Craniofacial electromyogram activation response: another indicator of anesthetic depth

Area of Science:

• Anesthesiology
• Neurophysiology
• Surgical Monitoring

Background:

• Craniofacial electromyography (EMG) preceding a stimulus is an unreliable predictor of subsequent movement response.
• Assessing anesthetic depth during emergence from general anesthesia requires reliable monitoring.
• The relationship between EMG activity and overt movement in response to stimuli needs further clarification.

Purpose of the Study:

• To evaluate the difference in anesthetic depth between the endpoint of EMG responsiveness and the endpoint of movement responsiveness to a stimulus.
• To determine if EMG activation in the absence of movement can predict impending movement.
• To assess the utility of EMG responsiveness for estimating individual patient anesthetic depth.

Main Methods:

• Measured EMG from frontalis and corrugator muscles, and between Fp2 and mastoid process during emergence from isoflurane anesthesia.
• Calculated estimated brain isoflurane concentrations ((C)isoBrain) during controlled anesthetic washout.
• Classified patient responses to stimuli as EMG activation only (EMG+), movement only (MV+), both (EMG+MV+), or no response.
• Defined and estimated (C)isoBrain at the EMG+ and movement endpoints to calculate the increment between them.

Main Results:

• In experimental patients, initial responses to stimuli included EMG+ (47%), EMG+MV+ (40%), and MV+ (3%).
• In 9 of 14 patients with an initial EMG+ response, a subsequent movement response occurred.
• The increment of (C)isoBrain between the EMG+ and movement endpoints was 0.11 +/- 0.04 vol% in these patients.

Conclusions:

• EMG activation in a non-moving patient indicates anesthetic depth is close to the movement threshold.
• EMG activation does not reliably herald movement, as it can occur simultaneously with movement.
• EMG responsiveness to stimuli can be utilized to estimate a patient's anesthetic depth.