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

The Narcotrend (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 during propofol sedation. 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 microg x ml(-1)), sedation was assessed clinically with the modified Observer's Assessment of Alertness/Sedation Scale and the Narcotrend stage was noted. The prediction performance of the Narcotrend 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. 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). The Narcotrend can monitor sedation with propofol. Other sedatives, anaesthetics and opioids should be used to test this monitor.