Background: Emergence following termination of a general anesthetic depends on the effect site concentration (Ce) of the drug declining to an awakening value (Ce-awake). Ce-awake has been described in adults, but is unknown in children.
Objectives: To determine Ce-awake in children following a target-controlled infusion (TCI) of propofol and to assess a Ce-driven TCI system’s ability to predict times to emergence from anesthesia.
Methods: Subjects undergoing elective surgery, aged 3 months to <10 years were recruited into three age-stratified groups. A target Ce of 3–4 μg·ml−1 was selected for induction and subsequently titrated to patient response and surgical stimulus. Preoperative acetaminophen, a remifentanil infusion and regional anesthesia were permitted for supplemental analgesia. State Entropy (SE) was monitored from induction to emergence. Emergence was defined as the time of first purposeful spontaneous movement (PSM). Time zero was defined as the end of propofol infusion. Based on a pilot study, a Ce-awake of 1.9 μg·ml−1 was chosen as the wake-up threshold used by the software to predict emergence times.
Results: Data was collected for 90 of 104 recruited patients. PSM occurred at a mean (sd) Ce of 2.0 (0.5) μg·ml−1 and an SE of 79 (11). There were no differences between age groups. A wide variation in emergence time was observed, with a mean (sd) of 16.9 (7) min, and a trend to more rapid emergence in older subjects.
Conclusion: A predicted Ce-awake of 2.0 μg·ml−1 in children aged 3 months to <10 years was identified with the selected model. For expert users of propofol in children, during shorter surgical procedures, TCI predicted emergence times do not offer significant clinical advantages.