Titration of propofol infusion using processed electroencephalogram during combined general and spinal anesthesia

To determine the necessary mean infusion rate of propofol during combined nitrous oxide (N₂O) and propofol spinal anesthesia by using the processed electroencephalogram (pEEG).

Twelve elective gynecological patients were monitored by a Dräger pEEG monitor under N₂O and propofol spinal anesthesia. To make it easier to detect an inadequate depth of anesthesia, muscle relaxants were not given and the patients breathed spontaneously through a laryngeal mask airway. Manual step-down infusion of propofol was employed to provide intraoperative hypnosis. Propofol infusion was titrated to maintain cardiorespiratory parameters within 20% of baseline and the 90th percentile of the spectral edge frequency (SEF 90) of the pEEG between 10 and 13.5 Hz.

The mean (SD) induction dose of propofol was 2.9 (0.4) mg·kg^-1. The mean (SD) maintenance infusion rate was 4.2 (0.5) mg·kg^-1·h^-1. The mean (SD) time from the end of propofol infusion to the opening of the patient's eyes was 5.4 (2.0) min. No gross movements or intraoperative awareness was recognized. The mean (SD) SEF 90 during the maintenance of anesthesia was 12.2 (1.5) Hz, which increased significantly to 16.2 (1.9) Hz at 1 min before the patients opened their eyes in reponse to verbal commands.

Titration of propofol infusion using SEF during combined general and spinal anesthesia provided a rapid recovery without any clinical signs of inadequate anesthesia.