an elongate shaft (i) attached to the body and (ii) 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 (i) a pair of electrically conductive elements, (ii) a first end for connection with a source of radio frequency electromagnetic energy, and (iii) a second end for connection to the first and second electrodes; and

a waveform generator that is the source of radio frequency electromagnetic energy and comprising:

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

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

wherein, in a tissue heating stage after a preheating stage and prior to a tissue sealing stage, the controller is operable to:

control the radio frequency signal generator to supply the radio frequency signal at a controlled voltage level to the first and second electrodes, the controlled voltage level starting at a starting voltage at a heating start time, increasing during the heating stage to a heating stage final voltage at a heating end time;

measure an impedance between the first and second electrodes during the supply of the controlled voltage level;

detect a minimum measured impedance between the first and second electrodes during the supply of the controlled voltage; and

declare the heating end time when a measured impedance is greater than the minimum measured impedance by a first predetermined amount; and

in the tissue sealing stage, the controller is operable to:

supply the radio frequency signal at a constant predetermined sealing voltage level to the first and second electrodes for a predetermined sealing time period having a sealing end time, the constant predetermined sealing voltage level being greater than the heating stage final voltage;

measure an impedance level between the first and second electrodes at the sealing end time;

compare a measured sealing impedance at the sealing end time with a predetermined reference value;

in response to the measured sealing impedance at the sealing end time being greater than the predetermined value, holding the controlled voltage level at a maximum voltage level for a predetermined hold time;

after the predetermined hold time, measure a post-hold sealing impedance;

reducing a power associated with the controlled voltage level and then measuring the impedance level again; and

in response to the sealing impedance measured after reducing the power being lower than the post-hold sealing impedance, terminate the radio frequency energy.

8 . The electrosurgical system according to claim 7 , wherein, after the tissue heating stage, in response to the measured impedance being less than the minimum measured impedance by the first predetermined amount, the controller is operable to:

repeat the tissue heating and tissue sealing stages until the measured impedance is greater than the minimum measured impedance by at least the first predetermined amount; and

supply the radio frequency signal at the starting voltage and increasing to the heating stage final voltage at each heating end time each time the tissue heating stage is repeated; and

increasing the heating stage final voltage linearly to the predetermined sealing voltage level each time the tissue sealing stage is repeated.