Oxygen Therapy: When Is Too Much Too Much?

H istorically, extreme care has been taken to avoid periods of hypoxemia with low blood oxygen levels in patients during anesthesia. This is particularly the case during surgery involving cardiopulmonary bypass (CPB), as hypoxemia is known to be potentially harmful. However, because hyperoxemia (excess oxygen in the blood) was believed to be relatively harmless, little effort went into avoiding this condition. Recent clinical data seem to suggest otherwise. The potentially dangerous effects of hyperoxemia include the extension of infarct size status post myocardial infarction, adverse neurologic outcomes, and higher mortality rates in patients receiving therapeutic hypothermia following return of spontaneous circulation after cardiac arrest. As data regarding the detrimental effects of hyperoxemia have appeared, there has been a renewed interest in the potential role it may play in ischemia-reperfusion injury, reactive oxygen species production, and inflammation. In this issue ofAnesthesiology, McGuinness et al, in their article “A Multicenter, Randomized, Controlled Phase IIB Trial of Avoidance of Hyperoxemia During Cardiopulmonary Bypass,” investigate the avoidance of hyperoxemia during CPB and the possibility of reducing postoperative acute kidney injury. They