[The effect of nitrous oxide on the central nervous system evaluated by the bispectral index under various levels of propofol anesthesia].
BACKGROUND
The effect of nitrous oxide either as a sole agent or with volatile anesthetic agents on the central nervous system has been well studied. However, it has not been clarified during various levels of propofol anesthesia. We therefore evaluated the effect of nitrous oxide on the central nervous system using bispectral index (BIS) and suppression ratio (SR) under various levels of propofol anesthesia.


METHODS
Twelve patients were enrolled for the study. After the administration of subarachnoid block, propofol was infused using a stepped down series (effect site concentration of 5, 4, 3 microg x ml(-1)) for 20 minutes. After obtaining BIS and SR at each concentration, nitrous oxide was added.


RESULTS
When 67% of nitrous oxide was added to the estimated effect site propofol concentration of 5 microg x ml(-1), BIS decreased and SR increased indicating that the nitrous oxide had a depressant effect on the central nervous system. On the other hand, nitrous oxide combined with 3 or 4 microg x ml(-1) of propofol did not cause significant changes in BIS and SR, suggesting that nitrous oxide did not have a suppressive effect.


CONCLUSIONS
We conclude that nitrous oxide has different effects on BIS according to their basal propofol concentrations.
Koitabashi
Toshiya
T
Department of Anesthesiology, Ichikawa General Hospital, Tokyo Dental College, Ichikawa 272-8513.
Ouchi
Takashi
T
Umemura
Naoji
N
D000328:Adult; D000771:Anesthesia, Intravenous; D001921:Brain / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004569:Electroencephalography / Q000187:drug effects*; D005260:Female; D006801:Humans; D008297:Male; D009609:Nitrous Oxide / Q000494:pharmacology*; D015742:Propofol / Q000008:administration & dosage / Q000097:blood; D013514:Surgical Procedures, Operative
D009609:Nitrous Oxide; D015742:Propofol