Skin impedance correlates to sedation grade, plasma propofol concentrations and bispectral index during a target-controlled infusion of propofol.
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.
Winterhalter
Michael
M
Department of Anaesthesiology, University of Duesseldorf, Duesseldorf, Germany. michael.winterhalter@med.uni-duesseldorf.de
Münte
Sinikka
S
Taschenbrecker
Peter
P
Hecker
Hartmut
H
Weilbach
Christian
C
Osthaus
Alexander W
AW
Gross
Matthias
M
Piepenbrock
Siegfried
S
Rahe-Meyer
Niels
N
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
D018686:Anesthetics, Intravenous; D015742:Propofol