• Satoshi Aihara, Satoshi Hagihira, Rieko Uno, and Takahiko Kamibayashi.
• Department of Anesthesiology, Kansai Medical University, 2-5-1 Shin-Machi, Hirakata, Osaka, 573-1191, Japan.
• J Anesth. 2024 Jun 1; 38 (3): 371376371-376.

PurposeThe effect-site concentration (Ce) at loss of response (Ce-LOR) to propofol closely correlates both with Ce as electroencephalographic alpha power becomes highest (Ce-alpha) and with Ce at onset of burst suppression (BS) (Ce-OBS), when no opioids are administered. Co-administration of opioids dose-dependently decreases Ce-LOR. We investigated the influence of remifentanil on the relationship between these three Ces.MethodsAfter receiving approval from our local ethical committee, with written informed consent, we enrolled 90 participants (ASA-PS I or II) who were scheduled for elective surgery. Participants were randomly assigned to three groups: constant remifentanil Ce 0 ng/ml (Remi_0); 1 ng/mL (Remi_1); and 2 ng/mL (Remi_2). We recorded both raw EEG and EEG-derived parameters on a computer. After reaching remifentanil equilibrium, we administered propofol using a target-controlled infusion pump such that propofol Ce increased to about 0.3 μg/mL/min. After determining Ce-LOR, we administered 0.6 mg/kg of rocuronium and started mask ventilation. The study protocol ended after observation of BS.ResultsThree participants were excluded. Ce-LOR in each group (Remi_0, Remi_1, Remi_2) was 2.00 ± 0.58 μg/mL, 1.43 ± 0.49 μg/mL, and 1.37 ± 0.42 μg/mL. Ce-alpha was 2.91 ± 0.63 μg/mL, 2.30 ± 0.41 μg/mL, and 2.12 ± 0.39 μg/mL. Ce-OBS was 3.80 ± 0.69 μg/mL, 3.25 ± 0.68 μg/mL, and 2.90 ± 0.57 μg/mL. In three other instances, Ce was decreased by remifentanil. Generalized linear model analysis revealed that remifentanil had no influence on the relationship between the three Ces.ConclusionDuring propofol anesthesia, even low concentrations of remifentanil shifted concentration-related electroencephalographic changes.© 2024. The Author(s) under exclusive licence to Japanese Society of Anesthesiologists.

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