Fig. 13. Simulation of approximate entropy (top ) and Bispectral Index (bottom ) values for equipotent combinations of propofol and remifentanil for 95% probability of no response to shouting and shaking (solid lines ) and 95% probability of no response to laryngoscopy (dashed lines ) based on the hierarchical interaction model. The lines start from the right back (high remifentanil, low propofol) and cross the concentrations plane toward the left front (low remifentanil, high propofol). The 95% isoboles are also plotted on the concentration plane to assist visualization. TCI = target-controlled infusion.