Fentanyl Efficacy in Anesthesia for Morbidly Obese Patients Undergoing Laparoscopic Sleeve Gastrectomy: A Prospective Randomized Trial of Dosage Calculations Based on Lean Body Mass (1 mcg/kg versus 2 mcg/kg)
Thanyarat Prommahachai, MD¹, Nampetch Tongsiri, RN², Akom Prommahachai, MD³
Affiliation : ¹ Division of Anesthesiology, Udon Thani Hospital, Udon Thani, Thailand; ² Division of Anesthetic Nurse, Udon Thani Hospital, Udon Thani, Thailand; ³ Division of Orthopedics, Udon Thani Hospital, Udon Thani, Thailand
Background: Fentanyl is a potent opioid analgesic commonly used in anesthesia for bariatric surgery due to its high efficacy. However, the appropriate fentanyl dosage for morbidly obese patients remains inconclusive.
Objective: To compare the efficacy of two fentanyl dosages at 2 mcg/kg versus 1 mcg/kg administered during induction before intubation in morbidly obese patients undergoing laparoscopic sleeve gastrectomy.
Materials and Methods: A prospective, randomized, single-blinded trial was conducted between November 2024 and July 2025. Adults, aged 18 years and older, with morbid obesity scheduled for laparoscopic sleeve gastrectomy under general anesthesia were randomized, one to one, to receive either 2 mcg/kg or 1 mcg/kg intravenous (IV) fentanyl during induction. Following intubation, all patients received 25 mcg IV fentanyl every 30 minutes. Outcomes included pain scores assessed by the visual analog scale (VAS) in the post-anesthesia care unit (PACU) and at 24 hours, intraoperative hemodynamic parameters, and postoperative blood sugar.
Results: Forty participants were enrolled. VAS scores at PACU showed no difference between groups. At 24 hours, however, the median VAS was significantly higher in the 2 mcg/kg group compared with the 1 mcg/kg group at 28 (IQR 19.87 to 50) versus 16.2 (IQR 0 to 26.6) (p=0.0059). Intraoperative analysis revealed that the 2 mcg/kg group experienced significant reductions in heart rate and systolic blood pressure from baseline to one-hour post-intubation. Conversely, postoperative blood glucose increased significantly in the 1 mcg/kg group. No differences were observed in analgesic and morphine consumption or perioperative complications.
Conclusion: A dose of 1 mcg/kg of fentanyl administered during the induction phase before intubation results in lower postoperative pain scores at 24 hours compared with 2 mcg/kg in patients with morbid obesity undergoing laparoscopic sleeve gastrectomy. Both fentanyl dosages effectively control intraoperative hemodynamic parameters.
Received 17 October 2025 | Revised 2 December 2025 | Accepted 3 December 2025
DOI: 10.35755/jmedassocthai.2026.1.03447
Keywords : Fentanyl; Dose; Morbid obesity; Laparoscopic sleeve gastrectomy; VAS; Lean body mass
