How is cryosurgery performed?

There are several ways to apply cryogens. Various sizes of swabs can be dipped in LN₂ and touched to the lesion to freeze it. Due to the rapid dispersal of cold, swabs do not result in as much tissue cooling as the direct application of LN₂ to the skin. Swabs are not used to treat malignancies. Various surgical instruments, such as hemostats and pick-ups (tweezers), can be used for cryosurgery of raised or pedunculated lesions. The surgical instrument is submerged in LN₂ for 20 to 30 seconds and then the target lesion is grasped with the instrument. It is best to use a separate swab or surgical instrument and cup of cryogen for each patient to avoid cross-contamination.

The spray technique uses modified thermoses that allow the LN₂ to spray out of a nozzle (see Fig. 52-1). The degree of freezing is changed by the nozzle size, the pressure in the thermos, the distance to the lesion, and the length of freeze. This apparatus can be used for several hours, and contamination is not an issue. It also can treat very large lesions. A modification of this technique is to use neoprene cones to confine the LN₂, causing a more concentrated freeze.

Some cryosurgeons use probes for freezing. A probe is a metal object that is cooled by the cryogen and applied to the lesion. The probe is usually the size of the lesion, but it can be applied multiple times for larger lesions. A probe can vary from a diameter of a few millimeters to a hollow brass doorknob. The disadvantages are that it is slower than the spray technique, a variety of sizes and shapes of probes are needed, and contamination can occur.