The effect of skin incision on the electroencephalogram during general anesthesia maintained with propofol or desflurane.

OBJECTIVE

A variety of effects of surgical incision on the electroencephalogram (EEG) during modern general anesthesia have been previously described; including both increases and decreases in both high and low frequencies in the EEG. What are the patterns commonly seen during routine clinical anesthesia?

METHODS

We analyzed pre-frontal EEG data from a previously published study (116 adult patients having general anesthesia maintained with either desflurane or propofol) (Leslie et al. in Anesthesiology 111:547-555, 2009), The EEG was quantified using seven estimated parameters: slope and intercept of the underlying non-oscillatory (logarithmically transformed) power spectrum, amplitude and frequency of the episodic frontal alpha (EFA) oscillation, peak power in the delta waveband, high frequency variability index, and bispectral index (BIS). We compared a 30 s EEG segment from 2 min before, with that 2 min after the surgical incision.

RESULTS

The pre-incision EEGs showed a wide spread of different values for the estimated EEG parameters, but the propofol group had increased EFA amplitude. Incision was associated with decreased EFA activity (p = 0.0004), and high frequency variability (p = 0.04, repeated measures ANOVA). The effects of the incision were independent of the type of drug used for maintenance of anesthesia, and on the pre-incision BIS. The loss of EFA tended to be associated with an increase in delta power (r = -0.39, p < 0.0001).

CONCLUSIONS

During anesthesia maintained with desflurane or propofol, surgical incision has modest effects on the EEG patterns. It does not cause an increase in high frequency power; the most consistent changes are a loss of EFA amplitude and burst suppression patterns. This effect is not strongly modified by the depth of anesthesia--as estimated by the BIS.