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From: Proceedings 10th World Congress of Cryosurgery
Rectal protection with a silicone insulating device during prostate cryosurgery: study in a canine model

November 1998
DM Zapzalka, JH Hulbert, MF Hoey, N MerryTC -Bischof]
Department of Urologic Surgery, University of Minnesota, Minneapolis, Minnesota; Department of Physiology, University of Minnesota, Mountain View, California; Bioheat and Mass Transfer Laboratory, Department of Mechanical Engineering, University of Minnesota

Introduction and Objectives: Cryosurgery for prostate cancer has been limited in its acceptance, in part, because of the complications associated with its use. The most morbid of complications is a rectourethral fistula occurring in up to 3.6% of patients secondary to freezing of adjacent rectal tissue. A silicone insulating device has been developed and tested in vitro to protect the rectum during cryosurgery. This device is now tested in vivo in a canine model.

Methods: Six dogs had the silicone insulating device (2 mm thickness) placed in Denonvilliers' fascia through a midline laparotorny incision. K-type thermocouples were placed on each side of the insulating device to record prostate and rectal temperatures. A cryoprobe was placed through the laparotorny incision and into the posterior periphery of the prostate near the silicone device. The prostate was frozen until the drop in temperature ceased on the prostate side of the insulating device, or the peripheral prostate temperature reached below -50C.

Results: Temperature data from the prostate side of the insulating device was compared to the rectal side using a pared t-Test. The temperature differential across the device was statistically different (P=0.01) at 5 minutes and at 10 minutes (P=0.003). The temperature differential across the insulating device at the time of conclusion of the freezing ranged from 14.8C to 52.4C. The mean temperature on the prostate side of the insulating device was -24.8C with the mean temperature being 11,6C on the rectal side. In only one dog did the temperature on the rectal side of the insulating device drop below freezing (-0.8C), with the temperature on the prostate side for this dog being notably colder (-51C).

Conclusion: These data confirm, in an animal model, the effectiveness of the silicone insulating device for protection of the rectum during cryosurgery of the prostate. This device will, therefore, allow colder temperatures to be achieved at the posterior periphery of the prostate during cryosurgery. Further study is warranted to develop a mode of transperineal placement of the device for eventual use in humans.

Source of Funding Research gift from Candela Corporation


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