BACKGROUND: Electroencephalogram (EEG) monitoring is now common but its usefulness is not always used to its full potential during anaesthesia. Besides helping the assessment of the level of anaesthesia, it may detect neuronal dysfunction1 and is the only method of detecting non-convulsive epileptic activity2. We describe two clinical cases demonstrating the importance of EEG power spectrogram in a case of intraoperative epileptic event and in a case of brain death. 
Case Report:
1) A 29 years old male, ASA II, was proposed to frontal oligodendroglioma removal. 
Craniotomy was performed under total intravenous anaesthesia (Remifentanil / Propofol). No muscle relaxant was used to allow cortical mapping during surgery.
Two convulsive tonico-clonic events occurred spontaneously, soon after tumour exposition. Preoperative sodium valproate was at a therapeutic level, and Thiopental and Levetiracetam were started. Towards the end of surgery, under muscle relaxation, two other events were detectable in the processed EEG. 
Ventilation and sedation was maintained until antiepileptic therapeutic optimization. At 32 hours the patient was successfully extubated after no more epileptic events were detected. 
2) A 62 years old female, ASA II, was admitted with subarachnoid hemorrhage secondary to intracranial aneurysm. She was proposed to endovascular aneurysm embolization. After an apparently successful and uneventful embolization under general anaesthesia, a difficulty in awaking was noted, with apnoea and absence of reflexes.
A normal EEG power spectrogram pattern for Propofol anaesthesia was progressively replaced by decreased activity in all frequencies. A new immediate angiography showed total absence of cerebral circulation and brain death was declared a few hours after.
DISCUSSION: The diagnosis of epileptic non-convulsive activity is a challenge during general anaesthesia with muscle relaxant use. Even when muscle relaxant is not used, as is the case of grand mal treatment, underdiagnosis is a cause of delay in recovery and prolonged ventilation. EEG monitoring by power spectrogram allows for epileptic activity detection during general anaesthesia or deep sedation.
LEARNING POINTS: Continuous EEG monitoring provides a dynamic monitoring of the brain. EEG power spectrogram is useful for epileptic events and even for possible early detection of brain death when conventional EEG can not be done. 

02 / Utility of processed electroencephalogram power spectrogram during general anesthesia. Two clinical cases: 1) intraoperative convulsion and 2) brain death