Fig. 8. (Top ) The influence of the steady-state or effect-site propofol concentration on resting Petco²at various constant remifentanil concentrations. (Bottom ) The influence of the steady-state or effect-site remifentanil concentration on resting Petco²at various constant propofol concentrations. Changing remifentanil concentrations causes marked reductions in resting end-tidal Pco², irrespective of the propofol concentration, while changes in propofol concentrations have less of an effect on resting Petco², irrespective of the remifentanil concentrations.