Factors Which Influence Intraluminal Temperature during Ho:YAG-Laser Exposure at an In-Vitro URS

Abstract

Introduction: The Ho:YAG-Laser is categorized as a potentially dangerous lithotripsy device (DIN: Class 4) for perforation which is mainly caused by the photonic energy the laser emits. Long time complications like ureteral strictures seem to be directed by thermal and mechanical injury. In this study different energy settings a) are being investigated, a DJ (double J stent) is placed beside the laser to simulate a therapy of a forgotten stent with reduction of the lumen b) due to the volume exploitation of the DJ, and direct contact between the laser fiber and the DJ in the ureter c) is simulated during laser exposure. Materials and Methods: We used the Ho:YAG-laser (Vera PulseTM, Coherent, Santa Clara USA) with a 365 μm diameter laser fiber. The settings of the laser were 0.6 J and 1 J pulse energy with a frequency of 5 Hz. The experimental setup was closely aligned with the clinical situation. The tip of the thermometer was attached inside the catheter through a puncture. The laser fiber was guided by means of a rigid URS video device (11.5 Ch). We had four different settings for a), b) and c) during the measurement: 1) Distance of 0.5 cm between the laser and the thermometer; without irrigation, 2) Distance of 0.5 cm between the laser and the thermometer; with irrigation, 3) Distance of 1 cm between the laser and the thermometer; without irrigation, 4) Distance of 1 cm between the laser and the thermometer; with irrigation. Results: The temperature in an empty ureter rises approximately by 5 ° C, when the laser energy is increased from 0.6 J to 1 J. When a DJ is inserted in the artificial ureter there is surprisingly almost no difference in the maximum temperature between the lower energy level (0.6 J) and the high energy level (1 J). However the time needed to reach the maximum temperature is noticibly less when using high energy levels. The reduction involume based on the placement of the DJ leads to a higher maximum temperature for the low energy setting. The third setting with direct laser fiber contact with the DJ produces the highest temperatures of up to 55 ° C. We think there must be a melting or burning of the DJ which leads to a temperature rise. Bubble formation was a sign of heating in the ureter in every setting without irrigation. A temperature fall off with increasing distance between the laser fiber and the thermometer is noticable when measuring without irrigation. Conclusion: There is no relevant heating with irrigation. Direct contact between the laser fiber and the DJ seems to evoke additional heating because of melting or underwater burning of the DJ. The maximum temperatures reached without irrigation are limited to a relatively small volume since the is a noticable temperature fall of when increasing the distance between the laser fiber and the thermometer.