Bispectral index, spectral edge frequency 95% and median frequency recorded at varying desflurane concentrations in pigs.

The objective of this study is to evaluate the usefulness of bispectral index (BIS), spectral edge frequency 95% (SEF) and median frequency (MED) in relation to a simple descriptive scale (SDS) as indicators of anaesthetic depth at different desflurane concentrations in swine. Sixteen pigs were randomly allocated to four groups. Electroencephalograms (EEG) were recorded during desflurane anaesthesia, and BIS, SEF and MED were calculated from the EEG. The agent was administered in pure oxygen at 1, 1.25, 1.5 and 1.7 MAC in randomized order. Anaesthetic depth was evaluated on a SDS. BIS decreased significantly (P<0.001) at the different anaesthetic dosages used. SEF decreased significantly (P<0.001) from basal to 1 MAC of desflurane. MED decreased significantly (P<0.001) from basal to 1 MAC and from 1 to 1.75 MAC. Good correlation was seen between SDS scores and BIS values and between SDS scores and MED values. BIS appeared to be useful to predict changes in anaesthetic depth at clinically used dosages of inhalant anaesthesia.