The purpose of this study is to evaluate whether actively suctioning the renal collecting system to induce a "collapse" state at the end of retrograde intrarenal surgery (RIRS) can reduce postoperative pain and infection in patients with kidney stones. Participants will be randomly assigned to either the experimental group (suction-induced collapse) or the control group (standard drainage). The study aims to determine if this simple surgical modification can improve early recovery outcomes and patient satisfaction.

While RIRS is a standard treatment for kidney stones, postoperative flank pain and infectious complications remain significant issues. These complications are often associated with elevated intrarenal pressure and residual irrigation fluid left in the kidney after surgery.

This prospective randomized controlled trial investigates the clinical efficacy of a "suction-induced collapse" technique using a suction ureteral access sheath (UAS). In the experimental group, at the conclusion of RIRS, active suction will be applied through the UAS until the renal collecting system is visually confirmed to be collapsed. In the control group, standard drainage will be allowed after irrigation stops, without active suctioning.

The primary outcome is postoperative flank pain intensity measured by the Numerical Rating Scale (NRS) in the recovery room. Secondary outcomes include pain scores on postoperative day 1, the incidence of infectious complications (fever, UTI, or sepsis) within 7 days, and the total amount of analgesics used. A total of 90 patients will be enrolled to ensure statistical power.

Inclusion Criteria:

• Patients aged 20 to 80 years.
• Patients diagnosed with kidney stones and scheduled for retrograde intrarenal surgery (RIRS).
• Patients who have voluntarily signed the written informed consent form

Exclusion Criteria:

• Participation in another clinical trial (drug or device) within 1 month prior to enrollment.
• Congenital abnormalities of the urinary or reproductive system.
• Presence of a pre-placed ureteral stent (pre-stenting) at the time of surgery.
• Solitary kidney.
• Uncontrolled urinary tract infection.
• History of ureteral reconstruction on the affected side.
• Pregnancy.
• Uncorrectable bleeding diathesis or ongoing therapeutic anticoagulation therapy.
• Contraindications to general anesthesia.
• Other conditions that the investigator deems inappropriate for participation in the study.

Individual participant data will not be shared to protect the privacy and confidentiality of the study participants, in accordance with the institutional review board's policy and the informed consent provided by the participants.

This is a single-blind study in which participants are unaware of their group assignment. Additionally, to ensure objective evaluation, the clinical staff (nurses) in the recovery room (PACU) who measure and record the primary outcome (NRS pain score) are blinded to the participants' treatment groups.