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[The influences of nitrous oxide and ketamine on electroencephalogram during propofol-anesthesia].

BACKGROUND
The influence of nitrous oxide and ketamine on electroencephalogram (EEG) during the induction of general anesthesia with propofol was quantitatively analyzed.


METHODS
Anesthesia was induced with propofol using TCI (target controlled infusion) system. Twenty-five adult patients (ASA I-II) were randomly divided into three groups: 1. anesthesia induced with propofol alone [Group-P (n=7)], 2. anesthesia induced with inhalation of nitrous oxide in addition to propofol [Group-PN (n= 10)] and 3. anesthesia induced with intravenous injection of ketamine in addition to propofol [Group-PK (n= 8)]. We studied the influence of nitrous oxide and ketamine on EEG by analyzing the relations between effect-site concentration of propofol and EEG-indices.


RESULTS
Additional injection of ketamine (Group-PK) increased BIS index during the maintenance of anesthesia from 43.4 +/- 8.2 to 71.8 +/- 6.5 in comparison with the contrasting group (Group-P). Nitrous oxide also increased the high frequency component in EEG.


CONCLUSIONS
When anesthesia is induced with nitrous oxide and/or ketamine together with propofol, and BIS is taken as an index of depth of anesthesia, the intracerebral concentration of propofol becomes excess.