Background: We previously showed that we could estimate required concentration propofol for maintenance of anesthesia from the effect-site concentration (Ce) of propofol at loss of response (Ce-LOR). Iwakiri H et al. showed that Ce-LOR and Ce at recovery of response (Ce-ROR) were similar in volunteer study. Then we made a hypothesis that we also could predict Ce at recovery of response (Ce-ROR) from Ce-LOR. Then we compared Ce-LOR and Ce-ROR in surgical patients under total intravenous anesthesia. We also investigated the influence of opioid concentration at recovery of response. 
Materials and Methods: After approval of the ethical committee of our institute and obtained written informed consent from the participants, we enrolled 26 female patients (aged 33-65) who were scheduled mammectomy for breast cancer. Besides the standard monitors, we used BIS monitor (BIS-XP) and all raw EEG packet as well as EEG derived parameters were recorded on a computer using our original software “BSA for BIS”. Propofol was infused using TCI pump (TE-371; TERUMO, TOKYO, JAPAN). Target concentration was adjusted so that Ce of propofol was gradually increased (about 0.3 μg/mL/min) and Ce-LOR was determined. After insertion of LMA, anesthesia was maintained by propofol and remifentanil. For transitional opioid, fentanyl 0.1 mg was administered near the end of surgery. We defined Ce-Opioids as the sum of Ce of fentanyl (Ce-Fen) and Ce of remifentanil (Ce-Remi) at recovery of response. We compared Ce-LOR and Ce-ROR. We also compared the difference of Ce-LOR and Ce-ROR, and Ce-Opioids. 
Results and Discussion: Average of Ce-ROR was 1.61±0.55 μg/mL (Mean±SD) and slightly but significantly lower than that of Ce-LOR; 1.94±0.66 μg/mL. The correlation coefficient between Ce-LOR and Ce-ROR was 0.62. And Ce-Opioids had little influence on the difference of Ce-LOR and Ce-ROR. 
Conclusion: Although Ce-ROR was fairly well correlated with Ce-LOR, we could not precisely predict when a patient regains consciousness from Ce-LOR. Furthermore Ce-Opioids had little influence on the relation between Ce-LOR and Ce-ROR. 
References: Anesth Analg 2005;100:107-10, J Anesth 2017;31:502-9

08 / Can we predict when a patient regains consciousness by estimated effect-site concentration of propofol at loss of response in TIVA?