Erector spinae plane block for postoperative analgesia in patients undergoing flexible ureteroscopy: a randomized controlled trial

BACKGROUND: Postoperative pain after flexible ureteroscopy (URS) is clinically significant. It involves both somatic and visceral components, especially from ureteral dilation and irritation by double-J ureteral stents. The erector spinae plane block (ESPB) is an interfascial technique with potential to modulate thoracolumbar nociceptive pathways. We aimed to assess the analgesic efficacy of ultrasound-guided ESPB during flexible URS. METHODS: In this prospective, randomized, assessor-blinded trial, 70 adults scheduled for elective flexible URS at a university hospital (February-August 2025) were randomized to receive either unilateral ESPB after general anesthesia induction or standard multimodal analgesia (Control). The primary outcome was postoperative pain (Numeric Rating Scale) in the first 24 h. Secondary outcomes included cumulative opioid use, time to first rescue analgesia, total rescue analgesic needs, and incidence of postoperative nausea and vomiting (PONV). Perioperative hemodynamic parameters were exploratory outcomes. RESULTS: Seventy patients were analyzed (ESPB, n = 35; Control, n = 35). Key findings included significantly lower resting Numeric Rating Scale (NRS) scores in the ESPB group from the sixth postoperative hour onward, with the greatest difference at 12 h (p < 0.001). The significant group-by-time interaction in pain scores was confirmed by nonparametric (nparLD, p < 0.001) and parametric (mixed ANOVA, p = 0.01) analyses. Movement-related pain scores were significantly reduced in the ESPB group at 6, 12, and 24 h. Although cumulative opioid use and time to first rescue analgesia did not differ, the ESPB group showed a lower incidence of PONV (5.7% vs. 34.3%; p = 0.01). Perioperative hemodynamic parameters remained comparable between groups. CONCLUSIONS: Ultrasound-guided ESPB reduced postoperative pain in a time-dependent manner and decreased PONV after flexible URS, but did not have a clear opioid-sparing effect. The statistically significant pain reduction was close to the threshold of clinical relevance, so its practical impact may be limited and should be interpreted with caution. ETHICAL COMMITTEE APPROVAL: 2024-KAEK-06-2502A05. TRIAL REGISTRATION: ClinicalTrials.gov NCT06826833, registered on 07 February 2025.