Systems and methods for variable injection flow

A medical device, comprising:

• an elongate body defining a distal end, a fluid delivery conduit, a fluid exhaust conduit, and a thermally transmissive region at the distal end;
• and
• a unitary distal insert partially disposed within the thermally transmissive region and coupled to the distal end of the elongate body, the distal insert defining:
• a first lumen extending through the unitary distal insert and being in fluid communication with the fluid delivery conduit,
• a second lumen extending through the unitary distal insert and being coaxial with the first lumen and being in fluid communication with the fluid exhaust conduit, and
• a plurality of openings within the thermally transmissive region in fluid communication with the second lumen.