Effects of Hypocarbia on the Pharmacodynamics of Sufentanil in Humans

Descriptors of power and frequency derived from power spectral analysis of the electroencephalogram (EEG) were used to determine the effects of low-dose sufentanil (0.1 μg/kg) on brain activity. The effects of hypocarbia alone and of hypocarbia with sufentanil in patients receiving a N2/O2 (70% 30%) anesthetic were also studied. Hypocarbia alone caused changes in most EEG descriptors from both the anterior (F3-C3) and posterior (P3-O1) EEG montages. All EEG descriptors in both hypocarbic and normocarbic patients significantly changed when sufentanil was administered, reflecting a shift of power into the lower frequency ranges. When the anterior EEG montages from the two groups that received sufentanil were compared, the delta power band, spectral edge 50 (median power frequency), and the relative power in the delta power band divided by the alpha plus beta power bands [D/(A + B)] in the hypocarbic group exhibited a significantly greater shift of power into the lower frequency range. It is concluded that (a) power spectral analysis is a sensitive measure of the effects of hypocarbia and small doses of sufentanil on the brain; (b) the power spectral analysis descriptors---delta power band, spectral edge 50, and [D/(A+B)]---are statistically the most sensitive to EEG changes induced by sufentanil; and (c) hypocarbia intensifies patient EEG response to sufentanil, as judged by changes in EEG descriptors.