The dynamic relationship between end-tidal sevoflurane and isoflurane concentrations and bispectral index and spectral edge frequency of the electroencephalogram
E. Olofsen et A. Dahan, The dynamic relationship between end-tidal sevoflurane and isoflurane concentrations and bispectral index and spectral edge frequency of the electroencephalogram, ANESTHESIOL, 90(5), 1999, pp. 1345-1353
Citations number
28
Categorie Soggetti
Aneshtesia & Intensive Care","Medical Research Diagnosis & Treatment
Background: Inhalational anesthetics produce dose-dependent effects on elec
troencephalogram-derived parameters, such as 95% spectral edge frequency (S
EF) and bispectral index (BIS), The authors analyzed the relationship betwe
en end-tidal sevoflurane and isoflurane concentrations (FET) and BIS and SE
F and determined the speed of onset and offset of effect (t(1/2)k(e0)).
Methods: Twenty-four patients with American Society of Anesthesiologists ph
ysical status I or II were randomly assigned to receive anesthesia with sev
oflurane or isoflurane. Several transitions between 0.5 and 1.5 minimum alv
eolar concentration mere performed. BIS and SEF data were analyzed with a c
ombination of an effect compartment and an inhibitory sigmoid E-max model,
characterized by t(1/2)k(e0), the concentration at which 50% depression of
the electroencephalogram parameters occurred (IC50), and shape parameters.
Parameter values estimated are mean +/- SD.
Results: The model adequately described the FET-BIS relationship. Values fo
r t(1/2)k(e0), derived from the BIS data, mere 3.5 +/- 2.0 and 3.2 +/- 0.7
min for sevoflurane and isoflurane, respectively (NS). Equivalent values de
rived from SEF mere 3.1 +/- 2.4 min (sevoflurane) and 2.3 +/- 1.2 min (isof
lurane; NS). Values of t(1/2)k(e0) derived from the SEF were smaller than t
hose from BIS (P < 0.05). IC50 values derived from the BIS were 1.14 +/- 0.
31% (sevoflurane) and 0.60 +/- 0.11% (isoflurane; P < 0.05),
Conclusions: The speed of onset and offset of anesthetic effect did not dif
fer between isoflurane and sevoflurane; isoflurane was approximately twice
as potent as sevoflurane. The greater values of t(1/2)k(e0), derived from t
he BIS data compared with those derived from the SEF data may be related to
computational and physiologic delays.