Anesthesia and monitoring
Dexmedetomidine, midazolam, and anticholinergic drugs were not permitted before surgery. Vital signs such as pulse oximetry, blood pressure (BP), and electrocardiography were monitored as soon as the patients arrived in the operating room. A Chinese brand of anesthesia depth monitor based on EEG, ConView system (ConView YY-105, Pearlcare Medical Technology Company Limited, Zhejiang, China), was used. Anesthesia index (Ai) is a digital indicator for anesthesia depth derived from the ConView [