Randomization and blinding
Participants were randomly allocated to one of two groups (Ventilation group and Apnea group) in a 1:1 ratio. Randomization was done by computer-generated random numbers with a fixed block size of eight and a 1:1 ratio. Randomized numbers were sealed in an opaque envelope. The investigator who was not involved in randomization and allocation opened the sealed envelope immediately before the study and performed anesthesia induction. Other investigators who were blinded to group allocation assessed the gastric antral CSA using ultrasound. They left the operating room and remained blinded during anesthesia induction. Other anesthesiologists who were not involved in the study recorded patient vital signs and ventilator parameters.