Friday, July 5, 2013

ELECTRIC EQUIPMENT 11 Cryosurgical Systems


CRYOSURGICAL SYSTEMS
Cryotherapy, the application of extreme cold to tissues and is a useful technique for the destruction of tissues. It is characterized by minimal bleeding or pain in the postoperative period. Cryosurgical systems are well established in many surgical specialities including:
•    General surgery,
•    Gynecology,
•    Dermatology,
•    Neurology, and
•    Urology.
     The first practical equipment for the control and maintenance of extreme low temperature in surgery was produced in 1962. The apparatus was not very sophisticated and used liquid nitrogen to achieve low temperature in the region of –196 degree Celsius. This very low temperature was subsequently found to exceed requirements, and Amoils developed a more simple apparatus which used nitrous oxide or carbon dioxide to achieve temperatures in the region of –70 degree Celsius. The design principles established by Amoils (Fig. 2.6) are still used in modern cryosurgical equipment which employs high-pressure, non-syphon cylinders of N2O and CO2.
•    Cryosurgical systems consist of flexible tubing connecting the gas flow control unit to a cryoprobe or working tip which comprises two concentric tubes
•    The inner tube delivers nitrous oxide or carbon dioxide at pressures between 4,000 kPa and 6,000 kPa to a narrow orifice in the end
•    The sudden expansion of this gas through the ‘Joule- Thompson Orifice’, produces a rapid drop in temperature of the probe surface forming an ice ball
•    The expanded gas is then returned at atmospheric pressure along the outer tube
•    Some cooling along the shaft of the probe occurs and can be a disadvantage, for example in neurosurgery
•    To overcome this, Spembley manufacture a probe which employs a reversed gas flow. This design enables the incoming gas to be carried to the probe tip via the outer of the two concentric tubes; it is allowed to expand through an annular orifice, being finally released through the central tube.
•    The incoming gas acts as an insulating barrier and the cooling is confined to the probe tip.

          Cryosurgery has been useful in the treatment of early skin cancer. It is being explored in the treatment of prostate, liver and bone.

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