A new method for evaluating the performance of depth-of-hypnosis indices - the D-value

An alternative statistic, the D-value, is presented for the evaluation of the performance of EEG-based depth-of-hypnosis measures against the Observers' Assessment of Alertness/Sedation scale. The measures considered here are spectral entropy, approximate entropy, Lempel-Ziv complexity and Higuchi fractal dimension. The study is based on recordings from 45 patients, divided into three groups of 15 recordings each. Patients of Group I received no remifentanil while patients of Groups II and III received 2 and 4 ng/ml effect compartment controlled remifentanil. All the patients received stepwise increased dose of propofol. The study shows that the D-value is a promising and flexible statistic for the evaluation of the discriminative power of the EEG measures with respect to the OAA/S scale. The D-value indicates well the dependence of the performance of the measures on the EEG frequency band as well as on remifentanil concentration.