An AEP/EEG hybrid index for monitoring the hypnotic depth during general anesthesia

The extraction of a consistent and reliable measure online and close to real time to assess the hypnotic level during anesthesia is a continuous challenge to the anesthetist and the biomedical engineer. Hemodynamic parameters such as heart rate and blood pressure are not, at least with the traditional single parameter versus time presentation, adequate for ensuring an optimal level of anesthesia, especially when using neuromuscular blocking agents (NMBA). The objective of this study was to define a hybrid index (HI) derived from the Auditory Evoked Potentials (AEP) and the Electroencephalogram (EEG). The index should reliably differentiate awake and asleep states in a graduated manner. Data was required from twenty patients scheduled for elective cardiac surgery. All patients were anesthetized with propofol and no other drugs were administered during the study period. The HI had a prediction probability Pk(SD) of 0.92(0.01) between awake and anesthetized values, which was significantly larger than the Pks of the individual parameters, AEP and EEG.