title: Evaluation of entropy for monitoring the depth of anesthesia compared with bispectral index: a multicenter clinical trial.
abstract: BACKGROUND
  As a new electroencephalogram (EEG) signal processing technique for monitoring the depth of anesthesia, entropy consists of two indices: reaction entropy (RE) and state entropy (SE). Our study compared entropy with classical bispectral index (BIS) in reduction of myoelectrical interference and noxious stimuli with EEG signals.
  
  
  METHODS
  Two hundred and eighty patients (ASA I-II, 18-60 years old) undergoing scheduled surgeries from seven medical centers were enrolled. Anesthesia induction was managed with propofol via the target-controlled infusion (TCI) system. The results of BIS, RE, SE, mean arterial pressure (MAP) and heart rate (HR) were recorded before anesthesia induction, at the moment of unconsciousness, before and 2 minutes after administration of muscle relaxant, and before and one and three minutes after the tracheal intubation.
  
  
  RESULTS
  The values of half maximum effective concentrations (EC50), 5% effective concentrations (EC05) and 95% effective concentrations (EC95) of propofol effect-site concentration at the onset of unconsciousness were 1.2 (1.1-1.3 µg/ml), 2.5 (2.4-2.5 µg/ml) and 3.7 (3.7-3.8 µg/ml), while those of the predicted plasma propofol concentration were 2.8 (2.7-2.9 µg/ml), 3.9 (3.8-3.9 µg/ml) and 4.9 (4.8-5.0 µg/ml), respectively. The values of BIS, SE and RE were 62, 59 and 63 when 50% of patients lost consciousness, and 79, 80, 85 and 42, 37, 44, respectively, when 5% and 95% of patients were unconscious. The values of BIS, RE and SE dropped two minutes after the injection of muscle relaxant, but there were no significant differences between RE and SE. MAP and HR increased visibly, which indicated a reaction to tracheal intubation; the values of BIS, RE and SE, however, did not display any significant changes.
  
  
  CONCLUSIONS
  This large-sample multicentric study confirmed the values of RE and SE as approximating BIS value, at the onset of unconsciousness during propofol TCI anesthesia. After elimination of myoelectrical activation, all values of RE, SE and BIS decreased significantly and the three indices were less sensitive to noxious stimuli than cardiovascular responses.
authors.affiliation: Department of Anesthesiology, Beijing Chaoyang Hospital, Capital Medical University, Beijing 100020, China.
authors.forename: Jian-dong
authors.initials: JD
authors.lastname: Gao
authors.forename: Yu-jie
authors.initials: YJ
authors.lastname: Zhao
authors.forename: Chen-shi
authors.initials: CS
authors.lastname: Xu
authors.forename: Jing
authors.initials: J
authors.lastname: Zhao
authors.forename: Yu-guang
authors.initials: YG
authors.lastname: Huang
authors.forename: Tian-long
authors.initials: TL
authors.lastname: Wang
authors.forename: Ling
authors.initials: L
authors.lastname: Pei
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
authors.forename: Li-nong
authors.initials: LN
authors.lastname: Yao
authors.forename: Qian
authors.initials: Q
authors.lastname: Ding
authors.forename: Zhi-ming
authors.initials: ZM
authors.lastname: Tan
authors.forename: Zhi-rong
authors.initials: ZR
authors.lastname: Zhu
authors.forename: Yun
authors.initials: Y
authors.lastname: Yue
mesh_terms: D000328:Adult; D000758:Anesthesia; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D001794:Blood Pressure; D004569:Electroencephalography; D004576:Electromyography; D019277:Entropy; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D015742:Propofol / Q000097:blood / Q000494:pharmacology*
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol