The goal of this clinical trial is to learn if intragastric administration of lidocaine can reduce postoperative nausea and vomiting in obese patients undergoing laparoscopic sleeve gastrectomy. The main question it aims to answer is:

Does administering 0.5% lidocaine via an orogastric tube reduce the incidence of postoperative nausea and vomiting (PONV) in the post-anesthesia care unit and within the first 24 hours after surgery compared to a placebo (normal saline)?

Researchers will compare the Lidocaine Group to the Placebo Group to see if the intervention lowers the PONV incidence.

Participants will:

• Receive the assigned study solution (either 0.5% lidocaine 20ml or normal saline 20ml) through an orogastric tube upon surgery completion and before extubation.
• Have their gastric tube clamped for 5 minutes to ensure mucosal exposure before removal.
• Undergo standardized total intravenous anesthesia and perioperative management according to the study protocol.
• Be assessed for nausea, vomiting, and other outcomes at specified time points postoperatively in the recovery room and at 6, 12, and 24 hours.

Postoperative nausea and vomiting (PONV) is a common complication following bariatric surgery, with incidence rates reaching up to 30-80%. In bariatric surgical patients, the burden of PONV is particularly high due to multiple risk factors, including surgical trauma to upper GI system, frequent opioid use, increased intra-abdominal pressure, altered gastric anatomy, and heightened sensitivity of gastrointestinal reflex pathways. Effective prevention and treatment of PONV in this population therefore represents a major clinical priority.

Current prophylactic strategies rely primarily on pharmacological agents such as serotonin (5-HT3) receptor antagonists, corticosteroids, dopamine antagonists, and multimodal combinations. Despite these measures, the incidence of breakthrough PONV remains significant, underscoring the need for additional safe, effective, and inexpensive interventions.

Lidocaine, traditionally used as a local anesthetic and antiarrhythmic, has gained attention in perioperative medicine for its systemic anti-inflammatory, analgesic, and opioid-sparing effects when administered intravenously. Evidence suggests that perioperative lidocaine can improve gastrointestinal motility, reduce visceral hypersensitivity, and facilitate earlier return of bowel function. These properties raise the possibility that lidocaine may also influence nausea and vomiting pathways by attenuating vagal afferent signaling, reducing local gastric irritation, and dampening inflammatory responses within the gastrointestinal mucosa.

Delivering lidocaine directly into the gastric cavity via an orogastric (OG) tube represents a novel and pragmatic approach. Unlike intravenous administration, intragastric instillation allows targeted mucosal exposure, potentially reducing afferent vagal stimulation that triggers nausea and vomiting. This method is technically simple, inexpensive, and feasible within the routine workflow of bariatric surgery, as OG tubes are already placed for intraoperative management.

This study aims to evaluate whether the administration of lidocaine via nasogastric tube can reduce the incidence of postoperative nausea and vomiting (PONV) in patients undergoing bariatric surgery. If effective, local lidocaine administration may serve as a simple, low-cost, and readily adoptable strategy to improve postoperative outcomes in bariatric surgery patients. This approach could expand the multimodal anesthesia regimen and optimize the enhanced recovery after surgery (ERAS) pathway for bariatric procedures.

Inclusion Criteria:

• Adults aged between 18 and 65 years old;
• American Society of Anesthesiologists (ASA) physical status classification II - III;
• Planned to undergo primary elective laparoscopic sleeve gastrectomy with general anesthesia;
• Capable of giving informed consent.

Exclusion Criteria:

• Known allergy, hypersensitivity or contraindication to lidocaine or amide - type local anesthetics;
• Previous significant liver or kidney dysfunction (e.g., ALT/AST > 3 times the upper limit of normal, GFR < 30 mL/min);
• History of epilepsy, cardiac conduction abnormalities or previous diagnosis of malignant hyperthermia;
• Pregnancy or lactation;
• Patients who received systemic lidocaine treatment during the operation;
• History of severe postoperative nausea and vomiting (PONV) or motion sickness, requiring multiple prophylactic medications;
• Emergency or revision bariatric surgery.