Introducing a New EEG Based Index for Monitoring Recall Under Sedation

This is a single centre prospective observational study that will investigate a new EEG based index in recognizing recall of anesthesia in sedated patients. Awareness under general anesthesia is a dreadful complication. Various EEG-based technologies (such as BIS and others) were developed in order to identify this condition during anesthesia, using an EEG sticker on the forehead measuring the frontal EEG activity. However, these monitors might be inaccurate due to lack of sensitivity to various hypnotic agents as well as sensitivity to muscle activity, which might lead to report of deep anesthesia in the awake patient. Due to the very low prevalence of awareness under general anesthesia it is difficult to validate or invalidate the effectiveness of these monitors directly. Nevertheless, sedation often involves much greater prevalence of awareness, which permits to evaluate identification of recalled awareness with much humbler sample size. The current available depth of anesthesia EEG based monitors are not effective in sedated patients since they are susceptible to muscle activity effect, which is present under sedation. Based on the current literature in the field of electrophysiology the investigators have developed the anterior/ posterior (A/P) index (in the range of 0-100) for appreciating the anesthetic level. It is based on a comparison of anterior brain activity levels to posterior brain activity levels in response to anesthetic medication. The novelty of the index is stem from the fact that it is based on analyzing EEG data from only 4 electrodes covering the frontal and posterior brain activity. The investigators have shown in a proof of concept study performed in Rambam Hospital, Haifa, Israel that this index is not dependent on muscle activity thus is the only index that can identify recall in sedated patients.