Reference Manual - IARC Screening Group

Treatment and Followup• Regulator with pressure gauge, cryotherapy unit holder, safety valve,and exhaust port.The cryotherapy unit is designed to connect to a compressed gas cylinder.A timer with a second hand also is desirable.Figure 7-3. Cryotherapy System 6Either compressed liquid carbon dioxide or nitrous oxide gas is used asthe coolants to freeze and destroy the cells of the cervix. Carbon dioxideis a common, inexpensive and safe gas costing about 50% less thannitrous oxide. It should be used “bone dry” or “medical grade” becausecontaminants affect the freezability of the cryosurgical equipment.Nitrous oxide has a lower freezing temperature (average -89 o C [-128.2 o F]versus -68 o C [-90.4 o F] for carbon dioxide) and, therefore, takessomewhat less time for treatment. The minimum working pressure shownon the gauge should be 40–70 kg per square centimeter (kg/cm 2 ). Theminimum temperature at the probe tip for effective freezing should be atleast -60EC (-76 o F). For more information about choosing an appropriategas cylinder, see Figure D-2 on page D-2.Cryoguns are designed to be used with a variety of cryotips. Anexocervical cryotip, which has a circular end (about 19 mm in diameter)with a raised “nipple,” is recommended for use when providing cervical6There are two types of fittings used to connect the regulator to the gas cylinder. In this picture, the United States(US) fitting is shown. A British fitting may also be used. For more information about the US and British fittings,see Appendix D on pages D-3 and D-4.Cervical Cancer Prevention Guidelines for Low-Resource Settings 7-11