Gases selected for cryotherapy should have their freezing point below the cryogenic range from −20 to −30 °C needed for tissue destruction. Nitrous oxide (N₂O) and carbon dioxide are used for cryotherapy as these gases provide excellent thermal transfer when circulating in the probe tip (Fig. 14.3) [8, 9].

Nitrous oxide produces lower temperatures to a greater depth than carbon dioxide [10]. The comparison of depth of tissue destruction is shown in Table 14.1.

Before proceeding to cryotherapy, the health provider must confirm that the patient is eligible for the therapy as per the eligibility criteria. An informed consent is taken. The clinician should explain the procedure to the patient and reassure her. The procedure is carried out under colposcopic guidance without anesthesia (Fig. 14.4).

Woman should be placed in a dorsal lithotomy position and Cusco’s speculum is inserted to expose the cervix. The cryoprobe surface is wiped with saline or coated with water-soluble lubricating jelly to provide good contact and firm application of the cryoprobe tip to the cervix and an optimal lowering of the tissue temperature. While applying cryoprobe, care is taken so that the vaginal walls are not in contact with the cryoprobe. No anesthesia is required except in very anxious patients who may be given NSAID 30 min prior to the procedure.

The probe should cover the lesion completely. The gas trigger in the cryogun is released and the gas escapes with a hissing noise. The gas circulating through the cryoprobe withdraws heat from the cervix till the freezing temperature is reached. As freezing progresses, ice forms on the cervix and on the cryoprobe. The rapidity of the ice-ball formation and efficacy of the procedure depend on:

Nitrous oxide based cryotherapy achieves a temperature of about −89 °C and carbon dioxide based system achieves −68 °C at the core of the tissue that is at the center of the ice ball. The temperature at the edge of the frozen tissue may be around −20 °C.The minimum temperature of the probe tip for effective tissue freezing should be −60 °C. An adequate freezing is achieved when the margin of the ice ball extends 4–5 mm past the outer edge of the cryotip; this will ensure that cryonecrosis occurs down to at least 5 mm depth [9].

The two methods of cryotherapy are as follows:

The double freeze technique produces more tissue destruction than the single freeze cycle [6, 12].

When thawing is completed, the ice on the cryoprobe is totally cleared and then the probe is removed by gently rotating on the cervix. After the procedure, the cervix is examined for any bleeding (Fig. 14.6).

The cryotip is washed with clean water until visibly clean. The high-level disinfection (HLD) of cryotip is done by boiling in water for 20 min or soaking the cryotip in chemical disinfectant for 20 min and then rinsed with water. It is critical that the hollow part of the cryotip is completely dry before it is used for the next case; otherwise the water would freeze and the probe could crack.