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Effect-site half-time for burst suppression and hypnosis with sevoflurane
- Pierre-Yves Lequeux, Farid Garoud, Gilbert Bejjani (18 February 2008)
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Pierre-Yves Lequeux Department of Anesthesiology, CHU-Tivoli, La Louviere, Belgium, Farid Garoud, Gilbert Bejjani
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Editor- We read with interest the article by Kennedy and colleagues about the difference of t˝(ke0) values of Sevoflurane obtained for BIS or for burst suppression ratio (BS) as measures of the hypnotic effect of the drug(1). The issue of Sevoflurane-induced changes of cardiac output as well as the use of BIS as a measure of drug effect are major problems. Unfortunately the authors did not measure cardiac output and cerebral blood flow (both can be performed with non- or minimally-invasive techniques). Indeed Sevoflurane is known to induce a dose-dependant decrease of both cardiac output and cerebral blood flow(2, 3) which could be of great concern at large doses such as those eliciting BS. This could explain why authors found a delay in the hypnotic effect of the drug (prolonged t˝(ke0)) at a higher ET Sevoflurane. Besides, the authors used the Bispectral index monitor to measure both BIS and BS. Pilge and colleagues demonstrated that the delay to obtain a BIS value can vary from 15 to 66 seconds depending on the starting and target BIS value, pointing out a limitation of this monitor for pharmacodynamic studies(4). Moreover variability of delays appears to be greater at low BIS values explaining why Kennedy and colleagues found a longer t˝(ke0) with a larger variability at a higher ET Sevoflurane. Furthermore as the exact BIS calculation processing remains largely unknown, the assertion “Processing of data for burst suppression follows a similar pattern to that for BIS so that the offset between values for BIS and burst suppression should be minimal” may be excessive. Although we had similar results to those of Kennedy and colleagues when we compared the Tpeak of propofol after a bolus of 1 mg/kg (Tpeak: 73±13 sec) or 3 mg/kg (Tpeak: 121 ± 43 sec)(5) and our opinion is that ke0 may vary with hypnotic state indicating that a direct PD model with only one equilibration rate constant (ke0) is inappropriate, the above- mentioned issues question the clinical relevance of the observations made by the authors. Dr P.-Y. Lequeux* Dr F. Garoud# Dr G. Bejjani$ * Staff Anesthesiologist, Department of Anesthesiology, CHU-Tivoli, La Louviere, Belgium # Resident, Department of Anesthesiology, Brugmann Hospital, Brussels, Belgium $ Staff Anesthesiologist, Department of Anesthesiology, Erasme Hospital, Brussels, Belgium References 1. Kennedy RR, Minto C, Seethepalli A. Effect-site half-time for burst suppression is longer than for hypnosis during anaesthesia with sevoflurane. Br J Anaesth 2008; 100: 72-7 2. TJ Ebert, CP Harkin, M Muzi. Cardiovascular responses to sevoflurane: a review. Anesth Analg 1995, 81, S11-S22 3. Mielck F, Stephan H, Weyland A, Sonntag H. Effects of one minimum alveolar anesthetic concentration sevoflurane on cerebral metabolism, blood flow, and CO2 reactivity in cardiac patients. Anesth Analg. 1999; 89:364-9 4. Pilge S, Zanner R, Schneider G, Blum J, Kreuzer M, Kochs E. Time delay of index calculation: analysis of cerebral state, bispectral, and narcotrend indices. Anesthesiology 2006; 104:488-94 5. Lequeux PY, Garoud G, Bejjani G, Barvais L. The Influence of the dose on the Time to Peak effect of Propofol, ISAP annual meeting 2006, Chicago, IL Conflict of Interest:None declared |
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