Effect of cough technique and cryogen gas on temperatures achieved during simulated cryotherapy

Using 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.Uninterrupted 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.CO2 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.Cryotherapy is a method for the treatment of cervical precancerous lesions [1,2] that is considered the most suitable option to use in low-resource settings with underserved populations because it is low cost, requires no anaesthesia or electricity, and has a low complication rate [3]. Although nitrous oxide (N2O)-based cryotherapy is effective [4,5], its limited availability and higher cost in developing countries make carbon dioxide (CO2)-based cryotherapy a more practical choice. 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. Although the cough technique is currently being used in developing-country low-resource settings, there are no published data on the validity of this approach or the impact of using the cough technique on the depth of tissue necrosis generated by these methods. We develop