ESP Block for Postoperative Analgesia in URS Surgery

The goal of this clinical trial is to determine whether the erector spinae plane (ESP) block provides better pain relief after flexible ureterorenoscopy (URS) surgery compared to standard analgesia alone. Researchers want to know: Does the ESP block reduce pain levels in the first 24 hours after surgery? Does it lower the need for opioid pain medication? Does it reduce the need for additional (rescue) pain treatment? Does it decrease the likelihood of postoperative nausea and vomiting (PONV)? Participants will be randomly placed into one of two groups: ESP Block Group: Participants will receive an ESP block using 20 mL of 0.25% bupivacaine under ultrasound guidance before surgery. Control Group: Participants will receive standard pain management without a nerve block. All participants will receive general anesthesia during surgery and multimodal pain management after surgery. Researchers will compare pain scores, opioid use, rescue analgesic needs, and the occurrence of nausea and vomiting between the two groups.