Bispectral index (BIS) is a commonly used clinical indicator to measure the depth of anesthesia. It obtains complex electroencephalogram (EEG) signals and analyzes the weighted sum of multiple sub-parameters, that is, measures the linear components (frequency and power) and non-linear components (phase and harmonics) of EEG, fit the mixed information of the power and frequency of the EEG into a quantitative index through dual-frequency analysis, the result is processed as an integer and represented by 0-100[1–3]. The display interface of the BIS monitor usually includes real-time BIS index, signal quality index, forehead EEG waveform, BS ratio, EMG index, and forehead EEG spectrogram, etc.[4, 5]. These graphics and parameters reflect the patient’s brain state and level of consciousness during general anesthesia, and have significant reference value for the judgment of the depth of anesthesia. However, during surgery, anaesthetists usually control the dose administered by focusing on parameters such as blood pressure, heart rate and BIS values, while ignoring the importance of the raw electroencephalographic signal (qEEG). The real-time EEG waveforms and spectrograms displayed on the BIS monitor interface are qEEG. Although they are less intuitive than BIS, they can fully reflect the patient’s anesthesia status, types and dosages of anesthetic drugs, and electrosurgical stimulation. Therefore, in order to judge the patient’s anesthesia level more accurately, a clear understanding of the expected qEEG pattern, as well as relevant knowledge of EEG waveforms and spectrograms is required. In order to use qEEG as a monitoring indicator, the anesthesiologist should have the ability to carefully analyze qEEG.
BS is a non-periodic EEG model in which high-amplitude slow waves (occasionally sharp waves) alternate with suppressive brain electrical activity. According to the amplitude of the wave, the brain waves are divided into burst waves and suppressed waves. The duration of BS ranges from a few seconds to a few minutes. The phenomenon of BS occurs from time to time in clinical anesthesia. Figure 1 shows normal EEG signal and BS signal within 10 seconds under general anesthesia, which were intercepted by the EEG signal analysis software eeglab. BS does not occur during physiological sleep, excessive anesthesia and age are the main factors leading to BS[11, 12]. The occurrence of BS decreases the metabolic rate of the brain. If BS occurs for a long time, it indicates that the patient is in a dangerous physical state and will suffer from reduced body temperature and hypoxia.
The detection of BS has extremely important significance in many aspects. Therefore, it is necessary to accurately determine the occurrence of intraoperative EEG BS. The EEG waveform and spectrogram respectively reflect the patient’s state of consciousness from the time domain and frequency domain, and can accurately detect and predict BS[14–16]. Anesthesiologists analyze and interpret qEEG through BIS, which can improve the understanding of patients’ brain states during general anesthesia, control the anesthesia dose, and reduce the occurrence of adverse prognosis. Recent studies have shown that discontinuous brain electrical activity can also be observed in children under general anesthesia[17–19], and BS occurs more in infants and young children. This article analyzes the relationship between the operation time, extubation time, ICU stay time, postoperative delirium (POD) and the duration of intraoperative EEG BS in 30 pediatric liver transplant patients, and then explores the inner relationship between intraoperative EEG BS and surgical quality and postoperative recovery. From the perspective of EEG time domain and frequency domain, BIS can detect and predict EEG BS, thereby reducing the incidence of BS and improving the quality of surgery.
The rest of this article is structured as follows. The second part introduces the methods and materials we use. The third part discusses and analyzes the results. Finally, the fourth part summarizes and prospects the research of this article.