gms | German Medical Science

Objective: Intraoperative awakening is a rare event with considerable risks for the patient due to sudden movements. A number of methods have been proposed to monitor depth of anesthesia, such as the Bispectral Index (BIS) and the Analgesia Nociception Index (ANI). In a pilot study, we had shown, that EMG from muscles targeted by the lower cranial nerves may predict awakening already before first changes of the BIS in many cases. We hypothesized that facial muscle and tongue EMG could predict patient movement during brainsurgery and may be superior compared to standard hemodynamic parameters or current monitoring technics for anesthetic depth.

Methods: In a series of 70 patients undergoing brain surgery in total intravenous anesthesia (TIVA) technique with propofol and remifentanil using target-controlled infusion (TCI) pumps, we evaluated the potential of facial and tongue EMG to predict awakening at the end of the surgical procedure. The EMG was analyzed using our peak detection software and offline compared to significant changes of the BIS and ANI.

Results: In approximately 60% of cases EMG preceded BIS increases by several minutes. BIS preceded facial EMG in approximately 30% while both methods showed increases at the same time in the remainder. ANI values showed excessively high variability throughout the surgical procedure while BIS, EMG, blood pressure and heart rate were stable. Furthermore, ANI did not show a clear increase at the end of the procedure during planned awakening.

Conclusion: The results suggest that EMG may provide warning signs minutes before the BIS. A combination of both should allow a lead-time of several minutes in most cases.