title: Spectral entropy as a monitor of depth of propofol induced sedation.
abstract: OBJECTIVE
  The aim of this prospective, observational study was to evaluate State and Response entropy (Entropy(TM) Monitor, GE Healthcare, Finland), indices as measures of moderate ("conscious") sedation in healthy adult patients receiving a low dose propofol infusion. Sedation was evaluated using: (I) the responsiveness component of the OAA/S scale (Observer's Assessment of Alertness/Sedation scale) and (II) multi-channel electroencephalogram (EEG) interpretation by a clinical expert.
  
  
  METHODS
  12 ASA I patients were recruited. A target-controlled infusion of propofol was administered (using Schnider's pharmacokinetic model) with an initial effect site concentration set to 0.5 microg ml(-1). A 4 minute equilibrium period was allowed. This concentration was increased at 4 minute intervals by 0.5 microg ml(-1) to a maximum of 2.0 microg ml(-1). State (SE) and Response (RE), entropy values were recorded for each 4 minute epoch together with clinical sedation scores (OAA/S) and continuous multi-channel EEG. The multi-channel EEG recorded during the final minute of each 4 minute epoch or "patient/time unit" was presented to a neurophysiologist who assigned a label "sedated/not sedated". SE/RE values were compared in patient/time units with clinical or EEG evidence of sedation versus those without.
  
  
  RESULTS
  Mean SE and RE values were less in patient/time units when clinical evidence of sedation was present, [mean = 86.8 (95% CI, 84.0-88.3) and 94.3 (95%CI, 92-96.1)], P = 0.002 and P = 0.001, respectively. In patient/time units assigned the label "sedated" by the clinical neurophysiologist assessing the multi-channel EEG, SE and RE values were less [mean = 87.5 (95% CI, 86.3-88.4) and 95.0 (95% CI, 93.8-96.1)] P = 0.001 and P < 0.001, respectively.
  
  
  CONCLUSIONS
  A statistically significant decrease in SE and RE values was demonstrated in patient/time units in which clinical or EEG evidence of sedation was present. We conclude that spectral entropy offers potential as a monitor of propofol induced sedation.
authors.affiliation: Department of Anaesthesia and Intensive Care Medicine, Cork University Hospital, University College Cork, Cork, Ireland. rsimahon@hotmail.com
authors.forename: Padraig
authors.initials: P
authors.lastname: Mahon
authors.forename: Robert G
authors.initials: RG
authors.lastname: Kowalski
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Fitzgerald
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Lynch
authors.forename: Geraldine B
authors.initials: GB
authors.lastname: Boylan
authors.forename: Brian
authors.initials: B
authors.lastname: McNamara
authors.forename: George D
authors.initials: GD
authors.lastname: Shorten
mesh_terms: D000328:Adult; D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D001364:Awareness / Q000187:drug effects; D016292:Procedural Sedation / Q000379:methods; D003243:Consciousness / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D016903:Drug Monitoring / Q000379:methods; D004569:Electroencephalography; D019277:Entropy; D006801:Humans; D007262:Infusions, Intravenous; D007600:Judgment / Q000187:drug effects; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009482:Neurophysiology; D011237:Predictive Value of Tests; D015742:Propofol / Q000008:administration & dosage*; D014894:Weights and Measures
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol