Published online by Cambridge University Press: 01 October 2007
To the best of our knowledge, the value of the plasma effect site equilibration rate constant (ke0) 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 (TPEAK) of propofol, a pharmacokinetic-independent descriptor of blood–brain equilibration, and ke0 derived from TPEAK with A-line auditory-evoked potential monitor and Aspect A-2000 bispectral index monitor in Chinese patients.
Two-hundred ASA I patients received a submaximal bolus dose of propofol (1.5 mg kg−1). TPEAK 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 TPEAK and four previously validated pharmacokinetic parameter sets of propofol, the ke0 was estimated according to a method proposed recently.
The mean TPEAK 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 TPEAKs (r = 0.147 and 0.031 for Groups AAI and BIS). The median ke0 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 ke0 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).
The TPEAK 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 TPEAKs of propofol from auditory-evoked potential index and bispectral index, and the values of ke0 calculated based on TPEAKs are different from previous reports and appear to be not affected by age. Further studies need to be taken to validate clinically the ke0 values of propofol.