Application of Cryoprobe
Make sure that there is adequate gas in the tank and that connections have been correctly made and tightened. The appropriate cryoprobe for the task must be used (see Equipment). Before beginning, make sure that the cryotherapy equipment is functioning correctly by depressing the foot switch and observing proper cooling of the tip.
If an incision will be required in the planned procedure, surgical preparation and draping are necessary. If no incision will be required, sterile techniques are not necessary.
After the appropriate anesthesia has been instituted (see Patient Preparation), the cryoprobe is applied while still warm to the tissue undergoing treatment. The footswitch is then depressed to allow coolant to flow to the tip. An ice ball should form at the tissue at the tip. Once tissue has started adhering to the tip, the probe should not be moved, because of the risk of tearing or breaking the tissue.
For cryoextraction of cataracts, after the cataract incision is made, the surface of the lens is dried and a room-temperature cryoprobe tip applied to the lens capsule. The cryogen is then released into the tip, causing the tip to cool rapidly and adhere to the lens capsule. Once adhesion is complete, the lens can be removed by pulling gently on the cryoprobe.
For retinal cryopexy, the probe is applied to the conjunctiva while the surgeon looks inside the eye with an indirect ophthalmoscope and gently presses on the probe. The pressure from the probe can be seen as an indentation in the retina. When the probe is in the correct position relative to the retinal break, the cryogen is released into the probe, and the retina can be seen to whiten as it freezes. Retinal swelling can be observed after the probe is removed, and scarring develops within about 1 week.
Complications
Complications of cryotherapy include the following:
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Overfreezing – Because cryotherapy causes tissue destruction, application of excessively cold temperatures or excessive duration of cryoapplication can damage normal tissue; the amount and duration of cryotherapy must be appropriate for the desired purpose
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Underfreezing – Application of cryotherapy without achieving appropriately low tissue temperatures will not yield the desired results
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Freezing nontarget tissue – This can occur if the cryoprobe is inadvertently applied to adjacent tissue that was not supposed to be treated
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Tissue cracking – This can occur if the probe is moved after it has adhered to the tissue; the probe should be allowed to defrost completely before an attempt is made to remove it from the tissue
