The goal of this randomized clinical trial is to find out whether giving an intravenous lidocaine + dexmedetomidine combination (LIDEX) during laparoscopic bariatric surgery can lower post-operative pain, inflammation, and oxidative stress in adults with obesity.

The main questions it aims to answer are:

• Pain control: Does LIDEX reduce pain 24 hours after surgery, as measured with the International Pain Outcomes Questionnaire (IPOQ)?
• Biomarkers: Does LIDEX lower blood levels of key inflammatory cytokines-interleukin-1 beta (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and interleukin-10 (IL-10)-and oxidative-stress markers-malondialdehyde (MDA), the reduced/oxidized glutathione ratio (GSH/GSSG), superoxide dismutase (SOD), and catalase-compared with the individual drugs or saline placebo?

Researchers will compare four groups: lidocaine alone, dexmedetomidine alone, LIDEX, and placebo (saline solution, a look-alike substance that contains no drug) to learn which approach works best.

Participants will:

• Receive an intravenous infusion of their assigned study drug(s) during surgery.
• Provide three small blood samples (before surgery, immediately after, and three hours after).
• Complete a short pain questionnaire (IPOQ) 24 hours after surgery.

Obesity is associated with chronic low-grade inflammation and persistent oxidative stress. Laparoscopic bariatric surgery-although highly effective for weight reduction-triggers an acute inflammatory cascade and a burst of reactive oxygen species that can amplify post-operative pain and delay functional recovery.

Intravenous lidocaine stabilises voltage-gated Na+ channels, limits ectopic neuronal firing and inhibits neutrophil priming; it also down-regulates the release of pro-inflammatory cytokines in abdominal procedures. Dexmedetomidine, a highly selective α2-adrenergic agonist, produces sedation and analgesia while attenuating sympathetic outflow, thereby reducing surgical catecholamine surges and cytokine release. Pre-clinical and clinical synergy studies indicate that combining these two agents (LIDEX) can provide additive anti-hyperalgesic, anti-inflammatory and antioxidant effects without increasing cardiovascular risk when each is dosed within its established therapeutic window.

In this protocol, a weight-adjusted intra-operative infusion of lidocaine plus dexmedetomidine is administered during bariatric surgery and compared with each single agent and saline. Peri-operative venous samples are collected for mechanistic profiling of systemic inflammatory and redox responses, and patient-reported pain is captured after surgery using a validated instrument. Haemodynamic parameters are continuously monitored to detect potential lidocaine toxicity or dexmedetomidine-related bradycardia and hypotension; predefined rescue algorithms are applied if thresholds are exceeded.

The study is designed to clarify whether the LIDEX combination can blunt the acute inflammatory-oxidative surge thought to drive sustained pain and metabolic stress after bariatric surgery, thereby informing future enhanced-recovery protocols that integrate multimodal analgesia with metabolic optimisation strategies.

Inclusion Criteria:

• Adults aged 18 - 60 years
• Male or female
• Elective laparoscopic bariatric surgery
• Post-operative pathway: post-anaesthesia care unit (PACU) followed by standard ward, with an expected in-hospital stay ≥ 24 h
• ASA physical-status II or III

Exclusion Criteria:

• Use of any loco-regional anaesthetic technique during the peri-operative period (transversus abdominis plane, paravertebral, spinal, epidural, erector spinae, or other abdominal wall blocks).
• Current substance abuse or illicit drug use.
• Previous abdominal surgery within the last 6 months.
• Known hypersensitivity or allergy to lidocaine, dexmedetomidine, amide local anaesthetics, or α₂-adrenergic agonists.
• Congestive heart failure, significant bradyarrhythmia, second- or third-degree atrio-ventricular block without pacemaker, severe hypotension, or current therapy with Class I/III anti-arrhythmic drugs.
• Estimated glomerular filtration rate (eGFR) < 60 mL min-¹ 1.73 m-² (moderate-to-severe renal impairment).
• Severe hepatic impairment (Child-Pugh C).
• Pregnancy or lactation.
• Chronic opioid consumption > 30 mg oral morphine equivalents per day for > 4 weeks
• Active seizure disorder, myasthenia gravis, or other neurologic disease contraindicating lidocaine infusion.
• Patient cannot communicate
• Patient does not want to fill in the questionnaire
• Participation in another interventional study within the past 30 days.
• Intra-operative conversion to open surgery.
• Insufficient biological sample for biomarker analysis.
• Premature discontinuation of the study drug during surgery for any reason that, in the judgement of the treating anaesthesiologist or investigators, prevents adequate exposure or assessment of safety variables (e.g., major haemorrhage > 200 mL, anaphylactic shock, failed intubation, inability to extubate, severe metabolic/respiratory acidosis, transfer to ICU while intubated).

De-identified individual participant data (IPD) that support the results reported in this study will be shared. This includes primary outcome data (IPOPQ responses), inflammatory cytokine levels (IL-1β, IL-6, TNF-α, IL-10), oxidative stress markers (MDA, SOD, catalase, GSH/GSSG ratio), and neutrophil respiratory burst results. All data will be anonymized and coded to protect participant confidentiality.

IPD will be available beginning 6 months after publication of the main study results in a peer-reviewed journal, and will remain available for up to 5 years after publication.

The de-identified individual participant data (IPD) that support the results of this study will be available to any interested researchers.

The data will be publicly accessible through an open-access Zenodo repository following publication of the main study results. No request or approval will be necessary. All data will be anonymized and will not contain any information that could identify participants. Supporting documents such as the protocol, statistical analysis plan, and informed consent form will also be available in the same repository.

Randomisation codes are generated in 13 permuted blocks of eight by an independent investigator who is not involved in patient care or outcome assessment. The codes are printed, placed in sequentially numbered, opaque, sealed envelopes, and handed to the study nursing team. Immediately before anaesthetic induction, a research nurse opens the next envelope and communicates the allocation to a second nurse-preparer (also independent from clinical care). This nurse draws up a visually identical 50 mL syringe containing lidocaine, dexmedetomidine, the fixed-dose combination (LIDEX), or 0.9 % saline, according to the code. Each syringe is labelled only with the participant ID and infusion rate. Emergency unblinding is allowed solely for patient-safety reasons and must be reported immediately to the Data and Safety Monitoring Board.