Prediction of depth of sedation and anaesthesia by the Narcotrend™ EEG monitor

Background. The Narcotrend(TM) (Monitor Technik, Bad Bramstedt, Germany) assesses sedation by automatic classification of EEG signals, using a scale first used for visual evaluation of the EEG. Limited information is available on its value, and only a few studies of the method exist. We set out to study the performance of the Narcotrend(TM) during propofol sedation. Methods. In 23 ASA I-II patients, aged 18-65 yr, about to have general anaesthesia, we induced anaesthesia in steps using a target-controlled infusion of propofol. After equilibration for 8 min at each predicted propofol concentration (0.5, 1.0, 2.0, 3.0 and 4.0 mug ml(-1)), sedation was assessed clinically with the modified Observer's Assessment of Alertness/Sedation Scale and the Narcotrend(TM) stage was noted. The prediction performance of the Narcotrend(TM) was assessed with the prediction probability P-K. A P-K value of 1.0 means an exact prediction on every occasion, while a P-K of 0.5 is no better than a 50:50 chance of being correct. Results. In 12 women and 11 men (age 42 (sd 11) yr), a total of 138 measurements were made; 129 were analysed and nine were of poor signal quality. The prediction probability for the corresponding level of sedation was P-K=0.92 (se 0.01); for the different target concentrations of propofol it was P-K = 0.91 (se 0.01). Conclusions. The Narcotrend(TM) can monitor sedation with propofol. Other sedatives, anaesthetics and opioids should be used to test this monitor.