[Effects of volatile anesthetics on cortical somatosensory evoked potential and Bispectral index].
OBJECTIVE
To improve the anesthetic environment in monitoring short-latency somatosensory evoked potentials (SSEP) during operation, we compared the effects of different anesthetics on SSEP and Bispectral index (BIS), which aim to select suitable anesthetics and their doses used intraoperatively.


METHODS
60 ASA I-II patients undergoing elective neurosurgery were randomly allocated into three groups: enflurane, isoflurane and desflurane group. The concentration of each volatile anesthetic was increased step by step from 0 to end-tidal 0.3, 0.5, 0.75, 1.0 and 1.5 MAC. The changes of cortical SSEP component N20 were recorded as well as Bispectral index (BIS) monitoring. The effects of three volatile anesthetics in various concentrations on short-latency SSEP and BIS were investigated.


RESULTS
All three volatile anesthetics significantly decreased N20 amplitude and prolonged N20 latency. The N20 waveform disappeared in some patients when the end-tidal concentration of enflurane reached 1.0 MAC, it occurred when that of isoflurane or desflurane was at 1.5 MAC. BIS monitoring showed BIS values were all under 60 when at 1.0 MAC in three group. For some patients in enflurane group and desflurane group, BIS values were above 60 (45-64, 44-61, respectively) when at 0.75 MAC, while those in isoflurane group were still less than 60 (39-58). And the amplitude or latency of cortical SSEP correlated poorly with BIS.


CONCLUSIONS
The effects of three volatile anesthetics on SSEP and BIS are significant in dose-dependent manner. Anesthetic regimen of 0.75 MAC isoflurane for intraoperative cortical SSEP monitoring may be optimal. It seemed that the correlation between BIS and short-latency SSEP was poor, although both are associated with the effects of anesthetics on cerebral cortex.
Zhang
Jun
J
Department of Anesthesiology, Huashan Hospital, Fudan University, Shanghai 200040, China.
Liang
Wei-min
WM
D000328:Adult; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000077335:Desflurane; D004569:Electroencephalography / Q000187:drug effects; D004737:Enflurane / Q000008:administration & dosage; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects*; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage / Q000031:analogs & derivatives; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D055815:Young Adult
D018685:Anesthetics, Inhalation; D004737:Enflurane; D000077335:Desflurane; D007530:Isoflurane