Introduction: The authors found so-called 'Double firing' phenomenon in which laser firing occurred not only in the laser fiber tip but also in its proximal part, and assuming that this phenomenon is caused by different breakdown rates between fiber jacket and fiber core. Therefore, this study is to establish a new safe-distance concept to prevent scope damage by analyzing breakdown of laser fiber jacket and fiber core.
Methods: To evaluate shortening of laser fiber during lithotripsy, 200µm or 365µm laser fiber was fixed in benchtop simulation model. Fiber tip was in contact with uniform phantoms stone and fiber tip submerged in 0.9% saline. Four different energy settings (1.0Jx10Hz, 1.0Jx30Hz, 2.0Jx10Hz, 2.0Jx30Hz) and two different fiber sizes (200µm and 365µm) were tested. After 3 minutes of use in each energy setting, length of fiber shortening and jacket burn were measured. Then fibers were stripped to measure length of core degradation.
Results: After 3 minute of laser firing, almost all stones were totally fragmented less than 1mm.
No statistical difference was found between lengths of fiber core degradation and jacket burn. (5.81±1.89mm vs 5.76±1.95mm, p=0.627) However, the length of fiber core degradation was longer than that of the jacket burn in 50% (40 of 80) of the samples and the mean difference in lengths between core degradation and jacket burn was 0.49±0.90mm in these samples.
Multivariate linear regression analysis showed that pulse energy had a greater effect on fiber breakdown than frequency and fiber caliber. Independent Mann-Whitney U test showed that the lengths of jacket burn and core degradation were longer at the higher power settings. Fiber core degradation occurred similarly with jacket burn except in the setting of 200µm fiber - 2J with 30Hz. The length of fiber core degradation was significantly longer than that of the jacket burn in the high power setting of 2J with 30Hz.
Conclusions: For prevention of double firing and safe usage of flexible ureteroscopy, we recommend to cut a little longer laser fiber than visible jacket burn periodically especially in high energy setting. Source of
Funding: This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No. 2019R1C1C1008339).