Vessel sealing algorithm and modes

Abstract

A method comprising sealing a vessel residing within tissue between jaws of forceps by sensing an amount of tissue held within the forceps, the sensing by passing electrical current through the tissue by way of the forceps. The method comprises heating the tissue using electrical current, the heating such that impedance of the tissue changes at a first predetermined rate, the first predetermined rate selected based on the sensing. The method comprises desiccating the tissue using electrical current, such that the impedance of the tissue changes at a second predetermined rate different than the first predetermined rate. The method comprises ceasing application of the electrical current to the tissue when impedance of the tissue reaches a predetermined value. Sensing the amount of tissue held within the forceps comprises varying electrical current flowing through the tissue through the forceps such that impedance of the tissue changes at a third predetermined rate.

We claim: 
     
         1 . A method comprising:
 sealing a vessel residing within tissue between jaws of forceps by:
 sensing an amount of the tissue held within the forceps, the sensing by controlling the electrical current delivered through the tissue by way of the forceps, wherein controlling the electrical current delivered changes an impedance of the tissue at a first predetermined rate of impedance change that is constant; 
 selecting a second and a third predetermined rate of impedance change based on the electrical current required to control the rate of change of impedance of the tissue at the first predetermined rate of impedance change, wherein the first, second and third predetermined rates of impedance change are all different from each other; and then 
 heating the tissue using the electrical current such that the impedance of the tissue changes at the second predetermined rate of impedance change; and then 
 desiccating the tissue using the electrical current, the desiccating such that the rate of change of impedance of the tissue changes at the third predetermined rate of impedance change; and then 
 ceasing application of the electrical current to the tissue when impedance of the tissue reaches a predetermined value. 
   
     
     
         2 . The method of  claim 1  wherein sensing the amount of the tissue held within the forceps further comprises:
 calculating a mean electrical current delivered to the tissue during the sensing to achieve the first predetermined rate of impedance change, the mean electrical current delivered during the sensing indicative of the amount of the tissue held within the forceps. 
 
     
     
         3 . The method of  claim 2  wherein the first predetermined rate impedance change is about −50 Ohms/second. 
     
     
         4 . The method of  claim 2  wherein controlling the electrical current flowing through the tissue further comprises varying the electrical current flowing through the tissue such that the impedance of the tissue changes at a rate of about −50 Ohms/second for about 100 milliseconds. 
     
     
         5 . The method of  claim 1  wherein heating the tissue further comprises varying the electrical current through the tissue to drive the second predetermined rate of impedance change to have a negative slope over the course of the heating. 
     
     
         6 . The method of  claim 5  wherein the second predetermined rate of impedance change is selected based on the amount of the tissue held within the forceps as determined by the sensing. 
     
     
         7 . The method of  claim 5  further comprising:
 detecting a mode selected by an operator, the detecting prior to the heating; and 
 wherein heating further comprises heating the tissue at the second predetermined rate of impedance change selected based on the amount of the tissue held within the forceps as determined by the sensing and the mode selected by the operator. 
 
     
     
         8 . The method of  claim 5  further comprising transitioning between heating and desiccation based on at least one selected from the group consisting of: after a lowest value of impedance of the tissue is reached; after a rate of change of impedance transitions from negative to positive; and after a lowest value of impedance of the tissue is reached and surpassed by a predetermined amount. 
     
     
         9 . The method of  claim 1  wherein desiccating the tissue further comprises varying the electrical current through the tissue such that the third predetermined rate of impedance change has a positive slope over the course of the desiccating. 
     
     
         10 . The method of  claim 9  wherein the third predetermined rate of impedance change is selected based on the amount of the tissue held within the forceps as determined by the sensing. 
     
     
         11 . The method of  claim 1 , wherein a seal cycle comprises the sealing, the heating, the desiccating, and the ceasing steps; and wherein the predetermined value is determined during the seal cycle. 
     
     
         12 . The method of  claim 9  further comprising:
 detecting a mode selected by an operator, the detecting prior to the desiccating; and 
 wherein desiccating further comprises desiccating the tissue at the third predetermined rate of impedance change selected based on the amount of the tissue held within the forceps as determined by the sensing and the mode selected by the operator. 
 
     
     
         13 . The method of  claim 1 :
 wherein desiccating the tissue further comprises varying the electrical current through the tissue such that the third predetermined rate of impedance change has a positive slope over the course of the desiccation; and then further comprising   desiccating the tissue using electrical current such that the impedance of the tissue changes at the third predetermined rate of impedance change having a positive slope different than the slope of the second predetermined rate of impedance change.   
     
     
         14 . The method of  claim 1  wherein desiccating the tissue further comprises varying the electrical current through the tissue such that the third predetermined rate of impedance change is defined by a set point impedance as a function of time, where the set point impedance as a function of time has the second predetermined rate of impedance change, wherein the third predetermined rate of impedance change comprises a predetermined path. 
     
     
         15 . The method of  claim 1  wherein desiccating the tissue further comprises varying the electrical current through the tissue such that a first derivative of the impedance as a function of time is the third predetermined rate of impedance change. 
     
     
         16 . A method comprising:
 sealing a vessel residing within tissue between jaws of forceps by:
 sensing an amount of tissue held within the forceps, the sensing by varying a sense power delivered through the tissue by way of the forceps such that an impedance of the tissue changes at a first predetermined rate of impedance change, the sense power delivered indicative of an amount of tissue held between the jaws; 
 selecting a second and a third predetermined rate of impedance change based on the sense power delivered, the first, second and third predetermined rates of impedance change are all different from each other; and then 
 heating the tissue using power, the heating such that the impedance of the tissue changes at the second predetermined rate of impedance change; and then 
 desiccating the tissue using power, the desiccating such that the rate of change of impedance of the tissue changes at the third predetermined rate of impedance change; and then 
 ceasing application of power to the tissue when impedance of the tissue reaches a predetermined value. 
   
     
     
         17 . The method of  claim 16  wherein sensing the amount of tissue held within the forceps further comprises:
 calculating a mean sense power delivered to the tissue to achieve the first predetermined rate of change of impedance, the mean sense power indicative of the amount of the tissue held within the forceps. 
 
     
     
         18 . The method of  claim 16  further comprising:
 detecting a mode selected by an operator, the detecting prior to the heating; and 
 wherein heating further comprises heating the tissue at the second predetermined rate of impedance change, selected based on the amount of the tissue held within the forceps as determined by the sensing and the mode selected by the operator. 
 
     
     
         19 . The method of  claim 16  further comprising transitioning between heating and desiccation based on at least one selected from the group consisting of: after a lowest value of impedance of the tissue is reached; after a rate of change of impedance transitions from negative to positive; and after a lowest value of impedance of the tissue is reached and surpassed by a predetermined amount. 
     
     
         20 . A method comprising:
 sealing a vessel residing within a tissue between a pair of jaws of forceps by:
 sensing an amount of the tissue held within the forceps, the sensing by delivering a constant sense power through the tissue by way of the forceps, and measuring a resultant rate of change of impedance of the tissue; 
 selecting a first and a second predetermined rate of impedance change based on the resultant rate of change of impedance delivered during the sensing, wherein the first and second predetermined rates of impedance change are different from each other; and then 
 heating the tissue, the heating such that impedance of the tissue changes at the first predetermined rate of impedance change; and then 
 desiccating the tissue, the desiccating such that the rate of change of impedance of the tissue changes at the second predetermined rate of impedance change; and then 
 ceasing application of power to the tissue when the impedance of the tissue reaches a predetermined value.