From: Proceedings 10th World Congress of Cryosurgery
The freeze-thaw cycles - optimal cryosurgical technique

November 1998
AA Gage
SUNY at Buffalo, Buffalo, N.Y. 14214

Cryosurgery must be performed in a manner that produces a predictable tissue response in an appropriate volume of tissue. The technique requires precise use of the freeze/thaw (F/T) cycle, every phase of which is injurious to tissue. For destruction of tissue, optimal use should be made of each phase of the cycle.

The cooling rate, intended to be as fast as possible, is a blend of fast and slow freezing,depending on the distance from the probe.

Cooling rate, whether fast or slow, is not as important as other factors. A cooling rate as slow as 3C/minute can produce intracellular ice in neoplastic cells.

Tissue temperature (TT) is the prime factor in cell death. Though substantial damage occurs at -20C to -30C, certain cell death requires TT colder than -40C to -50C.

The duration of freezing is important. The maintenance of freezing for several minutes will increase destruction in the -10C to -40C range because of solute-effect and growth of ice crystals.

The thawing rate should be slow and complete. This is an important destructive process which is enhanced by recrystallization, creating shearing forces in tissue, and by solute effect.

Repetition of the F/T cycle produces a greater volume of tissue death by its effect in the periphery of the frozen volume where the tissues were not cooled to lethal TT.

The interval between F/T cycles should be several minutes. The delay in repetition allows time for vascular stasis to develop, which will enhance the destructive effect of the second cycle.

Complete thawing, increased duration of freezing, longer F/T interval and repetition of the F/T cycle move the lethal TT closer to -20C and produce a more predictable destructive response in tissue, which is of critical importance in the treatment of cancer.

In clinical practice, deviations from optimal technique persist, and these may yield less than optimal results.


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