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ANESTHETIC PHARMACOLOGY

The Effects of Dexmedetomidine/Remifentanil and Midazolam/Remifentanil on Auditory-Evoked Potentials and Electroencephalogram at Light-to-Moderate Sedation Levels in Healthy Subjects

Matthias Haenggi, MD^*, Heidi Ypparila, PhD, Kathrin Hauser^*, Claudio Caviezel^*, Ilkka Korhonen, PhD, Jukka Takala, MD, PhD^*, and Stephan M. Jakob, MD, PhD^*

From the *Department of Intensive Care Medicine, University Hospital of Bern, Bern, Switzerland; and VTT Information Technology, Tampere, Finland.

Address correspondence and reprint requests to Stephan Jakob, Department of Intensive Care Medicine, Inselspital, Freiburgstrasse, CH-3010 Bern, Switzerland. Address e-mail to Stephan.Jakob{at}insel.ch.

Avoidance of excessively deep sedation levels is problematic in intensive care patients. Electrophysiologic monitoring may offer an approach to solving this problem. Since electroencephalogram (EEG) responses to different sedation regimens vary, we assessed electrophysiologic responses to two sedative drug regimens in 10 healthy volunteers. Dexmedetomidine/remifentanil (dex/remi group) and midazolam/remifentanil (mida/remi group) were infused 7 days apart. Each combination of medications was given at stepwise intervals to reach Ramsay scores (RS) 2, 3, and 4. Resting EEG, bispectral index (BIS), and the N100 amplitudes of long-latency auditory-evoked potentials (ERP) were recorded at each level of sedation. During dex/remi, resting EEG was characterized by a recurrent high-power low-frequency pattern which became more pronounced at deeper levels of sedation. BIS Index decreased uniformly in only the dex/remi group (from 94 ± 3 at baseline to 58 ± 14 at RS 4) compared to the mida/remi group (from 94 ± 2 to 76 ± 10; P = 0.029 between groups). The ERP amplitudes decreased from 5.3 ± 1.3 at baseline to 0.4 ± 1.1 at RS 4 (P = 0.003) in only the mida/remi group. We conclude that ERPs in volunteers sedated with dex/remi, in contrast to mida/remi, indicate a cortical response to acoustic stimuli, even when sedation reaches deeper levels. Consequently, ERP can monitor sedation with midazolam but not with dexmedetomidine. The reverse is true for BIS.

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