A study of the maximum permissible average power of a thulium fiber laser used in contact endoscopic lithotripsy of bile duct stones

Laser lithotripsy of gallstones, despite its effectiveness, carries the risk of thermal tissue damage due to heating of irrigation fluid (saline solution) by laser radiation. The paper presents the results of an experiment aimed at evaluating the dynamics of fluid temperature during 30 and 60 seconds of continuous laser emission under active irrigation (60 mL/min) and in a standing water environment at various average radiation power values. Laser exposure was performed using a new generation Urolase+ Premium thulium fiber laser (TVL) (VPG LaserONE, Russia). The average power varied between 5 and 70 W. Provided that irrigation fluid was continuously supplied at a temperature of 37°C, the maximum permissible radiation power that did not cause hyperthermia of the duct wall was 25 W for 30 and 60 seconds of activation. However, the use of room-temperature saline solution as an irrigation fluid at a flow rate of 60 mL/min ensures thermal safety during intraductal contact laser lithotripsy at all power levels of the Urolase+ Premium laser device, even during 60-second activations. In the case of intermittent water supply, it is recommended to continuously interrupt the laser radiation (emission duration no longer than 10 s) and follow it with subsequent irrigation to restore the optimal temperature.