People who undergo percutaneous nephrolithotomy (PNL), a procedure used to remove kidney stones, often experience pain after surgery. An ultrasound-guided erector spinae plane block (ESPB) is commonly used to help reduce this pain.

This study compares two different concentrations of bupivacaine, a local anesthetic medication, used during ESPB. Participants undergoing PNL will receive either 0.25% or 0.375% bupivacaine as part of their pain management.

Researchers will compare pain scores, the need for additional pain medication, and changes in blood markers related to inflammation after surgery. The aim of the study is to determine whether one concentration provides better pain control or influences the inflammatory response differently after PNL.

Percutaneous nephrolithotomy (PNL) is the standard treatment for large and complex renal stones. Despite its minimally invasive nature, postoperative pain remains an important clinical concern and may adversely affect recovery, mobilization, and patient satisfaction. Ultrasound-guided thoracic erector spinae plane block (ESPB) has been increasingly incorporated into multimodal analgesia protocols because of its simplicity, safety profile, and effectiveness in reducing postoperative pain.

The optimal concentration of bupivacaine for ESPB in patients undergoing PNL remains unclear. This study was designed to compare the effects of two different concentrations of bupivacaine (0.25% and 0.375%) administered during ultrasound-guided thoracic ESPB on postoperative pain control and inflammatory response following PNL.

Adult patients scheduled for elective PNL were enrolled. ESPB was performed at the T10 vertebral level under ultrasound guidance before surgery. Participants received 20 mL of either 0.25% or 0.375% bupivacaine. Standard perioperative anesthetic and postoperative analgesic protocols were applied to all participants.

The primary outcome was postoperative pain intensity assessed using Visual Analog Scale (VAS) scores at predefined postoperative time points. Secondary outcomes included intraoperative fentanyl consumption, postoperative tramadol consumption, patient-controlled analgesia requirements, postoperative nausea and vomiting, patient satisfaction, and perioperative changes in inflammatory biomarkers, including the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR).

Demographic characteristics, stone-related variables, operative data, and perioperative hemodynamic parameters were recorded. Statistical analyses were performed to compare postoperative pain outcomes, analgesic requirements, and inflammatory biomarker responses between the study groups.

Inclusion Criteria:

• Age between 18 and 70 years.
• Scheduled to undergo elective percutaneous nephrolithotomy (PNL).
• American Society of Anesthesiologists (ASA) physical status I-III.
• Received ultrasound-guided thoracic erector spinae plane block (ESPB) before surgery.
• Willing and able to provide written informed consent.

Exclusion Criteria:

• Inability to assess pain using the Visual Analog Scale (VAS).
• Advanced cardiovascular disease.
• Coagulopathy or bleeding disorders.
• Opioid use disorder.
• Body mass index (BMI) ≥ 40 kg/m².
• Infection at the planned injection site.
• Known allergy or hypersensitivity to bupivacaine, other local anesthetics, or study-related medications.
• Withdrawal of consent during the study period.

The study population consisted of adult patients undergoing elective percutaneous nephrolithotomy (PNL) for renal stone disease at a single tertiary care center between July 2024 and March 2025. Eligible participants were 18-70 years of age, classified as American Society of Anesthesiologists (ASA) physical status I-III, and received ultrasound-guided thoracic erector spinae plane block (ESPB) as part of perioperative analgesic management. A total of 60 participants were included and prospectively followed throughout the postoperative period.

Individual participant data will not be made publicly available because the informed consent obtained from participants did not include permission for public data sharing, and data confidentiality and privacy will be maintained in accordance with institutional and ethical requirements.