Values of the bispectral index do not parallel the hemodynamic response to the rapid increase in isoflurane concentration.
OBJECTIVE
To investigate the changes in hemodynamic variables and bispectral index (BIS) in response to a rapid increase in isoflurane or sevoflurane concentration.


METHODS
Thirty adult patients were anesthetized with either isoflurane (isoflurane group) or sevoflurane (sevoflurane group). Two minutes after induction of anesthesia with thiamylal, the inspired concentrations of isoflurane and sevoflurane were rapidly increased from 0.5 minimum alveolar anaesthetic concentration (MAC) to 3 MAC and maintained for five minutes. Heart rate (HR), mean arterial pressure (MAP), and BIS were measured every minute.


RESULTS
An increase in the anesthetic concentration caused increases in HR and MAP in the isoflurane group and a decrease in MAP in the sevoflurane group. Consequently, HR and MAP in the isoflurane group were significantly higher than those in the sevoflurane group. After inhalation of high concentrations, BIS significantly and progressively decreased in both groups.


CONCLUSIONS
BIS values decrease after a step increase in volatile agent concentration, whether or not a hyperdynamic action occurs.
Nakayama
M
M
Division of Anesthesia, Obihiro Kosei Hospital, and the Sapporo Medical University School of Medicine, Sapporo, Japan. miyabi@zc4.so-net.ne.jp
Hayashi
M
M
Ichinose
H
H
Yamamoto
S
S
Kanaya
N
N
Namiki
A
A
D000328:Adult; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D006439:Hemodynamics / Q000187:drug effects*; D006801:Humans; D007530:Isoflurane / Q000494:pharmacology*; D008738:Methyl Ethers / Q000494:pharmacology; D008875:Middle Aged; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane