Paralysed patients in the intensive care unit are unable to signal signs of discomfort or awareness and it is therefore especially important that their sedation is adequate. Derivatives of the EEG power spectrum have been evaluated as indices of anaesthetic depth1 . We have evaluated these indices in the intensive care unit in paralysed patients sedated with an infusion of propofol 2.16 (SD 0.32) mg kg-1 h-1 and alfentanil 8.85 (2.34) mg kg-1 h-1 (n = 6), or fentanyl 4.39 (2.58) mg kg-1 h-1 (n = 4). Ethics Committee approval was obtained and informed consent from relatives. With stable sedation, the EEG was recorded before, during and after routine physiotherapy using a Navigator system (Bio-logic, U.S.A.) with frontal and mastoid electrodes. The power spectra in 2-s EEG epochs were derived using fast Fourier transformation and displayed as a compressed spectral array. Individual power spectra were divided by area into 25th, 50th, 75th and 95th centiles and the frequencies of these centiles recorded (table XV). At least 300 epochs were studied in each patient.
Spectral analysis of the EEG can detect the reversible arousal provoked by physiotherapy. Our data suggest that the change in amplitude displayed using spectral analysis of the EEG is more reliable for monitoring depth of sedation than the change in frequency recorded in individual centiles in paralysed patients in the intensive care unit.
References:
1: Schwilden H. Ballire's Clinical Anaesthesiology 1989; 3:602-621.