Hyperoxia and oxidative stress in anesthesia and critical care medicine

Abstract

Oxygen administration is particularly relevant in patients undergoing surgery under general anesthesia and in those who suffer from acute or critical illness. Nevertheless, excess O2, or hyperoxia, is also known to be harmful. Toxicity arises from the enhanced formation of Reactive Oxygen Species (ROS) that, exceeding the antioxidant defense, may generate oxidative stress. Oxidative stress markers are used to quantify ROS toxicity in clinical and non-clinical settings and represent a promising tool to assess the optimal FiO2 in anesthesia and critical care setting. Despite controversial, the guidelines 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 pro-oxidant vs antioxidant status. Then, we summarize recent knowledge on the hyperoxia-related consequences in the most common anesthesia and critical care settings, such as traumatic brain injury or cardiac arrest. To this purpose, we searched the Pubmed database according to the following combination of key words: ("hyperoxia" OR "FiO2" OR "oxygen therapy") 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 conservative monitoring and use of oxygen, unless there is solid proof of its efficacy.

COVID-19-associated cardiovascular morbidity in older adults: a position paper from the Italian Society of Cardiovascular Researches

“…Fourth, although the correction of hypoxia with oxygen therapy remains the major life-saving concern in ICU patients, excess oxygen delivery or hyperoxia may cause considerable harm (Ottolenghi et al 2020). In facts, hyperoxia caused by breathing mixtures with > 40% oxygen markedly elevates reactive oxygen species (ROS) release in the circulation and contributes to tissue injury by oxidative stress (Nagatomo et al 2012).…”

Effects of Normoxia, Hyperoxia, and Mild Hypoxia on Macro-Hemodynamics and the Skeletal Muscle Microcirculation in Anesthetised Rats

“…Third, we observed a similar reduction in Hb levels in all groups, which was probably due to hemodilution and repeated blood sampling: this may have influenced the macro-hemodynamic and microvascular responses observed by contributing to changes in CaO 2 and blood viscosity. Fourth, we did not measure markers of oxidative stress ( 37 ) or inflammation ( 38 ): this may have helped to understand the pathophysiological basis of cardiovascular changes induced by hyperoxia. Moreover, we did not measure variations in NO levels and could not demonstrate the role of NO in microvascular perturbations induced by hypoxia/hyperoxia.…”

ACE/ACE2 Ratio: A Key Also in 2019 Coronavirus Disease (Covid-19)?

“…Indeed, oxygen therapy remains the major life-saving concern in intensive care unit (ICU). In ICU-patients, excess oxygen delivery may cause considerable harm in which redox stress plays a pivotal role (33)(34)(35). Therefore, additional therapies that limit redox stress and inflammation are needed, including those aimed at improving the ACE/ACE2 ratio.…”