Symbolic dynamics applied to EEG signal for monitoring anaesthetic depth during propofol infusion

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 anaesthetist. Haemodynamic 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. The objective of this study was to evaluate the symbolic dynamics applied to the EEG signal while awake and while asleep. Data was required from 10 patients scheduled for elective cardiac surgery. All patients were anesthetized with propofol and no other drugs were administered during the study period. The results showed significant difference between awake and anaesthetized values, hence concluding that the complexity measure might serve as an indicator of anaesthetic depth