Personalized Anesthesia: The Role of the Locus Coeruleus in Individual Anesthetic Responses

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PROJECT SUMMARY/ABSTRACT Millions of patients are placed into a reversible state of unconsciousness by anesthesiologists for life saving surgeries every year. The basic goals of anesthetic care are to reliably extinguish consciousness for the duration of surgery and afterwards to swiftly return the patient to their baseline cognitive state. Neither of these goals can be reliably achieved today, however. Some patients regain consciousness during surgery. Episodes of consciousness are not reliably detected by current intraoperative EEG-based monitoring and can result in post-traumatic stress and anxiety disorders. In contrast, other patients take a long time to resume normal cognition. This can manifest as postoperative delirium and cognitive derangements. Postoperative delirium affects millions of patients, costs 34 billion dollars annually, and can be a harbinger of ongoing cognitive decline. Such persistent impairments in cognitive function can last for many months. It is presently unclear why some patients experience peri-anesthetic complications while other patients that receive seemingly identical anesthetics have an uneventful perioperative course. To address this, we propose to study individual-based anesthetic pharmacology rather than the previous population-based approach. We have recently developed experimental and computational methods to quantify individual-based measures of anesthetic responses in mice. Using these methods, we discovered that conventional population-based pharmacological concepts such as drug potency are not sufficient to describe individual responses. We identified two independent measures that do capture the range of individual responses: sensitivity and resistance to state transitions (Rst). Sensitivity describes how often an individual is awake or anesthetized at an anesthetic dose, while Rst describes how frequently transitions happen between awake and anesthetized states. We demonstrated that pharmacology can differentially modulate sensitivity and Rst. We also demonstrated that chemogenetic activation of an arousal pathway – the locus coeruleus – decreases Rst without a change in drug sensitivity. Because Rst is completely obscured in population-based pharmacological studies, we hypothesize that Rst is the hidden variable that may help explain why some patients experience peri-anesthetic complications while others do not. We propose to investigate the mechanisms through which the locus coeruleus decreases Rst. Using pharmacologic and genetic approaches, we will identify the neurotransmitter systems used by the locus coeruleus to modulate Rst. Separately, we will identify the effects of the locus coeruleus on neurophysiologic state change, including correlates of behavioral Rst, using a high-density EEG system developed by our lab. Finally, we will identify the neuronal pathways through which locus coeruleus acts to modulate Rst. The proposed lines of investigation will clarify how activity of the locus coeruleus influences individualized anesthetic responses, and will be an important step towards delivering personalized anesthesia.