Auditory evoked potential index for monitoring depth of anesthesia during propofol-remifentanil anesthesia

Objective To investigate the feasibility of using auditory evoked potential index (AAI) to titrate the rate of propofol infusion during TTVA with propofol and remifentanil. Methods Sixty ASAⅠorⅡpatients of both sexes scheduled for elective laparascopic cholecystectomy under general anesthesia were randomly divided into 2 groups (n=30 each):ⅠAAI group andⅡcontrol group. Noninvasive BP,HR, ECG, SpO2 and PET CO2 were monitored during anesthesia. Anesthesia was induced with midazolam 0.02 mg·kg-1, fentanyl 15-4μg·kg-1 and propofol 1-2 mg·kg-1.Tracheal intubation was facilitated with vecuronium 0.1 mg·kg-1. The patients were mechanically ventilated. PETCO2 was maintained at 35-40 mm Hg. Anesthesia was maintained with infusion of propofol and remifentanil and intermittentⅣboluses of vecuronium. Remifentanil was infused at a constant rate of 0.2μg2kg-1·min-1. Propofol infusion rate was adjusted by AAI (Denmeter A/S Co, Denmark) in groupⅠ. AAI value was maintained below 30. In control group propofol infusion rate was adjusted according to the change in BP and HR (±15% of the baseline value before anesthesia) . The propofol infusion rate was adjusted by 0.01 mg·kg-1·min-1 every 5 min.The BP, HR, AAI value, propofol infusion rate were recorded before pneumoperitoneum (T1);after pneumoperitoneum (T2) ; the gall bladder was being isolated (T3); the peritoneum was being flushed (T4) and at the end of surgery (T5). The amount of propofol, vecuronium, and remifentanil consumed, the time from the end of operation to eye-opening on command, the time from the end of operation to orientation and extubation were also recorded. Results The two groups were comparable with respect to demographic data, duration of anesthesia and the amount of remifentanil consumed. There was no significant difference in the time from end of operation to eye-opening on command, to orientation and extubation between the two groups. The propofol infusion rate was significantly slower and the total amount of propofol infused was significantly less in AAI group than in control group. No patient claimed to have awareness during operation. Conclusion Monitoring the depth of anesthesia with AAI during TIVA with propofol-remifentanil can maintain adequate and smooth anesthesia with less anesthetic and avoid intraoperative awareness.