Study protocol and anesthesia
loss of consciousness, apnea
GASTRIC DILATATION, BRAIN
All participants were premedicated with intramuscular atropine (0.01 mg/kg) and midazolam (0.05 mg/kg) one hour before anesthetic induction. After entering the operating room, all participants were monitored for blood pressure, heart rate, oxygen saturation, and anesthesia depth. The level of consciousness and the depth of anesthesia were monitored using a patient state index (PSi) monitor (SedLine® Brain Function Monitoring, Version 1.8.1.4i, Masimo Inc., Irvine, CA, USA). The participants breathed 100% oxygen for three minutes and then started anesthesia induction when end-expiratory oxygen concentration was more than 90%. For anesthesia induction, a 1% lidocaine (30 mg) and propofol (1.0–1.5 mg/kg) bolus with continuous remifentanil infusion (0.05 mg/kg/minute) was used. In the Ventilation group, after loss of consciousness, participants received rocuronium (0.6 mg/kg) intravenously. The junior anesthesiologist performed two-handed mask ventilation 15 times/min in pressure-controlled mode (15 cmH2O) for two minutes with 100% oxygen and inhalational anesthesia using 2.0 vol% of sevoflurane. In the Apnea group, rocuronium (1.0 mg/kg) was administered after loss of consciousness, and 100% oxygen was maintained at 6 L/min through a facemask without positive pressure ventilation, while maintaining apnea for one minute before performing endotracheal intubation. The senior anesthesiologists measured gastric antral CSA using ultrasound. An 18-Fr Levin tube was then inserted by the same anesthesiologist who performed anesthesia induction. The Levin tube was inserted at least 60 cm and its position was confirmed through video laryngoscope that the Levin tube was accurately positioned in the esophagus.The surgeon evaluated the degree of gastric dilatation after carbon dioxide injection for laparoscopic surgery. Afterward, the anesthesiologist measured the amount of suctioned gastric contents and air using a 50-mL syringe through the Levin tube.