The aim of the current study is to compare the analgesic effects of both drugs in patients with obesity undergoing bariatric surgery.

Upon arrival to the operating room, routine monitors (electrocardiogram, pulse oximetry, and non-invasive blood pressure monitor) will be applied; intravenous line will be secured, and prophylactic antiemetic will be provided in the form of slow intravenous injection of 5 mg dexamethasone drugs.

Anesthesia Anesthesia will be induced with 2 mg/kg propofol, 2 mcg/kg fentanyl (lean body weight), and tracheal intubation will be facilitated by 0.6 mg/kg ideal body weight rocuronium after loss of consciousness. Anesthesia will be maintained with isoflurane 1-1.2% in oxygen and 0.1 mg/kg rocuronium every 30 minutes. Fentanyl boluses of 1 mcg/kg will be given if heart rate or/and systolic blood pressure >120% of baseline.

Postoperatively, pain assessments using the visual analogue scale (VAS) will be performed at rest and during movement (knee flexion) at 0.5, 4, 10, 18, and 24 h after leaving the operating room. If the VAS score is > 3 intravenous nalbuphine 0.1-0.2 mg/kg (lean body weight) titrated to response with maximum single dose of 20 mg and maximum daily dose of 160 mg.

Intravenous ondansetron 4 mg will be given to treat postoperative nausea or vomiting

Inclusion Criteria:

• adult (18-65 years) patients
• body mass index ≥35 kg/m2
• scheduled for laparoscopic bariatric surgery

Exclusion Criteria:

• American Society of Anesthesiologists (ASA) physical class IV,
• severe cardiac comorbidity (impaired contractility with ejection fraction < 50%, heart block, significant arrhythmias, tight valvular lesions),
• known obstructive sleep apnea or patients with STOP-bang score ≥5,
• baseline SpO2 <95%,
• renal impairment,
• allergy to any of study's drugs,
• history of gastrointestinal bleeding or ulceration, or inflammatory bowel disease

data from this study are available from the PI upon resealable request