Oxygen toxicity is an iatrogenic illness caused by exposure to high FIO2 during oxygen therapy. Oxygen saturation should be monitored in patients receiving supplemental O2. As the oxygen gets metabolized, some molecules convert to superoxide anions known as hydroxyl radicals, which are human tissue toxic. The resulting pathophysiological changes at the alveolar level result in decreases in lung compliance, diffusing capacity, and PaO2 levels. Central nervous system (CNS) toxicity can occur with exposure to high partial pressures of oxygen. Acute changes in the lungs resulting from oxygen toxicity consist of alveolar and interstitial edema, alveolar hemorrhages, and proteinaceous exudates. Further prolonged exposure to oxygen leads to a proliferative phase, which includes the proliferation of type II epithelial cells and fibroblasts, followed by collagen deposits. Exposure to FIO2s greater than 0.60 for as little as 24 to 48 hours can lead to severe irreversible pulmonary fibrosis.[6][7]

https://www.ncbi.nlm.nih.gov/books/NBK551617/