Aims: 

The main effect of several anaesthetic agents is their effect on arousal mechanisms. Yet, even very minor external stimuli may cause EEG arousal in deep anaesthesia at burst suppression EEG level. There are, however, considerable differences between anaesthetics, and the reactions in propofol anaesthesia are minimal. In this study we investigated the possible effects of reversal of neuromuscular blocking with neostigmine on EEG.

Methods: 

15 female patients undergoing gynaecological operation were studied. They received intravenous anaesthesia with propofol and remifentanil and muscle relaxation with rocuronium. EEG was collected with an Entropy (R) module of S/5 Anaesthesia monitor (GE Healthcare). EEG was then analyzed off-line with programs in Nicolet One EEG Monitor.

Results: 

In the end of the operation the patient was left untouched for 2–5 minutes. Neostigmine was then injected to reverse the effect of rocuronium. In four patients, no EMG was detected, and the EEG of those patients was analyzed in detail. During the rest period EEG slow activity gradually decreased. One minute after the injection of neostigmine there was an abrupt decrease of delta activity and increase of fast activity, which lasted approximately a minute. Several spectral parameters and ratios were calculated to verify the change, including spectral edge and alpha -delta ratio.

Conclusion: 

We report an EEG arousal phenomenon after reversal of muscle relaxation which had similar EEG pattern and temporal behaviour after neostigmine. This confirms earlier reports but this is the first paper to analyze in detail this pattern. This is important because it affects the EEG-based anaesthesia indexes and may cause false sign of lighter anaesthesia as the effect of neostigmine.