• Heidi Yppärilä, Silvia Nunes, Ilkka Korhonen, Juhani Partanen, and Esko Ruokonen.
• Department of Clinical Neurophysiology, Kuopio University Hospital, University of Kuopio, Kuopio, Finland. heidi.ypparila@kuh.fi
• Crit Care. 2004 Dec 1;8(6):R483-90.

IntroductionIn this observational pilot study we evaluated the electroencephalogram (EEG) and auditory event-related potentials (ERPs) before and after discontinuation of propofol sedation in neurologically intact intensive care patients.MethodsNineteen intensive care unit patients received a propofol infusion in accordance with a sedation protocol. The EEG signal and the ERPs were measured at the frontal region (Fz) and central region (Cz), both during propofol sedation and after cessation of infusion when the sedative effects had subsided. The EEG signal was subjected to power spectral estimation, and the total root mean squared power and spectral edge frequency 95% were computed. For ERPs, we used an oddball paradigm to obtain the N100 and the mismatch negativity components.ResultsDespite considerable individual variability, the root mean squared power at Cz and Fz (P = 0.004 and P = 0.005, respectively) and the amplitude of the N100 component in response to the standard stimulus at Fz (P = 0.022) increased significantly after interruption to sedation. The amplitude of the N100 component (at Cz and Fz) was the only parameter that differed between sedation levels during propofol sedation (deep versus moderate versus light sedation: P = 0.016 and P = 0.008 for Cz and Fz, respectively). None of the computed parameters correlated with duration of propofol infusion.ConclusionOur findings suggest that use of ERPs, especially the N100 potential, may help to differentiate between levels of sedation. Thus, they may represent a useful complement to clinical sedation scales in the monitoring of sedation status over time in a heterogeneous group of neurologically intact intensive care patients.

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