Fig. 12. (Top ) Response surface describing the interaction of propofol and remifentanil (Bayesian concentrations) on electroencephalographic Bispectral Index (•= individual Bispectral Index values above the surface; ○= individual Bispectral Index values below the surface). (Bottom ) Population predictions (○) and Bayesian predictions (•) plotted against individually determined Bispectral Index values.