title: Skin impedance correlates to sedation grade, plasma propofol concentrations and bispectral index during a target-controlled infusion of propofol.
abstract: OBJECTIVE
  Sympathetic activity, measured as changes in electrical skin impedance, may be used to assess the adequacy of general anaesthesia. The aim of this prospective study was to evaluate electrical skin impedance in comparison with bispectral index values and the Observer's Assessment of Alertness and Sedation (OAAS) scale during propofol infusion.
  
  
  METHODS
  Electrical skin impedance was measured with an electrosympathicograph. In 22 patients and eight healthy volunteers, anaesthesia was induced and maintained with propofol that was administered via a target-controlled infusion pump at increasing plasma concentrations. Bispectral index, electrosympathicograph and OAAS values were compared at six successive predicted target plasma concentrations (T 1-6: 0, 1.3, 1.7, 2.0, 2.4 and 2.8 microg ml(-1)).
  
  
  RESULTS
  The changes in the electrical skin impedance measured with the assistance of the electrosympathicograph correlated with the changes in bispectral index values at each measurement time point and during the whole course (P < 0.0001), with the target plasma propofol concentrations (P < 0.0001), and with the OAAS scale (P < 0.0001).
  
  
  CONCLUSIONS
  The observed correlations between electrical skin impedance, predicted plasma concentrations of propofol and OAAS scale appear to justify further investigation of skin impedance as a depth of anaesthesia monitor.
authors.affiliation: Department of Anaesthesiology, University of Duesseldorf, Duesseldorf, Germany. michael.winterhalter@med.uni-duesseldorf.de
authors.forename: Michael
authors.initials: M
authors.lastname: Winterhalter
authors.forename: Sinikka
authors.initials: S
authors.lastname: Münte
authors.forename: Peter
authors.initials: P
authors.lastname: Taschenbrecker
authors.forename: Hartmut
authors.initials: H
authors.lastname: Hecker
authors.forename: Christian
authors.initials: C
authors.lastname: Weilbach
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Osthaus
authors.forename: Matthias
authors.initials: M
authors.lastname: Gross
authors.forename: Siegfried
authors.initials: S
authors.lastname: Piepenbrock
authors.forename: Niels
authors.initials: N
authors.lastname: Rahe-Meyer
mesh_terms: D000328:Adult; D000758:Anesthesia; D018686:Anesthetics, Intravenous / Q000493:pharmacokinetics / Q000494:pharmacology*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D016343:Monitoring, Intraoperative / Q000379:methods; D015742:Propofol / Q000493:pharmacokinetics / Q000494:pharmacology*; D011446:Prospective Studies; D012867:Skin / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D055815:Young Adult
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol