[The relationship of individual sensitivities to fentanyl and those to propofol].

BACKGROUND: Individual variation in the sensitivity to anesthetics induces the delayed awakening and the severe postoperative pain at an inappropriate dose. We designed the study to see the correlation of the individual sensitivity to fentanyl and that to propofol which have different mechanism. METHODS: General anesthesia was induced using target controlled infusion system of fentanyl and propofol. Fentanyl effect-site concentration gradually increased towards a target plasma concentration of 3 ng x ml(-1) until the appearance of the subjective symptom such as dizziness, a sensation of warmth and other reactions. After this, propofol effect-site concentration gradually increased towards a target plasma concentration of 4 microg x ml(-1) until loss of consciousness (LOC). The effect-site concentrations of fentanyl at the symptom and propofol at loss of consciousness were measured. RESULTS: The correlation between the estimated effect-site concentration of fentanyl and propofol is not significant in the whole patient. However, a positive correlation between fentanyl and propofol was found in patients from 50s to 70s years of ages (r = 0.59). CONCLUSIONS: The correlation of the individual sensitivity to fentanyl and propofol was found in older age groups.