Cryotherapy can now be applied using a variety of delivery systems and cryogens. We compared the Cryotech LCS 3000 liquid nitrogen system (Spembly, Andover, UK) with the CRYOcare argon gas-based system (Irvine, CA, U.S.A.) using three different 3-mm cryoprobes: an old liquid nitrogen probe CN-probe), a new N-probe featuring gas bypass and an argon gas probe. Each probe was tested in two models: (i) fresh sheep liver at 20 degrees C-the probe was inserted to a depth of 1.5 cm; the rate of ice ball formation was monitored by recording radial temperatures every 15 s at 5, 10, 15, and 20 mm from the cryoprobe, and the ice-ball diameter was measured every 2.5 min. After 10 min, the probe wa warmed and the time taken until it could be extracted from the liver was recorded. (ii) Warm water bath-the probe was immersed in warm water (42 degrees C) for 15 min and the ice-ball diameter was measured at 5-min intervals. Radial temperatures in liver declined more rapidly (P < 0.001) and time to probe extraction was less (P < 0.01) when the argon gas system was used. The new N-probe performed better than its older counterpart, but was still slower than the argon gas system. In liver (20 degrees C), ice-ball diameters were similar after 10 min, but in warm water, they were larger when the new Nd probe was used (P < 0.02). It would appear that the argon gas system is initially faster, but it does not achieve as large an ice ball in a warm environment as the liquid nitrogen system. (C) 1997 Academic Press.
