Related Experiment Videos
Comparison of ocular microtremor and bispectral index during sevoflurane anaesthesia
L G Kevin1, A J Cunningham, C Bolger
1Department of Anaesthesia, Beaumont Hospital, Dublin 9, Ireland.
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.
Insights
Ocular microtremor (OMT) effectively monitors anesthesia depth, outperforming the bispectral index (BIS). This study shows OMT accurately predicts patient response to commands during anesthesia.
Area of Science:
- Anesthesiology
- Neurophysiology
- Medical Monitoring
Background:
- Current anesthesia depth monitors lack both simplicity and accuracy.
- Ocular microtremor (OMT), a physiological tremor, is dose-dependently suppressed by propofol.
Purpose of the Study:
- To evaluate OMT as a practical and reliable monitor for anesthesia depth.
- To compare OMT with the bispectral index (BIS) in predicting response to verbal command.
Main Methods:
- OMT was measured using a piezoelectric strain-gauge technique with eyes closed.
- OMT and BIS were recorded during propofol induction and sevoflurane maintenance, at varying sevoflurane concentrations, and during emergence.
Main Results:
- OMT significantly decreased post-induction and increased upon emergence.
- OMT demonstrated higher sensitivity (84.9%) and specificity (93.1%) than BIS (75.7% and 69.0%) in differentiating awake from anesthetized states.
- OMT suppression by sevoflurane was observed, though not dose-dependent between 1-2% end-tidal concentrations.
Conclusions:
- OMT is suppressed by sevoflurane and accurately predicts responsiveness to verbal commands.
- OMT shows potential as a valuable tool for monitoring the depth of hypnotic anesthesia.