• Br J Anaesth · Jan 2008

    Effect-site half-time for burst suppression is longer than for hypnosis during anaesthesia with sevoflurane.

    • R R Kennedy, C Minto, and A Seethepalli.
    • Department of Anaesthesia, Christchurch Hospital and University of Otago, Christchurch Rolleston Ave, Christchurch, New Zealand. ross.kennedy@chmeds.ac.nz
    • Br J Anaesth. 2008 Jan 1;100(1):72-7.

    BackgroundThe relationship between measures of drug effect such as bispectral index (BIS) and end-tidal (ET) levels of anaesthetic agents is described by the 'effect site equilibrium half-time', t(1/2)(ke0). There are limited data available on sevoflurane t(1/2)(ke0) during routine anaesthesia and surgery. Preliminary observations suggested t(1/2)(ke0) for the degree of hypnosis as estimated by BIS is different from that for burst suppression of the electroencephalograph, occurring at 'deep' levels of anaesthesia. This study aimed to determine and compare t(1/2)(ke0) for these two 'effects'.MethodsLarge changes in ET sevoflurane were produced in 13 subjects during surgery. ET sevoflurane, BIS, and burst suppression ratio (BSR) were recorded every 10 s. Data were divided into epochs with BIS>30 (BIS) or with BSR>10% (burst suppression). Using a non-parametric modelling technique, t(1/2)(ke0) was determined for each epoch.ResultsThere were 36 'BIS' and 20 burst suppression zones. Mean (sd) t(1/2)(ke0) for BIS was 3.48 (1.12) min and for BSR 9.9 (6.4) min. In all subjects, t(1/2)(ke0) BISConclusionsThe different values of t(1/2)(ke0) for these effects suggest different sites or mechanisms of action. These results also establish values of t(1/2)(ke0) which can be used to provide the real-time estimates of effect-site sevoflurane concentration in clinical practice.

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