Elective lumbar fusion surgery is associated with moderate to severe postoperative pain and often requires substantial perioperative opioid administration. Excessive opioid use may lead to adverse effects such as nausea, vomiting, sedation, respiratory depression, and delayed mobilization. Intravenous lidocaine infusion has been proposed as part of multimodal analgesia because of its analgesic, antihyperalgesic, and anti-inflammatory properties.

This randomized, placebo-controlled clinical trial aims to evaluate the effect of intraoperative intravenous lidocaine infusion on postoperative opioid consumption and early recovery outcomes in patients undergoing elective lumbar fusion surgery. Patients will be randomly assigned to receive either intravenous lidocaine infusion or placebo during surgery.

The primary outcome is cumulative postoperative opioid consumption within the first 24 hours after surgery. Secondary outcomes include intraoperative opioid consumption, postoperative pain scores, time to first rescue analgesic, quality of recovery, postoperative nausea and vomiting, time to mobilization, and length of hospital stay. In addition, inflammatory and oxidative stress biomarkers including interleukin-6 (IL-6) and markers of thiol-disulfide homeostasis will be measured preoperatively and postoperatively.

Lumbar fusion surgery is frequently associated with significant postoperative pain and often requires high doses of opioid analgesics during the perioperative period. Opioid administration may lead to several adverse effects including postoperative nausea and vomiting, sedation, respiratory depression, and delayed recovery. Therefore, multimodal analgesia strategies are increasingly used to improve postoperative pain control and reduce opioid requirements.

Intravenous lidocaine infusion has gained attention as an adjunct component of multimodal analgesia because of its analgesic, antihyperalgesic, and anti-inflammatory properties. Previous clinical studies have suggested that perioperative systemic lidocaine may reduce postoperative pain intensity, decrease opioid consumption, and improve recovery after surgery. However, evidence regarding its effectiveness in patients undergoing lumbar fusion surgery remains limited.

This prospective, randomized, placebo-controlled study will include adult patients aged 18-65 years with American Society of Anesthesiologists (ASA) physical status I-II who are scheduled for elective lumbar fusion surgery. Participants will be randomly allocated into two groups. Patients in the lidocaine group will receive an intravenous lidocaine bolus followed by continuous lidocaine infusion during surgery, whereas patients in the control group will receive an equivalent volume of normal saline infusion. The infusion will be maintained throughout the surgical procedure and discontinued at the end of surgery.

All patients will receive standardized general anesthesia and postoperative multimodal analgesia. Postoperative pain will be assessed using the Numerical Rating Scale (NRS). Rescue analgesia will be administered when clinically indicated.

The primary outcome is cumulative postoperative opioid consumption within the first 24 hours after surgery. Secondary outcomes include intraoperative opioid consumption, postoperative pain scores at predefined time points, time to first rescue analgesic requirement, postoperative nausea and vomiting incidence, quality of recovery measured by QoR-15, post-anesthesia care unit length of stay, time to mobilization, and hospital length of stay.

In addition, inflammatory and oxidative stress responses associated with surgery and lidocaine administration will be evaluated. Blood samples will be collected preoperatively and at 6 and 24 hours postoperatively to measure interleukin-6 (IL-6) levels and markers of thiol-disulfide homeostasis.

Inclusion Criteria:

• Age between 18 and 65 years
• Scheduled for elective lumbar fusion surgery under general anesthesia
• American Society of Anesthesiologists (ASA) physical status I-II
• Ability to provide written informed consent

Exclusion Criteria:

• Refusal to participate in the study
• ASA physical status ≥III
• Body mass index >35 kg/m²
• Known allergy or hypersensitivity to lidocaine or study medications
• Severe cardiac, hepatic, or renal disease
• Pregnancy
• Neurological disorders affecting pain assessment
• Chronic opioid use
• Use of opioids or antiemetic drugs before surgery
• Inability to cooperate with postoperative assessments

No plan to share individual participant data.

Participants, care providers, investigators, and outcome assessors will be blinded to group allocation. Lidocaine and placebo infusions will be prepared in identical syringes by an independent anesthesiologist not involved in patient care or outcome assessment.