Total intravenous anesthesia with ketamine/propofol: interaction or interpretation of hypnosis monitoring

Abstract

Introduction: High plasma concentrations of ketamine produce β-electroencephalographic activity; the direct relationship between these and the processed electroencephalographic index makes it doubtful in the presence of ketamine. When using ketamine, relative bands are useful.

Objective: To describe the usefulness of relative bands and the processed electroencephalographic index in hypnosis and whether different plasma concentrations of ketamine modify the on-site concentration effect of propofol.

Methods: A quasiexperimental study was carried out with thirty patients selected at convenience between 2016 and 2021 and distributed into three groups of ten individuals each. Group I participants were administered propofol target-controlled infusion (plasma concentration of 2.5 µg/mL), increased in 0.5 µg/mL every three minutes. In groups II and III, ketamine was additionally used at 0.3 µg/mL and 0.1 µg/mL doses, respectively. A Narcotrend EEG monitor was used to identify adequate hypnosis: β band was lower than 30 % and α band was between 20% and 40%, while processed electroencephalographic index was between 40 and 60 during one minute. The variables were propofol effect-site concentration, plasma concentrations of both drugs, processed electroencephalographic indexes, and band relativity. The statistics included means and standard deviations of propofol effect-site concentration, percentage of β and α bands, as well as of processed electroencephalographic index at the time of the hypnotic state. Student's test was used to determine the statistical difference between means.

Conclusions: The processed electroencephalographic index is questionable in the presence of ketamine. The percentage of α and β bands was useful in assessing hypnosis. The relationship between propofol effect-site concentration and ketamine plasma concentrations results from the impact of ketamine on the electroencephalography.