Neuromonitoring methods
The level of analgesia was recorded continuously using the proprietary index IOC2 (Index of consciousness 2,namely qNOX) (Angel-6000D Multi-parameter Anesthesia Monitor, Shenzhen Weihaokang Medical Technology Co., Ltd, Guangdong, China). IOC2was used in this study to estimate the responses of patients to noxious stimuli and analgesic levels [