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Effect of nitrous oxide on the bispectral index and the 95% spectral edge frequency of the electroencephalogram during surgery
Author(s) -
Hans P.,
Bonhomme V.,
Benmansour H.,
Dewandre P. Y.,
Brichant J. F.,
Lamy M.
Publication year - 2001
Publication title -
anaesthesia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.839
H-Index - 117
eISSN - 1365-2044
pISSN - 0003-2409
DOI - 10.1111/j.1365-2044.2001.1974-4.x
Subject(s) - bispectral index , nitrous oxide , anesthesia , propofol , medicine , sufentanil
We studied the effect of nitrous oxide on the bispectral index and 95% spectral edge frequency of the electroencephalogram in 20 patients undergoing lumbar surgery under general anaesthesia combined with epidural administration of 5 mg morphine. Anaesthesia was induced with propofol and sufentanil, and maintained with sevoflurane in air/oxygen adjusted to keep the bispectral index between 40 and 60. One and a half hours after the start of surgery, nitrous oxide was administered in a randomised sequence of concentrations (20, 40 and 60% end‐expired). Under steady‐state conditions, mean (SD) bispectral index and spectral edge frequency decreased as end‐tidal concentration of nitrous oxide increased, from 47.7 (4.3) and 15.6 (1.3) at 0% nitrous oxide to 39.8 (6.3) and 14.3 (1.8) at 60% nitrous oxide. A negative correlation was found between nitrous oxide concentration and bispectral index ( r = −0.48; p < 0.01) and spectral edge frequency ( r = −0.39; p < 0.05). We conclude that this dose‐dependent decrease in bispectral index and spectral edge frequency induced by nitrous oxide may reflect the level of analgesia associated with the anaesthetic regimen.