Advance of age decreases the minimum alveolar concentrations of isoflurane and sevoflurane for maintaining bispectral index below 50.
BACKGROUND
We investigated age-related differences in the minimum alveolar concentration (MAC) of isoflurane and sevoflurane for maintaining bispectral index (BIS) below 50 (MAC(BIS50)).


METHODS
One hundred and twenty young (<or=40 yr), middle-aged (41-69 yr), and elderly (>or=70 yr) patients were randomly allocated to one of the six groups. Anaesthesia was induced with isoflurane or sevoflurane in oxygen. After tracheal intubation, we arbitrarily started maintenance of anaesthesia in each group with end-tidal isoflurane and sevoflurane concentrations of 0.8 and 1.2 vol%, respectively. After 10 min at predetermined end-tidal isoflurane or sevoflurane concentrations, BIS was measured for 1 min. MAC(BIS50) of isoflurane or sevoflurane for each group was determined by up-down methodology.


RESULTS
MAC(BIS50) of isoflurane in young, middle-aged, and elderly patients was 0.82% end-tidal (95% confidence intervals 0.76-0.88), 0.67% (0.61-0.73), and 0.56% (0.51-0.61), respectively, and that of sevoflurane in young, middle-aged, and elderly patients was 1.28% (1.24-1.32), 0.97% (0.89-1.05), and 0.87% (0.84-0.90), respectively. For both isoflurane and sevoflurane, the MAC(BIS50) was significantly higher (P=0.002 and 0.001, respectively) in young patients and significantly lower (P=0.02 for both) in elderly patients than those in middle-aged patients.


CONCLUSIONS
Advance in age significantly decreased the concentrations of isoflurane and sevoflurane required to maintain BIS below 50. BIS correctly reflected age-associated decrease of end-tidal concentrations of isoflurane and sevoflurane required for maintaining adequate depth of anaesthesia during resting state.
Matsuura
T
T
Department of Anesthesiology, Osaka City University Graduate School of Medicine, 1-5-7 Asahimachi, Abeno-ku, Osaka 545-8586, Japan.
Oda
Y
Y
Tanaka
K
K
Mori
T
T
Nishikawa
K
K
Asada
A
A
D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D004569:Electroencephalography / Q000187:drug effects; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D011650:Pulmonary Alveoli / Q000378:metabolism; D000077149:Sevoflurane; D055815:Young Adult
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane