Transient Apnea During Flexible Ureteroscopic Lithotripsy

Respiration-related renal motion may reduce targeting stability during flexible ureteroscopic laser lithotripsy and thereby decrease lithotripsy efficiency. This single-center, three-arm randomized controlled trial evaluated whether transient apnea during active lithotripsy could improve lithotripsy efficiency while maintaining short-term physiologic safety. A total of 150 patients undergoing flexible ureteroscopic lithotripsy for renal stones were randomized in a 1:1:1 ratio to regular mechanical ventilation, small tidal-volume ventilation, or transient apnea. The primary outcome was active lithotripsy efficiency, defined as CT-based stone volume divided by active lithotripsy time. Physiologic safety was assessed using serial arterial blood gas measurements at baseline, 3, 6, and 9 minutes during the lithotripsy phase and 3 minutes after resumption of ventilation, together with continuous intraoperative cardiopulmonary monitoring.

Inclusion Criteria: 1. Age 18 to 80 years. 2. Scheduled for elective flexible ureteroscopic laser lithotripsy for renal stones under general anesthesia. 3. Preoperative CT confirming renal stones suitable for flexible ureteroscopic lithotripsy. 4. Stone size ≥10 mm and \