Spontaneous EMG activity for detection of arousal during general anaesthesia--comparison between recordings from...

Monitoring of the spontaneous electromyographic activity of the frontal muscles (FEMG) is used for detection of impending arousal during general anaesthesia. Since the irritation caused by an endotracheal tube in situ might enhance the sensitivity of neck muscles in detecting arousal, EMG recordings from sternocleidomastoid muscles (NEMG) were compared to FEMG recordings under five different clinical conditions with 10 patients in each group. Two Anesthesia and Brain Activity Monitors (ABM, Datex Instrumentarium, Helsinki) were used simultaneously for recordings. NEMG was more sensitive than FEMG in detecting increases in EMG activity under all five conditions, although less distinct under conditions with a profound (90-100%) neuromuscular blockade. The results thus support our initial hypothesis and favour the use of neck muscles for monitoring. This, however, does not allow simultaneous recording of EEG through the same electrodes.