Purpose: To investigate the changes in hemodynamic variables and bispectral
index (BIS) in response to a rapid increase in isoflurane or sevoflurane c
Method: Thirty adult patients were anesthetized with either isoflurane (iso
flurane group) or sevoflurane (sevoflurane group). Two minutes after induct
ion of anesthesia with thiamylal, the inspired concentrations of isoflurane
and sevoflurane were rapidly increased from 0.5 minimum alveolar anaesthet
ic 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 g
roup. Consequently, HR and MAP in the isoflurane group were significantly h
igher than those in the sevoflurane group. After inhalation of high concent
rations, BIS significantly and progressively decreased in both groups.
Conclusion: BIS values decrease after a step increase in volatile agent con
centration, whether or not a hyperdynamic action occurs.