In mild cases, hypoxia causes only inattentiveness, poor judgment, and motor in-coordination. Severe cases result in a state of complete unawareness and unresponsiveness where brain stem reflexes, including pupillary response to light and breathing reflex, stop.

Only blood pressure and cardiac function are maintained. If this persists, brain death is inevitable.

If the lack of oxygen to the brain is limited to a very brief period of time, coma may be reversible with varying levels of return to function, depending on the extent of injury. Sometimes seizures may occur, which may be continuous (status epilepticus).

Cerebral hypoxia can usually be deduced from the clinical history and examination. Testing is targeted at determining the cause of the hypoxia. These studies may include:

• Magnetic resonance imaging (MRI, a test which provides high-quality pictures of the brain)
• Electrocardiogram (EKG, a test of the electrical activity of the heart)
• Echocardiogram
• Blood tests (including arterial blood gases and blood sugar)
• Electroencephalogram (EEG, a test of brain waves, needed when seizures are suspected)
• Evoked Potentials (test to determine wheter certain sensations like vision and touch can reach the brain, causing an electric response)