Following laparoscopic bariatric surgery, multimodal analgesia is recommended to avoid the adverse effects of opioids by reducing their use. Although lidocaine, ketamine, and dexmedetomidine have been used as adjuvant analgesics, no studies have evaluated the superiority of their intra- and postoperative infusions as components of multimodal analgesia in bariatric surgery. The present study is aimed to compare lidocaine, dexmedetomidine, and ketamine in multimodal analgesia management following Sleeve Gastrectomy Surgery. Postoperative pain scores, the requirement for additional postoperative analgesia, retching, nausea and vomiting, time to mobilization, and hospital length of stay will be evaluated.

Patients will be divided into three groups.

Group L: The patients will receive intravenous lidocaine (2 mg/kg/h) immediately after anesthesia induction. At the end of the surgery, the dose will be decreased to 1 mg/kg/h. The infusion will continue until 12 hours after the operation.

Group K: The patients will receive intravenous ketamine (0.5 mg/kg/h) immediately after anesthesia induction. At the end of the surgery, the dose will be decreased to 0.3 mg/kg/h. The infusion will continue until 12 hours after the operation.

Group D: The patients will receive intravenous dexmedetomidine (0.5 mg/kg/h) immediately after anesthesia induction. At the end of the surgery, the dose will be decreased to 0.3 mg/kg/h. The infusion will continue until 12 hours after the operation.

Ketamine, lidocaine, and dexmedetomidine doses will be calculated according to ideal body weight, lean body weight, and actual body weight, respectively.

Randomization will be performed using a computer-generated random number list, and a statement indicating the patient's group will be placed in a closed envelope numbered according to the result. Each patient will be asked to choose an envelope, and the patients will be assigned to the study according to the group mentioned in the envelope.

Inclusion Criteria:

• Body mass index>35 kg/m2
• The American Society of Anaesthesiologists (ASA) physical status class II III
• Patients who will undergo an elective laparoscopic sleeve gastrectomy (LSG)

Exclusion Criteria:

• refusal to participate
• allergy to the study drugs
• chronic kidney disease (creatinine>150 μmol/L)
• mental illness
• liver, respiratory or oncological disease,
• cardiac dysfunction (ejection fraction <40%),
• uncontrolled hypertension,
• preoperative analgesic use,
• chronic pain,
• history of alcohol or drug addiction

Drugs to be used will be prepared 30 minutes before the surgery in the drug preparation room by a nurse who is not involved in the study. Investigators and patients will be blinded to the group assignments.