© 2017, Editura Clasium. All rights reserved.Oxygen is an element, which is used liberally during several medical procedures. The use of oxygen during perioperative care is a controversial issue. Anesthesiologists use oxygen to prevent hypoxemia during surgical procedures, but the effects of its liberal use can be harmful. Another argument for using high oxygen concentrations is to prevent surgical site infections by increasing oxygen levels at the incision site. Although inconclusive, literature concerning the use of high oxygen concentrations during anesthesia show that this approach may cause hemodynamic changes, altered microcirculation and increased oxidative stress. In intensive care it has been shown that high oxygen concentrations may be associated with increased mortality in certain patient populations such as post cardiac arrest patients. In this paper, a review of literature had been undertaken to warn anesthesiologists about the potential harmful effects of high oxygen concentrations.