Cognitive and Neurophysiological Outcomes Associated With EEG-Guided Administration of General Anesthesia

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Everyday in the United States, nearly 100,000 patients undergo general anesthesia and sedation for surgical and diagnostic procedures. Approximately 35% of all surgical procedures are performed on adults older than 65 years. Advanced age has been identified as a predominant risk factor for postopera...

Everyday in the United States, nearly 100,000 patients undergo general anesthesia and sedation for surgical and diagnostic procedures. Approximately 35% of all surgical procedures are performed on adults older than 65 years. Advanced age has been identified as a predominant risk factor for postoperative cognitive dysfunction (POCD) as well as postoperative delirium (POD), a more acute complication of major surgery. POD and POCD are commonly reported as being part of the same continuum. Although many factors, such as surgical stress, inflammation, and other comorbidities may contribute to POCD, there is evidence that anesthetic exposure plays a major role. Pre-clinical studies have demonstrated that exposure to anesthetic drugs is neurotoxic, and that older animals are particularly vulnerable. It is also generally understood that the elderly are more sensitive to anesthetics meaning that lower doses of anesthetic drugs are required to induce and maintain unconsciousness. Propofol and sevoflurane, two of the most commonly-used anesthetic drugs, induce a stereotyped sequence of brain oscillations with increasing drug concentration. These brain oscillations are directly related to the states of sedation and unconsciousness induced by anesthetic drugs, and readily observed using the EEG. At high concentrations, propofol and sevoflurane produce a pattern referred to as burst suppression, a deep state of brain inactivation in which brain activity is punctuated by long periods of neuronal and EEG silence. Elderly patients are far more likely to be in burst suppression, even when age-adjusted anesthetic dosing is used. Recent studies have shown compelling evidence that EEG burst suppression during anesthesia is an independent risk factor for POD and predicts deficits in cognitive function after surgery. Since burst suppression occurs at higher anesthetic doses, and is not required to maintain unconsciousness, an obvious implication is that cognitive outcomes might be improved if anesthesiologists used the EEG to maintain unconsciousness but avoid burst suppression. Although anesthesiologists and researchers have advocated the use of the unprocessed EEG and EEG spectrogram as tools to manage a patient's state of consciousness during general anesthesia for many decades, few anesthesiologists use the EEG in their routine practice. A major limiting factor has been the absence of training programs to teach anesthesiologists how to interpret the EEG in the context of their clinical practice. Alongside this problem, to date no studies have been conducted to measure the benefits, if any, of using the unprocessed EEG and EEG spectrogram for anesthetic management. In this study the investigators hypothesize that: 1) Anesthesiologists can be trained to read the unprocessed EEG and EEG spectrogram to manage general anesthesia; and 2) EEG-based anesthetic management to maintain unconsciousness but avoid burst suppression can improve patient outcomes.

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