Change of bispectral index (BIS) (A), surgical pleth index (SPI) values (B), and end-tidal sevoflurane concentrations (C) at major time points during general anesthesia in each group. The graphs show mean values ± standard deviation of each variable for every time points during general anesthesia. All data were collected at baseline, 1 minute after intubation (Intu+1 min), 5 minute after intubation (Intu+5 min), incision, 5 minute after incision (incision+5 min), 10 minute after incision (incision+10 min), 20 minute after incision (incision+20 min), 30 minute after incision (incision+30 min), 60 minute after incision (incision+60 min), end of surgery, and extubation. BIS values were well maintained between 40 and 60 during the surgery in both groups. For the SPI value and end-tidal sevoflurane concentration, there were no significant differences between the groups. SPI group: the surgical pleth index-guided analgesia group; control group: the conventional analgesia group. BIS = bispectral index, SPI = surgical pleth index.