Oxygen administration is particularly relevant in patients undergoing surgery under general anesthesia and in those whosuffer from acute or critical illness. Nevertheless, excess O2, or hyperoxia, is also known to be harmful. Toxicity arisesfrom the enhanced formation of reactive oxygen species (ROS) that, exceeding the antioxidant defense, may generateoxidative stress. Oxidative stress markers are used to quantify ROS toxicity in clinical and non-clinical settings andrepresent a promising tool to assess the optimal FiO2 in anesthesia and critical care setting. Despite controversial, theguidelines for the regulation of FiO2 in such settings suggest the adoption of high perioperative oxygen levels. However,hyperoxia has also been shown to be an independent mortality risk factor in critically ill patients. In this literature review,we discuss the biochemical mechanisms behind oxidative stress and the available biomarkers for assessing the prooxidant vs antioxidant status. Then, we summarize recent knowledge on the hyperoxia-related consequences in the mostcommon anesthesia and critical care settings, such as traumatic brain injury or cardiac arrest. To this purpose, we searchedthe PubMed database according to the following combination of key words: (“hyperoxia” OR “FiO2” OR “oxygentherapy”) AND (“oxidative stress” OR “ROS” OR “RNS” OR “lipid peroxidation”)AND (“anesthesia” or “surgery”or “intensive care”). We focused in the results from the past 20 years. available evidence points toward a conservativ monitoring and use of oxygen, unless there is solid proof of its efficacy.
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