Individual indicators of appropriate hypnotic level during propofol anesthesia: highest alpha power and effect-site concentrations of propofol at loss of response

Abstract

Background

Electroencephalogram (EEG) waveforms vary widely among individuals, this decreases the usefulness of BIS™ monitors for assessing the effects of propofol. Practically, anesthesia is only seen as too deep when evidence of burst–suppression is seen. We designed an experiment to help towards better assessment of individual anesthetic needs. First, to mark the Ce (effect-site concentration) of propofol at loss of response to calling name and gently shaking shoulders (LOR), we defined Ce-LOR. To mark the transient power increase in the alpha range (9–14 Hz), common to all patients, when propofol concentration gradually increases, we defined Ce-alpha as the highest recorded alpha power for Ce. We also defined Ce-OBS as the Ce of propofol at initial observation of burst–suppression. Then we tried to predict Ce-LOR and Ce-alpha from Ce-OBS, vice versa, and considered the significance of these parameters.

Methods

We enrolled 26 female patients (age 33–65) who were undergoing scheduled mastectomy. During anesthesia, we recorded all raw EEG packets as well as EEG-derived parameters on a computer from BIS-XP™ monitor. Propofol was infused using a TCI pump. Target concentration was adjusted so that Ce of propofol was gradually increased.

Results

We obtained the following regression equation; Ce-alpha or Ce-OBS = Ce-LOR × 0.87 + 1.06 + dummy × 0.83 (for Ce-alpha dummy = 0, and for Ce-OBS = 1; adjusted r = 0.90, p < 2.2e−16) by ANCOVA. At Ce-alpha, BIS was 50.2 ± 7.7.

Conclusion

Ce-alpha and Ce-OBS could be estimated from Ce-LOR. Based on Ce-LOR it is possible to manage the hypnotic level of individual patients.

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