Cerebral hypoxia occurs when there is not enough oxygen getting to the brain. The brain needs a constant supply of oxygen and nutrients to function. Cerebral hypoxia refers to the largest parts of the brain, called the cerebral hemispheres. However, the term is often used to refer to a lack of oxygen supply to the entire brain. In cerebral hypoxia, sometimes only the oxygen supply is interrupted. This can be caused by: Breathing in smoke (smoke inhalation), such as during a fire.