gms | German Medical Science

Objective: During surgery, lower cranial nerve (CN) EMG may show spontaneous activity without a surgical correlation. These episodes have been observed in association with sudden patient movement. In the study presented, this activity was quantified and correlated with the Bispectral Index (BIS) in order to evaluate the potential of lower cranial nerve EMG for monitoring of the depth of anaesthesia.

Methods: Spontaneous EMG-activity in muscles targeted by the cranial nerves IX, X and XII was quantified and correlated with the Bispectral Index (BIS) measured in 23 patients operated on for posterior fossa pathology. In a blinded retrospective analysis, the time interval from beginning build-up of the respective parameter (EMG-activity and BIS) until extubation was marked. The resulting time intervals were then compared between BIS and EMG.

Results: EMG build-up was seen 12.3 min and BIS build-up 5.9 min before extubation on the average. EMG thus provided longer "warning time" (p = 0.026). Isolated lower CN EMG channels preceded BIS in 53%, 62% and 70% (CN IX, X and XII). The earliest available EMG-channel preceded BIS in 67% of the patients by median 4.3 min. The beginning of EMG build-up in the earliest channel was found to be significantly earlier than BIS (p < 0.001).

Conclusions: Spontaneous EMG of muscles targeted by lower cranial nerves seems to correlate well with arousal reactions at the end of anesthesia. In many cases, this effect preceded BIS-changes. Thus, lower cranial nerve EMG-monitoring may be a valuable tool in monitoring adequate depth of anesthesia.