A comparison between bispectral index analysis and auditory-evoked potentials for monitoring the time to peak effect to calculate the plasma effect site equilibration rate constant of propofol.

BACKGROUND AND OBJECTIVES To the best of our knowledge, the value of the plasma effect site equilibration rate constant (k(e0)) of propofol has not been reported in Chinese patients. The aim of this prospective, randomized study was to examine the characteristics of the time to peak effect (T(PEAK)) of propofol, a pharmacokinetic-independent descriptor of blood-brain equilibration, and k(e0) derived from T(PEAK) with A-line auditory-evoked potential monitor and Aspect A-2000 bispectral index monitor in Chinese patients. METHODS Two-hundred ASA I patients received a submaximal bolus dose of propofol (1.5 mg kg(-1)). T(PEAK) was randomly measured by means of the A-line auditory-evoked potential monitor (Group AAI (auditory-evoked potential index), n = 100) or the Aspect A-2000 bispectral index monitor (Group BIS, n = 100). Using T(PEAK) and four previously validated pharmacokinetic parameter sets of propofol, the k(e0) was estimated according to a method proposed recently. RESULTS The mean T(PEAK) was 145 +/- 35 s (50-224 s) and 74+/-24 s (38-143 s) in Groups AAI and BIS, respectively (P < 0.01 between groups). There were no correlations between the patient's age and T(PEAK)s (r = 0.147 and 0.031 for Groups AAI and BIS). The median k(e0) in Group AAI was 0.64 min(-1) with the model of Marsh, 0.17 min(-1) with the Schnider model, 0.78 min(-1) with the Tackley model and 0.93 min(-1) with the Shafer model. The median k(e0) in Group BIS was 1.87 min(-1) with the model of Marsh, 0.83 min(-1) with the Schnider model, 2.14 min(-1) with the Tackley model and 2.48 min(-1) with the Shafer model (P < 0.01 between groups and models). CONCLUSIONS The T(PEAK) of propofol measured by the A-line auditory-evoked potential monitor is different from that measured by the Aspect A-2000 bispectral index monitor. The T(PEAK)s of propofol from auditory-evoked potential index and bispectral index, and the values of k(e0) calculated based on T(PEAK)s are different from previous reports and appear to be not affected by age. Further studies need to be taken to validate clinically the k(e0) values of propofol.