The combined effect of age and premedication on the propofol requirements for induction by target-controlled infusion

In this prospective study, we evaluated the combined influence of age and p remedication on propofol requirements for the induction of anesthesia and t heir hemodynamic effects using a target-controlled infusion. We studied 180 patients separated into three age groups: 20-39 yr, 40-59 yr, and more tha n 59 yr. In each age group, patients were randomly allocated to receive eit her no premedication (n = 20), fentanyl (2 mu g/kg) (n = 20), or midazolam (0.03 mg/kg) plus fentanyl (2 mu g/kg) (n = 20). The concentration of propo fol targeted for the induction was 5 mu g/mL, to be reached in 2 min. The d ose, time, and predicted plasma concentration of propofol at hypnosis were measured. Baseline and postinduction heart rate and arterial blood pressure were registered. Computer simulation was used to calculate the effect site propofol concentration at hypnosis. The concentration of propofol, effect site propofol concentration, time, and induction dose and their hemodynamic effect were significantly different among groups with respect to age and p remedication. The combined effect of the two factors was additive, but with out significant interaction. The propofol requirements were significantly l ess in the midazolam-fentanyl groups, regardless of age, and among the prem edicated patients older than 60 yr compared with the other age groups. We c onclude that the combined effect of age and premedication on the requiremen ts of propofol for the induction of anesthesia should be considered when th e concentration is targeted with a target-controlled infusion system.