The peak bispectral index time cannot predict early phase propofol pharmacodynamics with effect site-controlled infusion algorithm

OBJECTIVES: The plasma-effect site equilibration rate constant (ke0) of propofol was determined with peak bispectral index (BIS) time (T(PEAK)) in our previous study. The present study has been conducted to evaluate the ke0's performance with effect site-controlled infusion algorithm. MATERIALS AND METHODS: Forty unpremedicated patients were randomized to group TE1 (Schnider's pharmacokinetic model with ke0 adapted to T(PEAK) = 74s) and TE2 (T(PEAK) = 96s). In stage 1, all patients received propofol with effect-site concentration (Ce) controlled infusion. Once the pump had injected the mass of propofol necessary to achieve pre-set Ce and while the infusion was stopped, target was reset at 0 μg/ml. When BIS returned to 80 or above, then, in stage 2, the patients received plasma concentration controlled infusion for 10 min. The time of loss of responsiveness (LOR) and BIS were recorded. The differences of Ce at the time of LOR, lowest BIS between stages 1 and 2, hysteresis loop were used to evaluate the performance of ke0. RESULTS: In both groups, the calculated propofol Ce at the time of LOR in stages 1 and 2 differed significantly (P<0.01); the mean lowest BIS in stage 1 were significantly higher than those in stage 2 (P < 0.05).The relations of propofol Ce versus BIS revealed the apparent hysteresis loop. CONCLUSIONS: The study cannot clinically validate the accuracy of application of ke0 derived from the T(PEAK) = 74 s of BIS with Schnider propofol pharmacokinetic model.