Background and Aims Ultrasound-guided percutaneous cryoneurolysis provides analgesia using cold temperatures to reversibly ablate peripheral nerves. Cryoneurolysis probes pass a gas through a small internal annulus, rapidly lowering pressure and temperature, and forming an ice ball to envelope the target nerve. Analgesia is compromised if a nerve is inadequately frozen, and laboratory studies suggest that pain may be paradoxically induced with a magnitude and duration in proportion with incomplete ablation.
Methods A cryoprobe (PainBlocker, Epimed International, Dallas, Texas) was inserted into a piece of meat, a gas passed through for 2 minutes, and resulting ice ball width (cross-section) and length (parallel axis) measured using ultrasound with temperature evaluated in 9 concentric locations concurrently.
Results Greatest influence on ice ball size was probe gauge: change from 18 to 14 increased ice ball width, length, and volume by up to 70%, 113%, and 512%, respectively, with minimum internal temperature decreasing as much as from -5°C to -32°C. In contrast, alternating the type of meat (chicken, beef, pork) and the shape of the probe tip (straight, Coude) effected ice ball dimensions to a negligible degree. Ice ball dimensions and the zone of adequate temperature drop were not always correlated, and even within a visualized ice ball the temperature was often inadequate to induce Wallerian degeneration.
Conclusions Percutaneous probe design can significantly influence the effective cryoneurolysis zone; visualizing a nerve fully encompassed in an ice ball does not guarantee adequate treatment to induce desired Wallerian degeneration. How specific temperatures transfer from pieces of meat to the human body remains unknown.
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