Table 2. Combinations of Propofol and Remifentanil (Changing Propofol (P) Concentrations; Constant Remifentanil (R) Concentrations)

With the exception of two volunteers (3,11; propofol only), every volunteer received a stepwise increased–decreased infusion of propofol in the presence of a constant concentration of remifentanil. The propofol concentration indicated refers to the highest concentration achieved during the CNS depression–interaction phase (changing concentrations of the first drug and constant concentrations of the respective second drug). The concentration ranges were determined by pharmacodynamic considerations (see Methods). The remifentanil target for one volunteer (15) was erroneously set to 2 ng/ml instead of 1 ng/ml.