Monitoring Awareness and Pain Under Anesthesia Using a New EEG Based System

Plain-language summary

General anesthesia (GA) is the process of induction of unconsciousness in order to undergo surgery. Unlike sleep, a process of "anesthesia" is not related at all, 'Sleep' and does not include dreams - but is done by using drugs that cause a kind of "unconsciousness" control. The induction of GA includes combination of drugs - for sleep (inhalation anesthesia or hypnotic drugs intravenously), analgesia (opiates) and muscle relaxants. Since most of our patients paralyzed during surgery, the anesthesiologists have no way of knowing whether our paralyzed patient is asleep or awake. If the patient is awake and paralyzed, a situation named "awareness under anesthesia" it can cause him a traumatic experience that would leave him a cripple for his whole life. There are many stories about patients who lay paralyzed, awake, while been operated, who remembered every word of what happened during the operation and of course could not mark the anesthetist that they are awake. The anesthesiologist might suspect that his patient is awake and paralyzed through "signals" from the sympathetic nervous system - for example the increase in heart rate and blood pressure. But many of our patients receive different medications (eg, beta-receptor blockers that does not allow the rise of a pulse) obscuring the clinical signs, so that the patient is awake and paralyzed without being noticed by the anesthesiologist. Some patients are at a higher risk to suffer from awareness under anesthesia, because the anesthesiologist cannot provide "enough" anesthesia, due to their medical condition, for example: women in caesarean section under GA, patients in cardiac surgery or injured trauma patients. Twenty years ago, an EEG based tool, naming "BIS" was developed. Nowadays, BIS monitor's credibility is questionable 1. The effect of different hypnotic drugs is not uniform. 2. Recently it was shown that a paralyzed patient BIS index could fall mimicking a situation of a sleep - enabling a paralyzed patient being awake. Thus, it is not clear whether the calculation of the BIS monitor is based on physiological models that define what is consciousness, loss of consciousness and how consciousness arises. It seems that the BIS is only suitable for certain drugs - not as a general monitor for the level of anesthesia. The purpose of the present study is to develop a universal system for determining awareness under GA using an innovative algorithm for analyzing EEG waves, based on the physiological processes of attention and perception underlying the basis for sedation and GA.

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