© Springer-Verlag London 2017Abhay Rané, Burak Turna, Riccardo Autorino and Jens J. Rassweiler (eds.)Practical Tips in Urology10.1007/978-1-4471-4348-2_41
41. Technical Tips for Laser Lithotripsy
Department of Urology, Henri Mondor Hospital, AP-HP, Paris-Est University, Créteil, France
Laser fibers are characterized by their ability to fragment even the harder stones and also by their flexibility which allows them to reach each part of the urinary tract. Accordingly, they are presently routinely applied in different endourologic procedures: retrograde intrarenal surgery, percutaneous nephrolithotomy, ureteroscopy and bladder stones.
KeywordsLaser lithotripsyKidney stonesBladder stonesPercutaneous surgeryRetrograde intrarenal surgery
Lasers have revolutionized the treatment of urinary stone disease. Laser fibers are characterized by their ability to fragment even the harder stones and also by their flexibility which allows them to reach each part of the urinary tract. Accordingly, they are presently routinely applied in different endourologic procedures: retrograde intrarenal surgery, percutaneous nephrolithotomy, ureteroscopy and bladder stones. But the various endoscopes employed for these different approaches have specific technical characteristics especially regarding their flexibility and the diameter of their working channel and also the amount of irrigation fluid they are able to provide. Therefore, the size of the laser fiber and laser settings differ significantly according to the surgical procedure.
Retrograde Intrarenal Surgery
Flexible ureteroscopes are miniaturized instruments with a tiny working channel of 3.6 Fr. It is quite consensual to use small 200–270 μm fibers for many reasons. First, these fibers are the most flexible and are able to reach all parts of the collecting system including lower pole of the kidney. Furthermore, they allow ensuring adequate irrigation during the whole procedure. However, their small diameter permits transmitting only low power levels up to 15 W to the stone.
Before determining optimal laser settings, a clear understanding of the interaction between laser fiber and stone is required. There are three distinct effects that happen when firing on a stone: fragmentation, stone retropulsion, and fiber tip degradation [4, 5, 9]. It has been shown, that higher energy levels produce more ablation but also more retropulsion . Retropulsion occurs mainly on smaller stones that have low kinetic inertia. Retropulsion significantly reduces the efficacy of the fragmentation process, because it increases the distance of the tip of the laser fiber and the stone at the time of subsequent shots. It has also been shown, that with the same energy settings (Joule) small fibers produce the same ablation volume as bigger ones, but the crater is deeper and narrower . However, bigger fibers provoke more retropulsion. On the other hand, there is more fiber tip degradation on smaller fibers [4, 5, 7].
Considering these observations, four fragmentation strategies have been proposed during a flexible ureteroscopy :
Dusting – it uses small energy associated to high frequency. Low energy permits limited fragmentation and virtually no retropulsion, increasing the frequency allows accelerating the fragmentation procedure. Depending on the laser device, the laser settings could be 0.3 J and 50 Hz, 0.5 J and 30 Hz and 0.8 J and 20 Hz. The technique of dusting consists of “painting” the stone by moving the laser fiber on its surface.
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