[The influence of ketamine on the bispectral index, the spectral edge frequency 90 and the frequency bands power during propofol anesthesia].

To investigate the influence of ketamine on the bispectral index (BIS), the spectral edge frequency 90 (SEF 90) and relative power in four frequency bands (beta, alpha, theta, sigma), we studied 13 patients (ASA I-II) undergoing elective surgery. In the first study (n = 7), we administered ketamine (1.0 mg.kg-1, bolus, i.v.) during propofol anesthesia. Thirty minutes after the administration, BIS, SEF 90 and relative beta power increased significantly. In the second study (n = 6), bolus administration of ketamine (0.5 mg.kg-1 i.v.) followed by continuous infusion was started during propofol anesthesia. The infusion rate of ketamine was 0.5 mg.kg-1.h-1 for 30 minutes and then increased to 1.0 mg.kg-1.h-1. BIS, SEF 90 and relative beta power increased significantly after ketamine administration, but the parameters did not change in dose-related manner. We conclude that further investigation is necessary to use electroencephalographic parameters as an indicator of the anesthesia depth during propofol/ketamine anesthesia.