The sedative and electroencephalographic effects of regional anaesthesia

We studied sedation scores, the processed electroencephalogram and mean art erial pressure preoperatively in patients before and after spinal (n = 15) and lumbar epidural (n = 15) anaesthesia. We compared them with changes occ urring over time in a control group (il = 15), using the responsiveness com ponent of the Observer Assessment of Alertness and Sedation rating scale. T he electroencephalographic variables studied were bispectral index, 95% spe ctral edge frequency, median frequency and the power distribution between f requency bands alpha, beta, theta and delta. No differences were detected w ithin groups in sedation scores before and after intervention, or between g roups at either stage. No between-group differences were detected in electr oencephalographic variables. In the spinal group, spinal anaesthesia caused an increase in bispectral index, 95% spectral edge frequency, median frequ ency and beta frequencies, and a decrease in delta frequencies and mean art erial pressure. The increase in beta frequencies is similar to that seen in patients with low plasma concentrations of midazolam and may represent sub clinical sedation.