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BJA Advance Access published online on November 12, 2007
British Journal of Anaesthesia, doi:10.1093/bja/aem314
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© The Board of Management and Trustees of the British Journal of Anaesthesia 2007. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

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

R. R. Kennedy1,*, C. Minto2 and A. Seethepalli1

1 Department of Anaesthesia, Christchurch Hospital and University of Otago, Christchurch Rolleston Ave, Christchurch, New Zealand
2 Department of Anaesthesia and Pain Management, Royal North Shore Hospital, Sydney, Australia

* Corresponding author. E-mail: ross.kennedy{at}chmeds.ac.nz

Background: The 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’, t1/2(ke0). There are limited data available on sevoflurane t1/2(ke0) during routine anaesthesia and surgery. Preliminary observations suggested t1/2(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 t1/2(ke0) for these two ‘effects’.

Methods: Large 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, t1/2(ke0) was determined for each epoch.

Results: There were 36 ‘BIS’ and 20 burst suppression zones. Mean (SD) t1/2(ke0) for BIS was 3.48 (1.12) min and for BSR 9.9 (6.4) min. In all subjects, t1/2(ke0) BIS<t1/2(ke0) BSR. These differences were statistically significant (P<0.01). The pooled mean effect-site sevoflurane concentration producing a BIS of 50 was 1.23 (SD 0.34) vol% and for a BSR of 50% was 3.3 (0.50) vol%. There were considerable intra- and inter-subject variabilities.

Conclusions: The different values of t1/2(ke0) for these effects suggest different sites or mechanisms of action. These results also establish values of t1/2(ke0) which can be used to provide the real-time estimates of effect-site sevoflurane concentration in clinical practice.

Keywords: anaesthetics volatile, sevoflurane; monitoring, electroencephalography; model, pharmacokinetic

{dagger} This project was presented in part at the Euroanaesthesia Meeting, Vienna, Austria, May 2005.


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Effect-site half-time for burst suppression and hypnosis with sevoflurane
Pierre-Yves Lequeux, et al.
British Journal of Anaesthesia, 18 Feb 2008 [Full text]

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