Oxidative Stress Markers to Investigate the E ff ects of Hyperoxia in Anesthesia

: Oxygen (O 2 ) is commonly used in clinical practice to prevent or treat hypoxia, but if used in excess (hyperoxia), it may act as toxic. O 2 toxicity arises from the enhanced formation of Reactive Oxygen Species (ROS) that exceed the antioxidant defenses and generate oxidative stress. In this study, we aimed at assessing whether an elevated fraction of inspired oxygen (FiO 2 ) during and after general anesthesia may contribute to the unbalancing of the pro-oxidant / antioxidant equilibrium. We measured five oxidative stress biomarkers in blood samples from patients undergoing elective abdominal surgery, randomly assigned to FiO 2 = 0.40 vs. 0.80: hydroperoxides, antioxidants, nitrates and nitrites (NO x ), malondialdehyde (MDA), and glutathionyl hemoglobin (HbSSG). The MDA concentration was significantly higher 24 h after surgery, and the body antioxidant defense lower, in the FiO 2 = 0.80 group with respect to both the FiO 2 = 0.40 group and the baseline values ( p ≤ 0.05, Student’s t -test). HbSSG in red blood cells was also higher in the FiO 2 = 0.80 group at the end of the surgery. NO x was higher in the FiO 2 = 0.80 group than the FiO 2 = 0.40 group at t = 2 h after surgery. MDA, the main end product of the peroxidation of polyunsaturated fatty acids directly influenced by FiO 2 , may represent the best marker to assess the pro-oxidant / antioxidant equilibrium after surgery.