BJA Advance Access originally published online on June 11, 2008
British Journal of Anaesthesia 2008 101(2):213-221; doi:10.1093/bja/aen161
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Behaviour of spectral entropy, spectral edge frequency 90%, and alpha and beta power parameters during low-dose propofol infusion
1 Department of Anaesthesia and Intensive Care Medicine, Cork University Hospital, Cork, Ireland
2 Neonatal Brain Research Group, Department of Electrical Engineering, University College Cork, Cork, Ireland
3 Trinity College Institute of Neuroscience and Department of Psychiatry, Trinity College, Dublin, Ireland
4 School of Medicine, University College Cork, Cork, Ireland
* Corresponding author. E-mail: rsimahon{at}hotmail.com
Background: In this study we analyse the behaviour, potential clinical application and optimal cortical sampling location of the spectral parameters: (i) relative alpha and beta power; (ii) spectral edge frequency 90%; and (iii) spectral entropy as monitors of moderate propofol-induced sedation.
Methods: Multi-channel EEG recorded from 12 ASA 1 (American Society of Anesthesiologists physical status 1) patients during low-dose, target effect-site controlled propofol infusion was used for this analysis. The initial target effect-site concentration was 0.5 µg ml–1 and increased at 4 min intervals in increments of 0.5 to 2 µg ml–1. EEG parameters were calculated for 2 s epochs in the frequency ranges 0.5–32 and 0.5–47 Hz. All parameters were calculated in the channels: P4–O2, P3–O1, F4–C4, F3–C3, F3–F4, and Fp1–Fp2. Sedation was assessed clinically using the OAA/S (observer’s assessment of alertness/sedation) scale.
Results: Relative beta power and spectral entropy increased with increasing propofol effect-site concentration in both the 0.5–47 Hz [F(18, 90) = 3.455, P<0.05 and F(18, 90) = 3.33, P<0.05, respectively] and 0.5–32 Hz frequency range. This effect was significant in each individual channel (P<0.05). No effect was seen of increasing effect-site concentration on relative power in the alpha band. Averaged across all channels, spectral entropy did not outperform relative beta power in either the 0.5–32 Hz [Pk=0.79 vs 0.814 (P>0.05)] or 0.5–47 Hz range [Pk=0.81 vs 0.82 (P>0.05)]. The best performing indicator in any single channel was spectral entropy in the frequency range 0.5–47 Hz in the frontal channel F3–F4 (Pk=0.85).
Conclusions: Relative beta power and spectral entropy when considered over the propofol effect-site range studied here increase in value, and correlate well with clinical assessment of sedation.
Keywords: brain, EEG; monitoring, EEG