REDUCTION BY FENTANYL OF THE CP-50 VALUES OF PROPOFOL AND HEMODYNAMIC-RESPONSES TO VARIOUS NOXIOUS STIMULI

Background: Propofol and fentanyl infusion rates should be varied acco rding to the patient's responsiveness to stimulation to maintain satis factory anesthetic and operative conditions, However, somatic and auto nomic responses to various noxious stimuli have not been investigated systematically for intravenous propofol and fentanyl anesthesia. Metho ds: Propofol and fentanyl were administered via computer-assisted cont inuous infusion to provide stable concentrations and to allow equilibr ation between plasma-blood and effect-site concentrations, The propofo l concentrations needed to suppress eye opening to verbal command and motor responses after 50-Hz electric tetanic stimulation, laryngoscopy , tracheal intubation, and skin incision in 50% or 95% of patients (Cp -50 and Cp-95) were determined at fentanyl concentrations of 0.0, 1.0, 2.0, 3.0, and 4.0 ng/ml in 133 patients undergoing lower abdominal su rgery, The ability of propofol with fentanyl to suppress hemodynamic r eactions in response to various noxious stimuli also Was evaluated by measuring arterial blood pressure and heart rate before and after stim ulation. Results: The various Cp-50 values for propofol alone (no fent anyl) for the various stimuli increased in the following order: Cp-50l oss of consciousness, 4.4 mu g/ml (range, 3.8-5.0); Cp-50tetanus, 9.3 mu g/ml (range, 8.3-10.4); Cp-50laryngoscopy, 9.8 mu g/ml (range, 8.9- 10.8); Cp-50skin incision, 10.0 mu g/ml (range, 8.1-12.2); and Cp-50in tubation, 17.4 mu g/ml (range, 15.1-20.1; 95% confidence interval). Th e reduction of Cp-50loss of consciousness with fentanyl was minimal; 1 1% at 1 ng/ml of fentanyl and 17% at 3 ng/ml of fentanyl, A plasma fen tanyl concentration of 1 ng/ml (3 ng/ml) resulted in a 31-34% (50-55%) reduction of the propofol Cp(50)s for tetanus, laryngoscopy, intubati on, and skin incision, Propofol alone depresses prestimulation blood p ressure but had no influence on the magnitude blood pressure or heart rate increase to stimulation, Propofol used with fentanyl attenuated t he systolic blood pressure increases to various noxious stimuli in a d ose-dependent fashion. Conclusions: The authors successfully defined t he propofol concentration required for various stimuli, Tracheal intub ation was the strongest stimulus, The absence of somatic reactions for propofol does not guarantee hemodynamic stability without fentanyl. P ropofol with fentanyl was able to suppress motor and hemodynamic react ions to various noxious stimuli.