Abstract: Objective  To observe the effect of monitoring the depth of anesthesia by bispectral index (BIS) during open heart surgery under cardiopulmonary bypass. 
Methods  We selected 40 patients who underwent openheart surgery under cardiopulmonary bypass in People′s Hospital of Baise City, and divided them into two groups randomly, with 20 patients in each group. During anesthesia induction, 0.05 mg/kg of midazolam, 10 μg/kg of fentanyl, 0.3 mg/kg of cis-atracurium and 0.3 mg/kg of etomidate were given intravenously in both groups, and booster drugs were given to increase blood pressure if blood pressure dropped during induction period. The BIS values were observed and recorded at different time points, including immediately after intubation (T0), immediately after sternotomy (T1), at 10 min after the initiation of cardiopulmonary bypass (T2), at the time of the lowest nasal temperature (T3), the time of rewarming to 36 degrees (T4), the time of stopping cardiopulmonary bypass (T5). 0.5 μg·kg-1·h-1 dexmedetomidine was continuously pumped into both groups during the maintenance period of anesthesia, and 10 μg/kg of fentanyl was supplemented before skin cutting and sternotomy. In the observation group B, the dosage of propofol was adjusted by the change of BIS value, and the BIS value was maintained in the range of 40-60 during the operation. In the control group, BIS monitoring was also used but the chief anesthesiologist was blinded to the BIS values. The intraoperative dosage was adjusted by the anesthesiologist according to the traditional standard of blood pressure and heart rate. The intraoperative BIS values of the control group were collected from the monitoring records after the operation. The blood pressure of the two groups was kept within 20% of the preoperative basic value through the pump injection of vasoactive drugs. In this study, all of the key variables were recorded in detail, including the total dosage of propofol, vasoactive drugs and fentanyl; duration of anesthesia, duration of operation, the blocking time of ascending aorta, the time before establishing cardiopulmonary bypass, the time of postoperative extubation and the time totransfer out of cardiosurgery intensive care unit (CSICU) after surgery, the intraoperative memory of the patients within 3 days after the operations, and the date of postoperative discharge. 
Results  There was no statistically significant difference in the total amount of fentanyl used during surgery between two groups (P＞0.05). The total amount of propofol used during surgery in the observation group was smaller than that in the control group, and the amount of vasoactive drugs used during surgery was smaller than that in the control group (P＜0.05). The BIS values of the observation group were higher than those in the control group at all time points. The BIS values of both groups first decreased， and then increased with time, and then stabilized between groups, and the differences of interaction between groups,time points, and time points between groups were statistically significant (P＜0.05). The observation group had shorter time to tracheal extubation and length of hospitalization than the control group (P＜0.05). There was no statistically significant difference in the time to transfer out of CSICU after surgery (P＞0.05). 
Conclusion  The application of BIS in monitoring the depth of anesthesia during open heart surgery under cardiopulmonary bypass is of great value. It can reduce the use of narcotic and maintain hemodynamic stability through individualized medication under the guidance of BIS monitoring on the premise of ensuring the smooth operation. 

Key words: cardiopulmonary bypass, anesthesia, cardiac surgery, consciousness monitors