Comparison of ocular microtremor and bispectral index during sevoflurane anaesthesia.
BACKGROUND
A practical and reliable monitor of depth of anaesthesia would be a major advance on current clinical practice. None of the present monitors is both simple to use and accurate. Ocular microtremor (OMT) is a physiological tremor that is suppressed by propofol in a dose-dependent manner. We studied OMT during propofol induction and nitrous oxide-oxygen-sevoflurane maintenance of anaesthesia in 30 patients, and compared OMT with the bispectral index (BIS) as a predictor of response to verbal command.


METHODS
OMT was measured using the closed-eye piezoelectric strain-gauge technique. OMT and BIS were measured at specific times during the anaesthetic, including at loss of consciousness, at end-tidal sevoflurane 1 and 2%, and at emergence.


RESULTS
OMT decreased significantly after induction, did not decrease as end-tidal sevoflurane was increased from 1 to 2%, and increased at emergence in all patients. By logistic regression, OMT was more sensitive and specific than BIS in distinguishing the awake from the anaesthetized state (OMT, 84.9 and 93.1% respectively; BIS, 75.7 and 69.0%).


CONCLUSIONS
OMT is suppressed by sevoflurane and accurately predicts response to verbal command. OMT may be a useful monitor of depth of hypnosis.
Kevin
L G
LG
Department of Anaesthesia, Beaumont Hospital, Dublin 9, Ireland.
Cunningham
A J
AJ
Bolger
C
C
D000293:Adolescent; D000328:Adult; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D004569:Electroencephalography / Q000187:drug effects*; D005133:Eye Movements / Q000187:drug effects*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology*; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D012372:ROC Curve; D012680:Sensitivity and Specificity; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane