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The purpose of this study was to determine to mean effective dosage for propofol and sevoflurane that leads to the generation of burst-suppression pattern on electroencephalogram and electrocorticogram in general anesthesia. It is established that effective dosages that cause the generation of intermittent activity on electroencephalogram exceed those for electrocorticogram. This trend is common both for sevoflurane and for propofol. Discrepancies in the dosage for general anesthetics causing the suppression of electrical activity on electroencephalogram and electrocorticogram defined the «dissociation» of recorded patterns. Simultaneous recording of electroencephalogram and electrocorticogram showed cortical burst-suppression pattern together with the continuous pattern on scalp electrodes. It is concluded that rating and systematization for suppression patterns on electroencephalogram and electrocorticogram should be built upon the common foundation, but with allowances made for technical specifics. Categorization of suppression phenomenon on electrocorticogram implies the critical amplitude to be 20 mkV, whereas for electroencephalogram it is 10 mkV. More formal proposed methods for assessment of intermittent patterns of brain electrical activity during general anesthesia are based on the specific tasks for intraoperative neuromonitoring. Excessive levels of sedation causing rough depression of electrical activity should be avoided, since they may lead to false-negative results of the neuromonitoring.

Background. In 30 % of cases with epilepsy, it qualifies as medically intractable and requires surgical treatment. The need for improvement of epilepsy surgery effectiveness demands updating of the preoperative assessment protocols. Intraoperative wide-range electrocorticography is a novel technique for defining resection volume in focal structural epilepsy. Combined analysis of high-frequency and epileptiform activity provides additional information and allows prognosticating of surgery outcome. However, consistent evaluation of intraoperative monitoring results is only possible when general anesthetic effect on brain electrical activity is taken into account.Objective. This study was aimed at evaluation of anesthetic gas sevoflurane effect on high-frequency brain electrical activity, recorded directly from the cortex or deep brain structures.Design and methods. Eight patients were included in this study (2 females, 6 males), aged 19 to 47, with a long-term epilepsy (disease duration 15 to 38 years). Prolonged electrocorticographic monitoring was indicated to these patients, combined with eloquent zones mapping in some cases. Patients were implanted with grid electrodes on frontal and temporal cortex, and deep brain Spencer electrodes into the mesial temporal lobe. Wide-range electrocorticography was recorded during slow-wave sleep and intraoperatively under sevoflurane anesthesia. Pathological high-frequency oscillations (pHFOs) rate was counted.Results. In seven patients pHFOs were recorded extraoperatively. Pathological HFO rate varied between 13 and 30 % (mean — 19 %). Distribution of pHFO did not change due to anesthesia effects. Mean background noise amplitude was significantly decreased intraoperatively (z = 2.45; p = 0.014). This effect facilitated visual marking of pHFOs. There were no trends in comparison between extraoperative and intraoperative pHFO rate.Conclusion. Well-controlled levels of general anesthesia obtained with sevoflurane (0,9-1,1 MAC) showed minimal effect on high-frequency brain electrical activity. This allows thorough analysis of wide-range electrocorticogiaphy without waking the patient and provides more information about the extension of the epileptogenic zone and its resection rate intraoperatively.

Background. The search for new markers of the epileptogenic zone (EZ) for the surgical treatment of epilepsy is currently of relevance. Pathological high-frequency oscillations (pHFO) are considered to be a potential marker for EZ. Papers devoted to this topic are few and insufficiently systematized, mostly due to a small quantity of patients.Objective. This study was aimed to determine the diagnostic efficacy of high-frequency electrocorticography (HF ECoG) based on the epilepsy surgery outcomes.Design and methods. This is an original retrospective study of high-frequency bioelectrical activity parameters in 114 patients who underwent surgical treatment in the Polenov Neurosurgical Institute Clinic during 2017–2018. In the subgroup of patients with pharmacoresistant course of structural epilepsy (21 patients) on the preresective electrocorticogram, the pHFO index was higher than in the subgroup with intracerebral neoplasms (11 patients), which may be associated with a longer history and severity of the disease.Results. Through the analysis of the high-frequency component of the post-resective HF ECoG, it was shown that the presence or absence of pHFO in the range of 250–500 Hz does not affect the seizure outcome. The dynamics of the high-frequency activity index before and after the resection are statistically significant for the seizure outcome prediction for structural epilepsy surgery. In this study, the specificity of the pHFO dynamics analysis technique was 85.71 % and sensitivity equaled 58.33 %.Conclusion. Thus, the HF ECoG and the assessment of the dynamics of the pHFO index in the range of 250–500 Hz can complement the traditional method of intraoperative ECoG in the range of up to 70 Hz, including the prediction of the results of surgical treatment.