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.
Any questions be sent to drmmkapur@gmail.com
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