Oxygen is lifesaving.
Oxygen can also cause harm.
That tension is why oxygen targets in mechanically ventilated patients remain an important critical care question.
Hypoxemia is dangerous because oxygen delivery depends partly on arterial oxygen saturation. If saturation falls too low, tissue oxygen delivery may become inadequate.
But hyperoxemia can also be harmful. High oxygen exposure may increase oxidative stress, worsen absorption atelectasis, contribute to vasoconstriction, and potentially injure tissues.