A system for determining a likelihood of barotrauma occurring in a tissue during the formation of lesion in said tissue the system comprising: a tissue sensing circuit comprising: a tissue sensing signal source for generating a current AC excitation signal used in complex impedance measurements; and a complex impedance sensor for receiving an AC response signal developed by the current AC excitation signal and being dependent on a complex impedance between an electrode and said tissue; and an electronic control unit configured to: acquire at least one value for at least one component of the complex impedance between said electrode and said tissue; characterised in that said electronic control unit is further configured to: acquire a value for the power applied to said tissue during the formation of a lesion in said tissue; calculate a likelihood index of barotrauma occurring in said tissue based on said at least one value of said at least one complex impedance component and said power; wherein said ECU is further configured to assess the stability of said electrode based on predetermined stability criteria and to calculate said index responsive to a determination by said ECU that said electrode meets said predetermined stability criteria. a tissue sensing circuit comprising: a tissue sensing signal source for generating a current AC excitation signal used in complex impedance measurements; and a complex impedance sensor for receiving an AC response signal developed by the current AC excitation signal and being dependent on a complex impedance between an electrode and said tissue; and a tissue sensing signal source for generating a current AC excitation signal used in complex impedance measurements; and a complex impedance sensor for receiving an AC response signal developed by the current AC excitation signal and being dependent on a complex impedance between an electrode and said tissue; and an electronic control unit configured to: acquire at least one value for at least one component of the complex impedance between said electrode and said tissue; characterised in that said electronic control unit is further configured to: acquire a value for the power applied to said tissue during the formation of a lesion in said tissue; calculate a likelihood index of barotrauma occurring in said tissue based on said at least one value of said at least one complex impedance component and said power; wherein said ECU is further configured to assess the stability of said electrode based on predetermined stability criteria and to calculate said index responsive to a determination by said ECU that said electrode meets said predetermined stability criteria. acquire at least one value for at least one component of the complex impedance between said electrode and said tissue; characterised in that said electronic control unit is further configured to: acquire a value for the power applied to said tissue during the formation of a lesion in said tissue; calculate a likelihood index of barotrauma occurring in said tissue based on said at least one value of said at least one complex impedance component and said power; wherein said ECU is further configured to assess the stability of said electrode based on predetermined stability criteria and to calculate said index responsive to a determination by said ECU that said electrode meets said predetermined stability criteria.