Dangers of hyperoxia

Oxygen (O₂) toxicity remains a concern, particularly to the lung. This is mainly related to excessive production of reactive oxygen species (ROS). Supplemental O₂, i.e. inspiratory O₂ concentrations (FIO₂) > 0.21 may cause hyperoxaemia (i.e. arterial (a) PO₂ > 100 mmHg) and, subsequently, hyperoxia (increased tissue O₂ concentration), thereby enhancing ROS formation. Here, we review the pathophysiology of O₂ toxicity and the potential harms of supplemental O₂ in various ICU conditions. The current evidence base suggests that PaO₂ > 300 mmHg (40 kPa) should be avoided, but it remains uncertain whether there is an "optimal level" which may vary for given clinical conditions. Since even moderately supra-physiological PaO₂ may be associated with deleterious side effects, it seems advisable at present to titrate O₂ to maintain PaO₂ within the normal range, avoiding both hypoxaemia and excess hyperoxaemia.