BERKELEY, CA (UroToday Inc.) - Nitinol is truly the wonder material of endourology for the 21st century! This article highlights yet another potential application of this unique material. The authors describe a novel, proprietary, prototype, 1.83F nitinol sheath through which the 272 micron laser probe is inserted. By injecting the sheath with 60°C saline solution the nitinol sheath rapidly curls to a predetermined angle. Injecting 15°C saline causes the sheath to return to a straight configuration. Varying the temperature of the saline between 15° and 60°C creates graded degrees of curl to the sheath. In this preliminary ex vivo study, the authors were able to significantly increase the deflection of all major commercially available flexible ureteroscopes, by placing the sheath and laser probe through the working channel, compared to the ureteroscopes alone, with no devices in the working channel. This deflection was even greater than the active deflection of the scope without any instrument in the channel.

Many of the flexible ureteroscopes are being designed with intrinsic features to improve active deflection. However, these intrinsic features seem to be very fragile and prone to damage especially during exaggerated active deflection in an attempt to access a difficult lower pole calyx and stone. However, placing even the 200 micron laser probe may eliminate this access and render the stone untreatable. The concept of a sheath that would increase the deflection of the ureteroscope even with the laser probe in place is very intriguing. However, as this study demonstrates, the sheath does further reduce the flow of irrigant, beyond that of the laser probe alone. However, this is no more than with a 1.9F basket extraction device and this can usually be remedied by increasing the irrigant flow pressure.

As the authors point out, there remain several unanswered questions regarding the sheath and its use with the flexible ureteroscopes. Quite importantly is how the increased deflection of the ureteroscope may affect the fiber optics and deflection mechanism of the scope and ultimately the effect on scope durability. However, with this sheath perhaps the deflection mechanism of the scope will become less important and instead the temperature applied to the sheath within the working channel will control deflection. There also remains a concern of the impact of 45°C and 60°C saline on the urothelium and collecting system. However, only a small aliquot of the warmed saline (5-10cc) is necessary to cause deflection of the sheath. Once the sheath is deflected it remains so until a lower temperature solution is applied to cause straightening. This concept of a deflecting sheath is most exciting. It could be hypothesized that the actual covering material of the laser probe could be fashioned from this nitinol material thereby creating a treatment device that could be used to direct the scope and treat the pathology. This could also eliminate the need for scopes having an active deflection mechanism, which would thereby reduce the cost of these highly technical instruments. The possibilities are unlimited, and we will eagerly await further evaluation of this device.

J Urol 2005;173:131-34