THE INTERACTION OF ELTANOLONE AND FENTANYL WITH SPECIAL REFERENCE TO LOGISTIC-REGRESSION ANALYSIS

We investigated whether fentanyl decreases the serum concentrations of the steroid anesthetic eltanolone effective in producing loss of cons ciousness in 50% of patients (EC50induction) and in preventing movemen t at skin incision in 50% of patients (EC50induction). For anesthetic induction, patients received effect-site target concentrations of fent anyl 0.0, 1.5, 3.0, or 4.5 ng/mL and eltanolone 500, 750, 1000, or 120 0 ng/mL. Loss of response to verbal command was assessed after 10 min. For incision, patients received effect-site target concentrations of fentanyl 0.5, 1.5, 3.0, or 4.5 ng/mL and eltanolone 547-2926 ng/mL. Mo vement at incision was assessed at least 10 min after new targets were entered. Probability of loss of consciousness and of movement versus arterial serum concentration combinations were analyzed by logistic re gression. Dixon up-down analysis was used to estimate ET50incision eff ective target concentration combinations. In the absence of fentanyl, anesthesia was induced in only I of 12 patients, which suggests that t he EC50induction is >1500 ng/mL at fentanyl 0.0 ng/mL. With fentanyl ( 38 patients), eltanolone EC50induction was independent of fentanyl con centration, calculated as 628 ng/mL. For the incision phase (52 patien ts), logistic regression failed to generate a valid model. Dixon analy sis (43 patients) produced an eltanolone ET50incision of 2288 ng/mL at fentanyl targets of 0.5 ng/mL, 754 ng/mL at 1.5 ng/mL, 735 ng/mL at 3 .0 ng/mL, and 645 ng/mL at 4.5 ng/mL. Fentanyl reduced the serum conce ntration of eltanolone required to produce loss of consciousness and t he target concentration of eltanolone required to prevent movement to skin incision. Implications: Fentanyl reduced the serum concentration of eltanolone required to produce loss of consciousness and the target concentration of eltanolone required to prevent movement to skin inci sion. Future interaction studies of this nature using logistic regress ion should model responses to hypnotic alone separately from responses to hypnotic-analgesic combinations.