Background:
The aim of the study was to assess the influence of volatile induction of general anaesthesia with sevoflurane using two different techniques and intravenous anaesthesia with propofol on the possible presence of epileptiform electroencephalograph patterns during the induction of general anaesthesia.

Methods:
Sixty patients (age 18–70 years) were recruited. Exclusion criteria included a history of epilepsy, neurological or neurosurgical diseases, pre-existing EPs (epileptiform patterns) in initial EEG recordings, medication interfering with EEG patterns. Patients were randomly allocated into three different groups, namely: A (sevoflurane, increasing concentrations technique); B (sevoflurane, vital capacity technique); and C (intravenous propofol). The clinical and instrumental monitoring included arterial blood pressure, heart rate, standard electrocardiography II, arterial oxygen saturation, facial electromyography, fraction of inspired sevoflurane, fraction of expired sevoflurane, minimum alveolar concentration of sevoflurane, and BIS.

Results:
Neurophysiological analysis of EEGs showed different EPs: polyspikes (PS), rhythmic polyspikes (PSR), and periodic epileptiform discharges (PED). EPs (P < 0.05) were observed in group A (56%) and group B (37%), but not in group C. One patient in group B presented clinical seizures. No significant differences in the vital parameters and anaesthesia parameters between groups was observed, regardless of the presence of EPs, which were associated with both low and more likely high (falsely indicating awakening from anaesthesia) BIS scores.

Conclusion:
Our study shows that the BIS score variations do not identify epileptiform activity, which was associated with both low and high scores. In addition, the sevoflurane concentration reached either sedative or toxic concentrations