Oxygen in cardiac surgery: does more mean better?

Supplemental oxygen has been using in clinical practice for a long time, but there are still many questions regarding to its pitfalls and advantages. On the one hand, high fraction of inspired oxygen speeds up gas resorption behind closed airways and promotes atelectasis formation and pulmonary shunt. Hyperoxia may cause vasoconstriction, thereby compromising perfusion and hence, actual oxygen delivery. Hyperoxia may increase oxidative stress by boosting the production of reactive oxygen species, consequently aggravating ischemia-reperfusion injury. On the other hand, the vasoconstrictive stimulus of short-term exposure to hyperoxia before sustained ischemia may act as a preconditioner, with attenuation of ischemia-reperfusion injury. Hyperoxia induced vasoconstriction may counteract systemic inflammation induced vasoplegia and reduce vasopressor requirements. Hyperoxia may reduce gas microemboli by denitrogenation. Hyperoxia may reduce surgical site infection. During cardiac surgery, supplemental oxygen is conventionally employed with high concentration to secure oxygen reserves and prevent perioperative hypoxia. Consequently, arterial oxygen tension is kept mainly at supraphysiologic level, especially during operations and cardio-pulmonary bypass.The aim of the present review is to update information about optimal oxygen concentration and oxemia level. Oxygen is a crucial element in perioperative management of cardiac surgery patients. it’s obligatory to determine whether the changes accompanied with supraphysiologic level of oxygen are benign or they translate into a worsening of clinical outcomes.In conclusion, mild to moderate hyperoxia may be successfully used in cardiac surgery. The correct timing of applying supraphysiologic level of oxygen might be the key to reliably defeat patients from hypoxia and avoid hyperoxia induced undesirable consequences.