Table 3. Changing Remifentanil (R) Concentrations; Constant Propofol (P) Concentrations

With the exception of two volunteers (1,2; remifentanil only), every volunteer received a stepwise increased–decreased infusion of remifentanil in the presence of a constant concentration of propofol. The remifentanil 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).