Effect of Lidocaine Through Gastric Tube on PONV

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.

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.