Inclusion Criteria:  Age ≥ 20 years Body mass index ≥ 30 kg·m-2 Undergoing laparoscopic sleeve gastrectomy at Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan  Exclusion Criteria:  Pregnant or lactating women Severe cardiopulmonary distress, including left ventricular ejection fraction < 40%, double or triple vessel disease, New York Heart Association functional classification ≥ 3, peripheral oxygen saturation by pulse oximetry (SpO2) < 90% in room air, and moderate to severe pulmonary hypertension. Previous esophageal, gastric, or duodenal surgery. Previous head and neck surgery or radiation therapy Previous cervical spine injury High-degree cardiac arrythmia, including atrial fibrillation and severe atrioventricular block Use of cardiac pacemaker or automated implantable cardioverter defibrillator Chronic kidney disease, stage ≥ 4 (estimated glomerular filtration rate < 30 ml·min-1) Planned transferal to intensive care unit for mechanical ventilation QTc prolongation determined by a standard 12-lead electrocardiogram Patients using emetogenic or antiemetic drugs within 24 hours before surgery Patients requiring rapid sequence induction or fiberoptic awake intubation Patient refusal to participate