This study obtains an effect site model for White (Modified Marsh) pharmacokinetic propofol model. The plasma effect-site rate constant (ke0) obtained is affected by age.

In the Target Controlled Infusion pumps the first order plasma-effect-site steady-state rate constant (ke0) links the pharmacokinetics (PK) and pharmacodynamics (PD) for a given drug and it is used to predict the course of the effect and to calculate a theoretical drug concentration at the effect site. The PK model for propofol recently published by White et al. (derived from the Marsh model used by the Diprifusor®) include covariate as age and gender to describe the pharmacokinetics but does not incorporate a ke0.

Methods: 45 healthy adult patients will be scheduled for elective surgery with standard monitoring and BIS XP (Aspect) will received a White PK model-driven plasma target controlled infusion of propofol ( 12 ugml-1 or 10 ugml-1 over 65 years) to be reached in 4 min. After reaching the target, the infusion will be stopped obtaining a complete effect curve upon patient awakening. Calculated plasma concentration and EEG data were stored every one second. Loss (LOC) and recovery (ROC) of consciousness were assessed and recorded. The dynamic relationship between propofol Ce and its effect as measured by BIS will be modeled with an inhibitory Emax model using a population PK/PD approach with NONMEM V.

the Study take around 12 min.

Inclusion Criteria:

• ASA 1-2

Exclusion Criteria:

• less than 70% or more than 130% ideal body mass index,
• neurologic disorders,
• pregnancy,
• psychoactive medication intake during last 48 hours