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NTRODUCTION

Supplemental oxygen is often provided to patients in the intensive care unit (ICU). The cells utilize oxygen to generate energy; any hypoxemia affects cellular metabolism, and in turn, leads to organ failures. On the contrary, excess oxygen (hyperoxemia) is equally dangerous. The oxygen delivery to tissues drops when the partial pressure of oxygen (PaO2) falls below 60 mm Hg (oxygen-hemoglobin dissociation curve), which is monitored by arterial oxygen saturation (SpO2) by pulse oximetry at the bedside. So, any transient respiratory compromise may subject patients to episodes of severe hypoxia when low oxygen levels are targeted. Similarly, targeting lower SpO2 with the fear of hyperoxemia may lead to lesser oxygen delivery to an already compromised oxygen delivery secondary to shock or anemia or both, a scenario that is not infrequent in ICU. On the contrary, studies have shown that hyperoxemia causes vasoconstriction, reduces cardiac output and heart rate, and reduces coronary and cerebral perfusion.1 Also, excess oxygen supplementation can lead to free radical-mediated injury (e.g., reperfusion) when it depletes the antioxidant stores, which may aggravate organ injuries, especially in the brain and heart.