Fig. 2
Variations of Narcotrend index in group ND and NN. Note: Data are presented as mean ± standard deviation. *, compared with the Narcotrend index in the group NN at each time point, p < 0.05. Abbreviations: ND, Narcotrend monitor during the day (8:00–18:00), NN: Narcotrend monitor during the night (22:00–5:00). T1 (5 min before induction), T2 (beginning of mechanical ventilation), T3 (mechanical ventilation for 5 min), T4 (beginning of operation), T5 (operation for 10 min), T6 (operation for 30 min), T7 (end of operation)