Normal vs Low Tidal Volume Ventilation in Retrograde Intrarenal Surgery

Retrograde intrarenal surgery is commonly performed under general anesthesia for the treatment of renal stones. During the procedure, respiratory-related renal movement caused by positive-pressure ventilation may impair endoscopic image stability and reduce the efficiency of laser lithotripsy. This randomized controlled trial aims to compare the effects of normal ventilation and low tidal volume ventilation on intraoperative endoscopic image stability during RIRS using a video-based Motion Index. Eligible adult patients scheduled for elective RIRS under general anesthesia will be randomized in a 1:1 ratio to either normal tidal volume ventilation or low tidal volume ventilation. A standardized 60-second intraoperative video segment in which the stone and/or active laser lithotripsy is visible will be analyzed by blinded assessors. The primary outcome is the mean Motion Index value calculated from sequential video frames. Secondary outcomes include additional Motion Index parameters, laser activation time, anesthesia and surgical duration, intraoperative respiratory and hemodynamic safety parameters, vasopressor requirement, complications, and stone-free status at routine follow-up.

Inclusion Criteria: * Adult patients aged 18 years or older * Patients scheduled for elective retrograde intrarenal surgery under general anesthesia * ASA physical status I-III * Patients who are able to read and understand the informed consent form * Patients who provide written informed consent Exclusion Criteria: * Patients younger than 18 years * Pregnancy * Emergency surgery * Severe chronic obstructive pulmonary disease, severe restrictive pulmonary disease, or preoperative hypercapnia * Severe uncontrolled cardiovascular disease * Active urinary tract infection, sepsis, or untreated infectious focus * Cases in whom the standardized ventilation protocol is difficult to apply because of morbid obesity * Patients scheduled for an additional major urological procedure in the same session * Cases in which an intraoperative video recording of sufficient quality cannot be obtained * Patients in whom the study protocol cannot be safely continued according to the investigator's clinical judgment