Spectral processing
EEG data were obtained at a sampling rate of 500 Hz by using ConView. The ConView system is designed by Pearlcare Medical Technology Company Limited (Zhejiang, China), based on three different parameters of EEG: sample entropy (SampEn), 95% spectral edge frequency (SEF) and burst suppression ratio (BSR). The new anesthetic index named Ai is calculated with the algorithm based on decision tree and least square. Ai ranges from awake (80–99), to light sedation (60–80), general anesthesia during surgery (40–60), deep hypnotic state (< 40) and an isoelectric EEG (0). A multicenter clinical study has confirmed that the performance of Ai as a depth of anesthesia monitor was similar to that of BIS [We analyzed the EEG and Ai value across the period of the administration of s-ketamine and the 2-min EEG epochs that were selected 10 min before and 2–8 min after the administration of s-ketamine or saline in detail. We also analyzed the EEG during recovery period.The power spectra quantifying the energy in the EEG at each frequency were calculated using the multi-window spectrum algorithm in MATLAB R2018b (MathWorks, Natick, MA). The parameters used for statistical inference were as follows: time-bandwidth product = 3, number of tapers = 5, window size = 2 s, and window overlap rate = 99.5%. Group-level spectrograms were obtained by computing the median power across all subjects at each time point and at each frequency. We also computed the power and peak frequency at the time and frequency bands of interest, respectively. The peak frequency is the frequency with the highest power within a certain frequency band. We obtained the Ai value from ConView YY-105 directly.The mean power and peak frequency of the EEG signal were calculated for the following frequency bands: slow wave (0.3–1 Hz), delta (1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–25 Hz), gamma (25–50 Hz), and beta-gamma (12–50 Hz).