Administration of pure O2 to hypoxic patients is dangerous because
The respiratory centres maybe depressed in hypercapnic patients. Breathing may only be occurring due to the activation of peripheral chemoreceptors sensitive to the hypoxia. When pure Oxygen is given to the patients, the stimulus to the peripheral receptors is gone and may result in apnoea.
Apnea occurs due to hypostimulation of peripheral chemoreceptors
Pulmonary edema
DPG
Convulsions