Abstract
BackgroundCryotherapy is often used to treat cervical precancer in developing countries. There are different methods and cryogen gases used for cryotherapy, including the freeze-flush-freeze (cough) technique employed to minimize gas blockage. However, there is limited information to compare their effectiveness.MethodsUsing a tissue model, we compared temperature-time curves for four cryotherapy methods: uninterrupted freezing with nitrous oxide (N2O) and carbon dioxide (CO2), and two methods using a standard and extended version of the cough technique with CO2.ResultsUninterrupted freezing with both N2O and CO2 produced tissue temperatures less than -20°C (-40°C and -30°C respectively). CO2 cryotherapy procedures using the two cough techniques produced temperatures greater than -20°C in the model tissue.ConclusionCO2 cryotherapy using the cough technique may not achieve sufficiently low temperatures to produce the desired therapeutic effect. Other alternatives to the prevention of gas blockage should be developed.
Highlights
Cryotherapy is often used to treat cervical precancer in developing countries
We developed a system to compare the temperature profile at the probe and in a tissue model of three different CO2-based methods as well as the well-characterized N2O uninterrupted freeze
The extended cough technique for CO2 cryotherapy achieved a lower temperature for the probe (P = 0.0001) and tissue (P = 0.0001) measurements than the standard cough technique, the extended cough technique only achieved a minimum tissue temperature of -14°C. This laboratory-based evidence indicates that both cough techniques, used to prevent blockage of the cryogun during CO2 cryotherapy, significantly affected the temperature achieved at a 5 mm depth and did not achieve the minimum temperature of -20°C required for tissue destruction and therapeutic effects [7]
Summary
There are different methods and cryogen gases used for cryotherapy, including the freeze-flushfreeze (cough) technique employed to minimize gas blockage. The reported limitations to using CO2 include blockage of the cryogun during the cryotherapy procedure, inherently warmer tip temperatures due to the physical properties of the gas, and indications of lower therapeutic effect due to insufficient depth of tissue destruction during studies that employed a freeze-flush-freeze cycle ("cough technique") [6]. The "cough technique" has been recommended to avoid cryogun blockage during treatment [3]. It involves a cyclic momentary thawing of the cryogun probe by systematically interrupting freezing. The cough technique is currently being used in developing-country low-
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