Prospective evaluation of the time to peak effect of propofol to target the effect site in children

Background: The plasma‐effect site equilibration rate constant ( k e0 ) of propofol has been determined in children with the use of the time to maximum effect ( t peak ), however, it has not been validated. The objective was to measure the t peak; of propofol with two depths of anesthesia monitors in children and to evaluate these measurements with a target‐controlled infusion (TCI) system. Methods: Unpremedicated, ASA I children from 3 to 11 years were studied. In Part 1, children were monitored simultaneously with the bispectral index (BIS) and the A‐Line ARX‐index (AAI) from the Alaris A‐Line auditory‐evoked potential monitor/2. The t peak after a bolus dose of propofol was measured. In Part 2, the t peak measured was used to target the effect site with a TCI system. The median (MD) and the absolute median (MDA) difference between the predicted time of peak concentration at the effect site (Ce) and the measured time of peak effect in the index of depth of anesthesia ( t error ) was used to evaluate the performance of the system. Results: The BIS recordings were of a better quality than the AAI. The mean ± standard deviation t peak was 65 ± 14 s with the BIS ( n =25) and 201 ± 74 s with the AAI ( n =10)( P <0.001). Validation was only performed with the BIS monitor in 40 children, yielding an MD t error of −9.5 s and an MDA t error of 10.0 s. Conclusions: The small delay between the evolution of Ce of propofol and the observed effect suggests that this can be a useful model to target the effect site in children.