Background and Goal of Study
Propofol clearance is reduced when the hepatic blood flow (HBF) is decreased, which can be caused by pneumoperitoneum in patients in the head down position (HDP)[1]. This may alter the pharmacokinetics of propofol and worsen the predictive performance of target-controlled infusion (TCI). 
We investigated the predictive performance of propofol TCI during CO2 pneumoperitoneum in patients who underwent robotic-assisted radical prostatectomy in the head down position.
Material and Methods
This study was approved by institutional review board and registered at the UMIN-CTR(UMIN000011268).  Fifteen male patients received propofol TCI using the Diprifusor model. Propofol concentrations were measured at seven time points: T1) 15 min after anesthesia induction; T2) before the insufflation; T3), T4), and T5) 15, 60, and 90 min, respectively, after insufflation in the HDP; and T6) and T7) before and 15 min after the release of pneumoperitoneum in the HDP, respectively. 
The predictive performance of TCI was evaluated by calculating the performance errors (PE; [measured – predicted]/predicted) in propofol concentrations for each data point. Overall PE values were analyzed using a repeated-measures one-way analysis of variance (ANOVA) and multiple comparisons (Holm’s method). A value of P < 0.05 was considered significant. Furthermore, median PE (MDPE) and median absolute PE (MDAPE)[2] were calculated as measures of bias and accuracy, respectively. 
Results and Discussion
　A total of 104 blood samples were analyzed. ANOVA revealed significant differences in overall PE values. The multiple comparison analysis showed a significant difference in PE values between time points T4 and T5. The predictive performance of propofol TCI during pneumoperitoneum in the HDP was acceptable when the MDPE and MDAPE were -1.5% and 18.8%, respectively. Theoretically, the propofol concentrations could be approximately twice as those targeted in TCI due to the reduced HBF. In this study, the anesthesia procedure properly maintained the blood pressure, and thus the HBF may have been maintained.
Conclusion
The prediction performance of propofol TCI during CO2 pneumoperitoneum was acceptable in patients in the HDP.

12 / The predictive performance of propofol target-controlled infusion during CO2 pneumoperitoneum in patients in the head down position.