The human brain cells can carry out spontaneous, rhythmic, and comprehensive electrical activity. The waveform generated by recording the potential of this electrical activity over time is called an electroencephalogram (EEG) [6,7]. The dendrites of pyramidal neurons in the cerebral cortex are parallel to each other and perpendicular to the cortical surface, thus facilitating the generation of a large local potential field that can be measured through the skull and scalp, which is the EEG displayed on the brain function monitor in the clinic [8,9]. EEG data on the scalp shows the status of the cerebral cortex and subcortical structures, so anesthesiologists also often use EEG monitoring to understand the changes in intraoperative brain status, and EEG data also showed changes in the depth of anesthesia[10,11,12]. The Patient State Index PSI and SEF are also used clinically to monitor the depth of anesthesia intraoperatively.
Human brain cells can carry out spontaneous, rhythmic and comprehensive electrical activity. The wave pattern generated by recording the change of the potential of this electrical activity over time is called electroencephalogram (EEG)[6,7]. The dendrites of pyramidal neurons in the cerebral cortex are parallel to each other and perpendicular to the cortical surface, thus facilitating the production of a large local potential field that can be measured by the skull and scalp, which is the EEG shown on a clinical brain function monitor [8,9]. EEG data on the scalp show the state of the cerebral cortex and subcortical structures, so anesthesiologists often use EEG monitoring to understand changes in the state of the brain, and EEG data also showed changes in the depth of anesthesia [10,11,12]. Currently, patient status index (PSI) and spectral margin frequency (SEF) are also used to monitor the depth of anesthesia during surgery.
The results of this study showed that PSI and SEF both changed with ETSEV. As the ETSEV increased, the values of SEF and PSI decreased, suggesting deeper anesthesia and a negative linear regression relationship with both ETSEV. The results of this study demonstrated that PSI and SEF can respond to the role of the anesthetic drug sevoflurane in intraoperative sedation and maintenance of depth of anesthesia, providing clinical reference for anesthesiologists.
The PSI is only an EEG result generated after time-domain analysis. The PSI ranges from 0-100, and fluctuations in the range of 25-50 are generally normal, so it is possible to assess the depth of anesthesia to some extent. However, some studies have been shown [13,14] that this monitoring index is susceptible to the influence of age and brain development, especially in pediatric patients where the value fluctuates widely and is prone to delay. Therefore, in some specific patients this value does not better reflect the patient's depth of anesthesia.
The SEF is the result of frequency domain analysis on the basis of the original EEG, responding to 95% of the patient's total EEG power below a certain frequency value. Compared to the original EEG, SEF simplifies the form of power variation of various waves in the range of 0-30 Hz. The smaller the value of SEF suggests that 95% of the total EEG power is concentrated in the low-frequency region and the depth of anesthesia deepens, and vice versa[15,16]. It has been shown that SEF is not influenced by age and brain development, can more accurately and visually reflect EEG changes, correlates with the blood concentration of various anesthetic drugs, and can better reflect the intraoperative role of anesthetic drugs in maintaining the depth of anesthesia[17,18].
The results of this study showed that both SEF and PSI were negatively correlated with ETSEV, and the absolute value of the correlation coefficient was higher for SEF, demonstrating that SEF is more responsive to sevoflurane than PSI in maintaining depth of anesthesia. Meanwhile, the results of Bland-Altman consistency test showed that the SEF-L and SEF-R were consistent, indicating that there was no difference between the SEF of the left and right brain in indicating the depth of anesthesia of the patients, and both of them could reflect the sedative effect of sevoflurane.
However, there are some shortcomings in this study. Intraoperative anesthesia depth monitoring is influenced by a variety of factors other than age and brain developmental status. And some special surgical patients, such as emergency surgery, neurosurgical brain surgery or patients with psychiatric disorders, can also affect anesthesia depth, so such patients were excluded from this study. Also the number of cases selected for inclusion in this study was small, and the sample size for statistical analysis as completed data was also small, which may cause a large error in the trial results. Furthermore, only patients with general anesthesia for lower extremity surgery were included in this study, and the type of surgery was relatively homogeneous, which may also lead to test bias