British Journal of Anaesthesia, Vol 78, Issue 3 282-285, Copyright © 1997 by The Board of Management and Trustees of the British Journal of Anaesthesia
R. M. Sharpe, D. Nathwani, S. K. Pal, M. D. Brunner, C. Thornton, C. J. Dore and DEF. Newton
We have studied in 12 patients the effect of desflurane in nitrous oxide on
the electroencephalogram (EEG) and the early cortical auditory evoked
response (AER). After induction with desflurane, patients' lungs were
ventilated to maintain three different end-expiratory concentrations of
desflurane (1.5, 3 and 6%) during four consecutive 10- min periods before
surgery. As the end-expiratory concentration of desflurane was increased,
Pa and Nb (AER) amplitudes decreased and their latencies increased, and
spontaneous EEG showed an increase in amplitude and a slowing of frequency.
A linear relationship was demonstrated between log10 concentration of
desflurane and all variables (P = 0.001). Pa amplitude showed the greatest
linearity followed by the derived variable F95 of the EEG. From regression
slopes, mean percentage changes of each variable were calculated for a 1
MAC change in desflurane concentration, Pa amplitude showed the largest
change (mean 49% (95% confidence interval 40-56%) decrease for a 1 MAC
increase). This was greater than that of F95 for a similar confidence
interval, indicating better resolution. This study confirms that the early
cortical AER is affected by desflurane in a similar manner to that of other
anaesthetic agents and as such remains the most promising EEG derived
measure of depth of anaesthesia.
CLINICAL INVESTIGATIONS
Auditory evoked response, median frequency and 95% spectral edge during anaesthesia with desflurane and nitrous oxide
Academic Department of Anaesthetics, St Mary's Hospital Medical School, Northwick Park Hospital, Harrow HA1 3UJ; Department of Anaesthetics, Royal Free Hospital, Pond Street, London NWS 2QG; Institute of Medical Research, Statistics Department, Northwick Park Hospital, Harrow HA1 3UJ
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