This randomized controlled trial evaluates the effectiveness of ultrasound-guided retrolaminar nerve block in addition to standard multimodal analgesia for postoperative pain management in patients undergoing lumbar spine surgery. Fifty patients will be randomly assigned to receive either the retrolaminar block combined with standard pain management or standard pain management alone. The primary outcome is total opioid consumption in the first 24 hours after surgery. Secondary outcomes include pain intensity at multiple time points, time to first rescue analgesia, duration of sensory block, incidence of postoperative nausea and vomiting, length of hospital stay, patient satisfaction, and chronic pain development at 3 and 6 months follow-up.

BACKGROUND: Lumbar spine surgery is associated with significant postoperative pain, which can delay recovery and increase complications. Regional anesthesia techniques, specifically retrolaminar blocks, may provide superior analgesia compared to systemic opioids alone.

STUDY DESIGN: This is a prospective, randomized, controlled trial conducted at Clínica Universidad de Los Andes, Chile. Patients will be allocated using variable block randomization (block sizes 4 and 6) in a 1:1 ratio.

INTERVENTIONS: All patients will receive standardized general anesthesia (Propofol, Remifentanil, Rocuronium) and multimodal analgesia including paracetamol, metamizol, ketorolac, morphine, and pregabalin. The intervention group will additionally receive bilateral ultrasound-guided retrolaminar blocks with ropivacaine 0.5% (20 ml per side) at the end of surgery.

OUTCOMES: Primary outcome is cumulative morphine consumption via patient-controlled analgesia (PCA) during the first 24 postoperative hours. Secondary outcomes include pain scores (VAS 0-10) at 0, 6, 12, 24, 48, and 72 hours; time to first rescue analgesia; duration of sensory block; incidence of nausea/vomiting; hospital length of stay; time to ambulation; sleep quality; patient satisfaction; adverse events; and development of chronic pain at 3 and 6 months.

SAMPLE SIZE: 50 patients (25 per group) provides 80% power to detect a clinically significant difference in opioid consumption.

Inclusion Criteria:

• Adult patients aged 18-80 years
• Scheduled for elective lumbar spine surgery (with instrumentation)
• American Society of Anesthesiologists (ASA) physical status I-III
• Willing and able to provide written informed consent
• Able to use patient-controlled analgesia (PCA) device

Exclusion Criteria:

• Refusal to participate in the study
• Known allergy to local anesthetics (bupivacaine - levobupivacaine - lidocaine) or any study medication
• Contraindication to regional anesthesia (infection at injection site, coagulopathy)
• Chronic opioid use (daily use for >3 months prior to surgery)
• Severe psychiatric disorder that precludes informed consent
• Emergency surgery
• Diabetes mellitus with preoperative glucose >180 mg/dl
• Pregnancy or breastfeeding
• Body mass index (BMI) >40 kg/m²
• Reoperation or revision of the same level of previous spinal surgery

Individual participant data that underlie the results reported in the published article, after deidentification, will be available upon reasonable request.

Data will be available beginning 6 months and ending 5 years following article publication.

Data will be shared with researchers who provide a methodologically sound proposal for use in achieving the aims of the approved proposal. Proposals should be directed to rcoloma@clinicauandes.cl. To gain access, data requestors will need to sign a data access agreement. Data will be shared after approval by the principal investigator and the institutional review board.

Outcomes assessors (including pain evaluators and data collectors) will be blinded to group allocation.

The anesthesiologist performing the intervention and the patient cannot be blinded due to the nature of the procedure (performance of nerve block).

Postoperative care providers will also be blinded to treatment allocation.