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AbstractBackground:It has been postulated that laser insertion sheaths prevent mechanical damage to the inside of working channels of flexible ureteroscopes. The presented study, for the first time, aims at confirming this hypothesis and visualized the damage of the endoscopic working channel by video-endoluminal observation after a series of laser fiber passages with or without the protection of a laser fiber insertion sheath.Materials and Methods:Four nonassembled working channels of two different manufacturers (Olympus™, Wolf™) were tested in a deflection model (50° and 180°). Flexifib™ laser fibers (LISA laser products) with an optical core diameter of 273 μm were inserted through 0.9% NaCl irrigated working channels in cycles of 10 insertions either with or without protection of the Flexgard™ insertion sheath. After 30 insertions, the examination cycle was reduced to 5 insertions each cycle until breakage. Test cycles were followed by endoluminal video examination of the working channel with the 2.4F flexible fiber scope by Polydiagnost™. Damage to the working channel was classified as streaks with superficial stress marks of the surface, scratches with embossed margins, or perforations.Results:No scratching or perforation occurred in the insertion sheath group in up to 150 insertions in all working channels and both deflection grades. In the group without insertion sheaths, scratches were visible after 40 to 50 insertions with 50° deflection and 30 insertions with 180° deflection. Perforations of the working channels were seen after 95 insertions with 50° and 60 insertions with 180° deflection.Conclusions:Severe damage to working channels depends on the degree of deflection and may occur after 30 insertions only. Relevant damage to the working channel may be avoided by using a laser fiber insertion sheath. [ABSTRACT FROM AUTHOR]