Fig. 3. Correlation of measured plasma propofol concentration and Bispectral Index (BIS) at different time points ( empty symbols indicate target-controlled infusion/fixed infusion rate; filled symbols indicate BIS-titrated adjustment; circles, triangles, squares, and diamonds indicate the group mean ± SD for intubation, sternotomy, end of extracorporeal circulation, and end of operation, respectively). Data indicate a leftward (lower propofol) and upward (higher BIS) displacement with BIS-titrated propofol infusion as compared with target-controlled infusion according to the Marsh model ( A ). To address intersubject variability, individual correlations of measured plasma propofol concentrations versus BIS were performed for each patient over time indicating a moderate negative correlation for the group mean in both groups ( B : target-controlled infusion; C : BIS). Circle indicates patient with best fit, square indicates patient with median fit, and triangle indicates patient with worst fit.