• M Iannuzzi, E Iannuzzi, F Rossi, L Berrino, and M Chiefari.
• Department of Anaesthesiological, Surgical and Emergency Sciences, Second Service of Anaesthesia and Department of Experimental Medicine, Second University of Naples, Naples, Italy. micheleiannuzzi@libero.it
• Br J Anaesth. 2005 Apr 1;94(4):492-5.

BackgroundState entropy (SE) is a newly available monitor for depth of anaesthesia. We investigated whether the relationship between predicted effect-site propofol concentration and Bispectral Index (BIS) and SE values is useful for predicting loss of verbal contact and loss of consciousness during steady-state conditions.MethodsTwenty unpremedicated patients undergoing elective major abdominal surgery were recruited. A target-controlled infusion of propofol was administered using Schneider's pharmacokinetic model. The propofol infusion was set at an initial site effect concentration of 1.0 microg ml(-1) and increased by 1.0 microg ml(-1) steps every 4 min up to 6.0 microg ml(-1). A 4-min interval was chosen to ensure that steady-state effect-site concentrations were obtained. Propofol site effect concentrations and BIS and SE values were recorded at loss of verbal contact (LVC) and loss of consciousness (LOC). Population values for predicted effect-site concentrations at the clinical endpoints were estimated and correlated with BIS and SE values.ResultsFor LVC, the effect-site concentration for 90% of patients was 1.1 (1.1-3.2) microg ml(-1) and for LOC it was 2.8 (2.8-5.65) microg ml(-1). LVC occurred in 90% of patients at a BIS value of 70.2 (70.2-90.2) and an SE value of 60.3 (60.3-75.5), and LOC occurred at a BIS value of 38.2 (38.2-70.4) and an SE value of 42.2 (42.2-60.4).ConclusionsLVC and LOC occurred within a defined range of predicted effect-site concentrations. SE had a smaller range than BIS and greater correlation with effect-site concentration and may be more useful than BIS in predicting both LVC and LOC.

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