Percutaneous nephrolithotomy (PCNL) is an effective standard urological procedure for the fragmentation and removal of large renal calculi. Although PCNL is performed as a minimally invasive technique, dilation of the renal capsule and parenchymal tract, as well as peritubular distension caused by the nephrostomy tube, may result in severe postoperative pain. Various analgesic strategies have been described in the literature for postoperative pain management following PCNL. These include systemic opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), and several regional analgesia techniques. However, due to their adverse effect profiles, opioids and NSAIDs are not ideal options, particularly in patients with renal dysfunction. Regional techniques that have been utilized include local infiltration, intercostal nerve blocks, paravertebral blocks, and epidural analgesia.

The kidney is primarily innervated between the T10 and L1 segments, whereas the ureter receives innervation from T10 to L2. Based on this anatomical knowledge, unilateral regional blockade between T10 and L2 can provide adequate analgesia for PCNL procedures. Thoracic paravertebral block was previously a commonly preferred technique; however, it may be associated with complications such as intravascular injection, unintended epidural or intrathecal spread, and pneumothorax during its performance. In recent years, the number of reports describing the use of the erector spinae plane block (ESPB) as part of multimodal anesthesia for postoperative analgesia has increased. In ESPB, local anesthetic is injected into the interfascial plane between the transverse process of the vertebra and the erector spinae muscles, and has been reported to spread to multiple paravertebral spaces. ESPB is considered a peri-paravertebral block that can affect both visceral and somatic pain pathways.

The aim of this study is to evaluate the effect of ultrasound-guided erector spinae plane block on intraoperative and postoperative opioid consumption, postoperative pain scores, and quality of recovery in patients undergoing percutaneous nephrolithotomy.

This clinical trial is designed to evaluate the perioperative efficacy of ultrasound-guided ESPB in adult patients undergoing percutaneous nephrolithotomy under general anesthesia.

After enrollment, patients will be randomly allocated into two groups using a closed-envelope method: an ESPB group and a control group. All patients will receive a standardized general anesthesia protocol. Anesthesia induction will be performed with propofol 2 mg/kg Propofol®, Polifarma İlaç San.ve Tic. A.Ş., Türkiye), rocuronium 0.6 mg/kg (Esmeron®, Merck Sharp Dohme İlaçları LTD Şti, Türkiye)as neuromuscular blocker, and remifentanil 1 µg/kg (ultan, centurion pharma, İstanbul, Türkiye) as opioid. Additional rocuronium 0.1 mg/kg will be administered intraoperatively as needed to maintain muscle relaxation. Anesthesia will be maintained with 2% sevoflurane (Sevorane®, Abbott, Chicago, ABD) in 50% oxygen and a continuous infusion of remifentanil at 0.1-1 µg/kg/min, titrated according to hemodynamic responses. Invasive arterial blood pressure monitoring will be used for close hemodynamic follow-up in all patients.

In the ESPB group, following induction of general anesthesia and prior to surgical incision, an ultrasound-guided ESPB will be performed at the T10 transverse process level on the side of the surgical kidney. Under aseptic conditions, using an in-plane technique, a total of 20 mL of 0.25% bupivacaine (Marcaine® %0,5, AstraZeneca, İstanbul, Türkiye)will be injected between the erector spinae muscle and the transverse process. In the control group, no additional regional block or sham procedure will be performed; patients will undergo surgery under general anesthesia with the same standardized systemic analgesia protocol as the ESPB group.

Intraoperative hemodynamic parameters, including mean arterial pressure and heart rate, will be recorded at predefined time points, and total intraoperative remifentanil consumption will be documented. At the end of surgery, all patients will receive 15 mg/kg paracetamol and 0.5 mg/kg meperidine intravenously as part of the standard postoperative analgesic regimen. During postoperative ward follow-up, all patients will receive 15 mg/kg paracetamol four times daily. Postoperative pain intensity will be assessed using the Numeric Rating Scale (NRS; 0 = no pain, 10 = worst imaginable pain) at 0, 2, 4, 6, 12, and 24 hours after surgery. For patients with NRS ≥ 3, intravenous tramadol 1 mg/kg will be administered as rescue analgesia, and total postoperative tramadol consumption within the first 24 hours will be recorded.

Postoperative nausea and vomiting will be evaluated at 0, 2, 4, 6, 12, and 24 hours postoperatively, and the presence or absence of symptoms will be documented. Quality of recovery will be assessed at 24 hours after surgery using the Turkish validated version of the 15-item Quality of Recovery questionnaire (QoR-15T). The total QoR-15T score ranges from 0 to 150, with higher scores indicating better quality of recovery. Postoperative pain assessments and QoR-15T evaluations will be performed by nurses who are blinded to group allocation, ensuring assessor blinding.

The primary objective of this trial is to determine whether the addition of ESPB to standard general anesthesia reduces postoperative opioid consumption within the first 24 hours after percutaneous nephrolithotomy compared with standard systemic analgesia alone. Secondary objectives include the comparison of postoperative pain scores at predefined time points, intraoperative remifentanil requirements, hemodynamic stability, incidence of postoperative nausea and vomiting, and quality of recovery as measured by the QoR-15T. This study is expected to provide clinically relevant evidence regarding the analgesic efficacy and recovery benefits of ESPB in patients undergoing percutaneous nephrolithotomy.

Inclusion Criteria:

• Age ≥ 18 years.
• American Society of Anesthesiologists (ASA) physical status I-II.
• Scheduled for elective percutaneous nephrolithotomy under general anesthesia.
• Able to understand the study procedures and provide written informed consent.

Exclusion Criteria:

• Age < 18 years.
• ASA physical status III-IV.
• Refusal to participate in the study.
• Known allergy or contraindication to local anesthetics (bupivacaine), opioids, or study medications.
• Coagulopathy or anticoagulant therapy contraindicating regional block.
• Infection at the injection site.
• Severe psychiatric or cognitive disorder precluding reliable pain assessment or questionnaire completion.

The researchers performing the block procedures were not involved in the postoperative assessment.