• L G Kevin, A J Cunningham, and C Bolger.
• Department of Anaesthesia, Beaumont Hospital, Dublin 9, Ireland.
• Br J Anaesth. 2002 Oct 1;89(4):551-5.

BackgroundA 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.MethodsOMT 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.ResultsOMT 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%).ConclusionsOMT is suppressed by sevoflurane and accurately predicts response to verbal command. OMT may be a useful monitor of depth of hypnosis.

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