Cryosurgical instrument with vent means and method using same

摘要

A closed end surgical cryoprobe instrument may have a probe shaft diameter of 3 millimeters or less and can achieve and maintain freezing zone temperatures close to that of the liquid cryogenic refrigerant. Using sub-cooled liquid nitrogen at approximately -208 DEG C. freezing zone temperatures as low as -206 DEG C. can be achieved in under 1 minute. The liquid nitrogen supply tube is provided with a plurality of small vent holes to vent gas formed or present in the refrigerant supply tube to the return refrigerant flow channel. The vent holes also allow small amount of liquid nitrogen to vent into the return flow channel to further reduce the temperature differential between the sub-cooled liquid nitrogen supply and the counter current flowing return refrigerant. Heat transfer is maintained through nucleate boiling. In place of vent holes, narrow slits may be provided in the supply tube. Alternatively, a sintered porous metal supply tube can be used as the vent means.